Dhaka school of Economics University of Dhaka

An assignment on how we can treatment waste water!

Submitted by: Nahin Mahfuz Seam.

Class : BEcon 1st batch

Id no : 160121005

Roll no : 09

Subject : Environmental studies

Course ID : 103

Submitted to: Dr. Salma Sultan, Assistant professor, DScE, DU

WaterWater is very important for life. We need water to drink, to wash our hands, to cook, to water plants and many other things.

Without water, the plants would die and people and animals would go thirst

Water is the only substance that exists naturally on Earth in all three physical states of matter gas, liquid, and solid and it is always on the move among them. The Earth has oceans of liquid water and Polar Regions covered by solid water. Energy from the sun is absorbed by liquid water in oceans, lakes, and rivers and gains enough energy for some of it to evaporate and enter the atmosphere as an invisible gas, water vapor. As the water vapor rises in the atmosphere it cools and condenses into tiny liquid droplets that scatter light and become visible as clouds. Under the proper conditions, these droplets further combine and become heavy enough to precipitate (fall out) as drops of liquid or, or if the air is cold enough, flakes of solid, thus returning to the surface of the Earth to continue this cycle of water between its dense and vapor phases.

Wastewater treatment

Wastewater treatment is a process used to convert waste water which is water no longer needed or suitable for its most recent use - into an effluent that can be either returned to the water cycle with minimal environmental issue or reused. The latter is called water reclamation and implies avoidance of disposal by use of treated wastewater effluent for various purposes. Treatment means removing impurities from water being treated; and some methods of treatment are applicable to both water and wastewater. The physical infrastructure used for wastewater treatment is called a "wastewater treatment plant" (WWTP).

Processes usedPhase separation

Phase separation transfers impurities into a non-aqueous phase. Phase separation may occur at intermediate points in a treatment sequence to remove solids generated during oxidation or polishing. Grease and oil may be recovered for fuel or saponification. Solids often require dewatering of sludge in a wastewater treatment plant. Disposal options for dried solids vary with the type and concentration of impurities removed from water.

Production of waste brine, however, may discourage wastewater treatment removing dissolved inorganic solids from water by methods like and distillation.

Sedimentation

Solids and non-polar liquids may be removed from wastewater by gravity when density differences are sufficient to overcome dispersion by turbulence. Gravity separation of solids is the primary treatment of sewage, where the unit process is called "primary settling tanks" or "primary sedimentation tanks". It is also widely used for the treatment of other wastewaters. Solids that are heavier than water will accumulate at the bottom of quiescent settling basins. More complex clarifiers also have skimmers to simultaneously remove floating grease like soap scum and solids like feathers or wood chips. Containers like the API oil-water separator are specifically designed to separate non-polar liquids.

FiltrationColloidal suspensions of fine solids may be removed by filtration through fine physical barriers distinguished from coarser screens or sieves by the ability to remove particles smaller than the openings through which the water passes. Other types of water filters remove impurities by chemical or biological processes described below

OxidationOxidation reduces the biochemical oxygen deman of wastewater, and may reduce the toxicity of some impurities. Secondary treatment converts some impurities

to carbon dioxide, water, and biosolids. Chemical oxidation is widely used for disinfection.

Aeration tank of an activated sludge process at the wastewater treatment plant in Dresden-Kibitz, Germany

Biochemical oxidationSecondary treatment by biochemical oxidation of dissolved and colloidal organic compounds is widely used in sewage treatment and is applicable to some agricultural and industrial wastewaters. Biological oxidation will preferentially remove organic compounds useful as a food supply for the treatment ecosystem. Concentration of some less digestable compounds may be reduced by cometabolism. Removal efficiency is limited by the minimum food concentration required to sustain the treatment ecosystem.

Chemical oxidationChemical oxidation may remove some persistent organic pollutants and concentrations remaining after biochemical oxidation. Disinfection by chemical oxidation kills bacteria and microbial pathogens by adding ozone, chlorine or hypochlorite to wastewater.

PolishingPolishing refers to treatments made following the above methods. These treatments may also be used independently for some industrial wastewater. Chemical reduction or pHadjustment minimizes chemical reactivity of wastewater following chemical oxidation. Carbon filtering removes remaining contaminants and impurities by chemical absorption onto activated carbon. Filtration through sand (calcium carbonate) or fabric filters is the most common method used in municipal wastewater treatment.

