Session C5 Paper #211 Disclaimer—This paper partially fulfills a writing requirement for first year (freshman) engineering students at the University of Pittsburgh Swanson School of Engineering. This paper is a student, not a professional, paper. This paper is based on publicly available information and may not provide complete analyses of all relevant data. If this paper is used for any purpose other than these authors’ partial fulfillment of a writing requirement for first year (freshman) engineering students at the University of Pittsburgh Swanson School of Engineering, the user does so at his or her own risk. THE INTRODUCTION AND APPLICATION OF TERTIARY WATER TREATMENT Chang Chen, [email protected], Sanchez 5:00 PM, Yi Zheng, [email protected], Sanchez 5:00 PM Abstract— Tertiary treatment is the final cleaning process that improves wastewater quality before it is reused, recycled or discharged into the environment. There are two main reasons of requiring tertiary treatment. First, the lack of clean water, especially potable water, is one of the biggest issues worldwide that needs to be solved. Second, primary and secondary treatments are not able to produce potable and environmentally friendly water. The uniqueness, which is also one advantage, of tertiary treatment is its ability to remove excessive amounts of harmful compounds from wastewater to produce high quality water that can pass drinking water standards and thus support more lives on the earth. In addition, the treated water from tertiary treatment will not pollute aquatic environments. Due to the benefits that tertiary treatment can bring to societies, many countries use this process to treat water. In the city of Xiamen, China, BIOFOR, a technology used through tertiary treatment, helps protect the aquatic environment of this city by treating industrial wastewater before it is discharged into the environment. Davco is another technology that aims at removing nutrients in effluents. Most areas in North America put this technology into use. In Key West, Florida, people apply Davco to increase the amounts of water that can be purified by 350,000 gallons per day. Sustainability is significant to tertiary treatment since the purpose of this technology is to “uphold” the balance of natural water system. This paper is going to specifically talk about the reasons of using tertiary treatment, its basic work principles, how this process can benefit the world, some successful examples of applications of tertiary treatment, and how the word “sustainability” is significant to tertiary treatment. inside the Earth, in rivers, oceans, and ice on the surface of the Earth, and in the air and clouds above the Earth [1]. However, only a small amount of Earth’s water is fresh enough to drink. Out of all the water on the earth, only 2.5% of it is considered fresh [1]. Further analyzing the components of this limited clean water, humans only have access to 1.2%, which is surface water. The percentage of ground water is 30.1%, and the rest of drinkable water is frozen in the form of ice [1]. Even in the surface/other freshwater, the amount of water found in ground ice and permafrost is still high, up to 69% [1]. Based on these percentages, it is apparent that the amount of water that is easily accessible and potable on the Earth is limited. Though people know that clean water is precious, there is still a large number of people taking clean water for granted and wasting it. Take the U.S. as an example. Nearly 7 billion gallons of water are wasted each day, which is astonishing [2]. Besides surface and ground water, people also rely on rain to gain usable water and raise crops to provide food for themselves. Unluckily, based on the study of drought under global warming published by Dai in 2011, the amount of precipitation will decrease greatly in future years [3]. As a result, there will be a large increase in the amount of infertile land by the year 2050, which is indicated by the change of red areas in Figure 1 and Figure 2[3]. Areas that were able to successfully raise crops will not be able to do so because of the severe water shortage [3]. In order to improve the severe condition of the lack of water, tertiary treatment, which can produce clean and also drinkable water by removing excess phosphorous and nitrogen, is one way to solve the serious problem of the lack of clean water to a large extent. Keywords—advantages, aquatic environment, BIOFOR, nitrogen, phosphorus, sustainability, tertiary treatment. THE NECESSITY OF TERTIARY TREATMENT THE LACK OF CLEAN WATER Water is the source of life, but it is not