Biogas Valorisation to Biomethane

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1		Chipo Shonhiwa	--	3016	2023-09-28 15:04:22	\|
2	update references and layout	Rita Xu	-34 word(s)	2982	2023-10-04 15:26:43	\| \|
3	update layout	Rita Xu	-1 word(s)	2981	2023-10-09 08:57:58	\|

This entry is adapted from the peer-reviewed paper 10.3390/en16145272

Biogas consists of mainly methane, as a source of energy, and impurities such as carbon dioxide, hydrogen sulphide, water, and siloxanes. These impurities, such as hydrogen sulphide, reduce the biogas energy content and corrode equipment that store, transport, or utilise biogas.

biogas biogas valorisation biogas upgrading biomethane

1. Introduction

The constitution of the Republic of South Africa (RSA) stipulates that everyone is entitled to a safe environment for their health and well-being ^[1]. The negative environmental impacts of poor waste management have led the South Africa National Waste Management Strategy (NWMS) 2020 to focus on the reduction of waste going to landfills by 70% through reuse, recycling, recovery, and alternative waste treatment in the next 15 years ^[2]. Anaerobic digestion (AD), whose benefits are shown in Figure 1, has established itself as an alternative technology to rid of organic waste that is diverted from landfills, wastewater, and farming biomass residue while producing biogas, an alternative source energy, whose global consumption has increased by 90% from 65 GW in 2010 to 120 GW in 2019 ^[3]. Biogas has the potential to enhance sustainable development, reduce energy related pollution, enable communities to manage their waste in a beneficial manner, contribute to the abatement of climate change, and stop firewood-linked deforestation. However, biogas applications are limited by the presence of impurities, namely 25–45% carbon dioxide (CO₂), 20–20,000 ppm hydrogen sulphide (H₂S), 2–7% water (H₂O), traces of ammonia (NH₃), siloxanes ((CH₃)₂2SiO)_n, oxygen (O₂), carbon monoxide (CO), nitrogen (N₂), and volatile organic compounds (VOCs) ^[4]^[5].

Figure 1. Benefits of anaerobic digestion.

The presence of CO₂ decreases the laminar flame speed, combustion efficiency, flammability limits, calorific value, rate of burning, and range of flame stability ^[6]. It is not easy to ignite biogas at a Reynolds number above 1200 because of the decreased flammability limit. The higher the CO₂ concentration in biogas, the lower the burning velocity and the lower the energy content. Thus, raw biogas is only suitable for low energy demanding applications, such as cooking and lighting. It lowers the biogas density, which results in the increased frequency of refilling fuel tanks for vehicles utilising biogas ^[7]. Additionally, it forms dry ice on valves, which makes it difficult to store biogas in containers, resulting in limited uses and transportation.

H₂S forms salt in machines by reacting with metals such as lead. It also reacts with H₂O to form sulphur dioxide, and further reaction results in the formation of sulphuric acid, which causes the wearing/corrosion of appliances that use, store, or transport biogas ^[6]. H₂O accumulates and condenses on surfaces and parts of transporting pipes and equipment that use biogas, where it causes rusting. H₂O also react with NH₃ to form ammonium hydroxide, which corrodes some metals, especially aluminium and copper. NH₃ also reacts with oxygen to form nitrous oxide, which has a global warming potential that is 273 greater than that of CO₂, making it a great contributor to climate change ^[8].

Nyamukamba et al. (2020) gave a detailed account of siloxanes, which they described as the most harmful trace compounds found in biogas since they are converted to silica that damages gas engines, turbines, or any other equipment that utilises the biogas ^[9]. During the combustion of biogas, the siloxanes react with oxygen to form silicon dioxide, which forms a layer on the wall surfaces of engine components, for example, combustion chambers, spark plugs and valves. Silicon dioxide is an abrasive electrical and thermal insulator, which causes the wear and tear of the combustion chamber cylinder surface and the impairment of lubricant distribution. This reduces the engines maintenance interval and limits their life, resulting in increased operational costs. Thus, it is advisable to use clean gas; although, different equipment have different tolerances for siloxanes. If released into the atmosphere, silicon dioxide is dangerous to human beings, as it can cause cancer.

The concentration of CH₄, which determines the calorific value of the biogas, is affected by the type and source of feedstock used and the digester operating conditions ^[10]. To add value to biogas, the impurities must be removed. The removal of harmful substances prevents the degradation of equipment that uses the biogas.

