Assessing boat waste impacts on small wastewater treatment plant operations

Abstract

With implementation of the Clean Vessel Act Wastewater Project it is imperative to understand potential impacts of recreational boat waste on wastewater treatment plant operations. The Clean Vessel Act funds the creation of pumpout stations (similar to RV dump stations) to provide alternatives to disposal of recreational boat waste overboard (U.S. Fish and Wildlife Service). Boat waste is black water (water from toilets) from recreational boats that is pumped into on-shore pumpout tanks. In the past, this waste was often discharged directly into the surrounding water. As more boat waste is diverted from direct disposal, wastewater treatment plants located near pumpout facilities are often asked to accept this additional influent. Since many boating activities take place in remote areas, many potentially impacted treatment facilities are small (<0.1 million gallons per day, MGD). Thus, recreational boat waste may have a substantial impact to their operations. Characterizing and analyzing impacts of boat waste to these small facilities is an imperative first step to the successful treatment of this increasing wastewater source. This study presents results from a suite of tests which provide important measures of potential effects of boat waste on treatment processes. Testing was conducted to characterize boat waste and activated sludge from the Salish Sea (San Juan Islands and Puget Sound, Washington). Direct effects of shock-loading boat waste to activated sludge were additionally measured. Characterization revealed boat waste constituents were substantially more concentrated than typical raw wastewater. On average boat waste contained 60× the ammonia, 10× the COD, 20× the reactive phosphorus, 15× the salinity, and 7× the total suspended solids (TSS) of typical untreated domestic wastewater. Constituent concentrations in boat waste and activate sludge samples varied among sample locations and dates and resulted in varying impacts by boat waste on activated sludge properties. Increases in oxygen uptake rate, settling ability, and foaming were observed as boat waste was added to activated sludge at volumes of up to 10%. Furthermore, separate addition of a holding tank deodorant increased foaming in activated sludge samples.