Study On Treatment Of Landscape River By Constructed Wetlands With Functional Substrates

At present constructed wetlands (CWs) have been widely used as a kindof landscape water treatment technology, which can not only beautify theenvironment but also help ecological purification function. It also hasobvious advantages in the advanced treatment of effluent of municipalsewage plants, the in-lake river or landscape water treatment with highhydraulic loads and low nutrient concentrations. But in real application, itshows some problems in functional aspects and hydraulic characteristic ofsubstrates. The landscape water in China has suffered both point source andnon-point source pollution in different degrees. Since the poor liquidity ofwater body and lack of maintenacemanagement, most of landscape waterhas suffered eutrophication, which leads to the loss of landscape function.Four horizontal subsurface flow constructed wetlands (HFCWs) withdifferent substrates were constructed to investigate long-term treatmentperformance of CWs treating eutrophic landscape river water. Hydraulicefficiency was tested on CWs and new functional substrate was preparedwith perfomance testing, results of which would be used for designing andoperation parameters setting on HFCWs in engineering application. Thisstudy relys on the early nutrition of the lake (Erhai) water pollutionprevention technology and engineering demonstration project which belongsto the National Major Science and Technology Program for Water Pollutionand Treatment-Lake Theme. And this study is also supported by the scienceand technology project of the Ministry of Communication.During continuous operation at hydraulic loading rate (HLR) of0.3m~3/(m~2d) for15months, the removal efficiencies of turbidity, COD, TN,TP and NH4+-N in the SFCWs with mixed substrates were much higher thanthose in the traditional SFCW with gravels. Besides, plants were also contributed to the removal of nutrients. The removal efficiencies of all thepollutants were decreased when HLR was increased to0.6and1.2m~3/(m~2d). The impact on turbidity was small but the impact on COD, TNand TP was large. High HLR could be adopted for the purpose of improvingthe transparency of water while low HLR would be better for nutrientsremoval.For the problem of unsatisfied hydralic conditions, tracer tests were usedto confirm that different kinds of CWs have their own hydralic residencetime distribution density curves. Under the condition without substrate, thehydraulic efficiencies of CWs with different inflow configurations werelisted as follows, horizontal flow with multi-gallery was better thanhorizontal flow with one gallery, in which horizontal flow with eightgalleries was the best, with lowest effective volume ratio and value of shortcircuiting. Under the condition with substrates, the results showed thathorizontal flow with one gallery had better hydraulic efficiencies and tracerrecovery ratio.For the problem of bad performance ofsome substrates in realapplication, this study focused on preparation of ceramsite to improveperformance of functional substrate. When using waste clay as main rawmaterial, added with activated carbon and calcium silicate hydrate (CSH),the results of particle strength test showed that ceramsite with CSH hadbetter numerical tube pressure than that without CSH. Besides, ceramsitewith10%CSH was the highest. When using waste clay and fly ash as mainraw material, added with10%activated carbon as the same and anotheradditional additive among calcium chloride, ferric chloride and magnesiumsulfate respectively, ceramsite on phosphorus removal effect by static testwas investigated in wastewater. Additive composition and content on theeffect of phosphate removal were also investigated in the static test. Theresults showed that ceramsite with only10%calcium chloride was the beston phosphorus removal efficiency which reaches over85%.