ASHS 2025 Conference

Sustainable management of irrigation water is critical for soilless greenhouse production systems, particularly in ornamental plant cultivation, where agrochemical (pesticides, nutrients, and growth regulators) use is intensive. Recycled irrigation water carries agrochemicals from production surfaces, containers, substrates, and system components. Even at low concentrations, these compounds can be phytotoxic to sensitive crops or pose environmental risks if discharged. While recirculating irrigation systems improve water efficiency, they require the use of treatment technologies to remediate agrochemicals. Woodchip bioreactors, commonly used for nitrate removal, have also shown promise in remediating phosphates and pesticides. They provide a carbon source and growth matrix for diverse microbial communities. Typical anaerobic conditions facilitate denitrification, and the biofilm further increases the reactive surface area where pesticides can interact with degrading enzymes to enhance pesticide remediation. Integrating aerobic bioreactors as a secondary stage can promote dissolved organic carbon release and enhance degradation of certain pesticides. Hydraulic retention time (HRT) is a key design factor, influencing nutrient retention and pesticide removal by controlling contact time with bioreactor microbiomes. Shorter HRTs support nutrient recycling for irrigation reuse, while longer HRTs enhance nutrient and pesticide degradation through extended microbial processing. We evaluated the performance of a sequential two-stage non-aerated (stage 1) - aerated (stage 2) bioreactor configuration in reducing effluent pesticide concentration and load under varying hydraulic retention times (HRTs). Two two-stage systems, each consisting of two bioreactors, were installed at a Michigan wholesale greenhouse, treating recirculating operational water from an 11,500 m² production area. These systems operated for 160 days at HRTs of 30 (30HRT) and 60 minutes (60HRT) per stage, corresponding to bioreactor volumes of 1,135 L and 2,271 L per stage, respectively. Preliminary results indicate that both 30HRT and 60HRT systems treated an average daily volume of 36,225±2,395 L. Average recycled Total Nitrogen load was 91% and 2.6 kg d-1 for 30HRT, and 78% and 2.3 kg d-1 for 60HRTs, respectively. Phosphate and pesticide content is currently being analyzed, with early observations showing phosphate load shifts from non-aerated to aerated conditions. These results will be presented at the conference.