chapter 2. literature studybibing.us.es/proyectos/abreproy/20087/fichero/chapter+2.pdf · chapter...

CHAPTER 2. LITERATURE STUDY

5

CHAPTER 2. LITERATURE STUDY 2.1. ORGANIC MICROPOLLUTANTS. 2.1.1. Introduction.

During the past three decades, research on the impact of chemical

pollution has focused almost exclusively on the conventional priority pollutants (persistent organic pollutants – POPs) and this has been extensively reviewed recently. Today, these compounds are less relevant for many first world countries because emissions have been substantially reduced through the adoption of appropriate legal measures and the elimination of many of the dominant pollution sources. The focus has consequently switched to compounds present in lower concentrations but which nevertheless might have the ability to cause harm. One of the interesting characteristics of many of the chemicals that might cause this type of pollution is that they do not need to be persistent in the environment to cause negative effects. This is one reason why there is an increasingly widespread consensus that this kind of contamination might require legislative action sooner rather than later.

These chemicals are called organic micro pollutants, and pesticides,

hormones, pharmaceuticals and industrial chemicals are the most important groups. But there are also different denominations into this general definition.

For over 70 years, scientists have reported that certain synthetic and

natural compounds could mimic natural hormones in the endocrine systems of animals. These substances are now collectively known as endocrine-disrupting compounds (EDCs), and have been linked to a variety of adverse effects in both humans and wildlife. The newest emerging pollution issue is the presence of pharmaceuticals, personal care products (PPCPs) and hormonally active agents in various surface and ground waters, some of which have been linked to ecological impacts at trace concentrations. Not all the micro pollutants are EDCs but a wide range of pharmaceuticals, personal care products, pesticides, industrial chemicals, hormones and their metabolites have been examined and listed as hormonally active agents.

2.1.2. Endocrine disrupting compounds (EDCs) 2.1.2.1. Definition.

Perhaps the most difficult part of understanding the subject of endocrine

disruption involves a definition of the term. The environmental Protection Agency (EPA) has defined endocrine disrupting compounds (EDCs) as exogenous agents that interfere with the “synthesis, secretion, transport, binding, action or elimination of natural hormones in the body that are


6

responsible for the maintenance of homeostasis, reproduction, development, and/or behaviour” (EPA, 1997). However, definitions and opinions on what defines an EDC vary greatly. It is generally accepted that the three major classes of endocrine disruption endpoints are estrogenic (compounds that mimic or block natural estrogen), androgenic (compounds that mimic or block natural testosterone), and thyroidal (compounds with direct or indirect impacts to the thyroid).

2.1.2.2. Primary EDCs sources in the environment

Domestics wastes are the primary sources of these personal care products

and hormonally active agents in the environment. There are a broad variety of pharmaceuticals and personal care products that can be released into the environment. Analgesics, antibiotics, antiepileptic medicines, anti-inflammatory medicines, bath additives, blood lipid regulators, cough syrups, detergents, fragrances, hormones, hair care products, oral hygiene products, stimulants and sunscreens are some representative examples of them. Veterinary medicines might also have the potential to enter water sources, even in upland areas, through leaching from fields used to graze stock that are treated with drugs or disposal of manure from stock so treated. Other types of compounds that are potentially hormonal active agents are pesticides, plastic additives, polychlorinated biphenyls, brominated flame retardants, dioxins and hormones and their metabolites and can reach the drinking water sources due to agriculture activity and industrial discharges.

2.1.2.3. 80 Years of resarches

Although the topic of endocrine disruption is considered an “emerging

issue” in the water industry, scientists have known about the ability of natural and synthetic compounds to interfere with the hormone systems of animals for over 80 years. The discovery that certain compounds can mimic the endogenous hormones of animals was reported as early as the 1930s. In 1940, Stroud reported that certain synthetic chemicals were estrogenic. An article from the journal Science published in 1946 explained that the molecular configurations of natural and synthetic compounds influenced the degree of estrogenic and androgenic bioactivity in rodents. The ability of estrogenic and androgenic compounds to interfere with the natural metamorphosis of amphibians was reported as early as 1948. These early papers began to describe how the molecular configurations of natural and synthetic compounds could mimic the primary endogenous female hormone 17B-estradiol (E2) and the male hormone testosterone. More importantly, these early studies laid the foundation for how these hormone-mimicking compounds could result in reproductive toxicity.

The estrogenic activity of synthetic organic compounds was of little interest

to the environmental community until the discovery that the organochlorine


7

pesticide, DDT and its metabolites had endocrine-disrupting properties. The connection between endocrine disruption and reproductive failures in wildlife was not made until the 1980s, when it was reported that gulls living in areas contaminated with DDT exhibited deformed sex organs and skewed sex ratios. This was one of the first documented connections between an environmental contaminant and reproductive impacts via a hormone-mediated mechanism. Possible links between organochlorine pesticides, including DDT and its metabolites, and endocrine disruption were provided by researches in Florida, who discovered reproductive disorders in alligators in Lake Apopka.

More recent studies have further demonstrated the importance of

endocrine disruption compounds (like tributyltins, atrazine, alkylphenol polyethoxylate (APE) surfactants, and more) in wildlife populations (population declines and reproductive disorders including imposex-development of male sex characteristics in females- in marine gastropods, supernumerary and missing limbs in some amphibian populations (in particular frogs), reproductive abnormalities (changes in the levels of sex steroids, gonadal histology and increased levels of the female egg yolk precursor, vittellogenin, in male fish) in fish living below wastewater treatment plants. There are many other examples of exogenous compounds acting as EDCs, and more EDCs will likely be discovered as screening and testing methods become available.

Endocrine disruption also can be caused by naturally occurring

compounds, which is the case of estrogens from plant sources, known as phytoestrogens that have been linked to reproductive failures in animals since the 1930s.

Researches in the 1990s indicated that the pharmaceutical 17a-ethinyl

estradiol (EE2) could induce endocrine-disruptive effects in fish at concentrations present in some municipal wastewater treatment plants (WWTPs) effluents. This cause-effect relationship has simulated a great deal of new research on the identification of trace pharmaceuticals in the environment.

All these unexpected impacts of trace concentrations of EDCs on wildlife

raised concerns about the potential effects of these substances on humans. An interesting study involved exposure to the potent synthetic estrogen diethylstilbestrol (DES). The exposure was not as an environmental contaminant, it was used as a pharmaceutical administered to pregnant women. The experiment demonstrated that the human embryo/fetus was not immune to exogenous chemicals the act as hormones. DES is also used for certain agricultural applications such as increasing livestock growth and milk production.

Furthermore, decreases in human sperm quality and quantity over the past

five decades, sharp increases in breast, testicular, and prostate cancers reported over the past 40 years have been attributed to endocrine disrupting


8

compounds in the environment. But in the other hand, other scientists have refuted these arguments.

2.1.2.4. Lack of information about occurrence, analysis and removal rates

To date, most of the published literature has addressed the occurrence of

these compounds in sewage effluent and receiving waters. The public’s concern is more focused on human exposure although the risks associated with exposure to drugs are probably most significant with regard to the natural environment. Human exposure is especially critical in places that reuse water, where sewage effluent is released to streams and rivers that are used as a source of raw water for production of potable supplies for communities living downstream. Unfortunately there are only few data available on the occurrence of some of these pollutants (like pharmaceuticals) in point-of-use drinking waters (tap water at the sink). Two reasons can explain this extremely few data: On one hand the difficulty of analysis of pollutants and on the other hand the belief that modern treatment processes will remove micro pollutants from potable supplies. The majority of EDCs and PPCPs are more polar than traditional contaminants (higher water solubility), several have acidic or basic functional groups and they appear at trace levels (sub parts per billion or parts per trillion). Hence, analytical detection and removal processes have to be extensively reviewed to obtain higher efficiencies and better analytical data (different methods with lower detection limit). Normally, these compounds are resistant to conventional drinking and waste water treatment plants. Oxidation with chlorine and ozone can result in transformation of some compounds with reactive functional groups under the conditions employed in these plants. Advanced treatment technologies, such as activated carbon and reverse osmosis, appear viable for the removal of many trace contaminants but different studies show that there is a big possibility that drug compounds can pass through even modern, advanced water treatment facilities such as ozone and GAC treatments (probably as a result of physicochemical properties such as high water solubility and/or poor degradability). Some of them are the anti-epileptic drugs carbamazepine and primidone the lipid regulators clofibric acid, bezafibrate and gemfibrozil, the psychiatric drug diazepam, anti-neoplastic bleomycin among others.

