USING COMPUTER SIMULATION TO OPTIMIZE BNR DESIGN

The Clark County Sanitation District's 88 million gallon per day (mgd) wastewater treatment plant in Las Vegas, Nevada discharges its treated effluent to environmentally sensitive Las Vegas Wash and Lake Mead under strict seasonal ammonia and total phosphorus waste load allocations. At the current influent flow rate of 82 mgd, the allowable discharge effluent concentrations for ammonia-N and total phosphorus are 0.73 and 0.25 mg/l, respectively.Wastewater flows generated by residents, tourists, industries and businesses have been increasing rapidly. The Las Vegas Valley has been the fastest growing community in the United States over the past ten years, increasing at an average rate of 7.6 percent per year. To address future treatment needs that would accommodate this explosive growth, maintain treatment reliability, and anticipate future regulations, the District began design on a 20-mgd expansion to its existing secondary treatment facilities.During the design phase for the new secondary treatment expansion, computer simulation was used to: 1) help optimize and fine tune aeration basin design, 2) examine the effectiveness of alternative treatment strategies, 3) evaluate the impacts of future water quality standards, and 4) identify the influence of dynamic process variations on daily composite effluent quality. The Bio Win simulator was calibrated using dynamic influent diurnal patterns measured at Clark County, and then applied to quantify projected effluent quality for numerous operating strategies considered by the design team. As a result of being able to examine a wide variety of process options, the resulting design provides a highly flexible, innovative biological nutrient removal (BNR) configuration that is readily adaptable to a variety of alternative treatment configurations, and provides operators with substantial flexibility to meet future changes in effluent requirements.