2. Biogas Valorisation to Biomethane

The techniques for biogas upgrading can be classified into sorption, separation, and in situ techniques, as shown in Figure 2. Sorption and separation are further classified depending on the basis of operation: adsorption, physical or chemical absorption, high- or low-pressure permeation/membrane separation, and cryogenic methods ^[6]^[11]^[12]. Each method comes with its advantages and disadvantages, such as social-economic effects, ambient impacts, methane loss, amount of energy needed for the process, complexity of using the equipment, and the accessibility of equipment or skilled workforce to operate the equipment ^[7]^[13]^[14]. In situ techniques involve biological methods that make use of living organisms to convert CO₂ to CH₄ and H₂O inside the biodigester. This results in an increase in CH₄ from 60% to 96%, together with a reduction of H₂S to insignificant levels. Various chemicals are also used to convert CO₂ to CH₄ in biodigesters.

Figure 2. Biogas upgrading techniques.

2.1. Common Methods of Biogas Upgrading to Biomethane

Various techniques have been discussed in depth by a number of researchers ^[6]^[7]^[9]^[12]^[13]^[15]^[16]^[17]^[18]. Absorption is divided into physical (water and organic) and chemical scrubbing. Water scrubbing makes use of higher solubility of CO₂ and H₂S than the CH₄ in water. For example, CO₂ is 26 times more soluble than CH₄ at 25 °C. Organic scrubbing is similar to water scrubbing, in that it makes use of a different solubility, but it requires higher energy at higher temperatures for the regeneration of solvents. Popular solvents are selexol^®, rectisol, and genosorb^®, and they can absorb CO₂, H₂S, and H₂O.

Chemical scrubbing is based on dissolving impurities, such as CO₂ and H₂S, in biogas via a reversible chemical reaction between the absorbent and the absorbate. Commonly used absorbents, which dissolve more gases per unit solvent volume than water, include monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA). Thus, smaller upgrading units are required in comparison to water scrubbing units. However, the requirements for absorbent regeneration make the process more expensive than water scrubbing.

Pressure swing adsorption (PSA) is a mass transfer process, in which the adsorbent selectively retains some molecules of biogas on its surface, based on molecular size, which is driven by differential partial pressure. For example, an adsorbent material with 0.37 nm pores will retain CO₂, which has 0.34 nm pores, while allowing CH₄, which has pores that are 0.38 nm. Although H₂S is retained, it is advisable to pre-treat the biogas to remove H₂S because it makes it difficult to regenerate the adsorbent. The effectiveness of the adsorption process is governed by the pressure of the adsorbate, the temperature of the system, and the size of the pores of adsorbent material. Common adsorbents include activated carbon, metal-organic frameworks, zeolites, silica gel, and molecular sieves. To reduce CH₄ loss, Augelletti et al. (2016) proposed and simulated an adsorbent process that utilised Zeolite 5A adsorbent material in two sections ^[19]. The biogas is input into the first section, where 98.9% pure CH₄ is produced. This process results in methane recovery of more than 99% while consuming approximately 1.25 MJkg⁻¹ of biomethane. Thus, there is great potential for the improvement of the PSA technology performance.

Membrane separation is based on the selective permeation of certain gas molecules through a selective permeable membrane. The biogas separates into the permeate fraction, comprised of CO₂, H₂O, O₂, and H₂S, and the retentate fraction, made up of CH₄ and N₂. The most-used membranes are polymeric membranes, which are made from organic materials, such as polysulphone, polyimide, polycarbonate, polydimethylsiloxane, and cellulose acetate. The less-popular membranes are inorganic and mixed matrix membranes.

The cryogenic process separates CH₄ from the impurities in biogas using difference in phase change temperature and distillation characteristics of the constituent molecules. At 1 atm, CO₂ condenses at −78.2 °C and is removed from biogas, leaving mainly CH₄, which has a boiling point of −161.5 °C. To prevent the clogging of pipes from frozen substances, H₂S, H₂O, siloxanes, and halogens are removed before cryogenic cleaning. This technology is still in its infancy but has started to penetrate the market. The simplest cryogenic process maintains a constant pressure of 10 bar, while the temperature is decreased in steps that remove the impurities. At −25 °C, H₂O, H₂S, and siloxanes are removed. The second step partially removes CO₂ at −55 °C by liquefication, while the last step removes all CO₂ at −85 °C by solidification.

