Biological hydrogen production from organic wastewater by dark fermentation in China: Overview and prospects

High-efficient nitrogen removal from mature landfill leachate and waste activated sludge (WAS) reduction via partial nitrification and integrated fermentation-denitritation process (PNIFD)

Biological nitrogen removal from mature landfill leachate is ineffective due to the extremely low carbon/nitrogen (C/N) ratio. Moreover, a large amount of waste activated sludge (WAS) is inevitably generated from WWTPs during the municipal sewage treatment process. In this study, an innovative process was developed to enhance nitrogen removal from low C/N (1:1) mature landfill leachate and to reduce the WAS during a 300-day operation. Two sequencing batch reactors (SBRs) were involved in this process. Firstly, the mature landfill leachate was pumped into an aerobic reactor to undergo partial nitrification (PN-SBR). Then, the PN-SBR effluent and WAS were pumped into an anoxic reactor to undergo integrated fermentation and denitritation (IFD-SBR). The pH profile was treated as a real-time parameter to precisely control the duration of the PN and IFD processes. Partial nitrification and integrated fermentation-denitritation (PNIFD) system achieved a total nitrogen removal efficiency of 95.0% and an average nitrogen removal rate (NRR) of 0.63 kg/m³·d during the last operational phase. Due to a variety of refractory contaminants, the effluent COD concentration was 1865.9 mg/L and a 19.7% COD removal efficiency was obtained under an influent concentration of 2324.5 mg/L. Compared with the traditional nitrogen removal process, PNIFD not only decreased requirements for oxygen by 25% and the external organic carbon by 100%, but also achieved simultaneous reduction of external WAS. More than 53.7% of the external sludge was reduced during the IFD-SBR operational cycle, with an average external sludge reduction rate (SRR) of 5.09 kg/m³·d. Fermentation/denitritation related microorganisms, such as Anaerolineaceae, Acidimicrobiaceae and Thauera, accounted for up to 41.5% of the total abundance in the IFD-SBR. Based on the long and stable operation, this study provides a simple and promising approach for synchronous nitrogen removal and WAS reduction.

Biohydrogen production from co-fermentation of fallen leaves and sewage sludge

The co-fermentation of fallen leaves and sewage sludge was performed for the production of hydrogen at different mixing ratios. The experimental results indicated that the optimal mixing ratio of sludge to leaves was 20:80 (volatile solids (VS) basis), and the co-fermentation process showed a synergistic effect on biohydrogen production at this mixing ratio. The biohydorgen yield reached 37.8 mL/g-VS_added at the mixing ratio of 20:80, which was higher compared to the mono-fermentation of sludge (10.3 mL/g-VS_added) or the leaves (30.5 mL/g-VS_added). The VS removal was also highest (15.7%) at the mixing ratio of 20:80, which was higher compared to sludge mono-fermentation (6.2%) or leaves mono-fermentation (12.8%). Meanwhile, the co-fermentation process enhanced the biohydrogen production rate and led to a more efficient fermentation pathway. Microbial community analysis showed that the co-fermentation system enriched much more Clostridium, Bacillus and Rummeliibacillus genera, which was responsible for the synergistic effect on biohydrogen production.

Simultaneous waste activated sludge disintegration and biological hydrogen production using an ozone/ultrasound pretreatment

This paper offers an effective pretreatment method that can simultaneously achieve excess sludge reduction and bio-hydrogen production from sludge self-fermentation. Batch tests demonstrated that the combinative use of ozone/ultrasound pretreatment had an advantage over the individual ozone and ultrasound pretreatments. The optimal condition (ozone dose of 0.158 g O(3)/g DS and ultrasound energy density of 1.423 W/mL) was recommended by response surface methodology. The maximum hydrogen yield was achieved at 9.28 mL H(2)/g DS under the optimal condition. According to the kinetic analysis, the highest hydrogen production rate (1.84 mL/h) was also obtained using combined pretreatment, which well fitted the predicted equation (the squared regression statistic was 0.9969). The disintegration degrees (DD) were limited to 19.57% and 46.10% in individual ozone and ultrasound pretreatments, while it reached up to 60.88% in combined pretreatment. The combined ozone/ultrasound pretreatment provides an ideal and environmental friendly solution to the problem of sludge disposal.