Seawage Water

Submitted to, Dr. Anu Gopinath
Classification & characteristics of sewage and industrial
effluents
ASSIGNMENT
Submitted by, Ashish sahu
FSM-2019-20-04
KUFOS, Kerala

Classification & characteristics of sewage and industrial effluents
Introduction:-
• The production of fish in pond fertilized with waste water is a common practice in many
part of Asia and was also know in medieval Europe.
• Sewage fed fishery was developed in Germany at the end of nineteenth century and in India
(1930).
• Although satisfactory as source of nutrient, sewage present problems such as toxicity to fish,
accumulation of heavy metals and toxic substances in fish muscles and it also contains
various pathogenic microorganisms.
• With the launching of the Ganga action plan in 1985 there has been a renewed interest as
also vigor among engineers, scientist, and environmentalists.
• According to official view of central board for prevention and control of water pollution the
stop page of discharge of sewage in to river Ganga would reduce pollution to the extent to
75% further.
Treatment of sewage in low cost treatment plants such as stabilization ponds which do not
require high degree of skill and reuse of treated sewage and sludge for raising fish and vegetable
crops.
1. SEWAGE: MEANING, COMPOSITION AND DISPOSAL:
Meaning of Sewage:
‘Sewage’ is a collective noun used to represent liquid or solid wastes carried in sewers. It
consists of domestic water-borne wastes including human and animal excrete, washing waters and
everything that goes down the drains of a town or a city. It also consists of industrial water-borne
wastes as well as ground, surface and atmospheric waters which enter the sewerage system.
Sewage is the liquid waste discharged from domestic and industrial source within an area.
It is considered to be good fertilizer for ponds, having nitrogen and phosphorus as its main
constituents sewage contains bacteria and protozoa, manganese and nickel are also present, along
with some quantity of detergents. Sewage differs from sludge which consists of liquid wastes from
kitchen, and bathroom, but excludes faucal matter and urine.
The amount of sewage produced in our country is of the order of 3.61 million cubic
meters/day (about 800 million gallons/day). About 30% of the above amount comes from urban
areas. It is estimated that only about 20% of one day sewage production of our country is treated
and utilized, and the rest (about 80%) still remains untreated and unutilized.
Composition of Sewage: The composition of sewage mainly depends upon per capita
consumption of water and varies from place to place and season to season.
The sewage composition can be studied under following two heads:

1. Chemical Composition: Chemically, the sewage consists of approximately 99% water and
1% inorganic and organic matter in suspended and soluble forms. Lignocellulose, cellulose,
proteins, fats, and various inorganic particulate matter exist in suspended state, whereas
sugars, fatty acids, alcohols, amino acids, and inorganic ions constitute the soluble forms.
However, on an average, the sewage of towns in our country contains about 350 ppm
biodegradable organic matter, 52 ppm N2, 45 ppm potassium and 16 ppm phosphorus. Salts
of several heavy metals such as Zn, Cr, Ni, Pb, etc. are also present above permissible levels
in sewage.
.
2. Microbial Composition: The microbial population per milli litre of sewage may vary from a
few lacs to several millions. Various types of microorganisms, viz., micro-fungi, bacteria and
protozoa, collectively called ‘sewage fungus’, are known to grow profusely in sewage. In
addition, viruses and many micro-algal genera have also been recorded from sewage.
Bacteria occurring in sewage are mainly intestinal and soil inhabiting and their common
types are coliforms, streptococci, Clostridia, micrococci, Proteus, Pseudomonas, and
lactobacilli.
According to Saha et al (1958), Sewage of Kolkata has the following composition:-
• Dissolved oxygen
• Dissolved carbon
dioxide
• Alkalinity
• Free ammonia
• Nitrite
• Phosphate
• Suspended matter
• pH
• Nil
• 20.96 ppm
• 170-490 ppm
• 12.0-63.6 ppm
• 0.08 ppm
• 0.01-0.33 ppm
• 160-420 ppm
• 6.9-7.3
Classification of Sewage:
Sewage may be classified mainly into two types, namely, domestic and industrial. All
household wastes and human and animal excrete constitute domestic sewage, whereas the
industrial wastes constitute industrial sewage.
Since industrial wastes vary greatly in their composition (some may be highly alkaline such
as soda wastes, some highly acidic such as acid-mine drainage, and others toxic because of presence
of heavy metals, antibiotics, pesticides, etc.), the treatment of industrial sewage proves highly
difficult in comparison to domestic sewage.
Characteristics of Sewage:

