Wastewater Treatment

Simply defined wastewater is water that has picked up various contaminants during its use in domestic, industrial or commercial applications. In sequence to safeguard environment and in-turn public health these components must be removed before the wastewater can be put back into a natural water body. The natural cycles provide an insight into the natural basis of wastewater and stormwater management. For disposal of wastewater and stormwater within a natural ecosystem, as long as a natural purification capacity or assimilation capacity of the ecosystem is not exceeded, we could rely on the existing natural processes to assimilate the wastes without degrading the quality of the environment. On the other hand once the natural capacity is exceeded, engineered systems are required. Therefore, the same physical, chemical and biological processes taking place in nature can be used as a basis for technology development and for waste management.

Various unit operations of the wastewater treatment system are decided based upon the treatment objectives and pollutants present. Normally the wastewater treatment system is divided into primary, secondary and tertiary treatment. A brief account of these is presented below.

Primary Treatment involves physical removal of solid material. Screening removes grit (sand, stones and other large particles). Sedimentation settles out remaining particulate matter into a mudlike sediment called sludge which must be disposed off. Treated wastewater continues to secondary treatment or is released. Normally, 30 to 40% of pollutants are removed through primary treatment.

Secondary Treatment refers to biological treatment. Microorganisms, like as bacteria, play a significant role within the natural cycling of materials and particularly in the decomposition of organic wastes. The role of microorganisms is significant in the treatment of wastewater. In natural and engineered both treatment systems, microorganisms like as bacteria, protozoa, fungi,  and crustaceans play an necessary role in the conversion of organic waste to more stable less polluting substances. About 90 percent of pollutants are erased after secondary treatment.

Tertiary Treatment refers to advanced treatment to decrease concentrations of selected pollutants identified within effluent. It erased nutrients, organic pollutants, etc.