Waterwaste

Water is called our lifeline because without it, life cannot exist. Every living organism, from the smallest bacteria to the largest tree and animal, requires water to carry out essential life processes. Our own bodies are about 60-70% water. Water is needed for drinking, cooking, growing food, cleaning, industry, and countless other activities. It is the most essential resource for survival on Earth. No living thing can survive for more than a few days without water.

Sewage is the used water that flows out of our homes, schools, offices, factories, and hospitals. It comes from toilets, bathrooms, kitchens, laundries, and industrial processes. Sewage contains a variety of impurities, including human waste, food scraps, soap, detergents, oils, chemicals, and microorganisms. Because it is contaminated, sewage cannot be released directly into rivers or lakes without treatment, as it would pollute the water and spread disease.

Organic impurities in sewage come from living things or from natural materials. They include human and animal waste (feces, urine), food scraps from kitchens, vegetable and fruit peels, paper, cotton, wool, and other biodegradable materials. These organic impurities can be broken down by bacteria (decomposers) in a process called biodegradation. However, if too much organic waste is present, it can cause water pollution and lead to the growth of harmful microorganisms.

Inorganic impurities in sewage are those that do not come from living organisms or are not carbon-based in the way organic matter is. They include nitrates and phosphates (often from fertilizers and detergents), heavy metals like lead, mercury, cadmium, and arsenic (from industrial waste), and salts. Many inorganic impurities are not easily broken down by bacteria and can remain in the environment for a long time, causing pollution and health problems. Heavy metals are particularly toxic.

Sewage often contains high levels of nitrates and phosphates. These come from human waste, food waste, detergents, and fertilizers that wash into drains. While nitrates and phosphates are plant nutrients, too much of them in water bodies causes a problem called eutrophication. The excess nutrients cause rapid growth of algae (algal blooms). When these algae die and decompose, decomposing bacteria use up all the oxygen in the water, leading to the death of fish and other aquatic life.

Sewage often contains harmful microorganisms (pathogens) from human waste. When people drink water contaminated with sewage, they can contract waterborne diseases. Cholera (caused by Vibrio cholerae bacteria) causes severe diarrhea and dehydration. Typhoid (caused by Salmonella typhi) causes high fever and intestinal problems. Hepatitis A (caused by a virus) affects the liver. Other waterborne diseases include diarrhea, dysentery, polio, and giardiasis. Proper sanitation and water treatment prevent these diseases.

A Wastewater Treatment Plant (WWTP), also called a sewage treatment plant, is a facility designed to clean polluted water. It uses physical, chemical, and biological processes to remove solid materials, organic matter, nutrients, and harmful microorganisms from sewage. The treated water (effluent) can then be safely released into rivers, lakes, or oceans, or it can be reused for irrigation, industrial cooling, or even (after further treatment) as drinking water. Without WWTPs, our water bodies would become severely polluted.

Sanitation refers to the systems and practices that keep our environment clean and prevent the spread of diseases. This includes proper collection and treatment of sewage, safe disposal of garbage, clean drinking water supply, and hygiene practices like handwashing. Good sanitation is essential for public health. Poor sanitation leads to contamination of water and soil with human waste, which causes diseases like cholera, typhoid, and diarrhea. The Swachh Bharat Mission in India aims to improve sanitation across the country.

A sewer is an underground pipe or system of pipes that transports sewage (wastewater) away from buildings. Smaller pipes (laterals) collect sewage from individual homes and connect to larger pipes (mains), which eventually lead to a wastewater treatment plant. Some older systems carry both sewage and stormwater (combined sewers), while modern systems often keep them separate (separate sewers). Properly functioning sewers are essential for sanitation because they remove waste from populated areas and prevent it from contaminating drinking water or living spaces.

Aeration is a key step in secondary (biological) wastewater treatment. Large tanks of sewage are bubbled with air (or mechanically stirred to mix in air). This adds oxygen to the water. The oxygen allows aerobic bacteria (bacteria that need oxygen to live) to grow and multiply rapidly. These bacteria feed on the organic impurities in the sewage (human waste, food scraps, etc.), breaking them down into simpler, harmless substances. Aeration greatly speeds up the natural decomposition process.

The prefix “aero” means air or oxygen. Aerobic bacteria require oxygen to live, grow, and carry out their metabolic processes. They are used in the aeration tanks of wastewater treatment plants. Anaerobic bacteria (“an” means without) do not require oxygen. In fact, oxygen is often toxic to them. They live in oxygen-free environments like deep sediments, swamps, and the digestive tracts of animals. Anaerobic bacteria are used in the sludge digestion stage of treatment, where they break down organic matter without oxygen, producing methane gas.