(i) Biochemical Oxygen Demand (BOD) and Oxygen Consumption (OC) values are
extremely high in sewage.
(ii) The sewage organic matter undergoes anaerobic or partial decomposition resulting in
the production of obnoxious gases, namely, CH3, CO and H2S due to anoxic condition.
Besides being toxic, these gases react with water and produce acids.
(iii) Production of acids in large quantity make the sewage more acidic thus making it unfit
for supporting life activities.
(iv) Heavy metals are generally present in abnormal concentration in sewage.
All these characteristics of sewage, viz., anoxic condition, high acidity, high heavy metal
concentration, and reduced photosynthetic rate due to poor illumination cause death of oxygen-
dependent organisms such as aerobic microorganisms, plants and animals in sewage. This is the
reason why sewage is dominated by organisms capable of growing in anaerobic environments.
Disposal of Sewage:
Sewage disposal has become of prime importance now-a-days as it brings undesirable and
harmful effects on living beings. Untreated or inadequately treated sewage is generally disposed
of into natural water reservoirs without taking its pros and cons into account. It is so either
because we are indifferent to the consequences or because we assume that the water reservoirs
are sufficiently large and so located that sewage-dilution prevents hazards.
However, we can no longer rely on disposed-sewage dilution in our natural water reservoirs;
the solution of sewage pollution is not its dilution. It is necessary, therefore, that the sewage must
be treated before its disposal so that we can, on one hand, save organisms including men from bad
effects and, on the other hand, can utilized it to the maximum for our welfare.
Disposal of sewage as such or inadequately treated one, generally leads to following consequences:
1. Frequent dissemination of water-borne disease causing microorganisms in large number.
2. Depiction of dissolved oxygen in water leading to anoxic (oxygen-less) condition which may
ultimately kill O2 dependent aquatic life.
3. Creation of offensive odour and debris-accumulation due to which value of property decreases.
4. Increased danger of swimming in water and diminished value of water for other recreational
purposes.
Problems related to sewage-fed culture systems:
 Accumulation of silt and high organic matter at pond bottom.
 Incidence of parasites and fish diseases.
 Possibilities of pathogens being transferred to human.
 Accumulation of heavy metal in the system.
Heavy metal in sewage-fed system:-

