Research on Improving Biogas Production - Literature review Example

CURRENT RESEARCH ON IMPROVING BIOGAS PRODUCTION Name Institutional Affiliation Date Table of Contents 1.Introduction 2 1.1.Background 3 1.2 Report Objectives 3 1.3Relevant Issues 4 1.4Problems to be Solved 6 2.0. Methodologies and Analysis 8 2.1 Experimental methods including material preparation and characterization 8 2.4. Key Techniques 11 2.4.1 The pH Effect. 11 2.4.2 Co-Generation Systems for Biogas Plants 12 2.4.3 The Effect of Ambient Temperature in the Performance of Micro Gas Turbine with Cogeneration System in cold regions. 13 2.2.4. Carbon (IV) Oxide Fixation 14 3.0 Results 15 4.0 Discussion 16 5.0. Conclusions and recommendation 17 References 18 1. Introduction Biogas production dates back to 2000 to 300 years (Gurung & Oh, 2013). It has evolved over time, thus becoming a core source of alternate energy especially in the rural areas. The focus is on understanding the operational mechanism to the detail and improving the efficiency of methane gas production. This report will discuss the current research being done about biogas production with special focus on improving biogas plant treatment to increase the yield of biogas and use of cogeneration systems to generate such secondary products as heat and electricity at the same time with biogas. Other systems such as carbon (IV) oxide fixation and the efficiency of reducing this carbon (IV) oxide will be discussed. 1.1. Background According to Hearns (2006), statistical estimation shows that only about thirty percent of wastes that are produced are collected and disposed. More research shows that fifty to seventy percent of these wastes are bio-degradable which makes it very necessary to have such systems as biogas plants to utilize such abundant raw materials. With the expanding knowledge of biogas the demand is relatively increasing hence the need for an increase in production. Improving this production could be done in two major ways. I. One by maximizing the output from digester: If the speed of fermentation is increased and the plant capacity to get more substrate for the process is increased then this could be achieved. II. The second way would be constructing new digesters and introducing a pre-treatment step and also taking in new substrate. The challenge many institutions are still working on is step by step increase in the productivity process where so many institutions have been involved in research. 1.2 Report Objectives The main objectives and targets of this report are; 1. To explain the current status of biogas plants. 2. Explain the loop holes in biogas plant productions that need improvement and research. 3. To give solutions to the improvement opportunities in this biogas production systems. 4. Explain the scope of the current technological trends in biogas production research and 5. Give an insight into the co-generation systems associated with biogas plants. 1.3 Relevant Issues For biogas to manifest as a product, certain processes and parties are involved. Usually, it all starts with the bacteria in a process known as anaerobic digestion which decompose the wastes (Lin, Wu & Wang, 2009). This process involves a lot of chemical and biological knowledge application to understand it. The bacteria which form part of the biological aspect of the process are categorized in three forms that is; a) Facultative bacteria, b) Aerobic bacteria c) Anaerobic bacteria which are responsible for the production of biogas. Karlsson & Ejlertsson (2012) illustrate that aerobic bacteria grow in the presence of oxygen whereas anaerobic bacteria grow in the absence of oxygen. The facultative bacteria on the other hand can grow in mediums where there is or there is no oxygen. The process of biogas production occurs in three successive stages namely hydrolysis, acid formation and methane formation respectively. a) Hydrolysis Hydrolysis, also referred to as liquidation stage is where waste matter initially containing carbohydrates, lipids, proteins and inorganic mater which are broken down by bacteria. The breakdown involves reduction of complex long chained organic molecules into simpler shorter molecules which is done by action of extra cellular enzymes. This results in formation of simple molecules that can then undergo the acid formation stage. b) Acid Formation Stage Is where the fermented intermediate materials are transformed into acetic acid (CH3COOH) hydrogen and carbon (IV) oxide by acidic forming bacteria. This bacteria use all the present oxygen resulting in an anaerobic condition which fosters the work of methane-producing-micro-organisms that later start their action on the acidic media. They include the acetogenic and the acidogenic types. Furthermore, these bacteria ensure components with low molecular weight are reduced into alcohols, amino acids and organic acids as well as into other forms such as carbon dioxide, hydrogen sulphide and methane in traces. c) Formation of Methane. This is the final stage involving methanogenic bacteria- the bacteria that produce the methane. These bacteria are sensitive to pH and require a mildly acidic media with pH values not below 6.2. They act by converting the formed compounds during the acid formation stage into low molecular weighing compounds such as methane and carbon dioxide anaerobically. The resulting methane gas is usually affected by pressure, temperature and water vapour (Bensmann, Hanke-Rauschenbach & Sundmacher, 2013). The biogas formed is usually a mixture of gases in various percentages with methane taking 50 to 70 percent; carbon dioxide 30 to 40 percent; hydrogen 5 to 10 percent; nitrogen 1 to 2 percent; water vapour 0.3 and traces of hydrogen sulphide. 