gdaŃsk university of technology faculty of … · • splitting off the hydrogen atom from the...

GDAŃSK UNIVERSITY OF TECHNOLOGY

FACULTY OF CHEMISTRY

DEPARTMENT OF PROCESS ENGINEERING

AND CHEMICAL TECHNOLOGY

ENVIRONMENTAL REMEDIATION TECHNOLOGIES

CHEMICAL METHODS FOR WASTEWATER TREATMENT

FROM LANDFILLS - FENTON, OZONATION

AND PHOTOCATALYTIC REACTIONS

GDAŃSK 2018/2019

1. INTRODUCTION

Leachates can be defined as seepage waters from municipal waste landfills. They are characterized by

reduction properties and significantly increased parameters of biological and chemical oxygen demand

(BOD5 and COD), high concentrations of solutes, chlorides, sulphates and ammonium nitrogen compounds.

In contrast to municipal sewage, leachate from landfills is difficult to purify with biological methods.

In the last decade, intensive research has been undertaken to find effective methods of removing toxic

impurities that occur in water, sewage and leachates both in trace amounts and in relatively high

concentrations. One of the currently available technologies is Advanced Oxidation Processes (AOPs), based

on reactions involving hydroxyl ·OH radicals. Hydroxyl radicals are the strongest oxidant that can be used

for water and wastewater treatment (the oxidation potential is 2.80 V). They are generated, inter alia, during

the decomposition of ozone in the aquatic environment during chain radical reactions, as well as during

photolysis of hydrogen peroxide, chlorine, Fe(III) aqueous solutions, during Fenton reaction, or under the

influence of ionizing radiation.

The hydroxyl radicals are not selective and react with most of the dissolved organic and inorganic

compounds at a high degradation rate constant of the reaction. To increase efficiency in many oxidation

processes, several different oxidants are used, and reactions with the use of OH· radicals are only one of the

stages of the wastewater treatment process [Hoigne 1996]. AOPs are important for the treatment of sewage,

leachate, contaminated surface and groundwater as well as for the production of ultrapure water [Braun,

1996].

2. OVERVIEW OF OXIDATION METHODS

Among advanced oxidation technologies there are chemical and photochemical processes (light-

induced oxidation processes). In principle, they can be divided into two groups: technologies running at

atmospheric pressure and at ambient temperature (e.g. ozonolysis and photooxidation) and technologies

requiring the use of elevated temperatures and pressures (wet oxidation and supercritical water oxidation).

Chemical degradation methods:

• wet air oxidation (WAO),

• supercritical water oxidation (SCWO),

• electrochemical oxidation,

• oxidation with ozone and hydrogen peroxide,

• Fenton reaction

Photochemical processes:

• UV photolysis,

• processes using UV/H2O2,

• processes using UV/O3,

• processes using UV/H2O2/O3,

• photocatalytic degradation in aqueous semiconductor suspensions,

• photo-Fenton reaction,

• processes using ultrasounds [Prousek 1996].

Common features of NPU methods include:

• Organic pollutants are decomposed to carbon dioxide, water and ammonia (or nitrogen) and to

simple compounds such as low molecular weight organic acids (acetic and formic acid),

• In reaction systems, an oxidizer with high oxidation potential is generated. The free radical

mechanism dominates, and one of the most important reagents is the hydroxyl radical

• high oxidation potentials cause that AOPs belong to non-selective methods - all groups of organic

compounds and non-oxidized forms of inorganic compounds undergo oxidation.

Particular AOPs methods differ mainly in the method of generating the hydroxyl radical.

Oxidation of organic compounds proceeds through to one of three mechanisms:

• the hydroxyl radical accepts the electron from the organic substance to form a new radical, while

simultaneously reducing itself to the hydroxyl ion - it is the electron transfer reaction,

• splitting off the hydrogen atom from the molecule. This process creates an organic radical and water

- it is a hydrogen transfer reaction,

• addition of a hydroxyl radical to a double bond in alkenes and aromatic compounds, which leads to

the formation of a radical on the carbon atom - this is the addition reaction of the hydroxyl radical.

