Summary The pretreated cornstalk (CS) was employed for biohydrogen production through combining dark‐fermentative bacteria, cow dung, and photosynthetic bacteria, Rhodobacter capsulatus mutant in this work. In the first step, the cornstalk was pretreated with 0.75% NaOH, 12 IU/g‐CS cellulase, and 2400 IU/g‐CS hemicellulase under different hydrolysis time and temperature. The reducing sugar yields were very close under different conditions, and its maximum was 0.51 ± 0.01 g/g‐CS at hydrolysis 108°C for 2.0 hours. However, the H2 yield of dark fermentation enhanced with the increasing hydrolysis time and temperature, and the maximum was 156.7 ± 8.6 mL/g‐CS at hydrolysis 126°C for 2.0 hours. The biogas was only H2 and CO2, and no methane was found. In the second step, R. capsulatus ZYHAB3 with the mutation on both hvrA and hupAB genes was obtained from wild type (R. capsulatus SB1003) and the inactivation of both hvrA and hupAB genes remarkably enhanced nitrogenase activity. When the dark‐fermentation effluent was employed as a substrate, the H2 yield and maximum H2 evolution rate of ZYHAB3 were 2827.5 ± 283.5 mL/L and 40.9 ± 2.3 mL/(Lh), which increased by 44.5 and 39.1% compared with those of wild type, respectively. The high H2 yield of 439.4 mL/g‐CS was obtained from pretreated cornstalk through the 2‐step process, and the chemical oxygen demand removal rate achieved 90.6%. The results suggest that combining cow dung and R. capsulatus mutant (hvrA− hupAB−) could be a promising way to produce H2 form agricultural wastes.

Coal supercritical water gasification (SCWG) is famous for generating clean gas without SO x pollutant. Study of sulfur transformation characteristics can provide the basis of sulfur removal during hydrogen production by coal gasification in supercritical water (SCW) at the source. In this work, two coals produced from Linfen and Zhangjiamao in China (hereinafter to be referred as L-coal and Z-coal), were chosen as experimental feedstocks to investigate sulfur transformation characteristics during hydrogen production by coal gasification in SCW (550−750 °C, 20 min, 25 MPa). Sulfur transformation pathway and sulfur forms in the products were complex but detected comprehensively. H 2 S was the only gaseous product instead of SO x , whereas SO 4 2− was the main liquid−sulfur product. Inorganic and organic sulfur compounds were used to investigate sulfur transformation mechanisms. H 2 S had three sources as follows. First, among inorganic sulfur of raw coal, FeS 2 (Pyrite) was chemically stable in SCW lacking of hydrogen. When FeS 2 was in hydrogen atmosphere, H 2 S was generated and FeS 2 was converted to Fe 1−x S and Fe 3 O 4 under SCW. Second, H 2 S came from unstable sulfate minerals such as FeSO 4 which may decompose and be converted to Fe 3 O 4 . Third, organic sulfur, especially thiophene sulfur transformed to H 2 S. The two sulfur products H 2 S and SO 4 2− depend on H or OH free radical in SCW. More H free radical provided a reducing environment of SCW to generate H 2 S at higher temperatures, whereas more OH radical provided an oxidizing environment of SCW to generate SO 4 2− at lower temperatures, but the final trend was generating H 2 S when coal gasified completely at a higher temperature. The results of this study may provide an experimental basis of solving the SO x emission from coal at the source and demonstrate a promising clean utilization way of coal.