Sewage treatment plantsA typical municipal sewage treatment plant in an industrialized country may include primary treatment to remove solid material; secondary treatment to digest dissolved and suspended organic material as well as the nutrients nitrogen and phosphorus, and - sometimes but not always - disinfection to kill pathogenic bacteria. The sewage sludge that is produced in sewage treatment plants undergoes sludge treatment. Larger municipalities often include factories discharging industrial wastewater into the municipal sewer system. The term "sewage treatment plant" is nowadays often replaced with the term "wastewater treatment plant".

Tertiary treatment

Tertiary treatment is a term applied to polishing methods used following a traditional sewage treatment sequence. Tertiary treatment is being increasingly applied in industrialized countries and most common technologies are micro filtration or synthetic membranes. After membrane filtration, the treated wastewater is nearly indistinguishable from waters of natural origin of drinking quality (without its minerals). Nitrates can be removed from wastewater by natural processes in wetlands but also via microbial denitrification. Ozone wastewater treatment is also growing in popularity, and requires the use of an ozone generator, which decontaminates the water as ozone bubbles percolate through the tank, but this treatment is energy intensive. Latest, and very promising treatment technology is the use aerobic granulation.

Industrial wastewater treatment plantsDisposal of wastewaters from an industrial plant is a difficult and costly problem. Most petroleum refineries, chemical and petrochemical plants have onsite facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the local and/or national regulations regarding disposal of wastewaters into community treatment plants or into rivers, lakes or oceans. Constructed wetlands are being used in an increasing number of cases as they provided high quality and productive on-site treatment. Other industrial processes that produce a lot of waste-waters such as paper and pulp production has created environmental concern, leading to development of processes to recycle water use within plants before they have to be cleaned and disposed.

Industrial wastewater treatment plants are required where municipal sewage treatment plants are unavailable or cannot adequately treat specific industrial wastewaters. Industrial wastewater plants may reduce raw water costs by converting selected wastewaters to reclaimed water used for different purposes. Industrial wastewater treatment plants may reduce wastewater treatment charges collected by municipal sewage treatment plants by pre-treating wastewaters to reduce concentrations of pollutants measured to determine user fees.

Although economies of scale may favor use of a large municipal sewage treatment plant for disposal of small volumes of industrial wastewater, industrial wastewater treatment and disposal may be less expensive than correctly apportioned costs for larger volumes of industrial wastewater not requiring the conventional sewage treatment sequence of a small municipal sewage treatment plant.

An industrial wastewater treatment plant may include one or more of the following rather than the conventional primary, secondary, and disinfection sequence of sewage treatment:

An API oil-water separator, for removing separate phase oil from wastewater. A clarifier, for removing solids from wastewater. A roughing filter, to reduce the biochemical oxygen demand of wastewater. A carbon filtration plant, to remove toxic dissolved organic compounds from

wastewater. An advanced electro dialysis reversal (EDR) system with ion exchange

membranes.

Agricultural wastewater treatment plants

Agricultural wastewater treatment for continuous confined animal operations like milk and egg production may be performed in plants using mechanized treatment units similar to those described under industrial wastewater; but where land is available for ponds, settling basins and facultative lagoons may have lower operational costs for seasonal use conditions from breeding or harvest cycles.

Water treatment plants in BangladeshName Construction year Total production per dayChadni ghat plant 1874 02 corers literSonakanda 1929 05 corers literGodail 1989 03 corers literSaydabad 2002 22.5 corers liter

References:

http://scifun.chem.wisc.edu/chemweek/PDF/COW-Water-Jan2011.pdf

https://en.wikipedia.org/wiki/Wastewater_treatment

https://en.wikipedia.org/wiki/Sewage_treatment

http://bangladesh.gov.bd/site/page/2adc94cd-597d-492d-8e07-db4f1777204d/%E0%A6%AA%E0%A6%BE%E0%A6%A8%E0%A6%BF-%E0%A6%93-%E0%A6%AA%E0%A7%9F%E0%A6%83%E0%A6%A8%E0%A6%BF%E0%A6%B7%E0%A7%8D%E0%A6%95%E0%A6%BE%E0%A6%B6%E0%A6%A8

http://dwasa.org.bd/