Automated Methane Extraction - Coursework Example

Automated Methane Extraction Student’s Name: Institutional Affiliation : Automated Methane Extraction Introduction During the handlings and treatment of municipal wastewater, methane is emitted through anaerobic decomposition of organic materials. In collection and treatment of municipal wastewater, many developed countries depend on centralized aerobic wastewater treatment system. Few methane emissions are produced by these municipal wastewater treatment systems, but there can be a high rate of methane emissions from large amounts of biosolids. In developing countries, there is little or totally no collection and treatment of wastewater. This results in greater emission of methane because systems that do not exist tend to be anaerobic. Examples of such systems are lagoons, latrines, and septic systems. Methane from waste water has been estimated to produce 512 MMTCO2E of methane emissions. This accounts for 7 percent of the methane emission globally[Koc15]. There is growing importance of wastewater since the world's population is growing. In the coming 40 years, the global population is expected to increase by 9 billion people. This will lead to increased use of water and food consumption leading to increased production of waste water. Globally, emissions of methane from wastewater are estimated to grow by 19 percent between 2010 and 2030. The regions that are projected to experience the greatest growth are Africa, Asia, Middle East and South America. The following are benefits of capturing and using methane from wastewater treatment facilities: Conversion of waste products into sources of revenue Creation of renewable energy which can replace fossil fuels Reduction of GHGs and air pollutants associated with it Acts as a source of energy supporting energy independence Creates jobs associated with construction and operation and Enhancement of community image as an innovative and sustainable community. There are several approaches to wastewater methane mitigation recovery. The following are methods that can be used to recover methane: Methane can be recovered by installing anaerobic sludge digestion. This can take the form of new construction or be retrofitting anaerobic treatment systems. In this method of tapping methane, anaerobic digesters are used for processing wastewater biosolids to produce biogas. This can be used onsite to reduce the use of conventional fuel which would otherwise be used to produce thermal energy and electricity. Another way is through the installation of biogas capture systems at existing open air anaerobic lagoons. This method is considered the simplest and easiest method of biogas implementation. Instead of investing in a new centralized aerobic treatment plant, covers an existing lagoon to capture biogas can be a more economical way of reducing methane emissions. Other methods used to capture methane are installation of new and centralized aerobic treatment facilities or covered lagoons; installation of simple degassing devices at the affluent discharge of anaerobic municipal reactors; and, optimization of existing facilities and systems that are not being correctly operated as well as implementation of their proper operations and maintenance[Koc16]. One of the ways of lowering operation costs is through energy recovery in the waste water treatment plant. In the recent years, there has been an increase in operating cost of water treatment plants due to the ever increasing costs of energy. Because of this factor and shortages that have been reported in fossil fuels emphasize the conservation need and management of energy in waste water treatment facilities. Today, the consumption of energy is very high. Energy recovery can be offered as a good option towards lowering energy consumption, within the economic costs. One method that can be used to lower energy consumption is recoveries through anaerobic decomposition of organic compounds of waste water. Settled sewage flows into aeration tank in the activated sludge plant from where the sewage is combined with flocculated microorganisms concentrated suspension in the form of activated sludge. The process that follows is an injection of air via diffusers on the floors of aeration tanks to create turbulence for proper mixing of the settled sewerage and microorganisms. This activity will enable provision of enough oxygen and after that a final stage of settlement that will ensure separation of microorganisms to feed on the sewerage that has been settled leading to biological oxidization of the pollutant materials. The final stage of settlement follows that will ensure the separation of the activated sludge from the liquor that has been separated. This sludge having been activated will then be returned to the inlets of aeration tanks to treat more sewage that has settled. This effluent that is free from unwanted solid is always treated with sufficiency to be released to the river directly[Jim14]. There is raw sludge that results from the resulting treatment process that is pumped through a heated digester to make them appropriate for use in farmland. This digester is molded in such a way that it is a fully a reaction vessel that oxygen bacteria absence develops under significant state of alkalinity that lowers solid matter pollution to methane, organic fatty acids, carbon dioxide and a small portion of other gasses. The electricity used in the entire treatment process of 1000m3 of raw sewage is high. There are many factors that influence the production of gas during anaerobic digestion. Some of the most important factors are the solid content of the sludge, the time for retention, the digester temperature, and biodegradability of the organic materials. The volume of gas produced increases with an increase of the solid composure of the sludge that is coming in. However, the digester input of energy remains constant. The gas yield can also be increased by