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Sewage and Industrial Wastewater Treatment – Understanding the STP/ETP…

December 29, 2022December 29, 2022
by Nikita Chauhan

What is Wastewater?

Wastewater is a mixture of water and a variety of pollutants, including suspended solids, dissolved organic compounds, nutrients, and microorganisms. Domestic wastewater is typically composed of human waste, food waste, and paper products. Industrial wastewater may include toxic chemicals, heavy metals, oil and grease, and other pollutants.

Suspended solids are the largest component of wastewater and can include anything from toilet paper to food scraps. Dissolved organic compounds, such as detergents, food waste, and solvents, can also be found in wastewater. Heavy metals, salts, and nutrients are also present. Nutrients, such as nitrogen and phosphorus, are the primary sources of energy for microorganisms in wastewater. These microorganisms are responsible for breaking down organic matter, which in turn produces carbon dioxide and other gases. This decomposition is essential for the removal of some pollutants, such as ammonia and phosphorus from wastewater.

Health, Environment, and Social concerns associated with wastewater:

Health: Wastewater contains bacteria, viruses, and parasites that can cause diseases such as cholera, dysentery, hepatitis A, and typhoid. These diseases can spread through contaminated water. Wastewater also contains toxic chemicals, such as lead, arsenic, and mercury, which can cause serious health problems if ingested. Poorly treated wastewater leads to water pollution on its release, creating an even greater risk to public health.
Environment: Wastewater can have a damaging effect on the environment if it is not properly treated or disposed of. Untreated wastewater can pollute drinking water sources and contaminate soil, which can lead to water-borne diseases and the destruction of natural habitats. Wastewater can also cause algal blooms and oxygen depletion in water bodies, which can kill off fish and other aquatic life.
Social: Wastewater can have a significant impact on communities. Poorly treated or disposed wastewater can cause an increase in health risks to local residents. If wastewater is not managed properly, it can create an unpleasant living environment due to odor and the presence of vermin. Furthermore, wastewater has an adverse impact on the local economy, as it can contaminate agricultural land and decrease crop yields.

Precautionary measurements are taken to avoid wastewater-related issues

Precautionary measures are taken because untreated wastewater can cause a variety of negative environmental and health impacts.

To prevent these issues, precautionary measures are taken to ensure that wastewater is collected and disposed of properly. The collection of wastewater is usually done through sewer systems, septic tanks, or catchment basins. These systems allow for the safe collection and transport of wastewater to a treatment facility to remove pollutants and contaminants. Then water is released back into the environment.

Disposal of wastewater is also important in avoiding wastewater-related issues. Depending on the type of wastewater and the level of treatment it has undergone, it can be disposed of in various ways. Treated wastewater may be discharged into a local waterway, sprayed onto land, or recycled for use in industrial processes.

Wastewater collection

Wastewater collection systems typically include a network of pipes, manholes, and other structures such as pumping stations, treatment plants, and storage tanks. The collection systems are responsible for transporting wastewater from residences and businesses to a central drainage system.

Wastewater specific treatment

STP

A sewage treatment plant is a facility where wastewater is processed to remove pollutants and produce a treated effluent that is safe to return to the environment. Treatment processes may include physical, chemical, and biological processes to remove suspended solids, nutrients, and other pollutants. The treated effluent is typically discharged to a receiving water body such as a river, lake, or ocean.

Primary, Secondary, and Tertiary treatment process in STP:

Primary Treatment

It involves the physical removal of solids from wastewater. This is typically accomplished by screening, grit removal, and primary sedimentation. This is usually done by passing wastewater through large screens or grit channels to remove large debris, such as plastic, sticks, and rags. The wastewater is then pumped through a settling tank, which allows suspended solids to settle to the bottom and the clarified water to flow out of the tank. The settled sludge is usually sent to a secondary treatment process, such as anaerobic digestion or activated sludge. Primary treatment involves the addition of a coagulant and aims at removing grits, coarse solids, oil, and grease if any are present.

Secondary Treatment

This process uses bacteria and other microorganisms to break down organic matter from wastewater, such as food waste, soaps, and detergents, and convert it into a form to be released into the environment. The process usually involves aeration and clarification, using tanks, basins, and biological filters.