The conventional technologies described above need pre-treatment to remove mainly H₂S. The technologies that remove both CO₂ and H₂S have higher running costs and significant negative impacts on the environment. Microalgae-based technologies have been developed to remove both CO₂ and H₂S from biogas ^[20]^[21]^[22]^[23]. These processes use CO₂ for microalgae photosynthesis and use the oxygen produced during photosynthesis to oxidise H₂S. Several experiments were carried out with a high-rate algal pond (HRAP) connected to an external absorption column (AC) for the simultaneous removal of CO₂ and H₂S ^[21]^[24]^[25]. Although there was the 100% removal of H₂S, that for CO₂ was not 100%, and in some cases, it was less than 80%. Additionally, the produced gas contained nitrogen and oxygen gases, which presents a drawback of this technology in upgrading biogas. To overcome this hinge, Toledo-Cervantes et al. (2016) optimised both the process of the photosynthetic upgrading of biogas and the recovery of nutrients from the digestate in an algal-bacterial HRAP that is connected to a biogas AC by recirculating the settled liquid ^[20]. This reduced the concentration of CO₂ to 0.4 ± 0.1%, oxygen to 0.03 ± 0.04%, and nitrogen to 2.4 ± 0.2%, while increasing the CH₄ purity to 97.2 ± 0.2%, which meets most European biomethane standards.

Another upcoming technology that simultaneously removes CO₂, nitrous oxides, and H₂S from biogas is the adsorption of impurity molecules on a solid surface, making use of physical or weak van der Waals forces that cause different gaseous molecules to selectively attach onto solid surfaces ^[26]. Porous materials, such as biochar, clay, and silica gel, are used as adsorbents. Mulu et al. (2021) compared clay dry adsorption with wet carbonation methods of upgrading biogas ^[27]. For wet carbonation, the optimal clay-to-water ratio was 1:3 at 75 °C. Sodium hydroxide-activated clay increased CO₂ by more than five times. H₂S was 100% removed, and removal rate of 93.8% for CO₂ was achieved. Sethupathi et al. found that the adsorption capacities of biochar differ according to its properties ^[28]. The successful use of clay and biochar is beneficial to small-scale digesters, who find the conventional technologies to be expensive because of low economies of scale ^[6]. A novel process involving the use of the dry adsorption of wood ash and carbonation technologies in the upgrading of biogas was created ^[29]. In this study, 88% CH₄ purity and 2.30 mmolg⁻¹-wood ash CO₂ uptake were achieved. A biogas flow rate of 100 mlmin⁻¹ was achieved at an adsorbent-to-water ratio of 1:4 for carbonation. Changing the mass of activated wood ash in dry adsorption from 2.5 to 35 g resulted in an 8.9 to 67.9% increase of CO₂ removal, which is not a significant improvement. Thus, it is advisable to use raw wood ash for household AD.

Some researchers proposed that ex situ biogas upgrading technologies are economically viable when used on a biogas plant that produces more than 2400 m³d⁻¹ biogas and recommended in situ for small/medium biogas plants ^[30]. There are a number of in situ methods, such as the addition of H₂ into the reactor, bio-electrochemical systems, high-pressure anaerobic digestion, and the addition of additives such as biochar and an up-flow anaerobic sludge blanket.

The technologies (first generation biogas upgrading technologies) described above have the disadvantage of not utilising CO₂ as an energy source. Researchers have started working on second generation biogas upgrading technologies, which make use of CO₂ for energy storage ^[31]. Most of these strategies are still in the demonstration stage. In Denmark, a demonstration plant was set to catalytically convert the CO₂ from biogas to CH₄ ^[32]^[33]. The first section of the plant removes most impurities from biogas and converts them to nutrients that can be added to slurry. The biogas is then passed on to the second section, where CO₂ reacts with green H₂ to produce CH₄ using the Sabatier process. The green hydrogen is produced from the electrolysis of water using wind energy. A stable steady-state CO₂ conversion rate was achieved, with more than 90% of CO₂ turned to biomethane.

