| AFRICAN REGIONAL AQUACULTURE CENTRE, PORT HARCOURT, NIGERIA |
| ARAC/87/WP/12(12) |
| CENTRE REGIONAL AFRICAIN D'AQUACULTURE, PORT HARCOURT, NIGERIA |
M.N. KUTTY
African Regional Aquaculture Centre
Port Harcourt, Nigeria
Lectures presented at ARAC for
the Senior Aquaculturists course
UNITED NATIONS DEVELOPMENT PROGRAMME
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
NIGERIAN INSTITUTE FOR OCEANOGRAPHY AND MARINE RESEARCH
PROJECT RAF/82/009
JUNE, 1987
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2. DOMESTIC SEWAGE AND AGRICULTURAL WASTES
4. WATER QUALITY STANDARDS AND SITE SELECTION
AQUATIC POLLUTION
Industrialisation and other human activities have caused major changes in water quality, both inland and marine. Aquatic pollution is often considered as a major cause in the decline of resources from water. It is important to monitor the water condition before choosing the site for aquaculture and also subsequently for suitable management.
Pollutants can be of various types (see Table 12.I) for point and non-point sources of pollution). The point sources are essentially discharges of sewages and industrial effluents, and are easily identifiable and controllable. The non-point sources arise in part from natural phenomena, eg. soil erosion; irrigation return flows; outflow from fish farms (!), and are often diffuse, and so difficult to identify and control (see Table 12.II, & III). For more information refer Proceeding of the FAO/CIDA Workshop, (FAO, 1978).
To review, the major pollutants are:
Domestic sewage and agricultural wastes.
Detergents (loading of both nutrients and toxicants).
Pesticides - organophosphorus and organochlorine compounds.
Oil, oil dispersants and related petrochemicals.
Inorganic wastes, including heavy metals (mercury, chromium, lead etc.) (see handouts).
Radioactive materials.
Waste heat (Thermal pollution)
negative when heat kills or causes aquatic organisms to avoid heated water.
positive (non-pollution) when heated water can be recycled for growing aquatic organisms eg. culture of warm water finfish (ilapias) and freshwater prawn (Macrobrachium rosenbergii) in heated effluents (industrial waste) in temperate countries.
Pollution can influence aquatic life either directly or indirectly, in several ways, as shown below:
pH changes (increase in acidity)
Decreasing dissolved oxygen (most common index for pollution!)
Toxicity
Mechanical injury to gills (eg. from silt)
Thermal change of medium
Killing food organisms (through (a)) to (e) and
Destruction of spawning grounds.
Sewage pollution in waters could cause:
High B.O.D. load - increase in total solids and oxidisable materials.
Low D.O. (pO2)
High (pO2) and low pH
High NH3 concentration
High H2S concentration
High concentrations of heavy metals
High bacterial load
High nutrient load
All these lead to very poor conditions and would cause fish mortality or in less serious conditions sublethal effects on fish and other aquatic organisms.
Wastes from agricultural farms and fish ponds also cause pollution.
Sewage and effluents with high B.O.D. and nutrient loods can be used for production of fish if judiciously managed. Fish culture in sewage-fed ponds or water taken from stabilization or oxidation ponds, into which sewage flows, can be profitable, if the ambient water and products could meet the public health standards. To satisfy aesthetics the fish so produced if acceptable can be used for reduction as fish meal, if not directly for human consumption. In some countries in Asia sewage and sullage are recycled for pond fish production.
Both organophosphorus and organochlorine compounds used as pesticides are harmful to fish, but organophosphorus compounds are easily degradable (non-persistent in the environment and in the body of the fish unlike organochlorine compounds (chlorinated hydrocarbons eg. DDT, BHC, Endosulphan etc.) See also manual for “Fish culture in rice fields”.
Most countries have prescribed standards for effluents released into natural waters (see Tables 12 - II & III)
It is important to monitor quality of water by direct analysis and/or bioassy, (see practicals - Handouts - on “Species tolerances”) of water source, before choosing a site, which should be free of pollution. If water from streams and rivers are used the upstream area should be carefully studied for existing or potential pollution.
FAO. 1978. Proceedings of FAO/CIDA workshop on aquatic pollution in relation to protection of living resources, Mainla, Philippines, 17 January - 27 February, 1977. TF. RAS 34 (SWE). Suppl., 1. 459 p.