So, it has been reported that some of these compounds can cause human

health effects, they are reaching water sources, they are not detected with analytical methods and the worst aspect is that they can pass though even modern water treatment plants. Hence, there is an important risk that humans might be exposed to the problems related to drinking potable water that contain these compounds. It can be said that the risk that humans might be exposed to drugs through potable water drawn from contaminated supplies is likely to be relatively minor and it can be true, due to there are lots of sources that are not contaminated but it should be take into account that there is an increasing


9

demand on the fresh water supplies of the world. The first consequence of it is that greater incidences of indirect and direct water reuse situations are going to occur due to the spatial and temporal distances between waste water and drinking water will be reduced. As can be understood, the presence of these compounds in drinking water is provoking an increase in the general public’s already negative attitude to water reuse.

It was mentioned before that risks are not definitively proven but it has to

be remembered that drinking water should be a primary health concerned issue due to it is a direct pathway to the human body for any drug compound that could be present in water. Of course, this is the main important route but indirect ones are also necessary to consider, such as bodily interaction (bathing or showering in waters containing effluent) or ingestion (eating crops irrigated with effluent or grown on sewage-sludge-amended soil).

As it was mentioned in the introduction health considerations are not going

to be deeply considered but I’d just like to point out that the presence of antibiotics could also lead to the development of resistant pathogens, synergistic effects of mixtures of compounds are totally unknown and should be taken into account and possible interactions with other medications or even illegal drug substances that individuals might be taken will also need to be considered. At the same time, continual life-long exposure to trace levels of pollutants is an unexplored area of toxicology and the many possible issues that could theoretically be involved have not been extensively studied.

2.1.2.5. Future measures and interesting researches

To finish some ideas related to future measures and interesting research

are summarized to understand better the possible problems that could be related to these contaminants and try to minimize their impact in the natural environment in general and human health in particular.

The first idea would be to apply a precautionary principle and try to reduce

the levels of these compounds in drinking water before any harm is proved. As it was said before, it is unlikely that a serious problem exists now but a continual exposure to trace levels of them is a totally unknown aspect of toxicology. It is important to highlight that there is a huge amount of compounds that could be aim of study. But it is not practical to study all of them with the same intensity so one approach might be to develop a prioritization scheme to try to identify those compounds that might pose a risk to human health and therefore warrant further study. It is important to know more information of the toxicological impacts of trace levels of these compounds in water because once these impacts are quantified, safe exposure limits can be established. For the water industry it is


10

extremely important to know them because it will allow engineers to determine good removal rates.

Another field that should be intensively studied is related to analytical

techniques. Standardized analytical methods for detection of commonly occurring micro pollutants are critical. It is totally necessary that these methods are based on equipment that most laboratories could afford and have experts to operate. It is not practical to develop precise methods that cannot be practiced in any laboratory. The next step, after practical analytical methodologies are available, is to include testing for bioaccumulation of these contaminants in wildlife and humans and a further study should look for identify population-level impacts of them on wildlife and relate these effects to biomarkers.

The last (but not less important) field that requires an intensive research is

that related to micro pollutants removal. Some compounds have been studied and some reports of their removal by water treatment techniques are beginning to become available but there is still a lot of unknown aspects that should be considered to improve drinking water plants. It is critical to understand the size distribution of EDCs and PPCPs and their association with particulate and colloidal materials in raw drinking water supplies to asses removal across conventional WTPs designed for particular and colloidal removal. The oxidation capability of chloramines on these compounds reactive with chlorine should be quantified. It is extremely important to identify oxidation byproducts due to their endocrine and carcinogenic health risks. For improving their coagulation removal, nonionic polymers performance should be studied. Aerobic biofilms should be studied in comparison to nonbiological sand filters to quantify the potential benefits of changing the point of chlorination in a conventional WTP to optimize their removal. Related to membranes, partition and permeation coefficients across membranes should be determined. The initial and main objective of this work it was to study breakthrough curves for GAC packed columns with a variety of these compounds that is an unknown issue necessary to better understand their removal with this technique. Experiments with compounds in a water containing NOM to evaluate potential displacement/desorption of organics over time is also important. These and more aspects require an intensive research to improve micro pollutants removal.

2.1.3. Pesticides

At the beginning of this study, experiments with a bigger range of micro pollutants were considered. But due to some problems, the number of studied compounds has been reduced. Finally, just pesticides have been considered. For this reason and due to this is high concern family of micro pollutants in the whole world, special attention is paid on them below. Different families of them are summarised, their properties and characteristics, their uses and occurrences and examples of them are taken into account.


11

2.1.3.1. Definition

The Environmental Protection Agency (EPA or USEPA) defines a pesticide as "any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest", so a pesticide may be a chemical substance or biological agent (such as a virus or bacteria) used against pests including insects, plant pathogens, weeds, molluscs, birds, mammals, fish, nematodes (roundworms) and microbes that compete with humans for food, destroy property, spread disease or are a nuisance.

Pesticides can be classified according to chemical class (for example organochlorine, carbamate, organophosphorous or chlorophenoxy compounds) or according to their intended use (for example fungicide, herbicide, fumigant) and it is important to know both because the chemical structure of the pesticide and its use, determine its behaviour in the environment, occurrence in drinking water and toxicity to humans.

Both classifications are going to be developed, first according to chemical class and then according to their intended use.

2.1.3.2. Chemical Pesticides classification, uses and problems

Talking about chemical pesticides, an enormous amount of different groups can be named, such as acetamide, anilide, bromide, benzothiadiazole, chloroacetanilide, carbamate, dinitroaniline, halogenated hydrocarbon, organochlorine, organophosphate, pyridazine, phenoxy, pyrethroid, thiocarbamate, triazine or urea. Some interesting ideas of the most worldwide used, problematic or toxic are going to be resumed.

Organophosphate Pesticides

Organophosphates as a class have become the most frequently used pesticides because of their rapid breakdown into environmentally safe products. However, they have far more immediate toxicity than DDT and other related products. There are more than 40 different organophosphate pesticides on the market today, and they each cause acute and sub-acute toxicity. Some of them are Diazinon, Ethion, Fenthion, Malathion and Parathion.

These pesticides affect the nervous system by disrupting the enzyme that regulates acetylcholine, a neurotransmitter. Most organophosphates are insecticides and are active against a broad spectrum of them and are used on food crops as well as in residential and commercial buildings, on ornamental plants and in veterinary practice. They were developed during the early 19th century, but their effects on insects, which are similar to their effects on


12

humans, were discovered in 1932. Some are very poisonous (they were used in World War II as nerve agents).

Organophosphate pesticides account for about half of the insecticides used in the United States. Approximately 60 million pounds of organophosphate pesticides are applied to about 60 million acres of U.S. agricultural crops annually; non-agricultural uses account for about 17 million pounds per year.

Exposure of the general population to these pesticides occurs primarily from ingestion of food products or from residential use.

Carbamate Pesticides

Carbamate pesticides are derived from carbamic acid and kill insects in a similar way as organophosphate insecticides. Like the organophosphates, their mode of action is inhibition of cholinesterase enzymes, that regulates acetylcholine -a neurotransmitter-, affecting nerve impulse transmission

The carbamates are mainly used in agriculture, as insecticides, fungicides, herbicides, nematocides, or sprout inhibitors. In addition, they are used as biocides for industrial or other applications and in household products. Thus, these chemicals are part of the large group of synthetic pesticides that have been developed, produced, and used on a large scale in the last 40 years.

More than 50 carbamates are known, (such as carbaryl -the first carbamate that was introduced in 1956- and benomyl) and they can be classified into three different groups: The carbamate ester derivatives, used as insecticides (and nematocides), are generally stable and have a low vapour pressure and low water solubility, the carbamate herbicides (and sprout inhibitors) have the general structure R1NHC(O)OR2, in which R1 and R2 are aromatic and/or aliphatic moieties and carbamate fungicides that contain a benzimidazole group.

The light absorption characteristics of carbamates contribute to their rapid decomposition (by photodegradation or photodecomposition) under aqueous conditions. Thus, the hazards of long-term contamination with carbamates seem small.

Organochlorine Insecticides

Organochlorine insecticides are neurotoxins that have high lipophilicity, are very hydrophobic, and are chemically stable. Metabolic degradation in target and non-target organisms or environmentally by either chemical, photolytic, or


13

microbial processes is slow. As a result, organochlorine insecticides are persistent in the environment and have a long half-life.

There are three major types of organochlorine insecticides:

Dichlorodiphenylethanes: Such as DDT, DDD, TDE, Methoxychlor, Rhothane, Methlochlor, Perthane, Dicofol (Kelthane).

Chlorinated Cyclodienes: Such as Aldrin, Dieldrin, Endrin, Heptachlor, Chlordane, Endosulfan.

Chlorinated Benzenes & Cyclohexanes: Such as Lindane, Toxaphene, Mirex, HCB, HCH, Chlordecone (Kepone).

