Application of primary treated wastewater to short rotation coppice of willow and poplar in Mongolia: Influence of plants on treatment performance

The influence of short rotation willow coppice on wastewater treatment performance under Mongolian climatic conditions is still poorly understood. For this purpose, one bed planted with willow (Salix spec.) and Poplar (Populus spec.) trees and one unplanted bed (as control) were operated over two years with pre-treated domestic wastewater under the same operating condition (with a daily hydraulic load of 5 mm). The results showed better wastewater treatment performance for the planted bed. An average mass removal rate of 241 ± 14 g m−2 a−1 (86% removal efficiency), 130 ± 26 g m−2 a−1 (93% removal efficiency), 82 ± 11 g m−2 a−1 (80% removal efficiency) and 7.1 ± 1.2 g m−2 a−1 (85% removal efficiency) was observed for COD, BOD5, TN and TP respectively in planted bed over two study years. On the contrary in the unplanted bed, the average mass removal rate was found to be as 135 ± 1 g m−2 a−1 (59% removal efficiency), 121 ± 28 g m−2 a−1 (89% removal efficiency), 43 ± 1 g m−2 a−1 (43% removal efficiency) and 3.7 ± 0.2 g m−2 a−1 (46% removal efficiency) for COD, BOD5, TN and TP, respectively, over two study years. Additionally, the planted bed irrigated with pre-treated wastewater showed greater tree growth (height, biomass yield) as compared to the plants that were grown within the control area without any additional irrigation (i.e. natural growth). The results demonstrate that the presence of willow and poplar trees positively influences wastewater treatment performance and indicate that short rotation coppice irrigated with pre-treated wastewater can be an economically viable alternative for wastewater treatment and producing biomass for energy production in Mongolia.