Water Renew systems: wastewater polishing using renewable energy crops

Macronutrients concentrations were measured during the establishment year of short rotation coppice of Salix viminalis, Populus trichocarpa, Eucalyptus gunnii irrigated with secondary treated effluent. Twenty four plots of 12.25 m² located in Cranfield, Bedfordshire, UK on heavy fine clay were drip-irrigated in order to maintain their soil moisture at field capacity. Soil water was sampled at 30 cm and 60 cm with soil water suction cup samplers fortnightly. Willow and eucalyptus received more than 900 mm of effluent corresponding to more than 290 kg-N/ha, 30 kg-P/ha and 220 kg-K/ha. Poplar and unplanted plots received less than 190 kg-N/ha, 17 kg-P/ha and 120 kg-K/ha. For soil water nitrogen concentrations as for potassium concentrations, there was an irrigation effect only on eucalyptus planted plots. On all plots, there was no significant effect of tree presence or species. There was no phosphorus measurable in soil water samples. Groundwater chemistry was unaffected by irrigation. Thus, intensive irrigation of short rotation coppice during the establishment year should not be considered as a major threat to groundwater quality. Willows and eucalyptus can absorb almost a third more effluent than poplar and unplanted plots without having any significant effect on soil water chemistry.