lowering the rate of loading for the solid contents[Jim14]. The optional gas production occurs at a temperature of 35˚C. In order to save the energy used in the water treatment plan, we have to make use of the energy in the digester gas. This gas can be used in different ways including digester space heating, transport fuel, and on-site power generation among others. The table below shows the average consumption of energy for treatment of 1000m3 raw sewage. Table 1: Consumption of Energy in Treatment of Raw Sewage Process Average consumption of power (kWh) activated sludge. Preliminary treatment 5.4 Preliminary sedimentation 9.5 Recirculation pumping of activated sludge 17 Acration 130 Digestion tank (mixing and pumping) 28 Final sedimentation 5.4 Total input 195.3 There is well the establishment of the use of digester gas for digester heating. Convectional gas-fiber boilers are used by many anaerobic digesters together with a heat exchanger for transferring the heat of combustion to the sludge that has been digested. The efficiency percentage of this process is 50-60%. Although the use for generation of energy is practiced in some large treatment facilities for sewage, it is not common in smaller works because there is no attractive economics so far. Digester gas can drive internal combustion engines and steam turbines. In such a system, the gas is used to generate power. When power is generated, heat is recovered as aby-product when the engines are cooled as well as the exhaust gasses from the steam turbines. This by-product heat are used for space heating and digester. The two methods of energy utilization can be distinguished depending on the system of power generation used[Nab13]. The systems that can be used are: Total energy system: this is where electricity is generated using gas. Partial system of energy: this is where there is no generation of electricity using the gas produced Apart from the above methods of energy utilization, the following can also present wastewater methane utilization options: Digester gas purification to pipeline quality: this is where the wastewater purification facility can sell the well treated and pressurized biogas to the local natural gas facility. Direct sales of digester gas to the industrial user or electric power producer: biogas can be treated, delivered and sold to local industries and other power producers to be converted into electricity or heat. Digester gas to vehicle fuel: biogas can be treated and compressed on-site to produce methane of high quality capable of being used as vehicle fleet fuel. There are low thermal efficiencies associated with steam turbines. They are available for 1000kW power output and above. The use of these facilities is allowed only in large treatment facilities that may be in need of continuous low-pressure steam. Gas turbines are also associated with minimal efficiencies decreasing at part load. Gas turbines can be found for the energy output of 400kW onwards, though there is a very limited range to choose from. The most accepted use for digester gas is spark ignitions or dual fuel engines. These engines are either of 4 or 2 stroke types that can be naturally aspirated or turbo charged. The heat recovery may be from exhaust gasses, oil cooling, or cylinder walls. The temperature of the water when it is entering and exiting recovery heat exchangers is always between 50 to 60˚C and 80 to 90˚C respectively[Bel16]. There is a (CHP), parked Combined engine of Heat and Power system, consisting of combustion engine (internal combustion) driving a generator (AC Generator). This, in turn, produces electrical power that is capable of being used nationally, or rather electric power that may add value to the national grid of a country. Heat is tapped from the engine cooling system and exhaust. This heat is used for hot water and space heating. There is a range of size for parked CHP system from 15 to 1200kW output of electricity. There are low-cost, effective units that use automotive engines while others that are more expensive use units that are designed specifically for industrial gas turbines. Such a system can attain an overall of up to 90 percent fuel conversion efficiency and between 23 to 35 percent for electricity generation efficiency. On the other hand, heat production efficiency can be between 50 to 60 percent[Bel16]. Assignment 1 Methane (CH4) is emitted from natural gas and anthropogenic. Some of the activities which release methane are rice cultivation, fuel production, burning of biomass, and waste management. In the organic waste, methane is tapped from organic matter in with no presence of oxygen. This is also referred to as anaerobic decomposition. Treatment of water from municipal/domestic sewage and the waste coming from industries is done the treatment facilities of the town’s municipality and other effluent treatment plants that are privately and constructed and owned. In situations where this water contains organic constituents with high chemical oxygen demand, the treatment will be done anaerobically. Methane is produced as a greenhouse gas in the process of wastewater treatment. Emission of methane can be avoided if the waste water is treated and the sludge associated with the waste water. This can be done under aerobic conditions. There are ventures with effective technology which can be used to tap methane from wastewater and then later used for generation of power. It can also be burned open for the avoidance of releasing it into the air. There are industries and sectors that ar responsible for the emission of huge quantities of GHG including dairy industries, alcohol distilleries, beverage industries, palm oil industries, meat industries/slaughter house, and pulp and paper industries among others. The main constituent in the emission of these industries is methane which is has 21 times more potentiality than CO2 in regards to global warming.