2.1. Wet oxidation with air

The process of wet oxidation is carried out in the liquid phase, at elevated temperature (from 100 to 300 °

C) and under increased pressure (from 0.5 to 20 MPa). During the process, air or oxygen is pressed into

the reaction medium. Organic carbon is oxidized to CO2, organic nitrogen to ammonia or free nitrogen,

and organic chlorides and sulphides are converted into inorganic chlorides and sulphates. The

effectiveness of the method is based on two beneficial features of this reaction system:

• with the increase of temperature above 393K, the solubility of oxygen in aqueous solutions

increases significantly.

• increasing the temperature increases the rate of chemical reactions and improves the efficiency of

free radical formation.

Wet air oxidation is carried out in a heterogeneous gas-liquid system in the following stages:

a) transfer of oxygen from the gas phase to the gas-liquid interface,

b) transfer of dissolved oxygen from the gas-liquid interface to the liquid mass

c) chemical reaction between dissolved oxygen and substrates.

These features of wet oxidation make it a highly unselective process and the high temperature of the

process allows to achieve significant conversion rates of substrates and intermediate products ranging

from 70 to 100%. The wet oxidation process is considered to be effective when the concentration of

impurities in liquid or semi-liquid waste does not exceed 1.5 % -20 % by weight, and the amount of

treated wastewater is not less than 15-20 m3/day.

Over the years, the process of wet air oxidation has found application in:

• removing glycols, detergents, phenols, napholes and their derivatives, pesticides as well as synthetic oils

and resins from sewage,

• treatment of waste water streams that are too diluted for combustion and too concentrated for biological

treatment,

• the treatment of wastewater from the spirit industry (mainly from the distillation of fermentation broth),

• the oxidation of sewage containing cyanides and nitriles derived from galvanizing processes, from coke

ovens and from pharmaceutical synthesis processes,

• the oxidation of polyethylene glycols and surfactants,

• the regeneration of activated carbons used for the treatment of wastewater containing toxic and waste

organic compounds (Zarzycki, 2002).

At present, there are around 400 industrial wet

oxidation installations in the world. The most

popular installation is ZIMPRO® (USA) operating

on the basis of a flow tower reactor, which consists

of a vertical tank fed from the bottom with liquid

and gas. The flow in the reactor is laminar and the

products are discharged from the top of the reactor.

The ZIMPRO® installation diagram is shown in

Fig. 1

Fig. 1. Scheme of ZIMPRO® installation

Wastewater containing easily settling suspensions can be purified using the WETOX® method.

The oxidation process runs in a high-pressure reactor consisting of a horizontal tank, divided into sections,

each of which has an independent air supply and a stirrer. The device works based on the idea of a cascade

of reactors with perfect mixing. The advantage of the reactor is the possibility of wastewater treatment

containing easily sedimenting suspensions, and the disadvantage - the use of agitators, whose drive shafts

are led through the reactor wall to the outside, which requires expensive seals and special bearing.

2.2. Supercritical oxidation

In recent years, a number of applications have been developed for the long-known thermodynamic state of

the substance which is supercritical fluid. A special role as a medium alongside carbon dioxide plays

water, especially in the area oriented to environmental protection, because it turned out to be a very

promising environment for the oxidation of pollutants and organic waste. Oxidation in supercritical water

is carried out above the critical point of water (> 22 MPa and 374°C). The similarity of oxidation in the

supercritical condition is only formal for other wet oxidation processes, because above the critical point in

the reaction mixture we have a one-phase process, and thus the kinetics of the process lies solely in the

area of chemical kinetics.

Water in the supercritical state changes its properties as a solvent - from ionic to non-ionic. Oxidation in

supercritical water in relation to classical thermal methods provides practically complete mineralization.