Sedimentation is the first major treatment step after screening. Wastewater is held in large tanks called sedimentation tanks or clarifiers. The flow is slowed down so that heavier solid particles (sludge) sink to the bottom, and lighter materials like oils and grease (scum) float to the top. The settled sludge is removed for further treatment, and the floating scum is skimmed off. The partially clarified water then moves on to secondary (biological) treatment. Sedimentation is a physical process that does not involve chemicals or bacteria.

After primary and secondary treatment, the water still contains harmful microorganisms (pathogens) that can cause diseases like cholera and typhoid. Disinfection is the final treatment step that kills these pathogens. The most common method is adding chlorine (chlorination), which is effective and inexpensive. Other methods include using ultraviolet (UV) light, ozone, or other disinfectants. Disinfection makes the treated water safe to release into rivers or (after further treatment) to reuse. However, chlorination must be carefully controlled to avoid harmful byproducts.

Untreated sewage contains organic matter (feces, food waste) and pathogens (disease-causing microorganisms). When it enters a river, bacteria and other decomposers feed on the organic matter. They multiply rapidly and use up the oxygen dissolved in the water (biochemical oxygen demand or BOD). Low oxygen levels kill fish and other aquatic animals. The pathogens in the sewage can cause waterborne diseases in people who use the river water for drinking, bathing, or washing. The river becomes polluted and foul-smelling.

Cholera is caused by the bacterium Vibrio cholerae, which is found in water contaminated with human feces. It causes severe, watery diarrhea that can lead to rapid dehydration and death if untreated. Other bacterial diseases spread through contaminated water include typhoid (Salmonella typhi), dysentery (Shigella), and diarrhea (E. coli). Malaria and dengue are caused by parasites and viruses spread by mosquitoes, not directly by contaminated water. Cancer is not an infectious disease spread through water.

In the secondary treatment stage (aeration tank), large amounts of air are bubbled through the sewage. This encourages the growth of aerobic bacteria. These bacteria feed on the organic matter (human waste, food scraps, etc.) in the sewage, using it as food. They break down complex organic compounds into simpler, harmless substances like carbon dioxide, water, and more bacteria. The bacteria then form clumps (flocs) that can be settled out. This biological process is the most important step for removing organic pollution from sewage.

Many serious diseases, including cholera, typhoid, diarrhea, and polio, are spread when human feces contaminate drinking water or food. Proper sanitation means safely collecting, transporting, and treating human waste so that it does not come into contact with people. This includes toilets, sewers, and wastewater treatment plants. Good sanitation breaks the cycle of disease transmission. The Swachh Bharat Mission (Clean India Mission) has significantly reduced open defecation in India, leading to lower rates of waterborne diseases.

Before any other treatment, incoming sewage passes through screens. These are metal bars or mesh filters that catch large solid objects that could damage equipment or clog pipes. Items removed include sticks, leaves, rags, plastic bottles, sanitary products, toys, and other debris. This material (called screenings) is collected and disposed of in landfills. Screening is a physical pretreatment step. After screening, the sewage still contains smaller solids, organic matter, and dissolved impurities that need further treatment.

Sludge is the semi-solid material that settles at the bottom of sedimentation tanks. It is rich in organic matter. Instead of being wasted, it is treated further. In a sludge digester (an oxygen-free tank), anaerobic bacteria break down the organic matter over several weeks. This process reduces the volume of sludge and kills many pathogens. It also produces biogas, which is mainly methane (CH4). This biogas can be captured and burned to generate heat or electricity, making the treatment plant more energy-efficient.

Hepatitis A is a viral infection that affects the liver. It is spread primarily through the fecal-oral route, meaning when a person ingests food or water contaminated with the feces of an infected person. This often happens when sewage contaminates drinking water sources. Symptoms include jaundice (yellowing of skin and eyes), fatigue, abdominal pain, and fever. Unlike cholera and typhoid (which are bacterial), Hepatitis A is caused by a virus. Good sanitation and vaccination can prevent Hepatitis A.

Potable water (also called drinking water) is water that has been treated or naturally obtained and is safe for human consumption. It should be free from harmful levels of contaminants, including disease-causing microorganisms (pathogens), toxic chemicals, and excessive minerals. Potable water may still contain harmless dissolved minerals that give it taste. In most cities, tap water is treated to make it potable. In rural areas, people may drink from wells or springs, but these sources must be tested to ensure they are safe.

