128 - Performance and Microbial Community Characteristics of Planted Infiltration Galleries for High-volume Secondary and Tertiary Wastewater Treatment

The incorporation of Nature-based solutions like planted infiltration galleries into wastewater treatment is vital for sustainable protection of water resources. Planted infiltration galleries provide tertiary wastewater treatment in the soil matrix, while also providing ecosystem services. However, this application is limited by current irrigation regulations. We aimed to study the performance of a planted infiltration gallery under high irrigation volumes and to understand the impacts of wastewater on the microbial community. Lab-scale reactors were filled with sandy loam soil, and either planted with hybrid poplar trees or left without trees as a bare-soil control. Reactors were drip irrigated with synthetic wastewater formulated to match primary or secondary effluent characteristics. Ports in the side and bottom of the reactors allowed for effluent and soil sampling. DNA was extracted from soils and sequenced with Oxford Nanopore MinION technology. We observed enhanced removal of both nitrate and total nitrogen in planted reactors compared to bare-soil controls, with better performance in all reactors in warmer months. Conversely, greater COD removal was achieved in the bare-soil reactors. The microbial community composition in reactors receiving wastewater was not significantly different from clean-water controls. While total biomass was similar across all treatments, the abundance of the nitrogen cycling gene amoA was greater in reactors receiving wastewater than clean water controls. Positive impacts on tree growth were also observed with wastewater irrigation. This research suggests that planted infiltration galleries can be used to treat higher volumes of wastewater than permitted by current regulations, with minimal disruption to the soil microbial community