inexhaustible. On the earth, water seems to be almost everywhere, because the earth is capable of supporting millions of lives and looks like a blue ball from outer space. There are several places where Earth’s water resides: in the top section of the ground University of Pittsburgh, Swanson School of Engineering Submission Date: 03.31.2017 1 FIGURE 1 A. G. Dai. “Drought under global warming: A review”. Wiley Interdisciplinary Reviews: Climate Change. Yi Zheng Chang Chen This figure shows us the areas those are lacking of water around in the present. with excess chemicals is not usable is because too much phosphorus is harmful to one’s health, and it can negatively affect water quality and aquatic life. In this case, we need tertiary treatment to further treat water so that it will be drinkable and environmentally friendly. WORKING PRINCIPLE OF TERTIARY TREATMENT NITROGEN AND PHOSPHORUS REMOVAL The main purpose of tertiary treatment is to remove nitrogen and phosphorus left from primary and secondary treatment, from the water. Nitrogen, as molecules or ions, is present in many forms in our daily life. Most nitrogen exists in human body as organic amino compounds and urea, which are also the same forms of nitrogen present in wastewater. The produced water from tertiary treatment is much cleaner than the water from primary and secondary treatment, which is clear enough for industrial purpose or continuing daily life. However, it’s still not potable. Nitrates can seriously influence one’s health once consumed [5]. These nitrates always exist in form of ammonia in the septic tanks after the original organic nitrogen is broken down by microorganisms in the primary or secondary treatment. Ammonia, or NH3, should be the primary form of nitrogen leaving the secondary treatment. From here, the conversion of ammonia to nitrogen gas needs two steps to be complete. The first step is called nitrification. Nitrification is the process by which ammonium (NH4+) or ammonia (NH3) is oxidized into nitrite (NO2-) by ammonia-oxidizing bacteria or AOB, often Nitrosomonas spp, and the NO2- further oxidized into nitrate (NO3-) by nitrite-oxidizing bacteria or NOB, often Nitrobacter spp [6]. There are also two steps for nitrification. The first step is called nitritation. With addition oxygen or hydroxide, NH3 will be oxidized into hydroxyl-amine(NH2OH) with help of the enzyme monooxygenase [6]. Then, NH2OH is also oxidized into NO2- by the oxygen and hydroxides. After NH2OH is oxidized, electrons, oxygen and free hydrogen ions are converted into water. This reaction is shown in Equation 1. FIGURE 2 A. G. Dai. “Drought under global warming: A review”. Wiley Interdisciplinary Reviews: Climate Change. This figure shows us the areas those will lack of water in 2050. THE FLAW OF SECONDARY TREATMENT Secondary treatment is the second process in the water purifying system, which mainly uses naturally occurring biological processes, for example, bacterial decomposition, to remove remaining solids and organic materials, such as human waste, food, and soap, which were not removed in primary treatment [4]. The level of oxygen in wastewater will be altered at different stages during secondary treatment, producing aerobic (with sufficient amount of oxygen) and anaerobic environments (with little amount of oxygen) so that different bacterial communities can survive in order to remove different chemical components [4]. In the tanks of secondary treatment, the small solids and organic materials that are not screened out in the primary treatment will settle to the bottom of the tanks, producing a material called sludge [4]. The sludge will then be pumped into an oxygen-poor environment, which is called a fermenter tank [4]. In these tanks, sludge will be broken down, providing food for bacteria and assisting in removing phosphorus and nitrogen in later steps in secondary treatment [4]. After this, what is left in the fermenter tanks will be moved into anaerobic environments with wastewater from primary treatment [4]. Due to the fact that there is no oxygen present in the anaerobic environment to support bacteria, instead of consuming oxygen, the bacteria consume other organic materials for nutrition. For example, bacteria can consume nitrate, which will then be converted to nitrogen gas, removing nitrate from the wastewater in the process [4]. In an aerobic environment, bacteria will remove phosphorus instead of nitrogen [4]. During these processes, bacteria can successfully clear away certain amounts of phosphorus and nitrogen, producing water that is clean enough for people to use for daily activities, such