Untreated sewage contains large numbers of pathogens, including bacteria (like E. coli, Salmonella), viruses (like Hepatitis A, norovirus), and parasites (like Giardia). If a person swallows even a small amount of this contaminated water while swimming, they can become sick with diarrhea, vomiting, or more serious diseases. Pathogens can also enter the body through cuts, scrapes, or mucous membranes (eyes, nose, mouth). This is why beaches and swimming areas are often closed when sewage contamination is detected.

Septic tanks are common in rural areas and in some suburban neighborhoods where there is no municipal sewer system. Wastewater from toilets, bathrooms, and kitchens flows into a buried, watertight tank. In the tank, solids settle to the bottom (sludge) and lighter materials (scum) float to the top. Bacteria partially break down the organic matter. The liquid (effluent) flows out into a drain field (leach field) where it percolates through soil, which provides further treatment. Septic tanks must be pumped out periodically to remove accumulated sludge.

After screening, wastewater flows into a grit chamber. This is a long, narrow tank where the flow speed is carefully controlled. Heavy inorganic particles like sand, coffee grounds, eggshells, gravel, and small stones settle to the bottom, while lighter organic matter remains suspended and flows through. Removing grit is important because these abrasive particles would wear down (abrade) pumps and other mechanical equipment in the treatment plant. The settled grit is washed and then disposed of in a landfill.

Anaerobic bacteria are used in the sludge digestion stage of wastewater treatment. The sludge (settled solids from primary and secondary treatment) is placed in a closed, oxygen-free tank called a digester. Anaerobic bacteria break down the organic matter in the sludge over several weeks. This process reduces the volume of sludge (making it easier to dispose of) and kills many pathogens. It also produces biogas (mainly methane) as a byproduct. This biogas can be captured and burned as fuel to generate heat or electricity, helping to power the treatment plant.

Eutrophication is a major water pollution problem. When sewage or agricultural runoff containing high levels of nitrates and phosphates enters a lake or river, it acts like fertilizer for algae. The algae grow rapidly, forming dense, green “blooms” on the water surface. These blooms block sunlight from reaching underwater plants. When the algae die, decomposing bacteria break them down, using up all the oxygen in the water. This creates “dead zones” where fish and other aquatic animals cannot survive.

Sewage pollution gives water several characteristic signs. The organic matter in sewage decomposes, producing foul-smelling gases like hydrogen sulfide (rotten egg smell). The water often appears cloudy, dark, or greenish due to suspended solids and algae growth. You may see floating solids (like grease, scum, or pieces of waste). There may be visible foam from detergents. The oxygen level in the water is low (hypoxic), and you will see few or no fish or other aquatic animals. Clean water, in contrast, is clear, odourless, and supports diverse life.

Chlorination is the most common method of disinfecting drinking water worldwide. Chlorine (usually in the form of chlorine gas, sodium hypochlorite, or calcium hypochlorite) is added to water in carefully controlled amounts. It kills or inactivates disease-causing microorganisms, including bacteria (like E. coli, Salmonella, Vibrio cholerae), viruses (like Hepatitis A, norovirus), and some parasites. Chlorine also provides a “residual” effect, meaning it remains in the water as it travels through pipes to homes, preventing recontamination. However, chlorine must be used carefully as high levels can be harmful.

BOD is an important measure of water pollution. It measures the amount of dissolved oxygen consumed by microorganisms (bacteria) as they decompose organic matter in a water sample over a set period (usually 5 days). High BOD means there is a lot of organic pollution (like sewage) in the water. As bacteria break down this organic matter, they use up oxygen. If BOD is too high, the water becomes depleted of oxygen, killing fish and other aquatic life. Clean water has low BOD; sewage-polluted water has high BOD.

Natural water bodies like rivers, lakes, and ponds can be contaminated with sewage, animal waste, or agricultural runoff. These sources may contain harmful bacteria (E. coli, Salmonella, Vibrio cholerae), viruses (Hepatitis A, norovirus), and parasites (Giardia, Cryptosporidium). Drinking such water can cause serious gastrointestinal illnesses, including diarrhea, vomiting, cholera, typhoid, and hepatitis. Even if the water looks clean, it may still contain pathogens. Always boil, filter, or chemically treat water from natural sources before drinking.

The bar screen is the very first treatment step. It consists of a series of metal bars or a mesh placed across the flow of incoming sewage. It catches large solid objects that could damage pumps, clog pipes, or interfere with other treatment processes. Items removed include sticks, leaves, rags, sanitary napkins, plastic bottles, toys, and other trash. These screenings are periodically removed and disposed of in a landfill. Bar screens are a form of physical (not chemical or biological) treatment.

