Study On Effect Of Ecological Ditch System On Pollutant Retention In Farmland Drainage

Concrete ditchs were eco-constructed to study their process performances for removal of agricultural non-point source pollutants.For this purpose,a pilot-scale simulation study on three eco-reconstructed ditch systems differing in vegetation and substrate,noted as A-ditch(Vallisneria natans+shell powder),B-ditch(Vallisneria natans+volcanic rock)and C-ditch(Ceratophyllum demersum L.+volcanic rock),was conducted to look at their pollutant removal performances and removal kinetics.Based on a developed demonstration project located in Qiandaohu watershed,a field study was also performed to examine the on-site process performances on eco-constructed ditch ststem(234m length)for removal of agricultural non-point source pollutants.The results obtained are summarized as follows:(1)The pilot-scale simulation study with 42 days treatment duration has shown that,the TP 、NH3-N and COD The pollutant removal efficencies for A-,B-and C-ditch were found to be 81.6%、80.5% and 70.5% for TP,80.3%,83.5% and 83.2 for NH3-N and,84.3%、92.6% and 87.1% for COD.(2)The kinetics study on the A-,B-and C-ditch system has shown that,the first order kinetic model is efficient for predicting removal performance for TP,NH3-N and COD.Compared to the A-ditch and C-ditch,the B-ditch system(planted with Vallisneria natans and using volcanic rock as substrate)was found to have a better process performance on untake of the pollutants.(3)The field study based on the developed demonstration project has shown that,the eco-constructed ditch system examined with 234 m length can achive a process performance with pollutant removal efficencies of 61.2% for TP,52.3% for TN,and 43.4% for COD system.The surface removal rates of TP,TN and COD were found to be 1.67 g·d-1·m-2,20.97 g·d-1·m-2and 407.83g·d-1·m-2,respectively.(4)The field study based on a developed demonstration project has also shown that,the TP、TN and COD removal efficencies for the eco-constructed ditch was inceased with the increase of ditch area.Based on linear and nonlinear regression analysis,it was found the non-linear fitting analysis between ditch area and the removal amount of the pollutants has higher fitting degree in comparison with the the linear fitting analysis.It was also found that,for the eco-ditch system higher TP、TN and COD surface removal rates can be obtained with higher surface loading of the pollutants.