Introduction
As many countries around the world face high population and development growth, the water systems in place continue to face pressure as the demand for water continues to increase by the day. This high demand and use of water has led to an increase in effluent water discharges and raw sewage into the environment leading to environmental degradation and pollution.
Wastewater management activities have been developed to deal with the amount of effluent water in the environment and how this water can be recycled for reuse in domestic, industrial and agricultural functions (Shuping et al 2006).
For water to be termed as wastewater, it has to undergo degradation in the form of contamination by organic waste materials, nitrate and phosphate pollution as well as bacterial contamination. Wastewater can however be treated for re-use by incorporating wastewater management activities that will reduce the amount of contamination to a level that is not harmful.
Waste water management involves carrying out refinery activities on waste water so that it can be reused again for domestic, agricultural, and industrial purposes. Waste water management is carried out to reduce the amount of water that is disposed off in the environment as well as reduce the level of contamination in natural water sources.
Many countries practice wastewater management so that they can limit the overdependence of natural water sources such as rivers, lakes and streams. Waste water reduces the amount of energy, time and costs that go in to treating water for reuse in water treatment plants. The most crucial aspect of waste water management processes is the collection and treatment of the effluent water.
Wastewater Management
The main aim of conducting treatment procedures on waste water is to remove any suspended solid materials that are in the effluent water before it can be discharged into the environment (Perlman 2010). When it comes to wastewater management activities, many industrial facilities rely heavily on the use of physical, chemical, physio-chemical and biological processes to treat wastewater and make it safe for disposal.
Water processing plants that use chemical processes to manage the waste water have now turned to the use of zero-effluent techniques of waste management that ensure that the waste water can be re-used and the volume of waste water that is meant for disposal to the environment is minimized (Labrecque and Bedard 2004).
The satisfactory disposal of waste water will depend on the type of treatment that is used in treating the water before it is disposed off. Treating waste water before disposal is viewed to be an important activity as it prevents the contamination of the environment as well as preventing the contamination of other water resources such as rivers, lakes and streams.
Waste water management involves the use of technology to improve the quality of the waste water before it can be disposed or re-used.
The main aspects that underlie wastewater management involve the collection of the waste water to a central location such as a treatment tank where the water will be subjected to various treatment procedures. Because of the large volumes of wastewater, the treatment processes that are usually performed on the water have to be continuous to deal with the huge water volumes.
Types of Wastewater Treatment Systems
The features for most waste water treatment systems are usually determined by the nature of wastewater that is being treated and the amount of treatment that will be required to reduce the level contamination in the water. Wastewater can be treated by incorporating systems such as physical, biological, primary, secondary, chemical and tertiary treatment systems.
The minimum level of treatment required for waste water is the secondary treatment level but in cases where the level of contamination and pollution is high, the tertiary or advanced level of treatment is used (Viessman 2010) The various methods and techniques that can be used to treat wastewater are outlined below.
Conventional Treatment System
This wastewater approach incorporates the use of preliminary processes to remove heavy solid materials from the effluent water. The conventional treatment process eliminates the oxygen levels in the wastewater by metabolizing and flocculating the organic and non organic materials in the water.
The preliminary processes will incorporate screening techniques which will screen out coarse and medium sedimentary materials in the wastewater.
The process will also measure the water flows and remove grit, solid waste from the water by shredding these solids to eliminate them from the wastewater. The sludge that results from the purification of the waste water is usually thickened and processed for disposal or use in land filling or for agricultural purposes (Viessman 2010).
Primary and Secondary Treatment of Water
The most common method that is used in the primary wastewater treatment system is that of sedimentation. This method removes 30 to 50 percent of solid materials in the wastewater by suspending them for elimination. To suspend these solids, the waste water is aerated and oxygen levels increased in the settling tanks to allow for floatation.
The process of sedimentation in primary treatment systems must be done before any biological filtration process is performed. The organic material that remains from the primary treatment of waste water is usually extracted for use in the secondary treatment process for biological materials (Viessman 2010).
The use of the primary treatment system ensures that 60% of the suspended materials in the wastewater are removed (Perlman 2010). The main purpose of using primary treatment systems is to reduce the velocity of the wastewater so that suspended solids and floatable materials can settle in the surface of the water.
The primary treatment devices that are used in treating the water include septic tanks, sedimentation tanks, flocculators, chemical feed units and upward flow clarifiers.
The primary methods of treatment that are used in the secondary system are the use of activated sludge processes, biological contactors that are rotating and trickling filters.
