Strengthen high-loading operation of wastewater treatment plants by composite micron powder carrier: Microscale control of carbon, nitrogen, and sulfur metabolic pathways

Abstract

The concentration of activated sludge is a crucial factor influencing the capacity and efficiency of sewage wastewater treatment plants (WWTPs). However, high sludge concentrations can lead to sludge loss in the secondary sedimentation tank, resulting in reduced processing capacity, particularly during low-temperature stages and sludge bulking. This study investigated the impact of adding composite micron powder carriers (CMPC) in high-concentration powder carrier biofluidized bed (HPB) technology to the biochemical units of WWTPs on sludge concentration and settling performance. For the traditional activated sludge method (ASM), its hydraulic retention time (HRT) was 8 h, with an average effluent total nitrogen (TN) of 15.14 mg/L. Sludge bulking was prone to occur in low-temperature environments, resulting in a high average sludge volume index (SVI) of 560 mL/g. Conversely, with a CMPC dosage of 4 g/L, the HRT of HPB technology was 4.8 h, and the average effluent TN was 11.40 mg/L, with a removal efficiency of 67.43 %. During operation of HPB technology under high sludge concentration conditions (8 g/L), the average SVI remained at 85 mL/g, indicating excellent settling characteristics. Moreover, in the sequencing batch reactor (SBR), the SVI value of bulking sludge decreased from the original 695 to 111 mL/g by the 9th day of operation with the CMPC dosage of 2 g/L. At the same time, the filamentous bacteria almost disappeared, suggesting that CMPC inhibit the growth of filamentous bacteria. Metagenomic analysis demonstrated that CPMC enhance the utilization of small molecular fatty acids in activated sludge and promote electron transfer between nitrate and nitrite, thereby improving wastewater treatment capacity. Additionally, CMPC enhanced the relative abundance of Saprospiraceae in sludge, which accelerate the degradation of polysaccharides in extracellular polymeric substances, weaken sludge's hydrophilic properties, and improve sludge's settling performance. Overall, these findings suggested that CMPC effectively strengthen the high-loading operation of WWTPs by improving sludge concentration and sedimentation performance.