1.4 Problems to be Solved This research will be studied in a set of steps for easier modularized research and improvement as shown in the illustration diagram below. Pre-treatment In this step pollutants like sand, metal and plastic are removed from the substrate that comes into the system. The mixture undergoes structure breakdown to increase the yield of the substrate. There are various technologies that can be applied to the substrate depending on the type. This also influences the number of stages the substrate will be allowed to pass through. Lignocelluloses form the largest mass of biomass and they are found in wastes from agricultural material and forest residue (Mudhoo, 2012). They comprise three types of components that is lignin, cellulose and hemicelluloses that are interlinked together forming a crystal like structure. Their decomposition by bacteria is generally difficult because of its structural complexity their higher molecular weight. They, therefore, need appropriate pre-treatment to make them accessible by the hydrolytic enzymes hence resulting in the solubilisation of complex lignocelluloses (Kastanek et. al., 2010). This increases the general efficiency of the biogas plant. There are various methods used in pre-treatment that were designed over the recent years. They include physical which involves both mechanical and non-mechanical treatment, chemical acid or alkaline hydrolysis, solvent extraction and delignification are used and physico-chemical method where we have ammonia fibre and steam explosion as well as carbon dioxide explosion. Most researchers prefer alkali pre-treatment as one of the best method of enhancing biodegradation of complex materials since biological pre-treatment leads to a high a high rate of biodegradability very high costs (Komemoto et. al., 2009). Calcium hydroxide is used as the most preferred chemical added to organic matter to improve the biodegradability rate because it is cheap, easy to recover and easier to handle safely. Digestion stage This is the main part of the biogas plant harbouring the very important microbes that form biogas. The environmental conditions of the bacteria inside the digester can be controlled and in turn higher volumes of biogas can be produced. Monitoring and control of this digester involve temperature regulation, the mixing of the feed and retention time of the substrate. The amount and type of substrate entering the digester could also be controlled to achieve maximum yield. With advance in technology such control events as mixing can be automated by designing new models of digesters with automatic controls. This ensures efficiency in the products. Sludge treatment As an independent module this can be done in so many ways depending on the type of plant and the substrate. The water in it is removed and the result can be used as a fertilizer once inspected and found to comply with governments policies and regulations or disposed. In this report we will describe the use of an ultra filtration (UF) membrane as a current research application in the biogas manufacturing process where it is used to decrease the solid material in the water and in so doing so improve the capacity of the plant with less re-circulating material. 2.0. Methodologies and Analysis 2.1 Experimental methods including material preparation and characterization The methods researched for use in improving the general production procedure for biogas that have been identified as optimizing measures for biogas production include; a) Membrane Filtration. This is a new method under research that targets improving the capacity of the pretreatment. Here the process water is produced from the digestate, through rotation of a centrifuge. The slurry produced to be used as the feed is produced in the pretreatment chamber from the process water and the substrate entering the chamber. The problem usually comes where the dry solid content in the process water steadily increases which therefore means we can add less new substrate to the process but still produce slurry that can be pumped (Mudhoo, 2012). Ultra – filtration solves this issue where the membrane is used to filter out unwanted particles in the water. The process water during ultrafiltration goes through circulation loops that pass the liquid through the membrane. The setup is made of a 70litre inlet tank that filters the process water. In this