Abstract
Anaerobic co-digestion allows for under-utilised digesters to increase biomethane production. The organic fraction of municipal solid waste (OFMSW), i.e., food waste, is an abundant substrate with high degradability and gas potential. This paper investigates the co-digestion of mixed sludge from wastewater treatment plants and OFMSW, through batch and continuous lab-scale experiments, modelling, and microbial population analysis. The results show a rapid adaptation of the process, and an increase of the biomethane production by 20% to 40%, when co-digesting mixed sludge with OFMSW at a ratio of 1:1, based on the volatile solids (VS) content. The introduction of OFMSW also has an impact on the microbial community. With 50% co-substrate and constant loading conditions (1 kg VS/m3/d) the methanogenic activity increases and adapts towards acetate degradation, while the community in the reference reactor, without a co-substrate, remains unaffected. An elevated load (2 kg VS/m3/d) increases the methanogenic activity in both reactors, but the composition of the methanogenic population remains constant for the reference reactor. The modelling shows that ammonium inhibition increases at elevated organic loads, and that intermittent feeding causes fluctuations in the digester performance, due to varying inhibition. The paper demonstrates how modelling can be used for designing feed strategies and experimental set-ups for anaerobic co-digestion.
Highlights
In anaerobic digestion (AD), organic material is biologically degraded
AD is commonly used at wastewater treatment plants (WWTPs) for stabilizing mixed sludge
Two substrates were used for co-digestion in this study: (1) Mixed sludge from the WWTP Getteröverket in Varberg, Sweden and (2) OFMSW collected from households in Varberg, Sweden
Summary
In anaerobic digestion (AD), organic material is biologically degraded. In the process, the organic material is stabilised, thereby minimizing further biological activity, and energy-rich biogas (a mixture of mainly biomethane, CH4 , and carbon dioxide, CO2 ) is produced. In AcoD organic substrates, such as industrial or agricultural wastes, are fed to the digester in addition to the primary substrate, e.g., sewage sludge [5]. Due to its availability and characteristics, is the organic fraction of municipal solid waste (OFMSW) [7]. The AcoD of OFMSW and sewage sludge has a high potential to increase gas production at WWTPs [8,9,10,11,12,13,14]. With gene probes or DNA analysis, the microorganisms in the reactor can be identified and quantified [25] This knowledge is critical for understanding how different substrates, feed strategies, and operational modes impact the process. The experimental design and process performance are assessed by mathematical modelling and simulation of the processes
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