Water scarcity is the major problem that is faced all across the world. Although 2/3rd of the earths crust is made up of water but all this water is not available for drinking and for other human activities as either it is locked in the form of ice or present in the form of vast saline oceans and seas. It has been found out that 97% of the total water is salty that is of no use to human and animals (except marine animal) and the remaining three percent is available as freshwater. More than half of this three percent is locked in glacier and less than 0.01% is available as fresh water. So water resources are less as compare to human demand for water.
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Above this, the major part of water that can be consumed is getting polluted because of human activities. This polluted and untreated water is causing abundant water borne diseases. Then the world is facing a huge climatic change which is further aggravating the water problem. Some of the regions are getting more rain water than earlier and some are getting almost negligible. Experts even believe that the next World War would not be for oil or land but it will be for water.
Also because of improper use of water and lack of water treatment, the problem of water crisis will further increase where 884 million people are already not getting easy access to safe drinking water. And a further 2.5 billion people are getting difficult access to water for disposable and sanitation. Agriculture is also overusing and polluting the ground water thus depleting the natural source of water. So here water treatment plants will play important role.
Water crisis at present is the biggest problem according to the United Nations. Almost 25 countries of Africa, parts of China, Peru and Brazil in Latin America, some parts of Middle East like Iran, Chile, Mexico, and Paraguay are some of the countries that are facing the water crisis. Even other parts of the world are facing the varied levels of the water crisis. Because of acute shortage of water, the food problems are getting aggravated. About 40 million people in Africa are facing the problem of food shortage. It is expected that if the similar conditions will persist then there will be 500 million till 2025 who will suffer from these problems. Nature has its role but the major water problem is arising because of its increasing consumption and faulty usage. Major chunk of the problem can be solved if the wastewater treatment is taken very seriously and precautions at every step are taken to improve the water quality.
The supply and demand
The demand for fresh clean water delivered to our homes is ever increasing as more and more residential homes are being established. Although 70% of the world is covered with water, only 1% is fresh water and thus raises a need to recycle waste water to satisfy our needs. Efforts to continuously recycle waste water are always stressed upon as a shortage would mean a disaster in heavily populated areas. Governments have committed billions towards research and development to such projects. Fresh water is also needed in agriculture. The demand for water in this sector is very high as farmer need fresh water for crops and cattle. Therefore, stresses the demand for sewage water treatment plants to be built. Water from rivers and lake are inadequate to provide water for farm and residences alike.
The supply of sewage water treatment facilities are slowly dwindling. A crisis may arise from a lack of sewage water treatment plants as this would greatly reduce the supply of fresh water. Governments are desperately trying to keep up with the pace of development of the population but are slowly lagging behind. The supply of fresh water will be adequate for the next few years but if the development of sewage water treatment plant continues at its current pace it without a doubt a shortage would take place. Furthermore, the agriculture industry will be greatly impacted and the supply of food will go down as well leading to famine due to a shortage of water.
The prospects of this industry
The wastewater treatment industry most probably will be successful in future due to presence of new wastewater treatment technologies. Advanced Immobilized Cell Reactor technology is one of the new technologies which immobilize the organisms such as bacteria in the pores of the carbon matrix. This process can avoid the immobilized organisms from shock load application as the diffusion of the pollutants from bulk fluid phase to organisms follows Fick’s law.
Through conventional biological wastewater treatment, infinite electrical energy and vast land area are being consumed. Besides that, a huge investment in electromechanical equipment is involved which will bring about a huge total cost of operation. Generally, the total cost of operation for new technology is lowered compared to the convention technology. By using the new technology, the total cost of operation can be cut down to approximately 50 percent of the total cost of conventional treatment.
Furthermore, the biological oxygen demand and chemical oxygen demand are reduced by 94 percent and 90 percent respectively. Oxygen consumption in the new technology is lower than in conventional technology. The oxygen gas is supplied in the form if compressed air from the bottom of the reactor. Both liquid and gas streams are in counter-current direction which facilitates the oxidation of dissolved organics and desorbs the converted products. This is to make sure the activated carbon keep up its activity throughout the process.
Moreover, with all those new wastewater technologies such as Advanced Oxidation Process, NERV (Natural Endogenous Respiration Vessel), Wet oxidation and many others processes, wastewater treatment can be done efficiently. For instant, through the new technologies less land is required to use to build plant; the power consumption is lowered. Besides that, the requirement for electrical and mechanical equipment is lower compared to conventional technology.