method the water is rich in organic material in each loop as the liquid passes through the membrane, forming permeate which is then re-circulated back to the tank or directed to an outlet tank for further analysis. The permeate send to the outlet tank moves through a cooler avoiding formation of steam hence the loss of process water from the system. Thermometers and pressure meters are installed for monitoring and control of the process. Other measurements made include the electricity consumption rate, the rate of flow of the permeate. This whole process tries to ensure a concentrated liquid is in the inlet tank and the permeate moved to the outlet tank. Mixing This method is simply an improvement procedure applied to the digestate in the digester. This digester is basically a box without enough sensors to monitor the microorganism’s environment hence the possibility for more research and improvement especially with understanding of the mixing and stirring effect inside the digester. Current research shows that mixing effects have been studied and analyzed from computational fluid dynamic models of the digester (National Renewable Energy Laboratory (U.S.) & United States, 2000). The velocity and turbulence fields are important factors to note when studying mixing in the digester. Research is being done where a digester model of an axisymmetric shape with heights and radii of 19.5 and 8.5 meters respectively have the gas injection simplified allowing a high quality mesh. The recirculation system of the liquid through the outlet is designed such that it is on the bottom close to the centerline axis where the liquid is then reintroduced through an inlet trough in the side wall of the digester near the bottom. This method is supported by a set of momentum equations and turbulence used while tracking the volume of the liquid fraction of in the phase of the mixture. Electroporation The continuous study of biogas shows the possibility to improve the rate of production and yield of biogas by using different methods of pretreatment on the substrate. In this method pores are made in the cells by exposing the substrate to strong electrical fields. The cells are damaged and nutrients released to the environment leading to an increased rate of gas production. 2.4. Key Techniques Other factors affecting biogas production that have been studied and researched include: 2.4.1 The pH Effect. This as a factor affecting biogas production has been researched and results show that there is an improvement in the process performance in this pH regulated reactors. Adding for example hydrochloric acid to the reactors lowered the pH to about 0.2 to 0.4 units and as a result the methane production increased by about 50 percent. This shows the increase in the microbial ability to use the organic matter for biogas production. Temperature effect in Anaerobic Solubilisation of Waste during Biogas Production Methane fermentation and its effectiveness are limited by both acidogenesis and solubilisation (Pickel, 2010). For instance the solubilisation rate recorded for food waste at fifteen degrees and twenty five degrees Celsius was 47.5 percent and 62.2 percent respectively considering suspended solid waste removal. This rate was with time improved to late experimental periods under mesophilic conditions contrary to the general rate which was very low under thermophilic temperature conditions. 2.4.2 Co-Generation Systems for Biogas Plants There are a number of systems which run parallel to the bio-gas plant and usually they are dependent on these plants to run. They include; Combined Heat and Power System (CHP) This system simultaneously generates both electric and thermal energy ((Ruppert, Kappas & Ibendorf, 2013). This occurs during the last phase of the biogas production plant where the biogas generated is directed to an internal gas combustion engine for burning. This is after cleaning to remove all the unwanted compounds. The engine is then connected to an electric power generator where clean renewable energy is produced and is also properly connected with an electric power generator from where clean, renewable energy is produced. In the process heat is recovered from the exhaust gases where there is thermal energy production from the cooling system in the form of either steam or hot water. In many biogas plants, the CHP system is structured close to the anaerobic digesters and in properly constructed containers. Improving such systems has been done by combining biogas with fuel or biodiesel to ensure total efficiency usually in a 10 percent blending. A portion of the heat produced from the biogas plant production procedure is used in the plant to keep the digester at constant temperature. The Micro Gas Turbine Engine Co-generation System In this re-generative system, atmospheric air entering the system is filtered and used for cooling the alternator and other electronic devices (Ruppert, Kappas & Ibendorf, 2013). The air exiting the alternator is then compressed and directed through the regenerator, where it is heated with hot gases coming from the turbine before entering the combustion chamber (Basrawi et.al. 2014). This reduces fuel amount used to reach the operating temperature. Compressed fuel is burned at high pressure and temperature in the combustion chamber. It is then expanded through the turbine for energy extraction for use to drive the compressor and the alternator. Biogas is often preferred in these types of engines mainly because there is a reduced electric bill with higher energy efficiency. 