Conventional methods in waste water treatment
Keeping aside as pollutants, while considering the growth of countries economy, it is important to secure heavy metals for sustainable industrial production as they are one of the key components of various products {73(P)}. Considering its significance and toxicity as prior, scientists worldwide are being developed various treatment techniques to recover and to remove heavy metals from the industrial wastes qualitatively. There are varied conventional treatment options from the antiquity. Physical methods like mechanical screening, hydrodynamic classification, gravity concentration, flotation, magnetic separation, electrostatic separation and attrition scrubbing are being used by many researchers based on the physical characteristics of suspended particles application of physical treatment methods. To treat waste water with soluble heavy metals, chemical treatment methods like chemical precipitation, coagulation, complexation, activated carbon adsorption, ion exchange, solvent extraction, foam flotation, electron deposition cementation and membrane operations employing in many treatment plants legislative standards {1(P) 3, (9(P)) (21(P))}.
To detail in brief, due to its simple operation {22 in 1 (P)}, among the conventional treatment methods chemical precipitation is the most widely used method to treat industrial wastes with heavy metals. Which precipitates metals salts in to insoluble hydroxide, sulphide, carbonate and phosphate forms and which are further recovered/removed by increasing the particle size which made filtration easier {25 in 1(P)} by employing coagulation and flocculation processes {21 & 22 in 1(P)}. In addition, to precipitate the heavy metals in a weak acidic or neutralized catholyte into its hydroxide forms by passing the electricity current thorough a container containing heavy metals solution with cathode plate and insoluble anode {26 in 1(P)}.
In spite of number of chemical treatments techniques available today mentioned above. Due to considerable draw backs and lack of economic feasibility {Kidd et. al., 2009 in 93(P)} of all the treatment methods, industrial market is still looking towards the sustainable tool in order to minimize the coast of chemicals being used in the treatment, sludge management and also recovery strategies for crucial metals in an economical and sustainable fashion by keeping environmental safety at high prior.