as washing dishes and doing laundry [4]. Nevertheless, excessive amounts of nitrogen, phosphorus, and other chemicals still remain in the water after secondary treatment, making it impossible for people to drink or to discharge it into the environment. One reason why water NH4+ + 2 O2 N03- + 2H+ + H2O (Equation 1) It is important to note that this process requires and consumes oxygen. This contributes to the biochemical oxygen demand (BOD) of the sewage. The process is mediated by the bacteria Nitrosomonas and Nitrobacter which require an aerobic environment for growth and metabolism of nitrogen. Thus, the nitrification process must proceed under aerobic conditions [5]. The second step of nitrification is called nitratation. In this step, NH3NO2- is oxidized into NO3 - with the help of the nitric-oxide reductase (NOR) enzyme. A NOR enzyme is an enzyme that catalyzes the chemical reaction. After this reaction, the remaining oxygens, electrons, and protons assembles into water. We call them the first step and second step of nitrification, but it doesn’t matter which reaction 2 Yi Zheng Chang Chen occurs first. It is generally accepted that although there is much more NH4+ than NH3 present in places where nitrification takes place, it is NH3 that is the substrate for the bacteria, not NH4+ [6]. The second step of tertiary treatment is called denitrification. Bacteria also mediate this process like before. The denitrification process is a microbial facilitated process involving the stepwise reduction of nitrate to nitrite (NO2-) nitric oxide (NO), nitrous oxide (N2O), and, eventually, to nitrogen gas (N2) by the enzymes nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase [7]. Denitrification needs carbon to start the reduction reaction, so the dissolved oxygen (DO) level must be low. Carbon is necessary for the bacteria to thrive. Since the previous step, nitrification, requires low carbon content, we need to add extra carbon into the system. If the factory wants to lower the cost of this step, they can use a small amount of primary effluent, bypassed around the secondary process and nitrification reactor, as a carbon supply [7]. This would not affect the denitrification process because those un-nitrified compounds would appear in effluent. Since we need to remove all the nitrogen, we need to have an external source of carbon containing no nitrogen. The most commonly used one source is methanol. After nitrogen removal, the next focus is phosphorous removal phosphorus. Phosphorus is a common component of people’s daily wastewater and industrial wastewater. The principal forms are organically bound phosphorus, polyphosphates, and orthophosphates. Organically bound phosphorus originates from the body as food waste and, upon biological decomposition of these solids, is converted to orthophosphates. Polyphosphates are used in synthetic detergents, and contribute to, as much as, one-half of the total phosphates in wastewater [7]. Polyphosphates can be hydrolyzed to orthophosphates. Thus, the principal form of phosphorus in wastewater is assumed to be orthophosphates, although the other forms may exist. Orthophosphates consist of the negative ions PO43-, HPO42-, and H2PO4 –. These may form chemical combinations with cations [7]. About ten to thirty percent of phosphorus is removed by the secondary treatment. Normally, there are three ways to remove the remaining phosphorus in tertiary treatment. One is a physical process, which includes filtration for particulate phosphorus and membrane technologies; one is a chemical process, including precipitation, the main process, and physical-chemical adsorption, which is not necessary; and the last one is biological process, which includes assimilation and enhanced biological phosphorus removal. Chemical precipitation is used to deal with the inorganic phosphate. Precipitates are formed by adding a coagulant and wastewater. Metals, such as calcium, aluminum and iron are used in this process because they are relatively more active than other elements. For calcium, people usually use lime, or Ca(OH) 2 power or solid. It reacts with the with wastewater to produce calcium carbonate, which becomes reactants in a later reaction to remove phosphate. Because lime is a strong base, it will bring the pH value up and even goes above ten. Here, the calcium ions in the calcium carbonate will react with the phosphate to form the precipitate in hydroxyapatite. Because the reaction between the lime and the alkalinity of the wastewater, the quantity required will be independent of the amount of phosphate present. It will depend primarily