Sustainable duckweed biomass valorization for dark fermentative hydrogen production: Process evaluation under meso- and thermophilic operations

Abstract

Aquatic plants are rich in biomass and contain good amounts of carbohydrates and proteins which are amenable for valorization to generate bioenergy. Duckweed is rich in proteins and carbohydrates that grow abundantly in contaminated waterbodies, which is now tested for as a substrate for biohydrogen production. Dark-fermentative hydrogen production was done by hydrothermal pretreatment of duckweed biomass under 15 lbs pressure, evaluated under three different operating temperatures that cover mesophilic (35 °C) and thermophilic conditions (50 and 55°C). The study resulted in the maximum hydrogen production rate of 0.97 mmol/day in batch culture (160 mL) from 55 °C that was found superior to 50 °C (0.84 mmol/day) and 35 °C (0.38 mmol/day) operations. From the 7 days of operation, under uncontrolled pH conditions, substrate (chemical oxygen demand, COD) utilization was 57.27 %, which is higher than in mesophilic conditions (50.67 %). Efficient hydrolysate conversion was noticed with thermophilic conditions, especially under operation at 55 °C (416 mL H2/g of biomass) than mesophilic conditions (144 mL H2/g of biomass) suggesting that duckweed can be dependable biomass for hydrogen production, and the dark-fermentation can be an appropriate solution of aquatic weed biomass management in a sustainable approach.