Diatomite powder carrier improved nitrogen and phosphorus removal from real municipal wastewater: Insights into micro-granule formation and enhancement mechanism

With increasingly stringent standards for wastewater discharge, the need to upgrade the wastewater treatment process is urgent. This study established a novel wastewater treatment process based on powder carriers combined with a hydrocyclone separator. Wastewater treatment capacity was enhanced in-situ by the addition of diatomite powder carriers. Process characteristics and enhancement mechanism were further investigated. Results indicated that the TN removal efficiency increased from 61.53 ± 2.14 % to 78.79 ± 2.31 %, while the PO43−-P removal efficiency and COD removal efficiency reached 70.27 ± 0.69 % and 95.34 ± 1.06 %, respectively. The link of powder carrier and the hydrophobic effect of proteins promoted the formation of micro-granules, with an average particle size up to 244.8 ± 3.9 μm. Diatomite powder addition improved the settleability and prevented the sludge bulking, while the sludge concentration was increased by 26.8 %. Among all denitrification and phosphorus removal related genera, the unclassified_f_Rhodocyclaceae abundance increased from 1.29 % to 11.63 % after the diatomite addition, while the Acinetobacter abundance increased from 4.97 % to 10.85 %. Meanwhile, the correlation network became more complex and stable, and synergy between functional bacteria was facilitated. Metagenomic analysis demonstrated that the functional genes related to denitrification and poly-P biosynthesis and hydrolysis were enhanced. Especially, the up-regulation of genes related to the synthesis of polyhydroxyalkanoates (PHAs) further improved the reactor performance. These results will provide a theoretical basis for the development and application of powder carrier process.