Anaerobic co-digestion of microalgae Chlorella vulgaris and potato processing waste: Effect of mixing ratio, waste type and substrate to inoculum ratio

Abstract

This investigation aimed to evaluate the feasibility of potato processing waste (PPW) as a co-substrate for Chlorella vulgaris in batch biochemical methane potential (BMP) tests. Three parameters were examined: C. vulgaris and PPW mixing ratios (100:0, 75:25, 50:50, 25:75 and 0:100), PPW type (potato discarded parts (PPWdp) and potato peel (PPWp)), and substrate to inoculum ratio (0.5 and 1.0 SIRs). The mixing ratio was a significant factor with higher methane yields obtained with 25:75 C. vulgaris: PPW. The type of PPW also affected methane yield, as C. vulgaris co-digested with PPWdp increased methane yield by 22–47%, versus a 12–32% enhancement with PPWp. Moreover, a SIR of 1.0 led to an accumulation of soluble COD, resulting in decreased methane yield relative to a SIR of 0.5. Overall, the current study showed that PPW are suitable feedstocks for co-digestion with microalgae, with the enhanced methane yields attributed to a balance C/N ratio. However, the extra nitrogen in the seed inoculum of the BMP test may have obscured the full benefits and hidden some synergistic effects. Therefore, the follow-up studies should be carried out in continuous anaerobic digesters to verify the full potential of PPW as co-digestion substrate for microalgae.