ELIMINATION OF EXCESS ORGANIC SLUDGE FROM A MOVING-BED BIOFILM PROCESS

Total oxidation (TOX) of excess biomass by endogenous decay was applied for the elimination of secondary organic sludge as yielded by a moving-bed biofilm process utilizing PVA-gel beads as a biocarrier. In contrast to previous in-house studies treating industrial wastewaters essential free of influent suspended solids (SS), in this pilot study treatment of a municipal wastewater was considered, where influent SS could bear a significant impact on sludge decay. Excess sludge from the biological treatment units was accumulated in the TOX process where a sludge concentration of 8 g/L was maintained at a hydraulic retention time of 8 h, with low levels of effluent SS—usually below 10 mg/L—following secondary clarification. A solids mass-balance suggested a biomass yield in keeping with conventional biological treatment processes; however, this was thought to be artificially high due to the unquantifiable influence of influent SS. In addition, the observed endogenous decay coefficient was estimated to be three to four times higher than that of conventional activated sludge in keeping with results of other studies utilizing the PVA-gel biocarrier. Though further research is warranted to evaluate the effects of influent SS on the balance of solids in a TOX process over long-term operation, results here demonstrate that due to the favorable characteristics of sludge yielded from a PVA-gel process, greatly reduced production of waste sludge from municipal applications is feasible.