That creates the possibility of running a process in a closed circuit, in a more concentrated environment, at

a lower temperature, and in particular it eliminates the effect of secondary gas emissions. At the supercritical

point the water volume is 3 times higher than in normal conditions (d = 0.322 g·cm-3), and the dielectric

constant ε is only 5.3. As a result, under the conditions of the oxidation process, at a temperature of about

400°C and for a pressure between 23-26 MPa, the water occurs in the form of a dense gas. Organic

substances, including hydrocarbons, and molecular oxygen become mutually soluble with water, while

inorganic salts precipitate out of solution. These unique properties of supercritical water allow the contact

of oxygen and organic compounds in one phase, in which rapid and complete oxidation of organic

substances occurs at temperatures of 550-650°C. Under these conditions, the conversion rate can be over

99.99% for a one-minute residence time.

Oxidation in the supercritical state has found application in:

• oxidation of substances considered to be particularly dangerous or burdensome for the environment

due to its toxicity while being resistant to oxidation (nitrophenols, aliphatic and aromatic halogen

derivatives, polychlorinated biphenyls and dioxins),

• disposal of toxic and dangerous substances related to national defense,

• in oxidation processes, e.g. carbon monoxide, hydrogen, ammonia, methane or acetic acid,

• oxidation of wastewater from the paper industry and excess active sludge from municipal and

industrial treatment plants.

The schematic of the installation of the supercritical water oxidation process (MODEC® method)

is shown in Figure 2.

Fig. 2 Scheme of installation for supercritical oxidation

In general, the process proceeds as follows: the feed prepared in the tank (F) is a solution or a suspension

of fine particles of an organic substance. Liquid oxygen is used as the oxidant, which is pumped from the

tank (T) through a high-pressure pump through the evaporator (P). The feed and the oxidant meet in the

reactor (R). The reactor, as the most important part of the installation, must meet four basic conditions:

• the residence time must guarantee sufficiently deep oxidation,

• must be resistant to corrosive reaction environments and hydrodynamic conditions also a precipitation

of some reaction products,

• have an ability to utilize the heat of reaction.

The post-reaction stream, after leaving the reactor, gives off heat to the stream in the heat exchange system

(W).The system components are also the final cooling system (Ch) and the separation of reaction products

S1, S2

2.3. Oxidation with ozone and hydrogen peroxide

In many countries, ozone is the most widely used substance used to purify drinking water. It is

also used for the oxidation of pollutants in the case of industrial wastewater. One of the main advantages of

using ozone is its beneficial effect on the environment. The reaction products of ozone with chemical

compounds that are water contaminants are mostly non-toxic and biodegradable, and ozone itself transform

to form oxygen.

Ozone is known as the most selective oxidant. The oxidation reactions initiated by ozone in aqueous

solutions are mainly complex reactions. Ozone can react with organic substances in two ways: directly or

through radicals (secondary oxidant). The presence of solutes affects the oxidation process and thus the end

products obtained. The ozone can react with organic substances by various mechanisms. The simplest of

them is the basic reaction of ozone with an organic molecule. However, most of the reactions probably

occur between organic matter and hydroxyl radicals.The ozone oxidation potential is 2.07 V, while the

oxidation potential of hydrogen peroxide is 1.77 V. Therefore, hydrogen peroxide is also used as an oxidant

in wastewater treatment processes. Both oxidants are often used together. The use of hydrogen peroxide

significantly reduces the costs of wastewater treatment compared to the use of ozone alone. The probable

reaction mechanism is shown below:

𝐻2𝑂2 → 𝐻𝑂𝑂− +𝐻+

𝐻𝑂𝑂− + 𝑂3 → 𝐻𝑂𝑂∙ + 𝑂3

∙−

Ozonation is used, among others:

• for drinking water treatment (oxidation and precipitation of iron and manganese compounds,

improvement of taste, oxidation of organic compounds, etc.),

• for water treatment in swimming pools,

• for the treatment of process water (in cooling circuits, process water in the semiconductor materials

industry, in laundry facilities)

• for the treatment of municipal and industrial wastewater and leachate (disinfection of municipal

sewage, oxidation of organic compounds, improvement of biofilters)

