Optimization of Fenton combined with membrane bioreactor in the treatment of printing and dyeing wastewater

Effects of influent adsorbable organic halogens (AOX) and ammonia concentrations, hydraulic retention time (HRT) on the microbial community composition, functional genes abundance of anoxic/aerobic-membrane bioreactor (A/O–MBR) and its ability to treat raw and Fenton oxidized printing and dyeing wastewater (PDW) were evaluated. Fenton combined with A/O–MBR exhibited better treatment performance on chemical oxygen demand (COD) and AOX removal for PDW remediation. After six months’ optimization, at phase VII (50 mg/L AOX, 50 mg/L NH₄⁺–N, and HRT = 72h), 81.8 % of the COD and 94.6% of the AOX were removed in raw PDW A/O–MBR, and 92.0% of the COD and 100% of the AOX were removed in Fenton oxidized PDW A/O–MBR. An increase in ammonia level is conducive to the COD and AOX removal, whereas shortening the HRT in the A/O–MBR systems can drastically lower the COD and AOX removal efficiency. The metagenomics analysis indicates that an increase in AOX loading facilitates the accumulation of 2,4,6–TCP and 4–CP metabolism relevant genes, while significantly reduces the transcript per million (TPM) abundance of nitrogen removal functional genes. However, higher ammonia loading and shorter HRT promote the accumulation of AOX and nitrogen removal functional genes.