Selection and Planning of a Wastewater System in Oil Refinery
There are many advantages that can be derived from treating wastewater. First, wastewater can be reused for landscape gardening or for other purposes at home, and on the business side, it can be utilized for industrial purposes. Treating wastewater is the same as saving the environment from the many pollutants and chemical substances produced by refineries and industries. Wastewater treatment corresponds to recycling and reusing it; water economizes and impacts to the environment caused by human consumption are minimized.
Wastewater treatment poses a big challenge to engineers of oil refineries and big industrial establishments. Process industries produce a huge amount of wastewater, containing pollutants and toxic chemicals which are harmful to the environment. Choosing and implementing the appropriate wastewater treatment is a responsibility that requires a lot of wastewater management studies. Stringent legislations have to be adapted so that organizations involved follow the right and proper systems required of the site where wastewater treatment is to be implemented.
The objective of this report is to conduct a study on the different methods of wastewater treatment in refineries and process industries and to select and determine the appropriate wastewater treatment system for the Abu Dhabi oil refinery. Various refineries have different methods of implementing wastewater treatment systems. Determining the efficiency of these wastewater systems will be discussed critically in light of the effective and successful means of eliminating toxic chemicals and other pollutants in the wastewater in oil refineries.
In the United States, the system that looks after the quality of water coming out from a refinery is the National Pollutant Discharge Elimination System (NPDES) which is a regulation under the Clean Water Act. The agency responsible is the United States Environmental Protection Agency (EPA). (Veenstra, Mohr, & Sanders, 1998, p. 4)
There are laws that have to be strictly followed for the right and proper implementation of wastewater treatment and effective selection and planning of wastewater systems in any oil refinery. Not following these laws and not implementing an exact and effective wastewater system will create an environmental problem. Situation aggravates when continuous development, which may not be sustainable, is implemented by industries in the name of progress. Wastewater increases, pollution doubles and triples, the environment and all living things suffer in the process.
The issue of addressing environmental problems is a worldwide concern. The threat posed by climate change and global warming is pushing mother Earth to its near end. Sustainable development is far from the objection of environmental groups. Oil refineries continue to produce wastewater and pollutants which cause a considerable impact on the environment. Waste and hazardous materials continue to exist for as long as there are businesses and human activities. Organizations are becoming more complex and globalization seems to speed up activities that do not have substantial benefits to the environment.
Stringent measures have to be instituted by developed countries to avoid improper disposal of wastewater to the adjoining bodies of water or the seas. Eliminating waste requires a tough task in the implementation of rules and regulations and policies of the government. However, some oil refineries have long been involved in environmental protection by building necessary precautions such as treatment plants, water treatment systems, , and other pollution controls.
Refining oil causes environmental problems (Veenstra et al., 1998, p. 3). The discovery of refining oil can be traced back to the early years when humans invented crude lighting tools to light up their homes. This was during the later years of the ninth century when the substance was used to light lamps. Oil refining started to be of great importance to human activities because this was the early years of finding the importance of light. Kerosene was the common refined oil used to light up lamps.
With the advancement in technology, electricity, and other inventions, disposing of oil has become a problem. Used oil in refineries and industries mix with water, and there comes the difficulty in disposing of it. If a refinery throws out wastewater with many of its pollutants and chemical substances, it creates an environmental disaster.
Refining oil to produce other products creates environmental problems (Veenstra et al., 1998, p. 3). Toxic chemicals with hydrocarbon components can be found in refinery effluent water. Wastewater has to be treated first before it can mix with other bodies of water. When wastewater is treated, and all pollutants and chemical substances had been removed from the water, it becomes reusable and can be used for other purposes.
There are many toxic substances present in wastewater; some of these include hydrocarbons which impart undesirable taste, and naphthenic acid, which is harmful to plant and animal life and also alters natural balance. Hydrocarbon causes cancer, while animals that drink contaminated oil become seriously ill. Oil and gasoline are two substances which when mixed with water are difficult to separate.
The oil comes in various forms when mixed with water:
Free oil this is the oil that rises up to the surface of the water in the form of globules;
Emulsified Oil the oil that forms in a part of the water, the oil globules are as small as 20 microns or less that cannot rise to the surface of the water.
