MODERNIZATION, EXPANSION AND BNR UPGRADING OF A LARGE RBC TREATMENT SYSTEM

Stantec Consulting Limited was retained by the City of Grande Prairie (GP) in 1998 to upgrade its Rotating Biological Contactor (RBC) Wastewater Treatment Plant (WWTP).After 16 years of continuing population growth, the RBC treatment system was being overloaded beyond its capacity. The result was excessive build-up of biomass on the RBC media, decreased treatment efficiency, generation of periodic RBC fugitive odours, and the possibility of premature RBC shaft failure. In addition, the two original aerobic digesters were overloaded beyond capacity, difficult to maintain and were also a significant source of fugitive odours. As a result, the City decided to upgrade its WWTP. Upgrades were undertaken in two phases including voluntary biological phosphorus removal well in advance of Alberta Environment's 2007 effluent requirements.These upgrades included installation of a biofilter, and expanded sludge digestion capacity by use of an Autothermal Thermophilic Aerobic Digester (ATAD) system. The RBC treatment system's expansion and modernization program resulted in advanced biological nutrient removal, the first known large RBC-Activated Sludge full BNRWWTP in the world to date. This expansion and modernization program resulted in extended RBC life due to significant reductions in biomass build-up, increased WWTP capacity with minimal new infrastructure, and improved treatment performance and operational efficiency far beyond the present treatment requirements.To date, the monthly average BOD5, TSS, ammonia and total phosphorus effluent concentrations for the RBC-Activated Sludge BNR hybrid system, not including the final polishing lagoon, have been reduced from 17.1, 21.1, 24.5, 3.3 mg/L, to 5.7, 12.0, 1.1,0.49 mg/L respectively. Treatment efficiency for the same parameters improved from95.3, 95.3, 32.9, 26.7%, to 98.5, 96.8, 96.8, 93.3% respectively.Since start-up on October 2000, the monthly average BOD5, TSS, ammonia and total phosphorus final effluent concentrations discharged to the Wapiti River (after the final polishing lagoon) were reduced from 8.2, 5.3, 17.8, 3.5 mg/L, to 3.6, 3.1, 0.86, 0.44 mg/L respectively.