Membrane bioreactors (MBRs): Another wastewater treatment option is MBRs. These systems use membranes to separate suspended particles from the wastewater and then allow aerobic or anaerobic bacteria to break down the organic material. The end result is a stabilized effluent that meets environmental standards for safe discharge.

Sequential Batch Reactor (SBR): The SBR cycle is composed of several steps: fill, react, settle, decant, and idle. During the reaction stage, the wastewater is aerated and circulated to mix with the microbial population, allowing it to break off the organic matter. In the settling stage, the mixture is settled, allowing lighter biomass and organic matter to rise to the surface and be removed. In the idle phase, the tank is allowed to sit without any aeration or mixing, allowing the biomass to settle and the organisms to rest.

Moving Bed Biofilm Reactor (MBBR): MBBR is a type of wastewater treatment system that uses suspended carriers to provide a large surface area for the attached growth of biofilms. The carriers used in MBBRs provide a large surface area for biofilm growth, which helps to reduce the biomass size required for effective treatment.

Fluidized Bed Bioreactors (FBBR): FBBR is a type of secondary treatment for the removal of organic pollutants from wastewater. This allows microorganisms, such as bacteria and fungi, to colonize the particles and break down the organic pollutants. It is used in conjunction with primary treatment processes to achieve the highest level of pollutant removal possible.

Tertiary Treatment

The tertiary or chemical treatment process of sewage treatment plants typically involves the addition of chemicals such as calcium oxide, sodium hydroxide, and sodium carbonate to the wastewater. This process helps to break down organic matter and remove suspended solids and other contaminants. The process also helps to balance the pH of the water, reduce odors (Activated charcoal), and reduce the level of disease-causing organisms.

Activated charcoal is a carbon filtration that works to remove odor and color by adsorbing and trapping contaminants on the surface of its tiny pores. Activated carbon needs replacement as its capacity to work reduces gradually.

Chlorination: The process involves the addition of chlorine or chlorine-based compounds to the water to kill bacteria and other disease-causing microorganisms. The chlorine kills any disease-causing organisms, which helps to reduce the risk of water-borne diseases.

Ozonation is a form of the advanced oxidation process that produces extremely reactive oxygen species. Ozone is very reactive and readily oxidizes microorganisms, effectively killing them. Ozone oxidizes the cell wall, membrane, and internal components of microorganisms, damaging their structure and function. Ozone also disrupts the microorganism`s metabolic pathways, leading to cell death.

UV treatment – UV water disinfection technique disinfects by penetrating microorganisms and destroying their DNA. Chlorine and other disinfectants can produce toxic disinfection byproducts (THMs or Halo-acetic acids) as well as the dangers that come with their presence on site. Because UV light disinfection is a chemical-free method, it effectively eliminates any concerns about these byproducts.

The important water discharge parameters in STP are biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), and fecal coliform bacteria.

ETP

An effluent treatment plant (ETP) is a facility used to treat wastewater that is produced by industries and other sources. The treated wastewater (or effluent) is then released into the environment, usually a nearby river, lake, or ocean. ETP reduces the number of pollutants in the wastewater to the levels required by national and local environmental regulations.

In comparison with STP, ETP focuses more on reducing the number of chemical pollutants present in wastewater during its secondary treatment process.

Primary, Secondary, and Tertiary treatment process in ETP:

Primary Treatment

The primary treatment process in ETP typically involves the removal of suspended solids, oils, and other physical contaminants from wastewater. Wastewater is Treated by physical processes such as sedimentation, flocculation, clarification, and filtration.

Secondary Treatment

In secondary treatment, industrial effluent processes are modified as per the content and level of certain chemical pollutants. Following some of the industrial wastewater treatment processes will help to understand this concept better.

Oil and petroleum industry:

A vast amount of wastewater is generated from the extraction, refining, and transportation of petroleum products. This contains a variety of contaminants, including oil, grease, heavy metals, and other hazardous substances or pollutants. It helps to reduce the concentration of pollutants and contaminants in the effluent to a level that is safe for discharge into the environment. This is achieved through coagulation, flocculation, and biological treatment. The coagulation/flocculation process involves the addition of a coagulant, such as aluminum hydroxide chloride or aluminum sulfate, to the wastewater to remove suspended solids.

The biological treatment process utilizes microorganisms to break down organic material in the wastewater and reduce the concentration of pollutants. Finally, the N:P ratio is an important parameter for the treatment of oily wastewater by using oil-degrading bacteria. By using these techniques, secondary treatment can effectively reduce the contamination level of effluent and make it suitable for discharge into water bodies.

