REINVENTING ACTIVATED SLUDGE TREATMENT FOR BIOLOGICAL PHOSPHORUS REMOVAL

摘要

The Clark County Sanitation District (District) provides wastewater treatment andrndisposal for the unincorporated areas of Clark County, Nevada, located adjacent tornand around the City of Las Vegas. The plant treats municipal wastewater andrndischarges treated effluent to Lake Mead under stringent seasonal ammonia and totalrnphosphorus waste load allocations of 502 and 173 pounds per day respectively. ThernDistrict抯 service area covers approximately 187 square miles and serves anrnestimated 475,000 local residents as well as hotel and casino customers. The LasrnVegas Valley is one of the fastest growing areas in the United Stated with an averagernpopulation growth rate of 7.2 percent per year between 1993 and 1998. Wastewaterrnflows generated by residents, tourists, industries, and businesses have beenrnincreasing rapidly. In order to address future treatment needs which wouldrnaccommodate planned growth, anticipate future regulations, and maintain treatmentrnreliability, the District embarked on a plan to reinvent its treatment process to providerncost-effective wastewater treatment while meeting the needs of public health and thernenvironment.rnIn the past, lime was used at the District for phosphorus removal. Recently, thernDistrict converted from chemical phosphorus removal at their Advanced WastewaterrnTreatment (AWT) Plant to biological phosphorus removal in the Central Plant activatedrnsludge basins. Switching to biological phosphorus removal reduced the totalrnphosphorus in the secondary effluent from 3 mg/l to less than 0.6 mg/l on average.rnSubsequent basin modifications and process enhancements reduced the secondaryrneffluent total phosphorus and total suspended solids concentrations to 0.19 mg/l and 6rnmg/l on average, respectively.rnBy changing its treatment strategy from chemical to biological phosphorus removal,rnthe District was able to eliminate chemicals from the treatment process, automate thernsystem operation, and optimize the activated sludge basins resulting in totalrnphosphorus effluent concentrations below 0.2 mg/l while at the same time realizingrnsignificant capital, operating and maintenance cost savings.