Factors affecting the performance of on-site aerated fluidized-biofilm carrier reactors treating individual household wastewater

Abstract

The application of decentralized small wastewater treatment facility is increasing for individual households that do not have access to centralized sewage systems. However, how to achieve optimal facility operation and management is a topic of challenge in order to realize higher facility performance due to the large variations in both quality and quantity of the wastewater. In this study, 15 on-site facilities treating individual household wastewater based on aerated reactor of fluidized-biofilm carriers (FBCR) were targeted and the impacts of such indexes as waste sludge cleaning time and the content and activity of biofilm on the performance of the facilities were evaluated. Wastewater samples were collected from 15 FBCRs treating individual household wastewater, each with varying waste sludge cleaning time. These samples were subjected to measurements of suspended substances (SS), biological oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP). The measurement results, along with those from principal components analysis (PCA) and agglomerative hierarchical clustering (AHC), led to the classification of the facilities into three groups (G1, G2, and G3) based on their different treatment performances. For group G1, although the waste sludge cleaning time differed in 22–586 days, the effluent from its five facilities showed higher water quality, with effluent concentrations reaching 5.30 ± 2.46 mg/L (SS), 5.26 ± 1.80 mg/L (BOD), 36.20 ± 8.70 mg/L (COD), 10.63 ± 2.72 mg/L (TOC), 1.35 ± 0.22 mg/L (TP) and 26.46 ± 3.47 mg/L (TN). Remaining COD, TOC, N and P primarily existed in dissolved forms. Biofilm analysis indicated that maintaining suitable biofilm content and activity was important for stable biodegradation and effective adsorption of suspended matter, surpassing factors like sludge cleaning time in regulating water quality. The result for microbial activity and the content of extracellular polymeric substance (EPS) suggested that the sludge during its storage inside the facility contributed to further degradation of remaining dissolved substances and to overall sludge reduction. The findings are important for optimizing the operation and maintenance of FBCR facility and further improving the treatment performance.