Example: Microorganisms to remove oil contaminants such as Bacteria, Pseudomonas aeruginosa: P. aeruginosa bacteria are able to break down oil and petroleum products due to their ability to produce enzymes that are specific to hydrocarbons. Pseudomonas bacteria are usually introduced into wastewater as slurry. This slurry is made up of a combination of Pseudomonas bacteria, nutrients, and a carbon source. The carbon source is important because it provides the bacteria with the energy they need to break down the oil and petroleum-based pollutants.

Other common microorganisms used in the oil and petroleum industry for wastewater treatment include bacteria such as Acinetobacter, and Bacillus, and fungi such as Aspergillus and Trichoderma.

Textile industry (Dyes and paints, colorants,):

The main purpose of secondary treatment is to provide BOD removal beyond what is achievable by simple sedimentation. It also removes appreciable amounts of oil and phenol. The dissolved and colloidal organic compounds and color present in wastewater are removed or reduced to stabilize the organic matter. Textile processing effluents are amenable to biological treatments.

Textile waste also contains significant quantities of non-biodegradable chemical polymers. For non-biodegradable pollutants, filtration technologies are utilized in the textile industry to clean wastewater. Traditional membrane processes in textile wastewater treatment include the use of ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) membranes. The selection of membrane technologies for textile effluent relies on costs based on the balance between water flux and solute retention. RO also becomes less effective when osmotic pressure, is caused by high salt concentration in the feed wastewater. Becomes too high to obtain a reasonable transmembrane permeate flux without applying excess transmembrane hydraulic pressure.

The membrane filtration system typically consists of a series of membranes with differing pore sizes and compositions that are used to remove particles from the wastewater. The membranes are typically made from polymeric materials such as polyvinylidene fluoride (PVDF), polysulfone, or polypropylene.

Metallurgic, chemical, and Fertilizer industry:

This is usually done through the application of an activated sludge process, trickling filter, rotating biological contactors, and oxidation ponds. The activated sludge process is used to remove organic pollutants from wastewater by using a variety of microorganisms. Trickling filters use a bed of media on which microorganisms grow to degrade the organic pollutants. Rotating biological contactors use a series of rotating plastic disks on which microorganisms grow and degrade organic pollutants. Finally, oxidation ponds are used to provide long-term biological treatment.

Tertiary Treatment

The tertiary treatment or biological treatment process in an ETP is designed to remove organic and inorganic pollutants from wastewater. This process is typically used in applications where the effluent needs to be treated to a high level of purity. The water is then treated with chlorine, ultraviolet light, or ozone to kill any remaining bacteria, viruses, and other pathogens before it is released into the environment. Primary and secondary treatment typically gets wastewater only clean enough to discharge safely into the environment. Tertiary treatment can achieve levels of water purification that make the water safe for reuse in water-intensive processes or even as drinking water.

Tertiary wastewater treatment often works by using a combination of physical and chemical processes to remove harmful microbiological contaminants. The process usually involves filtration followed by additional disinfecting treatment. In some cases, tertiary treatment may also use other specialized treatments like lagoon storage, biological nutrient removal, and nitrogen and phosphorus removal.

Final water disposal activities:

All water either from STP or ETP is finally safely disposed into the environment or reused depending upon the quality of wastewater as follows.

Filters: Tertiary filtration components can contain a few different materials. Sand and activated carbon filters are common, and filters can also contain fine woven cloth. The filters come in a few types, including bag filters, drum filters, and disc filters. Backwash cleans the media components to ensure their continual functioning.

Disinfecting: The process of tertiary disinfection may take a few different forms. Chlorine is one of the most commonly used disinfectants in wastewater treatment. Ultraviolet light is a common disinfectant in tertiary treatment. Ozone is highly reactive and can destroy most microorganisms it comes into contact with.

Discharge: Once the wastewater has undergone tertiary treatment, it is ready for discharge back into the environment. Many municipalities have specific requirements for the discharge of treated water. Tertiary treatment should be sufficient to meet those standards, keep the environment clean and preserve human health, experts say.

Reuse: Many treatment plants use tertiary treatment specifically to make the water safe for human ingestion. Water that has received tertiary treatment is also suitable for numerous operations that require clean water. These include industrial and manufacturing processes, oil and gas extraction and refining, utilities cooling, and agricultural practices like irrigation.

