Biogas Utilization Research Articles

Carbon footprint of anaerobic digestion combined with ultrasonic post-treatment of agro-industrial organic residues

Anaerobic digestion (AD) of organic waste, although widely practiced, may require suitable accompanying treatments to enhance the degradability of complex materials. Since these may require significant efforts in terms of energy and chemical demand, careful assessment of their overall environmental sustainability is mandatory to evaluate their full-scale feasibility. The study aims to represent the environmental profile of ultrasonication (US) applied as a post-treatment of anaerobic digestion of agro-industrial organic residues. There is an interest in the US treatment for the processing of complex organic materials prior to AD in order to enhance the hydrolysis of complex organic substrates and increase the biogas yield of the biological process. An attributional, process-based life cycle assessment (LCA) study was applied to quantify and compare the potential environmental impacts of an AD plant, the biogas utilization options as well as the different digestate processing alternatives grouped into a set of 16 scenarios. Based on the results, upgrading of biogas and bio-methane use as vehicle fuel instead of energy generation from CHP or fuel cell was recommended due to the lower impact on GWP. Similarly, composting was a suitable option to reduce environmental impacts compared to belt drying. From the uncertainty analysis, AD without US as post-treatment proves to be more sustainable in terms of GWP compared to when US is used, showing net savings in GHG emissions especially when upgrading of biogas is applied. The analysis provides useful indications to policy makers to define sustainable management alternatives for organic residues as well as identify the environmental advantages associated with biogas utilization and digestate treatment and disposal alternatives.

Optimizing the co-digestion supply chain of sewage sludge and food waste by the demand oriented biogas supplying mechanism.

Co-digestion of sewage sludge with food waste is a beneficial pathway for sewage plants to enhance their biogas yield. This paper employs hybrid programming with system dynamics simulation to optimize such a co-digestion system from the perspective of demand-oriented biogas supply chain, thus to improve the efficiency of the biogas utilization. The optimum operational parameters of the co-digestion system are derived from the simulation model. It is demonstrated that the demand-oriented biogas supply mechanism can be effectively driven under market-oriented incentive policy. For better compensation of the external cost to assist the operations of the co-digestion supply chain, it is suggested that the substrate collection and transportation subsidy should be combined with the renewables portfolio standard to be implemented as the optimum incentives. The limitations of the study are discussed to lay the foundation for future improvements.

Analysis of a biogas-fed SOFC CHP system based on multi-scale hierarchical modeling

Biogas is an abundant renewable energy source which can be produced by anaerobic treatment of biological waste such as sewage sludge, agro-industrial waste, and industrial animal waste. The utilization of biogas instead of fossil fuels in a solid oxide fuel cell (SOFC)-based system is a promising choice to achieve a fossil-free and sustainable energy future. A biogas-fed decentralized SOFC combined heat and power (CHP) system model is proposed and analyzed. The system consists of a pre-reformer, an SOFC stack, an afterburner and a heat-recovery boiler. The system model integrates a multi-scale hierarchical three-dimensional SOFC stack model with zero-dimensional balance of power component models, which enables simultaneous investigations of both the overall system performance and the stack-internal distributed properties down to the electrode scale. The effects of steam/carbon ratio, biogas composition and operation voltage of the SOFC stack on the electrical and CHP efficiencies of the system, as well as the temperature gradient within the SOFC stack were studied. The proposed system model is demonstrated as an insightful and powerful tool for designing hybrid SOFC combined heat and power systems.

Carbon Nanotube Formation on Cr-Doped Ferrite Catalyst during Water Gas Shift Membrane Reaction: Mechanistic Implications and Extended Studies on Dry Gas Conversions

