Biomethane enhancement via plastic carriers in anaerobic co-digestion of agricultural wastes

Abstract

Two types of plastic carriers low-density polyethylene (LDPET) and high-density polyethylene (HDPET) were used as a support material for biofilm formation during anaerobic co-digestion of agricultural wastes. LDPET and HDPET were added separately to different reactors containing binary substrates: corn straw and cauliflower leaves (G 1), corn straw and cow dung (G 2), while ternary substrates corn straw, cauliflower leaves, and cow dung were used in G 3. Reactors containing either HDPET or LDPET carriers supported the enhancement of biogas and biomethane. Maximum daily biomethane (333.43 and 368.35 mL/day) was achieved after HDPET addition to G1 and G2 at day 10 and 12, respectively. The accumulative biomethane were significantly enhanced (p < 0.05) by 17.14% and 23.52%, compared with reactors having LDPET carriers 11.89% and 5.53%, respectively. HDPET addition to ternary substrates (G 3) resulted in highest biomethane production (31.61%) and total solids (31.70%) and volatile solid (61.63%) removal. The major short-chain fatty acids (SCFAs) detected in all groups were acetic acid (4–5 g/L) and propionic acid (2–3 g/L), and their conversion to biomethane was the highest with HDPET. Scanning electron microscopy (SEM) analysis of the supporting materials showed that the plastic carriers support the biofilm formation especially in the case of HDPET. This study demonstrated that addition of cost-effective plastic carrier (HDPET) to anaerobic digestion system supported the formation of biofilm, leading to significantly increase in substrate utilization and biomethane production.