TABLE 12.I MAJOR POINT AND NON-POINT SOURCES OF POLLUTANTS
(Source: FAO, 1978)
| Point sources of potential pollution | Non-point sources of potential pollution | ||
|---|---|---|---|
| (1) | Aluminium industry | (1) | Urban run-off |
| (2) | Sugar processing industry | (2) | Irrigation return flows |
| (3) | Beverage industry | (3) | Agriculture |
| (4) | Canned and preserved fruits and vegetable industry | (a) Manure disposal | |
| (5) | Confined livestock feeding industry | (b) Livestock production | |
| (6) | Dairy industry | (c) Cropping practices | |
| (7) | Fertilizer industry | (d) Fish culture | |
| (8) | Inorganic chemicals, alkalies and chlorine industry | (4) | Land treatment processes |
| (9) | Leather tannery | (a) Effluent disposal | |
| (10) | Meat products industry | (Septic tanks (on-site disposal) | |
| (11) | Metal finishing industry | (5) | Sub-surface injection |
| (12) | Organic chemical industry | (6) | Silviculture |
| (13) | Petroleum refining industry | (7) | Mine pollution |
| (14) | Plastic material and synthetic industry | (8) | Salt water intrusion |
| (15) | Pulp and paper industry | (9) | Hydrologic modifications, etc. |
| (16) | Steam generation and steam-electric power generation | ||
| (17) | Steel industry | ||
| (18) | Textile mill product industry | ||
| (19) | Treated and untreated sewage | ||
The point sources are essentially discharges of sewage or industrial effluents, and they represent identifiable and controllable sources of pollution. Non-point sources are more difficult to identify either because of their uncontrollable diffuse character or because they arise at least in part from natural phenomena, e.g. soil erosion. As a result, their significance in contributing to pollution is only poorly known and little work has been done in this regard even in many developed countries.
TABLE: 12: II. WASTE WATER EFFLUENT STANDARDS AND WATER QUALITY PARAMETERS
Industrial Effluent Standards of ISI1, India
(From CPHERI, National Environmental Engineering Research
Institute, Nagpur).
(Source: FAO, 1978)
| Tolerance limits for industrial effluents discharged | |||
| Into inland surface waters (IS:2490-1963) | Into public sewers (IS:3306-1963) | On land for irrigation (IS:3307-1965) | |
| BOD5 at 20°C | 30 mg/l | 500 mg/l | 500 mg/l |
| pH | 5.5 – 9.0 | 5.5 – 9.0 | 5.5 – 9.0 |
| Total suspended solids (passing 850 micron IS sieve) | 100 mg/l | 600 mg/l | - |
| Total dissolved solids (inorganic) | - | 2 100 mg/l | 2 100 mg/l |
| Temperature | 40°C within 15 m of outfall | ||
| Oils and grease | 10 mg/l | 100 mg/l | 30 mg/l |
| Phenolic compounds (as C6 H5 OH) | 1.0 mg/l | 5 mg/l | - |
| Cyanides (as CN) | 0.2 mg/l | 2 mg/l | - |
| Sulphides (as S) | 2.0 mg/l | - | - |
| Fluorides (as F) | 2.0 mg/l | - | - |
| Total residual chlorine | 1.0 mg/l | - | - |
| Insecticides | nil | - | - |
| Arsenic (as As) | - | - | |
| Barium (as BA) | - | - | |
| Cadmium (as Cd) | - | - | |
| Chromium (as Cr) | SI mg/l | 2 mg/l | - |
| Copper (as Cu) | individually | 3 mg/l | - |
| Lead (as Pb) | or | 1 mg/l | - |
| Mercury (as Hg) | collectively | - | - |
| Nickel (as Ni) | 20 mg/l | - | |
| Selenium (as Se) | - | - | |
| Silver (as Ag) | - | - | |
| Zinc (as Zn) | 15 mg/l | - | |
| Chlorides (as Cl) | - | 600 mg/l | 600 mg/l |
| Boron (as B) | - | 2 mg/l | 2 mg/l |
| Sulphates (as SO4) | - | 1000 mg/l | 1000 mg/l |
| Percent sodium | - | 60 mg/l | 60 mg/l |
| Alpha emitters, μc/ml | 10-7 | - | - |
| Beta emitters, μc/ml | 10-6 | - | - |
1 Indian Standards Institution, New Delhi, India.
TABLE. 12: III. Effluent Standards in Japan
(from Environment Agency, Japan)
(Source: FAO, 1978)
Substances related to the protection of human health
| Substance | Permissible limits |
|---|---|
| Cadmium and its compounds | 0.1 mg/l |
| Cyanide compounds | 1.0 mg/l |
| Organic phosphorus compounds | 1.0 mg/l |
| (Parathion, methyl parathion, | |
| methyl demetion, and EPN only) | |
| Lead and its compounds | 1.0 mg/l |
| Haxavalent chrome compounds | 0.5 mg/l |
| Arsenic and its compounds | 0.5 mg/l |
| Total mercury | 0.005 mg/l |
| Alkyl mercury compounds | Not detectable |
| ECB | 0.003 mg/l |
By the term “not detectable” is meant that the substance is below the level of detectability by the method designated by the Director General of the Environment Agency, Japan.
Parameters related to the protection of the living environment
| Parameter | Permissible limits |
|---|---|
| pH, discharge into coastal waters | 5.0 – 9.0 |
| - discharge into other public waters | 5.8 – 8.6 |
| BOD, COD | 160 mg/l |
| - daily average | 120 mg/l |
| Suspended solids | 200 mg/l |
| - daily average | 150 mg/l |
| N-hexane extracts, mineral oil | 15 mg/l |
| - animal and vegetable fats | 30 mg/l |
| Phenols | 5 mg/l |
| Copper | 3 mg/l |
| Zinc | 5 mg/l |
| Dissolved iron | 10 mg/l |
| Dissolved manganese | 10 mg/l |
| Chromium | 2 mg/l |
| Fluorine | 15 mg/l |
| Coliform number, daily average | 3.000/cm3 |