The lethal mechanism of action of organochlorine insecticides is a persistent opening of the sodium channels in neurons, resulting in repetitive firing of action potentials. K+ permeability is also reduced, calmodulin is inhibited, and Na, K, & Ca ATPase are also inhibited. These effects slow nerve repolarization.

Organochlorine pesticides have a high bio concentration factor and high bio magnification in the food chain. They were commonly used in the past, but many have been removed from the market due to their health and environmental effects and their persistence (e.g. DDT and chlordane).

Pyrethroid Pesticides

These pesticides were developed as a light stable synthetic version of the naturally occurring pesticide pyrethrin, which is found in chrysanthemum flower. They have been modified to increase their stability in the environment.

Pyrethroid pesticides are widely used as the main residential pesticide now that the once-dominant organophosphates, diazinon and chlorpyrifos, have been phased out. They are used in agriculture on crops like cotton, fruits, lettuce, grains and ornamental flowers. Some synthetic pyrethroids are toxic to the nervous system. And they are often used in combination with the synergist piperonyl butoxide.

Related to their mechanism of toxicity, it can be said that they are sodium channel toxins, that have a stereospecific affinity for nerve membrane sodium channels and prolong inactivation or sodium tail currents The next table shows a roughly classification of these compounds, as well as some basic characteristics are mentioned.


14

TABLE 2.1.1. PYRETHROID PESTICIDES CLASSIFICATION.

TYPE I TYPE II

Main characteristic

Non-cyano pyrethroids Alfa-cyano pyrethroids

Sodium tail currents

Short Longer

Effects DDT-like poisoning syndrome in animals Tremors, salivation and

seizures at high doses

Examples Permethrin, Resmethrin Cypermethrin,

Esfenvarelate

They have important health effects on human such as, irritant and allergic contact dermatitis, airway hyper responsiveness in asthmatics, dizziness, headache, fatigue, vomiting, diarrhea, pulmonary edema among others.

2.1.3.3. Uses classification

These have just been some basic ideas according to chemical classification, now a basic resume, will show concepts related to their use. Into this classification, a sub classification can be made, based on the life forms that are attacked by the pesticide. Two tables are used to shown all this possible areas of use.


15

TABLE 2.1.2 PESTICIDES ACTIVE AGAINST HIGHER LEVEL ANIMAL LIFE FORMS

TABLE 2.1.3 PESTICIDES ACTIVE AGAINST PLANTS AND LOWER LEVEL LIFE FORMS

PESTICIDE NAME

AREA OF CONTROL (USE)

Bactericides control of bacteria Herbicides control of weeds Fungicides control of fungi Plant Growth

Regulators modification of plant growth (examples: prevention

of lodging in wheat, earlier initiation of flowering, production of larger table grapes and stimulation of root growth of cuttings)

Virucides or viricides

control of viruses

Pesticide name Area of control (use) Acaricides control of spiders Avicides control of birds Chemosterilants control pest populations by sterilizing males. Insecticides control of insects Lampricides control of parasitic Lampreys in river systems Miticides control of mites Molluscicides control of snails and slugs Nematicides control of nematodes (roundworms) Rodenticides control of rodents including gophers, ground

squirrels, mice and rats Termiticide control termites Repellents and

attractants Insect Attractants Insect Repellents Bird Repellents Mammal Repellents


16

2.1.3.4. Worldwide used pesticides

To finish with these concepts about pesticides, chemical family and use, a table in which the most common pesticides appear is shown. 35 worldwide used pesticides are classified according to both classifications.

TABLE 2.1.4 CHEMICAL FAMILY AND USE OF PESTICIDES

PESTICIDE CHEMICAL FAMILY

USE

Alachlor CA HB Aldicarb CB AC IN NE Aldrin/Dieldrin OC IN TE Atrazine TR HB Bentazone BT HB Carbofuran CB AC IN NE Chlordane OC IN TE Chlorotoluron UR HB DDT OC IN 1,2-Dibromo-3-chloropropane HH FM NE 2,4-D PO HB 2,4-DB PO HB 1,2-dichloropropane HH FM 1,3-dichloropropane HH - - 1,3-dichloropropene HH FM FU IN

NE Dichlorprop PO HB IG Ethylene dibromide BR IN FU Fenoprop PO HB Heptachlor and Heptachlor

epoxide OC TE

Hexachlorobenzene OC FU Isoproturon UR HB Lindane OC IN MCPA PO HB MCPB PO HB Mecoprop PO HB Methoxychlor OC IN Metolachlor AM HB Molinate TC HB Pendimethaline DA HB Pentachlorophenol OC FU HB IN Permethrin PY IN Propanil AN HB Pyridate PA HB


17

Simazine TR HB 2,4,5-T PO HB Trifluralin DA HB

The next tables resume the codes used above.

TABLE 2.1.5 CODES FOR CHEMICAL FAMILY

CODE CHEMICAL FAMILY AM Acetamide AN Anilide BR Bromide BT Benzothiadiazole CA Chloroacetanilide CB Carbamate DA Dinitroaniline HH Halogenated hydrocarbonOC Organochlorine PA Pyridazine PO Phenoxy PY Pyrethroid TC Thiocarbamate TR Triazine UR Urea

TABLE 2.1.6 CODES FOR USE

CODE USE AC Acaricide FM Fumigant FU Fungicide HB Herbicide IG Growth regulatorIN Insecticide NE Nematicide TE Termiticide

Due to aldrin, dieldrin and atrazin were the pesticides used in experiences

additional information about them is resumed below.


18

2.1.4. Aldrin and dieldrin 2.1.4.1. Chemical identity

In this study, the two chemicals are discussed together because aldrin

readily changes into dieldrin once it enters either the environment or your body. Aldrin and dieldrin are the common names of two structurally similar

compounds that were once used as insecticides. They are chemicals that are made in the laboratory and do not occur naturally in the environment.

The scientific name (CAS chemical name) for aldrin (or aldrine) is

1,2,3,4,10,10-hexachloro-1,4,4α,5,8,8α-hexahydro-1,4-endo,exo-5,8-dimethanonaphthalene and its CAS number is 309-00-2. The abbreviation for the scientific name of aldrin is HHDN. Technical-grade aldrin contains not less than 85.5% aldrin. Some synonyms and trade names (also called brand names) used for aldrin include Aldrec, Aldrex, Aldrex 30, Aldrite, Aldrosol, Altox, Compound 118, Drinox, Octalene and Seedrin.

The scientific name for dieldrin (dieldrine) is 1,2,3,4,10,10-hexachloro-6,7-

epoxy-1,4,4α,5,6,7,8,8α-octahydro-1,4-endo,exo-5,8-dimethanonaphthalene and its CAS number is 60-57-1 The abbreviation for the scientific name for dieldrin is HEOD. Technical-grade dieldrin contains not less than 85% dieldrin. The trade names used for dieldrin include Alvit, Dieldrix, Octalox, Quintox, and Red Shield.

It’s important to know that aldrin is the ISO common name for material

containing more than 95% of the pure compound; the pure compound has the ISO common name HHDN and the 5R,8S isomer has the BSI common name isodrin.

In the next table its identification numbers are resumed:

TABLE 2.1.7 ALDRIN AND DIELDRIN IDENTIFICATION NUMBERS

ALDRIN DIELDRIN CAS REGISTRY 309-00-2 60-57-1 NIOSH RTECS IO2000000 IO1750000 EPA HAZARDOUS WASTE P004 PO37 OHM/TADS 7215090 7216516 DOT/UN/NA/IMCO shipping IM06.1

NA2762 UN 2761

HSDB 199 322 NCI C00044 C00124


19

2.1.4.2. Physical and chemical properties

Aldrin molecular formula is C12H8Cl6 and dieldrin molecular formula is

C12H8Cl6O. Their structure molecule is shown below.

FIGURE 2.1.1 ALDRIN AND DIELDRIN MOLECULES STRUCTURE

The most important physico-chemical properties are resumed in the next

table.

TABLE 2.1.8 ALDRIN AND DIELDRIN PHYSICO-CHEMICAL PROPERTIES

ALDRIN DIELDRIN Molecular

weight 364,92 380,91

Density 1.70 g/cm3 1.75 g/l at 25ºC Log Kow 7.4 6,2 Log Koc 7,67 6,67 Solubility in

water 0.027 (at 27°C) 0.20 (at 20°C) also

reported

0.1- 0.195 mg/l (at 20 – 29 °C)

Melting point 104ºC (pure) 49-60ºC (technical)

176-177ºC (pure) 95ºC (technical)

Boiling point 145ºC at 2mm Hg Vapor pressure 2.31 x 10-5 mm Hg at

20ºC. 400µPa at 20°C

Henry’s Law constant

4.96 x 10-4 atm m3/mol at 25ºC

5,2 x 10-5 atm m3/mol at 25ºC


20

Technical dieldrin contains 85% dieldrin and 15% insecticidally active related products. Minimum concentration is 95% of the 85%/15% mixture (not less than 80.75% dieldrin).

