Comparative wood anatomy, composition and saccharification yields of wastewater irrigated willow cultivars at three plantations in Canada and Northern Ireland

Conventional wastewater treatment strategies can have high financial costs which often leads to discharge of undertreated wastewater into the ecosystem. In parallel, the cultivation of willows for bioenergy can be limited due to their high water demand. Despite the potential for treatment using willow plantations, the effect of wastewater irrigation on biomass development and biofuel potential has yet to be investigated across different cultivars and sites. Here, the effect of secondary treated wastewater irrigation on wood anatomy, biomass composition and enzymatic saccharification were investigated in one poplar and thirteen willow cultivars planted at one of three sites in either Canada or Northern Ireland. There was significant anatomical and compositional variation between cultivars at all three sites, but wastewater irrigation had little impact on biomass development. Vessel and fibre cell frequencies ranged between cultivars from 129 to 178 and 4322-7058 per mm2, with average transverse areas of 838-1278 and 120-190 mu m2, respectively. Glucan and lignin content varied from 42.3 to 50.7% dry matter (DM) and 27.3-32.4% DM, respectively, whereas glucose release varied from 50 to 160 mg g-1 of glucan or 30-90 mg g-1 of DM. Glucan content and fibre cell frequency had significant positive correlations with glucose release yields, whereas average fibre cell area had an inverse correlation. These findings suggest both cell wall structure and tissue morphology could be important factors when considering biomass recalcitrance to deconstruction. Maintenance of biomass quality during irrigation provides evidence that integration of dedicated bioenergy production with environmental wastewater treatment using willow phytofiltration has potential as a promising clean biotechnology.