2.4. Fenton's reaction

Over one hundred years ago, J.H. Fenton (1884) discovered that Fe2+ ions strongly catalyze the

oxidation reaction with hydrogen peroxide of some organic acids. Subsequent studies have shown that a

mixture of H2O2 and Fe2+ is able to oxidize many other organic substances at moderate temperatures and

under normal pressure. The reaction has become one of the most effective AOP techniques. Currently, AOP

processes using hydrogen peroxide, in addition to the classic Fenton reaction, also include reactions in

H2O2/Fe2+, H2O2/Fe2+/UV and H2O2/Fe3+/UV systems. Research on the mechanism of oxidation showed the

formation of hydroxyl radicals by catalytic decomposition of hydrogen peroxide in acidic solution. The

Fenton reaction produces an iron ion, a hydroxyl radical (OH·) and a hydroxyl ion (OH-).

Fe2+ + H2O2 → Fe3+ + OH− + OH•

OH• + H2O2 → HO2 • +H2O

Fe3+ + • HO2 → Fe2+ + H+ + O2

Fe2+ + • HO2 → Fe3+ + HO2–

Fe2+ + OH• → Fe3+ + OH−

The oxidative effect of Fenton's reagents strongly depends on:

• pH of the solution,

• the ratio of H2O2 and Fe2+ concentrations,

• temperature

• amount of hydrogen peroxide in relation to the load of pollutants initial concentration of iron ions.

With the increase in the concentration of iron ions and hydrogen peroxide, the efficiency of the oxidation

reaction increases, however, too high concentrations of both reagents may cause a decrease in the reaction

rate. The pH range in which the oxidation occurs is from 3 to 5, but the optimum pH value for the Fenton

reaction is between 3 and 4. In contrast, the weight ratio of catalyst to hydrogen peroxide is 1:5 [Bigda

1995].

Fenton reagent is an effective oxidant of many organic substances and almost all organic compounds

containing hydrogen can be oxidized by hydroxyl radicals produced by the Fenton reaction. The group of

chemical compounds for which the Fenton reaction cannot be effectively used include, for example, acetic

acid, acetone, chloroform, methylene chloride, n-paraffin.

The main advantage of the Fenton process, as compared to other methods of wastewater treatment, is

the lack of H2O2 residues in the post-reaction system and catalytic only amounts of Fe2+ used in the reaction.

In addition, the Fenton reaction is carried out at ambient or slightly higher temperature (293-303 K) using

the heat of reaction to warm the mixture. This is an important advantage of this process, because it does not

require installation of a heat exchanger in the reactor, and energy is used to mix and dose reagents. The

Fenton reaction is used both for pre-treatment as well as for lowering COD before further biological

treatment of wastewater, or for the mineralization of toxic and difficult to biodegrade contaminants.

The Fenton process has been applied to several types of wastewater:

• process waters generated during the synthesis of chemicals, drugs, insecticides, dyes, explosives (TNT,

RDX);

• sewage from refineries;

• wastewater from the production of polymers containing phenol or formaldehyde;

• wastewater generated in the wood industry containing, among others cresols and copper compounds;

• sewage generated as a result of soil cleaning [Bigda 1995].

Waste water oxidation under industrial conditions is carried out in non-pressurized batch reactors.

A typical reactor is a non-pressurized tank with a stirrer. Process control is based on the sensors' indications,

which continuously measure temperature, pH and oxidation-reducing potential. The diagram of the reactor

for wastewater oxidation using the Fenton reagent is shown in Fig. 3.

Fig. 4 Scheme for Fenton reaction system

The dosing of reagents is carried out using dosing pumps. The tank is first filled with sewage and then the

pH is corrected (before adding the catalyst) with dilute sulfuric acid.

2.5. UV photolysis

Direct UV photolysis involves the excitation of a molecule by photon absorption, resulting in a

chemical reaction. The direct effect of UV radiation can be:

• conversion of organic compounds into other,

• breaking of chemical bonds,

• complete degradation of organic compounds

UV radiation causes the dissociation of oxidizing compounds and the formation of highly reactive

radicals capable of degrading organic pollutants. Direct photochemical degradation with UV radiation is

only in the case where the incident light is absorbed by the contamination. Highly fluorinated or chlorinated

saturated aliphatic compounds can be effective eliminated by homolysis of carbon-halogen bonds.