Wastewater Treatment

Wastewater Management and Its Important Components

December 23, 2022December 23, 2022
by Nikita Chauhan

The drainage systems and wastewater collection are important components of proper collection and disposal of the city’s infrastructure. They are responsible for maintaining a safe and healthy environment by preventing the spread of diseases and pollutants. The drainage systems and wastewater collection are most often divided into two main components. The collection system includes sewers and pipes, and the treatment system, which includes wastewater treatment plants. The drainage system collects rainwater runoff and sewage from homes, businesses, and other sources. Then transports the collected wastewater to a treatment plant, where it is treated, cleaned, and released back into the environment.

Drainage System:

The drainage system is a network of pipes, drains and other structures used to collect and remove surplus water and waste from buildings, roads, and other areas. It is an integral part of modern life, allowing for the removal of rainwater, sewage, and other waste materials.

The drainage system is typically composed of two components. A surface drainage system collects and disposes of rainwater and surface runoff. A subsurface drainage system collects and removes waste water from buildings.

Surface drainage systems are designed to collect and convey excess water away from roads, buildings, and other areas. They usually consist of a series of underground pipes and channels that collect runoff from rooftops, driveways, and other surfaces. The collected water is then directed to a storm sewer, which carries it away from the area. In some cases, the water is directed to a nearby water body or a natural wetland.

Subsurface drainage systems are designed to collect and remove wastewater from buildings. These systems are typically comprised of a series of pipes and drains that collect wastewater from plumbing fixtures, such as toilets and sinks. It is then directed to a septic tank or a public sewer system, where it is treated before being discharged into a nearby water body.

Wastewater Collection:

Wastewater collection systems typically include a network of pipes, manholes, and other structures such as pumping stations, treatment plants, and storage tanks. The pipes are usually constructed from PVC, concrete, or iron and they come in a variety of sizes and shapes to accommodate different types of wastewater. The manholes are used to allow access to the pipes for cleaning and maintenance, and they are usually equipped with safety equipment such as gas detectors and airflow monitors.

Wastewater collection systems are responsible for transporting wastewater from residences and businesses to a central drainage system. In most cases, wastewater is collected through a network of underground pipes that lead to a sewage treatment facility. The drainage system works in conjunction with the wastewater collection system by receiving wastewater from the collection system and then distributing it to the treatment facility. The drainage system removes excess water from the surrounding area and provides a safe and efficient disposal of wastewater.

Wastewater Collection Categories:

Wastewater collection systems can be divided into two categories: sanitary sewers and combined sewers. Sanitary sewers are wastewater systems that collect it from homes and businesses and transport it to a wastewater treatment plant, while combined sewers collect both stormwater and wastewater and transport them to a wastewater treatment plant. The drainage flow rate is the amount of water that is discharged from a drainage system over a given period of time. This rate is usually expressed in cubic feet per second (CFS). The drainage flow rate can be affected by factors such as the size of the drainage system, the slope of the terrain, the amount of rainfall or snowmelt, and any obstructions in the flow.

The volume of water collected in wastewater treatment plants (WTPs) is determined by the size of the plant and its capacity. Normally, the size and type of treatment process used will determine the volume of water that can be processed in a given period of time. The capacity of WTPs can range from 1.9 million liters per day to over 80 million liters per day. Water collected by WTPs depends on the amount of wastewater generated by the community and precipitation in the area.

Treatment and Discharge:

Pumping stations are used to move wastewater from low-lying areas to higher points where it can be more easily transported. Treatment plants used to clean and treat wastewater involves a combination of physical, chemical, and biological processes.

Physical processes involve the removal of large suspended solids, such as sand, gravel, and other debris. This is usually done through sedimentation, filtration, or centrifugation. Chemical processes involve the addition of chemicals, such as chlorine or alum, to break down organic matter and other pollutants. Biological processes involve the use of microorganisms, such as bacteria, to break down organic matter in wastewater.

The treated wastewater is then discharged into a receiving water body, such as a river, lake, or ocean.

Tabulation of general wastewater parameters

By tabulating general wastewater parameters, Population Control Board is able to understand the impact of wastewater on the environment. This information can then be used to develop measures to reduce the negative impacts of wastewater on the environment.

