Question

Briefly explain wastewater treatment (biological treatment).

Answer 1

Wastewater treatment is a process in which the dirty wastewater or sewage water is processed such that it can be discarded to rivers, seas, and the water cycle.

Complete answer:
Cities and towns have sewerage systems to carry the wastewater from homes, hotels, industries, factories, and other places. This water is sent to the sewage treatment plant where the wastewater is treated and when considered to be safe, released into other water sources like rivers. The wastewater treatment goes through different stages where wastewater is treated to remove physical, chemical, and biological contaminants present in it.
Stages include a pre-treatment process that involves wastewater going through larger horizontal and vertical bars to remove large substances like plastic material, cans, etc. Primary Treatment process: Wastewater is passed through grids slowly so that substances like sand, stone, pebbles, and soil settle down at the bottom. Secondary treatment (Biological treatment): All biological or organic waste is removed in the aeration tank. In the last stage, the Tertiary treatment process: Here leftover water is treated with chlorine to remove the phosphorus compound and other chemical compounds.
Secondary wastewater treatment (Biological treatment): It is aimed to remove biodegradable waste present in wastewater. Secondary wastewater treatment is carried out by two methods: Physico-chemical methods (involves chemical oxidation, Adsorption, absorption, etc.) and biological treatment methods (involves the use of microorganisms). Types of microorganisms used,
Based on food requirements: Autotrophic- prepare their own food, Ex. Algae, Heterotrophic- Depend on external food source Ex. Bacteria.
Based on oxygen demand: Aerobic- they survive in presence of oxygen; Anaerobic- they can survive in absence of oxygen, Facultative- they are capable of adapting to any environment (aerobic or anaerobic).
Biological treatments:
Aerobic biological treatment: It is a costly treatment but also acts very fast. In this treatment, complex organic compounds in presence of aerobic bacteria and oxygen are converted into carbon dioxide, ammonia, energy, and water. This contains two systems,
Suspended and attached culture system: In the suspended process the microorganism used for the treatment of wastewater are present in a liquid medium, Ex. Activated sludge process. In the attached process the microorganisms used for degradation are attached to a solid surface like a stone and here we can use both aerobic and anaerobic microorganisms, Ex. Trickling filter, Bio towers, Rotating biological contactor (RCB).
Anaerobic biological treatment: It is a slow process. Here complex waste with anaerobic bacteria is converted into methane, carbon dioxide, hydrogen gas, water, and energy. All three gases produced are used as biological fuel i.e. as biogas.

Note: Many wastewater treatment plants do not prefer using anaerobic processes or anaerobic microorganisms as these organisms produce methane as a byproduct which cannot be released into the atmosphere, hence it is collected and treated to produce energy.