RATING OF HENRICO COUNTY BNR PLANT TREATMENT CAPACITY USING A CALIBRATED ACTIVATED SLUDGE MODEL

The Henrico County Water Reclamation Plant (WRP)incorporates two parallel BNR processes, the Oxygen Activated Sludge (OAS) process and the Diffused Air Activated Sludge (DAS) process. The total treatment capacity of the existing plant was given as 45 mgd.The WRP required upgrading and expansion to deal with the increasing wastewater flow and associated load. A number of plant upgrading options for the existing BNR process were evaluated using a calibrated Biowin™ simulation model. The rating of the potential BNR treatment capacity followed a step-wise approach:Assessment of historical process performance using a mass balance approach.Calibration and verification of the Biowin™ process simulation model, using at least two independent data set, covering both winter and summer operational conditions.Formulation of different process retrofitting and expansion options, making best use of the available infrastructure.Rating of the retrofitted/expanded BNR process treatment capacity, using the calibrated Biowin™ model.The existing BNR process reliable winter treatment capacity was rated as 36 mgd (with no alkalinity addition) and 42 mgd (with alkalinity addition). The reliable winter treatment capacity can be increased to 69 mgd with the introduction of flexible PE feed points and flexible anoxic/aerobic swing compartments.