UV photolysis is used to eliminate:

• chlorinated and nitrated aromatic compounds,

• phenols,

• halogenated aliphatic compounds.

2.6. Processes using UV/H2O2

In the process of in-depth oxidation with the participation of hydrogen peroxide and UV radiation,

hydroxyl radicals are generated in the photolysis results of hydrogen peroxide. The widely accepted

mechanism of H2O2 photolysis is the homolysis of oxygen-oxygen bonds with the formation of two

hydroxyl radicals.

The advantages of using H2O2 in comparison to other methods of chemical or photochemical wastewater

treatment are: widespread availability, thermal stability, total solubility in water, and much lower cost than

when using, for example, ozone. In degradation processes in the H2O2/UV system, the most commonly used

light source is a low-pressure mercury lamp. It emits mainly radiation with a wavelength of 253,7 nm, which

is about 70% of the light energy emitted by the lamp. If hydrogen is introduced into the hydrogen peroxide

aqueous solution exposed to UV radiation, they will be included in the H2O2 chain reaction cycle (Fig.4).

Fig. 4 Oxidation Mechanism in H2O2/UV.

2.7. Processes in O3/UV system

Oxidation of compounds by means of ozone assisted by UV radiation is one of the most commonly used

processes of oxidation of various types of pollutants. The combined action of ozone and UV radiation is

also one of the most advanced techniques in the technological aspect. The essence of processes using ozone

and UV is ozolonolysis causing the formation of H2O2. In this way, the combination of UV and ozonation

is more effective than the sum of these two individual processes (synergistic effect). This method is used

for compounds that are resistant to ozonation. It is the most commonly used AOP method for a wide range

of pollutants. The process is used in the I or II-stage system. In a one-stage system, wastewater is

simultaneously treated with ozone and irradiated with UV radiation. In the II-stage system, the wastewater

is ozonized in the first reactor and then partially oxidized, along with the residual ozone, they pass into the

second reactor, where they are irradiated with UV radiation.

The disadvantage of the method, as in all methods using ozone, is the low solubility of ozone in water

and the associated poor mass exchange, high cost of ozone generation and its corrosiveness. Tests on real

waste water from industry textile (both general and chemical dry cleaners) showed that the combined use

of ozone and UV radiation allows to obtain better results in the distribution of pollutants. It depends on the

type of sewage and the parameter analyzed (Kos, 1998, Perkowski, 200).

2.9. Photocatalytic degradation in aqueous semiconductor suspensions

Heterogeneous photocatalysis using semiconductor suspensions is a method that is becoming more

and more popular. Most of the data on photocatalytic reactions using semiconductor suspensions concern

metal oxides (TiO2, ZnO, SnO2, WO3), sulphides (CdS, ZnS), selenides (CdSe) and tellurides (CdTe).

TiO2 is characterized by a number of advantages, including: a relatively low price, high oxidation potential,

non-toxicity, high chemical stability, high oxidation potential of photogenerated charge carriers, moreover,

it is not soluble in most reaction environments. Due to its photocatalytic properties it is used for: production

of self-cleaning coatings on the surface of panels, fabrics, glass, foils, car mirrors, soundproofing panels,

cement, paints, pigments, materials used in the process of deodorization of rooms. In addition, it is used in

the processes of wastewater treatment, water from organic contaminants and microorganisms.

The photoactivation of TiO2 is possible when the incident radiation energy is equal to or greater

than the bandgap energy (see Figure 5). The value of TiO2 bandgap energy, i.e. the energy that separates

the valence band from the conduction band, is in the range of 3.0-3.2 eV depending on the crystal structure.

It corresponds to a radiation of wavelength below 388 nm, hence TiO2 is activated by light from the UV

range. The first stage of the photocatalytic reaction mechanism is the absorption of photon, which involves

the transfer of the electron from the valence band to the conduction band.