Wastewater management systems must be designed and operated to ensure that they adequately collect, and treat the wastewater and prevent environmental contamination.

Wastewater management systems should also be designed to prevent flooding and maintain an acceptable level of water quality. This may include the installation of pumps, detention basins, and other structures to reduce the effects of flooding. It may also include the use of stormwater management systems to prevent soil erosion and runoff of polluted wastewater.

In nature, wastewater treatment occurs in natural ponds, wetlands covered with mangroves, and heavy plantation and water lagoons.

Similarly, when these natural phenomena are applied for wastewater treatment by artificial means, both natural, as well as artificial resources are utilized. At the beginning of the process, wastewater is allowed to stabilize and remove suspended solids particles by aggregation, flocculation, and sedimentation in waste stabilization ponds. Then the water slowly flows to artificial wetlands where the plantation of diverse phytoremediation plants sequesters many pollutants and clears water to the maximum extent by phytoremediation process. Furthermore, in natural processes, the wastewater from wetlands enters the natural water bodies and water streams.

Constructed wetlands:

Constructed wetlands are artificial wetlands that are specifically designed to treat wastewater. They consist of a shallow body of water with a bed of gravel or sand and vegetation planted in them. As wastewater is pumped into the wetland, it flows slowly through the gravel or sand and is filtered by the plants, soil, and microorganisms. The microorganisms break down organic matter and suspended solids, while the plants and soil filter out pollutants and heavy metals.

Water Lagoons:

Lagoons are made up of a series of interconnected ponds, which are designed to capture, store, and treat wastewater. Each lagoon is filled with wastewater that is circulated and aerated, allowing beneficial bacteria and enzymes to break down harmful contaminants. This process helps to reduce the amount of organic matter, toxins, and other pollutants in the water, making it safe for reuse or discharge. As the water moves through the lagoons, suspended solids settle to the bottom, providing a nutrient-rich environment for beneficial bacteria and other organisms to thrive. The bacteria and other organisms help to further break down the contaminants and create a clean, safe effluent.

Importance of Wastewater management

Conservation of Resources: It helps to conserve valuable resources, such as energy and water, by recycling.
Preservation of Human Health: Wastewater management reduces the risk of water-borne diseases and helps in preserving public health.
Reduced Pollution: It helps to reduce the pollutant level in water sources and helps to protect aquatic ecosystems and wildlife.
Improved Water Quality: Water quality in rivers and lakes can be improved and making them safer for human use.
Reduced Contamination: It helps to reduce contamination of drinking water sources and ensure that they are safe for human consumption.
Economic Benefits: Proper wastewater management can help to reduce the costs of water treatment and disposal, providing economic benefits.

Conclusion:

Wastewater management is a complex process to manage. The infrastructure of a drainage system in wastewater management is a basic requirement. Improper drainage and wastewater management lead to wastewater-related issues in society that affects the quality of life. Poorly designed drainage systems can lead to poor sanitation, water pollution, and various serious water-related health hazards. Impotent drainage system flooding during rainy seasons may occur due to water logging which causes life and economic losses. Proper management is essential to avoid above mentioned damages. By investing in an efficient infrastructure and technology, wastewater can be well managed and we can enjoy a hygienic life.

Algal Products

Microalgae for Wastewater Treatment

November 4, 2022December 9, 2022
by Nikita Chauhan

What is Wastewater?

Any water that has been contaminated by human interventions is considered wastewater. Wastewater basically originates from domestic, industrial, commercial, or agricultural applications. It also includes surface runoff or stormwater and any sewer input or sewer infiltration is also referred to as wastewater.

Types of Wastewaters

Sewage: sewage is wastewater that develops and comes from domestically produced wastes like toilets, food, laundry, and other wastes. The contaminants that originated in sewage water are from domestic sewage and suspended and dissolved pollutants.

Non-sewage: Non-sewage refers to all other varieties of wastewater other than sewage. It contains wastewater originating from industrial washing applications, rainwater, stormwater, and industrial effluent. It doesn’t have any additional dangerous pathogens like sewage.

Water Pollutants and their Origin

Pollutants are materials, present in concentrations that could harm creatures (including people, plants, and animals) or exceed environmental quality standards.

