Abstract
ABSTRACT Effects of antimicrobial compounds on dry anaerobic digestion (dry-AD) processes were investigated. Four compounds with known inhibition effects on traditional wet digestion, i.e. car-3-ene, hexanal, 1-octanol and phenol were selected and investigated at concentrations of 0.005%, 0.05% and 0.5%. Food waste (FW) and Paper waste (PW) were used as model substrates, all assays were running with the substrate to inoculum ratio of 1:1 (VS basis) corresponding to 15% TS in reactors. Generally, increasing concentrations of inhibitors resulted in decreasing methane yields with a few exceptions; in all these specific cases, long, lag phase periods (60 days) were observed. These adaptation periods made possible for the microbial systems to acclimatize to otherwise not preferred conditions leading to higher methane yields. Comparing the effects of the four different groups, phenols had the highest inhibitory effects, with no methane production at the highest amount added, while the lowest effects were obtained in cases of car-3-ene. Furthermore, the results showed that adding inhibitors up to a certain concentrations can repair the balance in AD process, slowing down the degradation steps, hence making it possible for the methanogens to produce a higher amount of methane. This phenomenon was not observed in case of PW, which is already a slow degradable substrate in its nature.
Highlights
Anaerobic digestion (AD) to produce biogas has been a successful treatment of different organic wastes, but has provided a solution for solving environmental, health and energy challenges [1,2,3]
In case of food waste, the results showed that the addition of inhibitors up to a concentration of 0.05% would rather improve the performance of the system leading to up to 84% more methane yield compared to the control (Table 1)
Since all assays were running with the substrate to inoculum ratio of 1:1 (VS basis) to achieve high initial solids of 15% total solids (TS) in the system, the assays running with Food waste (FW) were seemed to be overloaded
Summary
Anaerobic digestion (AD) to produce biogas has been a successful treatment of different organic wastes, but has provided a solution for solving environmental, health and energy challenges [1,2,3]. Wastes from Food and Paper industries are carbon-rich feedstocks with high TS content which makes them suitable for dry-AD processes. The production of pulp and paper involves several process steps, like material preparation, pulping, bleaching, washing/filtering, screening, and drying or paper making aiming to get pulp or paper, respectively [12]. From this manufacturing process, a large amount of different waste streams are generated, such as wastewater and solid wastes [13]. Dry-AD process is suitable for treating the solid wastes generated while meeting the industry’s energy demand. The generated paper waste (PW) contains mostly hemicellulose and cellulose which are difficult for the microorganisms to degrade and as such the degradation process is slow
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