2.1.4.3. Appearance Pure aldrin and dieldrin are white odorless powders, while technical-grade

aldrin and dieldrin are tan to dark brown and light brown respectively powders with a mild chemical odor.

2.1.4.4. Uses

Aldrin and dieldrin are highly effective pesticides used to control soil

insects such as termites, corn rootworm, wood borers, wireworms, rice water weevil, and grasshoppers. They have been widely used to protect crops such as corn and potatoes, and have been effective to protect wooden structures from termites. Dieldrin has also been used against insects of public health importance. Although the use of them has been severely restricted or banned in many parts of the world since the early 1970s, they are still used in termite control in some countries.

Aldrin and dieldrin were designated as persistent organic pollutants in 1997

by the Governing Council of the United Nations Environment Programme (UNEP, 1997).

2.1.4.5. Environmental Behavior

Aldrin and dieldrin can enter the environment from accidental spills or leaks

from storage containers at waste sites. In the past, aldrin and dieldrin entered the environment when farmers used these compounds to kill pests on crops and when exterminators used them to kill termites. Aldrin and dieldrin are still present in the environment from this past use. Aldrin is readily metabolized to dieldrin by both plants and animals. As a result, aldrin residues are rarely found in foods and animals, and then only in small amounts and you can find dieldrin in places where aldrin was originally released.

In soil, aldrin is removed by oxidation to dieldrin and evaporation. In

temperate climates, only 75 % is oxidized within a year of application. The disappearance of dieldrin is very slow under these conditions; the half-life is approximately 5 years. Under tropical conditions, both oxidation and further disappearance of dieldrin are rapid, 90 % disappearing within 1 month, primarily by volatilization. It binds strongly to soil particles and is very resistant to leaching into groundwater

Due to its persistent nature and hydrophobicity, aldrin is known to

bioconcentrate, mainly as its conversion products.


21

2.1.4.6. Toxicity Aldrin is toxic to humans. The lethal dose of aldrin for an adult man has

been estimated to be about 5g, equivalent to 83 mg/kg body weight. Signs and symptoms of aldrin intoxication may include headache, dizziness, nausea, general malaise, and vomiting, followed by muscle twitchings, myoclonic jerks, and convulsions.

Occupational exposure to aldrin, in conjunction with dieldrin and endrin,

was associated with a significant increase in liver and biliary cancer, although the study did have some limitations, including a lack of quantitative exposure information, because of that is not classifiable as to its carcinogenicity in humans. There is limited information that cyclodienes, such as aldrin, may affect immune responses.

Other toxicity information obtained in laboratory experiments are

reproductive effects in rats, acute oral LD50 for guinea pigs and rats, no evidence yet of a teratogenic potential, has low phytotoxicity, variable toxicity to aquatic organisms and the acute toxicity of aldrin to avian species varies in the range of 6.6 mg/kg for bobwhite quail to 520 mg/kg for mallard ducks.

2.1.4.7. Legal situation Aldrin is banned in many countries, including Bulgaria, Ecuador, Finland,

Hungary, Israel, Singapore, Switzerland and Turkey. Its use is severely restricted in many countries, including Argentina, Austria, Canada, Chile, the EU, Japan, New Zealand, the Philippines, USA, and Venezuela.

2.1.5. Atrazin 2.1.5.1. Chemical identity

The chemical name of this triazine substance is 2-chloro-4-ethylamine-6-isopropylamino-S-triazine and its CAS number is 1912-24-9. Some trade and other names of atrazine, include: Aatrex, Aktikon, Alazine, Atred, Atranex, Atrataf, Atratol, Azinotox, Crisazina, Farmco Atrazine, G-30027, Gesaprim, Giffex 4L, Malermais, Primatol, Simazat, and Zeapos.

2.1.5.2. Physical and chemical properties

The molecular formula is C12H14ClN5.

The most important physico-chemical properties are resumed in the next table.


22

TABLE 2.1.9 ATRAZINE PHYSICO-CHEMICAL PROPERTIES. Molecular weight 215.69 Log KOW 2.75 Solubility in water 33 mg/l (at 25 °C) Melting point 176 C Vapour pressure 0.04 mPa at 20 C

2.1.5.3. Appearance.

Atrazine is a white, crystalline solid, but it is available as dry flowable, flowable liquid, liquid, water dispersible granular and wettable powder formulations

2.1.5.4. Uses

Atrazine is a selective triazine herbicide used to control broadleaf and grassy weeds in corn, sorghum, sugarcane, pineapple, Christmas trees, and other crops, and in conifer reforestation plantings. It is also used as a nonselective herbicide on non-cropped industrial lands and on fallow lands.

2.1.5.5. Environmental Behaviour:

Breakdown in soil and groundwater

Atrazine is highly persistent in soil. Chemical hydrolysis, followed by degradation by soil microorganisms, accounts for most of the breakdown of atrazine. Hydrolysis is rapid in acidic or basic environments, but is slower at neutral pHs. Addition of organic material increases the rate of hydrolysis. Atrazine can persist for longer than 1 year under dry or cold conditions. Atrazine is moderately to highly mobile in soils with low clay or organic matter content. Because it does not adsorb strongly to soil particles and has a lengthy half-life (60 to >100 days), it has a high potential for groundwater contamination despite its moderate solubility in water. Atrazine is the second most common pesticide found in private wells and in community wells. Trace amounts have been found in drinking water samples and in groundwater samples in a number of states. A 5-year survey of drinking water wells detected atrazine in an estimated 1.7% of community water systems and 0.7% of rural domestic wells nationwide. Levels detected in rural domestic wells sometimes exceeded the MCL. The recently completed National Survey of Pesticides in Drinking Water found atrazine in nearly 1% of all of the wells tested.


23

Breakdown in water

Atrazine is moderately soluble in water. Chemical hydrolysis, followed by biodegradation, may be the most important route of disappearance from aquatic environments. Hydrolysis is rapid under acidic or basic conditions, but is slower at neutral pHs. Atrazine is not expected to strongly adsorb to sediments. Bioconcentration and volatilization of atrazine are not environmentally important. Atrazine has been detected in each of 146 water samples collected at 8 locations from the Mississippi, Ohio and Missouri Rivers and their tributaries. For several weeks, 27% of these samples contained atrazine concentrations above the EPA's maximum contaminant level (MCL).

2.1.5.6. Toxicity

Atrazine is slightly to moderately toxic to humans and other animals. It can

be absorbed orally, dermally, and by inhalation. Symptoms of poisoning include abdominal pain, diarrhea and vomiting, eye irritation, irritation of mucous membranes, and skin reactions. At very high doses, rats show excitation followed by depression, slowed breathing, incoordination, muscle spasms, and hypothermia. After consuming a large oral dose, rats exhibit muscular weakness, hypo activity, breathing difficulty, prostration, convulsions, and death. Atrazine is a mild skin irritant. Rashes associated with exposure have been reported. The oral LD50 for atrazine is 3090 mg/kg in rats, 1750 mg/kg in mice, 750 mg/kg in rabbits, and 1000 mg/kg in hamsters. The dermal LD50 in rabbits is 7500 mg/kg and greater than 3000 mg/kg in rats. The 1-hour inhalation LC50 is greater than 0.7 mg/L in rats. The 4-hour inhalation LC50 is 5.2 mg/L in rats.

2.2. DRINKING WATER PRODUCTION FROM SURFACE AND GROUNWATERS.

2.2.1. Introduction. General ideas

The main idea that we have to keep in mind, when a drinking water

treatment must be design is that for many compounds there are a variety of processes or combinations of them that can be used in an effective way. The decision is influenced by several factors, such as the concentration of the constituent to be removed or controlled, the regulatory requirements, the economics of the processes, and the overall integration of a treatment process in the water supply system.

After water has been abstracted, it undergoes several types of treatment in

order to make it safe to drink. But this combination of techniques to ensure


24

safety water is not unique. There are some steps that are common to every process and others that can vary from one to each other. Treatment of drinking water traditionally employs screening, settling, filtration and disinfection steps, although not all steps are used in every case, and the arrangement and variations on each differ from facility to facility, and around the world.

The principal objective of water treatment is the production of safe and

aesthetically appealing water that is protective of public health and in compliance with current water quality standards. The primary goal of a water public or private water utility is to provide treated water without interruption and at a reasonable cost to the consumer. Some activities are necessary for meeting these objectives, such as the protection and management of the watershed and the conveyance system, effective water treatment and effective management of the water distribution system to ensure water quality at the point of the use.

In the next table, typical constituents found in surface waters that are

necessary to remove, inactivate or modify to meet water quality standards are shown.

