Interesting and Useful Facts About Sewage Treatment
Sewage treatment is the process of removing contaminants from wastewater and household sewage. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants to produce environmentally safe treated wastewater (or treated effluent). Sewage treatment is a crucial public health measure that prevents the spread of disease. In this blog, we will explore some fascinating facts about how sewage treatment works and its importance to public health and the environment.
History of Sewage Treatment
Sewage treatment has been practiced in various rudimentary forms since ancient times. Some of the earliest sewage systems include the cloaca maxima in Rome and sewers systems constructed during the Indus Valley civilization. However, it was only in the late 19th century that concerted efforts were made to construct centralized, large-scale sewage treatment systems in major cities to address public health concerns. Early sewage treatment focused on physical processes like screening, sedimentation and filtration. Chemical treatment was introduced in the early 20th century, followed by biological sewage treatment methods. Activated sludge process, trickling filters, oxidation ponds and anaerobic digestion became common as sewage treatment technology advanced over the 20th century. Many developed countries mandated sewage treatment by law to tackle pollution in water bodies. Today, a variety of sophisticated techniques are used in the multiple stages of the sewage treatment process.
Sewage Treatment Process
Sewage treatment generally involves three main phases - primary, secondary and tertiary treatment. Primary treatment removes solid waste and particles, usually by screening and sedimentation. Screening is done to remove larger debris and sedimentation allows suspended solid waste to settle at the bottom. Secondary treatment removes dissolved organic matter using biological treatment processes. Here, microorganisms are used to consume organic contaminants for their own growth. Common methods include activated sludge process, trickling filters, oxidation ponds etc. Tertiary treatment is an advanced purification process to remove specific pollutants like nitrogen, phosphorus, heavy metals etc. Methods include filtration, absorption, disinfection and nutrient removal through biological or chemical techniques. Chlorination is a widely used disinfection method. The treated water is then discharged into the environment or reused. Sewage sludge from the process is disposed separately.
Sewage Treatment Methods
Activated sludge process is the most common method used for secondary sewage treatment. It involves aeration of wastewater along with microorganisms that form an activated sludge. This sludge consumes organic matter reducing it to carbon dioxide, water etc. The nutrient-rich activated sludge is recycled and re-aerated to continue treating incoming wastewater. Trickling filters work by passing wastewater through a medium like stones, plastic or wood on which a layer of microbial slime grows. The microbes in the slime consume and remove organics. Oxidation ponds are large shallow ponds that enable natural purification through algae and bacteria. The ponds require a large area but are low-cost to build and operate.
Anaerobic digestion is a process where organic matter is broken down by microorganisms in absence of oxygen, producing biogas. The nutrient-rich digestate can be used as fertilizer. Membrane bioreactors allow very high microbe concentrations to be maintained, making the process compact. Moving bed biofilm reactors are also compact systems using microbes attached to small plastic pieces that move through the wastewater.
Importance of Sewage Treatment
The main aim of sewage treatment is to protect public health and prevent environmental pollution. Removing human waste and other contaminants reduces the spread of infectious diseases like cholera, typhoid, dysentery, hepatitis etc. that occur through contaminated water. Properly treated sewage enables the safe reuse of nutrient-rich wastewater for irrigation and supplements water supply. Sewage treatment is crucial to avoid polluting water bodies like rivers, lakes, seas and groundwater with contaminants, toxic chemicals, microplastics etc. that severely damage ecosystems. It prevents phenomena like eutrophication, which results from excess nutrients in waterbodies and causes algal blooms and death of aquatic life. Sewage treatment also reduces foul odors that can cause nuisance to local residents. Overall, sewage treatment protects the health of the wider community and environment.
Sewage Treatment Capacity
The sewage treatment capacity varies widely across the world. Developed countries generally have comprehensive sewage treatment infrastructure covering a majority of the population. For example, in the US, close to 95% of the population is served by centralized collection systems connected to wastewater treatment plants. But many developing countries have a long way to go. In India, it is estimated that only about 37% of sewage generated is treated before being discharged into water bodies. This results in extremely high levels of water pollution across the country's rivers, lakes and coastal areas. Expanding sewage treatment infrastructure poses major financial and technological challenges for local governments.
Modern sewage treatment focuses not just on pollution control but also resource recovery. Phosphorus, a limited and non-renewable resource, can be recovered from sewage sludge and recycled as fertilizer. As phosphorous reserves get depleted, this provides a sustainable source. Biogas generated from anaerobic digestion of sewage sludge is a valuable renewable energy resource. Biogas can displace fossil fuels to generate electricity and heat. The organic matter in sludge can also be broken down into biofuels. Reusing the large volumes of water from sewage treatment for purposes like irrigation, industry or even drinking after advanced purification helps tackle water scarcity in cities. These methods help create environmental and economic benefits.
Sewage Treatment Issues
A variety of complex issues continue to challenge sewage treatment systems globally. Growing urban populations are increasing the load on existing facilities in many cities. Cost of infrastructure and high energy needs pose challenges. Operational issues like odors, noise and sludge disposal affect surrounding communities. Maintaining consistent treatment during rainy and dry weather fluctuations is difficult. Industrial wastewater from factories containing heavy metals, toxins and drug residues can pass through and disrupt biological treatment processes. Microplastic fibers from garments are now abundantly found in sewage sludge. Other emerging pollutants like pharmaceuticals and antibacterial residues require advanced techniques for removal. And climate change is likely to compound many of these problems in the future. Continued technology development, infrastructure investment and process improvements are needed to tackle these challenges.
Several technological and operational innovations are underway to improve sewage treatment. Automation and remote sensors are enabling smarter system control and performance monitoring. New techniques like forward osmosis, ozone and activated carbon can enhance contaminant removal. Decentralized small-scale treatment systems and modular plants are gaining favor. Renewable energy systems help make operations carbon-neutral. Nutrient and resource recovery are being prioritized to transition to circular economy systems. Implementing these innovations along with a continued focus on protecting public and ecological health will be key for the future sustainability of sewage treatment worldwide.
Sewage treatment is an often overlooked and underappreciated public health service. But the fascinating processes, techniques and infrastructure involved in cleaning millions of gallons of wastewater every day protect human lives and the environment in invaluable ways. Continued research, innovation and investment are crucial for sewage treatment to overcome emerging challenges and develop into an even more effective, efficient, sustainable and ecologically regenerative system in the future. Robust sewage treatment infrastructure is a key foundation of healthy, thriving communities and environments.
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