Field engineering application of agricultural farmland surface runoff pollution treatment by combined bioreactor and constructed wetlands

Agricultural non-point pollution is the biggest pollution source in China from 2009, the treatment of agricultural surface runoff is very important to mitigate the eutrophication of rivers and lakes because agricultural surface runoff is one key type of non-point source pollution. In this study, agricultural farmland surface runoff in Chengdu Plain was treated for one year (2017 ~ 2018) by the combination treatment technology of new material (waste fir and Hemlock sawdust as substrate) bioreactor for denitrification and Vertical-flow Constructed Wetland (VFCW, planting Cyperus alternifolius L.) combining zeolite and Lanthanum-modified activated Alumina (γ-Al2O3) as absorption agent for dephosphorization. This engineering application is successively joint three treatment processes (sedimentation unit → dephosphorization unit → denitrification unit) with 5 paralleling groups. The results show that the average removal rate of total nitrogen (TN) and total phosphorus (TP) from agricultural surface runoff at farmland in the denitrification bioreactor (filled fir sawdust) were 29.64% and 66.56%, respectively. The average TP removal rate of VFCW with Lanthanum-modified γ-Al2O3 was 60.44%, while it was 51.66% in VFCW without Lanthanum-modified γ-Al2O3. The denitrification rate of fir sawdust bioreactor was better than both hemlock sawdust bioreactor and mixed hemlock-fir sawdust bioreactor. Overall, the combination of fir sawdust bioreactor for denitrification and VFCW filling some Lanthanum-modified γ-Al2O3 was the best treatment application for agricultural farmland surface runoff treatment.