Fig. 5. Scheme of TiO2 particle photoexcitation, CB- conduction band, VB- valence band

In the valence band of the photocatalyst, an electron gap (called hole) is created. Generated charge carriers:

holes and electrons can be recombined in the crystal lattice or cause fluorescence or heat generation. They

can also migrate to the photocatalyst surface and participate in redox chemical reactions with H2O, OH-, O2

molecules adsorbed from the aqueous solution and organic compounds. Hydroxyl radicals are formed as a

result of the oxidation reaction between holes and a water molecules or a hydroxyl anions. On the other

hand, the oxygen anion radical is formed during the reaction of electrons with adsorbed oxygen. The oxygen

anion radical can generate a hydrogen peroxide molecule and a hydroxyl radical. The reaction of

photocatalytic oxidation of organic compounds can be expressed in a general way:

𝑜𝑟𝑔𝑎𝑛𝑖𝑐 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒 + 𝑂2 𝑇𝑖𝑂2,ℎ𝑣→ 𝐶𝑂2 + 𝐻2𝑂 +𝑚𝑖𝑛𝑒𝑟𝑎𝑙 𝑎𝑐𝑖𝑑𝑠

The above equation indicates the total mineralization of organic compounds. During the photocatalytic

reaction the mineralization step is the last stage of an oxidation. The intermediate stage of the photocatalytic

reaction is the formation of intermediate degradation products.

Many factors influence the photocatalytic degradation process. Among them the most important are:

• type of semiconductor,

• proper preparation of its surface,

• intensity of incident light,

• solvent,

• temperature,

Natural organic matter (NOM),

• pH of the solution (in the case of aqueous solutions) [Zarzycki, 2002].

Reduction

Oxidation

3. REFERENCES

Barrat P.A., Baumgartl A., Hannay N., Vetter M., Xiong F. (1996), CHEMOX™ Advanced Waste

Water Treatment with the Impinging Zone Reactor, „Oxidation Technologies for Water and

Wastewater Treatment" Goslar, Germany, May 12-15 1996 Bigda R.J., Consider Fenton's chemistry for wastewater treatment, Chemical Engineering Progress 12,

62-66, 1995 Braun A.M., Oliveros E. (1996), How to evaluate photochemical methods for water treatment

Intemational Conference „Oxidation Technologies for Water and Wastewater Treatment" Goslar,

Germany, May 12-15 1996 Fox M.A., Dulay M.T., Heterogeneous photocatalysis, Chem. Rev. 93, 341-

357, 1993 Hoigne J., Intercalibration of OH radical sources and water quality parameters. Intemational

Conference „Oxidation Technologies for Water and Wastewater Treatment" Goslar, Germany, May

12-15 J996 Goslar, Germany, May 12-15 1996 Guha AK., Shanbhag P. V., Sirkar K.K., Multiphase ozonołysiis oforganics m wastewater by a novel

membranę reactor, AlChE Joumal 41 (8), (1995) Kowal AL., Świderska-Bróż M., Oczyszczanie wody, PWN Warszawa (1996) Langlais B, Reckhow D.A., Brink D.R., Ozone in water treatment. Application and Engineering,

AWWA Research Foundation & Lewis Publisher (1991) Legrini O., Oliveros E., Braun A. M., Photochemical Processes for Water Treatment, Chem. Rev. 93,

671-698, 1993, Luck F., A review ofindustrial catałytic wet air Oxidation processes, Catalysis Today 27, 195 -202 (1996)

Prousek J. (1996), Advanced Oxidation process for water treatment. Chemical process, Chem. Listy 90,

229-23 Prousek J. (1996), Advanced Oxidation process for water treatment. Photochemical process,

Chem. Listy 90, 307-315 Roche P., Volk C., Carbonnier F., Paillard H., Ozone Science & Engineering 16, 135-55 (1994) Trapido M., Yaressinina Y., Munter R., Ozonation of phenols in wastewater from oil shale chemical

treatment, Environmental Technology 16 (30), 233-241 (1995) Zarzycki R., Imbierowicz M., Rogacki G., Filipiak T., Nowoczesne metody unieszkodliwiania

odpadów. Mat. seminarium naukowego "Ochrona środowiska w przemyśle - techniki i technologie".

