Microbes in Sewage Treatment

CHAMELI DEVI PUBLIC SCHOOL INDORE BIO PROJECT SESSION 2016 - 2017 TOPIC - MICROBES IN SEWAGE TREATMENT

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INDEX 1. Introduction 2. What is sewage 3. Origins of sewage 4. General information 5. Microbial processes 6. Microbes in sewage treatment 7. Sewage treatment 8. Process steps

- Pretreatment - primary treatment. - secondary treatment. - tertiary treatment. - Fourth treatment stage 9. odor control 10. Energy requirements

11. Sludge treatment and disposal

12. Treated sewage reuse

Introduction Sewage treatment is a process in which the pollutants are removed. The ultimate goal of sewage treatment is to produce an effluent that will not impact the environment . In the absence of sewage treatment, the results can be devastating as sewage can disrupt the environment. The general processes of sewage treatment are primary, secondary and tertiary treatment. Primary treatment involves physical separation of sewage into solids and liquid by using a settling basin. The liquid sewage is then transferred to secondary treatment which focuses on removing the dissolved biological compound by the use of micro-organisms. The micro-organisms usually use aerobic metabolism to degrade the biological matter in the liquid sludge. Then tertiary treatment is required to disinfect the sewage so that it can be released into the environment. The solid sewage separated from primary treatment is transferred to a tank for sludge digestion which involves anaerobic degradation using micro-organisms. What is sewage ? waste matter from domestic or industrial establishments that is carried away in sewers or drains for dumping or conversion into a form that is not toxic. or waste material (such as human urine and feces) that is carried away from homes and other buildings in a system of pipes Origins of sewage Sewage is generated by residential, institutional, commercial and industrial establishments. It includes household waste liquid from toilets, baths, showers, kitchens, and sinksdraining into sewers. In many areas, sewage also includes liquid waste from industry and commerce. The separation and draining of household waste into greywater and blackwater is becoming more common in the developed world, with treated greywater being permitted to be used for watering plants or recycled for flushing toilets. Sewage may include stormwater runoff or urban runoff. Sewerage systems capable of handling storm water are known as combined sewer systems. Industrial waste water include Toxic chemical, Organic wastes, Heavy metals.

General informations physical environment

The environment of the sewage treatment plant has to be controlled precisely because bacteria are sensitive to the oxygen level, pH level, temperature, and level of nutrient. In order for efficient degradation of biological matter to occur, these factors are controlled manually. Sewage composition Sewage is composed of organic matter such as carbohydrates, fats, oil, grease and proteins mainly from domestic waste. It also contains dissolved inorganic matter such as nitrogen species and phosphorous species mainly from agricultural use . It is essential to remove the nutrients before they are released to the environment because it interferes natural habitats by altering the chemical composition such as pH or oxygen level both directly and indirectly. Oxygen level Oxygen level is an important factor to secondary and tertiary treatment processes. Secondary treatment, oxygen is required as a terminal electron acceptor in organic matter degradation. For example, nitrification by Nitrosomonas and Nitrobacter species requires dissolved oxygen to occur . Oxygen in secondary treatment is provided manually by pumping oxygen into the sewage continuously which occurs in an aeration tank . In tertiary treatment, the removal of excess organic matter is enhanced by settling the sewage in a lagoon. This process is also aerobic, but it depends on the diffusion of oxygen because most organic matter has been degraded by secondary treatment. The oxygen in the air allows the microbes to respire aerobically.What are the products of the aerobic respiration of carbohydrates like glucose? pH Acidity plays a crucial role in the breakdown of organic matter because pH affects the solubility of compounds which indirectly affect the accessibility by bacteria. Also, bacteria responsible for organic matter degradation are sensitive to the pH of the environment. Extremely high or low pH levels are able to kill bacteria, deposition of organic matter occurs due to lack of degradation. Hence, the pH of sewage treatment is controlled to be around 7. A nitrifier in secondary treatment, Nitrosomnas requires a pH between 6~9 in order to be viable . Temperature The effect of temperature is influential for secondary treatment, but it is not important in primary treatment. Bacterial growth is sensitive to temperature because high temperature can increase the fluidity of the phospholipid bilayer which leads to cell lysis. However, bacteria are known to have higher enzymatic activity at higher temperature because of increased thermal energy. For example, when thermophilic sludge treatment is compared to mesophilic treatment, the sludge biodegradability is higher with thermophilic degradation . Hence the temperature has to be controlled precisely to maximize the efficiency of degradation but also allow the cell to remain viable Nutrients availability There are a lot of nutrients available in the sewage because of human waste and agricultural runoff. Bacteria can harvest the electron from organic matter and transfer it to a terminal electron acceptor which results in the break down of organic matter and energy conservation.