A nanocrystalline chromium-doped ferrite (FeCr) catalyst was shown to coproduce H2 and multiwalled carbon nanotubes (MWCNTs) during water gas shift (WGS) reaction in a H2-permselective zeolite membrane reactor (MR) at reaction pressures of ~20 bar. The FeCr catalyst was further demonstrated in the synthesis of highly crystalline and dimensionally uniform MWCNTs from a dry gas mixture of CO and CH4, which were the apparent sources for MWCNT growth in the WGS MR. In both the WGS MR and dry gas reactions, the operating temperature was 500 °C, which is significantly lower than those commonly used in MWCNT production by chemical vapor deposition (CVD) method from CO, CH4, or any other precursor gases. Extensive ex situ characterizations of the reaction products revealed that the FeCr catalyst remained in partially reduced states of Fe3+/Fe2+ and Cr6+/Cr3+ in WGS membrane reaction while further reduction of Fe2+ to Fe0 occurred in the CO/CH4 dry gas environments. The formation of the metallic Fe nanoparticles or catalyst surface dramatically improved the crystallinity and dimensional uniformity of the MWCNTs from dry gas reaction as compared to that from WGS reaction in the MR. Reaction of the CO/CH4 mixture containing 500 ppmv H2S also resulted in high-quality MWCNTs similar to those from the H2S-free feed gas, demonstrating excellent sulfur tolerance of the FeCr catalyst that is practically meaningful for utilization of biogas and cheap coal-derived syngas.

Upgrading of Biogas to Methane Based on Adsorption

Upgrading raw biogas to methane (CH4) is a vital prerequisite for the utilization of biogas as a vehicle fuel or the similar field as well. In this work, biogas yield from the anaerobic fermentation of food waste containing methane (CH4, 60.4%), carbon dioxide (CO2, 29.1%), hydrogen sulfide (H2S, 1.5%), nitrogen (N2, 7.35%) and oxygen (O2, 1.6%) was upgraded by dynamic adsorption. The hydrogen sulfide was removed from the biogas in advance by iron oxide (Fe2O3) because of its corrosion of the equipment. Commercial 13X zeolite and carbon molecular sieve (CMS) were used to remove the other impurity gases from wet or dry biogas. It was found that neither 13X zeolite nor CMS could effectively remove each of the impurities in the wet biogas for the effect of water vapor. However, 13X zeolite could effectively remove CO2 after the biogas was dried with silica and showed a CO2 adsorption capacity of 78 mg/g at the condition of 0.2 MPa and 25 °C. Additionally, 13X zeolite almost did not adsorb nitrogen (N2), so the CH4 was merely boosted to ac. 91% after the desulfurated dry biogas passed through 13X zeolite, nitrogen remaining in the biogas. CMS would exhibit superior N2 adsorption capacity and low CO2 adsorption capacity if some N2 was present in biogas, so CMS was able to remove all the nitrogen and fractional carbon dioxide from the desulfurated dry biogas in a period of time. Finally, when the desulfurated dry biogas passed through CMS and 13X zeolite in turn, the N2 and CO2 were sequentially removed, and then followed the high purity CH4 (≥96%).

ORGANIC CYCLE SYSTEM: THE RECYCLING OF BIOGAS SLUDGE OF COW MANURE AS BIOCHAR FOR BIOGAS PURIFICATION

The increase in intensive using of production elements has been reflected on the increasing of organic waste. Without appropriate treatment, waste leads to the contamination of environment. The conversion of organic waste into material with economic value will contribute to increasing productivity, for example in biogas system. Today, the utilization of waste, biogas sludge, as bio-fertilizer has been developed. However, the utilization of biogas sludge from cow manure as biochar is still rare. The aims of this study were to investigate the recycling of biogas sludge from cow manure as biochar in biogas purification. Biochar made of biogas sludge from cow manure as adsorbent in biogas purification leads to the cycle loop of biogas system. We also investigated the effect of mass variation of biochar made of biogas sludge from cow manure on biogas purification performance. The variation of zeolite and biochar made of biogas sludge with mass ratio of 0:80; 20:60; 40:40; 60:20; and 80:0 had been put inthe adsorption column of biogas purification. The results showed that the increase in biochar mass affected on methane enrichment of biogas. The highest methane enrichment was performed by biochar with ratio 40:40. The utilization of biochar mass above 50% of the total mass per each column decreased methane enrichment. From this study, we concluded that biogas sludge has potential to be used as adsorbent in biogas purification. Biochar from biogas sludge leads to organic cycle system in biogas system that provides option in sustainable energy and additional benefits for farmers.

