A computer docking study has been carried out on the crystal surfaces of cellulose Ialpha crystal models for the carbohydrate binding module (CBM) protein of the cellobiohydrolase Cel7A produced by Trichoderma reesei. Binding free energy maps between the CBM and the crystal surface were obtained by calculating the noncovalent interactions and the solvation free energy at grid points covering the area of the unit cell dimensions at the crystal surface. The potential maps obtained from grid searches of the hydrophobic (110) crystal surface exhibited two distinct potential wells. These reflected the 2-fold helical symmetry of the cellulose chain and had lower binding energies at the minimum positions than those for the hydrophilic (100) and (010) crystal surfaces. The CBM-cellulose crystal complex models derived from the minimum positions were then subjected to molecular dynamics (MD) simulation under an explicit solvent system. The (110) complex models exhibited larger affinities at the interface than the (100) and (010) ones. The CBM was more stably bound to the (110) surface when it was placed in an antiparallel orientation with respect to the cellulose fiber axis. In the solvated dynamics state, the curved (110) surface resulting from the fiber twist somewhat assisted a complementary fit with the CBM at the interface. In addition to the conventional Generalized Born (GB) method, the three-dimensional reference interaction site model (3D-RISM) theory was adopted to assess a solvent effect for the solvated MD trajectories. Large exothermic values for the noncovalent interactions appeared correlated to and were mostly compensated by endothermic values for the solvation free energy. These gave total binding free energies of -13 to -28 kcal/mol. Results also suggested that the hydrogen bonding scheme was not essential for substrate specificity.

Nitrate contamination of groundwater has become a serious issue affecting the quality of drinking water and human health. An energy-efficient, low-cost, and simple reactor was developed to remove nitrate via hydrogenotrophic denitrification (HD). Hydrogen (H 2 ) supply was optimized by using a continuous supply of hydrogen (1-15 mL/min). The results revealed that the optimal condition was 5 mL/min, which yielded a nitrogen removal efficiency of 86.4% and a hydrogen effectiveness of 199 mg-N/g-H 2 . In the subsequent experiment, an intermittent hydrogen supply was used to improve the hydrogen effectiveness and hydrogen consumption. Using a cycle with a short period of hydrogen supply (3 min with hydrogen supply and 7 min with no hydrogen supply), excellent nitrogen removal efficiency (96.5%) was achieved, and the hydrogen effectiveness increased to 744 mg-N/g-H 2 . Furthermore, bacteria belonging to the Proteobacteria phylum and Betaproteobacteria class were the major components of the microbial community. However, Hydrogenophaga spp. (39.3%) was dominant under the continuous system, whereas Thauera spp. (58.5%) was the most abundant species under the intermittent system. In this study, Hydrogenophaga spp., Thauera spp., and Rhodocyclaceae, which were responsible for HD, afforded in efficient nitrogen removal from groundwater.

The physicochemical and biological characteristics of milli-microbubbles were compared to evaluate their performance on hydrogenotrophic denitrification (HD) for groundwater treatment in remote areas. The hydrogen supply was controlled at 1.14 L/d with 40 mgN/L of NO 3 -N. The microbial community structure in two bubble reactors was investigated by high throughput sequencing. Microbubbles enhanced biodegradation in the HD system, providing a maximum nitrogen removal efficiency of 99%. Approximately 50% of total hydrogen was utilized for biological nitrate removal with the highest hydrogen effectiveness achieved at 1.21 g N/g H 2 . In contrast, millibubbles achieved less than 10% efficiency and 9.9% of total hydrogen was consumed for biological nitrogen removal. Thauera spp., Hydrogenophaga spp. and Rhodocyclaceae of Proteobacteria phylum were the dominant bacteria in the microbubble reactor, whereas Methyloversatilis spp. was dominant in the millibubble reactor, in which a relatively low amount of hydrogen (0.6 mg/L) was dissolved. The differences can be attributed to the higher hydrogen transfer efficiency (45×10 -3 s -1 ) and lower rising velocity (0.31 mm/s) of the microbubbles system than the millibubbles system (2×10 -3 s -1 and 480 mm/s). The micro-hydrogen bubble technology affords increased hydrogen effectiveness, reduced energy consumption, and modified system design. Therefore, it is more appropriate for enhancing HD.

The anaerobic ammonium oxidation (anammox) process holds great promise for treating nitrogen-contaminated water; stable nitrite-nitrogen (NO2--N) production is significant to anammox performance. In this study, partial hydrogenotrophic denitrification (PHD) was used to stably and efficiently produce NO2--N from nitrate-nitrogen (NO3--N). An investigation of the effects of initial pH on the PHD process revealed that a high NO2--N production efficiency (77.9%) could be ensured by setting an initial pH of 10.5. A combined PHD-anammox process was run for more than three months with maximal ammonium-nitrogen (NH4+-N), NO3--N, and total dissolved inorganic nitrogen removal efficiencies of 93.4, 98.0, and 86.9%, respectively. The NO2--N to NH4+-N and NO3--N to NH4+-N ratios indicated that various bioprocesses were involved in nitrogen removal during the anammox stage, and a 16S rRNA gene amplicon sequencing was performed to further clarify the composition of microbial communities and mechanisms involved in the nitrogen removal process.