In common usage, a sewer is specifically a pipe or channel that carries sewage (wastewater containing human waste) from buildings to a treatment plant. A drain (or storm drain) carries rainwater, surface runoff, or sometimes non-toxic wastewater from places like roof gutters or patios. In modern “separate sewer systems,” sewers and storm drains are completely separate. In older “combined sewer systems,” both sewage and stormwater flow in the same pipe, which can cause overflows during heavy rains.

Giardia lamblia (often just called Giardia) is a microscopic protozoan parasite that causes a diarrheal illness called giardiasis. It is spread through swallowing water contaminated with the feces of an infected person or animal. Giardia is a common contaminant of untreated river and lake water, especially in areas with beavers or other wildlife. It has a protective outer shell (cyst) that allows it to survive outside the body and resist chlorine disinfection to some extent. Boiling water is the most reliable way to kill Giardia cysts.

Aeration is the main biological treatment step (secondary treatment). Large tanks (aeration basins) are filled with sewage from primary sedimentation. Air is pumped in through diffusers at the bottom, or mechanical mixers churn the surface. This adds oxygen to the water. The oxygen allows aerobic bacteria and other microorganisms to thrive. These microbes feed on the organic matter (feces, food waste, etc.), breaking it down into carbon dioxide, water, and more microbes. The microbes then clump together into “flocs” that can be settled out later.

After primary (sedimentation) and secondary (aeration and final sedimentation) treatment, the water still contains harmful pathogens (bacteria, viruses, parasites). Disinfection is the final treatment step that kills these pathogens, making the water safe to release into the environment. The most common method is chlorination (adding chlorine). Another method is UV (ultraviolet) light, which damages the DNA of microorganisms. Ozone is also used. After disinfection, the treated water (effluent) can be discharged into a river, lake, or ocean, or it can be reused for irrigation or industrial purposes.

Untreated sewage contains organic matter that decomposes in the river, using up oxygen (high BOD) and killing fish. It also contains pathogens that cause diseases like cholera and typhoid in people who use the river water. By treating sewage, we remove most of the organic matter (reducing BOD) and kill or remove most pathogens. This protects aquatic life and public health. Treated sewage still contains some nutrients (nitrates, phosphates), which can still cause some eutrophication, but it is much less harmful than raw sewage.

Older cities often have combined sewer systems. In these systems, both wastewater from homes and businesses (sewage) and rainwater from streets and roofs (stormwater) flow through the same underground pipes to the treatment plant. The problem with combined sewers is that during heavy rain, the volume of water can exceed the capacity of the treatment plant. To prevent flooding, the system is designed to overflow, releasing a mixture of untreated sewage and stormwater directly into rivers or lakes. These are called Combined Sewer Overflows (CSOs) and are a major source of water pollution.

E. coli is a bacterium that lives in the intestines of humans and warm-blooded animals. It is present in large numbers in feces. While most strains of E. coli are harmless, their presence in water indicates that the water has been contaminated with fecal matter. If E. coli is found, there is a high chance that other, more dangerous pathogens (like those causing cholera or typhoid) may also be present. Water testing labs check for E. coli as an “indicator organism.” Safe drinking water should have zero E. coli.

After the aeration tank, the water contains a mixture of treated water and suspended clumps of bacteria (flocs) that have consumed the organic waste. This mixture flows into a secondary sedimentation tank (clarifier). Here, the flow is slowed, and the heavy bacterial flocs settle to the bottom. This settled material is called “activated sludge.” Some of this sludge is returned to the aeration tank to maintain the bacterial population, and the rest is sent to the sludge digester. The clear water from the top flows on to disinfection.

Nitrates and phosphates in sewage come from several sources. Human waste (feces and urine) contains both nitrogen and phosphorus. Food waste also releases these nutrients as it decomposes. Laundry detergents and dishwasher detergents traditionally contained high levels of phosphates as water softeners (though many modern detergents are “phosphate-free”). Some industrial processes also contribute. When these nutrients reach lakes and rivers, they cause eutrophication (excessive algae growth). Many wastewater treatment plants have special nutrient removal steps to reduce nitrates and phosphates before discharge.

