In this study, a biofilter was developed with a ZVI/PHBV/sawdust (ZPS) composite for treating simulative secondary effluent from wastewater treatment plants. Results showed that effluent concentrations of NO3–N and TP in the ZPS biofilter were stable below 2.0 mg/L and 0.1 mg/L, corresponding to 95% NO3–N removal and 99% TP removal, respectively. Microbial community analysis revealed that the transformation of dominant taxa from Dechloromonas to Clostridium sensu stricto\_7 from 30 d to 120 d suggested that the ZVI-induced succession of dominant fermentation bacteria ensured the stable carbon supply for denitrification. Co-occurrence network analysis showed that the ZVI directly enhanced the interaction of microbial community. Fe-related bacteria occupied a key position in the rare species, which might maintain the function of iron-mediated organic matter decomposition and denitrification. These findings provide an alternative for advanced removal of nitrogen and phosphorus in biofilters packed with ZPS composites.

With the advancement of water ecological protection and water control standard, it is the general trend to upgrade the wastewater treatment plants (WWTPs). The simultaneous removal of nitrogen and phosphorus is the key to improve the water quality of secondary effluent of WWTPs to prevent the eutrophication. Therefore, it is urgent to develop the applicable technologies for simultaneous biological removal of nitrogen and phosphorus from secondary effluent. In this review, the composition of secondary effluent from municipal WWTPs were briefly introduced firstly, then the three main treatment processes for simultaneous nitrogen and phosphorus removal, i.e., the enhanced denitrifying phosphorus removal filter, the pyrite-based autotrophic denitrification and the microalgae biological treatment system were summarized, their performances and mechanisms were analyzed. The influencing factors and microbial community structure were discussed. The advanced removal of nitrogen and phosphorus by different technologies were also compared and summarized in terms of performance, operational characteristics, disadvantage and cost. Finally, the challenges and future prospects of simultaneous removal of nitrogen and phosphorus technologies for secondary effluent were proposed. This review will deepen to understand the principles and applications of the advanced removal of nitrogen and phosphorus and provide some valuable information for upgrading the treatment process of WWTPs.

Effective control of nitrogen and phosphorus simultaneously is of great significance to satisfy the strict requirement of the ecological health of receiving waters. In this study, PHBV/ZVI composites made from solid carbon (poly-3-hydroxybutyrate-cohyroxyvelate, PHBV) and zero-valent iron (ZVI) were proposed to be functional fillers in biofilters for advanced wastewater treatment. Results showed that high-rate treatment performance was obtained with nitrate and phosphorus removal efficiencies of 79-97% and 97-98% in the biofilters packed with PHBV/ZVI composites. Lower N2O and CH4 emission (56.3-129.2 mu g m(-2) h(-1)) were also achieved simultaneously, further indicating the superiority of PHBV/ZVI composites applied in the wastewater treatment. High-throughput quantitative-PCR (HT-qPCR) results uncovered that the existence of ZVI could enrich carbon degradation genes (manA, gam and mxa) and facilitate denitrifier utilize organic matters more efficiently, as evidenced by up-regulations of genes involved in nitrate reduction (nirS and nosZ). Meanwhile, higher Fe concentration and less functional genes inducing lower activities of phosphate metabolism and in PHBV/ZVI systems indicated ZVI corrosion and coprecipitation were the main pathway of phosphorus removal. Network and redundancy analysis highlighted the role of ZVI in the removal of pollutants with keystone genes changed (pox and napA) and genes distribution remodeled compared to single PHBV fillers. Further, the activities of dehydrogenase (DHA) and nitrite reductase (Nir) enzymes also increased by the modulation of microbes, which explicitly interpreted the synergistic promotion of PHBV and ZVI on the denitrification process. These findings provided an alternative for the advanced treatment of wastewater and improve the understanding of C, N and P cycling in the co-occurrence of PHBV and ZVI.

The solid carbon source (poly-3-hydroxybutyrate co 3 hyroxyvalerate, PHBV) and manganese oxide mineral (Mn ore) were proposed firstly as co-substrates for eliminating nutrients and sulfamethoxazole (SMX) in this study. Results showed that high-rate nitrate and phosphate removal could be achieved in PHBV/Mn ore systems with the average efficiencies of 90% and 66.7%, respectively, although the addition of SMX decreased denitrification performance by 4.5-10.5%. SMX was removed mainly via biodegradation of enriched denitrifying microbes, with the average removal efficiency of 20-50% in PHBV/Mn ore systems, which was higher than that in PHBV systems. The existence of Mn ore markedly shaped the microbial community structure, leading to the dominant bacteria transforming from Microscillaceae to Sporomusaceae. The genera of Geobactor, Desulfovibrio and Anaerovorax were found to maintain the stability of microbial system as keystone species. Surprisingly, large amount of Mn(II) was accumulated, which not only verify the involvement of Mn cycling in decontamination process, but also might explain the propagation of ARGs (tnpA-04 and tnpA-05) in host microorganisms. Therefore, the optimized mixture proportion of PHBV and Mn ore should be further estimated avoiding Mn (II) accumulation in the effluent. On the whole, these results might shed light on new insight for advanced treatment of nutrients and emerging pollutants in biofilm reactors.

ABSTRACT: A higher denitrification rate was realized via controlling the mass ratio of pyrite and poly(3-hydroxybutyrate-hydroxyvalerate) (PHBV) under natural aerobic conditions. The results showed that the suitable mass ratio of PHBV and pyrite could be 1:2 with its removal efficiency of nitrogen and phosphorus of 99.7 and 53.4%, respectively. The PHBV/pyrite system has formed the spatial patterns of the biofilm community, such as Dechloromons attached to the pyrite surface, Rhodocyclaceae attached to the PHBV surface, and Acidovorax attached to the suppled sludge, which highlighted that the autotrophic??? heterotrophic synergy was achieved. The difference analysis among functional genes detected by high-throughput quantitative polymerase chain reaction indicated that the surface of pyrite in the pyrite/PHBV system is the hot area of methane production, the denitrifying process, and phosphorus removal. Network analysis indicated that there was a closer connection among functional genes on the pyrite surface, also supporting the speculation that pyrite was the hot area for the interaction of various genes in the pyrite/PHBV system. The key gene co-occurrence revealed that lig, nirS, and aspA are the keystone genes for cellulose degradation, denitrification, and S cycling, respectively. These results suggested that the pyrite surface was the hot area for denitrification, phosphorus removal in the blending system with pyrite and PHBV for nitrogen and phosphorus removal.