In this article we will discuss about the industrial effluent standards for disposal.
Industrial Effluent Standard for Disposal on Land:
The use of industrial effluent of irrigation purposes has been quite popular, particular from food processing industries, pharmaceutical industries, pulp and paper industries. While using the effluent for irrigation care should be taken that it should percolate into the field and do not create the problem of mosquito and fly breeding. The industrial wastes can be treated in oxidation ponds or lagoons and disposed of accordingly.
The maximum quantity of effluent to be disposed off by this method depends on the effluent-holding capacity of soil, topography of land, crop, field area and climatic conditions etc.
If more quantity of effluent is applied on the land, it may cause concentration of various constituents which may be deleterious to crop, decrease soil permeability and even contaminate the ground water table. Therefore, it is necessary to fix the maximum limit of certain constituents, in effluents, so that it should be at par with normal accepted irrigation water in quality.
ADVERTISEMENTS:
According to IS: 3307-1965 following are the tolerance limits for industrial effluents discharged on land for irrigation purposes:
(i) The total dissolved inorganic solids should not exceed 2100 mg/l,
(ii) 5-day BOD at 20°C, should not exceed 500 mg/l,
(iii) pH-value of effluent should be between 5.5 to 9.0,
ADVERTISEMENTS:
(iv) Quantity of sulphates and grease should not be more than 30 mg/l, and
(v) Quantity of boron should not exceed 2 mg/l.
Disposal of Industrial Effluent into Sewers:
If the industrial effluent is discharged into public sewers without proper treatment, it may create sewage treatment problems, deteriorates sewer and its appurtenances, increase maintenance cost of sewerage system and also increase stream pollution.
The toxic elements present in the effluent are inimical to biological activity in the treatment plant. Presence of inflammable and toxic volatile matter may cause explosions in the sewers or in the treatment plants.
ADVERTISEMENTS:
Sulphates of effluent tend to form sulphuric acid which corrode the sewers. Oils, grease and tar may stick to the sides of the sewer and reduce the carrying capacity of the sewer. Therefore, it is utmost necessary to limit the concentration of the above contents.
According to IS: 3306-1965, the tolerance limits for industrial effluents discharged into public sewer are as follow:
(i) Its pH-value should be between 5.5 to 9.0,
(ii) 5-day BOD at 20°C should be between 5.5 to .9.0,
ADVERTISEMENTS:
(iii) Lead, copper and zinc should not exceed 1.0,3 and 15 mg/l respectively,
(iv) Effluent temperature should not exceed 45°C,
(v) Quantity of suspended solids should not exceed 600 mg/l,
(vi) Chromium, nickel and cyanide should not exceed 2% each,
ADVERTISEMENTS:
(vii) Effluent containing solids, such as straw, plastic, wood, paint residue, gross solids form cannery wastes, cinder, ash, sand, tar, rag, hair, metal shavings, garbage, broken glass etc., should not be discharged into public sewers.
(viii) Phenolic compounds, sulphates and total inorganic dissolved solids should not exceed 51,000 and 2100 mg/l, respectively.
(ix) Suspended solids should not exceed 600 mg/l, and
(x) Chloride and boron should not exceed 600 and 2 mg/l respectively.
Industrial Wastes Treatment:
Industrial wastes mainly consist of the following:
(i) Effluents obtained from various industrial processes,
(ii) Industries floor washings,
(iii) Condensate water,
(iv) Sanitary and faecal wastes.
The quality of industries water vary from industry to industry, therefore each industry or group of industries require thorough study to choose the best treatment method for its sewage. It is always not necessary to treat the entire industry waste. Some in plant measures may be adopted to reduce or even eliminate the objectionable matter.
Following are the common measures used for industries waste pre-treatments:
(i) Use of soft detergents, instead of hard detergents for eliminating the foam nuisance. This is known as ‘process change’.
(ii) Recovery of silver from photographic wastes, which provides a primary treatment. It is known as recovery of material.
(iii) Refuse of water in industrial processes, such as collecting cooling waters from boilers, eliminating its heat and reusing it.
(iv) Mixing of acidic and alkaline wastes together, for neutralizing each other and making the mixture more nearer to the normal value of pH. This process is known as mixing of trade wastes.
The industrial wastes are usually treated by the following processes:
(i) The suspended solids are removed by screening or settling tanks,
(ii) Oils, grease and fats are removed by floatation and skimming. This process can be aided by chemical treatment in necessary,
(iii) Colloidal matter is removed by floatation with coagulants and electrolytes following by sedimentation and filtration,
(iv) Excessive alkalinity or acidity is removed by adding chemicals or mixing acidic waste with alkaline waste or vice-versa,
(v) Reoxygenation of wastes are done by aeration,
(vi) Decolorization of waste is done by chemical treatment with sedimentation or filtration or both.