TABLE 2.2.1 TYPICAL CONSTITUENTS FOUND IN SURFACE WATERS CLASS TYPICAL CONSTITUENTS FOUND IN

SURFACE WATER Floating and

suspended materials Branches, leaves, algal mats, soil particles

Colloidal constituents Clay, silt, organic materials, pathogenic organisms, algae, other microorganisms

Dissolved constituents

Organic compounds, tannic acids, hardness ions, inorganic salts, radionuclides

Dissolved gases None Inmiscible liquids Oils and greases The specific levels to which the various constituents must be removed or

inactivated are defined by several regulations, but the ability to measure trace quantities of contaminants in water is improving continuously and by the same time, the knowledge of the health effects of these contaminants is growing. Due to these advancements water quality regulations are becoming more complex. Consequently, engineers in drinking water field must be familiar with how standards are developed, the standards that are currently applicable and what changes can be expected in the future so that the treatment facilities can be design and operated in compliance with current and future regulations and so that consumers can be assured of an acceptable quality water.


25

Water quality criteria is an important but at the same time a controversial aspect of the water supply field. Water quality concern has grown considerably due to findings that associate low levels of some constituents to higher incidence diseases such as cancer. There are a lot of reasons that support the importance of water quality standards and regulations related to engineers’ work. Standards affect the selection of raw-water sources, choice of treatment processes and design criteria, range of alternatives for modifying existing treatment plants to meet current or future standards, treatment costs and residual management.

The development of water quality criteria and standards is a relatively

recent phenomenon in the course of human history. The first standards were promulgated at the beginning of the century, but there have been numerous improvements since then, particularly in the last 30 years.

2.2.2. International standards and regulation A number of agencies have developed drinking water regulations. They

include standards for individual countries or group of countries. The most important has been the World Health Organization (WHO) and their standards are known as the Guidelines for Drinking Water Quality (WHO, 1993). These standards are considered recommendations and guidance only, not mandatory requirements. The WHO guidelines contain recommendations, health-based standards, monitoring, measurement and removal for microbial quality and waterborne pathogens, chemical constituents, radionuclides and aesthetic aspects.

Throughout the world the recommendations made by the WHO are used to

define drinking water. Within the European Union these recommendations have been used as a basis for directive 98-83. Whose legal name is Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for human consumption as amended by Regulation 1882/2003/EC

This Directive concerns the quality of water intended for human

consumption and its objective is "to protect human health from the adverse effects of any contamination of water intended for human consumption by ensuring that it is wholesome and clean ". To this effect, the water must be free "from any micro-organisms and parasites and from any substances which, in numbers or concentrations, constitute a potential danger to human health”. This directive therefore focuses on:

• Thirty parameters which have individual parametric values that must be adhered to. These parameters might pose an immediate health risk (such as the microbiological contamination of water whose presence


26

might indicate a health risk arising from any pathogenic bacteria that are present), or long term risks (when exposed on a life-long basis) such as toxic chemical substances (certain metals and pesticides).

• In addition, adhering to the guidelines of an additional list of around twenty parameters that have an indicator function(microbiological, physico-chemical or organoleptic parameters which have no direct bearing on public health) is indicative of the optimal running of water treatment facilities and the water distribution network.

The next table summarize WHO recommendations and EU Directive

standards for some of these important parameters.

TABLE 2.2.2 WHO RECOMMENDATIONS AND EU DIRECTIVE STANDARDS

EU DIRECTIVE WHO Parameter Guide

Level Max.

Admissible Concentration

1993

Temperature (°C) 12 25 AcceptableTurbidity (NTU) 0.4 4 5 Color (Hazen

Units) 1 20 15

Odor (Threshold number)

0 12°C : 2 Acceptable

Taste (Threshold number)

0 25°C : 3 Acceptable

pH 6.5-8.5 - 6.5-8.5 Chlorides (mg/l Cl) 25 - 250 Sulphates (mg/l

SO4) 25 250 250

Aluminium (mg/l Al) 0.05 0.2 0.2 Dry solids at 180°C

(mg/l) - 1500 1000

Nitrates (mg/l NO3) 25 50 50 Nitrites (mg/l NO2) - 0.1 3 Ammonium (mg/l

NH4+) 0.05 0.5 1.5

Permanganate value (mg/l O2)

2 5 -

Hydrocarbons - 0.01 0.001-1


27

(mg/l) Detergents (mg/l) - 0.2 - Iron (mg/l) 0.05 0.2 0.3 Manganese (mg/l) 0.02 0.05 0.1 Fluorine (mg/l) - 0.7-1.5 1.5 Arsenic (mg/l) - 0.05 0.01 Pesticides (µg/l)

- per substance

- total

- -

0.1 0.5

0.03-100 -

2.2.3. Overview of methods used to treat water There is a big amount of methods for the treatment of water and new

methods are still being developed. Normally, it is necessary a combination or sequence of them to meet regulation but this water treatment trains depends on the quality of untreated water and the desired quality of the treated water. Below, an overview of the various methods is shown and two tables summarize two important ideas, (1) typical unit operations and processes used for the treatment of water and (2) application of treatment processes for the removal of specific constituents. In this chapter, I’m going to focus on the processes used for treatment of surface water and for drinking water applications but in these two tables some applications could be referred to ground waters and/or wastewater treatments too.

The constituents in water can be removed by physical, chemical and

biological means and the specific methods are classified as physical unit operations, chemical unit processes and biological unit processes. Some basic ideas related to fundamental principles involved are resumed below.

Physical unit operations Treatment operations in which change is brought about through the

application of physical forces are classified as physical unit operations and the most important include screening, mixing, gas transfer, sedimentation and filtration.

Chemical unit processes Treatment processes, in which the removal or treatment of contaminants is

brought about by the addition of chemicals or by chemical reactions, are classified as chemical unit processes and chemical precipitation and disinfection are two important examples.


28

Biological unit processes. Treatment processes in which the removal of contaminants is brought

about by biological means are classified as biological unit processes. Nitrification and denitrification are the best-known biological processes that have been used for water treatment but biofiltration is very important as a removal of biodegradable organic matter.

Table 2.2.3 tries to highlight typical unit operations and processes, a brief

description of it and its typical application in water treatment.


29

TABLE 2.2.3 TYPICAL UNIT OPERATIONS AND PROCESSES USED FOR THE TREATMENT OF WATER.

Operation/process Description Typical application in water treatment

Physical unit operations Adsorption The accumulation of a material at the interface

between two phases Removal of dissolved organics from

water using granular activated carbon (GAC) or powdered activated carbon (PAC)

Aeration The process of contacting a liquid with air by which a gas is transferred from one phase to another: either the gas phase to the liquid phase (gas absorption) or the liquid phase to the gas phase (gas stripping)

Removal of gases from groundwater; oxygenation of the water to promote oxidation of iron and manganese.

Distillation Separation of components of liquid from liquid by vaporization and condensation

Used for desalination of sea water.

Filtration (media) The removal of particulate material in a filter bed composed of a granular medium through transport and attachment to the filter media.

Removal of solids following coagulation, flocculation, gravity sedimentation or flotation

Filtration (membrane microfiltration)

Membrane filtration used for the removal of colloidal material (0.1 to 1.0 mm) by means of straining (size exclusion)

Used to remove turbidity, bacteria and protozoa like Giardia and Cryptosporidium

Filtration (membrane ultrafiltration)

Membrane filtration used for the removal of sub micrometer particles (0.001 to 0.03 mm) by means of straining (size exclusion)

Used to remove turbidity, some viruses, bacteria and protozoa like Giardia and Cryptosporidium

Flocculation Aggregation of particles that have been chemically destabilized through coagulation

Used to create larger particles that can be more readily removed by other processes such as gravity settling or filtration

Flotation, dissolved Removal of fine particles and flocculant particles Removal of particles following


30

air with specific gravity less than water or very low settling velocities

coagulation and flocculation for high-quality raw waters that are low in turbidity, color, and/or TOC or experience heavy algal blooms.

