Recognizing the challenges of anaerobic digestion: Critical steps toward improving biogas generation (original) (raw)
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Journal of Renewable and Sustainable Energy
Anaerobic digestion (AD), one of the most promising routes for producing clean energy from biodegradable wastes, encounters difficulties at operational and mechanistic levels impacting its overall efficiency. Along with other solutions to overcome this problem, biochar has arrived as a worthwhile additive to enhance the performance of the process. This review aims to discuss various perspectives of biochar addition to an anaerobic digester. It summarizes the mechanism of biochar action during AD. A direct inter-species electron transfer offers a synergistic mechanism specifying different aspects of biogas production. The importance of characteristics of biochar (ion-exchange capacity, surface properties, electrical conductivity, and hydrophobicity) has been explained in enhancing AD performance. Studies indicate that a surface area >150 m2/g and a particle size <1 cm can be referred to as benchmark along with its supporting properties apt for AD. Researchers have recommended v...
Energy Conversion and Management, 2020
Applying carbon-based additives can be an ideal strategy to maximise biogas yield, due to low operating costs and high adaptability to large scale implementation. Although several studies have revealed the positive impact of carbon-based additives on biogas generation, the mechanisms and reasons behind this have not yet been comprehensively studied for anaerobic digestion of organic waste. The mechanism of direct interspecies electron transfer (DIET) has been widely used to describe the effect of carbon-based additives on anaerobic processes. However, there are other mechanisms which are associated with this process. In this study, activated carbon and biochar were used as additives in anaerobic digestion (AD) of the organic fraction of municipal solid waste. Thermogravimetric, physical and chemical analyses were conducted to investigate the effect of these additives on the degradation process. The results showed a direct relationship between the thermogravimetric characteristics and the reaction rate. Using 20 g/L biochar significantly increased the rate of AD for all types of biochar, as confirmed by the thermogravimetric results. The physical properties of the additives, including electrical conductivity and surface area, were found to influence only the rate of AD process and not the biogas production yield. Biochar showed more promising results in terms of biogas generation compared to activated carbon due to its ability to adsorb ammonia nitrogen. Although activated carbon efficiently increased the organic degradation rate, concentrations higher than 10 g/L dramatically increased the ammonia nitrogen concentration, which resulted in hindering the methanogenic bacteria activity due to its inhibitory effect. As a result, biogas generation yield did not increase using a high concentration of activated carbon.
2021
The generation of huge amounts of food waste due to the increasing population is a serious global issue. The inadequate management of food waste and lack of proper handling approaches have created adverse negative impacts on the environment and the society. The use of traditional disposal (i.e. landfilling) and treatment (i.e. incineration and composting) methods are not considered to be efficient for managing food waste. Thus, anaerobic digestion (AD) has proven to be promising and cost-effective, as an alternative technology, for digesting and converting food waste into renewable energy and useful chemicals. However, mono-digestion of food waste suffers from process inhibition and instability which limit its efficiency. Adding biochar that has high buffering capacity and ensures optimum nutrient balance was shown to enhance biogas/methane production yields. This review reports on the physicochemical characteristics of food waste, the existing problems of food waste treatment in AD as well as the role of biochar amendments on the optimization of critical process parameters and its action mechanisms in AD, which could be a promising means of improving the AD performance. Also, this review provides insights regarding the selection of the desired/appropriate biochar characteristics, i.e. depending on the source of the feedstock and the pyrolysis temperature, and its role in enhancing biogas production and preventing the problem of process instability in the AD system. Finally, this review paper highlights the economic and environmental challenges as well as the future perspectives concerning the application of biochar amendments in AD.
Foods
This study proposed the selection of cost-effective additives generated from different activity sectors to enhance and stabilize the start-up, as well as the transitional phases, of semi-continuous food waste (FW) anaerobic digestion. The results showed that combining agricultural waste mixtures including wheat straw (WS) and cattle manure (CM) boosted the process performance and generated up to 95% higher methane yield compared to the control reactors (mono-digested FW) under an organic loading rate (OLR) range of 2 to 3 kg VS/m3·d. Whereas R3 amended with unmarketable biochar (UBc), to around 10% of the initial fresh mass inserted, showed a significant process enhancement during the transitional phase, and more particularly at an OLR of 4 kg VS/m3·d, it was revealed that under these experimental conditions, FW reactors including UBc showed an increase of 144% in terms of specific biogas yield (SBY) compared to FW reactors fed with agricultural residue. Hence, both agricultural and...
Biomass Conversion and Biorefinery
Anaerobic digestion (AD) is a well-known biological conversion process to obtain a gaseous biofuel from organic matter: in fact, upgrading biogas to biomethane is a mean to substitute conventional natural gas. It is also known that biochar can improve the biogas production in AD processes. In this work, different biochars have been produced from various feedstocks at different process conditions. Biochars obtained from the carbonization of wheat straw (WS) and poplar (P) were produced in a Thermo Gravimetric Analyser at lab scale, at a temperature of 400 °C and 2 h of retention time at the maximum temperature, with a heating rate of 20 °C min−1. Another biochar from poplar (Pc) was also produced in a pilot plant (CarbOn, RE-CORD) working in oxidative pyrolysis conditions, at a temperature range between 500 and 600 °C. Biochars were oxidized with Oxone® using two different methods (ball-milling and simple aqueous solution mixing) to increase the amount of functional groups on their s...