Types of Pollutants:

Organic and biological Pollutants: Organic pollution is a type of chemical pollution caused by persistent organic pollutants as they are difficult to remove or degrade once released into the environment, such as Dichlorodiphenyltrichloroethane (DDT). Other than organic pollutants biological pollutants originate from biological material that includes liquid manure, sewage treatment sludge, etc.
Inorganic Pollutants: Inorganic pollutants are the compounds of inorganic by-products arising from various industrial applications that include, chemical, pharmaceutical, textiles and dyeing industries, paints, etc. Examples of inorganic metal pollutants are arsenic, cadmium, lead, mercury, chromium, aluminum, etc.

The major water pollutants are biological matter like feces, and human and animal body fluids containing bacteria, viruses, and parasites. And industrial pollutants include insecticides, pharmaceuticals, plastics, toxic chemicals, fertilizers, and pesticides.

Depending upon the application of industrial products their origin of water contamination can be categorized into centralized and distributed sources. Whereas a point-source contaminant, like a sewage discharge or outfall pipe, enters the water from a single conduit or channel.

So, whatever the source, all type of wastewater requires treatment before releasing it into the natural water body. Most commercial and industrial manufacturing plants strictly need to process their wastewater and recycle it, despite it many continuing to produce untreated wastewater. This leads to an issue of a rise in synthetic compounds in wastewater that is harmful to nature. To remove pollutants from wastewater, effective wastewater treatment solutions are mandatory.

What is Wastewater treatment?

The process of transforming wastewater or used water into water that may be safely released back into the environment is known as wastewater treatment. The methods and procedures utilized to clean up contaminated water are referred to as industrial wastewater treatment.

Conventional Ways of Wastewater Treatment

Primary (or Physical) Treatment: To remove any suspended sand particles from wastewater, a physical procedure (Sedimentation, Aeration, and Filtration) is used. Wastewater’s velocity is decreased to allow all of the suspended particles to fall to the ground as a result of gravity. The settling substance is referred to as sludge or bio soil.
Secondary (or Biological) Treatment: It is a biological process (Aerobic, Anaerobic, and Composing) that uses bacteria, algae, and microorganisms to take up the organic material in the wastewater. All of the organic contaminants are consumed by microbes, who then transform them into carbon dioxide, water, or energy for their further development or as byproducts.
Tertiary (or Chemical) Treatment: The pollutants or biological agents mostly pathogens that remain after secondary treatment are treated in tertiary treatment. Use of oxidizing agents like Chlorine liquid, Ozon gas, and UV rays, that kill most of the pathogen and make water free of pathogenic contamination. Through the employment of stronger and more sophisticated treatment systems, wastewater effluent is made even cleaner during this treatment process.

Conventional wastewater treatments eliminated major pollutants but they are unable to remove dissolved nutrients and toxic metals. This wastewater also contains nitrogen, phosphorus, ammonia, and bacteria. This often acts as a source of NPK contamination in a local water body. These pollutants lead to the eutrophication of waterbody once released into the environment which deteriorates the local water ecosystem.

Additionally, the traditional wastewater treatment method now has many drawbacks. Including increased chemical needs, high maintenance costs, sludge disposal issues, higher space and energy needs, and degradability issues. Therefore finding additional or even alternative options with conventional methods is very essential.

Why Microalgae for Wastewater Treatment?

Credit: Euronews Next

In order to handle wastewater treatment ponds naturally and economically, natural methods like employing microalgae cultures are now being studied. In terms of its capacity to remove NPK nutrients, coliform bacteria, and heavy metals, the microalgal approach competes favorably with conventional treatments. Microalgae are so effective at absorbing pollutants that other bacterial species can’t do. Microalgal species like Chlorella, Scenedesmus, Nannochloropsis, Phormedium, Botryococcus, Synechocystis, Spirogyra, etc., are well known for their effective wastewater treatment abilities.

Microalgae, serve as an indicator of water quality, with some strains proliferating in polluted water while others thrive in unpolluted water. Also, Algae can be used in wastewater treatment for a range of purposes. Some of these are used for the removal of coliform bacteria, reduction of both chemical and biochemical oxygen demand, and also removal of heavy metals.

Bio-treatment with microalgae is particularly attractive because of their photosynthetic capabilities, converting solar energy into useful biomasses and incorporating polluting NPK nutrients. Wastewater treatment by microalgae generates biomass. It could be utilized for developing various other products, such as fertilizers and biofuels.