on the alkalinity of the wastewater. The lime dose required can be approximated at 1.5 times the alkalinity as CaCO3. Neutralization may be required to reduce pH before subsequent treatment or disposal. Recarbonation with carbon dioxide (CO2) is used to lower the pH value [2]. The processes for aluminum and iron are about the same. Aluminum or hydrated aluminum sulfate is usually used to precipitating phosphates and aluminum phosphates (AlPO4). The basic reaction is shown in Equation 2. Al3+ + HnPO43-n ↔ AlPO4 + nH+ (Equation 2) This seems like a simple equation; however, it has a lot of requirements on the environment. It must be considered that there are many competing reactions and their associated equilibrium constants and the effects of alkalinity, pH, trace elements found in wastewater. The rate and efficiency of precipitation decrease as the concentration of phosphorus decreases. The phosphorus can be removed completely in ideal case. Ferric chloride or sulfate and ferrous sulfate also known as copperas, are all widely used for phosphorous removal [2]. The basic reaction is shown in Equation 3. Fe3+ + HnPO43-n ↔ FePO4 + nH+ (Equation 3) Ferric ions combine to form ferric phosphate. They react slowly because of the natural alkalinity, so a coagulant aid, such as lime, is normally add to raise the pH to enhance the coagulation [5]. UVC RADIATION AND H2O2/UVC PROCESS Secondary treatment, such as Conventional municipal wastewater treatment plants (MWWTPs), are not able to entirely remove micro-pollutants, such as pharmaceuticals, personal care products, pesticides, detergents and various industrial additives. This kind of pollutions needs higher level treatment to be removed. Tertiary treatment is used for the final step wastewater treatment. Tertiary treatment removes pharmaceuticals in the product water from secondary treatment with advanced oxidation processes (AOPs) and electrochemical AOPs (EAOPs) like UVC, H2O2/UVC, anodic oxidation (AO), AO with electrogenerated H2O2 (AO-H2O2), AO-H2O2/UVC and photoelectro-Fenton (PEF) using either UVC radiation (PEF-UVC) or UVA radiation (PEF-UVA) [1]. We are focusing on UVC in this paper. UVC refers to ultraviolet light with wavelengths between 200 – 280 nanometers (nm). Light in the UVC wavelength can be used for disinfecting water, sterilizing surfaces, destroying harmful micro-organisms in food products and in air [6]. However, the H2O2/UVC process can make a higher ability 3 Yi Zheng Chang Chen to remove TMP because H2O2 is separated and makes hydroxyl radicals. The electrogeneration of H2O2 can make oxidants directly without any problem or danger of transportation, operation, and storage of these oxidants. To filter out soluble iron ions or compounds, people add iron at neutral pH into the wastewater and that causes the precipitation of iron oxides, which can filter the light in the process of PEF-UVC. For the iron remained dissolved, people use Fenton’s reaction and increasing the organic removal [5]. However, H2O2 electrogeneration also is able to remove active chlorine species, this could make the whole process less efficient since active chlorine can remove impurities. UVC radiation can dissolve micropollutants. Some of the micropollutants don’t have stable structure, so they directly photolyase when they meet the light. In this case, the light from radiation excites the pollutant and causes the transfer of an electron from the excited state to ground state of oxygen molecule. Also, the light can cause homolysis to which forms organic radicals to react with the oxygens to reach the same result [7]. once consumed, the purified water after tertiary treatment is drinkable for humans. As a result of tertiary treatment, the amount of potable water will increase, supporting more humans around the world with enough clean water to consume every day throughout their lives. As we all know, the lack of fresh water is one of the most significant issues worldwide, resulting in water and food poverty, and prevalence of diseases in the areas that do not have sufficient water to maintain the lives of people living there. India is one victim of water shortage. The population of India is more than 1.2 billion [8]. However, 77 million of India’s population is not able to access fresh water [8]. Even worse, the usage of unclean water in India causes a great number of diseases there. According to the estimation provided by The World Bank, 21% of communicable diseases are related to unclear water [8]. Once the amount of fresh water is increased due to the use of tertiary treatment, the predominant issue of a lack of clean