Critical Review of Pollution Control Technologies

Abstract

The effluent generated from the industries is mostly treated using primary, secondary, tertiary and the advance treatment methods. The first step in the water pollution control is to minimize the pollution load in effluent that can be effected by preventing the raw materials or products from entering into the effluent streams. Segregation of highly polluting effluent stream from the low polluting stream followed by treatment of each effluent stream separately, gives better performance of the effluent treatment system [1]. In some cases, effluent of one industry can become the raw material of the other industries. For instance, the molasses (highly polluting effluent stream) generated from the sugar mill is used as a raw material in the fermentation (distillery) industry for production of alcohol. The second step in the effluent treatment is to collect and equalize the effluent streams that are discharged at different intervals from different stages of product manufacturing. The equalization ensures uniform characteristics in terms of pollution load, pH and the temperature. Screening and oil trap, prior to the equalization, is provided for removal of the floating solids or oil. The effluent is further treated in the primary treatment unit including addition of the coagulants such as lime, alum and polyelectrolyte followed by clariflocculator or flocculator and settling tank. Selection of the appropriate coagulants and doses of the coagulants are determined on the basis of the treatability study of effluent samples. The primary treatment helps in reduction of the total suspended solids (TSS). A significant reduction in biochemical oxygen demand (BOD) and chemical oxygen demand (COD) concentrations is also achieved. The primary treatment is followed by the secondary treatment i.e. aerobic biological treatment process and the settling, which further reduces BOD and COD concentrations in the effluent. The effluent with high BOD and COD concentrations, as in the case of slaughter houses and distilleries etc., two stage biological treatment system is preferred. Installation of an anaerobic (biomethanation) reactor prior to the aerobic treatment can facilitate recovery of methane gas and manure. The methane gas can be used as fuel in the boilers, fluid heaters and DG sets. The advance treatment technologies involving evaporation and incineration are also practiced. The advance oxidation and electrochemical coagulation process of effluent treatment have been explored for the treatment of industries.