Urea promotes alkaline anaerobic fermentation of waste activated sludge for hydrogen production

Hydrogen production from waste activated sludge (WAS) represents a promising pathway for sustainable energy generation. This study explores the impact of urea on enhancing hydrogen production during alkaline fermentation of WAS, with the aim of reducing alkali use. Experimental results revealed that treating WAS with 90 mg/g VSS urea at a constant pH of 9.5, followed by anaerobic fermentation for 10 days, yielded 24.57 mL/g VSS of hydrogen, which is 1.42 times higher than the fermentation at constant pH 9.5 without urea. Additionally, urea exposure reduced NaOH consumption by 40.74 % and 15.79 % at constant pH 10 and 9.5, respectively, achieving a cost-effective hydrogen production at 9.16 USD/m³ H₂. The observed reduction in NaOH consumption is attributed to free ammonia from urea decomposition, which acts as an NH₃/NH₄⁺ buffer. Mechanistic analysis suggests that urea disrupts hydrogen bonds within proteins, enriching hydrogen-producing microbes while inhibiting hydrogen-consuming ones, thereby promoting hydrogen production.