Microbial electrolysis cell produced biogas as sustainable electron donor for microbial chromate reduction

Microbial electrolysis cell (MEC) is an attractive technology to produce biogas containing hydrogen (H2) and methane (CH4). Both gaseous products are effective electron donors for chromate [Cr(VI)] bioreduction when either is applied individually. However, microbial Cr(VI) reduction driven by H2 and CH4 mixture remains poorly understood. This study investigates Cr(VI) biotransformation supported by fluctuant MEC-produced biogas. Synergy between H2 and CH4 promoted Cr(VI) detoxification. Maximum Cr(VI) removal rate reached 1.81 ± 0.17 mg/L·d with 200.5 ± 13.6 μmol H2 and 203.3 ± 9.0 μmol CH4 produced by MEC at 0.6 V in a 4-d cycle. Biogas yield and H2/CH4 mole ratio were mainly regulated by Geobacter and Methanobacterium. The process in which Cr(VI) reduced to insoluble Cr(III) was proposed in two major pathways. A single autohydrogenotrophic genus (e.g., Hydrogenophaga, Thiobacillus) oxidized H2 independently coupled with Cr(VI) reduction. Cr(VI) reduction was also achieved through CH4-metabolizing microorganisms (e.g., Methanobacterium, Methanosaeta), which convert CH4 into organic metabolites to donate electrons for heterotrophic Cr(VI) reducers (e.g., Geobacter, Anaerolineaceae). Genes relevant to Cr(VI) reduction (yieF) and CH4 oxidation (mcrA) increased significantly. Electrons were effectively transferred through extracellular cytochrome c and intracellular nicotinamide adenine dinucleotide. This study offers an innovative route to sustainable bioremediation of Cr(VI)-polluted groundwater and promising direct utilization of mixed biogas from MEC.

UPGRADING BIOGAS TO A BIOMETHANE BY USE OF NANO-STRUCTURED CERAMIC MEMBRANES

In order to meet the demands of growing economies while considering environmental implications, the use of clean and renewable sources of energy has increasingly become of interest. Biogas utilisation is a means by which these rising needs can be met. This involves the use of waste materials; which are deposited on a daily basis by agriculture, sewage, household, to produce energy that may be used for heating, electricity, transportation and other daily needs. This paper would look into the use of nano-structured ceramic membranes for the upgrading of biogas to a high value fuel that can be used for a variety of purposes. The use of membranes offers great advantages including low running costs, high efficiency and the elimination of the need for phase change of the gas. Experiments were carried out using membranes of different pore sizes (15nm, 200nm and 6000nm) to ascertain which would be the most suitable for use in terms of permeability and yield of product gas. The 15nm membrane showed the greatest exit flow of methane compared to carbon dioxide and a mechanism approaching an ideal knudsen regime. Taking into account the effect of molecular weight and viscosity, these results show that the smallest membrane pore size of 15nm had a greater impact on the flow mechanism and thus improvement can be made by modification of the membrane to achieve a mechanism of surface diffusion of the particles.

Advances in biogas valorization and utilization systems: A comprehensive review

The emission of greenhouse gases and global warming are the major environmental concerns that has affected the normal geochemical cycles and climate conditions on the earth. However, a controlled production, conversion and utilization of these gases for energy generation in day to day activities of human beings can solve the problem of climate change effectively. Biogas has been recognized as a source of renewable energy available to considerably accelerate the socio-economic development. It is a multifaceted fuel containing methane, carbon dioxide and water vapors with multiple utilization options. Biogas can be valorized either directly or indirectly for various applications like the production of value-added chemicals or as a replacement of natural gas. This review article provides an in-depth analysis of various biogas valorization methods (physical, chemical and biological) for its efficient and eco-friendly utilization. The review intends to fill-up the knowledge gap through critically reviewing biogas cleaning and upgrading methods for biomethane and bio-CO2 production for various applications including power plants, transport and value-added chemicals. The review article also highlights the conversion of biogas into fine chemicals and products of commercial importance. Chemical, biological and hybrid systems of biogas utilization are described in detail. The opportunities and impediments associated with the valorization of biogas, biomethane and bio-CO2 have also been discussed. The paper highlights that most of the approaches to the implementation of biogas are in their infancy stage. It also identifies the bottlenecks, policies and future research and developments that are still needed in this relatively emerging field.

