Diversity Manipulation of Psychrophilic Bacterial Consortia for Improved Biological Treatment of Medium-Strength Wastewater at Low Temperature

Papermaking wastewater treatment coupled to 2,3-butanediol production by engineered psychrotrophic Raoultella terrigena

The simultaneous bioremediation and bioconversion of papermaking wastewater by psychrotrophic microorganisms holds great promise for developing sustainable environments and economies in cold regions. Here, the psychrotrophic bacterium Raoultella terrigena HC6 presented high endoglucanase (26.3 U/mL), xylosidase (732 U/mL), and laccase (8.07 U/mL) activities for lignocellulose deconstruction at 15 °C. mRNA monitoring and phenotypic variation analyses confirmed that cold-inducible cold shock protein A (CspA) facilitated the expression of the cel208, xynB68, and lac432 genes to increase the enzyme activities in strain HC6. Furthermore, the cspA gene-overexpressing mutant (strain HC6-cspA) was deployed in actual papermaking wastewater and achieved 44.3%, 34.1%, 18.4%, 80.2% and 100% removal rates for cellulose, hemicellulose, lignin, COD, and NO3--N at 15 °C. Simultaneously, 2,3-butanediol (2,3-BD) was produced from the effluent with a titer of 2.98 g/L and productivity of 0.154 g/L/h. This study reveals an association between the cold regulon and lignocellulolytic enzymes and provides a promising candidate for simultaneous papermaking wastewater treatment and 2,3-BD production.

Efficient carbon removal and excellent anti-clogging performance have been achieved in multilayer quartz sand horizontal subsurface flow constructed wetland for domestic sewage treatment

The present study aimed to investigate the application of a multilayer quartz sand substrate horizontal subsurface flow constructed wetland (HSFCW) for campus sewage treatment. It aimed to assess the pollutant removal efficiency and anti-clogging performance under the suggested maximum organic loading rate (250 g/m²/d). The results of the multilayer HSFCW (CW6) were compared to the mololayer HSFCW (CW1) for the removal of the chemical oxygen demand (COD), solid accumulation, and microbial communities. During operation, the combination conditions of high hydraulic loading rate (HLR) with low COD concentration were better for COD removal under a high organic loading rate (OLR) of 200-300 g/m²/d. The maximum removal rate reached 80.4% in CW6 under high HLR, which was 13.8% higher than that in CW1, showing better adsorption and biodegradation ability of organic matter. Impressive clogging resistance capacity was found in CW6 due to the lower contents of the insoluble organic matter (IOM) that are prone to clogging, indicating full degradation of organic matters, particularly IOM, in CW6 under high HLR. Less abundance of unclassified Chitinophagaceae (under low HLR), Pedobacter and Saccharibacteria_genera_incertae_sedis (under high HLR) in CW6, which contributed to aerobic membrane fouling, helped to prevent clogging. Moreover, Brevundimonas, Cloacibacterium, Citrobacter, Luteimonas contributed to IOM degradation, thus further enhancing the anti-clogging performance. In view of the better clogging resistance performance, the application of CW6 operated under high HLR and low COD concentrations was recommended to achieve economical, efficient, and steady COD removal for domestic sewage treatment in long-term operation.