A review of biochar properties and their roles in mitigating challenges with anaerobic digestion
Renewable and Sustainable Energy Reviews, 2019
Anaerobic digestion (AD) is an established organic waste management technology, producing biogas and organic fertiliser as end-products. Despite being an established technology, AD still faces key challenges, including process inefficiencies due to substrate-induced instability and product quality assurance; inability to digest highly lignocellulosic biomass without pre-treatment; and management of effluents and emissions. Commercial grade carbon-based materials have been employed as stabilising agent to improve process efficiency. Biochar, a by-product from biomass pyrolysis, has recently been identified as a sustainable alternative material to commercial grade carbon-based adsorbent used in AD. This review highlights the challenges with the AD process and the limitations of the various conventional approaches in its management. An exposition of the characteristics of biochar and the physico-chemical properties of biochar, that can simultaneously promote AD process stability, increase biomethane yield rate and the agronomic quality of digestate, are presented and discussed.
Journal of Cleaner Production, 2021
The conversion of food waste and sludge into biogas via anaerobic digestion technology is gaining attention in recent years, which plays a significant role in waste valorization into bioenergy and promotes environmental sustainability. Biochar is a carbonaceous material produced via thermochemical conversion of biomass waste, and tailoring biochar for diverse environmental applications adheres to the principle of circular economy. The emerging application of biochar as an additive in the anaerobic digestion of food waste and sludge has been intensively investigated in the last few years. However, a comprehensive understanding of multifunctional roles of biochar and its mechanisms in the production of biogas via miscellaneous/complex anaerobic digestion process is yet to be attained. This review scrutinizes the key roles of biochar as an additive and emphasizes the influences of biochar characteristics on the anaerobic digestion processes and their capability to address the foremost challenges. This review also evaluates the techno-economic and environmental impacts of biochar synthesis and its emerging application for biogas production via anaerobic digestion to make the integrated process more economical and environmentally sustainable, and identifies challenges and prospects for future studies.
Evaluation of Potential Substrates for Biogas Production via Anaerobic Digestion: A Review
2017
The anaerobic digestion of organic matter is now a widely-used technology, to address both energy and environment challenges. Biogas can be produced by landfill gas (LG), or produced at sewage treatment plant, in anaerobic digestion of industrial, municipality and agricultural treatment. Biogas contains 50 ̶ 70% methane and 30 ̶ 50% carbon dioxide as well as small amounts of other gases, nevertheless, the quality of biogas composition is dependent on the substrate type and technology used. Thus, this paper reviews the methane yield from various feedstocks. Sewage sludge has shown positive methane yield, nevertheless its conversion may be optimized by applying co-digestion process with organic fraction municipality waste (OFMSW) as a cosubstrate. Although pulp and paper mill sludge has high methane potential, the amount of methane yield is dependent on the pulp and paper process used and activated sludge plants (ASPs). Generally, methane yield from AD of slaughterhouse range between 160m 3 /ton kg VS-500 m 3 /ton kg VS, depending on the amount of blood presented and processes used.
Options for Enhanced Anaerobic Digestion of Waste and Biomass—a Review
Journal of Biosystems Engineering, 2020
Introduction Anaerobic digestion (AD) is a promising technology because it is economically feasible, environmentally friendly, and socially acceptable. Moreover, biogas generation from organic waste is considered to be the future of bio-energy. Purpose In this paper, we review the substrates available for biogas production, different methods for improvement of AD processes (two-stage anaerobic digestion and digestate recirculation) and various pre-treatment techniques used to enhance biogas generation. Method Two-stage digestion and co-digestion of two or more substrates appear to be promising techniques for enhanced anaerobic digestion. These techniques could help to maintain the nutrient balance in a system without the further addition of nutrients, in addition to enhancing biogas generation. Results Pre-treatment of various substrates is mainly used to increase the hydrolysis rate and thus enhance the efficiency of AD processes.
Frontiers in Energy Research, 2023
Anaerobic digestion (AD) processes can face operational challenges or flaws such as substrate structure and characteristics complexity, process complexity, low productivity, inefficient biodegradability, and poor stability, which suppresses or reduces biogas and biomethane production. As a result of the need to overcome these challenges/shortcomings and improve or enhance biogas and biomethane yield, process intensification methods have gained attention. There is some literature review on pretreatment and co-digestion as a means of improving AD performance; however, there is no systematic information on the various strategies required for improving AD performance and, in turn, increasing biogas/biomethane yield. The AD process produces biogas, a valuable renewable biofuel. Biogas is composed primarily of biomethane and other undesirable components such as carbon dioxide, oxygen, hydrogen sulphide, water vapour, ammonia, siloxanes, nitrogen, hydrocarbons, and carbon monoxide, which a...