Abstract
This paper explores the feasibility of flexible biogas production by co-digestion of food waste and sewage sludge based on experiments and mathematical modeling. First, laboratory-scale experiments were carried out in variable operating conditions in terms of organic loading rate and feeding frequency to the digester. It is demonstrated that biogas production can achieve rapid responses to arbitrary feedings through co-digestion, and the stability of the anaerobic digestion process is not affected by the overloading of substrates. Compared with the conventional continuous mode, the required biogas storage capacity in flexible feeding mode can be significantly reduced. The optimum employed feeding organic loading rate (OLR) is identified, and how to adjust the feeding scheme for flexible biogas production is also discussed. Finally, a simplified prediction model for flexible biogas production is proposed and verified by experimental data, which could be conveniently used for demand-oriented control. It is expected that this research could give some theoretical basis for the enhancement of biogas utilization efficiency, thus expanding the applications of bio-energy.
Highlights
Bio-energy has the unique advantage that it can be stored and controlled according to a targeted schedule; it is applicable for compensating the differences between power demand and supply that arise at peak times or when production bottlenecks occur [1,2,3]
Adaption of configurations is expensive and difficult to implement, especially for already-built biogas plants [11]. Another method for achieving flexible biogas production is targeted variation of the feeding scheme, which can be manipulated by varying the substrate addition time and intervals, in order to coordinate the actual variations of biogas production with the electricity demand trend; related researches can be found in Mulat et al [12] and Zealand et al [13]
It is demonstrated that the highest biogas production rate appeared within 2 h after feeding in all experimental groups, which proved the system’s fast response to the pulse feedings by co-digestion of food waste and sewage sludge
Summary
Bio-energy has the unique advantage that it can be stored and controlled according to a targeted schedule; it is applicable for compensating the differences between power demand and supply that arise at peak times or when production bottlenecks occur [1,2,3]. Some specific technologies of flexible biogas production have already been researched; for instance, Linke et al [10] and Lemmer et al [6] focused their attention on the adaption of a two-stage systembiogas plant configuration that generates liquid substrates with a high content of degradable organic matter. This can be fed in variable amounts into fixed-bed digesters to increase the biogas production instantly. The most commonly used flexible method is addition of degradable substrates for just-in-time biogas production
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