Advanced treatment of biologically pretreated coal gasification wastewater using a novel expansive flow biological intermittent aerated filter process with a ceramic filler from reused coal fly ash

Abstract

A novel expansive flow biological intermittent aerated filter (BIAF) process was employed for the advanced treatment of real biologically pretreated coal gasification wastewater (CGW) which had poor biodegradability and a low carbon/nitrogen ratio. The results indicated that the expansive flow BIAF with reused coal fly ash and clay as a ceramic filler exhibited efficient performance for pollutant removal. The effluent concentrations of COD, total phenols, NH₄⁺-N, and total nitrogen (TN), were 39.5, 4.8, 6.3, and 18.8 mg L⁻¹ respectively, with a turbidity of 3 NTU and chromaticity of 26 degrees at the optimal hydraulic retention time of 9 h, meeting the standards for the reuse of water. Moreover, most toxic and refractory pollutants were also eliminated. Meanwhile, intermittent aeration not only significantly increased nitrate and nitrite reductases, but also successfully improved simultaneous nitrification and denitrification activity which facilitated TN removal. The results of high-throughput sequencing represented that the biological process included 28 major bacteria which were affiliated to 7 phyla, where Thermomonas, Methylococcus and Comamona were the most important functional genera. After stable operation for 192 h, the optimal backwashing time was 6 min when the air and water intensities were 8 and 2.5 L (s m²)⁻¹, respectively. These results demonstrated that the expansive flow BIAF process, with the advantages of efficient, economical and sustainable development, was beneficial to engineering applications.