Jnnapura Lake is a perennial fresh water body located at the outskirt of Bhadravathi
township of Karnataka state, India. Lake water is used for irrigation and aquaculture practices.
This water body is located at 130 42N latitude and 750 38E longitudes. It receives untreated
sewage from residential areas, wastes from small scale industries and agricultural runoff from the
surrounding areas. Various (Cu, Zn, Pb, Cd, Ni, and Co) heavy metal levels were measured in
jannapura lake water b/w October 2004 and June 2005. Concentrations of heavy metal in the
water, sediment, fish and plankton samples were are analyzed by atomic Absorption
Spectrophotometer. The copper values varied from 1.04-1.30mg/L. the concentration of Zn, Pb, 0.
Cd, Ni, and Co deviated from 0.35-0.92, 1.3-2.8, 0.06-0.094, 0.009-0.098 and 0025-0.046mg/L
respectively. The metals present in water were in the order of Pb>Cu>Zn>Cd>Ni>Co. metals
leaves in the sewage inlet drain; lake sediment and water were compared with published criteria.
All the heavy metals concentrations in the water and sediment exceeded the permissible limits as
per WHO standards. The comparison revealed that the metal load in the sediment ranged from
the moderate to heavy pollution categories.
Solutions:
 Regulate sewage intake the pond.
 Provide freshwater for dilution and use of prophylactic.
 Depuration of fish in freshwater before marketing
Treatment of Sewage:
Our objectives behind the sewage treatment would be to kill pathogenic microorganisms,
prevent anoxia, raise the pH to alkaline side, increase photosynthetic rate, reduce organic content,
etc. When these objectives are achieved by the way of treating the sewage, the conditions
prevailing in a natural water reservoir are induced in sewage water and the latter can be reused.
Sewage treatment processes are many and varied. We will discuss only those sewage treatment
processes which are generally applied in single dwelling unit situations and municipal situations.
Single Dwelling Unit Treatment Processes:
1. Outdoor Toilets:
Where plumbing installations cannot be undertaken for any reason, the toilets or water
closets may be constructed outdoors. While this arrangement is undertaken, care could be taken
to see that flies have no access to these and changes of drainage from these, joining water supplies,
are eliminated.
2. Septic Tanks:
These are used for residential quarters. All the residential sewage is passed through
suitable pipes leading to a tank located at a suitable place and made of metal or concrete. The
heavy particles of sewage settle down and undergo anaerobic decomposition whereas the gases
and clear water are allowed to go out through perforated pipes ramified within the ground.
The septic tank device should be so fitted that the sewage does not drain by any chance into
water supply of the residence. The sludge in the tanks must be periodically removed to prevent
clogging of the pipes.

3. Imhoff Tank:
This is, in fact, a modification of septic tank and is generally used to treat larger community
sewage. It consists of two chambers, one above the other. The top chamber receives sewage and
the heavier particles settle into the lower chamber and slowly decompose under anaerobic
conditions.
The gas liberated (mainly methane) can be drawn out through a passage and utilized as
fuel. The sewage effluent (remaining sewage water) is either let into larger body of water, or is
subjected to aerobic decomposition. The sludge is periodically removed, aerated and used as
manure.
Municipal Treatment Processes:
Municipal sewage treatment systems carry out various steps involved (Fig. 32.3). These steps are,
namely, primary (or mechanical) treatment, secondary (or biological) treatment, and tertiary (or
final) treatment.

1. Primary (or Mechanical) Treatment:
When the sewage arrives at a sewage treatment plant, it is first subjected to mechanical (or
physical) means, viz., flowing, dilution and sedimentation to remove its coarse solid materials. The
sewage is passed through a series of filters of graded openings and then allowed to flow through
sedimentation units (tanks, basins, etc.).
The mechanical process consists of screening and filtration, so as to remove coarse
suspended matter. Floating solids including fats and oils, as well fine suspended material are
removed by skimming and sedimentation. Sedimentation is done by letting the sewage into a tank
at a high velocity. When the sewage enters a large tank from a sewage channel, there is sudden
drop of velocity, resulting in sedimentation.

Coarse solid materials are concentrated in and collected from sedimentation units; these
particulate materials are collectively called ‘sludge’. Following sedimentation, the sludge and
liquid affluent are processed separately during secondary treatment.
2. Secondary (or Biological) Treatment:
This is purely a biological treatment of mechanically treated sewage and concerns microbial
activity which biodegrades organic substrates and oxidizable inorganic compounds. This treatment
accomplishes two important phases, namely, aerobic phase and anaerobic phase.
The aerobic phase consists of aerobic digestion of sludge by various filters (e.g., trickling
filters), oxidation ponds and activated sludge process, and the anaerobic phase is represented by
anaerobic digestion of sludge.
The biological treatment of sewage consists of oxidation of organic matter into Co2, H2O,
sulphate etc., by using bacteria.
Before sewage is added to a pond, it is diluted with fresh water so as to maintain the
dissolved oxygen content, and reduce co, NH3, H2S etc. below the danger level. After
sedimentation and dilution, sewage is stored in tanks so as to allow bacterial action for oxidizing
organic matter.

