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<h2 class="wp-block-heading"><strong>Objectives of wastewater treatments</strong></h2>
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<p>The traditional aim of wastewater treatment is to enable wastewater to be disposed of safely, without being a danger to public health and without polluting watercourses or causing other nuisances. Recovering energy, nutrients, water, and other valuable resources are other important aims of wastewater treatments.</p>
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<p>Wastewater is contaminated with a variety of microbial pathogens and other organic and inorganic pollutants. If they are not controlled through wastewater treatment, these can contribute to environmental and public health problems.</p>
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<p>Apart from microbial pathogens, wastewater contains suspended solids (measured as turbidity and/or total suspended solids (TSS)), oxygen-depleting organic matter (measured as biochemical oxygen demand (BOD) or chemical oxygen demand (COD)), and nutrients (i.e., nitrogen and phosphorus). All of these adversely affect the receiving water bodies.</p>
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<p>Because domestic water use is considered non-consumptive, the process returns most of the extracted water back to the environment, where it lowers water quality. It has been estimated that every cubic meter of untreated wastewater discharged to surface water makes 8–10 m<sup>3</sup> of freshwater unusable.</p>
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<h2 class="wp-block-heading"><strong>What is in Wastewater?</strong></h2>
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<p>Wastewater is mostly water by weight. Other materials makeup only a small portion of wastewater but can be present in large enough quantities to endanger public health and the environment.</p>
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<p>Practically, anything that can be flushed down a toilet, drain, or sewer can be found in wastewater. Even household sewage contains many possible pollutants. The wastewater components that should be of most concern to homeowners and communities are those that can cause disease or detrimental environmental effects.</p>
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<h2 class="wp-block-heading"><strong>Organisms</strong></h2>
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<p>Many different types of organisms live in wastewater. Some are essential contributors to treatment activities. A variety of bacteria, protozoa, and worms consume certain carbon-based (organic) pollutants in wastewater and break down them. During the process of wastewater treatment, organisms turn wastes into carbon dioxide, water, or new cell growth.</p>
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<p>There are plentiful bacteria and other microorganisms in wastewater and they help to do most of the treatment. Any wastewater treatment systems are designed mostly to rely on biological processes.</p>
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<h2 class="wp-block-heading"><strong>Pathogens</strong></h2>
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<p>Many disease-causing viruses, parasites, and bacteria are present in wastewater. They can enter into water from anywhere in the community. These pathogens commonly originate from people and animals that are infected with or are carriers of a disease. Gray water and black water from typical homes contain enough pathogens to create a risk to public health. Hospitals, schools, farms, and food processing plants are other likely sources in communities that may contain pathogens.</p>
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<p>Some illnesses from wastewater-related sources are relatively common. For example, Gastroenteritis can result from a variety of pathogens in wastewater. Hepatitis A, typhoid, polio, cholera, and dysentery are other important wastewater-related diseases. Outbreaks of these diseases can occur as a result of drinking water from wells polluted by wastewater, eating contaminated fish, or recreational activities in polluted waters. Some illnesses can be spread by animals and insects that come in contact with wastewater.</p>
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<h2 class="wp-block-heading"><strong>Organic Matter</strong></h2>
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<p>Organic materials are found everywhere in the environment. They are composed of carbon-based chemicals that are the basic elements of most living things. <em></em></p>
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<p><em>In addition to water which constitutes about 70% of a cell's mass, cells are composed of carbon-based compounds that may contain up to 30 or so carbon atoms. These carbon-based compounds include the four biological macromolecules that make up all living things:&nbsp;</em><em>carbohydrates, lipids, proteins, and nucleic acids.</em><em></em></p>
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<p>Organic materials in wastewater originate from plants, animals, or synthetic organic compounds, and enter wastewater in human wastes, paper products, detergents, cosmetics, foods, and from agricultural, commercial, and industrial sources.</p>
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<p>Organic compounds are a combination of carbon, hydrogen, oxygen, nitrogen, and other elements. Many organics are proteins, carbohydrates, or fats and are biodegradable. It means they can be consumed and broken down by organisms. However, even biodegradable materials can cause pollution. Too much organic matter in wastewater can be disturbing to receiving waters.</p>
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<p>Large amounts of biodegradable materials are dangerous to lakes, streams, and oceans. It is because the organisms use dissolved oxygen in the water to break down the wastes, reducing or depleting the supply of oxygen in the water needed by aquatic life. It results in fish kills, odors, and overall degradation of water quality.</p>