Microbial processes There are several microbial processes, and the microbial processes can be catergorized into aerobic and anaerobic. Aerobic After primary treatment, liquid and solid phases are physically separated. The liquid phase is treated with aeration to allow aerobic degradation of the nutrients. The two important microbial processes at this stage are nitrification and phosphorous removal. Nitrification occurs in two discrete steps. First of all, ammonium is oxidized to nitrite by Nitrosomonas.spp, and nitrite is further oxidized to nitrate by Nitrobacter.spp . Phosphorous removal can occur biologically by the process of “enhanced biological phosphorous removal.” The process is demonstrated by the cell taking up phosphorous within their cell, and the biomass is filtered . Anaerobic In the liquid component of sewage, denitrifying bacteria reduce nitrate into dinitrogen gas which liberates nitrate from the sewage . The solid component of the sewage separated in primary treatment is fermented by bacteria anaerobically. Key microorganisms Microorganiasms can also be categorized by its metabolism. Microorganisms with aerobic microbial process

Members of the Nitrosomonas genus is a gram negative bacterium responsible for the first stage of nitrification in sewage. They oxidize ammonium into nitrite. This bacterium prefers a pH around 6-9 and nitrify optimally at 20-30°C . Members of the Nitrobacter genus is a gram negative bacterium responsible for the second stage of nitrification in the sewage. It oxidizes nitrite to nitrate using oxygen as a terminal electron acceptor. The bacteria has an optimum pH of 6~8, and an optimum temperature of 0~40°C . Microorganism with anaerobic microbial process Members of Pseudomonas genus is a gram negative denitrifying bacteria that use the chemical energy in organic matter to reduce nitrate into dinitrogen gas . Also, members of the bacteroidetes phylum are the gram negative bacteria responsible for the anaerobic fermentation of the solid sludge .

Microbes in sewage treatment

All living things, including ourselves and microbes, need food to grow, maintain and repair their cells, and to provide a source of energy for life. However, we cannot digest all of the food we eat and what remains undigested, ends up in the sewage system. About 10 billion litres of sewage are produced every day in England and Wales and this has to be treated to remove harmful substances and pathogenic microbes before the waste can be safely released into the environment. The main component of sewage is organic matter (undigested food) but there are other substances such as oil, heavy metals, nitrogen and phosphorous compounds (from artificial fertilisers and detergents) which also have to be removed. Here you will consider the important role of microbes in the sewage treatment process. Sewage is actually a mixture of all types of waste water, including rain water and domestic water from toilets, baths and sinks. When sewage arrives at a treatment works.

it is first filtered to remove large objects (e.g. condoms, tampons and cigarette ends) which have got into the system. These usually go to a landfill site or incinerator. The remaining material is then allowed to ‘settle’so that much of the solid material drops to the bottom of a tank. This solid material is then removed and usually buried in landfill, burnt or, after further treatment, used as fertiliser on agricultural land.

Aerobic respiration is the most efficient way of breaking down organic matter although some compounds in the effluent are not broken down completely. The tanks often contain porous solid materials, on which biofilms can develop, increasing the numbers of microbes and so the efficiency of the breakdown process. During this process, a fairly solid material known as activated sludge is formed.