City sewage is extensively used for fish culture in Kolkata. The sewage is diverted through
a system of drains, to sedimentation tanks. After sedimentation and dilution at 1:4 with fresh
water, it is added to fishery pond at monthly intervals. Fingerlings of Rohu, Catla and Marigal are
stocked in the ratio of 1:2:1 giving an average yield of 1,850 kg/ha of fish.
Tilapia:
Tilapia is the most suitable species for culture in sewage irrigated ponds because it grows fast and has lesser
demand of DO. Air breathing fishes can also be easily cultured in such ponds. Carps are highly sensitive to chemical
changes in water. Hence they are cultured in ponds receiving diluted sewage water. Fresh water prawn
(Macrobrachium rosenbergii) has also been reported to grow fast in paddy fields receiving sewage water. Studies have
shown that fish cultured that fish cultured in sewage water pond do not have any bacterial infection that may be
harmful to man. On the other hand they have taste and higher nutritive value.
I. Aerobic Phase of Secondary Treatment:
(i) Aerobic Digestion in Trickling Filters:
Trickling filter consists of generally 6-10 feet deep bed of crushed stone, gravel, slag, or
similar material. The sewage effluent is sprayed over the surface of the bed; the spraying saturates
the effluent with oxygen. The bed surface becomes coated with aerobic microbial flora consisting
of microalgae, micro-fungi, bacteria, and protozoa.
As the effluent seeps over, the aerobic microbes degrade the organic matter. However, the
treated effluent collected at the bottom of the tank is passed to sedimentation tank and, like
activated sludge process, the effluent follows tertiary treatment. Aerobic digestion of sewage
organic matter in a trickling filter is a very slow process.
(ii) Oxidation Ponds:
Oxidation pond sewage-treatment is recommended for small communities in rural areas
where suitable and sufficient land is available. Oxidation ponds (also called Lagoons or

Stabilization Ponds) are generally 2-5 feet deep shallow ponds designated to allow direct wind
action and algal growth on the sewage effluent.
Oxygen supplied from air and produced as a result of algal photosynthesis fulfils
biochemical oxygen demand (BOD) of sewage effluent and thus helps in maintaining aerobic
condition in sewage effluent. In such condition the aerobic microbes grow rapidly and digest
organic matter. Chlorella pyrenoidosa is a common algal representative grown in oxidation ponds.
(iii) Activated Sludge Process:
In this process, the mechanically treated sewage effluent (serge liquid) is pumped into a
sedimentation or settling tank wherein the sewage floes and settles out. A portion of sewage ‘floe’
is returned to activate a new batch of mechanically treated sewage effluent, and the rest is pumped
to activated sludge digester where air is blown by several jets.
Thus, in the presence of plentiful oxygen, oxidation of sewage effluent is brought about by
aerobic microorganisms which break down organic matter to CO2 and H2O. Now the effluent is
passed through a sedimentation tank. Though about 90% of the organic matter of the effluent is
digested via this process, the effluent still contains considerable amount of nitrate and phosphate,
etc.
It is, therefore, not safe to discharge effluent at this stage into a large body of water ds both
nitrate and phosphate can cause eutrophication. Now the effluent, which looks clear at this stage,
is subjected to tertiary (final) treatment for further purification.
II. Anaerobic Phase of Secondary Treatment (Anaerobic Digestion of Sludge):
The sludge collected after primary (mechanical) treatment of sewage is subjected to
anaerobic (oxygen- free) digestion in separate tank designed especially for the purpose. Since
anaerobic condition prevails in this tank, the anaerobic microbes bring about digestion of organic
matter by degrading them to soluble substances and gaseous products (methane, 60-70%; CO2, 20-
30%; and smaller amounts of H2 and N2).
This gas mixture can be used for operating power for the sewage plant or as a fuel. Recently,
Municipal Corporation of Delhi has started supplying this gas mixture to about 100,000 people for
cooking purposes.