Mixing Mixing and blending of two or more solutions through input of energy

Used to mix and blend chemicals

Nanofiltration High-pressure membrane filtration used for removal of dissolved sub micrometer particles (0.001 to 0.01 mm) by straining (size exclusion)

To produce potable water from ocean, sea or brackish water; water softening; removal of specific dissolved contaminants such as pesticides and removal of NOM to control DBP formation

Reverse osmosis High-pressure membrane filtration used for removal of dissolved sub micrometer particles (0.0001 to 0.005 mm) by solution/diffusion and exclusion

To produce potable water from ocean, sea or brackish water; water softening; removal of specific dissolved contaminants such as pesticides and removal of NOM to control DBP formation

Screening, coarse Passing untreated water through coarse screen to remove large particles from 20 to 150 mm and larger

Used at the intake structure to remove sticks, rags and other large debris from untreated water by straining on screen

Screening, micro Passing water through stainless steel or polyester media for removal of small particles from 0.025 to 1.5 mm from untreated water by straining on a screen

Used for the removal of filamentous algae

Sedimentation Separation of settable solids by gravity Used to remove particles greater than 0.5 mm generally following coagulation and flocculation

Ultraviolet light disinfection

Use of UV light to inactivate microorganisms Inactivation of microorganisms such as viruses, bacteria and protozoa usually used


31

in conjunction with a chemical that can produce a lasting residual in the distribution system

Ultraviolet light oxidation

Use of UV light to oxidize complex organic molecules and compounds

Used for oxidation of N-nitrosodimethylamine

Chemical unit Processes Advanced oxidation Use of chemical reactions that generate highly

reactive short-lived hydroxyl radicals (OH-) for purpose of oxidizing chemical compounds; typical reactions that produce these radicals, listed from most common to less common: O3, peroxone, O3 and UV radiation and H2O2and UV radiation

Oxidation of certain humic compounds, pesticides and chlorinated organics and some taste and odor compounds like MIB and geosmin found in surface waters and contaminated groundwaters.

Chemical disinfection Addition of oxidizing chemical agents to inactivate pathogenic organisms in water

Disinfection of water with chlorine, chlorine compounds or ozone

Chemical neutralization

Neutralization of solution through addition of chemical agents

Control of pH; optimizing operating range for other treatment processes

Chemical oxidation Addition of oxidizing agent to bring about change in chemical composition of compound or group of compounds

Oxidation of iron and manganese for subsequent removal with other operations and processes; control of odors; removal of ammonia

Chemical precipitation

Addition of chemicals to bring about removal of specific constituents through solid phase precipitation

Removal of heavy metals, phosphorous

Coagulation Process of destabilizing colloidals so that particle growth can occur during flocculation

Addition of chemicals such as ferric chloride, alum and polymers to destabilize particles found in water

Ion exchange Process in which ions of given species are Removal of hardness, nitrate, NOM, and


32

exchanged from insoluble material by ions of different species in solution

bromide; also complete demineralization

Stabilization Addition of chemical to render treated water neutral with respect to formation of calcium carbonate scale

Stabilization of treated water before entry into distribution system

Biological unit processes Biofiltration (liquid

phase) Rapid granular media filter operated for dual

purpose of particle removal and removal of biodegradable organic matter by biological oxidation

Removal of biodegradable organic matter (BOM) following ozonation and oxy anions of halogens (bromate, chlorate..)

Denitrification Biological conversion of nitrate (NO3-) to nitrogen gas (N2)

Conversion of nitrate found in some surfaces wastes to nitrogen gas

Nitrification Biological conversion of ammonia to nitrate Conversion of ammonia found in some surface wastes to nitrate for subsequent removal by denitrification


33

In the next table, representative constituents that may have to be removed from surface and ground waters to meet specific water quality objectives are identified, as well as the treatment operation and processes that can be used for their removal. Normally, for most of the contaminants different processes can be used and the final selection will depend (among other factors) on what additional constituents must be removed and how complimentary are the processes being considered.


34

TABLE 2.2.4 APPLICATION OF TREATMENT PROCESSES FOR THE REMOVAL OF SPECIFIC CONSTITUENTS Constituent Process Applicability

Physical parameters In-line filtration Works well in low-turbidity, low-color waters. Pilot

studies should be performed to establish performance and design criteria

Direct filtration Applicable for low to moderate turbidity and colored waters. Pilot studies should be performed to establish performance and design criteria. Shorter filter runs than conventional treatment

Conventional treatment Works well in moderate to high-turbidity waters. More operational flexibility than direct or in-line filtration. Sedimentation basin detection time allows for NOM, taste and odor and color removal in combination with sedimentation. Sometimes can be designed without piloting if local regulatory agency guidelines are followed.

Turbidity/particles

Membrane filtration-microfiltration, ultrafiltration

Effective at removing turbidity, bacteria and protozoa-sized particles. Viruses may be removed by some types of ultrafiltration membranes. Works well on low-turbidity waters or with pretreatment for particle removal. Natural organics can foul membranes. Pilot testing required demonstrating particle removal and potential for organic fouling. Easily automated and space requirements are much smaller than conventional plants.


35

Slow sand filtration Primary removal mechanisms are biological and physical. Works well in low-turbidity waters. When used in conjunction with granular activated carbon (GAC), effective at taste and odor removal. Surface loading rates are 50 to 100 times lower than rapid filtration so filters are very large. Most commonly used by small communities, but there are very large plants in operation throughout the world.

Lime-soda softening Applicable for moderate to extremely hard waters. Historically the most common method for removal of hardness

Ion exchange Most common in small installations. Disposal of regenerate solutions can be a problem

Hardness

Nanofiltration Often referred to as low-pressure reverse osmosis membranes. Applicable for moderate to extremely hard waters. Disposal of concentrate may be the limiting factor in using nanofiltration.

Total dissolved solids (TDS)

Reverse osmosis, ion exchange, distillation

Used for desalination with ocean, sea and brackish water. Reverse-osmosis concentrate and ion exchange regenerate solution disposal may be the limiting factoring selecting these treatment processes

Inorganic chemical parameters Nitrate Biological denitrification, reverse

osmosis, ion exchange Biological denitrification requires the use of special

organism to reduce nitrate to nitrogen gas. Reverse osmosis will reduce nitrate levels in drinking water, but this process is used primarily for treating high TDS and salt water. Ion exchange with anionic resins is attractive when


36

brine disposal is available. Fluoride Lime softening,

coagulation/precipitation, activated alumina

Lime softening will remove fluoride from water both by forming an in soluble precipitate and by co precipitation with magnesium hydroxide. Alum coagulation will reduce fluoride levels to acceptable drinking water standards but requires very large amounts of alum to do so. Contact with fluoride-containing water with activated alumina will remove fluoride

Arsenic Coagulation/precipitation, activated alumina, ion exchange, reverse osmosis

Conventional coagulation with iron or aluminum salts is effective for removing greater than 90 % of As (V) at pH levels of 7 or below. As with fluoride, is strongly adsorbed/exchanged by activated alumina. As (III) is difficult to remove but is rapidly converted to As(V) with chlorine

Selenium Coagulation/precipitation, activated alumina, ion exchange, reverse osmosis

Conventional treatment techniques using alum or ferric sulfate coagulation and lime softening have been investigated for selenium removal. Activated alumina has also been investigated for its potential to remove Se (IV) and Se (VI). Although strong-base anion exchange resins have not been thoroughly investigated for selenium removal, it appears that it could be successful, but they are not selective for selenium

Sulfide Oxidation Typically found in groundwaters as H2S and is responsible for taste and odors similar to rotten eggs. Removal is most common through aeration and chlorination

Iron/manganese Oxidation, polyphosphates, ion exchange

Typically found in ground waters or lake waters with low dissolved oxygen. Removal is most commonly through


37

precipitation by oxidation using aeration or chemical addition for removal by sedimentation or filtration. Greensand filtration in which oxidation and filtration take place simultaneously is also common. The use of polyphosphate precipitation is another method that can be used for the removal of iron and manganese. Iron oxidizes much more readily than does manganese

Sulfate Reverse osmosis Reverse osmosis is most common for removal of sulfate from seawater

Organic chemical constituents Volatile organics,

pesticides/herbicides Air stripping, coagulation, adsorption,

advanced oxidation For volatiles, air stripping process is recommended.

Usually volatile organic compounds (VOC) removal from the gas phase is required post treatment. For nonvolatile components, coagulation or adsorption process can be used. Low-pH coagulation can be used to remove significant amounts of TOCs and some volatile organic compounds

Natural organic matter

Enhanced coagulation, adsorption, ion exchange, reverse osmosis

Enhanced coagulation can be used to remove significant amounts of NOM as measured by TOC and is the most widely used process for NOM removal. GAC adsorption, post filtration is also very effective in removing NOM. Ion exchange is limited by disposal of the high-TDS regeneration brine. The high cost of RO and concentrate disposal issues limit the use of this process for NOM removal.

Disinfection Enhanced coagulation, adsorption, Strategies for the control of DBPs include alternative


38

byproducts alternative disinfectants disinfectants (ozone, chloride dioxide, chloramines and ultraviolet light) or removal of DBP precursor material (NOM) through enhanced coagulation or adsorption on activated carbon. GAC can be used to remove bromate, a DBP formed from ozone and bromide.