This contains a mix of microbes and undigested material. Since it contains all of the essential microbes to break down incoming waste, some of it is added to batches of new sewage (Figure 5). After this aerobic digestion, and a variety of other purification procedures, the liquid portion of the sewage is usually safe to discharge into rivers or the sea. The remaining activated sludge material is subjected to various other types of biological processes to reduce further the amount of organic matter it contains. Anaerobic bacteria are often used in this subsequent stage, since, although they grow more slowly, they can break down more complex materials that are difficult to degrade using microbes that respire aerobically. The gases produced in this anaerobic process are carbon dioxide and methane, a mixture called biogas, which can be collected and subsequently burned for energy production.

Sewage processing reduces the concentration of potentially harmful bacteria such as E. coli and Salmonella in the original sewage as many of them die during the processing because the conditions are not appropriate for them. It is also important to reduce the amount of organic compounds in the effluents released into rivers from sewage works. If this is not done, then microbes naturally present in the river use the organic compounds as a source of energy and reproduce in huge numbers. Since they respire aerobically, they use up much of the oxygen dissolved in the water, leaving little for other organisms such as invertebrates or fish, many of which will die. Sewage must therefore be treated to reduce the amount of organic matter, and thus reduce the Biological Oxygen Demand or BOD, defined as the amount of oxygen required by the aerobic microbes to decompose the organic compounds in a sample of water. The process of sewage treatment can be thought of as a complex form of composting.

The compost heap which you may have in your garden is like a miniature sewage treatment works. The centre usually becomes anaerobic as existing oxygen is used up. Closer to the top of the heap aerobic processes take place. Apart from the raw material, the other big difference between a sewage treatment works and a compost heap is that inside a compost heap, temperatures become high – well above 60 °C – which is detrimental to most species of microbes, but in which some can flourish. Sewage treatment

Sewage treatment is the process of removing contaminants from wastewater, primarily from household sewage. It includes physical, chemical, and biological processes to remove these contaminants and produce environmentally safe treated waste water (or treated effluent). A by-product of sewage treatment is usually a semi-solid waste or slurry, called sewage sludge, that has to undergo further treatment before being suitable for disposal or land application. Sewage treatment may also be referred to as wastewater treatment

For most cities, the sewer system will also carry a proportion ofindustrial effluent to the sewage treatment plant which has usually received pre-treatment at the factories themselves to reduce the pollutant load. If the sewer system is a combined sewer then it will also carry urban runoff (storm water) Process steps Sewage collection and treatment is typically subject to local, state and federal regulations and standards.

Treating waste water has the aim to produce an effluent that will do as little harm as possible when discharged to the surrounding environment, thereby preventing pollution compared to releasing untreated waste water into the environment.

In highly regulated developed countries, industrial effluent usually receives at least pretreatment if not full treatment at the factories themselves to reduce the pollutant load, before discharge to the sewer. This process is called industrial wastewater treatment. The same does not apply to many developing countries where industrial effluent is more likely to enter the sewer if it exists, or even the receiving water body, without pretreatment. Industrial waste water may contain pollutants which cannot be removed by conventional sewage treatment. Also, variable flow of industrial waste associated with production cycles may upset the population dynamics of biological treatment units, such as the activated sludge process. Sewage treatment generally involves three stages, called - primary treatment. - secondary treatment. - tertiary treatment.

Pretreatment Pretreatment removes all materials that can be easily collected from the raw sewage before they damage or clog the pumps and sewage lines of primary treatment clarifiers. Objects commonly removed during pretreatment include trash, tree limbs, leaves, branches, and other large objects. The influent in sewage water passes through a bar screen to remove all large objects like cans, rags, sticks, plastic packets etc. carried in the sewage stream. This is most commonly done with an automated mechanically raked bar screen in modern plants serving large populations, while in smaller or less modern plants, a manually cleaned screen may be used. The raking action of a mechanical bar screen is typically paced according to the accumulation on the bar screens and/or flow rate. The solids are collected and later disposed in a landfill, or incinerated. Bar screens or mesh screens of varying sizes may be used to optimize solids removal. If gross solids are not removed, they become entrained in pipes and moving parts of the treatment plant, and can cause substantial damage and inefficiency in the process.

