Comparison of Variable and Constant Loading for Mesophilic Food Waste Digestion in a Long-Term Experiment

Abstract

Operators of commercial anaerobic digestion (AD) plants frequently note the challenge of transferring research results to an industrial setting, especially in matching well-controlled laboratory studies at a constant organic loading rate (OLR) with full-scale digesters subject to day-to-day variation in loadings. This study compared the performance of food waste digesters at fluctuating and constant OLR. In a long-term experiment over nearly three years, variable daily OLR with a range as wide as 0 to 10.0 g VS L−1 day−1 (weekly average 5.0 g VS L−1 day−1) were applied to one laboratory-scale digester, while a pair of control digesters was operated at a constant daily loading of 5.0 g VS L−1 day−1. Different schemes of trace elements (TE) supplementation were also tested to examine how they contributed to process stability. Variable loading had no adverse impact on biogas production or operational stability when 11 TE species were dosed. When TE addition was limited to cobalt and selenium, the stability of the variable-load digester was well maintained for nearly 300 days before the experiment was terminated, while the control digesters required re-supplementation with other TE species to reverse an accumulation of volatile fatty acids. This work demonstrated that variation in daily OLR across quite a wide range of applied loadings is possible with no adverse effects on methane production or stability of food waste digestion, giving confidence in the transferability of research findings. The positive effect of variable OLR on TE requirement requires further investigation considering its practical significance for AD industry.

Effects of co-substrates’ mixing ratios and loading rate variations on food and agricultural wastes’ anaerobic co-digestion performance

“…This was explained by the inappropriate atmosphere caused by FW properties and particularly to the relatively low C:N ratio which hindered the anaerobes growth [55] [55]. Hence, mono-digestion of FW is more resistant with moderately low and constant OLRs [58], and basing on the current findings, 2.4 kg VS/m 3 .d was the optimal OLR ensuring a performant development of the process for FW 100 .…”

Monitoring of Food Waste Anaerobic Digestion Performance: Conventional Co-Substrates vs. Unmarketable Biochar Additions

“…In the same context, Kumar et al, (2015) revealed that under an OLR higher than 2 kg VS/m 3 •d, an intensive concentration of propionate hardly convertible to acetate caused FW anaerobic digestion failure, which might explain the R1 behavior during the current research [56]. Therefore, focusing on the OLR limitations, particularly for a large scale, mono-digestion of FW was more resistant with moderately low and constant OLRs [57,58]. One of the main objectives of this experimental work was to evaluate the effects of agricultural and industrial waste on FW anaerobic process performance operated at different OLRs.…”

“…As methanogens adapt poorly to pH fluctuations, either a high or a low pH had the same effects on microbes in terms of functional inhibition. Table 4 shows that an increase in OLR of 4 kg VS/m 3 •d was followed by an alkaline pH at about 8.16 ± 0.28, which might hinder methanogen progress with reference to Song et al, (2020), who reported that a pH range of 6.8-7.5 was required for healthy microbial growth [58]. Certainly, pH variation definitely impacted methanogenesis progress.…”

Effect of Pasteurisation on Methane Yield from Food Waste and Other Substrates in Anaerobic Digestion

“…Pasteurisation is still required for hygienisation purposes, but it is not an effective strategy to increase methane yield. When poor performance in AD of food waste is encountered, monitoring of trace elements and choice of adequate loading of the reactor are usually effective strategies to overcome this [63], while pre-treatment of the substrate is not a promising approach.…”