Simultaneous phosphorus and nitrogen removal with different C/N ratios in a low oxygen aeration system: Microorganisms and mechanisms.

In this study, a combined system with simultaneous nitrification, denitrification, and phosphorus removal was operated in continuous low oxygen aeration mode, and the effect of lower oxygen aeration (dissolved oxygen [DO] 0.5-1.5 mg/L) on its performance was examined. The combined system consisted of sludge and high-efficiency biological packing and was operated using four carbon/nitrogen ratios (C/N) with being 10:1, 8:1, 6:1, 10:1. Experimental results showed that the combined system could perform an efficient nitrogen and phosphorus removal under low DO and C/N ratio of 8:1 condition, and removal efficiencies of chemical oxygen demand (COD), NH4 + -N, and PO4 3- -P were 80.01%, 99.03%, and 89.51%, respectively. High-throughput analysis indicated that the functional species of denitrifying bacteria, including Ferruginibacter Azospira, Comamonas, Bacilli, Hyphomicrobium, Thauera, and Comamonadaceae, were important participants in biological nutrient removal. Meanwhile, Acinetobacter was enriched in the combined system, which contributed to phosphorus removal. PRACTITIONER POINTS: A combined system was operated firstly under continuous low oxygen condition. The lower dissolved oxygen (DO) of the combined system was maintained at 0.50-1.5 mg/L level. The combined system could realize simultaneous phosphorus and nitrogen removal under C/N ratio of 8:1. Several functional bacteria were enriched in the coupled systems.

New insights into denitrification and phosphorus removal with degradation of polycyclic aromatic hydrocarbons in two-sludge system.

Polycyclic aromatic hydrocarbons (PAHs) have led to failure of waste water treatment plant operations. In this study, a two-sludge system was used to solve this problem of simultaneously removing phosphorus, nitrogen, and PAHs. The results showed that increasing the maximum PAHs concentration to 15 mg/L did not have any negative effect on the removal rates of total nitrogen (79.68%) and chemical oxygen demand (75.94%); however, the phosphorus removal efficiency decreased to 61.16%. The system exhibited a stronger degradation ability for phenanthrene. Thauera, Hydrogenophaga, and Hyphomicrobium were enriched, which resulted in good denitrification, and contributed to PAHs removal. PAHs mixture promoted PAHs functional genes but restrained denitrification functional genes. However, single naphthalene enhanced denitrification functional genes, which confirmed the feasibility of denitrification coupled with PAHs degradation. In conclusion, for the removal of pollutants from sewage treatment, nitrogen and phosphorus removal coupled with PAHs could be maintained by selecting a two-sludge system.