water is solved to a large extent, and more people will be healthier and happier because they have a sufficient amount of clean water. Another way for UVC radiation to dissolve micropollutants is that it can form different kinds of reactive species like hydroxyl radicals (OH), peroxyl radicals (ROO), singlet oxygen (1O2), carbon-centered radicals and excited triplet states by reactions involving the irradiation of recalcitrant dissolved organic matter (DOM) available in the effluent [5]. Different from UVC radiation, H 2O2/UVC process produce hydroxide ions by direct homolytic cleavage of the peroxide by putting peroxide under the UVC light. Since H2O2 is very unstable, it dissociates into water, hydroxide ions and oxygen by the light. The hydroxide ions would increase the UVC radiation oxidation power. As discussed in the previous paragraphs, the process of nitrification needs hydroxides to react. However, hydroxides are unstable and they are basic, so it’s hard to store and transports them. In this case, H2O2/UVC process can solve these two questions because H2O2 itself is neutral and harmless, and all the processes can react in one place. H2O2/UVC can be a technology to improve the whole tertiary treatment process. It’s still a new technology and factories or companies seldom use it because it also has a setback: it’s expensive since H2O2 is not cheap. PROTECT THE ENVIRONMENT Being environmentally friendly is the second advantage of using tertiary treatment. Nitrogen and phosphorus are necessary nutrients needed by organisms living in aquatic environments. However, too much nitrogen and phosphorus will have negative effects on animals and fish, and the quality of the water will decrease. Excess nutrients can cause water in the environment to be so nutrient-rich that algae can grow rapidly, and people are not always able to remove it as fast as it grows [9]. The quick growth of algae can then reduce the amount of oxygen in the water to a large extent, causing organisms to die, and resulting in polluted water environment [9]. Since tertiary treatment can remove excessive amounts of phosphorus and nitrogen from water, the water is safe for organisms, and usable by people. Purified water can be used to irrigate farmland without polluting the soil and ground water. Along with fertile soil, more crops can be raised to feed an increased number of people around the world. THE SETBACKES OF TERTIARY TREATMENT BENEFITS TO THE WORLD Although tertiary treatment can increase the amounts of potable water provided for people and produce environmentally friendly water that can be safely discharged into the aquatic environment, it does have some setbacks. One disadvantage of this process is that it can be affected by temperature. One benefit that tertiary treatment will bring to society is increasing amounts of clean water that is both safe to drink by individuals and safe to discharge into the environment. The main purpose of this process of water treatment is to produce cleaner water with smaller amounts of phosphorus and nitrogen, which has two other major benefits to the world. TEMPERATURE EFFECTS SUPPORT LIVES When people put tertiary treatment into use at different places, the water treated by this process will not always meet drinking and dischargeable water standards because of the difference in temperature. For example, in wetlands, the removal of nutrients from wastewater can be negatively First, unlike water produced from secondary treatment, which contains excessive amounts of phosphorus and nitrates that will have negative effects on human health 4 Yi Zheng Chang Chen impacted by temperature [10]. As temperature increases, many reactions tend to be more efficient. However, there is a range of temperature in order to achieve the highest efficiency. If temperature of surrounding environment is above or below this range, the reactions will not be optimal and thus reduce the amounts of chemicals that need to be removed from wastewater [10]. More specifically, temperature not only has bad influence on organic decomposition, but also on al nitrogen cycling reactions, such as nitrification and denitrificaiton [10]. Based on the study of the effects of temperature in treating wetlands conducted by Robert H. Kadlec and K. R. Reddy, there is a seasonal correlation between temperature and the reduction of nitrogen: from 1.04 to 1.11 for removing ammonium nitrogen, and from 1.04 to 1.16 for eliminating nitrate nitrogen [10]. In addition, for nitrogen cycling processes, the temperature coefficient fluctuates from 1.05 to 1.37 during isolated conditions [10]. For nitrogen