This article throws light upon the four main industries that cause pollution. The industries are: 1. Electroplating Industry 2. Steel Industry 3. Cane Sugar Industry 4. Paper Industry.
1. Electroplating Industry:
Generally the plating wastes have the following composition:
The recommended method for the removal of wastes is as follows:
Separation and drying of solids – The cyanide effluent can be treated by alkaline chlorination in one reactor, the chromium by ferrous sulphate reduction in another reactor and the two treated effluents, mixed together along with acid effluents containing other toxic metals in a third reactor to precipitate the heavy metals at a pH of 8.5 and above.
The metals are treated with FeSO4 to reduce Cr (vi) ions and other are precipitated by adjusting pH. The sludge containing metal precipitates may be dried on sand beds and disposed of on fallow land as a filling material of flow sheet combining all these operations is shown ahead (ISI: 7453- 1974).
2. Steel Industry:
Iron and steel industry leads to discharge a large quantity of suspended and colloidal matter. They reduce the penetration of sunlight and reduce photosynthesis activity of micro-organisms of polluted water bodies. They also lead to heavy siltation of streams and lakes and affect the flow and life in water bodies.
The average chemical characteristics of by-product coke oven effluents consist of – (1) dissolved solids (2) cyanide 12-50 mg/1 (3) Phenol -140-150 mg/1 (4) Sulphide—30—40 mg/1 (5) C.O.D. -1400-2000 mg/1 (6) B.D.0,-700-1200 mg/1 (7).
3. Cane Sugar Industry:
The characteristics of combined effluents from sugar factory can be summarized as follows:
Molasses have extremely high BOD of the order of 900,000 mg/l hence proper care should be given in the mill for molasses not to spill over into waste waters.
4. Paper Industry:
The characteristics of paper industry waste on average are as follows:
The treatment of effluent is done in two stages:
1. Primary Treatment:
Which is called chemical clarification, and
2. Secondary Treatment:
Which is called activated sludge process.
In Primary treatment, chemical clarification is done in three stages:
(i) Chemical coagulation with hydrated lime,
(ii) Chemical coagulation with (alum + lime) at pH 10.5 to 11.0 and
(iii) pH adjustment to 6—7. The first and 2nd stages are followed by flocculation and sedimentation. Thus with primary treatment, we achieve removal of BOD and COD up-to 90% respectively.
In Secondary treatment, the activated sludge process is capable of converting most organic waste (soluble and insoluble) into more stable inorganic forms or to cellular mass, resulting into highly reduced BOD and COD values. The process is performed in presence of heterogeneous microbial culture composed of bacteria protozoa, rotifiers and fungi.
After secondary treatment, the increased bio-mass is disposed of and the remainder returned lo aeration units. After secondary treatment, DO level is also maintained by air saturation technique. The flow sheet is shown in the diagram 4.
The dewatered sludge is heated and ash is used to make concrete blocks or brick.
The presence of toxic heavy metals ions in industrial waste waters has become a matter of concern in recent years. The toxic heavy metal ions which pose potential danger from the industrial waste waters include lead, mercury, copper, cadmium, zinc and nickel.
Precipitation, ion-exchange, evaporation, reverse osmosis, electrodialysis, adsorption by activated carbon and clays, solvent extract ion and cementation arc some of the techniques that have been used for removing heavy metal ions from industrial waste waters (1).
Ion exchange methods can be efficient but synthetic ion-exchange resins are relatively expensive. Many of the methods which are used at present to scavenge the heavy metal ions from industrial waste waters are either uneconomical or are unable to meet effectively the stringent water quality limits for waste effluents, usually much less than 1ppm. for each heavy metal.
Interest has arisen recently in the investigation of some unconventional method and materials for scavenging heavy metal ions from industrial waste waters. Insoluble starch xanthates have been found to be very useful for removing heavy metal ions from solutions.
Agricultural waste materials such as waste wool, Pcanutskin, Walnut expeller meal, modified cotton and modified barks have been investigated by various workers to study their effectiveness in binding heavy metal ions. Many of these agricultural by products are widely available and are of little or no economic value and some of them in fact present in a disposal problem.
The use of coastal red woodbark, water hycinth, black and red oak, western hemlock, pine and sweet gum bark for scavenging toxic heavy metal ions has been reported by several workers. The efficiency of commonly available Indian barks such as Babul, Accacia Arabica for the retrieval toxic heavy metal ions has been evaluated by Kudesia in 16978.
I have been observed that the bark of babul absorbs about 99% heavy metals from the effluents thus it can be used as an effective tool for the removal of metals from the industrial effluents. Moreover as the raw material is very cheap hence the technique can be used without any investment.
Further studies with other plants are going on & will helpful in preventing environmental pollution and giving a clue for the recovery of heavy metals thus saving crores of rupees wasted in purchasing these metals year by industrialists.
Industrialization has brought along with it the hazards of environmental pollution as it has the material comforts. This has gradually increased our concern about the unplanned side effects which may arise from releasing chemicals into our immediate surroundings. These chemicals form one of the major polluting sources which are discharged by industries without any care.
In fact metals are primarily released by ores and processing of recycled metal products. When they are used in industries for the manufacture of various products or other articles then after reaction is over, they come out us unwanted products and so released from the industries without any dilution or treatment.