2019 ASHS Annual Conference

Slow sand filters (SSF) were used to treat drinking water before the advent of modern water treatment systems. Recently, small-scale (column) studies of SSFs have demonstrated their potential to remove plant pathogen propagules from water. However, no evaluations of performance of mid- to large-scale remediation of nutrient or pathogen treatment efficacy were found in the literature. Thus, we installed two pilot scale SSFs (2.5M across, 2M deep) in South Carolina. Each SSF was filled using water from a recycled irrigation pond, in a continuous-flow system through each SSF. Once a week about 400mL of Phytophthoranicotianaeinoculum was added to each SSF, bringing total inoculum density above the sand layer to approximately 25 zoospores/mL. Each filter was spiked 1 time per week for 6 weeks. Effluent from each SSF was captured at least daily and the presence and activity of P.nicotianaewas confirmed via leaf baiting bioassay. We monitored SSF startup (how long it takes for the microbial communities at the sand water interface to become active and help remove P.nicotianae) and long-term performance for presence and activity of P.nicotianaein both the influent (above the sand) and effluent. These SSF performed well, substantially removing P.nicotianaezoospores from solution, resulting in minimal breakthrough events during the establishment period and no breakthrough events after the short establishment. These SSFs required minimal maintenance and energy inputs for proper functioning, which is a benefit to growers. Some considerations of these systems that will be discussed include their relative size, treatment rate, and maintenance for optimal performance.