Dissolved Oil this is the type that cannot be separated by gravity except through biological treatment or through absorbents. (Veenstra et al., 1998, p. 5)
The different forms determine what kind of separator to be used to clean the wastewater. There are various ways of treating or separating oil from wastewater. This is discussed in chapter 4 of this report.
The effluent system at the Abu Dhabi refinery, collects oily water from the refinery site, separates oil from the wastewater and discharges water into the sea. During the separation process, oil is recovered and returned to the oil refining process. Oily sludge is not re-usable and disposed of offsite. However, the existing Oily Water Sewer System, oil/water separation system, oil recovery systems and the effluent disposal system have limitations in delivering a water quality that presents environmental marine requirements for effluent disposal.
The world continues to need clean water because of the rapid increase in population added with fast development and construction growth that tends to damage the environment, the worlds biodiversity and ecological balance. Oil is a needed product and although there are reports that supply from oil-producing countries will be scarce in the near future, oil productions impact on the environment cannot be undermined. Oil refineries continue to generate wastewater that needs effective and manageable treatment. Wastewater management remains a big challenge to oil refineries and big industrial corporations.
The worlds water systems continue to face pressure as the demand for water continues to increase day by the day. This high demand and use of water have 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.
Most countries, especially those in the Middle East which have less rainfall, need to reuse water because of the big demand for freshwater coming from streams and natural resources. They have to optimize the reuse of water, otherwise, there will be a big scarcity of water. In many areas around the globe, water is a great necessity. In our existence, the need for water is equal to the need for food.
The primary objective of wastewater treatment is to remove suspended solid materials in the effluent water, such as oil so that it can be discharged into the environment.
The following are some of the wastewater treatments being implemented by oil refineries around the world. Discussion on this subject is of paramount importance since we can get knowledge and recommend some for implementations in other oil refineries.
Case Study done on wastewater management
Wastewater Treatment in Saudi Arabia
Oil refineries abound in Saudi Arabia, one of the worlds largest oil-producing and exporting countries. While oil is abundant in this region of the world, water is a limited resource. However, the country produces wastewater faster than it creates usable water. The country has to recycle wastewater and reuse it in homes and industries. Desalination technology is one of its main sources of potable water, but desalination is very costly, it costs 6 Saudi riyals for every cubic meter of water. Saudi Arabia has to rely on reusable water to ensure savings for the government. Recycled water is a big boost to Saudi waste management techniques. (Ministry of Economy, Trade and Industry, 2009)
Saudi Arabia maintains five oil refineries, with Riyadh Refinery Plant as one of the biggest. (Ministry of Economy, Trade and Industry, 2009) The plant is located inland and has wastewater treatment plants, which are not found in the same location but are several kilometers apart. Their treatment facilities treat secondary water for the cooling tower, boiler feed water, and so forth. The Riyadh Refinery takes its water from the secondary treated water.
The application of wastewater reuse at Saudi Aramco has reduced the cost of industrial water because of the application of excellent technology by experienced Saudi engineers and experts. Regulations and standards for the preservation and protection of the environment, especially on wastewater management and oil and water separation, are being enforced by the Presidency of Meteorology and Environment (PME) Regulations and Standards. (Ministry of Economy, Trade and Industry, 2009)
Wastewater Treatment in Kuwait
The Shuaiba Industrial Area (SIA) is the largest industrial complex located near Kuwait City. Occupants in this area are petrochemicals, oil refineries, and other large commercial and industrial corporation headquarters. The big challenge of treating the wastewater and transforming it into something clean and useful lies in the hands of the Shuaiba Area Authority, the government arm that manages the complex. The objective of the SAA is to make wastewater reusable for industrial and agricultural purposes. (Al-Muzaini, 1997, p. 57-8)
The Shuaiba Area Authority found that wastewater in the area could be reused.
The Suhaila area generates a great amount of water, an estimated 3,000 m3/d of sanitary wastewater, but could reach up to 50,610 m3/d, with the planned expansion and installation of additional buildings and facilities. (Al-Muzaini, 1997, p. 59)
The processors of the SIA include bar screens, parallel plate separators, filtration and chlorine disinfection.
