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.