3. Tertiary (or Final) Treatment:
Since the sewage-effluent treated during secondary treatment process still contains non-
biodegradable organic pollutants (if sewage contains industrial wastes) and mineral nutrients
particularly nitrogen and phosphorus salts, it is subjected to tertiary (or final) treatment for their
removal.
If not so, the sewage effluents containing nitrogen and phosphorus salts can cause serious
eutrophication in aquatic ecosystems. Non-biodegradable organic pollutants are normally removed
by using activated carbon filters whereas phosphorus and nitrogen salts by chemical treated.
Phosphorus salts are precipitated by liming and the nitrogen present mainly as ammonia is
removed by volatilization (vigorous aeration at elevated temperature) at a high pH. These
treatments result in a high-quality effluent which does not cause eutrophication.
The find step of tertiary treatment is disinfection which is commonly accomplished by
chlorination using either sodium or calcium hypochlorite (NaOCl or CaOCl2 respectively) or
chlorine. Now the effluent is a clean water and is considered microbiologically safe even for human
consumption.

Another methods:
Radiation / Ozone: Ultraviolet radiation is used for disinfection of water. Many
pathogens, including viruses can be killed with relatively low levels of radiation. For UV treatment
to be effective the solids must be removed before treatment. UV systems are a low maintenance,
low risk method of disinfection.
Low levels of ozone dissolved in the water will also remove most pathogens. Ozone will
improve particulate filtration and reduce the dissolved organic waste in the water. Low levels of
ozone in the air are detrimental to human health. Residual ozone is toxic to fish at low levels and
should be monitored.
Sewage utilization in aquaculture
 The sewage effluents in fish pond act in the same manner as organic fertilizers and liberate
nitrogen phosphorus and trace element which stimulated the production of fish food
organism in the culture system.
 Phytoplankton starts appearing within 3-5 days of sewage application and generally
continues to grow up to 15-20 days. Depending on the availability.
 The small particles the micro fines which are basically assemblage of bacterial colony.
Provide direct source of food to the zooplankton and benthos and they solar energy
dependent food cycle is by passed.
Carp culture in sewage:-
An aquaculture sewage treatment plant comprising duckweed and fish culture has been
recently developed by central institute of fresh water aquaculture, Bhubaneswar (Orissa) the
aquatic macrophytes used for treatment of domestic sewage are Azolla spp. Spirodella spp. Wolffia
and Lemna spp. The plant consists of two sewage fed fish ponds (50m 20m 2m) for stocking fish

species. Two marketing pond are constructed 940m 20m 2m) for stocking harvested fish the treated
sewage water is drained into the river for recycling through an outlet from the fish pond.
The sewage after sedimentation and stabilization is let into the duckweed ponds. Where it
is retained for 2-3 days and emptied and dried to remove the sludge that accumulates at the
bottom. After chemical analysis of effluent and estimation of plankton population, this is let into
the fish pond. Carp fry and fingerlings are introduced into the pond for polyculture. The following
proportion of species is recommended:
• Catla 25%
• Rohu 25%
• Mrigal 25%
• Silver carp 15%
• Common carp 10%
Wastewater-fed aquaculture in India:-
• It is estimated that at present there are more than 130 wastewater aquaculture units in
India covering about 10,000ha, Almost 80% of these are located in west Bengal. In west
Bengal, sewage is extensively used as a fertilizer for fish pond.
• One of the major sewage irrigated fisheries is in Kolkata, popularly known as Vidyanathi
spill area.
• Simultaneously sewage-fed fish culture started at four sites in India namely- Nagpur,
Bhilai, Madras, Bhopal.
• Population covered by the outfall channel capacity was 4 million Kolkatans over an area of
94.50 Km2 the DWF channel starting from the Tapsia covers a length of 32 km to reach to
the river Kulti Gong at Ghusighata.
Global scenario of wastewater aquaculture:-
The use of organic wastes in fish culture has been in vogue much before history. Silkworm
wastes were used in fish pond in china more than 4,000 years ago. The earliest published work
on the use of wastes in fish culture was by fan lai in china around 460 BC this may be equally
true for ancient civilization like India and Egypt. Subsequently in recent year wastewater
based fish culture gained momentum in china, Taiwan, Indonesia, Philippines, Hong Kong,
Hungary, Malaysia, Israel, USA, Germany, Australia and Canada.
Biotic community in wastewater aquaculture:-
Rich nutrient status of sewage fish ponds is reflected in the occurrence of high
phytoplankton density since the nutrient released from the sewage effluents are directly utilized
by these organisms. Phytoplankton consists mainly of chorophyeoae with following predominated
genera.
Chemical properties of sewage-enriched fish pond:-