It was first noted that sanitary wastewater was collected by a gravity sewer system but discharged without treatment into the open sea. This causes environmental problems. At present, the area uses septic tanks in discharging some 15% of sanitary wastewater. Sea cooling water is used for cooling the wastewater, then treated and discharged to the open sea. Treated wastewater in the Shuaiba Area is now being used for various purposes such as landscape irrigation, industrial and sanitary uses.
The Shuaiba Area Authority wastewater management has produced cost-effective methods so that establishments and refineries can conform to standing government regulations on wastewater reuse. SAA has developed regulations and codes to guide the treatment of wastewater and its eventual reuse. Following the rules of the SAA, the SIA has produced sanitary wastewater that can be used for landscape irrigation. This is very much needed by Kuwait since the area has less rainfall throughout the year.
Wastewater Treatment in Pakistan
Wastewater treatment has been applied by the Attock Refinery Limited in Pakistan. The company processes four crude mixes which range from light-sweet, light-sour, heavy and high total acid number crude oil. It uses crude distillation units in its processing of wastewater. Oily wastewater passes through the boilers then through oil-water separators, and onto the equalization tank. The oil is separated and sent to a primary treatment composed of the slant-rib coalescer (SRC), and the dissolved air flotation (DAF). (Ahmed, Alam, & Khurshid, et al., 2009)
Figure SEQ Figure * ARABIC 1 Block Diagram of ARL wastewater stream
Figure SEQ Figure * ARABIC 1 Block Diagram of ARL wastewater stream
The block diagram shows how the refinery processes wastewater with the wastewater streams at ARL. The Pakistan regulatory body on environmental quality standards enforces the Environmental Protection Act 1997 which limits pH and oil & grease (O&G). The technology implemented by ARL controls pH, including total suspended solids or TSSs, O&G and COD. The first step analyzes the parameters in the effluent streams in order to determine the outcome and impact these have created on the main effluent streams. The majority of the pH and TSS values come from the boiler blowdown water. This amount of water passes through the non-oily stream. Amounts of pH, COD and O&G mostly come from the wastewater stream, and the oily stream caused a great effect on the pre-treater. A great amount of oil can be found in the heavy crude unit.
Processing wastewater consisted of
Water coming from the three boilers and softener backwash contains a great amount of TSS and TSDs or total dissolved solids. The pH above 12 does not meet the standards. ARL uses water treatment chemicals such as phosphate which is used in controlling scaling, sulfite and ammonia to control the pH. But before treating, the wastewater is sent to the non-oily wastewater stream, first mixing this with treated oily wastewater, and then the water is flowed out of the refinery. This process violates Pakistans quality standards, so other measures had to be added to make it compatible with the law. (Ahmed et al., 2009, p. 2)
Spent caustic is an outcome of the naphtha treatment. The process results in what is termed sour naphtha and kerosene. When the chemical alkyl mercaptans were added to the naphtha and kerosene, it resulted in alkyl disulfides. When a catalyst was added into mercaptans and other nitrogen compounds, the chemicals are dissolved.
In the treatment process, 3% caustic strength was used for naphtha/kerosene, a process before washing, and 8%-10% for the settler. In other words, for the naphtha 8-10% settler, the quantity was 6.5 m3 at a 6-time monthly disposal. This is shown in their sources and quantity of caustic drainage.
A few historical notes for the plant state that the spent caustic through oily streams, then onto the initial stage of the pre-treatment process which was being carried by the oily water. The high pH produced strong emulsions causing a deceleration in the process.
The cooling towers in the block diagram created a stream going to the non-oily one. This concerns the concentration of pH, TSSs, TDSs, COD and O&G. The process used chemicals such as phosphate, biospheres and disperse, and some others that control pH.
Continuous analysis was conducted on the boiler with its blowdown water that produced neutralization. Sulfuric acid was used for purposes of reducing the costs and minimizing further chemical consumption. According to the companys research studies, a very small quantity of about 0.4 ml of a concentration of pure H2SO4, which is approximately 98%, per liter of boiler blowdown water (BBDW), is needed to bring down a pH < 9. This is a requirement by Pakistan regulations.