2.4.3 The Effect of Ambient Temperature in the Performance of Micro Gas Turbine with Cogeneration System in cold regions. This was studied over the range of 10-40 °C. It was observed that if the solution concentration in absorption chillers was too high or the temperature is was very low, crystallization occurred hence interrupting the operation of the system. Decrease in ambient temperature was therefore to be followed by a corresponding decrease in the temperature of the generator to prevent crystallization. 2.2.4. Carbon (IV) Oxide Fixation Carbon dioxide capture has been a challenge to many businesses today as penalties for production are faced if the emission is not reduced. Microalgae provide a possibility for its fixation. Normally one hundred turns of algal biomass can fix up to around one hundred and eighty three tons of carbon dioxide. Carbon (IV)Oxide fixation has to be added either in bicarbonate form or as a gas because the algae mature so fast that they cannot efficiently take carbon dioxide from the water. This forms the greatest part of their feeding process through photosynthesis during the day. Such a system can be developed to run at a biogas plant production where waste carbon dioxide can be fed to the system to fix it up. Meanwhile the algae would also help in the decomposition of the waste hence speeding up the process and contributing to the overall efficiency of the system. 3.0 Results This research is so extensive in various countries and at institutional level. Some institutions have recorded positive results better than others. All this research contributes to the overall improvement of biogas systems. The study on temperature showed that production of biogas at temperature of 15-20 degrees Celsius is low compared to that of 35-50 degrees Celsius. Production rates averaged 0.599L. In colder temperatures they were at about 0.046l per litre of slurry which is far much lower than the production in warmer temperatures (Taherzadeh & Karimi, 2008). The highest methane production was observed in pre-treatment having the highest concentration of solid lime. Kaar and Holtzapple from research show that pre-treatment using slake lime raised the enzymatic hydrolysis of corn stover nine times higher than that which was generated corn stover that was untreated. Currently the recommended conditions for pre-treatment are lime loading at 0.075 per g of dry biomass, water loading o 5 g for every gram of dry biomass followed by heating for 4 h at 120°C. Conclusions from these results show that temperature, chemical concentration, time of pre-treatment and inoculums amount have huge considerable effects on the digestibility of organic wastes. Biogas production was higher when in mesophilic conditions while it was very small in thermophilic temperatures. A shortening of the hydraulic retention capacity with time is expected when in thermophilic conditions. From research alkali pre-treatment has been identified one of the best preferable method of enhancing biodegradation of complex materials using calcium hydroxide as the most preferred chemical since it is cheap, easy to recover and easier to handle safely. 4.0 Discussion From the improvement made in biogas production method , control of odour can be termed as one resulting advantage of this process where it has been drastically reduced with the implementation of anaerobic digesters contrary to the uses of aerobic treatment procedures hence the overall cost of disposal is also very much reduced.It should, therefore, be noted that in cold regions overall system efficiency can be increased by decreasing the temperature when the ambient temperatures are very low in the absorption chiller evaporator according to the above discussed effect of temperature (United States, 2007). Physical pre-treatment is very costly while physicochemical treatment demands a lot of energy hence increasing the overall expenses of the plant thus the whole process. Biological pre-treatments involving microbes is also possible but is not very much controlled since it leads to a high rate of biodegradability hence very high costs. The use of the thermal energy produced from Combined Heat and Power System enables the considerable decrease of the biogas plant’s cost of operation - thus it is advised that thermal energy produced from the CHP system (self-consumption) should be exploited maximally (Srivastava & Hancs, 2014). There are several current trends in research on going about biogas production. Some of them currently being done are in areas related to lipid production, photosynthesis research in microalgae and aerobic and anaerobic oxidation with ammonium at highly salty areas. Currently in Norwegian Agriculture there is Biogas Reactor Technology research program that has the task to make biogas technology cost effective, strong and well situated for their use called BIONA. It focuses on three main areas that is; sensor technology and process optimization, ammonia tolerant biogas processes and high rate biogas reactors of the type UASB which are integrated in existing farm infrastructure. 