Study on dyeing wastewater treatment at high temperature by MBBR and the thermotolerant mechanism based on its microbial analysis

• Higher performance was achieved at increasing temperature for dyeing wastewater.
• COD removal exhibited two peaks at 40 °C and 50 °C, max NH3-N removal was at 35 °C.
• Caldilinea (35–45 °C), Rubellimicrobium, Pseudoxanthomonas (≥50 °C) was dominant.
• Process of thermotolerant mechanism establishment of the sludge is proposed.
• “Two-stage enrichment” of different thermophilic communities was the key procedure.

The dyeing wastewater treatment under increasing high temperature condition was studied in MBBRs. Results showed that as the temperature increase, the COD removal exhibited two best performances at 40 °C and 50 °C, and the maximum NH3-N removal was obtained at 35 °C and 40 °C. The optimum temperature for extracellular polymeric substances (EPS) yield is 45 °C and the humic acid was the major contributor. Microbial community was analyzed by the association of DGGE, real-time PCR and high-throughput sequencing technologies. The highest abundance of AOB (characterized by amoA genes) was obtained at 35 °C, and it confirmed that the biofilm (attached on fillers) can facilitate the AOB abundance maintaining in the sludge. The “precursor and successor” thermophilic communities were enriched and dominant at different temperature stages, which mainly conclude genera Caldilinea (from 35 °C to 45 °C) and genera Rubellimicrobium and Pseudoxanthomonas (over 50 °C), respectively. It meant the thermophilic community displayed great evolution at the critical temperature “45 °C|50 °C”. Additionally, the process of thermotolerant mechanism establishment of the sludge in the MBBRs is proposed and the “two-stage enrichment” of different thermophilic communities was considered as the key procedure.

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