Towards reliable and robust anaerobic digestion

Water Science and Technology, 1983

Six different conversion processes are identified in the degradation of particulate organic material (biopolymers) to methane. Hydrolysis of particulate material is followed by the degradation of the hydrolysis and intermediary products by five independent groups of microorganisms. Process and growth kinetic data for the six processes are reviewed. The kinetic data are applied to the design of an anaerobic digester for raw domestic sludge. Variations in loading rates primarily affect acetate decarboxylation and, thereby, may cause shifts in pH which, in turn, cause the digester to operate in the acidic regime.

Applied microbiology and biotechnology, 2018

Waste treatment and the simultaneous production of energy have gained great interest in the world. In the last decades, scientific efforts have focused largely on improving and developing sustainable bioprocess solutions for energy recovery from challenging waste. Anaerobic digestion (AD) has been developed as a low-cost organic waste treatment technology with a simple setup and relatively limited investment and operating costs. Different technologies such as one-stage and two-stage AD have been developed. The viability and performance of these technologies have been extensively reported, showing the supremacy of two-stage AD in terms of overall energy recovery from biomass under different substrates, temperatures, and pH conditions. However, a comprehensive review of the advantages and disadvantages of these technologies is still lacking. Since microbial ecology is critical to developing successful AD, many studies have shown the structure and dynamics of archaeal and bacterial com...

Water science and technology : a journal of the International Association on Water Pollution Research, 2001

The IWA specialised group on anaerobic digestion (AD) is one of the oldest working groups of the former IAWQ organisation. Despite the fact that anaerobic technology dates back more than 100 years, the technology is still under development, adapting novel treatment systems to the modern requirements. In fact, most advances were achieved during the last three decades, when high-rate reactor systems were developed and a profound insight was obtained in the microbiology of the anaerobic communities. This insight led to a better understanding of anaerobic treatment and, subsequently, to a broader application potential. The present "state-of-the-art" paper, which has been written by members of the AD management committee, reflects the latest achievements and sets future lines for further development.

2003

Anaerobic digestion is an established technology for the treatment of wastes and wastewater. The final product is biogas: a mixture of methane (55-75 vol%) and carbon dioxide (25-45 vol%) that can be used for heating, upgrading to natural gas quality or co-generation of electricity and heat. Digestion installations are technologically simple with low energy and space requirements. Anaerobic treatment systems are divided into 'high-rate' systems involving biomass retention and 'low-rate' systems without biomass retention. High-rate systems are characterised by a relatively short hydraulic retention time but long sludge retention time and can be used to treat many types of wastewater. Low-rate systems are generally used to digest slurries and solid wastes and are characterised by a long hydraulic retention time, equal to the sludge retention time. The biogas yield varies with the type and concentration of the feedstock and process conditions. For the organic fraction of municipal solid waste and animal manure biogas yields of 80-200 m 3 per tonne and 2-45 m 3 per m 3 are reported, respectively. Co-digestion is an important factor for improving reactor efficiency and economic feasibility. In The Netherlands co-digestion is only allowed for a limited range of substrates, due to legislation on the use of digested substrate in agriculture. Maximising the sale of all usable co-products will improve the economic merits of anaerobic treatment. Furthermore, financial incentives for renewable energy production will enhance the competitiveness of anaerobic digestion versus aerobic composting. Anaerobic digestion systems currently operational in Europe have a total capacity of 1,500 MW, while the potential deployment in 2010 is estimated at 5,300-6,300 MW. Worldwide a capacity up to 20,000 MW could be realised by 2010. Environmental pressures to improve waste management and production of sustainable energy as well as improving the technology' s economics will contribute to broader application. Amino acids sugars Free long chain fatty acids + glycerol Volatile fatty acids, alcohol Methane carbon dioxide ammonia Hydrolysis Acidogenesis Acetogenesis Methanogenesis Acetic acid Suspended, colloidal organic matter protein carbohydrate lipid Hydrogen carbon dioxide Figure 1. Simplified schematic representation of the anaerobic degradation process [1].

Ecological Engineering and Environment Protection, 2021

Anaerobic digestion is a biotechnological process, in which microorganisms degrade the complex organic matter to simpler components under anaerobic conditions to produce biogas and fertilizer. This process has many environmental benefits, such as green energy production, organic waste treatment, environmental protection and greenhouse gas emissions reduction. It has long been known that the two main communities of microorganisms (acidogenic and methanogenic) taking part in the anaerobic digestion differ in many aspects e.g. their optimal conditions for cell growth and development. Therefore, the anaerobic digestion in a single bioreactor (BR) (single-phase process) required selected optimal conditions, taking into account the slow-growing methanogens at the expense of fast-growing acidogens, which affects the efficiency of the whole process. This has led in recent years to development of two-stage anaerobic digestion, in which the processes are divided into a cascade of two separate...