Carbon emission and energy potential of a novel spatiotemporally anaerobic/semi-aerobic bioreactor for domestic waste treatment

The biogas generation mechanism and its utilization potential in a novel spatiotemporally anaerobic/semi-aerobic bioreactor (STASAB) system with three activated bioreactors (C1, C2 and C3) was analyzed. Methane generation potential was obtained by measurements and estimation methods with similar values of 23.38 and 27.79 kg CH4/t waste, respectively. CH4 and CO2 production was quickly achieved in the STASAB, and the total amount of CH4 and CO2 was low due to the mixed leachate-recirculation operation process among bioreactors, which were at different stages of operation. The microbial communities in different bioreactors were diverse. The leachate-recirculation operation was a critical parameter to effectively enhance the microbial community structure in the STASAB, which can regulate CH4, CO2 and N2O production with global warming potential of 7.479 kg CO2e/(t·d). The STASAB had higher energy potential of 1.011 kWh/(t·d) compared with that of conventional landfills and sequentially anaerobic/semi-aerobic bioreactors. Moreover, direct electricity production in the STASAB is recommended for energy utilization with 38.38% GHG emission reduction, and with 131.43 million CNY (Chinese Yuan) benefit per year for national rural waste disposal via utilization of biogas from the STASAB for power generation. Hence, the STASAB shows a notable potential for treating domestic waste in rural areas.

Analysing household biogas utilization and impact in rural Ethiopia: Lessons and policy implications for sub-Saharan Africa

This paper analyses the current utilization level, performance and impact of domestic biogas plants in rural Ethiopia from a case study in four districts. Data were collected from a cross-sectional survey of 605 randomly selected households and direct field examination of 32 digesters. The study finds that, despite growing efforts, the dissemination and use of biogas plants in rural Ethiopia is still low. Of the total 32 biogas plants investigated, only 21 were found functional. Most of the digesters constructed are of 6m3 capacity and the main feedstock used is cow-dung. The average quantity of biogas produced from a 6m3 functional plant was calculated at 0.61 m3/day; of which 0.50 m3/day is consumed for cooking and 0.11 m3/day is consumed for lighting. This implies that the current level of biogas use could replace the consumption of 631.7 kg of fuelwood and 25 L of kerosene per user household per year. However, comparative analysis of the total energy consumptions of biogas user and non-user households revealed that the effect of biogas use in reducing household fuelwood and kerosene consumption was insignificant. Given the high capital cost of biogas installation, the findings suggest that a thorough revisiting of existing biogas dissemination and utilization approaches is critical if the technology is to induce significant impact on the rural energy supply. In view of this, important lessons and policy implications drawn from this case study and international experiences are analysed and discussed.

Strategies to Promote Biogas Generation and Utilisation from Palm Oil Mill Effluent

Palm oil mills generate a large amount of wastewater, known as palm oil mill effluent, during the production of crude palm oil. The high organic contents in palm oil mill effluent have an excellent potential for biogas utilisation. Besides, such effluent must be further treated before discharge or reused in milling processes. In this respect, an integrated biogas and wastewater treatment system should be developed. The aim of this paper is to synthesise and optimise an integrated biogas and wastewater treatment system via a process systems engineering tool that yields maximum economic performance. To illustrate the proposed approach, a typical palm oil mill case study in Malaysia is presented. The variation in palm oil mill effluent availability is considered to evaluate the changes in performance and ensuring the flexibility of the developed system. As shown in the results, implementation of integrated biogas and wastewater treatment system in a typical 60 t/h mill in Malaysia could export up to 1.9 MW electrical power on average. Alternatively, 110,800 GJ/year of compressed biomethane can be produced when feed-in to the national grid is not available. The implementation of integrated biogas and wastewater treatment system successfully reduces greenhouse gas emissions by 50,430 t CO2e/year as compared with the conventional open ponding system practiced in the industry. Lastly, feasibility studies and strategies to promote biogas utilisation in the industry are performed.