Łódź, (1996) „Zaawansowane techniki utleniania w ochronie środowiska” pod redakcją Romana

Zarzyckiego Łódź, (2002)

THE AIM OF THE EXCERCISE

The aim of the exercise is to evaluate an efficiency of phenol oxidation reaction using three AOP

systems: a) photocatalytic oxidation in TiO2 suspension, b) Fenton reaction and c) ozonation and

comparison of these three methods.

CALIBRATION CURVE OF PHENOL CONCENTRATION

Phenol concentration will be determined spectrophotometrically. For quantitative analysis, it is

necessary to make a calibration curve. In the flasks with a capacity of 50 cm3 prepare standard solutions (5

cm3 each) of phenol at a concentration of 10, 20, 30, 40 and 50 mg/dm3 and add successively 7.5 cm3 of p-

nitroaniline (PNA) and 2 cm3 of sodium nitrite solution. Then, shake and cool 10 min in an ice bath. Next,

add 15 cm3 of sodium carbonate solution, fill up to required volume with water. Measure absorbance of

colored solution at λ= 480 nm.

FENTON’S REACTION The measurement of phenol oxidation using the Fenton method is carried out according to the following

procedure: a) Fill the glass reactor with 1dm3 of model phenol solution at a concentration of 50 mg/dm3 and 0.5 dm3

of distilled water. The pH of the solution should be adjusted to pH 3-4 with a sulfuric acid solution. The

acidic reaction of the solution prevents the precipitation of iron hydroxide after the addition of the catalyst, b)turn on the magnetic stirrer and set the required speed of rotation at 500 rpm,

c) Prepare a solution of iron(II) sulphate. Dissolve 3 g of FeSO4x7H2O in distilled water, adjust the pH with

sulfuric acid to a value of 3-4 and dilute to 100 cm3 with distilled water,

d) Collect a "0'-sample into a 25 cm3 flask, basify with NaOH solution to pH=10.

e) Add to reaction solution 1.5 cm3 of 30% hydrogen peroxide solution and 15 cm3 of previously prepared

catalyst solution,

f) Reaction should be carried out for 20 minutes. Samples of volume 25 cm3 should be taken every 5 min, of which 10 cm3 should be designated for determination of phenol, and the remaining 15 cm3 for possible repetition of the assay - note: after collection the samples should be alkalinized (using NaOH solution) to stop the reaction.

Determination of phenol concentration

Determination of phenol involves the coupling of phenol with diazoated p-nitroaniline in an alkaline

solution. The resulting colored compound is determined colorimetrically (480 nm wavelength).

Procedure:

1. Transfer 10 cm3 of the phenol solution to a 100 cm3 flask. Add 15 cm3 of paranitroaniline and 4 cm3 of

sodium nitrite, then cool down in an ice bath for 10 minutes.

2. After cooling, add 30 cm3 of sodium carbonate and fill with water up to required volume.

3. The concentration of phenol should be determined spectrophotometrically via measurements of

absorbance at 480 nm.

OZONATION

Apparatus:

To measure the efficiency of phenol oxidation the apparatus presented schematically in Figure 6 is

used. Ozone is generated in a generator / 4 / based on electrical discharges. The efficiency of the generator

is regulated by changing the gas flow rate. The source of air or oxygen supplied to the ozonator is gas

cylinder /1/. The gas flow rate is regulated using rotameter /2/ and gas cylinder valves. The ozonator is

connected to the autotransformer and the voltage and the primary current are measured using a voltmeter

/6/ and ammeter /5/. Secondary voltage data is a dependence (transformer ratio): Uw = 36 Up. Oxidation

of the phenol solution is carried out in the reactor /7/.

