The purpose of a wastewater treatment plant is to clean and purify sewage and water before returning them to the environment. Water that has been treated by these plants is free of solids and pollutants, organic matter is broken down, and oxygen is restored. A total of four operations are used to achieve these results: preliminary, primary, secondary, and sludge treatment. The wastewater and solids are normally delivered to treatment plants’ collection tanks and basins through a network of sewers connecting homes, commercial buildings, schools, and street grates.

The process consists of the following phases: 

Pretreatment Phase

In the pretreatment phase of wastewater treatment plants, the ‘easy pickings’ are removed. Large waste materials, such as tree limbs, garbage, leaves, cans, rags, plastic bottles, diapers, and other waste, are raked away using bar screens. The water inflow rate in many plants is regulated by equalization basins and grit chambers of different types. Overflows from heavy rains are handled in basins until the sewage is ready for treatment. 

Primary Treatment

A primary clarifier can be used to collect wastewater after pretreatment. It consists of a large basin and sedimentation tanks. Particles that are smaller settle out as a result of gravity. A mechanical scraper collects solid matter and conveys it to hoppers connected to equipment for treating sludge. This phase involves using surface skimmers to remove grease and oil if it wasn’t removed during pretreatment. The oily matter is sometimes whipped into a froth by air blowers to facilitate the removal of grease from water during pretreatment. During primary treatment, grease is removed from some plants.

Secondary Treatment

Following aeration and agitation, beneficial microorganisms break down organic matter into sludge by adding beneficial microorganisms to the wastewater. Plants employ alternative strategies to break down sludge. The waste material can be passed over the biofilm by plants that culture a mass of microbes. Some plants mix biomass with waste materials, producing activated sludge that can be recycled and reprocessed. A biological floc is formed by removing carbon and nitrogen from organic waste. Saponification is the process of mixing fats with lye in order to produce soap and glycerol from the collected fats.

Sludge Treatment

After treating the water and biosolids, or sludge, the last step is to dispose of them. Solid waste can be disposed of in a landfill due to gravity’s separation of organic waste from heavier grit. Following centrifugation, the remainder of the primary sludge passes through a thickener into digesting tanks with anaerobic bacteria. This plant can generate electricity by utilizing methane produced by these tanks. A partial deodorizer can be applied to stabilize sludge after it has been deodorized and used as fertilizer for the soil.

Many city dwellers don’t have to worry about wastewater in their houses because wastewater management plants provide running water. During the treatment process, toxic substances and pathogens are removed from the wastewater before it is released safely into rivers and oceans as it leaves the house.

Explore More