Impacts of High-Strength Boat Waste on Activated Sludge Processes

Abstract

Decisions to accept side-stream wastes at municipal wastewater treatment facilities require knowledge about potential impacts on plant operations. Among potential waste streams, coastal communities are increasingly asked to accept boat waste (sometimes termed boat sewage). Boat waste is black water (water from toilets) from recreational boats and yachts. Efforts to decrease the discharge of boat waste directly into natural waters have resulted in increased requests to wastewater treatment plants located near boat-waste pump-out facilities to accept this waste stream. In this study, boat waste is characterized from pump-out facilities on the Salish Sea (located in the northwest corner of Washington State, USA). Impacts on activated sludge function of shock loading up to 10% boat-waste volumes were evaluated. Measured concentrations showed boat waste to contain 60× the ammonia, 10× the chemical oxygen demand (COD), 20× the reactive phosphorus, 15× the salinity, and 7× the total suspended solids (TSS) of typical sewered wastewater. When added to activated sludge, boat waste often increased oxygen uptake rates, settleability, and foaming. These responses were primarily linked to boat-waste strength, although deodorants added by boat owners were also implicated. Quadrupole time-of-flight liquid chromatography mass spectrometry (LC/Q ToF-MS) was used to compare organic compounds within boat waste and three common deodorant products. These results documented that shock-loading boat waste can create conditions leading to treatment upset and that results differ between sources of activated sludge. Continued research is required to evaluate the potential for adaptation of activated sludge microbial communities to boat-waste impacts, including high-nitrogen ammonia loadings.