Elsevier

Bioresource Technology

Volume 189, August 2015, Pages 409-412
Bioresource Technology

Short Communication
Increased anaerobic production of methane by co-digestion of sludge with microalgal biomass and food waste leachate

https://doi.org/10.1016/j.biortech.2015.04.028Get rights and content

Highlights

  • Effect of different mixing ratio of S, F and A was investigated.

  • Each substrate showed different degrees of digestibility.

  • Mixing ratio of 1S:1F:1A led to an enhancement of methane yield.

Abstract

The co-digestion of multiple substrates is a promising method to increase methane production during anaerobic digestion. However, limited reliable data are available on the anaerobic co-digestion of food waste leachate with microalgal biomass. This report evaluated methane production by the anaerobic co-digestion of different mixtures of food waste leachate, algal biomass, and raw sludge. Co-digestion of substrate mixture containing equal amounts of three substrates had higher methane production than anaerobic digestion of individual substrates. This was possibly due to a proliferation of methanogens over the entire digestion period induced by multistage digestion of different substrates with different degrees of degradability. Thus, the co-digestion of food waste, microalgal biomass, and raw sludge appears to be a feasible and efficient method for energy conversion from waste resources.

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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