Changing Feeding Regimes To Demonstrate Flexible Biogas Production: Effects on Process Performance, Microbial Community Structure, and Methanogenesis Pathways

Abstract

Flexible biogas production that adapts biogas output to energy demand can be regulated by changing feeding regimes. In this study, the effect of changes in feeding intervals on process performance, microbial community structure, and the methanogenesis pathway was investigated. Three different feeding regimes (once daily, every second day, and every 2 h) at the same organic loading rate were studied in continuously stirred tank reactors treating distiller's dried grains with solubles. A larger amount of biogas was produced after feeding in the reactors fed less frequently (once per day and every second day), whereas the amount remained constant in the reactor fed more frequently (every 2 h), indicating the suitability of the former for the flexible production of biogas. Compared to the conventional more frequent feeding regimes, a methane yield that was up to 14% higher and an improved stability of the process against organic overloading were achieved by employing less frequent feeding regimes. The community structures of bacteria and methanogenic archaea were monitored by terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA and mcrA genes, respectively. The results showed that the composition of the bacterial community varied under the different feeding regimes, and the observed T-RFLP patterns were best explained by the differences in the total ammonia nitrogen concentrations, H 2 levels, and pH values. However, the methanogenic community remained stable under all feeding regimes, with the dominance of the Methanosarcina genus followed by that of the Methanobacterium genus. Stable isotope analysis showed that the average amount of methane produced during each feeding event by acetoclastic and hydrogenotrophic methanogenesis was not influenced by the three different feeding regimes.I nterest in a demand-driven biogas supply for flexible electricity production with the aim of balancing the supply of electricity generated from sources producing fluctuating amounts of electricity, such as solar and wind sources, has increased recently. Different strategies can be employed to obtain a demand-driven biogas supply, including a strategy involving a conventional biogas plant with biogas storage or a strategy involving a conventional biogas plant with a biogas upgrade to biomethane for subsequent storage in a natural gas grid (1-3). Conventional biogas production with integrated heat and power (CHP) plants are normally run on a semicontinuous substrate feeding regime in order to provide a constant biogas output and electricity generation (4).Alternatively, flexible biogas production that adapts biogas output to energy demand can be implemented by feeding management, including varying the feeding regimes and substrate composition. The production of larger amounts of biogas can be achieved immediately after feeding, and smaller amounts of biogas production are achieved during the nonfeeding period. Compared to the conventional operation of biogas plants with biogas storage, flexible biogas produc...

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“…pulse feeding produced a higher methane yield than continuous feeding). 55 The effects of lower and higher efficiencies of the AD facility were considered by inputting the minimum and maximum SMY of silage and slurry from Irish literature. [18][19][20][21]27,[35][36][37][38][39] Silage and slurry mono-or co-digestion characteristics, and associated methane production costs, with lower or higher methanogenesis efficiency than in the respective baseline scenarios are presented in Table 4.…”

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