[Fit16]. Waste Water Treatment Waste water treatment in anaerobic lagoons that are not covered is the current trend in the industries such as sugar and palm oil among others. Water from these industries undergoes treatment process in uncovered anaerobic lagoon system without recovery of methane. These lagoons have a depth greater than 2 meters. This is a suitable environment under which anaerobic bacteria rapidly grows and help in the organic compound breakdown. These are the organic compounds that are present in the waste water. What follows is a generation of methane from the organic content of the water that is later discharged into the air/atmosphere. The anaerobic digesters that are covered (GHG reduces emissions in the example that follows) is capable of collecting methane gas that has been generated (CH4). This type of project works with 60-65 percent efficiency as compared to 40-50 percent of open anaerobic lagoons. The gas which is collected is purified and used to generate electricity in the gas engine. The diagram that follows illustrates how methane is captured and utilized. It is a scientific method of methane extraction known as carbon credit project. Figure 1: Capturing and Utilizing Methane According to the sector responsible for wastewater treatment, there are about 151 methane and biogas voidance and projects of utilization officially listed under CDM globally. The emission reduction of GHG CO2 is averagely at 1, 16,142 tCO2 annually. As compared with carbon dioxide, methane is considered a potent greenhouse gas. This is because methane has molecules which are larger than carbon dioxide physically and absorbs wavelength radiation which are longer than carbon dioxide. The natural environment is under serious threat because of global warming. If there is increased concentration of methane in the atmosphere, it can trigger global warming efficiently. Projects directed towards GHG emission reduction can trap methane from facilities of wastewater treatment and help in reducing global warming and its associated impacts. The trapped gas can also be used to generate electricity that can be used onsite or added to the national grid[Zha14]. As elaborated by the diagram above, anaerobic transformation of organic substances is a standard technology with the aim of environmental protection. It protects the environment through the treatment of waste and also wastewater. The whole process leads to the production of an end product known as biogas. Biogas is a combination of methane and CO2, and it is considered a useful source of renewable energy. This is a simple technological procedure with minimal requirement of power input. The process is used to change organic materials that are in form of solid waste, wastewater, and biomass into methane. With the ever increasing demand of sustainable renewable energy production, there is a desire for a much wider application of technology to extract methane and naturally occurring gas. In the 1980s, there were projects that were initiated to produce biogas from domestic and industrial waste, but many were terminated because of insufficient economic viability. There is renewed attention on the production of methane from waste because it helps in reduction of carbon dioxide emissions and also reduces the emission of methane as a greenhouse gas. The growing market demand for renewable energy is in support of this trend as well as the optimization of technologies of anaerobic digestion. This can be seen by the development of co-digestion system and modern high rate. The following are the basic principles of anaerobic digestion[Dan14]. Basic Principles of Anaerobic Digestion Anaerobic microbiological decomposition is the procedure resulting to energy being derived from micro-organisms and grows by organic material metabolization in an environment without oxygen. The result is the production of methane (CH4). There are four phases under which anaerobic digestion can be subdivided, and each face needs its characteristic group of micro-organism. The following are the four phases of anaerobic digestion process: Hydrolysis: this is the process where biopolymers that are non-soluble are converted to organic compounds that are soluble. Acidogenesis: under this process organic compounds which are soluble are converted to carbon dioxide and VFA (volatile fatty acids) Acetogenesis: this is the point where VFA is converted to H2 and acetate acid. Enzymes for hydrolysis are excreted by acidogenic bacteria and soluble organisms converted to alcohol and volatile fatty acids. The next stage is the conversion of volatile fatty acids and alcohol by acetogenic bacteria to hydrogen or carbon dioxide and carbon dioxide. The next stage involves methanogenic bacteria which utilizes hydrogen or acetic acid and CO2 to produce a gas known as methane[Wil13]. It is important that biological transformation discussed above maintain sufficiently attached in the entire procedure for stable digestion to proceed. This will, in turn, prevent accumulation of intermediate compounds. A very good example is where there is a decrease in pH as a result of the accumulation of volatile fatty acids. Under this condition, methanogenesis cannot take place again, and this will decrease the pH further. The pH will decrease even further with an increase in hydrogen pressure. When hydrogen pressure becomes too high, there will be the formation of reduced volatile fatty acids, and this decreases pH. Since anaerobic digestion is a biological procedure, there are environmental factors affecting the entire process, for example pH, temperature, and toxicity and alkalinity. These factors are as discussed below: Controlled digestion takes the following forms of divisions: psychrophilic (10-20˚C), thermophilic (50-60˚C) or mesophilic (20-40˚C) digestion. It is important to note that the processes of conversion become very slow when the temperatures are low. On the other hand, psychrophilic digestion requires a longer retention period leading