5.0. Conclusions and recommendation It can be noted that biogas production is a wide and very extensive research topic to handle. Biogas is one of the cheapest energy sources with a large raw material for renewable energy production. The co-generation systems, carbon (IV) oxide fixation as well as new design models for the process improvement are areas that provide a lot of opportunities for research. Currently a lot of research is being done to fully commercialize this product. Focus has been put on design of co-generation systems as mandatory constituents of biogas plants to ensure exploitation is maximum. Countries such as India which have a lot of waste material coming from their large numbers of cattle have switched to this environmentally conducive source of renewable energy. I would recommend that everyone with the means to adopt this green energy for sustainable economic growth. References BASRAWI, FIRDAUS, YAMADA, TAKANOBU, NAKANISHI, KIMIO, & NAING, SOE. (2014).Effect of ambient temperature on the performance of micro gas turbine with cogeneration system in cold region. Effect of Ambient Temperature on the Performance of Micro Gas Turbine with Cogeneration System in Cold Region. Elsevier. http://hdl.handle.net/10213/1832. BENSMANN, A., HANKE-RAUSCHENBACH, R., & SUNDMACHER, K. (2013).Reactor configurations for biogas plants - a model based analysis. Chemical Engineering Science. 104, 413-426. GURUNG, A., & OH, S. (2013). Conversion of traditional biomass into modern bioenergy systems: A review in context to improve the energy situation in Nepal. Renewable Energy. 50, 206-213. HEARNS, E. C. (2006). Focus on biotechnology research. New York, Nova Science Publishers. LIN Y, WANG D, WU S, & WANG C. (2009). Alkali pretreatment enhances biogas production in the anaerobic digestion of pulp and paper sludge. Journal of Hazardous Materials. 170, 366-73. KARLSSON, A., & EJLERTSSON, J. (2012). Addition of HCl as a means to improve biogas production from protein-rich food industry waste. Biochemical Engineering Journal. 61, 43-48. KASTANEK F., MALETEROVA Y., DOUSKOVA I., DOUCHA J., ZACHLEDER V., & KASTANEK P. (2010). Utilization of distillery stillage for energy generation and concurrent production of valuable microalgal biomass in the sequence: Biogas-cogeneration-microalgae-products. Energy Conversion and Management. 51, 606-611. KOMEMOTO K, LIM YG, NAGAO N, ONOUE Y, NIWA C, & TODA T. (2009). Effect of temperature on VFA's and biogas production in anaerobic solubilization of food waste. Waste Management (New York, N.Y.). 29, 2950-5. MUDHOO, A. (2012). Biogas production pretreatment methods in anaerobic digestion. Hoboken, N.J., Wiley. http://www.books24x7.com/marc.asp?bookid=49557. NATIONAL RENEWABLE ENERGY LABORATORY (U.S.), & UNITED STATES. (2000). A biopower triumph -- The gasification story. Washington, D.C, United States. Dept. of Energy. http://www.osti.gov/servlets/purl/757164-yglBrV/native/. PICKEL, J. L. (2010). An evaluation of alternatives for enhancing anaerobic digestion of waste activated sludge. Waterloo, Ont, University of Waterloo. RUPPERT, H., KAPPAS, M., & IBENDORF, J. (2013). Sustainable bioenergy production-- an integrated approach. Dordrecht, Springer. http://public.eblib.com/choice/publicfullrecord.aspx?p=1317524. TAHERZADEH, M.J., & KARIMI, K. (2008). Pretreatment of lignocellulosic wastes to improve ethanol and biogas production: A review. Molecular Diversity Preservation International (MDPI) AG. Molecular Diversity Preservation International (MDPI) AG. http://hdl.handle.net/2320/3930. SRIVASTAVA, S. P., & HANCS?K, J. (2014). Fuels and Fuel-Additives. Hoboken, Wiley. http://public.eblib.com/choice/publicfullrecord.aspx?p=1598818. UNITED STATES. (2007). Improved Biomass Utilization Through Remote Flow Sensing. Washington, D.C., United States. Dept. of Energy. Office of Energy Efficiency and Renewable Energy. http://www.osti.gov/servlets/purl/901283-wTRx3o/. Read More

Karlsson & Ejlertsson (2012) illustrate that aerobic bacteria grow in the presence of oxygen whereas anaerobic bacteria grow in the absence of oxygen. The facultative bacteria on the other hand can grow in mediums where there is or there is no oxygen. The process of biogas production occurs in three successive stages namely hydrolysis, acid formation and methane formation respectively. a) Hydrolysis Hydrolysis, also referred to as liquidation stage is where waste matter initially containing carbohydrates, lipids, proteins and inorganic mater which are broken down by bacteria.