Recent Developments in Biogas Manufacture and Biogas Utilization: A Review

The various developments in the areas of biogas manufacture and utilization have been surveyed. This includes alternate / multiple substrates that could be economically employed for biogas production, biogas enrichment (carbon dioxide removal), biochemical desulfurization of biogas, utilization of enriched, desulfurized biogas as automobile fuel (in place of CNG, LNG), for the production of syngas and a host of chemicals (including nitrogenous fertilizers) therefrom, production of phosphatic biofertiliser from ADS (anaerobic digester sludge) and synthesis of liquid fuels (mainly, motor gasoline) using Fischer – Tropsch process. The technical details and economic viability of each process have also been analyzed and highlighted.

Recent advances on anaerobic digestion of swine wastewater

Anaerobic digestion is a valuable technology for the elimination of biodegradable pollutants and stabilization of agro-industrial wastes. This review focuses on the AD of wastewaters derived from swine production within the scope of wastewater treatment and bioenergy production. Fundamental principles of AD as a biochemical and microbiological process are described. The effect of essential parameters is also examined in the context of swine wastewater, especially the relation between chemical and operational factors, process stability and performance. The review continues with a discussion of current trends and future achievements in AD research of swine wastes, namely co-digestion with carbon-rich substrates, integration with pretreatment methods, process enhancement via the use of additives, and digestate management. Finally, a brief outlook on the economy of biogas utilization is provided to better understanding the future of AD as biotechnology for on-farm treatment of swine wastewater.

The potential use of human urine as a solvent for biogas upgrading

Biogas upgrading through chemical absorption is an energy-intensive and costly process, but it is essential for the higher-value utilization of biogas as biomethane. The loss of absorbents and the energy consumption for their regeneration lower the economic viability of the process. This study investigated the potential of human urine as an economical and sustainable source of solvent for biogas upgrading. Hydrolyzed urine (HU) is rich in ammonia (>4.4 g N/L) and alkaline (approximately pH 9), which makes it attractive as an absorbent to capture CO2. The hydrolysis characteristics of urine were assessed with and without urease addition at different temperatures (4, 25, and 35 °C). Urease induced immediate urine hydrolysis, and temperature had a more significant effect on the hydrolysis rate when urease was not added. Conductivity, but not pH, proved to be a reliable indicator for monitoring urine hydrolysis. The CO2 capture capacity observed in the biogas upgrading experiments with simulated biogas (60% CH4 and 40% CO2, v/v) was 0.41–0.53 mol CO2/mol total ammonia nitrogen (TAN). The experiments using real biogas (71% CH4) showed that CO2 was effectively captured by HU with complete removal of H2S (2440 ppmv). This study is the first to demonstrate the direct use of HU as a sole solvent for biogas upgrading and suggest the possibility of recovering fertilizer material (e.g., ammonium bicarbonate, NH4HCO3) from the spent HU. The results suggest interesting opportunities to improve the economic feasibility of biogas upgrading and to valorize human urine.

Economic Feasibility and Comprehensive Benefit Evaluation of Rural Household Biogas Utilization: Evidence from China

It is of great significance for the scientific formulation or adjustment of rural energy policy in the new era to explore the current situation of rural household biogas utilization and make a comprehensive evaluation of the benefits of biogas and its derivatives. Based on the field survey data of Qionglai, Sichuan Province, this study uses AHP to build a comprehensive evaluation index system, uses financial indicators to calculate the economic benefits of household biogas, and establishes the weight and score of the index system to comprehensively evaluate the economic, ecological and social benefits of biogas and its derivatives utilization in the survey area. The research results show that the economic benefits and social benefits of rural household biogas are good, but the ecological benefits are not up to the ideal level. Under the background of rapid development of new rural construction and urbanization, the government still needs adjusting policies, so as to meet the challenges of structural changes in the domestic energy consumption market.

