Enhancement of biogas production from sunnhemp using alkaline pretreatment

This study investigates enhancing the biogas production of sunnhemp by pretreatment, before the anaerobic digestion and co-digestion processes, to address the complex and recalcitrant structure of the plant. Fresh sunnhemp harvested at a cutting interval of 50 days is used in the study. Five systems (each with a 5 litre useable volume) are operated semi-continuously with five different ratios of the feedstock by feeding separate feedstocks every five days with a hydraulic retention time (HRT) of 40 days. The system operates at room temperature (30 degrees C). The study uses sunnhemp as 20% of the feedstock and also considers sunnhemp mixed with cow manure at different ratios, with the weighed sunnhemp being pretreated with dilute sodium hydroxide. Pretreatment of sunnhemp before digestion produces a methane (CH4) yield 89% greater than that of the untreated sunnhemp. It requires 3.597 kg of dry sunnhemp to produce 1 m3 of CH4 and the annual CH4 yield per hectare is 19,015 m3. In the pretreatment of sunnhemp before co-digestion, the increased CH4 yield depends on the amount of pretreated sunnhemp in the feedstocks. However, the %CH4, the CH4 production level and the system stability depend on the optimal ratio of the sunnhemp to cow manure. The initially prepared sunnhemp to cow manure ratio is recommended at 10 g:10 gin 80 mL of water. At this ratio, the %CH4 and the CH4 yield are 53.84% and 313 kg chemical oxygen demand (COD) removed, respectively, and the COD removal efficiency is 56.4%. Sunnhemp has high potential and it is worth pretreating before producing biogas. Using sunnhemp to produce biogas is recommended to decrease greenhouse gas emissions and mitigate global warming. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.