Rotating Biodisks Recarbonate Alkaline Wastewater

Lime addition to raw wastewater as an upgrading technique can significantly aid a rotating biological contactor (RBC) plant in producing effluents in compliance with federal discharge permit limitations for biochemical oxygen demand (BOD₅), amonia nitrogen and phosphorus. Low-level lime addition does not require recarbonation and does not produce the sludges typical of high pH lime treatment schemes. The pilot RBC process provided BOD₅ removal when subjected to an influent pH of 9.5 for hydraulic loading rates of 2.0, 3.0, and 4.0 gpd/sq ft (0.08, 0.12, and 0.6m³/m²⋅ day). In addition to the removal of phosphorus, lime pretreatment reduced the organic loading on the RBC process and allowed for recarbonation by microbial populations which produced carbon dioxide, thereby forming carbonate alkalinity necessity for nitrification after the initial BOD₅ had been removed. The resultant pH after recarbonation was also in the optimal range for nitrification.