Exocellular Polymeric Substances, Bioflocculation and Sludge Settling Properties in a Combined Anaerobic/Activated Sludge Process

• Main Author: Luque, Jackeline
• Format: Others
• Published: ScholarWorks@UNO 2005
• Subjects: EPS in anaerobic/aerobic systems
• Online Access: http://scholarworks.uno.edu/td/264; http://scholarworks.uno.edu/cgi/viewcontent.cgi?article=1297&context=td

Combined anaerobic/aerobic processes for municipal wastewater treatment is quite recent; the studies developed have shown these processes are feasible for the removal of organic, nutrient substances and reduction of sludge produced. Previous studies developed at the Marrero Wastewater pilot plant (fully aerobic system) revealed that the minimum solids contact chamber hydraulic residence (HRT) time in which bioflocculation occurs satisfactorily (effluent SS concentrations < 20 mg/L) is 15 min; however, in the combined anaerobic/aerobic system HRT< 100 minutes resulted in poor floc settling properties and turbid supernatants. Exocellular polymeric substances (EPS) have been found to be the key factor for bioflocculation to occur. Past studies in fully aerobic pilot plant demonstrated that the concentration of EPS increased with mixed liquor concentration and solids retention time. The main purpose of this research is to determine the effect of mixed volatile suspended solids(MLVSS), solids retention time(SRT), and dissolved oxygen(DO) in the production of EPS in the combined anaerobic/ solids contact chamber and its relationship with settling parameters. To carry out the objectives of this investigation three experimental phases were developed : 1) The MLVSS concentration was varied between 1000-4000 mg/l, keeping the SRT and DO as constant as possible 2) The SRT was changed between 2-8 days, keeping the MLVSS concentration between 1500-3500 mg/l and DO between 2-3 mg/l 3) the DO concentration was varied between 0-5mg/l. For a DO of zero, EPS were extracted from the sludge produced in the anaerobic reactor. Analysis of the data showed that the combined system proved to be unstable producing unexpected results such as no clear relationship between MLVSS and EPS. For a DO of zero, no EPS are produced and no flocculation takes place; therefore, effluents with poor quality can be expected from anaerobic treatment units. To meet secondary effluent standards in aeration chamber, capable of promoting the transformation from anaerobic to aerobic biota, and the generation of EPS, high SRT and HRT is required. Under these conditions the system anaerobic/solids contact chamber has an excellent potential for providing secondary treatment for municipal wastewater; nevertheless, the system is not as stable as the conventional aerobic one and bulking problems are common and difficult to content.