Advances in Bioscience and Biotechnology, 2015

The search for alternative energy and fuels has motivated researchers to focus on renewable and sustainable means of getting them instead of relying on the conventional way of energy and fuel production. Anaerobic digestion is a biochemical process during which complex organic matter is decomposed in absence of oxygen, by various types of anaerobic microorganisms. The process of Anaerobic digestion is appropriate for all waste water treatment systems given that the solid can be introduced to the system at an acceptable concentration. Biogas, the product of anaerobic digestion process is a clean and renewable form of energy which can be a substitute for conventional sources of energy which are causing ecological-environmental problems and at the same time depleting at a faster rate. This paper reviews the anaerobic digestion process and its complexities; it covers different stages involved in the process, the substrate used in the process, the relationship between the substrate and microorganisms and important operating parameters such as pH, temperature and loading rate.

Anaerobic Digesters: Perspectives and Challenges

Microbial Biotechnology, 2019

Biogas production is a biotechnological process realized by complex bacterial, archaeal and likely fungal communities. Their composition was assessed in nine full-scale biogas plants with distinctly differing feedstock input and process parameters. This study investigated the actually active microbial community members by using a comprehensive sequencing approach based on ribosomal 16S and 28S rRNA fragments. The prevailing taxonomical units of each respective community were subsequently linked to process parameters. Ribosomal rRNA of bacteria, archaea and fungi, respectively, showed different compositions with respect to process parameters and supplied feedstocks: (i) bacterial communities were affected by the key factors temperature and ammonium concentration; (ii) composition of archaea was mainly related to process temperature; and (iii) relative abundance of fungi was linked to feedstocks supplied to the digesters. Anaerobic digesters with a high methane yield showed remarkably similar bacterial communities regarding identified taxonomic families. Although archaeal communities differed strongly on genus level from each other, the respective digesters still showed high methane yields. Functional redundancy of the archaeal communities may explain this effect. 28S rRNA sequences of fungi in all nine full-scale anaerobic digesters were primarily classified as facultative anaerobic Ascomycota and Basidiomycota. Since the presence of ribosomal 28S rRNA indicates that fungi may be active in the biogas digesters, further research should be carried out to examine to which extent they are important players in anaerobic digestion processes.

Biogas from anaerobic digestion of sewage, food processing, animal and other wastes typically contains about 55% to 70% CH 4 and 30% to 45% CO 2. In some cases, much higher CH 4 content are reported, over 70% (see Chapter 2 of main report) and even up to 90% CH 4 in some cases. High methane content in biogas would be desirable, as it would reduce, in some cases even avoid, the need for CO 2 removal from the biogas, and direct utilization (after H 2 S and moisture removal) as a vehicular fuels and other applications requiring compression. This Appendix briefly examines the potential for achieving high (>70%) methane content in the biogas as part of the anaerobic digestion process of dairy manures, to reduce or even avoid the need for a separate CO 2 removal operation. Biogas production from organic substrates involves an internal redox reaction that converts organic molecules to CH 4 and CO 2 , the proportion of these gases being dictated by the composition and biodegradability of the substrates, as already briefly discussed above. For the simplest case, the conversion of carbohydrates, such as sugars (e.g., glucose, C 6 H 12 O 6) and starch or cellulose (C n H n-2 O n-1), an equal amount of CH 4 and CO 4 is produced (50:50 ratio): CnHn-2On-1 + nH 2 O ½ nCH 4 + ½nCO 2 (1) In the case wastes containing proteins or fats, a larger amount of methane is produced, stoichiometrically from the complete degradation of the substrate. For proteins, the process is as follows: C 10 H 20 O 6 N 2 + 3H 2 0 5.5 CH 4 + 4.5 CO 2 + 2NH 3 (2) This yields a CH 4 :CO 2 ratio of 55:45; the exact biogas composition will depend on the individual substrate protein. For fats and vegetable oil (triglycerides), a typical CH 4 :CO 2 ratio is 70:30: C 54 H 106 O 6 + 28 H 2 O 40 CH 4 + 17 CO 2 (3) These simplified examples can change according to effects from several factors: • Reactions are often incomplete (typically up to half of the cellulose is refractory to microbial anaerobic degradation, and lignin is completely inert, for example). • By-products are produced and voided in the digester effluent (e.g., acetic, propionic and other fatty acids and metabolites). • Bacteria use these reactions to make more bacteria; thus, there is also some biomass produced as part of these metabolic processes.

The quest for a sustainable and effective waste management is highly increasing due to several environmental and economic concerns such as climatic change and diminishing resources of fossil energy and raw materials. Anaerobic digestion (AD) is the most promising alternative for disposal of many different kinds of organic wastes because of its inherent high energy recovery, elimination of greenhouse gases and rendering pathogens and odorous emissions innocuous.AD is a process by which microorganisms break down biodegradable material in the absence of oxygen. It involves four major steps: hydrolysis, acidogenesis, acetogenesis and methanogenesis. Hydrolysis is the rate-limiting step of the overall process degradation. The paper is an overview of the process of AD, its applications and means of enhancement for sustainable waste management and renewable energy production.