There is a second phase to this application, which analysed the spend caustic of the treating process. Analysis from the laboratory revealed that high COD values were produced by the oily portion from the spent caustic, and this was caused by the sweetening process. The logical move was to remove the oily layer, thereby reducing 80% 90% reduction of caustic COD. What remained of the spent caustic was mixed with the rest of the water going down.
Further laboratory results were conducted by ARL. A pit was constructed, with a capacity of 0.1 million gallons. The purpose of this was to provide room for the water collected coming from the boiler. Wastewater coming from the boiler had a controlled temperature of 80 to 90C. A cooling process of two hours occurred in the first two pits. Then the spent caustic was pumped to the next half of the pit reaching a rate of 1 tpd. Sulfuric acid was added to the wastewater to allow the pH to reach 8. The water would then pass to the third or fourth portions of the pit before it is exited.
The operation made the use of desalter oil and water separator quite was successful and very much improved.
Wastewater Treatment in Europe
The Duna Refinery wastewater management has been continuously upgraded to meet the demands of wastewater reuse. The refinery has to meet the specifications of the EU regulations; it has recently upgraded its wastewater treatment plant with the introduction of a state-of-the-art dissolved air flotation unit cyclic activated sludge (CASS) and biological grade which is automatic. (Isak et al., 2008, p. 125)
The Duna Refinery has to comply with European standards on wastewater management in order to reduce environmental pollution and abuse of Europes water reserves. The European Committee instituted the Best Available Techniques program (BAT) to minimize environmental effects from commercial establishments such as those processing oil and other pollutant-producing businesses. Using BAT means enterprises should have adequate knowledge of the environmental performance of the business and the corresponding best solutions.
Under the BAT regulations, a refinery should have a wastewater treatment system to manage and treat chemicals and pollutants in the wastewater and can discharge wastewater, or process crude oil to a maximum of 1, or between 0.5 to 1.0. It is estimated that the Duna Refinery is about 1.38 which is beyond the requirement of the BAT. The company is expected to be confronted with fines and penalties from the EU Committee. (Isak et al., 2008, p. 125)
Wastewater Treatment in Romania
The Petromidia Refinery Complex has a petroleum refinery and petrochemical plant. The objective is to process 4.8 million tons of crude oil annually. This refinery complex in Romania produces fuel for jets; wastewater is an outcome. Like any other refinery complex, the Petromidia Refinery needs proper wastewater management to reduce environmental impact, minimize costs in operations and go for the reuse of treated wastewater. The water source for the complex is from the , and the process water is pumped at a rate of 1,700 cubic meters per hour. (Rompetrol Refinery Complex, 2002, p. 1)
Improved water management was implemented by a team that generated benefits like the reduction of costs in environmental compliance, optimization of energy consumption and equipment, and reduction of wastewater from the plant to the open water.
It is necessary that water management be implemented in complexes such as this because of the many benefits that it can generate.
Improvement of wastewater management was implemented by a team who saw it fit to create a plan first before they had to implement something. They formulated steps with the objective of improving the companys wastewater management.
The first is on information gathering. Like any other activity, information was focused on their particular objective, water management. They gathered information on water use, how wastewater is produced, processed, and treated. Important data on flow rates were obtained from the various plant sites. They also took a water samples to determine the characteristics of the water from the plants. Next, they developed and analyzed some methods to improve water management. On this particular activity, they focused on improving equipment design, rehabilitation of existing structures, and other modifications.
They also conducted awareness and training on the personnel and workers present inside the plant. Finally, they developed an implementation plan for their recommendations. Various benefits can be derived for the improvement of wastewater management, but the best benefit points to environmental preservation.
Types of wastewater treatment
This process utilizes API (American Petroleum Institute) separators and CPI (corrugated plate interceptors) in separating oil from wastewater.
