Category: Water, Wastewater & Storm water
With implementation of the Clean Vessel Act Wastewater Project it is important to determine potential impacts of recreational boat waste on wastewater treatment plant operations. Boat waste is black water from recreational boats that is pumped into holding 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 pump-out facilities are often asked to accept this additional influent. Since many boating activities take place in remote areas, many potentially impacted wastewater treatment facilities are small (<0.1 MGD) so projected influents may have a substantial impact to their operations.
This study presents analysis of potential effects of boat waste on activated sludge processes. Testing was conducted to characterize boat wastes from the Salish Sea (San Juan Islands and Puget Sound, Washington). Direct effects of shock-loading boat waste to activated sludge were additionally measured. Three parameters were tested on solutions of varying ratios of boat waste to activated sludge: specific oxygen uptake rate (SOUR), sludge volume index (SVI), and foaming. Results were compared to tests conducted with chemical boat waste additives and sea water added separately to identify specific components of concern in boat waste. Preliminary testing revealed that boat waste chemical oxygen demand (COD) was up to 10 times higher than traditional influent and ammonia concentrations were 20 times higher. Furthermore, with increased boat waste additions, foaming increased and microbial activity (evaluated via the SOUR method) decreased.
These results will interest wastewater treatment plant operators and their consulting engineering firms when making decisions about either accepting boat waste or designing for treatment of this increasing wastewater source.
Jennifer Kersh– Graduate Student, Research Assistant, University of Washington, Seattle