Experimental Study On The Treatment Of Domestic Wastewater By The Subsurface Flow Constructed Wetland

Because of high water quality stability, strong resistance to shock loading, low infrastructure and operating cost, easy to maintenance, effective to remove organism, nitrogen and phosohorus,etc, the constructed wetland is a very useful sewage treatment process at present. This technology has already been applied in the treatment point and plane source pollution in agriculture, sewage and nutrient-rich water in China.This paper studied two single vertical-flow constructed wetlands: the soil-slag-pearl sand wetland (Wetland 1) and the ceramic rings-vermiculite-gravel wetland (Wetland 2). Through three test systems (two single vertical-flow wetlands and their hybid wetlands), the impact of the constructed wetlands on the variation of dissolved oxygen (DO) concentration, chemical oxygen demand (COD), five days biochemical oxygen demand (BOD5), Kjeldahl nitrogen (KN) and total nitrogen (TN) was researched, and the removal dynamic connection of different hydraulic loadings was also established. The conclutions are below:When the water level was in the zero, compared with the Wetland 1, the Wetland 2 had stronger ability of oxygen transfer, absorbtion and removing COD, BOD5, KN and TN. However, both single vertical-flow constructed wetlands can help transfering the oxygen in the atmosphere reaeration and plants, and building a suitable environment to remove organism and KN; but they are not good for removing total nitrogen.The improved single vertical-flow constructed wetland was benefit for atmosphere reaeration both under the small variation (40 cm, 30 cm, 20 cm and 10cm) and the big variation (between 40 cm and 0 cm) of water lever , expecially when the water leve changed dramatically, the oxygen increased obviously at this time; the Good DO environment can help improving removal of COD and BOD5 , not the variation of water level; the removing rates of TN and TKN increased relatively higher as the water level changed dramatically; the differences of the removal capacity were determined by DO environment, matrix adsorption and plant;The hybrid vertical-flow constructed wetland was formed by combined Wetland 1 and Wetland 2 together; although the concentration of the effluent DO was lower, compared with the single vertical-flow wetlands and the improved single vertical-flow constructed wetland, it had the best effect for the removal of COD, BOD, KN and TN.When the hydraulic loadings changed between 5 cm3/cm2·d and 20 cm3/cm2·d, the removal rate of COD, BOD, KN and TN of the hybrid vertical-flow constructed wetland reduced as the hydraulic loadings increased; When the hydraulic loadings changed between 8 cm3/cm2·d and 10 cm3/cm2·d, it was best for the removal of COD, BOD, KN and TN. The kinetic analysis showed that the Formula 1 kinetic model can explain the degradation of COD, BOD, KN and TN in the hydrid vertical-flow constructed wetland system very good.