Treatment and valorization of a primary municipal wastewater by a short rotation willow coppice vegetation filter

Abstract

The objective of this study was to evaluate the treatment efficiency of a short rotation willow coppice (SRWC) vegetation filter for the treatment of wastewater from a municipal primary effluent in a humid continental climate context. The experimental work was carried out at pilot scale on a willow plantation located in Québec, Canada. The experimental design included nine plots that were irrigated with groundwater (L0 = 14 mm/d) or two primary effluents (L1 = 10and L2 = 16 mm/d) for 111 days. This research showed that SRWCs operated on coarse-textured soils allow efficient removal of organic matter (91% of COD for L1 and L2) and nitrogen (98% of TKN for L1 and L2) from wastewater. It was also shown, in this case, that the total nitrogen loading should be used as the limiting design parameter to minimize the risk of contaminating underground drinking water sources with nitrates. Almost complete removal of total phosphorus was observed during this experiment (98% for L1 and L2). However, a significant increase in soil available phosphorus was observed following the L2 treatment, which suggests an eventual phosphorus soil profile saturation in the event of continued wastewater irrigation. Avoiding such a saturation would require chemical phosphorus removal upstream of SRWC vegetation filters. Finally, an imbalance between irrigation and willows needs was observed as a result of irrigating plots at a constant hydraulic loading rate. Thus, irrigation of an SRWC with wastewater should be modulated according to willow seasonal transpiration trends to allow a better allocation of water and nutrients according to plant needs, and in doing so, increase treatment efficiency and resources valorization.