Pretreatment may include Grit removal, Flow equalization, Fat and grease removal.

Primary

treatment It consists of temporarily holding the sewage in a quiescent basin where heavy solids can settle to the bottom while oil, grease and lighter solids float to the surface. The settled and floating materials are removed and the remaining liquid may be discharged or subjected to secondary treatment. Some sewage treatment plants that are connected to a combined sewer system have a bypass arrangement after the primary treatment unit. This means that during very heavy rainfall events, the secondary and tertiary treatment systems can be bypassed to protect them from hydraulic overloading, and the mixture of sewage and storm water only receives primary treatment. Secondary treatment It removes dissolved and suspended biological matter. Secondary treatment is typically performed by indigenous, water-borne micro-organisms in a managed habitat. Secondary treatment may require a separation process to remove the micro-organisms from the treated water prior to discharge or tertiary treatment.

It include Fixed-film or attached growth, Suspended-growth, Secondary sedimentation List of process types Activated sludge Aerated lagoon Aerobic granulation Constructed wetland

Membrane bioreactor Rotating biological contactor Sequencing batch reactor Trickling filter Tertiary treatment It is sometimes defined as anything more than primary and secondary treatment in order to allow rejection into a highly sensitive or fragile ecosystem (estuaries, low-flow rivers, coral reefs,...). Treated water is sometimes disinfected chemically or physically (for example, by lagoons and microfiltration) prior to discharge into astream, river, bay, lagoon or wetland, or it can be used for the irrigation of a golf course, green way or park. If it is sufficiently clean, it can also be used for groundwater recharge or agricultural purposes. It is also called "effluent polishing." The purpose of tertiary treatment is to provide a final treatment stage to further improve the effluent quality before it is discharged to the receiving environment

Filtration Lagoons or ponds Biological nutrient removal Nitrogen removal Phosphorus removal

Disinfection

Fourth treatment stage Micropollutants such as pharmaceuticals, ingredients of household chemicals, chemicals used in small businesses or industries, environmental persistent pharmaceutical pollutant (EPPP) or pesticides may not be eliminated in the conventional treatment process (primary, secondary and tertiary treatment) and therefore lead to water pollution. Odor control Odors emitted by sewage treatment are typically an indication of an anaerobic or "septic" condition. Early stages of processing will tend to produce foul-smelling gases, withhydrogen sulfide being most common in generating complaints. Large process plants in urban areas will often treat the odors with carbon reactors, a contact media with bio-slimes, small doses of chlorine, or circulating fluids to biologically capture and metabolize the noxious gases. Other methods of odor control exist, including addition of iron salts, hydrogen peroxide, calcium nitrate, etc. to manage hydrogen sulfide levels. Energy requirements For conventional sewage treatment plants, around 30 percent of the annual operating costs is usually required for energy. The energy requirements vary with type of treatment process as well as waste water load. Sludge treatment and disposal

The sludges accumulated in a wastewater treatment process must be treated and disposed of in a safe and effective manner. The purpose of digestion is to reduce the amount of organic matter and the number of disease-

causing microorganisms present in the solids. The most common treatment options include anaerobic digestion, aerobic digestion, and composting. Incineration is also used, albeit to a much lesser degree. Sludge treatment depends on the amount of solids generated and other site-specific conditions. Composting is most often applied to small-scale plants with aerobic digestion for mid-sized operations, and anaerobic digestion for the larger-scale operations.

Treated sewage reuse With suitable technology, it is possible to reuse sewage effluent for drinking water, although this is usually only done in places with limited water supplies,