A Study On The Characteristics And Operational Performance Of Hybrid Biofilm-Activated Sludge Process

As the environmental and legislative constraints increase, more and more existing and to-be-built wastewater treatment plants (WWTPs) are being urged to increase treatment capacity and to improve performance for nitrogen and phosphorus removal to control eutrophication in their receiving water bodies. To meet these demands, the novel hybrid processes, which combined the activated sludge and biofilm processes, were developed on the basis of analyzing the existing theories and processes of biological nitrogen and phosphorus removal (BNPR). Theoretical analyses and pilot studies were conducted to analyze the pollutants removal characteristics in the hybrid biofilm-activated sludge processes. It was to be expected that some theoretical and technical support could be provided for upgrading existing overloading WWTPs and improving efficiency of BNPR system.A hybrid SBF-AS system was developed by the author to investigate its ability to improve pollutants removal by the activated sludge (AS) and/or submerged biofilm (SBF) systems. The relation between suspended sludge and attached biofilm in the hybrid process was analyzed through comparing difference in pollutants removal efficiency of the three processes. In the hybrid process, the resistance of substrate flowing into the attached film was greater than that into the suspended sludge. The substrate in the liquid phase could flow into the attached biofilm and was removed only if its concentration exceeded a critical value. In this study, the critical substrate concentration were about COD=100mg/L and NH3-N=4mg/L. The higher of substrate concentration in the liquid phase, the greater the extent of substrate removed by the attached biofilm. Thus, the biofilm-carrier in the hybrid system should be packed in the fist 2/3 or 3/4 section of the plug-flow aerobic tank to maximize its ability to remove pollutants. When the influent COD load increased, the suspended sludge in the hybrid process moderated the COD load in advance, which was favorable to the nitrifier growth and associated nitrification in the attached biofilm. The microbial population and microenvironment in the hybrid process were more complicated than that in the activated sludge and/or submerged biofilm systems. That could...