The American Petroleum Institute (API) has set some studies on the implementation, parameters and efficiencies of oil-water separators. They have designed their separators into long rectangular basins, with more time for the seclusion of the wastewater. This is the first objective of the separation process: to allow the water to float at the surface of the water. When the oil floats at the surface of the water, the process of separation can now be executed. There are several containers called bays in which the water can be maintained. The purpose of having several bays is to allow a laminar flow in the separator, thereby having an effective separation. The basins have scrapers allowing the oil to move downstream and onto a pipe or drum. These scrapers move at the bottom of the water, making the solids of the water collected to a trough. Sludge is dried and incinerated or disposed of properly. Oil-water separators are usually covered to avoid emissions in the air, as provided for by U.S. laws. (Wong & Hung, 2004, pp. 189-90)
API separators use water temperature and density of the oil globules in the process of separation. A kind of test known as susceptibility to separation (STS) is used to determine how much oil can be separated through gravity separation. An API separator can be effective to globule diameters the size of 0.015 cm, which is equivalent to 15 microns. (Wong & Hung, 2004, p. 190)
API separators also involve the application of constructed pits wherein wastewater streams are directed to a single sewer system and into the pits, and then the oil is separated from the water.
API Separators can actually remove 150 micron and other large droplets to lower the level of oil concentration, probably about 150 mg/L. API separators are usually not recommended because they do not meet the requirements of the Clean Water Act. An API Separator does not perform the specifications predicted by Stokess law. (Veenstra et al.,1998, p. 6)
The equation of Stokess law states
Variables stated in this equation are the viscosity and the size. The viscosity of the continuous liquid, along with the droplet and its size, should be known. When these are given, the solution now can proceed by finding the value of the size of the separator and the rise velocity. Stokess law has the objective of describing the motion of solid particles as they fall in a liquid. A droplet rise has a negative sign. (Veenstra et al.,1998, p. 6)
Parallel Corrugated Plate Separators
On the other hand, oil separation can also be executed with the use of parallel and corrugated plate separators. These are actually plates installed in the separators, inclined at an angle of 45 to collect large amounts of oil-water but the basins are smaller than the usual separator. The flow of the oil in the wastewater is manipulated. The coalescing action of the plates enables the separators to have an effective separation. Oil droplets with the size of 0.006 mm (6 microns) can be separated from the oil.
These are also known as coalescing plate separators. The plates reduce the distance that droplets can go before they are being seized, and the size of the separator basins is made smaller. The technique is the tilting of the separator to minimize space. Commercial types of this kind are available and some companies sell patented coalescing plate separators.
Dissolved air flotation (DAF) or induced air flotation (IAF) belongs to this category. DAF is effective in treating wastewater that cannot be treated by gravity. Using DAF or IAF systems can remove heavy oil and solid particles in the water. The process uses flotation aids like the usual coagulants and flocculants. DAF uses pressure on the influent wastewater at 3-5 atm, after that, the pressure is released, producing bubbles that carry oil particles at the surface of the water. These particles are removed by a collector, which can be mechanized or another form of equipment. DAF can reduce BOD by up to 50% of oil. (Wong & Hung, 2004, p. 191)
The use of air flotation has been recommended by many authors because of the relatively little space it can provide and the short time needed to impound the wastewater. (Lavallee and Nadreau, 1997, cited in Rigas et al., 2000, p. 245)
Showing oil removal by Dissolved Air Flotation. Source: Treatment of oilfield and refinery wastes, by Wong & Hung (2004, p. 191).
Table 1: showing oil removal by Dissolved Air Flotation. Source: Treatment of oilfield and refinery wastes, by Wong & Hung (2004, p. 191).
Separation by gravity
This is a flotation process which of course uses gravity. The oil droplets are allowed to float on the surface of the water, after which separation occurs. The oil droplets float and this is where separation is effective. It is known as the natural way, but presently there are other ways added to modify the process.
