Studies On The Performance Of Tidal Flow Constructed Wetland For Treating Highly Contaminated River Water

Constructed wetland which has good treatment efficiencies with its uniqueadvantages of lower power consumption and investment, and better environmentalconditions than other water treatment processes, was widely promoted and applied toimprove the water quality of the contaminated water bodies both at home and abroad.However, the traditional wetlands run by using a continuous stream that the bed wouldshow an anoxic environment which is not conducive to the wastewater treatment for along time.A new type of constructed wetland, called tidal flow constructed wetland, whichruns through the simulation of tidal operation mode that is "instantaneous influent,instantaneous effluent".The tidal flow system is periodically filled with water anddrained dry,"wet/dry" cycle alternating intermittent operation namely. Because of theway to add the wastewater to the system in an instant, and the contact between the fillerand the air in the resting time, lots of oxygen would be entrained into the system, thus,the transmission rate and consumption of oxygen of the system could be significantlyimproved, as well as the condition of the traditional constructed wetland system withlow DO which is an important limitation for the decontamination capabilities. Thanks tothe alternating movement of wastewater and air, an anaerobic-aerobicmicroenvironment which is much helpful to remove the pollutants forms constantly inthe tidal flow system, thus the treatment efficiencies of the system be strengthened.A small-scale experimental unit of the tidal flow constructed wetland system wasconstructed to have a study on highly contaminated river water treatment. In order tomake a significant reverence to the practice application of the tidal flow system, thefollowing were studied:(1) Change of DO concentration in the experimental tidal flowconstructed wetland system;(2) the removal efficiencies of SS and organics in the experimental tidal flow constructed wetland system;(3) the removal efficiencies of N and P inthe experimental tidal flow constructed wetland system;(4) the main factors which affect theremoval efficiencies in the experimental tidal flow constructed wetland system.The experiment results showed that：(1) the influent mode of tidal flow couldsignificantly take lots of oxygen into the system;(2) in the reaction period, the removalefficiencies of SS, TN, NH3-N, TP, PO43-_P,COD and BOD5could gradually increasewith the reaction time，and the final removal rates reached94.20%,55.53%,48.03%,83.46%,67.50%,93.90%and96.08%, respectively;(3) the removal efficienciesgradually increased along with the vertical distance for the pollutants of SS, TN, NH3-N,COD and BOD5, and their removal rates that above the central location of samplingpoints were much faster than below, while TP and PO43-_P had a different trend;(4)during a half year’s experiment, the system had good removal efficiencies andshowed a great capacity to resist the influence of load, the average removal rates of SS,TN, NH3-N, TP, PO43-_P,COD and BOD5were94.30%,49.14%,48.34%,79.40%,78.34%,81.52%and83.39%, respectively;(5) the removal rate of NH3-N waseasier affected by the temperature than TN; the unit removal load of TN, TP, CODand BOD5was affected by the influent load, but the constructed wetland had a greatcapacity to resist the influence of load; the concentration of DO would not be a limitingfactor for pollutants removal any more.