Nitrate-mediated anaerobic microorganism-sponge iron system promoting simultaneous nitrogen and phosphate removal...

Piggery tail water (PTW), the biochemical unit effluent rich in nitrogen and phosphorus, causes eutrophication when directly discharged, threatening the ecological environment. Stricter standards and environmental regulations necessitate the urgent development of green, low-carbon advanced treatment technologies. This study introduces a nitrate-mediated anaerobic microorganism-sponge iron (mic-Fe⁰) system, which leverages microbial metabolism, in situ iron oxidation, and iron-phosphorus biomineralization to enhance nitrogen and phosphorus removal. A 262-day column experiment was conducted to compare three systems (abiotic sponge iron (s-Fe⁰), microbial s-Fe⁰, and nitrate-mediated mic-Fe⁰) and to optimize s-Fe⁰ dosage (5 %-15 %, V/V). The results indicated that when the s-Fe⁰ dosage was 10 %, the system achieved 83.55 % nitrate removal and 87.53 % total phosphorus (TP) removal, reducing the effluent TP concentration to 2.55 ± 1.06 mg/L, a 60 % decrease compared to the abiotic s-Fe⁰ system (6.33 ± 1.83 mg/L). Several analytical techniques revealed that the nitrate-mediated mic-Fe⁰ system exhibited the highest iron corrosion among all experimental groups and generated substantial iron-phosphorus minerals, such as vivianite and strengite. This confirmed that microbial-induced biocorrosion accelerated iron dissolution and promoted phosphorus fixation. Simultaneously, nitrate mediation further enhanced the corrosion process, facilitating the sustained dissolution of s-Fe⁰ and thereby achieving efficient phosphorus removal. Additionally, the enrichment of autotrophic and heterotrophic denitrifying bacteria expanded the nitrogen cycling pathway, enabling efficient nitrogen removal under low carbon-to-nitrogen ratios. This study elucidates the mechanism of enhanced nitrogen and phosphorus removal in the nitrate-mediated mic-Fe⁰ system, offering a novel strategy for the advanced treatment of PTW.