Natural gravitational separation is executed in big tanks. A method known as enhanced gravitational separation is done using centrifugal force. Other refineries use distillation. There are also those who use reverse osmosis and absorption, but these methods are sometimes expensive and too costly on the part of the company. (Veenstra, 1998, p. 6)
This process uses chemicals with aluminum or ferric salts and can only be done when there are suspended solid particles still present after the action of the gravity separation. The flocculants are mixed with and circulated in the water. The advantage to this kind of action is that the sulfides can be removed with the solid particles and low levels of hydrocarbon can be attained. However, the action can also produce large quantities of hydrocarbon with sludge. (Veenstra, J. et al., 1998, p. 6)
These processes include those which apply biological treatment in various forms. Biological processes make use of microorganisms like bacteria in decomposing the wastewater to produce water free of contaminants and other substances. Microorganism or sludge is formed in the wastewater wherein carbon dioxide is produced. Biological treatment includes aerobic and anaerobic treatment. The technique in aerobic is the use of bacteria in the treatment process; carbon dioxide is an outcome. In composting, sawdust is used in the treatment process. (Naik, 2010)
The process of water treatment uses several stages of biological removal reactors. The first stage, which utilizes the sequential batch reaction, includes the removal of oil and grease and other hydrocarbons emitted by petroleum substances. The second stage utilizes a submerged fixed-film, a kind of biological reactor, which is used to spread the sulfur-oxidizing bacteria to produce the effluent quality of the water by eliminating the organic sulfur compounds. The succeeding stage is nitrification which involves removing the ammonia. (Peeters & Theodoulou, 2005)
Anaerobic biological degradation
This is a biological treatment that involves the degradation of organics in wastewater. The process involves fermenting long-chain compounds into simple compounds by using a particular form of bacterium known as microbial consortia which reduces the compound into sulfate. (Chemical Business, 2006)
When the wastewater is now laden with sulfate, it passes through biological treatment. The presence of sulfide allows a depletion of oxygen which kills aerobic microorganisms. Further aerobic biological treatment is applied. Surface aerators and diffuse aerators are two processes using equipment that add oxygen to the organics of wastewater. This is done in order to produce complete oxidation, agitate the aerobic biological process, and maintain the level of dissolved oxygen at the standard 204 mg/l. (Chemical Business, 2006, p. 58)
The anaerobic treatment process involves fermenting the sludge at a particular temperature that excludes the presence of oxygen. The biological treatment removes solids in the wastewater. Another aim of a biological process is to reduce bad odor as well as destroy pathogenic organisms that might be harmful to the environment or impede biological activities. (Gautam, Kumar, & Sabumon, 2007, p. 299)
Processes that belong to this category are the filtration types.
This is a process using substances known as microfilters which can hold smaller particles such as the ones which are even smaller than pores. They can retain the bacteria but cannot separate other materials which are colloidal. A common microfilter is a certain organic polymer with even pore dimension. (Isak et al., 2008, p. 129)
The process also utilizes microfilters, but with different pore diameters, which range from 0.0015 0.2 micrometer particle in size. The water that passes through ultrafiltration does not need more sterilization. It can then be used for industrial purposes.
The filtration now involves nanofilters, which are used to remove dissolved molecules even down to the smallest molecular mass of treated water. The nanofilters have extremely small pore diameters that exert operational pressure which is greater than other filters, like the ultrafilter. (Isak et al., 2008, p. 129)
The process of converting nitrates and nitrites into nitrogen gas is called nitrification. Nitrogen can be found in the water and can produce or transform into other substances. The process of reducing nitrogen in the water involves a complicated biological process. Once it has transformed into gas, it can now be allowed to evaporate. The treatment in this method needs storage tanks, bio-reactors, and other filters and storage equipment. (Shulder et al., 2010, p. 62)
Reverse osmosis is used for separating minerals from seawater. Nevertheless, it is also used in the field, not just in seawater. Reversed osmosis puts into action the process of natural osmosis in the reverse. The water passes through a thin skin surface that is applied with an amount of pressure. It produces 25% concentrate of pure water. With this process, wastewater can then be discharged to the open sea or for whatever purpose it is deemed. (Isak, Sjtri, Kondor, & Gyry, 2008, p. 125; Shao, 2008)
Multiple angle separators
The process is an improvement of the coalescing plate separator wherein the action done is plugging the solid particles in the wastewater with oil.
Figure SEQ Figure * ARABIC 2 Oil Separator Series Fiberglass. SOURCE: Condensed from Pan American Environmental. Web.
Figure SEQ Figure * ARABIC 2 Oil Separator Series Fiberglass. SOURCE: Condensed from Pan American Environmental. Web.
This is an example of an oil separator. It removes oil, fuel, and other toxic substances from wastewater. It is a highly compact oil separator that uses a coalescing media.
