Article pubs.acs.org/EF
Enhanced Hydrogen Production from Sewage Sludge by Cofermentation with Forestry Wastes Guang Yang† and Jianlong Wang*,†,‡ †
Collaborative Innovation Center for Advanced Nuclear Energy Technology, INET, Tsinghua University, Beijing 100084, P. R. China Beijing Key Laboratory of Radioactive Wastes Treatment, Tsinghua University, Beijing 100084, P. R. China
‡
ABSTRACT: Dark fermentation of sewage sludge (i.e., the byproduct of biological sewage treatment process) is a promising way for renewable hydrogen production. However, low carbohydrate content and low C/N ratio essentially limited hydrogen production efficiency from sewage sludge. In this study, three raw forestry wastes with higher biodegradable carbohydrate content (fallen poplar leaves, flower waste, and sheared ryegrass) were added into a batch sludge fermentation system, aiming to explore an effective and practically feasible method to enhance hydrogen production from sludge. The results showed that the hydrogen yield from sole sewage sludge increased from 11.2 to 20.8, 32, and 51.7 mL/g-volatile solids (VS)added with the addition of poplar leaves, flower waste, and ryegrass as co-substrates, respectively, with relevant increase ratios of 0.85, 1.85, and 3.60 times, respectively. Model simulation results indicated that the lag time of sludge fermentation was also shortened through the addition of the above three raw forestry wastes as co-substrates. Meanwhile, the VS removal for sole sludge fermentation increased from 3.4% to 7.2, 12.7, and 18.6% by co-fermentation with poplar leaves, flower waste, and ryegrass, respectively. The enhancement from co-fermentation might be due to the addition of more biodegradable carbohydrate, more suitable C/N ratio of substrate, and higher carbohydrate utilization. After fermentation, the acetate-type fermentation was predominant in all four groups. Cofermentation with these forestry wastes did not change the dominant hydrogen fermentation type. This study demonstrated that it was feasible to enhance hydrogen production and sludge reduction by co-fermentation with poplar leaves, flower waste, and ryegrass.
1. INTRODUCTION Hydrogen is a promising energy source for sustainable development because of its clean combustion byproduct (H2O) and high energy yield (141.9 J/kg). Currently, the primary hydrogen producing technologies (e.g., oil reforming, coal gasification, and water electrolysis) are commonly unsustainable, energy consuming, and cost-intensive.1 To this regard, biological processes for renewable hydrogen production are more preferred including dark fermentation and photo fermentation. Among the above two biological processes, dark fermentation seems to be more practically feasible because of the advantages of stable hydrogen yield, fast hydrogen production rate, simple operation conditions, low energy demand, and low operating cost.2 More attractively, many kinds of organic wastes could be directly used as substrates in dark fermentation including food waste,3 sewage sludge,4 forestry waste,5 agricultural waste,6 and algae biomass,1 which could simultaneously achieve renewable energy (i.e., hydrogen) recovery and waste treatment. Among these organic wastes, sewage sludge derived from the biological sewage treatment process has drawn increasing attention in dark fermentation due to high organics content (more than 60% of dry weight), abundance (e.g., annual dry sludge production of 6.5 million tons in China in 2015), and a stable source. However, the hydrogen production efficiency of sole sewage sludge fermentation is usually unsatisfactory (0− 25.2 mL/g-volatile solids (VS)added) due to the limitations of low carbohydrate content (
