Research On Purification Technology Of "Ditch-wetland" In The Paddy Fields Drainage

Rice Paddy ecological system in the estuary of Liaohe is a paralic zone, which is notonly an ecological barrier, but also a significant source of nitrogen and phosphorusdelivering in Liaodongwan water area. paddy fields drainage ditch both the linear wetlandcharacteristics and the adjacent wetland system, as a preventable and restrainingtechnology in the process of agricultural non-point source pollution, it has so manyadvantages, such as removal of nitrogen and phosphorus pollutant, low cost, efficient, highapplicability. Centring on the constitutive characteristics of ditch, hydraulic condition ofdifferent wetland and ditch-wetland federation technology, simulative ditch and wetlandanalog system were built up in the laboratory to simulate the purification of nitrogen andphosphorus in the paddy fields drainage ditch. The main conclusions are:Firstly, based on selecting different plants and matrixes, different ditch systems werebuilt up to verify that ditch’s constitutive characteristics have some influence on theremoval efficiency of nitrogen and phosphorus pollutant. The results showed thatecological system with plants has an obvious effect on the purification of nitrogen andphosphorus than the conventional ditch. Arranged high to low, the effect of different plantsin removing nitrogen pollution is: Acorus calamus Linn, Typha Augusta Borg et Chapeau,Scirpus valid Va hl. Arranged high to low, the effect of different plants in removingphosphorus pollution is: Acorus calamus Linn, Typha Augusta Borg et Chapeau, Scirpusvalid Va hl. The improvement of the matrix can effectively promote the purification effect.Arranged high to low, the effect of different matrixes in removing nitrogen pollution is: themixture of sand and soil, the mixture of coal cinder and soil, and simple soil. Arrangedhigh to low, the effect of different matrixes in removing phosphorus pollution is: themixture of coal cinder and soil, the mixture of sand and soil, and simple soil. In theconstruction of the ditch, selecting the appropriate group of matrix and plant according tothe main pollutants to transform the ditch contributes to giving full play to its ecologicalfunction. While the nitrogen plays a dominant role in the pollutant, the mixture of fine sand and soil is recommended as the matrix, and Acorus calamus Linn is recommended as theplant. While the phosphorus plays a dominant role in the pollutant, the mixture of coalcinder and soil is recommended as the matrix, and Acorus calamus Linn is recommendedas the plant.Secondly, by changing the hydraulic gradiant of wetland and hydraulic detention time,hydraulic load was indirectly changed, research on how does the wetland can actuallyinfluence the purification of nitrogen and phosphorus pollutants was carried out. Theresults showed that wetland system is influenced by hydraulic condition; when thehydraulic water level of wetland is between10cm and15cm, hydraulic detention time isabout6d, the wetland has the better purification effect.Finally, on the basis of monomer experiment of ditch system and wetland system,research on how does the ditch-wetland federation system effect the purification ofnitrogen and phosphorus pollutants were carried out. The results showed that in thecondition of low concentration inflow, hydraulic detention time of the ditch should not belong, wetland as the main purification unit when the ditch play a drainage role in thesystem. In the situation of the hydraulic detention time of all kinds of pollutants is too long,it will not only increase the pollutant load of the ditch, but also bar the wetland fromplaying its function, and even cause serious influence on wetland plants and entire system.In the condition of median concentration inflow, under the premise of guaranteeing theditch drainage requirements, extending the hydraulic detention time properly is beneficialfor wetland to remove the pollutants efficiently. All in all, it’s better to keep the ditchdetention time about12h. In the condition of high concentration inflow, the lack of ditchdetention time will cause high pollutant load, which is bad for entire system to functionwell. Under the premise of guaranteeing the ditch drainage requirements, extending thedetention time as long as possible can effectively paly the integrity of ditch and wetlandsystem,24h of detention time is the best.