to a larger reactor volume. This is contrary to mesophyll digestions that need fewer reactor volumes. When pathogen removal becomes an important issue or when water is discharged at high temperature, it becomes suitable for thermophilic digestion. High loading rates can be applied during thermophilic treatment. It is also worth noting that in temperatures as low as 0˚C anaerobic digestion can occur. However, methane production rate will increase with an increase in temperature till maximum of 35-37˚C temperature is reached. At this level of temperature there is involvement of range mesophilic organism. The choice of temperature will be determined by the biogas yield and the relation between energy requirements[Cap15]. Thermophilic bacteria replace mesophilic at high temperature resulting in methanogenic activity at a maximum temperature of about 55˚C or above. Step 1 of anaerobic digestion may take place at a range that is wide, of pH value while methanogens only continue with neutral pH. However, there is a lower rate of methane production for pH outside the range of 6.5-7.5. In order to keep in the right position/state the optimal pH range necessary for methanogenesis, there must be an adequate amount of hydrogen carbonate in the solution. This is always denoted as bicarbonate alkalinity. Methane Production Potential The quantity of organic matter available in the waste streams is quantified by COD (Chemical Oxygen Demand) to predict the potentiality of biogas production. This oxygen being equal to the organic compound can be oxidized and rated or compared by a chemical oxidizing agent that is strong. This is the stage where anaerobic digestion, the biodegradable COD found in the organic materials is reserved in the final product. The new products here are methane bacterial mass that has been newly formed. Advantages of Anaerobic Treatment The following are advantaged of anaerobic treatment: Anaerobic digestion produces a source of energy through the recovery of methane. The processes of anaerobic treatment use minimal energy. The requirement of energy at ambient temperature ranges from 0.05-0.1kWh/m3 (0.18-0.36MJ/m3) relying upon the pumping needs and recycling affluent. Another advantage of anaerobic treatment is that there is a reduction of solids to be handled. There is a reduction of production of extra sludge depending on biodegradable COD in anaerobic treatment as likened to the procedures of aerobic. Anaerobic treatment is also characterized by felicitation of sludge dewatering With anaerobic treatment, there is stabilization of raw materials The end product of anaerobic treatment is odour free[Atk15]. There is an almost retention of fertilizer nutrients nitrogen (N), potassium (K) and phosphate (P) Very high loads that exceed the values of 30 g COD/1/day at ca. 30˚C to 50g COD/1/day at ca. 40˚C can be handled by the modern anaerobic treatment process. The sludge resulting from anaerobic treatment process can be stored for long without the need for feeding. The cost of construction of anaerobic treatment facility/process is relatively low as compared to conventional systems. Contrary to convection systems, the space requirements anaerobic treatment are very low. Biodegradable compounds are effectively removed during anaerobic treatment leaving some reduced compounds in the affluent. Other compounds that are left are organic N-compounds, ammonium, pathogens and sulphide organic P-compounds. A complementary treatment step will be required depending on the further use. Demerits of Anaerobic Treatment Even though the anaerobic treatment advantages outweigh the disadvantages by far, the disadvantages are numerous and can be summarized as follows: Because of the methanogenic bacteria’s high sensitivity to a bigger amount of chemical compound, the anaerobic organisms can adapt to these compounds. If the installation of the first setup lacks seed sludge that is appropriate, it may be very time consuming because of the minimal yields of anaerobic bacteria. When treating water with sulphurous compound, the treatment can produce bad smell and odour as sulphide is being formed. In order to avoid this smell, a microaerophilic post-treatment step should be employed to convert sulphide to elemental Sulphur[Lof97]. Conclusion Methane emission associated with anaerobic digestion of primary and secondary sludge contributes to about three-quarters of the overall methane emission. It causes larger greenhouse gas emission and footprint than carbon dioxide emissions which can be prevented by using biogas for generation of energy. Through efficient handling of ventilation air of sludge handling facilities, emission of methane can be reduced. It is also important to note that methane present in waste water is for a large part aerobically oxidized in the activated sludge tanks. In order to decrease emission of methane from wastewater treatment, this could be exploited. Methane is emitted from municipal water treatment plants[Kob14]. Being a potent greenhouse gas contributing to climate change, it is necessary to abate the emission if we are to achieve an urban water management that is sustainable. Therefore, it is important to know more about the amount of methane emitted from a particular water treatment plant as well as the sinks and sources of methane on the facility. References Koc15: , (Koch, Helmreich, & Drewes, 2015), Koc16: , (Koch, Plabst, Schmidt, Helmreich, & Drewes, 2016), Jim14: , (Jimenez, et al., 2014), Nab13: , (Nabarlatz, Arenas-Beltran, Herrera-Soraca, & Nino-Bonilla, 2013), Bel16: , (Bellaton, et al., 2016), Fit16: , (Fitamo, Boldrin, Boe, Angelidaki, & Scheutz, 2016), Zha14: , (Zhao, et al., 2014), Dan14: , (Danielsson, et al., 2014), Wil13: , (Williams, 2013), Cap15: , (Capelle, Dacey, & Tortell, 2015), Atk15: , (Atkins, Santos, & Maher, 2015), Lof97: , (Loftfield, Flessa, Augustin, & Beese, 1997), Kob14: , (Kobayashi, Kuramochi, Maeda, Tsuji, & Xu, 2014), Read More