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<p>The amount of oxygen organisms need to break down wastes in wastewater is referred to as the biochemical oxygen demand (BOD) and is one of the measurements used to assess overall wastewater strength.</p>
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<p>Some organic compounds are more stable than others. They cannot be quickly broken down by organisms. It creates an additional challenge for treatment. This is true of many synthetic organic compounds developed for agricultural and industrial uses.</p>
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<p>In addition, certain synthetic organics are highly toxic. Pesticides and herbicides are toxic to humans, fish, and aquatic plants. They are often disposed of improperly in drains or carried in stormwater. When receiving those into water bodies, they kill or contaminate fish, making them unfit to eat. They also can damage processes in treatment plants. Benzene and toluene are two toxic organic compounds mostly found in some solvents, pesticides, and other products.</p>
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<h2 class="wp-block-heading"><strong>Oil and Grease</strong></h2>
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<p>Fatty organic materials from animals, vegetables, and petroleum are not quickly broken down by bacteria. They also cause pollution in receiving environments. When large amounts of oils and greases are discharged to receiving waters from community systems, they increase BOD. Also, they may float to the surface and harden, causing aesthetically unpleasing conditions.</p>
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<p>They also can trap trash, plants, and other materials, causing foul odors, and attracting flies, mosquitoes, and other disease vectors. In some cases, too much oil and grease causes septic conditions in ponds and lakes and prevents oxygen from the atmosphere from reaching the water.</p>
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<h2 class="wp-block-heading"><strong>Inorganics</strong></h2>
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<p>Inorganic minerals, metals, and compounds, such as sodium, potassium, calcium, magnesium, cadmium, copper, lead, nickel, and zinc are common in wastewater from both residential and nonresidential sources. They can originate from a variety of sources in the community. These include industrial and commercial sources, stormwater, inflow from leaky manhole covers, and infiltration from cracked pipes. Most inorganic substances are relatively stable, and cannot be broken down easily by organisms in wastewater.</p>
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<p>Large amounts of many inorganic substances can contaminate soil and water. Some are toxic to animals and humans and may accumulate in the environment. For this reason, extra treatment steps are often required to remove inorganic materials from industrial wastewater sources. For example, heavy metals which are discharged with many types of industrial wastewater, are difficult to remove by conventional treatment methods.</p>
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<h2 class="wp-block-heading"><strong>Nutrients</strong></h2>
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<p>Wastewater often contains large amounts of nutrients, nitrogen, and phosphorus in the form of nitrate and phosphate, which promote plant growth. Organisms only require small amounts of nutrients in biological treatment, so there normally is an excess available in treated wastewater. In severe cases, excessive nutrients in receiving waters cause algae and other plants to grow quickly depleting oxygen in the water. If deprived of oxygen, fish and other aquatic life may die, emitting foul odors.</p>
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<h2 class="wp-block-heading"><strong>Solids</strong></h2>
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<p>Solid materials in wastewater can consist of organic and/or inorganic materials and organisms. The solids must be significantly reduced by treatment or they can increase BOD when discharged to receiving waters and provide places for microorganisms to escape disinfection. They also can clog soil absorption fields in onsite systems.</p>
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<p><strong>Settleable solids</strong> - Certain substances, such as sand, grit, and heavier organic and inorganic materials settle out from the rest of the wastewater stream during the preliminary stages of treatment. On the bottom of settling tanks and ponds, organic material makes up a biologically active layer of sludge that aids in treatment.</p>
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<p><strong>Suspended solids </strong>- Materials that resist settling may remain suspended in wastewater. Suspended solids in wastewater must be treated, or they will clog soil absorption systems or reduce the effectiveness of disinfection systems.</p>
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<p><strong>Dissolved solids</strong> - Small particles of certain wastewater materials can dissolve like salt in water. Some dissolved materials are consumed by microorganisms in wastewater. But others, such as heavy metals, are difficult to remove by conventional treatment. Excessive amounts of dissolved solids in wastewater can have adverse effects on the environment.</p>
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<h2 class="wp-block-heading"><strong>Gases</strong></h2>
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<p>Certain gases in wastewater can cause odors, affect treatment, or are potentially dangerous. Methane gas, for example, is a byproduct of anaerobic biological treatment and is highly combustible. Special precautions need to be taken near septic tanks, manholes, treatment plants, and other areas where wastewater gases can be collected.</p>
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<p>The gases hydrogen sulfide and ammonia can be toxic and pose breathing problems. Ammonia as a dissolved gas in wastewater also is dangerous to fish. Both gases emit odors, which can be a serious nuisance. Unless effectively contained or minimized by design and location, wastewater odors can affect the mental well-being and quality of life of residents. &nbsp;</p>
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