Methane Production of Pistia Stratiotes as a Single Substrate and as a Co-Substrate with Dairy Cow Manure

Mono anaerobic digestion (AD) of dairy cow manure (DCM) is constrained by high moisture, ash and crude fibre content. Anaerobic co-digestion DCM and other biomass is one of the methods to overcome this drawback. This study aimed to evaluate: methane production from different parts of Pistia stratiotes (PS), methane production from the mixed substrate of PS and DCM in different proportions of PS in terms of volatile solids (VS) (0%, 7.99%, 14.91%, and 20.94%) using continuous digesters, and the potency of biogas yield from the digested slurry. Methane production from the whole plant, shoot system, and root of PS was 405.68, 416.82, and 326.42 L/kg VS, respectively. The highest methane production was obtained from the shoot system because that part contained higher crude protein and hemicellulose contents. Utilization of PS as a co-substrate for AD of the DCM can increase methane production by 28.65–56.98% compared to the control digester. No effect on pH, total ammonia nitrogen and total volatile fatty acid indicated that PS was suitable as a co-substrate of DCM and can significantly increase methane yield of the mixed substrate. AD of digested slurries showed that to recover the biogas production from the mixed substrate, the post-digestion treatment should be applied before the slurries are used as organic fertilizer.