The activated sludge process involves feeding the wastewater into a tank that is aerated to allow for the breakdown of microorganisms in the effluent water which results in the formation of a microbial floc that settles below the tank. The sludge is then returned to the aerated tank for secondary settling.
The aerated tanks have trickling filters and rotating biological contactors that are used to support the microbial flocs which have slime growths. The trickling filters and biological contactors are used in the treatment process to extract the organic materials or suspended solid materials from wastewater as it flows through the various stages of treatment.
The sludge deposits or microbial flocs that settle below the tank are collected in a tank known as the secondary clarifier as the water flows out. The secondary treatment of wastewater removes 90 percent of suspended solids in the water (Viessman 2010).
Tertiary Water Treatment
Tertiary treatment systems are viewed to be the additional processes that are performed on the wastewater after it has gone through both the primary and secondary treatment systems. This method is employed when the two stages have failed to reduce the level of contamination in the water.
For example, to reduce the amount of phosphorous in the water, the waste waters that are discharged to the receiving waters will have to undergo a eutrophic treatment procedure (Veissman 2010).
Physical Treatment Processes
For the treatment of waste water to be complete and effective physical treatment processes have to be performed on the water to ensure it is safe for disposal or re use. The physical process of waste water treatment will involve performing sedimentation, filtering, and aeration procedures on the water.
In the sedimentation process, physical aspects that are related to the settling of suspended solids such as gravity are performed on the waste water. The sedimentation process involves holding the waste water for a short period of time in a storage tank that has been put under quiescent conditions. These conditions will allow for the heavy solids to settle and also eliminate the clarified effluent (Naik 2010)
Sedimentation is one of the common physical procedures that are conducted at the beginning and end of the treatment process. The aeration process involves adding oxygen to the wastewater so that the chemical compounds and bacteria in the water are reduced.
Another physical process that can be used to treat waste water is by filtering where the water is passed through a filter that separates the suspended solids from the waste water (Naik 2010)
Chemical Treatment Process
The chemical treatment system involves the use of chemical processes such as chlorination, neutralization, coagulation and ozonation to reduce the amount of chemicals and bacteria in the water. Chlorination involves mixing the waste water with chlorine so as to kill bacteria and reduce the rate of decomposition in the water.
Ozonation involves the use of a chemical known as ozone to disinfect the water form any bacteria that might be present as well as reduce the levels of contamination in the water. Neutralization is another chemical process technique that is used to treat waste water. This process involves adding acid such as lime to the water so that the pH levels can be adjusted to a neutral level (Naik 2010).
Apart from neutralization, waste water can also be treated by performing the coagulation process which will entail adding chemicals such as polyvalent metals, ferric sulfate, ferric chloride, lime or aluminum sulfate to the waste water through a chemical reaction that will result in the formation of insoluble end products.
These insoluble end products will be used to remove toxic substances such as hazardous chemicals or bacteria from the wastewater (Gautam et al 2007).
Biological Treatment Processes
This treatment process involves the use of biological micro organisms such as bacteria in the decomposition of the waste water to create stable end products. Micro organisms or sludges are formed in the waste water after which the waste is converted into carbon dioxide, or clean water. The biological treatment methods that can be used to treat wastewater are aerobic and anaerobic treatment methods.
The aerobic process involves the use of bacteria to consume the organic matter in the wastewater and convert it to carbon dioxide. Composting is also used in the aerobic process to treat the wastewater. The process of composting involves mixing the sludge with carbonated sources of material such as sawdust that will be used to treat the water (Naik 2010).
The anaerobic treatment process involves fermenting the sludge at a particular temperature that excludes the presence of oxygen. The use of biological treatment in wastewater management activities is meant to remove any solids that might be organic or inorganic in nature.
Biological processes are also performed on the water to reduce bad odor as well as destroy pathogenic organisms that might be harmful to the environment and that might impede biological activities (Gautam et al 2007).
Preliminary Wastewater Treatment Systems
This method of water treatment is used in most factory plants to protect the pumping of equipment and facilitate the treatment of wastewater by removing or reducing the size of suspended solids or organic materials that are in the wastewater. Such solids include items such as plastic bottles, paper bags or other solid materials that float in water.
The devices are also used to remove any heavy inorganic materials that are present in the waste water during the treatment process. The devices that are mostly used for this procedure include grit chambers, pre-aeration tanks, grinders, cutters and shredders as well as screen that will be used to separate the cut up materials from the waste water.
Chlorination can also be used in the preliminary treatment to kill bacteria or organic bacteria that is in the water (Waste materials 2010).