In a conclusion, wastewater treatment industries have a good prospect in the future with the help of new technologies. By using all those new technologies, waste water treatment can be done efficiently with lower overall lifecycle costs, lesser energy and equipment needed. We are sure that there is more new technologies will be invented in order to improve the wastewater treatment.
The impact on the environment
When the waste water is mixed with the waste materials such like garbage, household waste, toilets liquid and disposable things, the resulting product called sewage or waste water. This sewage water is normally will undergo a few process before it is release to the environment but there are still some impact on the environment. One of the impacts on the environment is agricultural impacts. The sewage water contains salts which is soluble that may accumulate in the root zone with possible harmful effect on soil health and crop yield. The physical and mechanical properties of the soil, such as dispersion of particle, stability of aggregates, soil structure and permeability are very sensitive to the types of exchangeable ions present in irrigation water. Thus, when effluent use is being planned, several factors related to the soil properties must be taken into consideration. On the other hand the effect of dissolved solids in the irrigation water on the growth of plants is also another aspect of agriculture which we have to concern. Dissolved salts increase the osmotic potential of soil water and increase the osmotic pressure of the soil solution which increases the growth and the yield of most plants decline progressively as osmotic pressure increases. In addition the one of the environment impact is ecological impact where the drainage water from waste water irrigation schemes drains particularly into small confined lakes and water bodies and surface water, and if phosphatesin the ortho phosphate form are present, the remains of nutrients may cause eutrophication. Here the overloading organic materials resulting in decrease in dissolved oxygen may lead to changes in the composition of a aquatic life such as fish deaths and reduced fishery. The eutrophication potential of waste water irrigation can be assessed using biological indices, which in turn can be qualified in monitory units using economic valuation techniques. The hidden impact on the environment is the increase on the production of green house emissions. The large agriculture reuse project might cause to the environmental externalities associated with pumping water uphill which emits greenhouse gas. Another impact is on the health. The sewage water contains pathogenic microorganisms like bacteria, viruses, protozoan’s and parasitic worms, the diseases and signs related with such infection are also diverse including typhoid,dysentry and cholera, diarrhea and vomiting. the concentration of he pathogens in waste water is dependent on the source population and the susceptibility to infection varies from one population to another. So basically he waste water is actually harm for the nature even though its treated and release to the environment so as a human being we should not dispose the waste into the water thus our water will be clean and the cost of the treatment can be reduced.
The Processes involved in this industry
Pre-Treatment(prepared by Brian Lee CL, 0902669)
Pre-treatment consists of three sub-stages which are Screening, Grit Removal and Fat and Grease Removal. Pre-treatment is done to remove materials which are easily collected such as debris, leaves and trash which would damage or clog up pumps and skimmers of the primary treatment.
Screening is used to remove large objects such as leaves, twigs and cans in the sewage stream. This is normally done with a giant mechanical rake bar which is automated. The rake bar revolves around a central axis at a rate varying on the accumulation and flow rate of the sewage stream. The screens vary in sizes to optimize solid removal. Objects accumulated are collected and disposed in landfills.
Grit is minute granules such as sand or stone. The wastewater is channeled to a chamber where to velocity of the water is adjusted so that the grit would settle at the bottom of the chamber. Grit may cause damage to the pumps or other equipment. Grit removal may not necessary in smaller plant.
Fat and grease are groups of compounds which are generally insoluble in water. The fat and grease are normally found floating on the surface of the water. In some plants, the fat and grease are removed by using skimmers to collect the fat and grease on the surface of the water in a small tank. However this can also be done in the Primary treatment stage in the same manner.
2) Primary treatment (prepared by Tan HY, 0903497)
Primary wastewater treatment is the second step in the wastewater treatment process ahead of the preliminary treatment of a headwork’s, involves the physical separation of suspended solids from the wastewater flow using primary clarifiers. The objective of primary treatment is the removal of settle able organic and inorganic solids by sedimentation, and the removal of materials that will float (scum) by skimming. Approximately 25 to 50% of the incoming biochemical oxygen demand (BOD5), 50 to 70% of the total suspended solids (SS), and 65% of the oil and grease are removed during primary treatment. Some organic nitrogen, organic phosphorus, and heavy metals associated with solids are also removed during primary sedimentation but colloidal and dissolved constituents are not affected. The effluent from primary sedimentation units is referred to as primary effluent.