Sewage is a dark coloured foul-smelling fluid organic and inorganic solid in dissolved and
suspended forms. Contain 90-99% water, 10-70 mg/liter nitrogen, 7-20 mg/liter phosphorus and
12-30 mg/liter potassium. One of the major change that occurs in sewage-fed fish pond due to high
BOD value of water reduction DO level. Fluctuation of DO is reported during day and night time
due to the presence of high density of phytoplankton in the system. Low value for during night
hours supported decomposition activities.
In spite of that spread of this fish farming system remains as a Kolkata affair mainly because of
two major fear psychosis of pathogens from the system to handlers and consumer through fish,
and presence of heavy metals in the system.
Aquaculture and sewage treatment:-
An aquaculture- based sewage treatment plant (ASTP) designed in India has incorporated
cultivation of duckweed prior to application of fish pond and post-fish culture depuration, with the
objective of refinement of sewage-fed fish culture and sewage treatment through aquaculture
practiced.
Design and construction model to treat 1 MLD sewage:- A model for treating one million
liters/day of sewage, from a population of about 20,000 is described here.
Source: A receiving chamber for sewage feeds the effluent to the ASTP.

Duckweed culture complex: It comprises 18 ponds with brick lining (25mX8mX1m), with three
series of six ponds in a row. The sewage is retained here for a period of two days, with free passage
b/w the series.
Fish ponds:- Two fish ponds (50mX20mX2m) receive the treated sewage from the duckweed
ponds and retain it for three days.
Depuration ponds:- Two depuration ponds (40mX20mX2m ) with freshwater, also used as
marketing ponds, provide for depuration of fish for a week before marketing. As the fish harvest
is occasional, these ponds are also used for the culture of grass carp, fed with duckweeds from the
system.
Outlet: Sewage outlet drains are provided from the fish and depuration ponds for drainage into
natural waters.
Candidate fish species for sewage fed fish culture: Depending on the area of operation,
different fish species could be used. Tilapia (Oreochromis spp) and mandarin fish (Siniperca
chautsi) are some of the species that are cultured in sewage fed water in China and other countries.
The ASTP provide for retention of sewage for two days in duckweed ponds and three days in fish
ponds.
The models as shown in have been used in several Indian villages for community sanitation and
aquaculture, with modification. Typically, one –third of the pond of the size of 0.2-0.4 ha, at the
inlet end serves as the receptor of sewage from soiled waste from community latrines.
Ganga action plan sewage treatment – kalyani model
Kalyani sewage-fed fish farm represents a small model of sewage treatment through
aquaculture. The entire system involved two stabilization pond of 0.5 ha each two facultative or
oxidation ponds of 1.00 ha each and series of four maturation ponds (fish ponds) of 1 ha each,
located in such way that inlets and outlets of ponds placed diagonally facilitating the water course
in zig-zag way leading to the river Hooghly .

