waste water management

1. 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

2. Water
Water 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 substancethat 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
properconditions, these droplets further combine and becomeheavy 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 disposalby 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).

3. Processes used
Phase separation
Phase separation transfers impurities into a non-aqueous phase. Phase separation
may occurat 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 bottomof 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.
Filtration
Colloidal suspensions of fine solids may be removed by filtration through fine
physical barriers distinguished from coarserscreens 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
Oxidation
Oxidation reduces the biochemical oxygen deman of wastewater, and may reduce
the toxicity of some impurities. Secondarytreatment converts some impurities

4. 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
Biochemicaloxidation
Secondarytreatment 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.
Chemicaloxidation
Chemical 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.
Polishing
Polishing 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 absorptiononto activated carbon. Filtration through sand
(calcium carbonate) or fabric filters is the most common method used in municipal
wastewater treatment.

5. Sewage treatment plants
A typical municipal sewage treatment plant in an industrialized country may
include primary treatment to remove solid material; secondarytreatment 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 plants
Disposal 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 disposalof
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 producea 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.

6. 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 disposalof small volumes of industrial wastewater, industrial wastewater
treatment and disposalmay 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 forseasonal use conditions from breeding or harvest cycles.

7. Water treatment plants in Bangladesh
Name Construction year Total production per day
Chadni ghat plant 1874 02 corers liter
Sonakanda 1929 05 corers liter
Godail 1989 03 corers liter
Saydabad 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/