Other methods used to capture methane are installation of new and centralized aerobic treatment facilities or covered lagoons; installation of simple degassing devices at the affluent discharge of anaerobic municipal reactors; and, optimization of existing facilities and systems that are not being correctly operated as well as implementation of their proper operations and maintenance[Koc16]. One of the ways of lowering operation costs is through energy recovery in the waste water treatment plant.

In the recent years, there has been an increase in operating cost of water treatment plants due to the ever increasing costs of energy. Because of this factor and shortages that have been reported in fossil fuels emphasize the conservation need and management of energy in waste water treatment facilities. Today, the consumption of energy is very high. Energy recovery can be offered as a good option towards lowering energy consumption, within the economic costs. One method that can be used to lower energy consumption is recoveries through anaerobic decomposition of organic compounds of waste water.

Settled sewage flows into aeration tank in the activated sludge plant from where the sewage is combined with flocculated microorganisms concentrated suspension in the form of activated sludge. The process that follows is an injection of air via diffusers on the floors of aeration tanks to create turbulence for proper mixing of the settled sewerage and microorganisms. This activity will enable provision of enough oxygen and after that a final stage of settlement that will ensure separation of microorganisms to feed on the sewerage that has been settled leading to biological oxidization of the pollutant materials.

The final stage of settlement follows that will ensure the separation of the activated sludge from the liquor that has been separated. This sludge having been activated will then be returned to the inlets of aeration tanks to treat more sewage that has settled. This effluent that is free from unwanted solid is always treated with sufficiency to be released to the river directly[Jim14]. There is raw sludge that results from the resulting treatment process that is pumped through a heated digester to make them appropriate for use in farmland.

This digester is molded in such a way that it is a fully a reaction vessel that oxygen bacteria absence develops under significant state of alkalinity that lowers solid matter pollution to methane, organic fatty acids, carbon dioxide and a small portion of other gasses. The electricity used in the entire treatment process of 1000m3 of raw sewage is high. There are many factors that influence the production of gas during anaerobic digestion. Some of the most important factors are the solid content of the sludge, the time for retention, the digester temperature, and biodegradability of the organic materials.

The volume of gas produced increases with an increase of the solid composure of the sludge that is coming in. However, the digester input of energy remains constant. The gas yield can also be increased by lowering the rate of loading for the solid contents[Jim14]. The optional gas production occurs at a temperature of 35˚C. In order to save the energy used in the water treatment plan, we have to make use of the energy in the digester gas. This gas can be used in different ways including digester space heating, transport fuel, and on-site power generation among others.

The table below shows the average consumption of energy for treatment of 1000m3 raw sewage. Table 1: Consumption of Energy in Treatment of Raw Sewage Process Average consumption of power (kWh) activated sludge. Preliminary treatment 5.4 Preliminary sedimentation 9.5 Recirculation pumping of activated sludge 17 Acration 130 Digestion tank (mixing and pumping) 28 Final sedimentation 5.4 Total input 195.3 There is well the establishment of the use of digester gas for digester heating. Convectional gas-fiber boilers are used by many anaerobic digesters together with a heat exchanger for transferring the heat of combustion to the sludge that has been digested.

Read More