Sewage water, which includes wastewater from toilets, kitchens, bathrooms, and other sources, particularly those originating from human and vegetable waste, must undergo biological treatment to prevent the decomposition of organic matter. This type of wastewater is commonly referred to as “domestic wastewater.” It is processed in a specialized sewage treatment plant dedicated to this purpose.
Purpose of Sewage Treatment Plant:
The primary objective of sewage treatment is to produce treated effluent that can be safely discharged into the environment with minimal or no adverse impact on the surroundings. Additionally, the treated effluent can potentially be reclaimed for reuse. This goal is accomplished by eliminating impurities from the sewage, making it an essential component of waste management.
In some sewage treatment processes, a byproduct called sewage sludge is generated, which can undergo further treatment to ensure safe disposal or potential reuse. In specific situations, this treated sewage sludge may be referred to as “biosolids” and find application as a fertilizer.
Working of sewage treatment plant:
Sewage treatment typically consists of two primary stages: primary and secondary treatment. More advanced treatment methods also include a tertiary treatment phase that incorporates additional polishing processes.
Primary Treatment:
In the primary treatment stage, a portion of the suspended solids and organic matter is removed from the sewage. This is achieved by allowing the sewage to flow slowly through basins known as “primary sedimentation tanks.” In these tanks, heavy solids settle to the bottom, while oil, grease, and lighter solids float to the surface and are skimmed off. Primary settling tanks are often equipped with mechanical scrapers that continuously move the collected sludge towards a hopper at the tank’s base, from where it is pumped to sludge treatment facilities. The remaining liquid may then be discharged or subjected to secondary treatment. In some cases, sewage treatment plants connected to combined sewer systems have bypass arrangements after primary treatment to protect secondary and tertiary treatment systems during heavy rainfall events. In such instances, a mixture of sewage and stormwater receives primary treatment only. Primary sedimentation tanks are typically expected to remove 50-70% of suspended solids and 25-40% of biological oxygen demand (BOD).
Secondary Treatment:
The secondary treatment stage is designed to remove as much solid material as possible. Biological processes are employed to break down and eliminate the remaining soluble material, particularly the organic fraction. This can be achieved through suspended-growth or biofilm processes. Microorganisms responsible for consuming organic matter in sewage proliferate and form biological solids, also known as biomass. These microorganisms aggregate into flocs, biofilms, and, in specific processes, granules. In various treatment methods, the biological floc, biofilm, and residual fine solids can then settle as sludge, resulting in a liquid with significantly reduced solids content and pollutants. Secondary treatment aims to reduce organic matter, measured as biological oxygen demand (BOD), using aerobic or anaerobic processes. The microorganisms involved in these processes are sensitive to the presence of toxic substances, although high concentrations of these substances are not typically expected in municipal sewage.
Design Aspects:
- Population Equivalent
- Process Selection
- Odor Control
- Energy Requirements
- Co-Treatment of Industrial Effluent
- Design Considerations for Secondary Treatment Processes
- Non-Served Areas
Environmental Impacts:
Sewage treatment plants can have significant repercussions on the ecological health of receiving waters, potentially leading to water pollution, particularly when employing basic treatment processes that lack nutrient removal capabilities.
Water pollution, resulting from human activities, occurs when contaminants are introduced into water bodies, impeding their ability to serve their natural ecosystem functions. Water pollution often stems from one of four primary sources: sewage, industrial discharges, agricultural runoff, and urban stormwater. For instance, the inadequate treatment of wastewater before discharge into natural water bodies can degrade aquatic ecosystems and pose health risks to individuals who use polluted water for drinking, bathing, washing, or irrigation. Providing clean drinking water is a vital ecosystem service offered by freshwater systems; however, around 785 million people worldwide lack access to clean drinking water due to pollution.
How can Hyper Help with this?
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