The main objective of wastewater treatment is to ensure safe and eco-friendly disposal of industrial effluents. Wastewater can be generally classified as a mixture of domestic sewage, industrial wastewater and surface water which makes its way into the sewers. The wastewater treatment process greatly depends on the standards set for the effluent quality before the water is allowed to merge with the rivers or used for agricultural irrigation.
There are several methods and wastewater treatment procedures which largely includes a combination of physical, chemical and biological methods to achieve best results. Broadly classified under six different methods, wastewater treatment process removes organic matter, suspended solids and nutrients from wastewater.
This is the first stage of the wastewater treatment process which uses a screen to remove solid inorganic materials. The screens consisting of upright bars remove large pieces of trash like plastic, paper, soft drink cans etc. The raw sewage which is known as influent is cleaned off large objects, thereby protecting the pump and other moving parts. The offensive materials is then disposed off at landfills.
Using the process of sedimentation along with certain chemicals, the colloidal solids are removed from the wastewater. The primary sludge which is pushed towards the center is pumped away for further treatment, while the wastewater is moved for secondary treatment.
The wastewater is next passed into large rectangular tanks which includes use of micro-organisms which breaks down suspended organic solids. Otherwise known as the activated sludge process, this step includes use of aeration tanks where microbes consume organic waste. High concentration of organic material in the wastewater is treated using activated sludge, trickling filters and Rotating biological contactors. The treated wastewater makes it way to the tertiary phase of wastewater treatment.
Use of disinfectants to reduce pathogens is a critical step in wastewater treatment which involves the use of chlorine. Depending on the influent, every wastewater treatment plan has different operations before it can pump the treated water back into the river.
The sludge treatment can be done by either thermal destruction, gas to grid or anaerobic digestion. Each of these steps are aimed at treating the sludge and putting it to good use. The gas produced during the anaerobic process contains methane which is used to generate electricity. The residual liquid is pumped back to the aeration tanks for further treatment.
The last process in the wastewater treatment procedure includes the release of treated water back into the river or stream. Bio-monitoring is an extremely critical step which determines whether the treated water has an adverse impact on flora and fauna.