Effect of different seeding sludge on the energy recovery potential of food waste during anaerobic digestion

Increasing food waste (FW) generation has been a growing environmental challenge for many countries. In Singapore, 796,000 tonnes of FW was generated in 2013, with only 13 per cent of the FW recycled. The recycling rate could be increased by adopting anaerobic digestion (AD), which is a biological process that efficiently converts organic matter into biogas. Due to the high degree of waste stabilisation and controlled methane generation, AD is regarded as a more sustainable treatment method for FW. Seeding sludge contains a consortia of microbes that are responsible for the conversion of organic matter to methane. A suitable seeding sludge can shorten start-up time and enhance biogas production. Therefore, the source of seeding sludge plays a crucial role in the fate of the AD process. The objective of this study was to compare the performance of two different seeding sludge for the AD of FW: (1) anaerobic sludge from water reclamation plants (WRP) in Singapore; and (2) anaerobic sludge from palm oil mill effluent (POME) digesters in Johor, Malaysia. This was achieved by comparing the evolution of bacterial and archaeal communities in anaerobic digesters inoculated with WRP sludge (R1) and POME sludge (R2) over 30 days. Biomass from R1 and R2 were sampled for terminal restriction fragment length polymorphism to detect the shift of microbes throughout the study. This study showed that WRP sludge (R1) took a shorter start-up time as compared to POME sludge (R2). The overall performance of R1 was also superior to that of R2. Information from both reactor performance and microbial community analysis suggested how the differences in the initial microbial consortia of WRP sludge and POME sludge affected the start-up and behaviour of FW anaerobic digesters. Knowledge gained from this study could aid future works in optimising the AD of FW through bioaugmentation.