TWO STAGE ANAEROBIC DIGESTION AND LIQUID STORAGE ACHIEVES ENHANCED PATHOGEN AND VECTOR ATTRACTION REDUCTION

The Town of St. Johnsbury, Vermont owns a secondary wastewater treatment facility (WWTF) discharging to the Passumpsic River. The WWTF provides secondary treatment using rotating biological contactors (RBCs). Sludge is stabilized using two-stage anaerobic digesters. The stabilized biosolids are stored in a reinforced concrete holding tank between annual land application on restricted agricultural sites.The Town has been land applying digested biosolids in liquid form for the past eleven years. Data has been collected to demonstrate compliance with EPA 40 CFR Part 503, and Vermont Department of Environmental Conservation (DEC) Residual Waste Management Program regulations. This paper documents ways to improve pathogen and vector attraction reductions in land applied biosolids.The Town's biosolids management program will be presented including:Raw sludge quantitiesRaw sludge total and volatile solids concentrationsDigester residence time and volatile solids loadingsMixing intensityDigester operating temperatureVolatile solids reductionSupernatant quantity and qualitySludge Storage Tank decant quantity and qualityFecal Coliform concentrations for raw sludge, first stage digester sludge, second stage digester sludge and liquid storage tank biosolids at various time intervals prior to land application to demonstrate pathogen reduction during each treatment stage.Biosolids metals concentrationsLand application information including nutrients, cumulative site life calculations, soil, plant tissue and groundwater monitoring results.Data from the Town of St. Johnsbury is useful in demonstrating that Federal and State regulatory standards can be exceeded by combining two traditional treatment processes prior to beneficially reusing wastewater biosolids which will aid in achieving public acceptance of these programs. Extended storage of anaerobically digested liquid biosolids provides improved vector attraction reduction, and enhanced pathogen reduction. An additional one to two log reduction in fecal coliform concentrations has been achieved by providing liquid biosolids storage prior to land application.