Effects of various pretreatments on biohydrogen production from sewage sludge

The sewage sludge of wastewater treatment plant is a kind of biomass which contains many organics, mainly carbohydrates and proteins. Four pretreatments, acid pretreatment, alkaline pretreatment, thermal pretreatment and ultrasonic pretreatment, were used to enhance biohydrogen production from sewage sludge. The experimental results showed that the four pretreatments could all increase the soluble chemical oxygen demand (SCOD) of sludge and decrease the dry solid (DS) and volatile solid (VS) because the pretreatments could disrupt the floc structure and even the microbial cells of sludge. The results of batch anaerobic fermentation experiments demonstrated that all of the four pretreatments could select hydrogen-producing microorganisms from the microflora of sludge and enhance the hydrogen production. The hydrogen yield of the alkaline pretreated sludge at initial pH of 11.5 was the maximal (11.68 mL H-2/g VS) and that of the thermal pretreated sludge was the next (8.62 mL H-2/g VS). The result showed that the hydrogen yield of pretreated sludge was correlative with its SCOD. The hydrogen yields of acid pretreated sludge and alkaline pretreated sludge were also influenced by their initial pH. No methane could be detected in the anaerobic fermentation of alkaline pretreated sludge and thermal pretreated sludge, which suggested that these pretreatments could fully inhibit the activity of methanogens. The volatile fatty acids (VFA) production in anaerobic fermentation of alkaline pretreated sludge was the maximum and the next is that of thermal pretreated sludge.