2.2. Biogas Industry Status in South Africa

AD in South Africa started by the construction of a digester at a pig farm in Johannesburg in 1957, and the gas was used to run a six-horse-power Lister engine ^[34]^[35]. Since then, biodigesters have been installed by households, farmers, various institutions, and companies. There has been growing effort to understand opportunities and challenges in the biogas industry. This has led individuals, companies, government departments, and researchers to form organisations that work on biogas; one of these is the Southern African Biogas Industry Association (SABIA) in 2013, which has the representation of the industry in the country. In 2021, SABIA and the World Biogas Association requested the South African Minister of Environment, Forestry, and Fisheries to integrate biogas into national plans to enhance the achievement of the government commitment to the Paris Agreement ^[36]. This would enhance the growth of the biogas industry. Currently, 43 organisations, including one academic institution, are registered with SABIA ^[37]. Most of these companies have websites, but not much information is found on some of them.

Prior to 2000, mainly small-scale biodigesters were installed to produce biogas for space heating and cooking from livestock manure ^[35]. To date, the feedstock is diverse, including slaughterhouse waste, chicken waste, fruit waste, sugarcane bagasse, municipal solid waste, wastewater, cattle waste, and pig waste to name a few ^[34]. For the feedstock sources captured in the national biomass inventory, of which the majority is sugar and municipal solid waste in the KwaZulu-Natal, Gauteng, and Western Cape Provinces, it has been estimated that a total of 3 million Nm³d⁻¹ of biogas can be produced, as shown in Figure 3 ^[38]. Awareness raising and information sharing are being promoted, and tools that will enhance decision-making by interested stakeholders, such as a biogas guidebook for South Africa, have been developed, and some are available for free on websites ^[39].

Figure 3. Biogas potential yield by sector (Nm³d⁻¹).

The number and size of biogas plants have increased since the introduction of the technology, with household/domestic/micro producing <0.5 kW_e, small-medium (

0.05 \geq 1 {MW}_{e}

) and large-scale digesters being installed across the country ^[40]^[41]. In 2018, a total of 700 biodigesters were installed ^[34]^[41]. As a result of difficulties in finding information on the number of installed biodigesters, the 2018 installation of 350/700 was used to set a baseline for micro-biodigesters at 350 biodigesters in 2021 ^[41]^[42]. Thus, this research assumed the same baseline year and total installed biodigesters. This implies that in 2021 there were 350 small-medium and large-scale biodigesters. Plant benefits include selling electricity, saving by not buying electricity from Eskom, collecting gate fee revenue, and selling CH₄ and CO₂. In addition to these monetary benefits, the facilities also practice good waste management, which keeps their environments clean.

Currently, most biogas is being converted into electricity. A financial analysis was performed for small-medium scale commercial biogas plants that convert biogas into electricity under the current scenario, where waste is dumped in landfills and energy cost is low with subsidies from the government ^[40]. Small-scale plants were found not viable, while medium-scale plants were viable for facilities that have high waste management costs, such as abattoirs. The conclusions made indicated that high waste management costs, the availability of huge feedstock volumes, and high on-site energy needs enhance the financial viability of biogas commercialisation.

The price of electricity on the market is half the price of compressed biomethane when both are measured in gigajoules, being R235 GJ⁻¹ and R111 GJ⁻¹ for transport fuel and electricity, respectively ^[43]^[44]. Additionally, the taxes and levies that are put on liquid fuels are exempted on gaseous transport fuels. This makes the use of biogas as a fuel a more attractive option on the market. Thus, biogas producers will want to sell their gas to the transport sector if the infrastructure permits. However, their hopes may be frustrated by limited gas-filling stations, which are still very scarcely scattered in the country, as shown in Figure 4. Taking into account the limited gas-fuelling stations and the limited range travelled by a full tank of gas vehicle compared to conventional liquid fuel (diesel or petrol) vehicles, it is recommended that the focus be on fuelling vehicles that have recurring short routes, such as minibus taxis and public city buses ^[38].

Figure 4. The location of natural gas fuelling stations.

An assessment used to find the feasibility of using biomethane as a fuel for public transport revealed that a total of 230 ktony⁻¹ dry feedstock is available in Johannesburg and can generate 91.6 million Nm³y⁻¹ fuel grade CH₄, which can be used by approximately 2700 buses ^[45]. The study identified two sites that can be used for locating more than 2000 Nm³h⁻¹ biogas facilities to produce biogas and upgrade it to fuel up to 600 city buses ^[44].