removal, the temperature coefficient is between 0.988 and 1.16 [10]. Even more, when in colder environments, the cold weather may cause a seasonal decline of treatment, leading to an overall decrease in efficiency of tertiary treatment and passive implications of water quality [10]. pollution was further intensified because of the rapid increase of nutrients in the water, especially phosphorus and nitrogen, [12]. Even worse, companies always discharged industrial wastewater into aquatic environments without purifying it first [12]. All the reasons above lead to the serious water pollution in Xiamen. Degremont, a company that focuses on water purification, works with Xiamen to help it solve the serious issue of polluted water [13]. During the collaboration, they succeeded in constructing a conventional treatment line, which was then followed by the erection of another 100,000 m3/d treatment line [13]. In addition to these achievements, by using BIOFOR technology, the plant in Xiamen can discharge 300,000 m3 of environmentally friendly water into the environment everyday [13]. DAVCO DAVCO, another application of tertiary treatment, is used by Key West, Florida to remove an even greater amount of nutrients in wastewater to protect its fragile marine environment [14]. DAVCO has several stages for removing nutrients. As the index of stage increases, the amount of nutrients that can be removed also rises. Since the ability of eliminating nutrients is different, how the tanks are constructed is not same. In the second stage of nutrients removal tanks, each of them is divided into five parts: Inf EQ, anoxic zone, aerobic zone, aerobic digester, and clarifier at the center of the tanks. The effluent will first enter the Inf EQ, passes through anoxic zone, and finally enter aerobic zone. After the wastewater is purified in aerobic zone, it will then go to clarifier to be further treated. In clarifier, the water is separated into three streams. One stream is clean enough and will get out of the tank. The second stream will go to aerobic digester. The third stream will enter anoxic zone to go through the whole process again in order to be further treated. The produced water from this stage has total nitrogen that is less than 8 mg/L [15]. In the fourth stage of nutrient removal tanks, the anoxic zone is divided into a primary zone and secondary zone. In addition, it also includes a reaeration zone after the secondary anoxic zone. The effluent still enters Inf EQ first. After this, the wastewater will flow through the tank following the order of primary anoxic zone, aerobic zone, secondary anoxic zone, and a reaeration zone. The wastewater will move into the clarifier from reaeration zone. The treated water from forth stage will have total nitrogen less than 3 mg/L. The only difference between the forth stage and fifth stage is the use of anaerobic zone before primary anoxic zone in fifth stage. The total nitrogen present in the treated water will still be less than 3 mg/L. However, the total phosphorus existed in the water will be less than 1 mg/L [15]. Because of its capability of removing nutrients from wastewater and producing potable and dischargeable water, DAVCO is used widely and has many achievements. Every part of North America applies DAVCO to treat effluent since it can meet the standards of the amounts of nutrients SUCCESSFUL EXAMPLE OF TERTIARY TREATMENT Tertiary treatment is successful in removing phosphorus and nitrogen to further improve the quality of water so that the produced water can be safe enough to drink or discharged into the aquatic environment without polluting it. BIOFOR One application of tertiary treatment that is used by several countries is BIOFOR [14]. BIOFOR is a technology which aims at clearing away pollutants, such as ammonia, through tertiary treatment so that the treated water can meet the standards for drinking and dischargeable water [14]. The working principle of BIOFOR is simple. The wastewater that needs to be purified will be pumped from the bottom of the tank to the filter surface area [14]. After this, the water will flow through a filter media, in which nitrogenous pollutants will be removed because of the high concentration of fix-film biomass [14]. China is one country that uses BIOFOR to treat wastewater in order to safely discharge it into the aquatic environment. The condition of water in Xiamen was worrying before BIOFOR was put into use. Since aquiculture is one significant way to earn money, and the government was less restrictive on the amount of aquatic organisms each person could raise. People raised too many aquatic