Radionuclides Aeration, detention time Simple aeration is effective. Packed tower aeration can

be used for removal of very high levels. Mixing and detention time may control low-level radon contamination

Radon

Adsorption Carbon used for adsorption may be a low level radioactive disposal problem

Radium Coagulation The selected process depends on the level of contamination. Residuals may represent a low-level radioactive waste disposal problem

Uranium Lime softening, ion exchange, reverse osmosis

The selected process depends on the level of contamination. Residuals may represent a low-level radioactive waste disposal problem

Microbial parameters Bacteria Conventional treatment, membrane

filtration, reverse osmosis, disinfection Bacteria can be removed through conventional

processes, including sedimentation and filtration. Membrane processes provide a positive barrier to most bacteria. Given sufficient dose and contact time, all common disinfectants are effective at inactivation of bacteria

Viruses Conventional treatment, membrane filtration, reverse osmosis, disinfection

Viruses can be removed through conventional processes, including sedimentation and filtration.


39

Membrane processes with low-molecular weight cutoff such as some ultrafiltration membranes can be used for virus removal. Pilot studies are required with membranes to demonstrate effective control. All common disinfectants, with the exception of chloramines, are effective at inactivation of most viruses. Chloramines require a long contact time at high doses for effective virus disinfection

Protozoan cysts Conventional treatment, granular media filtration, reverse osmosis, high pressure membranes, disinfection

Pathogenic cysts and oocysts (Giardia and cryptosporidium) require high levels of disinfectants to inactivate. Effectiveness in decreasing order is ozone > chlorine dioxide >chlorine >> chloramines. Conventional treatment as well as granular media filtration is effective at removing cysts and oocysts. Membrane processes provide a positive barrier for cysts. UV irradiation is also effective.

Algae Copper sulfate, conventional treatment, dissolved air flotation, micro screening

Copper sulfate application in raw-water storage areas has been used to control algae blooms. Moderate to severe seasonal algae bloom situations can be handled through careful control of conventional processes: sedimentation and filtration. Direct filtration and in-line filtration can experience extremely shortened filter runs during algae episodes. For persistent algae problems, dissolved air flotation processes or contact clarification devices should be considered. Micro screening may be used at the head works of a treatment plant for filamentous algae removal.


40

Aesthetic parameters Source control with copper sulfate

and reservoir destratification (in situ aeration)

Many taste and odor problems are associated with algae growths and reservoir turnover. Copper sulfate applied in the source water is effective at controlling algae growth. Aeration is appropriate for use in relatively shallow raw-water storage areas where seasonal turnover of stratified water releases taste and odor compounds

Taste and odors

Oxidation with chlorine, ozone, potassium permanganate and chlorine dioxide

Chlorine may be used to control taste and odors from H2S but is not effective at algal taste and odors and may even make these types of taste and odors worse. Chlorination of industrial chemicals such as phenols intensifies objectionable tastes. Ozone is viewed as one of the most effective oxidants for reducing taste and odors and has the additional benefit in that it can also be used for disinfection. Permanganate is effective for removal of some algae taste and odors at alkaline pH but not the most common taste and odor compounds MIB and geosmin. Additionally, overdosing results in pink water and the formation of black deposits in the distribution systems and household and industrial appurtenances. Chlorine dioxide is effective at controlling many tastes and odors but is not effective in reducing geosmin and MIB. Pilot or bench testing should be performed to determine the best oxidation approach


41

Adsorption with GAC and PAC GAC as a filter medium can be very effective for low to moderate taste and odor levels. Replacement is usually on a 3-5 year cycle. In slurry form, PAC can be added to the coagulation process for taste and odor control. PAC is specially effective in contact clarification devices

Coagulation/precipitation High coagulation doses and low pH can be effective even for very high color levels. Bench or pilot testing is recommended

Adsorption with GAC Granular activated carbon bed life can be short depending on the levels and empty bed contact time

Color

Oxidation with chlorine, ozone, potassium permanganate and chloride dioxide; low-pressure reverse osmosis

Effectiveness is generally ozone > chlorine > chlorine dioxide > KmnO4. pH can affect the efficiency and some colors may return after oxidation. Pilot or bench studies are recommended. Reverse osmosis is very effective but expensive


42

In the development of systems for water treatment three main steps should be kept in mind: the design, construction and operation of water treatment facilities. The initial design is based on water quality data, regulatory requirements, water quality issues, consumer concerns, construction challenges, operational constraints, water treatment technology and economic feasibility, without forgetting the human creativity to develop a water treatment plant design. Then this design is transformed into a permanent facility through the construction process and becomes an operational water treatment facility with the addition of raw materials and operator know-how.

When we talk about general considerations involved in the selection of

water treatment processes, three key pieces of information have to be pointed out: source water quality, required and/or desired quality of the treated water, and required plant production and operational goals.

Normally the first step is to know if we are going to process surface or

groundwater. For surface water, the information should include typical water, event water and source stability. When we talk about event water quality, we are referring to aspects such as spring runoff, summer algae growth, fall reservoir turnover and minimum winter water temperatures. Many source water quality characteristics can affect treatability and the next table summarizes them.

TABLE 2.2.6 SOURCE WATER QUALITY CHARACTERISTICS THAT AFFECT TREATABILITY

Physical characteristics

Turbidity and particulates

Organic characteristics

NOM, disinfection byproducts precursors, color and chlorine demand

Microbial constituents Protozoa (Cryptosporidium and Giardia), viruses, bacteria, and heminths

Chemical parameters pH, alkalinity, hardness and corrosivity Inorganic constituents Iron, manganese, arsenic and bromide Aesthetic Color, taste and odor Constituents of

regulatory concern SOCs, VOCs, some inorganic constituents,

radionuclides, algae and biological stability The required and/or desired treated water quality also imposes constraints

on the treatment process. Treated water quality is directly impacted by current and future regulatory compliance, the quality objectives of the utility, consumer expectations and political constraints. Achieving treated water quality goals frequently means more than one process is necessary to address a quality issue, this concept is known as multiple-barrier approach.


43

Plant production and operational goals can vary and sometimes can be at

odds with each other. Typical productivity operational goals can include filtration efficiency, filter run length, terminal head loss, filter maturation volume (volume of water filtered to waste), and disinfection Ct value [the residual disinfection concentration C (mg/l) multiplied by the contact time t (min)]. Operator knowledge is a huge source of information that is practical and useful in designing a new plant. Operational information that may be available could include what processes and types of chemicals are being used, how to treat changes in raw-water quality, what the operators like and do not like about their plant and how the new plant may be more efficient, easier to operate and more flexible for meeting future regulations.

2.2.4. Synthesis of water treatment trains As it was said before there are a lot of different processes available for

drinking water treatment. Probably, experience is one of the most useful tools when we want to treat the same or similar source water. But, when there is a lack of experience or when there is a desire to provide for a different degree of treatment it is necessary to develop special studies. These special studies include bench-scale study in the laboratory, pilot plant testing and plant-scale simulation testing.

Due to I am paying special attention to surface waters and the quality of

these waters can varied, different treatment trains can be considered as successful alternatives. Four common treatment trains are considered below, but they are just general trains that can experiment some modifications depending on the factors commented before. They can be named as conventional water treatment, direct and inline filtration treatment, direct micro filtration treatment and reverse osmosis treatment. Basic ideas related to them are resumed below.

Conventional water treatment They are typically used to treat surface waters with water quality issues

such as high turbidity (typically >20 NTU), high colour (>20 c.u.) or high TOC (>4 mg/l) and the treatment train consists of coagulation, flocculation, sedimentation, granular media filtration, and disinfection. In general, it can be said that this kind of plants have more operational flexibility, are hydraulically stable and require less operator attention. Surface loading rates are typically low, so these processes require a large surface area.


44

Direct and inline (contact) filtration. Direct filtration treatment trains are typically used to treat higher quality

surface waters with low turbidity (typically


45

understandable that the reliability of treatment trains is extremely important. It is not the only parameter that should be precisely controlled but it is probably the primordial. If engineers want to be sure that this issue is addressed, they need to design systems that include multiple barriers to limit the presence of pathogens in the treated drinking water. When we talk about barriers it can be referred to source protection, additional treatment and even additional security in the design and operation of the water distribution system. It can be shown that multiple barriers will increase the reliability of the system, even if the overall removal capability is not significantly different. The most interesting and world wide used techniques applied as multiple barriers are considered below. Adsorption on activated carbon is not commented in this chapter due to a special section (2.3) is dedicated to it.

2.2.6. Membranes

2.2.6.1 Introduction and classification. Membrane technologies are playing an increasingly important role in the

treatment of water and wastewater, but I am going to focus in surface and groundwater treatment for drinking water production. Some reasons that explain the more widespread use of this technique are the more stringent regulations (due to growing public health concern in addition to stricter legislation) that cannot be effectively met by conventional treatment processes, a growing demand for water for different uses, a decrease in available fresh water supplies and increased emphasis on the use of brackish water or reclaimed wastewater as a source and a better performance and lower costs of membranes due to technological advances.

