Anaerobic co-digestion: micro to full-scale

Abstract

Anaerobic digestion (AD), by its simultaneous provision of sustainable energy generation and means of recycling organic material, is a technology integral to the successful implementation of the circular economy. As a sustainable biogas technology, AD provides a broad range of benefits encompassing waste treatment, environmental protection, increasing the economic value of otherwise low-value material as well as the production of electricity, heat and of advanced gaseous biofuels. While AD is widely applied in industry to treat organic waste, there exists a strategy to increase biogas production whilst leveraging existing AD infrastructure through co-digestion. Anaerobic co-digestion (AcoD) involves the simultaneous anaerobic digestion of two or more biodegradable waste streams.Whilst AcoD offers great potential for enhanced methane production, incompatible substrates or the overdosing of co-substrates can lead to process failure; however, dosage strategies can be managed to avoid organic overloading and the subsequent process failure.Temperature is known to significantly impact the biochemical and physio-chemical processes involved in AD. Whilst most digesters are controlled at mesophilic (37°C) or thermophilic (55°C) temperatures, other AD systems -such as covered anaerobic lagoons -are operated at ambient temperature conditions and can be subject to seasonal variations of up to 20°C. Few studies have been conducted at psychrophilic temperatures; understanding the impact of temperature on co-digestion capacity is, therefore, vital to inform seasonal dosage strategies for these ambient AD systems.An understanding of the temperature dependency of co-digestion required the investigation of the impact of operating temperature on long-term anaerobic digestion performance, metabolic activity rates, and microbial composition of different feedstocks. Four bench-scale continuous digesters, of which two treated mixed sewage sludge (SS) and two treated pig manure (PM), were operated at 1-1.5 g VS L -1 d -1 for over 600 days and transitioned through three operating temperature regimes (37°C, 25°C and 15°C, each greater than 100 days). Minimal change in operational performance was observed between 37°C and 25°C for both the SS and PM systems; however, at 15°C, process stability and performance of both systems was greatly reduced due to slower process kinetics and reduced substrate degradability. The PM system experienced greater process instability than the SS system at 15°C due, in part, to higher degradable OLR and a greater imbalance between upstream and downstream metabolic activity levels.Characterisation of metabolic activity rates were performed using batch activity tests with model substrates and temperature adapted inoculum sourced from the bench scale continuous digesters. The metabolic activity rates measured for the SS and PM systems at 37, 25 and 15°C were hydrolysis of cellulose, gelatin, and oleic acid; fermentation of glucose and glycerol; degradation of propionate and butyrate; and aceticlastic and hydrogen...

The Biogas Production from Brewery Waste: A Case Study for Tanzania Breweries Company Limited (Arusha-Branch)

“…Normally, Methanosaeta and Methanosarcina, dominates in anaerobic digesters depending upon the type of waste and digester [18]. The second group is the hydrogenotrophic methanogens that hydrogen and carbon dioxide produced methane from H 2/ CO 2 , whereas only a few species of methanogens are believed to be capable of utilizing acetate as a substrate [19]. However, estimated that stoichiometric ratio about 70% of the methane formed in anaerobic digesters which derived via the acetate pathway.…”