• Energy Research

Recently, upflow microaerobic sludge blanket (UMSB) system has been developed to remove ammonium and organic matter simultaneously. This study aims to establish influent and operational conditions promoting anammox-based nitrogen removal process in the UMSB reactor by using a modified Activated Sludge Model. Experiments were performed on a laboratory-scale UMSB reactor treated piggery wastewater for over two years. With the experimentally determined model parameters, the established model well simulated the UMSB reactor performance. The maximum anammox growth rate was calibrated to be 0.41 d-1 at 35 °C. Further simulations showed that UMSB reactor operated with high influent organics or nitrogen loading rates at temperature above 15 °C can achieve efficient nitrogen removal (>70%). The nitrogen loading over 0.6 kg N/(m3·d)) significantly favors anammox activity. UMSB could also be a promising system for nitrogen removal from low-strength ammonium wastewater with fluctuated COD influence. These results provide support to UMSB design and operational optimization.

Abstract Archaea play dominant roles in nutrient cycling, but the archaeal community and function in coastal wetlands with different stress patterns remain poorly understood. Here, two typical coastal wetlands of the Yellow River estuary, Zone A with only tidal erosion and Zone B with runoff and tidal invasion, were selected to explore the possible differences in archaeal community and function and evaluate the influential factors. Compared with Zone B, Zone A had higher levels of total nitrogen, available phosphorous (AP) and pH. Thaumarchaeota was the most abundant archaeal phylum, followed by Euryarchaeota in Zones A and B. Candidatus_Nitrosopelagicus (30.85% in Zone A, 36.04% in Zone B) and Candidatus_Nitrosopumilus (24.10% in Zone A, 39.01% in Zone B) were the dominant ammonia-oxidizing archaea in both zones, and Haloarcula and Haloferax were the dominant denitrifying halophilic archaea in Zone A. Organisms from methanogenic genera Methanobrevibacter, Methanocorpusculum and Methanosarcina were enriched in Zone A. Anaerobic methanotrophic Candidatus_Methanoperedens (ANME-2d) had relatively low abundance in Zones A and B. These archaea were the key factors in maintaining the carbon and nitrogen cycles in coastal wetlands. Moreover, nitrification was relatively active in Zone B, and denitrification and methanogenesis dominated in Zone A. Redundancy analysis revealed that AP, NH4+–N, pH, salinity and moisture played important roles in the determination of archaeal community composition at the genus level. Microbial community and PICRUSt analysis indicated that the archaeal communities changed significantly, but the functions were relatively stable for both zones. This finding suggests that environmental selection in similar habitats could lead to functional convergence. The relative gene abundances of nitrate reductase were relatively high, indicating that aside from denitrification, a large amount of nitrite as an electron acceptor was present to perform nitrite-driven anaerobic methane oxidation via reverse methanogenesis. The findings help in understanding the impacts of different stress patterns on archaeal community composition and functional potential in coastal wetlands.

Bicarbonate (HCO3-) has been extensively researched as a buffer in anaerobic digestion. The effect of HCO3- concentration on syntrophic butyrate oxidation process was evaluated by batch culturing of anaerobic activated sludge, and the mechanism was further revealed by the changes of Gibbs free energy (ΔG) and the interspecies transfers of electron and proton. The results showed that butyrate degradation rate was enhanced by 32.07% when the supplement of HCO3- increased from 0 to 0.20 mol/L. However, methane production and acetate degradation were strongly inhibited by HCO3- more than 0.10 mol/L. More function of HCO3- was found as 1) decreasing the ΔG of syntrophic methanogenesis of butyrate while increasing the ΔG of methanogenesis of acetate, 2) enriching M. harundinacea and M. concilii, 3) increasing the diffusion rate of protons between the syntrophic consortia. This work would increase the anaerobic digestion efficiency by enhancing the interaction of the syntrophic consortia.