In primary sedimentation tanks, not only do heavy solids (sludge) settle to the bottom, but lighter materials like grease, oil, soap scum, and other floating debris rise to the surface. A mechanical skimmer (a rotating arm or belt) slowly moves across the water surface and pushes this floating material (called scum) into a collection trough. The scum is then removed and disposed of, often sent to the sludge digester or incinerated. Removing scum prevents it from clogging downstream equipment and improves the quality of the treated water.

Open defecation (defecating in fields, forests, or near water bodies instead of in a toilet) is a major public health problem in some parts of the world, including parts of India. The main reasons include poverty (cannot afford to build a toilet), lack of government infrastructure, lack of awareness about the health risks, and traditional habits. Open defecation contaminates soil and water sources, leading to diarrheal diseases, which are a leading cause of death in young children. The Swachh Bharat Mission has made great progress in reducing open defecation in India by building toilets and promoting behavior change.

Primary treatment (physical) removes about 60% of suspended solids but little of the dissolved organic matter. Secondary treatment (biological) uses aerobic bacteria to break down the dissolved and finely suspended organic matter, removing about 85-90% of BOD. Most modern WWTPs have both primary and secondary treatment. Some also have tertiary (advanced) treatment to remove nutrients (nitrates, phosphates) and other specific pollutants. Primary treatment alone is not sufficient to prevent water pollution; secondary treatment is essential.

Hepatitis A is a viral infection that affects the liver and is spread through the fecal-oral route, often by drinking water contaminated with sewage. Cholera and typhoid are caused by bacteria (Vibrio cholerae and Salmonella typhi, respectively). Dysentery can be caused by bacteria (Shigella) or by a parasite (Entamoeba histolytica). Hepatitis A is the only viral disease in this list. Other waterborne viral diseases include norovirus (causes vomiting and diarrhea), rotavirus (a major cause of diarrhea in children), and poliovirus (causes polio, now largely eradicated through vaccination).

Manholes are vertical access shafts from ground level down to the underground sewer pipes. They are covered with heavy cast iron lids. Workers can enter manholes (with proper safety equipment) to inspect the pipes for cracks or blockages, remove debris that is clogging the line, or perform repairs. Manholes are typically placed at intervals along sewer lines, at changes in pipe direction, and at junctions where multiple pipes meet. They are essential for maintaining the sewer system and preventing backups and overflows.

Aerobic bacteria are called “aerobic” because they require oxygen to survive and carry out their metabolic processes. They use oxygen in cellular respiration to break down organic molecules (like the organic waste in sewage) and release energy. Without oxygen, they cannot produce energy and will die. This is why aeration tanks in WWTPs are constantly supplied with air—to provide the oxygen these bacteria need to do their job of consuming organic pollution. In contrast, anaerobic bacteria do not use oxygen and are often killed by it.

Sludge is the thick, semi-solid material that settles to the bottom of sedimentation tanks (primary and secondary). It is a mixture of water, organic matter (feces, food waste), inorganic particles, and microorganisms. Sludge must be treated further before disposal because it contains pathogens and can cause pollution. Treatment typically involves anaerobic digestion (where bacteria break down the organic matter, producing methane gas), dewatering (removing water), and then either land application (as fertilizer, after proper treatment) or disposal in a landfill.

Boiling is one of the most effective and reliable methods of disinfecting water. Bringing water to a rolling boil for at least 1-3 minutes (longer at high altitudes) kills or inactivates virtually all types of disease-causing microorganisms, including bacteria (E. coli, Salmonella, Vibrio cholerae), viruses (Hepatitis A, norovirus), and parasites (Giardia, Cryptosporidium). Boiling does not remove chemical pollutants, dissolved solids, or sediment. However, for making biologically contaminated water safe to drink (such as from a river, lake, or well suspected of sewage contamination), boiling is excellent.

In the activated sludge process (secondary treatment), the bacteria that consume organic waste are collected in the secondary clarifier. If all these bacteria were removed, the aeration tank would have no bacteria to treat incoming sewage. Therefore, a portion of this settled sludge (called return activated sludge or RAS) is pumped back into the aeration tank. This “recycles” the bacterial population, ensuring there are always enough microbes to break down the organic waste. The excess sludge (waste activated sludge or WAS) is sent to the sludge digester.

Water is our lifeline not only because we drink it, but also because it is essential for sanitation. We use water to flush toilets, which carries human waste away through sewers. We use water to wash our hands, bodies, clothes, and dishes, removing germs and preventing the spread of disease. We use water to clean streets and public places. Without sufficient clean water, proper sanitation becomes impossible, leading to the spread of waterborne diseases. Therefore, water and sanitation are deeply connected and both are essential for public health.