Plant Screening And The Purification Efficiency For Eutrophic Wastewater In Constructed Wetland System

Eutrophication became more and more serious problem of water environment with rapid development of economy.Constructed wetland was a new developing technology using soil-plant-microorganism system to treat wastewater as a little cost technology in both capital investment and operation environment-friendly.Plants played a vital role in wetland system.The purification ability and the bio-ecological character of the tested plants were studied through static water culture experiment, small-scale plots of hybrid flow constructed wetland was established and domestic sewage purification results was studied.The work was done as follow:1.The study of plant screening of constructed wetland:The eutrophic waters with ammonia nitrogen(NH₄⁺-N)being the main component of nitrogen was studied,eight plants were selected,such as Lythrum salicaria,Oenanthe javanica,Scirpus validus, Iris pseudacorus,Acorus tatarinowii,Arundo donax var versicolor,Hydrocotyle vulgaris,Nymphoides peltatumf,and the purification ability and the bio-ecological character of them were studied through water culture experiment.It was found that most of plants could live normally in wastewater and there was apparent purification for wastewater,but Ar.and Ny.withered during their growth,so that they were not used in the following experiment.Oe.could grow stably,and had a better effect especially in shorter treatment time.Ly.grew quickly and had higher biomass,had the highest nitrogen uptake and nitrogen storage,Ir.had the highest phosphorus uptake and phosphorus storage.Ac.had the lowest RGR,while had the highest nutrient concentration and best effect.In the plant maturation period,when treatment time was more than 2d,along with the removal efficiency of TP exceeding 60%,while above 80%even 90%at 8d, Hy.had the highest removal efficiency for TP(93.35%).With the increasing of treatment time,plants systems had different efficiencice for NH₄⁺-N removal.Hy.and Ac.had the better removal efficiency for NH₄⁺-N at 8d,94.90%and 90.52% respectively.But for CODcr,the removal efficiency in plants system was higher than the non-plants system at 2d.When treatment time was nore than 2d,there was no significance increase of CODcr removal efficiency by plant.2.The experimental study of hybrid flow constructed wetlands treating domestic sewage:The research investigated the removal efficiencies of CODcr,TP,TN and NH₄⁺-N from domestic sewage under different hydraulic retention time(HRT,3,2 and 1d)in the stimulated hybrid flow wetlands.The main results showed that the removal efficiency of CODcr,TP,TN and NH₄⁺-N increased with the extending of HRT.When HRT was 3 days,CODcr,TP,TN and NH₄⁺-N decreased 38.67%, 79.83%,93.13%and 96.27%,respectively.In the wetland system,the reduction of TN and NH₄⁺-N mainly centralized in the sector A and D of hybrid flow wetland system, while the removal of CODcr and TP were in the sector A and B.The removal efficiency of this stimulated wetland was better in the wastewater with higher pollutant concentrations than lower concentrations.