Membrane processes are modern physicochemical separation techniques

that use differences in permeability of water constituents as the separation mechanism. During membrane treatment, water is pumped against the surface of a membrane, resulting in the production of product and waste streams. The membrane typically is a synthetic material, semipermeable. During operation, permeable components pass through the membrane and impermeable components are retained on the feed side. As a result, the product stream is relatively free of impermeable constituents and the waste stream is concentrated in impermeable constituents.

Firstly, some ideas about the four pressure-driven membrane processes

currently used in municipal water treatment are summarized. They are reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF) and microfiltration (MF). According to two distinct physicochemical processes they can be classified as membrane filtration (UF and MF) and reverse osmosis (RO and NF).


46

Filtration can be defined as a process that separates suspended particles from a liquid phase by passage of the suspension through a porous medium (either membranes or granular media). In membrane filtration, the feed stream is a suspension, or two-phase system and the primary goal of membrane filtration is to produce a product stream (water) from which the targeted solids have been completely removed, which is similar to the goal of granular filtration.

On the other side, osmosis is the preferential diffusion of water through a

semipermeable membrane in response to a concentration gradient. In reverse osmosis, the feed stream is a solution, or single-phase system, in which the constituents targeted for removal are truly dissolved solutes and the objective of this technique is to reduce the concentration of these solutes in the product water.

In the table below, a resume of some ideas is shown.

TABLE 2.2.6 HIERARCHY OF PRESSURE-DRIVEN MEMBRANE PROCESSES

Physicochemical

process Type of

membrane Pore

dimension Solute

removed Membrane

filtration Microfiltration 0.1 mm Particles

Sediment Algae Protozoa Bacteria

Membrane filtration

Ultrafiltration 0.01mm Small colloids

Viruses Reverse osmosis Nanofiltration 0.001 mm Dissolved

organic matter Divalent

ions (Ca2+, Mg2+)Reverse osmosis Reverse

osmosis Nonporous Monovalent

Species(Na+, Cl-) General schematics of the integration of these processes for drinking water

treatment can be seen.

o MF or UF is employed for particle and microbial removal. The only necessary pretreatment is a prescreening and they are operated with only residual disinfection in many surface water applications. But, this membrane treatment does not remove substantial levels of natural organic matter (NOM). Because of this,


47

o MF and UF can be employed in conjunction with a coagulant or adsorbent (PAC addition) to get greater removal of organic compounds or DBP precursors (undesirable in drinking water).

o For groundwaters, RO and NF are employed only with pretreatment (cartridge filtration, pH adjustment and/or addition of a sequestering agent) for removal salts or natural organic matter.

o However, for surface water or water reuse applications, greater pretreatment for RO and NF is required. In these situations, integrated membrane systems using dual membrane treatment can be taken into account. UF or MF is employed as a pretreatment for high pressure membrane applications.

o The last schematic refers to a conventional treatment as a pretreatment for NF. In this scheme, NF is used as a final process in a treatment train that can be used for a greater NOM removal.

Due to there is not enough place in this thesis to explain lots of aspects

related to membrane process, the next table summarizes several process characteristics comparing membrane filtration and reverse osmosis.

TABLE 2.2.7 MEMBRANE FILTRATION AND REVERSE OSMOSISI COMPARISION

Process

characteristic Membrane

filtration Reverse Osmosis

Objectives Particle and microorganism removal

Sewater desalination, brackish water desalination, softening, NOM removal for DBP control, specific contaminant removal

MEMBRANE TYPES

Microfiltration and ultrafiltration

Nanofiltration and reverse osmosis

Typical source water Fresh surface water

Ocean or sea water, brackish groundwater, colored water

Membrane structure Homogeneous or asymmetric

Asymmetric or thin film composite

Most common Hollow fiber Spiral wound


48

membrane configuration Dominant exclusion

mechanism Straining Differences in solubility

or diffusivity Removal efficiency of

targeted impurities Frequently

99,9999% or greater Typically 50-99%,

depending on objectives Most common flow

pattern Dead end Tangential

Operation includes backwash cycle

Yes No

Influenced by osmotic pressure

No Yes

Influenced by concentration polarization

No Yes

Noteworthy regulatory issue

Integrity monitoring

Concentrate disposal

Typical transmembrane pressure

0,2-1 bar 5-85 bar

Typical permeate flux 30-170 l/m2*h 1-50l/m2*h Typical recovery > 95% 50 % (for seawater) to

90% (for coloured groundwater)

Competing processes Granular filtration

Carbon adsorption, ion exchange, precipitative softening, distillation

2.2.6.2. Advantages Membrane processes present several advantages when compared with

classical separation techniques (coagulation, flocculation, settling, slow and rapid sand filtration and multimedia filtration)

• They constitute an effective barrier to particles, organic micro pollutants,

pesticides and microorganisms.

• The reduction of the final chlorinating dose because of the absence of bacteria and viruses.

• The exclusion of all additions.

• They reduce sludge disposal


49

• They ensure constant water quality standards regardless of the raw

water variations.

• They work in a simple reliable automated operating regime with minimal manpower using compact modular plants.

Now, that some general ideas have been said, a more detailed study of the

most interesting applications of membranes is going to be developed, focusing in the particular characteristics of this technique.

2.2.6.3. Membrane applications

Desalting Mainly, membrane technology has been growth because of its importance

in desalting processes. Desalting practices may be categorized generally into three broad classes.

1. Distillation processes, which include multistage-flash

evaporation, multiple-effect evaporation and vapor compression.

2. Membrane processes, which include RO, NF, electrodialysis reversal (EDR).

3. Other processes, which include ion exchange, freezing,

hybrid and other miscellaneous processes. Distillation technology is the most important technique in this application,

but the percent of worldwide desalting capacity by membrane processes has been steadily increasing (RO is the 23% and ED the 5% of the worldwide desalination capacity.

Control of disinfection by-products As a result of new DBP regulations (middle of nineties), there has been a

growing interest in employing membrane processes for removal of precursors to DBPs.

In one hand, RO and NF are used for removal of NOM. NF has been

employed primarily for groundwaters containing relatively low total dissolved solids, but with high total hardness, color and DBP precursors. Several investigators have been demonstrated that NF is capable of controlling


50

precursors to chlorinated organic compounds, in general, greater than 90% removal of THM and haloacetic acid precursors is achievable.

In the other hand, the removal of NOM using MF and UF is always

considerably less than NF. The reason is because of the large variation of pore sizes (0.05-5µm) and membrane materials associated with them. Some removal results obtained in important experiments are 15% removal of the total organic carbon (TOC) and total trihalomethane formation potential (THMFP) from a stream (0.2µm MF membrane) or 30% removal of TOC using 0.05 µm ceramic tubular membrane. In both cases the THMFP was reduced by 10-20%. But, if this treatment is combined with the use of a coagulant the removal of NOM, including DBP precursors materials is much higher. Using ferric chloride as a pretreatment to MF, reduction in THMFP can be improved by approximately 30%.

Disinfection. One of the primary applications of MF and UF is for the removal of

microorganisms. The protozoa Giardia and Cryptosporidium have been the principal organisms controlling disinfection in surface water supplies, since the epidemic in Milwaukee, USA. Optimally operated conventional treatment plants (conventional flocculation, sedimentation and filtration) are not able to provide the necessary removal of 4 to 6 logs for Giardia and Cryptosporidium and Crystosporidium is especially resistant to traditional disinfectants like chlorine and chloramines.

Viruses are the smallest organisms of concern to the water community,

ranging from 0.02 to 0.08 µm, followed by bacteria (0.5 -10 µm) and protozoan cysts and oocysts (3-15µm). The pore sizes for MF and UF range from 0.01 to 5µm. Thus, it is apparent that removal of these organisms is specific to the particular membrane and its pore size distribution. This is if we just take into account membrane as a simple physical barrier, but other physical/chemical mechanisms also play a role in the removal of microorganisms. Anyway, experiments developed in a variety of different MF and UF membranes showed that Cryptosporidium, Giardia, total coliform bacteria, Escherichia coli and enterococci were removed to detection limits of their respective assays. The removal of viruses by membranes is very specific to the membrane and the virus and although laboratory waters are useful to estimate the removal capabilities of membranes under conservative conditions, the extent of virus removal will vary in natural waters.

In summary, it is generally accepted today in the scientific community that

MF and UF can provide complete removal of most bacteria and all protozoan cysts of concern as long as the membrane and associated system components are intact and operating correctly. In the case of UF, virus removal is also achieved.


51

Pesticides and other micro pollutants. In many countries, it is common to eliminate pesticides and other trace

organics using activated carbon filters but in some situations the use of nanofiltration process can be also economically competitive. This can occur when the water that is going to be treat has a relatively high content of organic and humic substances, so the filter running time decreases (due to competitive adsorption) and consequently, the costs for the activated carbon

chapter 2. literature studybibing.us.es/proyectos/abreproy/20087/fichero/chapter+2.pdf · chapter...

Documents