Short CommunicationIncreased anaerobic production of methane by co-digestion of sludge with microalgal biomass and food waste leachate
Introduction
The anaerobic wastewater process is an economically attractive alternative to aerobic treatment methods because costs related to electricity, maintenance, and operations may be offset by methane production (Sutton et al., 2011). In addition, anaerobic processes do not require an aeration unit, and this can account for nearly one-half of the total energy input for biological wastewater treatment (Park and Craggs, 2007). For this reason, many recent studies have examined anaerobic digestion for treatment of organic wastes (food waste, sewage sludge, dung, etc.). In particular, for efficient production of biogas as an energy source, recent research has focused on co-digestion, the simultaneous anaerobic digestion of multiple organic wastes in a single digester. In most cases, the use of co-substrates can improve biogas yields due to positive interactions in the digestion medium. This may be because use of multiple substrates may supply nutrients that are missing from a single substrate (Zhang et al., 2011) or may dilute toxic compounds from a single substrate to below the toxic thresholds (Sialve et al., 2009).
The characteristics of Korean food waste, such as high moisture content, high salinity, and low pH, have made it difficult to use as the sole substrate for biogas production in an anaerobic digestion process. In particular, ∼70–90% of the food waste consists of leachate. The low sulfur content and the ability to uptake CO2 from generated biogas make microalgal biomass a good option for anaerobic digestion (Converti et al., 2009, Sialve et al., 2009). Therefore, this study examined the co-digestion of food waste leachate with microalgal biomass as a method to improve methane production. Previous research has examined diverse organic substrates with food waste in anaerobic co-digestion, but there has been little research into co-digestion of food waste with microalgal biomass. Co-digestion of food waste with microalgal biomass might overcome the problems of separate digestion of each substrate, which are related to C/N ratio, pH, and salinity.
The present study tested the process stability and methane production of anaerobic co-digestion of saline food waste leachate with microalgal biomass by use of different mixing ratios of food waste leachate, microalgal biomass, and raw sludge.
Section snippets
Inoculum and substrates for anaerobic co-digestion
Seed micro-organisms and raw sludge were collected from the anaerobic digestion tank of the municipal sewage treatment plant in Busan, South Korea. Food waste leachate was taken from a waste processing plant in Busan, South Korea (Supplementary Fig. 1a). The microalgal biomass, Chlorella sp., was generously provided by Daesang Co. (South Korea), and concentrated microalgae were refrigerated at 4 °C prior to use (Supplementary Fig. 1b). Table 1 shows the physicochemical characteristics and
Effect of different substrate combinations on methane production
Fig. 1 shows the cumulative methane production with different mixtures of food waste leachate (F), algal biomass (A), and raw sludge (S) over 42 days. After incubation, there was a lag phase before methane production commenced. With increasing the raw sludge portion or decreasing the algal sludge and food waste leachate portions in the mixtures, this lag phase was shortened. VFA and soluble COD (sCOD) concentrations increased during this lag phase (Supplementary Fig. 2). Methane production
Conclusion
This research examined the effect of substrate composition (different ratios of food waste leachate, algal biomass, and raw sludge) on production of methane during anaerobic digestion. Co-digestion of food waste and microalgal biomass led to low methane generation, mainly due to the lack of bio-degradable organics and the high-salt environment. However, the addition of raw sludge to these two other substrates led to a proliferation of methanogens during entire digestion period. These and
Acknowledgement
This study was supported by Grant KK-1506 from the Korea Institute of Toxicology.
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2022, Science of the Total EnvironmentCitation Excerpt :KW can cause environmental pollution when exposed to the environment without treatment (Shi et al., 2020). The leachate produced by KW can cause the pollutions of soil and groundwater environment (Kim and Kang, 2015). After a period of time, KW produces gas with a foul smell and environmental hazards (Cao et al., 2021).