On the other hand, primary treatment is the minimum level of reapplication treatment required for wastewater irrigation. It may be considered sufficient treatment if the wastewater is used to irrigate crops that are not consumed by humans or to irrigate orchards, vineyards, and some processed food crops. However, to prevent potential nuisance conditions in storage or flow-equalizing reservoirs, some form of secondary treatment is normally required in these countries, even in the case of non-food crop irrigation. It may be possible to use at least a portion of primary effluent for irrigation if off-line storage is provided.
Primary sedimentation tanks or clarifiers may be round or rectangular basins, typically 3 to 5 m deep, with hydraulic retention time between 2 and 3 hours. Settled solids (primary sludge) are normally removed from the bottom of tanks by sludge rakes that scrape the sludge to a central well from which it is pumped to sludge processing units. Scum is swept across the tank surface by water jets or mechanical means from which it is also pumped to sludge processing units.
2) Secondly treatment (prepared by Harintharan S, 1101379)
The secondary treatment in this sewage treatment is one of the most important part in this process. This process is basically designed to remove the waste product from the sewage. This system is also classified as fixed-film or suspended-growth systems. The secondary treatment contain a few processes, the 1st process is activated sludge. This activated sludge is majority from the plants which encompass the variety of mechanisms and processes that use dissolve oxygen to promote the growth of biological flock that substantially removes organic material. This process basically change the ammonia to nitrite and nitrate and ultimately to nitrogen gas. The 2nd process is this treatment is the Surface-aerated basins also known as Lagoons. This process basically removes the BOD from the sewage water. In an aerated basin system, the aerators provide two functions: they transfer air into the basins required by the biological oxidation reactions, and they provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater and microbes).However, they do not provide as good mixing as is normally achieved in activated sludge systems and therefore aerated basins do not achieve the same performance level as activated sludge units. The biological oxidation in the Surface-aerated basins is sensitive to the temperature and the rate of reaction increase with the temperature. The suitable temperature for this process is in between 0 °C and 40 °C. Besides that the constructed wetland is one of the process also. This process is a process which cleans the drainage of animals and used to recycle the waste water. The constructed wetland are known to be highly productive systems as they copy natural wetlands, called the “Kidneys of the earth” for their fundamental recycling capacity of the hydrological cycle in the biosphere and they provide a high degree of biological improvement but depending on design. The next process is the filter beds which is knows as oxidizing beds are used where the settled sewage liquor is spread onto the surface of a bed made up of coke, then liquor is typically distributed through perforated spray arms, then distributed liquor trickles through the bed and is collected in drains at the base, and the biological films of bacteria, protozoa and fungi to reduce the organic content. The next process is the Biological aerated filters are a combine filtration with biological carbon reduction, nitrification or denitrification. It’s a dual processer in purpose of to support highly active biomass that is attached to it and to filter suspended solids. Carbon reduction and ammonia conversion occurs in aerobic mode and sometime achieved in a single reactor while nitrate conversion occurs in anoxic mode. This process is operated either in up flow or down flow configuration depending on design specified by manufacturer. In addition the Rotating biological contactors are the next process in this secondary treatment. This is actually a secondary mechanical treatment system which is capable of withstanding surges in organic load.
The rotating disks support the growth of bacteria and micro-organisms present in the sewage, which break down and stabilise organic pollutants. Oxygen is obtained from the atmosphere as the disks rotate. As the micro-organisms grow, they build up on the media until they are sloughed off due to shear forces provided by the rotating discs in the sewage. Effluent from the system is then passed through final clarifiers where the micro-organisms in suspension settle as sludge. The sludge is withdrawn from the clarifier for further treatment. After that the membrane bioreactor combine activated sludge treatment with a membrane liquid-solid separation process. The component on this system uses low pressure for microfiltration or ultra-filtration membranes and eliminates the need for clarification and tertiary filtration. The elevated biomass concentration in the system process allows for very effective removal of both soluble and particulate biodegradable materials at higher loading rates. The final process in this secondary treatment is the secondary sedimentation where the process is to settle out the biological flock or filter material through a secondary clarifier and to produce sewage water containing low levels of organic material and suspended matter.
4) Tertiary treatment (prepared by Raiminder S, 0904743)
The main purpose of the tertiary treatment is to ensure that the treated water which is to be released on to the environment is biologically accepted by all other fresh water organisms such as weeds and algae. This part of the treatment includes processes like physical water treatment, lagooning, and excessive nutrient removal processes.to ensure that the discharged water is raised in effluent quality before proceeding to the final stages.
