Study On Plant Species Selection And Wastewater Purification Efficiency In Constructed Wetlands In Beijing

Constructed wetlands,as wastewater treatment and water environmental enhancement technology with high wastewater purification efficiency,low energy input and low operation and maintenance costs,were developed in the 20th century 70's.At present,constructed wetlands were designed and widely used in the treatment of industrial wastewater,municipal or domestic sewage and agricultural run-off sewage treatment around the world.Vegetation was one of the most important component of wetlands,and one of the key factors of wastewater purification efficiency in constructed wetlands.Nevetheless,there were kinds of wetland plant species in the world,and all of them had strong regionalisms.Different wetland plant species'purification efficiencies for different kind of pollutants were distinct.It would have important theoretical and practical significance to screening for some wetland plant species,which were effect in wastewater purifying and suit for the local region.Study on wetland plant species selection aimed to investigate the purification efficiencies for domestic sewage in wetland plant ponds using five wetland plant species,Phragmites australis,Typha orientalis,Oenanthe javanica,Menyanthes trifoliate and Salix viminalis.Experiment with six plant dispositions in static water environment was conducted in Yanqing County of Beijing from June to November 2008.After six months monitoring on pH,chemical oxygen demand(COD),total nitrogen(TN)and total phosphorus(TP),results indicated that wetland plants were capable for removing pollutants from wastewater,and the purification efficiencies increased with increasing temperature and plant growth before September,but this increasing tend slow down or the purification efficiencies decreased from September.Purification efficiencies for pollutants were different among the five wetland plant species and six wetland dispositions.For the five wetland plant species,Typha orientalis,Menyanthes trifoliate,Phragmites australis and Salix viminalis got the best purification efficiencies for pH,COD,TN and TP,respectively.The purification efficiencies of Typha orientalis and Salix viminalis were the greatest for all these four pollutants.Compared plant disposition with the single plant,plant dispositions were more efficient for pH and TN removing,but less efficient for COD and TP than single plants.Phragmites australis and Menyanthes trifoliate were suitable for plant dispositions with other species in pollutants removing,while the purification efficiencies of single Typha orientalis,Salix viminalis and Oenanthe javanica performed better compared to plant dispositions.Small pilot models for waterfowl wastewater treatment had been operating in Beijing Wildlife Rescue and Rehabilitation Center.The constructed wetland including free water surface wetlands and sub-surface flow wetlands,emergent,free floating and floating-leaved macrophytes,as well as sand,loam and gravel,while application of artificial floating islands,The available data from the examination confirmed that constructed wetlands had a good performance in the removal of various pollutants.August or September were the two best months for pH removing.For COD,TSS and TP removing,August,September and early November took good performances,respectively.Concerning TN,we'd better to choose in the end of November,but in the early September to remove.The study also found that Pistia stratiotes had a strong absorption of pollutants in wastewater.However,because of its short growth cycle,plants would brown rot soon.And it's very likely to cause secondary pollution if it was not timely salvaged.So we should pay more attention on the management of Pistia stratiotes if we use it in constructed wetlands in Beijing.