Novel micro-granular sludge process for highly efficient treatment of low-strength and low C/N ratio municipal wastewater

A novel high-concentration powder bio-carrier (HPB) process was developed for the high-load treatment of low-strength municipal wastewater with low carbon/nitrogen (C/N) ratio (similar to 3). The powder carrier facilitated the rapid micro-granulation of sludge within 20 days and the average particle size increased rapidly from 47 mu m to 210 mu m. Accordingly, the concentration of mixed liquid volatile suspended solids (MLVSS) increased from 1.8 g/L to 4.3 g/L, which enabled the HPB process to maintain a short hydraulic retention time (HRT) of 3.6 h. Correspondingly, the high volumetric load of 0.4-1.3 kg chemical oxygen demand (COD)/(m(3)center dot d) and 0.12-0.24 kg total nitrogen (TN)/(m(3)center dot d) could be achieved and twice higher than those of conventional activated sludge process, e.g., anaerobic/anoxic/oxic process. The carrier-induced sludge granulation also significantly optimized the microbial structure, and the high-throughput sequencing revealed the increasing abundances of denitrifying bacteria and anammox bacteria, which was consistent with the nitrogen removal efficiency rising from 44.6% to 77.4%. Accordingly, the enhanced nitrogen removal could be achieved with TN of effluent steadily below 5 mg/L. Especially, the mass balance analysis on carbon and nitrogen further indicated the advantage of newly developed HPB process in carbon source saving for nitrogen removal. All the results are believed to suggest a promising strategy for the highly efficient treatment of low-strength municipal wastewater.

Automated summary

A novel high-concentration powder bio-carrier (HPB) process was developed for the high-load treatment of low-strength municipal wastewater with low C/N ratio, which facilitated rapid sludge micro-granulation and enhanced nitrogen removal efficiency. The process achieved higher volumetric load and optimized microbial structure, leading to promising results for the highly efficient treatment of low-strength municipal wastewater.