Application of duckweed-fish-based treatment method:-
• Duckweed wastewater treatment is potentially suitable for small- scale application at rural
level and for medium-sized facilities at community, (Peri) urban and industrial level.
• The duckweed treatment plants installed so far almost exclusively treat domestic or
agricultural wastewaters. Hardly any literature is available on the treatment of specific
industrial wastewaters (Gijzen and Khondker 1997).
Advantages of duckweed-fish based system:
• Resource recovery: besides treatment of sewage, the system helps in conversion of nutrient
from sewage to protein in the form of fish flesh and duckweed biomass. The revenue
generated can support more than 30% of the recurring expenditure of the system.
• Less sophisticated technology with easy adaptability.
• Flexibility of establishment as decentralized treatment system depending on land
availability and sewage volume, thus making it suitable for small towns and cities.
• Environmental-friendly system utilizing minimum energy input.
• Cost-effective biological treatment system.
Limitation of duckweed-fish-based system:-
• Fish being one of the components of the system, it is suitable only for treating domestic
sewage. The system may not be applicable for wastewater containing industrial effluents.
• Relatively larger land requirement.
• Applicable only for weak sewage with maximum BOD levels of 140-150 mg/liter thus require
a separate pre-treatment system for treatment of strong sewage.
• Possible problem of pests for duckweed.
• The retention time defendant on sewage concentration and temperature.
Economic and financial implication of wastewater treatment:-
• Although the responsibility for collecting treating and disposing of urban wastewater will
normally lie with a local water or sewage authority or municipality. Farmers wishing to
take advantage of the effluent are often able and willing to pay for what they use but are
not prepared to subsidize generally disposal costs.
• Since wastewater treatment is a major cost in effluent use system, accepting that local
authorities are fully responsible for wastewater collection, it is essential that treatment
process selection is made in conjunction with decisions on crop and irrigation system
selection.
Policy issues:-
• The legislative framework for effluent use in agriculture can have a significant influence on
project feasibility. A coherent national policy for wastewater use in agriculture is essential.

This must define the division of responsibilities among involved ministries and authorities
and provide for their collaboration.
• Realistic standards must be adopted to safeguard public health and protect against adverse
environmental impacts. Environmental issues associated with wastewater use are the main
subject of a UNEP (1991) document.
• The national water policy (NWP) is the position of the government of India on water
resource issues ranging from drought and flood management to drinking water provision.
The NWP, 2002 calls for intensifying research through recycling and re-use of water.
Relevant problems:
• There are three fundamental problems with the wastewater aquaculture. Frist, most of the
potential benefits as specified are in the nature of public goods and hence are subject to free
riders problem. The benefits flow to the country as a whole or even to the humanity at large-
in fact, both present and future generation.
• The second major problem is that the current yield rate of most wastewater resource in this
region.
• Third, the weak economics of aquaculture on wetland and the consequent lack of economic
strength of the traditional dweller on wetland make them very susceptible to various
negative externality effects from non-aquaculture activitis.
• The legal framework governing use of wetland in west Bengal that although the government
had initially started protecting the private property rights in wetland and water bodies so
as to promote aquaculture.
Industrial Waste Water
Industrial waste water is responsible for as much as 16%
of the world’s annual freshwater withdrawals. This
effluent is typically comprised of particulate media,
microorganisms, and chemicals which can harm
ecosystems and infiltrate the human drinking water
supply. Crystar® FT is poised to interrupt this cycle of
consumption and pollution by providing a cost-effective
solution for the filtration of aggressive industrial
wastewater as part of the water recycling process.

Reference:
• Second edition Handbook of fisheries and aquaculture (Dr. S.Ayyappan) (Page No. 449-468
Published by New Delhi).
• An introduction to fisheries (Dr. S.S.Khanna)
• (Page No. 498-500 Published by Silver line publication, 1683-956, Kalyani Devi, Allahabad-
211003 UP).
• Google.
• Wikkipedia.

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