Study on the Treatment of Soybean Product Wastewater by Heterotrophic Nitrification-Aerobic Denitrification Acinetobacter

Abstract

Soybean product wastewater (SPW) is organic wastewater generated during the processing of soybean products. Soaking, pulping, boiling, pressing and fermentation load SPW with high organic, N and P content, rendering it easily putrescible and malodorous. If discharged directly without treatment, it will cause serious harm to the receiving environment and human health. Heterotrophic Nitrification-Aerobic Denitrifying Microorganisms (HNADMs) have significant advantages in treating high-nitrogen organic wastewater, but there is currently no research report on using Heterotrophic Nitrification-Aerobic Denitrification (HN-AD) strains to treat SPW. Therefore, this study screened HN-AD strains from epiphytic aggregates of cyanobacteria in Taihu Lake through enrichment culture and gradient dilution-plate streaking, and optimized the process conditions for SPW using methods such as single-factor controlled variable method and response surface design experiments. On this basis, combined with molecular biology techniques such as whole-genome scanning, high-throughput sequencing, and functional gene polymerase chain reaction (PCR) amplification, the nitrogen removal pathways of HNADMs were explored. The main results are as follows: (1) With the existing HN-AD strain Acinetobacter CW-1 treating 3.3-fold-diluted SPW at 25 °C, 240 rpm, pH 5.26 and no external carbon, simultaneous removal of NH₄⁺-N, DTN, DTP and COD reached 99.4 %, 85.3 %, 28.0 % and 60.0 %, respectively. (2) Genome and HN-AD gene scans show strain CW-1 funnels NH₄⁺-N through three routes: GDH, GS-GOGAT, and the full HN-AD chain (NH₄⁺→NH₂OH→NO₂⁻→NO₃⁻→NO₂⁻→NO→N₂O/N₂).