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In physical water treatment, much of the residual suspended matters are removed using only physical processes such as sedimentation method and the infamous filtration method. In the sedimentation method, the water is place in a certain tank to allow all the remaining heaver objects to sink down to the bottom of the container. After few hours went most of the dense object are separated from the water, the cleared effluent or waste stream is removed. Sedimentation is one of the most common methods, quite often used at the beginning and the end of many water treating processes. Another physical method that is commonly used in the sewage water treatment system is the filtration method. In filtration, the water is allowed to pass through filters to separate the contaminating solids from the water. Sand filter is a common filter used in this process. In a number of wastewater treatment methods, semi-solid contaminants like grease and oil are allowed to float on the surface of the water, and then they are physically removed.
Besides the in lagooning where lagoon is a stationary system having a continuous flow: several ponds working in parallel in which the inlet flow and the outlet flow are equals form lagoon plants. The lagooning technique is a natural and very efficient technique that consists in the accumulation of wastewater in ponds or basins, known as biological or stabilization ponds, where a series of biological, biochemical and physical processes take place. In these ponds or lagoons, certain types of the microorganism are actually supported as these “biological agents” help in treating the water further by removing the fine particulates. These types of biological ponds are usually classified as anaerobic ponds or oxidation ponds depending on the shape, depth, organic rate, level of treatment of that particular lagoon itself.
The excessive nutrient removal is the most viral step in the last stages of the water treatment before the water is released to the environment. When the previously treated water comes to this area of the system, the nutrients level mainly nitrogen and phosphorus in the water is checked. Where when found in excess, the excessive nutrient removal step is carried out. This is because if the unchecked water supply is to be released into the natural water system (river, pond, etc.) it will cause a sudden increase in the native microorganism population of that certain water system. Some of the native microorganisms which are commonly found in ponds today are usually weeds, algae, and cyanobacteria. Therefore, after the sudden rapid grown in the population of these microorganisms, the number of algae for example, becomes unsustainable which causes most of them to die and eventually decay. The following decay process would substantially increase the biochemical oxygen demand (BOD) in that particular pond, which would cause the other fresh water living organism such as fishes to die as well.
Firstly, the nitrogen removal process is carried out. There are various methods of removing nitrogen, each with advantages and disadvantages. However, the biological treatment method is used most commonly. With this method, organic nitrogen and ammonia nitrogen is converted into nitrous and nitrate nitrogen in an aerobic environment, and is dispersed into the atmosphere as anaerobic nitrogen gas. Therefore the gas is removed from the water and released to the atmosphere. And as there is no secondary pollution, this can be called an effective method.
In the removal of phosphorus is usually carried out using a method called enhanced biological phosphorus removal (EBPR). The first process in EBPR is the mainstream biological treatment process. Where the utilizing of aerobic and solids separation zones and the provision of return activated sludge are carried out. The next is a first side stream process for anoxic/anaerobic “selection” of desirable BPR organisms such as the polyphosphate accumulating organisms (PAOs). Finally, a second side stream process serves to ferment organic material in some of the return activated sludge to produce food utilized in the first side stream selection process. The system permits the three processes to be separated from each other by creating two side streams, allowing all three processes to be controlled separately and optimized in satisfying their own specific goals. Besides this biological method, the removal of phosphorus can also be done via chemical precipitation, usually with salts of iron, aluminum, or lime. Chemical precipitation is usually more reliable, easier to operate, and requires smaller equipment footprint than biological removal. But the main back draws of this chemical method is that it may form excessive sludge production as hydroxides precipitates and the chemical used in this method might be considered expensive.
5) Disinfection (prepared by Lim CS, 1001012)
The main purpose of disinfection in the wastewater treatment is to provide a degree of protection from contact with infectants and pathogen organisms which will cause waterborne diseases such as cholera, dysentery and hepatitis. Disinfection is also used to reduce the load of microorganisms in the wastewater to be discharged to the environment. Primary, secondary and even tertiary treatments do not fully remove the incoming waste load and microorganisms in the water stream and as a result, many microorganisms still remain in the wastewater. Therefore, various methods of disinfection are introduced such as chemical methods, physical methods and biological methods.
The effectiveness of disinfection depends on different factors including the quality of wastewater being treated, disinfectant dosage, type of disinfection being used and others. For instant, cloudy wastewater will not be treated efficiently due to less contact time between ultraviolet light and microorganisms. These microorganisms are shielding by those solid matters in wastewater stream and it reduces the contact time. Generally, long contact times, high concentration of disinfectant and optimum temperature and pH value will increase the effectiveness of disinfection.