The biogas sector is faced with historical challenges that may hinder the uptake of the technology, and as a result, all efforts used to valorise biogas into biomethane will be in vain. They include high capital costs for the design and construction of biogas digesters; the seasonal variation of feedstock, which may result in failure of the digester because of insufficient substrates; limited research to come up with local solutions to operational challenges; the cheap disposal of waste to landfills; the failure of previously installed biodigesters; and the presence of impurities in biogas, which reduce its calorific value and damage appliances using the gas ^[46]. Another drawback is the absence of a long-term demand for biomethane and enabling regulatory framework to support investment in biogas upgrading ^[38].

There are opportunities in the sector that would enhance its growth. The Renewable Energy Independent Power Producer Procurement Program (REIPPPP) aims to produce electricity from renewable energy resources, such as wind and biomass ^[47]. SABIA encourages municipalities and Eskom to buy surplus electricity from biogas plant operators ^[48]. The National Environmental Management: Waste Act has resulted in an improved regulatory environment; however, it still needs further improvement ^[49].

References

RSA. The Constitution of the Republic of South Africa; South African Government: Pretoria, South Africa, 1996.
Department of Environment Forestry and Fisheries. National Waste Management Strategy 2020; Department of Environment Forestry and Fisheries: Pretoria, South Africa, 2020.
Abanades, S.; Abbaspour, H.; Ahmadi, A.; Das, B.; Ehyaei, M.A.; Esmaeilion, F.; El Haj Assad, M.; Hajilounezhad, T.; Jamali, D.H.; Hmida, A.; et al. A Critical Review of Biogas Production and Usage with Legislations Framework across the Globe. Int. J. Environ. Sci. Technol. 2022, 19, 3377–3400.
Angelidaki, I.; Treu, L.; Tsapekos, P.; Luo, G.; Campanaro, S.; Wenzel, H.; Kougias, P.G. Biogas Upgrading and Utilization: Current Status and Perspectives. Biotechnol. Adv. 2018, 36, 452–466.
Ahmad, N.E.; Mel, M.; Sinaga, N. Design of Liquefaction Process of Biogas Using Aspen HYSYS Simulation. J. Adv. Res. Biofuel Bioenergy 2018, 2, 10–15.
Mulu, E.; Arimi, M.M.M.; Ramkat, R.C. A Review of Recent Developments in Application of Low Cost Natural Materials in Purification and Upgrade of Biogas. Renew. Sustain. Energy Rev. 2021, 145, 111081.
Kapoor, R.; Ghosh, P.; Kumar, M.; Vijay, V.K. Evaluation of Biogas Upgrading Technologies and Future Perspectives: A Review. Environ. Sci. Pollut. Res. 2019, 26, 11631–11661.
Understanding Global Warming Potentials. Available online: https://www.epa.gov/ghgemissions/understanding-global-warming-potentials (accessed on 11 February 2023).
Nyamukamba, P.; Mukumba, P.; Chikukwa, E.S.; Makaka, G. Biogas Upgrading Approaches with Special Focus on Siloxane Removal—A Review. Energies 2020, 13, 6088.
Seman, S.Z.A.; Idris, I.; Abdullah, A.; Shamsudin, I.K.; Othman, M.R. Optimizing Purity and Recovery of Biogas Methane Enrichment Process in a Closed Landfill. Renew. Energy 2019, 131, 1117–1127.
Bambokela, J.E.; Muzenda, E.; Belaid, M. Prospective synergy of biogas upgrading technologies with carbon capture and sequestration (CCS) techniques. In Proceedings of the International Conference on Industrial Engineering and Operations Management, Paris, France, 26–27 July 2018; IEOM Society International: Paris, France, 2018; pp. 3236–3249.
Schmid, C.; Horschig, T.; Pfeiffer, A.; Szarka, N.; Thrän, D. Biogas Upgrading: A Review of National Biomethane Strategies and Support Policies in Selected Countries. Energies 2019, 12, 3803.