The breakdown involves reduction of complex long chained organic molecules into simpler shorter molecules which is done by action of extra cellular enzymes. This results in formation of simple molecules that can then undergo the acid formation stage. b) Acid Formation Stage Is where the fermented intermediate materials are transformed into acetic acid (CH3COOH) hydrogen and carbon (IV) oxide by acidic forming bacteria. This bacteria use all the present oxygen resulting in an anaerobic condition which fosters the work of methane-producing-micro-organisms that later start their action on the acidic media.

They include the acetogenic and the acidogenic types. Furthermore, these bacteria ensure components with low molecular weight are reduced into alcohols, amino acids and organic acids as well as into other forms such as carbon dioxide, hydrogen sulphide and methane in traces. c) Formation of Methane. This is the final stage involving methanogenic bacteria- the bacteria that produce the methane. These bacteria are sensitive to pH and require a mildly acidic media with pH values not below 6.2. They act by converting the formed compounds during the acid formation stage into low molecular weighing compounds such as methane and carbon dioxide anaerobically.

The resulting methane gas is usually affected by pressure, temperature and water vapour (Bensmann, Hanke-Rauschenbach & Sundmacher, 2013). The biogas formed is usually a mixture of gases in various percentages with methane taking 50 to 70 percent; carbon dioxide 30 to 40 percent; hydrogen 5 to 10 percent; nitrogen 1 to 2 percent; water vapour 0.3 and traces of hydrogen sulphide. 1.4 Problems to be Solved This research will be studied in a set of steps for easier modularized research and improvement as shown in the illustration diagram below.

Pre-treatment In this step pollutants like sand, metal and plastic are removed from the substrate that comes into the system. The mixture undergoes structure breakdown to increase the yield of the substrate. There are various technologies that can be applied to the substrate depending on the type. This also influences the number of stages the substrate will be allowed to pass through. Lignocelluloses form the largest mass of biomass and they are found in wastes from agricultural material and forest residue (Mudhoo, 2012).

They comprise three types of components that is lignin, cellulose and hemicelluloses that are interlinked together forming a crystal like structure. Their decomposition by bacteria is generally difficult because of its structural complexity their higher molecular weight. They, therefore, need appropriate pre-treatment to make them accessible by the hydrolytic enzymes hence resulting in the solubilisation of complex lignocelluloses (Kastanek et. al., 2010). This increases the general efficiency of the biogas plant.

There are various methods used in pre-treatment that were designed over the recent years. They include physical which involves both mechanical and non-mechanical treatment, chemical acid or alkaline hydrolysis, solvent extraction and delignification are used and physico-chemical method where we have ammonia fibre and steam explosion as well as carbon dioxide explosion. Most researchers prefer alkali pre-treatment as one of the best method of enhancing biodegradation of complex materials since biological pre-treatment leads to a high a high rate of biodegradability very high costs (Komemoto et. al., 2009).

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