Rotating biological contactors (RBCs) are widely utilized in aerobic wastewater treatment due to their high stability, efficiency, and ease of maintenance. The choice of disc carrier material for biofilm formation is a critical factor influencing treatment performance. In the context of rural domestic wastewater treatment, the biofilm carriers must balance cost-effectiveness and high efficiency. This study focuses on the aerobic unit of a combined anoxic denitrification–deodorization filter–aerobic RBC system, specifically, the waterwheel-driven aerobic RBC, and evaluates three types of biofilm carrier media: felt, carbon felt, and nonwoven fabric. The study compares their pollutant removal performance and biofilm enrichment characteristics to identify the optimal material. The results indicate that RBCs using nonwoven fabric as the biofilm carrier exhibit superior nitrification efficiency and biocompatibility compared to the other materials, achieving average removal rates of 84.3% for COD_Cr and 80.5% for ammonia nitrogen. While the addition of nonwoven fabric slightly reduced the driving efficiency of the waterwheel-driven aerobic RBC, it significantly enhanced oxygen transfer efficiency, which explained the enhanced organic degradation and ammonia nitrification. During the biofilm stable phase, the two-stage waterwheel-driven RBC with a nonwoven fabric carrier achieved average COD_Cr and ammonia nitrogen removal rates of 86.76 ± 0.85% and 92.15 ± 1.49%, respectively. Nonwoven fabric demonstrates significant potential as a biofilm carrier for aerobic rotating biological contactors.

The integration of anoxic filter and aerobic rotating biological contactor shows promise in treating rural domestic sewage. It offers high efficiency, low sludge production, and strong shock resistance. However, further optimization is needed for odor control, pollutant removal, and power consumption. In this study, the investigation on a one-pump-drive lab-scale device of retention anoxic filter (RAF) integrated with hydraulic rotating bio-contactor (HRBC) and its optimal operation mode were conducted. During the 50-day operation, optimal operation parameters were investigated. These parameters included a 175 % reflux ratio (RR), 5-h hydraulic retention time in the RAF (HRT_RAF), and 2.5-h hydraulic retention time in the HRBC (HRT_HRBC). Those conditions characterized a micro-aerobic environment (DO: 0.6–0.8 mg/L) in RAF, inducing improved deodorization (89.3 % sulfide removal) and denitrification (85.9 % nitrate removal) simultaneously. During the operation period, 84.79 $\pm$ 3.87 % COD, 82.71$\pm$ 2.06 % ${\text{NH}}_4^{+}$-N, 74.83 $\pm$ 2.06 % TN, 91.68$\pm$ 2.12 % S²⁻, and 89.04 $\pm$ 1.68 % TON were removed in RAF-HRBC. Based on large amount of operational data, organic loading rate curves of RAF-HRBC were validated and calibrated as a crucial reference to aid in full-scale designs and applications. The richness of microbial community was improved in both RAF and HRBC. In the RAF, the autotrophic sulfide-oxidizing nitrate-reducing bacteria (a-son) and heterotrophic sulfide-oxidizing nitrate-reducing bacteria (h-son) were selectively enriched, which intensified the sulfide removal and denitrification process. In the two-stage HRBC system, the 1st stage RBC was primarily composed of organics degraders, while the 2nd stage RBC consisted mainly of ammonium oxidizers. Overall, the integrated RAF-HRBC process holds significant potential for simultaneously improving pollutant removal and in-situ odor mitigation in decentralized domestic sewage treatment. This process specifically contributes to enhancing environmental sustainability and operational efficiency.