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With the shortage of phosphorus resources, the concept of phosphorus recovery from wastewater is generally proposed. Recently, phosphorus recovery from wastewater in the form of vivianite has been widely reported, which could be used as a slow-release fertilizer as well as the production of lithium iron phosphate for Li-ion batteries. In this study, chemical precipitation thermodynamic modeling was applied to evaluate the effect of solution factors on vivianite crystallization with actual phosphorus containing industrial wastewater. The modeling results showed that the solution pH influences the concentration of diverse ions, and the initial Fe2+ concentration affects the formation area of vivianite. The saturation index (SI) of vivianite increased with the initial Fe2+ concentration and Fe:P molar ratio. pH 7.0, initial Fe2+ concentration 500 mg/L and Fe:P molar ratio 1.50 were the optimal conditions for phosphorus recovery. Mineral Liberation Analyzer (MLA) accurately determined the purity of vivianite was 24.13%, indicating the feasibility of recovering vivianite from industrial wastewater. In addition, the cost analysis showed that the cost of recovering phosphorus by the vivianite process was 0.925 USD/kg P, which can produce high-value vivianite products and realize "turn waste into treasure". [Display omitted] • Modeling effectively predicted the vivianite optimum crystallization conditions. • LMA was rarely used to accurately determine the content of vivianite. • Provide new ideas for phosphorus recovery from industrial wastewater. [ABSTRACT FROM AUTHOR]

The coupled process of thiosulfate-driven denitrification (NO 3 −→NO 2 −) and Anammox (TDDA) was a promising process for the treatment of wastewater containing NH 4 +-N and NO 3 −-N. However, the high concentration of SO 4 2− production limited its application, which needs to be alleviated by an economical and effective way to promote the application of TDDA process. In this study, TDDA process was started in a relatively short time by stepwise replacing nitrite with nitrate and operated continuously for 146 days. Results presented that the average total nitrogen removal efficiency of 82.18% can be acquired at a high loading rate of 1.98 kg N/(m3·d) with maximum nitrogen removal efficiency up to 87.04%. It was observed that the increase of S/N ratio improved the denitrification efficiency and slightly inhibit the Anammox process. Batch tests showed that Sulfammox process appeared in TDDA process under certain conditions, further contributing 2.59% nitrogen removal and 10.46% sulfur removal (14.42 mg/L NH 4 +-N and 37.68 mg/L SO 4 2--S were removed). This finding was mainly attributed to the reduction of sulfate in TDDA system to elemental S0 or HS−, which subsequently was used as an electron donor to realize the recycling of sulfate (SO 4 2--S) pollutants and promote the sulfur-nitrogen (S–N) cycle. High-throughput analysis displayed that Anammox bacteria (Candidatus_Kuenenia), Sulfur-oxidizing bacteria (Thiobacillus) with relatively high abundance of 5.37%, 7.74%, respectively, guaranteeing the excellent nitrogen and sulfate removal performance in the reactor. The enrichment of phyla Chloroflexi (31.79%), Proteobacteria (31.82%), class Ignavibacteriales (10.55%), genus Planctomycetes (13.57%) further verified the exitence of Sulfammox process in the TDDA reactor. This study provides a new perspective for the practical application of TDDA in terms of reducing the production of high concentration SO 4 2− and saving operational cost and strengthening deeply nitrogen removal. • The TDDA was started in a short time via stepwise replacing nitrite with nitrate. • The Highest TN removal (87.04%) was acquired at the NLR of 1.98 kg N/(m3·d) in TDDA. • Sulfammox process appeared in TDDA process which accelerated S–N cycle of system. • The contributions of various nitrogen and sulfur removal pathways were investigated. • The enrichment of Ignavibacteriales (10.55%) verified the exitence of Sulfammox. [ABSTRACT FROM AUTHOR]

The coupled process of thiosulfate-driven denitrification (NO 3 −→NO 2 −) and Anammox (TDDA) was a promising process for the treatment of wastewater containing NH 4 +-N and NO 3 −-N. However, the high concentration of SO 4 2− production limited its application, which needs to be alleviated by an economical and effective way to promote the application of TDDA process. In this study, TDDA process was started in a relatively short time by stepwise replacing nitrite with nitrate and operated continuously for 146 days. Results presented that the average total nitrogen removal efficiency of 82.18% can be acquired at a high loading rate of 1.98 kg N/(m3·d) with maximum nitrogen removal efficiency up to 87.04%. It was observed that the increase of S/N ratio improved the denitrification efficiency and slightly inhibit the Anammox process. Batch tests showed that Sulfammox process appeared in TDDA process under certain conditions, further contributing 2.59% nitrogen removal and 10.46% sulfur removal (14.42 mg/L NH 4 +-N and 37.68 mg/L SO 4 2--S were removed). This finding was mainly attributed to the reduction of sulfate in TDDA system to elemental S0 or HS−, which subsequently was used as an electron donor to realize the recycling of sulfate (SO 4 2--S) pollutants and promote the sulfur-nitrogen (S–N) cycle. High-throughput analysis displayed that Anammox bacteria (Candidatus_Kuenenia), Sulfur-oxidizing bacteria (Thiobacillus) with relatively high abundance of 5.37%, 7.74%, respectively, guaranteeing the excellent nitrogen and sulfate removal performance in the reactor. The enrichment of phyla Chloroflexi (31.79%), Proteobacteria (31.82%), class Ignavibacteriales (10.55%), genus Planctomycetes (13.57%) further verified the exitence of Sulfammox process in the TDDA reactor. This study provides a new perspective for the practical application of TDDA in terms of reducing the production of high concentration SO 4 2− and saving operational cost and strengthening deeply nitrogen removal. • The TDDA was started in a short time via stepwise replacing nitrite with nitrate. • The Highest TN removal (87.04%) was acquired at the NLR of 1.98 kg N/(m3·d) in TDDA. • Sulfammox process appeared in TDDA process which accelerated S–N cycle of system. • The contributions of various nitrogen and sulfur removal pathways were investigated. • The enrichment of Ignavibacteriales (10.55%) verified the exitence of Sulfammox. [ABSTRACT FROM AUTHOR]