Chinea, L.; Slopiecka, K.; Bartocci, P.; Alissa Park, A.H.; Wang, S.; Jiang, D.; Fantozzi, F. Methane Enrichment of Biogas Using Carbon Capture Materials. Fuel 2023, 334, 126428.
Lottering, L.E. Optimization and Feasibility Study of a Biogas to Biomethane Plant. Master’s Thesis, University of Johannesburg, Johannesburg, South Africa, 2019.
Kabeyi, M.J.B.; Olanrewaju, O.A. Biogas Production and Applications in the Sustainable Energy Transition. J. Energy 2022, 2022, 8750221.
Olugasa, T.T.; Odesola, I.F.; Oyewola, M.O. Biogas purification and compression for use in spark ignition engines. In Proceedings of the International Conference of Mechanical Engineering, Energy Technology and Management, IMEETMCON, Ibadan, Nigeria, 4–7 September 2018; pp. 274–280.
Baena, F.M.; Mónica, M.; Galán, R.; Vega, F.; Vilches, L.F.; Navarrete, B. Biogas Upgrading by Cryogenic Techniques. Environ. Chem. Lett. 2019, 17, 1251–1261.
Wanderley, R.R.; Knuutila, H.K.; Jakobsen, P. Analysis and Selection of Optimal Solvent-Based Technologies for Biogas Upgrading. Fuel 2021, 303, 121327.
Augelletti, R.; Conti, M.; Annesini, M.C. Pressure Swing Adsorption for Biogas Upgrading. A New Process Con Fi Guration for the Separation of Biomethane and Carbon Dioxide. J. Clean. Prod. 2017, 140, 1390–1398.
Toledo-Cervantes, A.; Serejo, M.L.; Blanco, S.; Pérez, R.; Lebrero, R.; Muñoz, R. Photosynthetic Biogas Upgrading to Bio-Methane: Boosting Nutrient Recovery via Biomass Productivity Control. Algal Res. 2016, 17, 46–52.
Bahr, M.; Diaz, I.; Dominguez, A.; Gonzalez-Sanchez, A.; Muñoz, R. Microalgal-Biotechnology as a Platform for an Integral Biogas Upgrading and Nutrient Removal from Anaerobic Effluents. Environ. Sci. Technol. 2013, 48, 573–581.
Meier, L.; Stará, D.; Bartacek, J.; Jeison, D. Removal of H2S by a Continuous Microalgae-Based Photosynthetic Biogas Upgrading Process. Process Saf. Environ. Prot. 2018, 119, 65–68.
Posadas, E.; Szpak, D.; Lombó, F.; Domínguez, A.; Díaz, I.; Blanco, S.; García-Encina, P.A.; Muñoz, R. Feasibility Study of Biogas Upgrading Coupled with Nutrient Removal from Anaerobic Effluents Using Microalgae-Based Processes. J. Appl. Phycol. 2016, 28, 2147–2157.
Serejo, M.L.; Posadas, E.; Boncz, M.A.; Blanco, S.; García-Encina, P.; Raúl, M. Influence of Biogas Flow Rate on Biomass Composition During the Optimization of Biogas Upgrading in Microalgal-Bacterial Processes. Environ. Sci. Technol. 2015, 49, 3228–3236.
Posadas, E.; Serejo, M.L.; Blanco, S.; Pérez, R.; García-Encina, P.A.; Muñoz, R. Minimization of Biomethane Oxygen Concentration during Biogas Upgrading in Algal-Bacterial Photobioreactors. Algal Res. 2015, 12, 221–229.
Upadhyay, A.; Kovalev, A.A.; Zhuravleva, E.A.; Kovalev, D.A.; Litti, Y.V.; Masakapalli, S.K.; Pareek, N.; Vivekanand, V. Recent Development in Physical, Chemical, Biological and Hybrid Biogas Upgradation Techniques. Sustainability 2023, 15, 476.
Mulu, E.; M’Arimi, M.; Ramkat, R.c.; Kiprop, A. Biogas Upgrade Using Modified Natural Clay. Energy Convers. Manag. X 2021, 12, 100134.
Sethupathi, S.; Zhang, M.; Rajapaksha, A.U.; Lee, S.R.; Nor, N.M.; Mohamed, A.R.; Al-Wabel, M.; Lee, S.S.; Ok, Y.S. Biochars as Potential Adsorbers of CH4, CO2 and H2S. Sustainability 2017, 9, 121.
Mulu, E.; M’Arimi, M.M.; Ramkat, R.C.; Mecha, A.C. Potential of Wood Ash in Purification of Biogas. Energy Sustain. Dev. 2021, 65, 45–52.
Zhao, J.; Li, Y.; Dong, R. Recent Progress towards In-Situ Biogas Upgrading Technologies. Sci. Total Environ. 2021, 800, 149667.
