Impact of artificial mixing and oxygenation on bacteria in a water transfer reservoir: Community succession and the role in water quality improvement

Hydrogen generated by electrochemical water splitting as electron donor for nitrate removal from micro-polluted reservoir water

Extremely limited organic carbon sources and aerobic environment in micro-polluted reservoir water make conventional denitrification exceptionally challenging. As a result, total nitrogen (TN) concentration in most reservoir waters exceeds standard value year-round. In this study, for the first time, we constructed a mini water-lifting and aeration system (mini-WLAS) to remove nitrate in actual reservoir water. In the mini-WLAS, H2 was produced through electrolysis of reservoir water without adding any electrolyte, and the ascending water flow carried the generated H2 from lower layer to upper bacteria layer. The maximum denitrification rate reached 0.29 mg (L·d)-1 under dissolved oxygen (DO) concentration of 6-8 mg L-1, 6.04 times higher than that of the control group. There is almost no accumulation of NH4+-N, NO2--N, and N2O, and the concentration of CODMn decreased by 55.2 %. More importantly, the pH stayed near-neutral steadily throughout the whole process. Microbial community analysis showed that the abundances of hydrogenotrophic denitrifying bacteria (HDB) were 2 orders higher than those in the control system. Some HDB could work under aerobic conditions, providing an explanation for the excellent denitrification performance under high DO. This study provides a novel perspective for TN removal from reservoir water.

Recirculating aquaculture system as microbial community and water quality management strategy in the larviculture of Scylla paramamosain

The structure and function of the water microbial community can change dramatically between different rearing modes. Yet investigations into the relationships between microbial community and water quality remain obscure. We provide the first evidence that rearing modes alter bacterial community and water quality in the rearing water of the mud crab (Scylla paramamosain) larvae. The juveniles in the recirculating aquaculture system (RAS) had a higher viability than those in the water exchange system (WES). RAS had the significantly lower levels of total ammonia nitrogen (TAN), NH3, NO2--N, total nitrogen (TN), total dissolved solids (TDS), and chemical oxygen demand than those of WES. The number of significantly different amplicon sequence variants between rearing modes increased as the larvae developed. NH3, TAN, TDS, NO2--N, and TN were closely related to the late alterations in water bacterial community. Both the FAPROTAX tool and quantitative PCR analysis showed enhanced nitrogen cycling functional potential of water bacterial community of RAS. Random forest analysis identified the enriched water bacteria especially heterotrophic bacteria such as Phaeodactylibacter, Tenacibaculum, and Hydrogenophaga, which were vital in removing nitrogenous compounds via simultaneous nitrification and denitrification. Notably, RAS could save 18.5 m3 of seawater relative to WES in larviculture on the scale of 2.5 m3. Together, these data indicate that RAS could function as microbial community and water quality management strategy in the larviculture of crab.