Enhancing nitrogen removal in combined sewage overflows by using bio-fluidized bed with ceramic waste powder carriers: effects and mechanisms.

Micron-size ceramic waste powder (< 75 μm and 75-150 μm) was used as the carrier in a high-concentration powder carrier bio-fluidized bed (HPB) to treat simulated overflow sewage (CSOs). The sludge extracellular polymers (EPS), electron transfer capacity of EPS, nitrogen removal pathways, and microbiological characteristics were analyzed to gain insights into the nitrogen removal pathways and mechanisms. The results showed that only the effluent from the HPB (< 75 μm) could meet the stringent pollutant discharge standards in China of 50 mg/L for COD_Cr and 15 mg/L for total nitrogen from beginning to end. Meanwhile, the electrochemical performance tests indicated that the electron accepting and donating capacities of the sludge EPS in the HPB (< 75 μm) were 42.75% and 32.73% higher than those in the conventional activated sludge, meaning that ceramic powder carriers can increase the extracellular electron transfer capacity of the sludge and accelerate the denitrification process. Also, metagenomics analysis results showed that the relative abundances of the denitrification-related Nor genes were 28-39% higher in the HPB (< 75 μm) and HPB (75-150 μm) than in the conventional activated sludge (CAS). These results show that ceramic waste powders have the potential to be used as carriers in HPB systems to treat CSOs.