Figure 6 Scheme of the ozonization system. 1 - a cylinder with compressed air, 2 – rotameter, 3 - gas dryer, 4 - ozone generator,

5 – ammeter, 6 – voltmeter, 7 – reactor, 8 - scrubber for absorbing unreacted O3, 9 - scrubbers with KI solution, 10 - gas meter

The method of carrying out the measurements is as follows:

1. Fill the column with a model phenol solution of concentration 50 mg/dm3 to a volume of 2 dm3.

2. Adjust the pH of the solution in the column with NaOH to 10-12.

3. Take a "0" sample into the bottle made of amber glass.

4. Open the ozone supply valve to the column /7/ and simultaneously close the valve to the hood.

5. Adjust the gas flow rate due to the change in flow resistance,

6. Ozonation should be carried out for 20 minutes (from the moment ozone bubbles appear in the

column 7 /). Take samples of the solution into amber-glass bottles every 5 min, of which 10 cm3

should be used to determine phenol concentration,

7. In order to terminate the ozonization process:

- open the valve to the hood and at the same time close the valve supplying ozone to the reactor,

- turn off the power supply of the ozone generator to high voltage,

- after 2 minutes, stop the air flow (oxygen),




Procedure:






PHOTOCATALYTIC PHENOL DEGRADATION IN THE UV/TiO2 SYSTEM

1. 1 dm3 reactor fill with 1dm3 ml of phenol solution (Co = 50 mg/dm3) and 2 g of the photocatalyst,

2. Place the reactor in a holder and cover with alumina foil,

3. In order to reach the state of equilibrium, leave the reactor for 10 minutes.

4. Then take a zero sample and turn on the UV lamp,

5. Reaction should be carried out for 20 minutes. Take samples of the solution into amber-glass bottles

every 5 min, of which 10 cm3 should be used to determine phenol. The collected solution should be

separated from the photocatalyst by means of a syringe filter (PLEASE REMEMBER TO

REGENERATE THE FILTERS)

6. Turn off the lamp after 20 minutes.




Procedure:






REPORT:

1. The purpose and scope of the exercise, a precise description of the apparatus.

2. Measurement results.

3. Determination of the calibration curve of the phenol solution (graph, necessary calculations).

4. Determination of phenol degradation kinetics - necessary graphs and calculations.

5. In the case of the report on the last classes, the exercise should compare the efficiency of phenol

oxidation in individual processes.

FENTON REACTION – REPORT

Date of the exercise ..............................

L.p. Name and Surname

1

2

3

4

5

Table 1. The results of measurements of standard solutions

Phenol concentration [mg/l] Absorbance

10

20

30

40

50

Table 2. Results of measurements and observations of phenol oxidation.

Time Phenol

concentration

Visual

assessment

Absorbance Solutions

(color)

[min] [mg/dm3]

0

5

10

15

20

X – absorbance Y – concentration of phenol [mg/dm3]

OZONATION - REPORT



1

2

3

4

5

Gas flow rate:

Table 1. Results of measurements and observations of the process

Table 2. Measurement results of standard solutions

Phenol concentration [mg/l] Absorbance

10

20

30

40

50

Time

[min] Absorbance

Phenol

concentration

[mg/dm3]

Visual assessment of the process

Color of

the solution

The size

of the bubbles Foam formation

0

5

10

15

20

PHOTOCATALITIC DEGRADATION IN TiO2 SUSPENSION - REPORT



1

2

3

4

5

Photocatalyst used: ...................................................

Tabela 1. The results of measurements of standard solutions

Table 2. Results of measurements and observations of phenol oxidation.

Time Phenol

concentration

Visual

assessment

Absorbance of olutions

(color)

[min] [mg/dm3]

0

5

10

15

20

Phenol concentration [mg / l] Absorbance

10

20

30

40

50






PHOTOCATALITIC DEGRADATION OF PHENOL

IN TiO2 SUSPENSION

TEACHER: dr inż. Izabela Wysocka

STUDENTS:

1

2

3

4

5

GROUP:

DATE OF PERFORMING

THE EXERCISE:

REPORT SUBMISSION

DATE:






FENTON REACTION


STUDENTS:

1

2

3

4

5

GROUP:

DATA OF PERFORMING

THE EXERCISE:

REPORT SUBMISSION

DATE:






OZONATION


STUDENTS:

1

2

3

4

5

GROUP:

DATA OF PERFORMING

THE EXERCISE:

REPORT SUBMISSION

DATE:

gdaŃsk university of technology faculty of … · • splitting off the hydrogen atom from the...

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