Sewage treatment is the process of removing from municipal wastewater the contaminates that come mainly from household sewage and industrial wastewater. There are several physical, chemical, and biological processes that are used to remove contaminants to produce treated wastewater, called treated effluent, in a form that is safe enough to release into the environment. Sewage treatment often involves three stages. In the first stage, large solids are removed to reduce the amount of organic matter and solids in the wastewater. In the second stage, the wastewater is treated with biological processes that consume the organic matter and convert it into carbon dioxide and water. In the final stage, advanced treatments like chemical treatment, filtration, and disinfection are used to remove the remaining contaminants so the wastewater can safely be discharged into water bodies for use in irrigation or industrial cooling.
When we speak of “sludge,” we are talking about a product that is mostly water with lesser amounts of solid material that have been removed from liquid sewage. Primary sludge would include solids that are removed via settling tanks called clarifiers that are built to remove the solids being continually deposited by sedimentation. Treating sludge is primarily focused on reducing the water to reduce sludge weight and volume in order to reduce health risks and disposal costs. To reduce infectious microorganisms like viruses and bacteria, the treatment is normally accomplished through heating during digestion or incineration. Energy may also be recovered from sludge through the methane gas produced during anaerobic digestion. Experts in wastewater, sewage, and sludge treatment are normally going to be engineers and chemical experts with experience in things like anaerobic digestion and fermentation.
Advances in sewage and sludge treatment have been made in recent years to improve the efficiency and effectiveness of the treatment process. Some of these advances include:
- Membrane bioreactors (MBRs). These use a combination of activated sludge treatment and membrane filtration to remove contaminants from wastewater. This technology has been found to be more effective than traditional treatment methods, producing higher-quality effluent.
- Anaerobic digestion. AD is a process that uses microorganisms to break down organic matter in sludge. This process produces biogas, which can be used to generate electricity or heat. It is a more sustainable method of sludge treatment, as it reduces the amount of waste that needs disposal.
- Nutrient removal. Nutrient removal is becoming increasingly important as regulations on nitrogen and phosphorus become stricter. Advances in nutrient removal technology include biological nutrient removal, which uses microorganisms to remove nitrogen and phosphorus from wastewater, and chemical precipitation, which uses chemicals to precipitate out these nutrients.
- Thermal hydrolysis. Thermal hydrolysis is a process that uses high-pressure steam to break down organic matter in sludge. This process makes the sludge easier to digest in anaerobic digestion, improving the efficiency of the process and reducing the amount of sludge that needs to be disposed of.
Overall, advances in sewage and sludge treatment are helping to make the process more sustainable and efficient, reducing the environmental impact of wastewater treatment and improving the quality of effluent produced.
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