Influence of flame quenching and crevice gas on hydrocarbon emission formation in an enriched biogas dual-fuel engine – An experimental and theoretical investigation

Enriched biogas is a promising alternate fuel candidate for compression ignition engines which are used in transportation sector. However, utilization of enriched biogas in compression ignition engines under dual-fuel mode suffer a major problem of high hydrocarbon emission particularly at part load operations. Main causes for this problem are inadequately understood which foils for active penetration of dual-fuel technology in the automotive market. To address this research gap, the current work is focused to investigate the effects of flame quenching and crevice gas (i.e., trapped between cylinder barrel and piston rings) on hydrocarbon emission formation. Investigation was carried out on enriched biogas dual-fuel engine of 3.7 kW rated power at 1500 rpm at part load of 50%. It was explored that both quench and crevice hydrocarbon emissions together are in the range of 60% to 92% of total hydrocarbons. Total hydrocarbon emission level increased from 2 g/kWh with base diesel operation to 56 g/kWh with 77% enriched biogas energy share. Overall, it is emerged that the crevice mechanism plays a dominant role for high hydrocarbon emission levels in enriched biogas dual-fuel engines.

Future transport policy designs for biomethane promotion: A system Dynamics model

In this paper, we present a dynamic simulation tool for biomethane policy design in Latvia. A new System Dynamics based computer simulation model covering the whole biogas-to-biomethane value chain including bioresource availability, biogas production and biogas utilization pathways is proposed. The goal of the model is to evaluate the efficiency of a set of policy instruments on increasing the transition from biogas for electricity production to biogas upgrading to be used as a transportation fuel thus contributing to national renewable energy targets in the transport sector by 2030. According to the modeling results, policy design should be focused on two directions, reducing the existing support mechanisms for electricity producers and subsidizing biomethane production, namely. Additional benefits are brought by tax policies aiming to increase the price of competing fossil fuels.

Biogas beyond CHP: The HPC (heat, power & chemicals) process

The techno-economic feasibility of three biogas utilization processes was assessed through computer simulations on commercial process simulator Aspen HYSYS: HPC (biogas to methanol), BioCH4 (biogas to biomethane) and CHP (biogas to heat & electricity). The last two processes are already used commercially with the aid of subsidy policies. The economic analysis indicates that, without these policies, none of these attain economic self-sustainability due to high overall manufacturing costs. The estimated minimum support cost (MSCs) were 108, 62 and 109 €/MWh for the HPC, BioCH4 and CHP processes, respectively. The model could explain currently practised government subsidies in Italy and Germany. It was seen that the newly proposed HPC process is economically comparable to the traditional CHP process. Therefore, the HPC process is a possible alternative to biogas usage. A support policy was proposed: 50, 66, 158 and 148 €/MWh for available heat, methane, electricity and methanol (respectively); the proposed energy policy results in a 10% OpEx rate of return for any of the processes, thus avoiding a disparity in the production of different products.

Multi-objective optimal design for integrated palm oil mill complex with consideration of effluent elimination

To reduce greenhouse gas (GHG) impact while sustaining palm oil mill (POM) profitability, Malaysia has recognised POME-derived biogas as a renewable energy. Biogas utilisation for on-site fuel replacement and grid electricity contribution is encouraged by government schemes such as Feed-in-tariff (FiT). Nevertheless, adoption rate of biogas facility is still low among Malaysian POMs. An integrated palm-oil based complex (POBC) was proposed for GHG mitigation by integrating POM and refinery processes while addressing sustainability concerns. This study presented a multi-objective optimisation model-based approach to aid POBC planning at maximised economic potential and net energy, while minimising its GHG emission, water footprint (WFP) and land footprint (LFP) for environment protection. Trade-offs between biogas recovery and POME elimination strategies were considered. The developed fuzzy model was applied to case study and analysed under different multi-objective scenarios. In comparison with baseline study, the economic potential of sustainable POBC increase by 6.7% at USD 39.31 × 106 with 88%, 74% and 91% improvements in GHG footprint, WFP and LFP by compromising 76% net energy. Effect of FiT revenue towards POBC synthesis was investigated. Pareto front was generated to verify the fuzzy results and visualise the relationship between objective functions. The optimisation model and optimal results shall provide input to Malaysian POMs on the sustainability benefits of POBC.