organisms within the limited amount of water [12]. As a result, the hydrodynamic was decreased to a large extent, and the ability of water to self-purify was also reduced, leading to the pollution of the water [12]. Because of the feces from growing aquatic organisms, and the food put into the water for feeding those living things, the 5 Yi Zheng Chang Chen allowed to be present in the water, especially municipal and industrial companies [15]. In addition, DAVCO also manages to save millions of maintenance and operating costs for cities, which can then be used to develop the economy and society [15]. DAVCO is also expected to expand the capacity of treating water in Key West, Florida from 500,000 gallons per day to 850,000 gallons per day, providing more water for citizens [14]. companies. Manufacturing development can earn countries a lot of money, making them rich, and promote the development of new technologies. However, industrial countries have a big setback: industrial waste pollution. Due to the fact that wastewater treatment system can cost certain amount of money and cause companies have less profits, some factories, especially small and medium sized one, are not willing to build a wastewater treatment system and directly pour wastewater into rivers or lakes. Since excessive amounts of chemicals exist in wastewater, the usage of such water could cause diseases for humans and pollute the environment. If industries can use tertiary treatment as the last step of treating water, over eighty percent of harmful components would be removed, producing more potable and environmentally friendly water. Tertiary treatment mainly removes nitrogen and phosphorus from the water left from primary and secondary treatment. To remove nitrogen, there are two steps to be used. The first one is called nitrification. Nitrification is the process by which ammonium (NH4+) or ammonia (NH3) is oxidized into nitrite (NO2-) by ammonia-oxidizing bacteria or AOB, often Nitrosomonas spp, and the NO2- further oxidized into nitrate (NO3-) by nitrite-oxidizing bacteria or NOB, often Nitrobacter spp [6]. The second step of the whole process is called denitrification. The denitrification process is a microbial facilitated process involving the stepwise reduction of nitrate to nitrite (NO2-) nitric oxide (NO), nitrous oxide (N2O), and eventually, to dinitrogen (N2) by the enzymes nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase [7]. In experiment, nitrogen can be completely removed from wastewater after being treated by these two steps; in actual cases, they can remove over eighty percent of the nitrogen due to loss of reactants and process variability. Sustainability requires technologies to be “green”, which means that a sustainable technology should have positive effects to the environment. As one part of wastewater treatment, tertiary treatment can certainly be a great example of a sustainable technology. It cleans wastewater and makes it drinkable. It saves water by reducing the amounts of wastewater and keeping producing fresh water. If the majority of factories could use this technology to treat their wastewater, the problem of water pollution and lack of drinkable water could be solved to a large extent. It’s an advantage to use treatment to save water and making it drinkable. The main idea of sustainability is reducing resource use, especially for natural resources. Natural resources, such as water, can slowly regenerate by itself. However, using resources without controlling them would destroy this natural balance. People should reduce the use of resources and keep the natural balance. As mentioned at the beginning, sustainability is defined as:” The ability to be sustained, supported, upheld, or confirmed.” To “upheld” is our goal. These sustainable technologies are making a better future for human beings. People cannot live without water, and that is why tertiary treatment and wastewater treatment is necessary. They are not only saving water and reducing cost, but also saving water for the future. In this case, sustainability is significant to tertiary treatment since the WHAT’S NEXT Tertiary treatment has contributed a lot to making our lives better. It produces more potable for people to drink, which support more humans around the world. In addition, the treated water from tertiary treatment is also friendly to the environment so that when it is discharged into the aquatic environment, individuals do not have to worry about polluting the environment or being harmful for plants and animals. However, everything is not perfect. The technologies that people use