Chlorination is one of the chemical methods which is commonly used for disinfection in the wastewater treatment. It is widely used through the world due to its low cost and long-term history of effectiveness. Chlorine can be applied in two general ways, liquid and gas. Chlorine in gaseous form is generally added to the wastewater stream rather than liquid form which is also known as hypochlorite because the former costs lesser than the latter. When chlorine dissolves in pure water, hypochlorous acid is formed followed by hypochlorites which are known as “free” residual chlorines
Chlorine is an extremely active oxidizing agent which will react with many other substances in the water stream. For instant, it reacts rapidly with such compounds as hydrogen sulfide, ferrous iron and manganese which found in industrial wastewater. However, if all of the chlorine is consumed in these reactions, no disinfection will result. Hence, to accomplish disinfection, sufficient chlorine is added into wastewater stream to satisfy the chlorine demand and produce residual chlorine which will destroy bacteria.
There are few factors which will affect the effectiveness of chlorination. Among the factors are pH, temperature, turbidity, control system and many others. However, chlorination brings some disadvantage to environment. Chlorination of residual organic material can generate chlorinated-organic compound which may be harmful to the environment. Those residual chlorines are toxic to aquatic species; therefore, dechlorination is needed, adding to complexity and cost of treatment.
However, chlorination becomes less favoured as disinfectant due to rising cost and it had found to be toxic to aquatic species. As a result, ozone and ultraviolet begin to be used as disinfectant. Ultraviolet (UV) light is more environmental friendly to be used as no chemicals are used and leave no toxic residual. Ultraviolet radiation and damages the genetic material of microorganisms, destroying their ability to reproduce. Before pass through the UV disinfection unit, the wastewater must pass through an advanced pretreatment component. Wastewater flows in the stream parallel to the UV light in a thin film in order to increase the contact time.
To increase the effectiveness of the UV light, the UV radiation must come in direct with pathogen organisms and other microbial in the wastewater stream. The effectiveness of a UV disinfection system is affected by few factors including characteristics of the wastewater, the contact time, intensity of UV radiation and many others. Turbidity, flow rate of water stream and suspended solids are also play an important roles in UV disinfection. These factors must be kept at low levels to ensure proper treatment.
Disinfection of wastewater, primarily by chlorination, has played an important role in the reduction of waterborne disease. However, there are more new disinfection processes are being developed in order to maximize the effectiveness of disinfection.
Role of engineer in this industry
The Chemical Engineering is the profession that combines chemistry and engineering concepts that help to solve problems related to world hunger, pollution of our environment, creating new materials, or meeting demands for energy. Chemical engineers develop low cost processes for useful chemical products, which make it possible for both poor nations and the United States to manufacture important fertilizers.
The roles of a chemical engineer in waste water treatment have to minimize the waste across the plant or reduction of waste loading to the treatment plant. Other than that, chemical engineer need to state whether it’s systems for the treatment and reuse of wastewater, process water treatment for industry, high-purity water for sensitive medical or scientific applications, or systems to supply clean drinking water to people and their families.
Besides that, as a chemical engineer also responsible for providing expertise in their respective discipline as it applies to the hazard analysis of the process being studied. Therefore, we also in charge for attending the initial hazard analysis kick-off meeting. On the other hand, we are also required to be available to the team as required with the understanding that the team leader will give adequate advance notice when their expertise is required. Lastly we are necessary to provide documents of any existing safeguards and procedures.
Skills/ knowledge required
Many types of skills and knowledge are required for chemical engineer in waste water treatment. They required intensive knowledge in wastewater treatment technologies, so that they will more easy to solve the problems when they face the difficulty. On the other hand, they also need expertise in equipment design, influent water treatment, effluent monitoring, and wastewater recycling.
In addition, proficiency in computer, programming, modeling and data analysis, for example AutoCAD, Microsoft Office, FOTRAN, Origin, Maple, Polymath, and other software are also the knowledge needed for chemical engineer. Moreover, strong technical writing, presentation, and project management skills are also useful skill for chemical engineer in order to present the researches after they have completed.
Besides the skills at above the hazard and operability study (HAZOP) technique also needed for a chemical engineer working in industry. The HAZOP technique is most popular in most industry because that is technique which is structured and systematic examination of a planned or existing process or operation in order to identify and evaluate problems that may represent risks to personnel or equipment, or prevent efficient operation. Otherwise, HAZOP as well a qualitative technique based on guide-words and is carried out by a multi-disciplinary team (HAZOP team) during a set of meetings.
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