Sludge Treatment
The solid waste that is removed after the primary and secondary treatment of the water is performed constitutes what is referred to as sludge. It is important to treat sludge before it is disposed off into the environmental as this material contains some hazardous chemicals that might pose some risk to the environment.
The treatment of sludge basically involves the removal of part or all of the water in the sludge to reduce the water volume. The treatment of sludge is also done to increase the decomposition of organic solids that are putrescible in nature to mineral or stable organic solids. The methods that can be used to accomplish this process include elutriation, wet oxidation, centrifuging or incineration (UNEP 2010).
Screening Systems
This is viewed to be one of the oldest systems of water treatment. Wastewater screening removes gross pollutants from the water so that the downstream equipment is protected from extensive damage and also prevent floating solids from entering the settling and septic tanks. The devices that are used in the screening process include wire meshes, rods, parallel bars and grating bars.
The types of screen are divided into four categories which include the coarse screens, fine screens, very fine screens and microscreens. The coarse screens have openings that are more than 6 millimeters that are used to remove large solids such as bottles, rags, paper bags and debris. Such screens include catenary screens, reciprocating rake screens and cable driven coarse screens (ESCWA 2003).
The fine screens have size openings of 1.5 to 6 millimeters that are used for reducing the amount of suspended solids during the primary treatment levels. Fine screens include rotary drum screens, rotary vertical disk screens, endless band screens and vibrating screens.
The very fine screens have a size opening of 0.2 to 1.5 millimeters that are used to reduce the amount of suspended solids during the primary treatment level. The micro screens have small size openings that are 0.001 to 0.3 millimeters in size. These types of screens are used in the secondary and tertiary levels of wastewater treatment (ESCWA 2003).
Flotation Wastewater Treatment
This is an operation that is used to remove the solid or liquid particles in the wastewater by incorporating the use of fine gas and air bubbles. The gas bubbles are trapped in the particle structure of the suspended solids that will make the solid buoyant.
Particles that have a higher density than the liquid will rise with the buoyancy. Once the particles have floated to the surface they are eliminated out of the water by filtering or screening. The primary device that is used in the flotation process is oxygen or air. Other devices that can be used in the process include chemical additives that can be used in enhancing the skimming process.
The flotation methods that can be used on suspended solids include air flotation where gas in introduced into the liquid stage, dissolved air flotation where air is injected while the wastewater is subjected to high atmospheric pressure, vacuum flotation where the wastewater is saturated by using air in an aeration tank or in a waste water pump. A partial vacuum is then applied to dissolve the air.
The chemical additives method of flotation involves the use of chemicals in creating a surface that will easily adsorb the air bubbles in the settling tank. Chemicals such as ferric salts and aluminum are used in this technique of flotation (Metcalf and Eddy et al 2003).
Natural Treatment Systems
These wastewater treatment techniques are designed to incorporate the use of physical, biological and chemical processes that occur in natural ecosystems such as the interactions that take place in plants and vegetation, soil composition and nutrients, water and micro organisms. Natural treatment systems include the treatment of land, floating acquatic plants, and constructed wetlands.
These treatment processes are usually performed after mechanical pretreatment techniques have been done on the wastewater.
Land treatment involves the controlled application of the wastewater at a rate that can be compared to the natural chemical, biological and physical process that takes place naturally on the land. The types of land treatment systems that are used are slow rate systems, overflow and rapid infiltration systems (Metcalf and Eddy et al 2003).
The slow rate system involves applying the wastewater to vegetated lands through the incorporation of techniques such as sprinklers and irrigation methods. The wastewater is applied within a duration of 4 to 10 days so that the aerobic conditions in the water can be maintained.
The rapid infiltration technique involves using intensive methods to apply the water such as hydraulic and organic loadings at an intermittently and shallow infiltration rate. The overflow treatment process involves treating the wastewater as it flows down a network of vegetated terraces that are sloppy. The water is applied in an intermittent pattern to the upper parts of each terrace.
This allows the water to flow down to the other terraces through runoff collection channels. The devices that are used in the overflow technique include high pressure sprinklers, gated pipes, and low pressure sprays (ESCWA 2003).
Conclusion
The treatment of waste water has become a critical activity due to the diminishing water resources in the world that have arisen due to high population growth and developments in the urban worlds. The treatment of wastewater is therefore seen to be an important activity in minimizing the over reliance on natural water resources as well as reduce the amount of water that is disposed off into the environment.
Wastewater treatment activities are also viewed to be important in reducing the amount of hazardous chemicals and solid wastes that are found in the water as they eliminate these materials during the treatment process. The various techniques that have been outlined are all effective methods of carrying out wastewater management activities.
References
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