Natural Treatment Systems
These techniques combine several methods to produce effective treatment or separation of oil from wastewater. The methods include physical, biological and chemical processes which may occur in natural ecosystems. For instance, the natural ecosystem has its own way of treating itself through interactions between plants, soil and water, along with the corresponding nutrients and microorganisms. Lands are treated together with the floating aquatic plants and wetlands. However, the treatment usually occurs after a mechanical pretreatment process. Land treatment systems to be used are slow rate systems, or overflow and rapid infiltration systems (Tchobanoglous, Burton, Metcalf & Eddy, 2004).
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, p. 23)
The water-pinch technology is a technique in treating wastewater that was introduced in the 1990s. This system utilizes an analysis of the lowest flowrate target for consumption of freshwater and generation. It can be used as a means to and effluent treatment systems. (Mann and Liu, 1999, p. xi)
Some companies benefited from it even at its early application. The system was implemented by a company known as Monsanto Company, which operated in Wales. Other companies studied and copied the system because Monsanto reaped benefits from its use, some of which was a reduction of 30 percent from the cost of implementation, and savings of $11.5 million due to a reduction of the capital expenditures for the construction of wastewater treatment facility. Water-pinch technology became popular and has then been applied in commercial and research applications.
There are various techniques for the treatment of wastewater. But first, wastewater has to be analyzed. The principle used in water pinch analysis is the application of contaminants; in other words, this is a battle between contaminants. The process involves applying contaminants in order to eliminate the present contaminants which are harmful to the environment. The application of one or a mass of contaminants requires several methods, which may be mathematical, graphical or computer-based. (Mohammadnejad et al., 1011, p. 89)
Water-pinch technology has become popular and has since been applied in commercial and research applications.
Ships are also carriers of wastewater and their disposal can be costly to the environment. Ships carry with their gasoline and ballast water which have hydrocarbons. Ballast water contains contaminants.
Cooling water in refineries also uses oil, and this can be dangerous to the environment if engineers managing wastewater in refineries dont know how to handle it.
Consciousness in environmental issues has led some companies around the world to find solutions in the form of technological innovations or inventions to minimize wastewater environmental abuse.
There has to be an overall view of the various ways of waste products, including collection and treatment and subsequent disposal of wastewater. The treatment to be implemented would depend on what type of wastewater is produced by the oil refinery.
Initial planning of wastewater treatment plant includes the following aspects:
The various data and information gathered from the field surveys should be put together, inputted into a database, and carefully studied;
What type of wastewater collection and system will be implemented?
How will the treated wastewater be disposed of?
What sewer systems are in place? How are these maintained?
What health benefits will the treatment plant provide? (Arceivala & Asolekar, 2007, pp. 38-9)
Approaches in wastewater collection systems
Wastewater collection systems can be centralized or decentralized. Decentralization has been applied to provide low cost of construction of the treatment plant and proper disposal of the treated water. In a centralized system, the length and scope of the plant are quite high. In a decentralized system, the final product in the treatment can result in reused water for process, irrigation and gardening, and the disposal of the wastewater into a stream or adjoining body of water.
Aside from these considerations, the following factors are also important to determine in the planning stage:
What does the oil refinery require of the effluent water as to its cleanness?
What is the nature of the wastewater to be treated?
What are the properties and chemical substances found in the wastewater?
What are the other properties of the particles and substances found in the wastewater?
What are the costs involved in treating the wastewater?
Finally, how will the treated water be disposed of? (Cheremisinoff, 2002, p. 2)
Determining the costs of the treatment site is an important parameter to be considered. These parameters include the land where the treatment is to be built, the cost of operating the plant, and the maintenance costs needed. These are all needed in the budgeting process. (Papadopoulos, Tsagarakis, & Yannopoulos, 2007, p. 581)
If all these things have been considered and determined, then it is time to select the appropriate wastewater treatment system for the Abu Dhabi refinery.
Wastewater Treatment System Selection
The objective of this section is to discuss further the various wastewater treatment systems and select the best water treatment for the Abu Dhabi oil refinery. Wastewater treatment selection would depend on the kind of wastewater generated by the oil refinery, and the objectives of the firm. However, effective treatments have been cited in the preceding sections. More of these effective wastewater treatments will be provided in this chapter.