Villadsen, S.N.B.; Fosbøl, P.L.; Angelidaki, I.; Woodley, J.M.; Nielsen, L.P.; Møller, P. The Potential of Biogas; the Solution to Energy Storage. ChemSusChem 2019, 12, 2147–2153.
Gaikwad, R.; Villadsen, S.N.B.; Rasmussen, J.P.; Grumsen, F.B.; Nielsen, L.P.; Gildert, G.; Møller, P.; Fosbøl, P.L. Container-Sized CO2 to Methane: Design, Construction and Catalytic Tests Using Raw Biogas to Biomethane. Catalysts 2020, 10, 1428.
MeGa-stoRE—Final Report of Project No 12006; Center for Energy Technologies: Herning, Denmark, 2015.
Mutungwazi, A.; Mukumba, P.; Makaka, G. Biogas Digester Types Installed in South Africa: A Review. Renew. Sustain. Energy Rev. 2018, 81, 172–180.
Manala, C.; Madyira, D.; Mbohwa, C.; Shuma, R. Summary-view: Biomass anaerobic respiration technology in South Africa. In Proceedings of the 7th International Conference on Appropriate Technology, Victoria Falls, Zimbabwe, 23–26 November 2016.
World Biogas Association. Available online: https://www.worldbiogasassociation.org/south-african-and-world-biogas-associations-urge-s-a-government-to-integrate-biogas-into-their-plans-to-meet-paris-agreement-commitments/ (accessed on 12 June 2023).
SABIA. Available online: https://sabia.org.za/membership-directory/company (accessed on 16 June 2023).
Department of Environmental Affairs of South Africa. Facilitation of Large-Scale Uptake of Alternative Transport Fuels in South Africa—The Case for Biogas; Department of Environmental Affairs of South Africa: Pretoria, South Africa, 2015.
DFFE. Biogas Guidebook for Small- to Medium-Scale Industrial Biogas Plants in South Africa; Department of Forestry, Fisheries, and the Environment: Pretoria, South Africa, 2021.
Gogela, U.; Salie, Y.; Pineo, C.; Basson, L. The Business Case for Biogas from Solid Waste in the Western Cape; GreenCape: Cape Town, South Africa, 2017.
SANEDI; UJ-TRCTI; UJ-PEETS; SABIA. Sector Development Plan for the Micro-Digester Sector in South Africa: Pathways to Growth and Sustainability by 2030; South African National Energy Development Institute: Johannesburg, South Africa, 2022.
Muvhiiwa, R.; Hildebrandt, D.; Chimwani, N.; Ngubevana, L.; Matambo, T. The Impact and Challenges of Sustainable Biogas Implementation: Moving towards a Bio-Based Economy. Energy Sustain. Soc. 2017, 7, 20.
Laks, R. The Potential for Electricity Generation from Biogas; Energy Research Centre of the Netherlands: Petten, The Netherlands, 2017.
William, S.; Mapako, M.; Szewczuk, S.; Blanchard, R.; Hugo, W. Biogas for Mobility: Feasibility of Generating Biogas to Fuel City of Johannesburg Buses. In Proceedings of the International Conference on the Industrial and Commercial Use of Energy (ICUE), Cape Town, South Africa, 15–16 August 2017; pp. 1–8.
Niklasson, J. Can Organic Waste Fuel the Buses in Johannesburg? Master’s Thesis, Linköping University, Linköping, Sweden, 2018.
Mukumba, P.; Makaka, G.; Mamphweli, S. Biogas Technology in South Africa, Problems, Challenges and Solutions. Int. J. Sustain. Energy Environ. Res. 2016, 5, 58–69.
South African Government. Available online: https://www.gov.za/about-government/government-programmes/renewable-independent-power-producer-programme (accessed on 15 June 2023).
Creamer Media’s Engineering News. Available online: https://www.engineeringnews.co.za/article/biogas-holds-great-power-generation-potential-2021-03-19 (accessed on 15 June 2023).
South African Government. Available online: https://www.gov.za/documents/national-environmental-management-waste-act (accessed on 15 June 2023).

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Chipo Shonhiwa

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Update Date: 09 Oct 2023

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