Treating waste materials in the sewage treatment plant is separated in different stages. The preliminary treatment method is the first stage. In the preliminary treatment, it includes flow equalization, grinding, screening, extraction of grease, measurement of flow and removal of grit. The screenings and also grits are sent to the landfill while the oil is sent to sludge handling facilities at the sewage treatment plant. The succeeding stage would be the main treatment. This includes gravity settling in removing the suspended solids. At this point, around 60% of the entire suspended solids in a household wastewater are taken out. The grease that floats over the sedimentation tank is skimmed off together with the debris that is obtained at the bottom of the tank.
The next stage is the secondary stage. At this stage, it’s designed to remove the dissolvable organics from the wastewater. The secondary stage treatment involves biological process and also secondary settling. Activated sludge is considered the most popular biological process though there are a number of biological processes which can be taken. In the activated sludge process, the microbes or biomass feast upon the organic matter in the wastewater. There exist various types of activated sludge systems and they also differ based on the speed the wastewater remains in the biological reactor and the time the microbes stay there.
The activated sludge systems also vary if the air or oxygen is added, how gas is put and exactly where the wastewater penetrates the biological reactor along with the number of tanks and how it’s mixed. The biological treatment system where the biomass is attached is likewise utilized. The examples of systems which contains biomass absorbed to rocks plastic are trickling filters and biological towers. During the biological treatment, biomass generated are settled in the secondary clarifiers. The settled secondary sludge or biomass is piped to the sludge-management systems. They could also be sent back to the biological reactor at the right amount needed to maintain the suitable biomass level. At the secondary clarifiers, the hydraulic detention time within the place is about 2 hours.
The biological system is designed based on the age of sludge. In the standard activated-sludge system, about 5 to 7 hours is required to retain the sewage in the reactor. Because of the recycling of sludge from the secondary filter, the biomass stays in the reactor for roughly ten days. Following the secondary treatment and clarification, disinfection follows in most sewage treatment plant. Chlorine is mostly utilized in disinfection. Then again, due to the environmental effect of chlorine, de-chlorination of wastewater is performed just before discharge.
In a few sewage treatment plant facilities, they make use of another stage before disinfection. This stage is referred to as the tertiary treatment or advanced treatment. Among the most widely used advanced systems involved are filtration to sand, ion exchange, adsorption to activated carbon, other membrane processes, coagulation-flocculation, nitrification-dentirification and fine screening. The sewage treatment systems used for community sewage vary from the systems used by industry. The wastes from the industries can pose other issues which may need special applications of the modern technologies. Industrial wastes are sometimes pre-treated before release to the sewer.