through tertiary treatment can be affected by the change of temperature. As a result, the amount of removal nutrients may be reduced, which will not meet people’s expectations. So when companies and citizens are satisfied by the amount of clean water that the technologies used in tertiary treatment can produce, engineers and scientists should still improve the process of tertiary treatment so that it can be used in many different areas without being affected by the environments. After all, the object of engineers is solving problem existed in the world and make the planet we live in a better place. SUSTAINABILITY OF TERTIARY TREATMENT Sustainability is defined as:” The ability to be sustained, supported, upheld, or confirmed” in dictionary. We are in a highly developed period. Everything is advancing quickly and new technologies are invented every day. However, the life span of most of the new technologies is not long, resulting in waste of energies and materials. Since the environmental protection becomes one of the most famous topics around the world, engineers are now paying more attention to the sustainability of technologies. In this case, tertiary treatment is a great example of the technology which has sustainability. Sustainability, in the case of tertiary treatment, means that fresh water can be continuously produced, assuring all the living things the enough amounts of water to live long and prosper. The lack of water is a serious issue worldwide. It seems that water is everywhere on the earth, especially in the sea, which covers seventy three percent of the surface area of the earth. However, only about 2.5 percent of the whole water is drinkable or useable and only 1.2 percent of total global water can be accessed by humans. Based on these percentages, it is apparent that the amount of water that is easily accessible and potable on the Earth is extremely limited. Most countries in the world are developing countries and a quick way to develop a country is to develop economy, which relies on the advancements of industries and 6 Yi Zheng Chang Chen purpose of this technology is to “uphold” the balance of natural water system. http://www.businesswire.com/news/home/2016112800500 6/en/Evoqua-Supply-Field-Erected-WastewaterTreatment-Plant-Key [15] “Davco Field-Erected Wastewater Treatment Systems”. Accessed 03.01.2017 http://docplayer.net/storage/53/31031511/1488560876/j7 mjJUvs0fhM6ShpBNJl4Q/31031511.pdf SOURCES [1] “The World’s Water”. USGS. 12.2.2016. 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Accessed 03.01. 2017 https://www.boundless.com/microbiology/textbooks/boun dless-microbiology-textbook/microbial-metabolism5/anaerobic-respiration-49/nitrate-reduction-anddenitrification-314-7650/ [6] "Water Treatment Solutions." Lenntech . Web. 03 Mar. 2017. Accessed 03.01.2017 http://www.lenntech.com/phosphorous-removal.htm [7] “Tertiary wastewater treatment”. NPTE IIT Kharagpur Web Courses. Accessed 03.01.2017 http://nptel.ac.in/courses/105105048/M23L38.pdf [8] “India’s Water Crisis”. Water.org. Accessed 02.27.2017 http://water.org/country/india/ [9] “Nutrition Pollution: The Problem”. United States Environmental Protection Agency. Accessed 02.27.2017 https://www.epa.gov/nutrientpollution/problem [10] R. H. Kadlec, K. R. Reddy. “Temperature Effects in Treatment Wetlands”. 2001. Accessed 03.02.2017 https://soils.ifas.ufl.edu/wetlands/publications/PDFarticles/258.Temperature%20effects.pdf [11] “BIOFOR”. Treatment solutions. 2017. Accessed 03.01.2017 http://www.degremont technologies.com/~degremon/BIOFOR-R-463 [12] “The level of water pollution in Xiamen in 2016 and its main pollutants.” 10.18.2016. Accessed 03.01.2017 http://www.smilegogo.com/fanwen/96463.html [13] “Xiamen wastewater treatment plant China”. SUEZ's degremont water handbook. Accessed 03.01.2017 https://www.suezwaterhandbook.com/casestudies/wastewater-treatment/Xiamen-wastewatertreatment-plant-China [14]“Evoqua to Supply Field-Erected Wastewater Treatment Plant in Key West, Florida”. 11.28.2016. Accessed 03.01.2017 ACKNOWLEDGEMENTS We would like to thank our writing instructors for helping us develop ideas before the start of outline, which laid the foundation for our complete paper. We also have many thanks for people in writing center for assisting us on grammars and sentence structures to help us clearly express our ideas and change our contents to make the paper better. In addition, we appreciate the assistance from librarians when we had troubles finding sources to explain the working principles of tertiary treatment in the paper. 7
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