Wastewater Treatment Using Enhanced Hybrid Constructed Wetland System Of Vertical-flow And Horizontal-flow

In this research,enhanced hybrid constructed wetland system of vertical-flow (VF)and horizontal-flow(HF)using a zeolite,clinoptilolite in the vertical-flow constructed wetland(VF2-HF2)was designed,to chemically store ammonia in cold temperatures and regenerate biologically the ammonia adsorped under the conditions that are more conducive for nitrification,to solute poor nitrogen removal in colder climates.The other hybrid constructed wetland system of vertical-flow and horizontal-flow(VF1-HF1)filled with gravel instead of zeolite in VF was also designed,to find out the removal difference in COD,NH₄⁺-N,TN and TP between the two systems.As well,the kinetics of zeolite biological regeneration and enhanced denitrification by harvested leaves of hydrophyte in the horizontal-flow was investigated in the laboratory research.When hydraulic retention time(HRT)was 4.4～17.6d,with COD 120～300 mg·L-1,NH₄⁺-N 12～33 mg·L-1,TN 24～42 mg·L-1,TP 2.8～9.4 mg·L-1 in the influent,the removal efficiency of COD,NH₄⁺-N,TN and TP was 64%～94%,4%～72%,3%～71%,15%～98%in VF1-HF1,and was 82%～99%,52%～98%,34%～91%,20%～98%in VF2-HF2.When HRT is above 4.4d,the concentration of COD, NH₄⁺-N,TN and TP in the effluent of VF2-HF2 can steadily comply to the standard of I level-B of discharge standard of pollutants for municipal wastewater treatment plant(GB18918-2002).Therefore,when the effluent should comply to the standard of I level-B of GB18918-2002,and treatment ability and zeolite biological regeneration are considered,it is advised to operate with HRT=17.6d for VF1-HF1,with HRT=8.8d for VF2-HF2.The main mechanism responsible for organic matter removal is the microbial activity of aerobic and anaerobic bacteria,the types of substrate have no significant influence on the degradation of COD,which mainly act as the carrier of microorganism growth.The iris and bulrush have a more vigorous root system,and provide an expanded surface area for attached microbial growth and additional nutrient uptake.Therefore,they have an higher removal efficiency of COD than reed. HRT has the significant influence on the removal efficiency of NH₄⁺-N in spring, summer and autumn,that of TN and TP in spring,summer and winter.There was a very strong positive correlation between influent load and removal rate of NH₄⁺-N, TN and TP.The removal path of nitrogen shows that biological removal accounts for 69%;the adsorption of zeolite accounts for just 16%,which proves the happen of biological regeneration of zeolite in warm climates.The removal path of phosphorus shows that the removal of phosphorus is mainly happened in VF1,substrate adsorption accounts for 84%,plant absorption just accounts for 4%,which is proved that the removal of phosphorus in high load wastewater treatment by plant harvest is limited.The result of zeolite biological regeneration showed that ion-exchange of NH₄⁺-N mainly happened in two days,the saturated adsorption capability of zeolite is 3.32mgN·g^-1.The influence of cation concentration,aeration,nitrifying bacteria and heterotrophic bacteria on the regeneration efficiency fits the fist order kinetic reaction. The regeneration efficiency can be raised by 1.5%with aeration on the basis of regeneration of cation concentration,7.7%with heterotrophic bacteria,and 48.9% with nitrifying bacteria.When heterotrophic bacteria and nitrifying bacteria coexisted in a reactor,the functions of nitrifying bacteria and heterotrophic bacteria were inhibited by substrate competition when the regeneration times were above 80d.The determination of cation concentration before and after zeolite biological regeneration showed that K⁺ and Na⁺ took an important role in the biological regeneration,which is consistent with the separation factor between NH₄⁺-N and other cation.It is feasible that harvested plants are used to supply carbon source for denitrification in HF reactor,the rate of denitrification is the fastest after 7～11d added of harvested cattail.The denitrification kinetic constant can be raised by 0.72 times because of the growth of live reed plant,3.56 times because of the addition of the leaves of dead cattail,10.35 times because of the addition of harvested cattail after pretreatment.The rate of NH₄⁺-N released goes up after the harvested cattail pre-treated by NaOH alkali solution.The result of PCR-DGGE shows that the Shannon-Wiener changes with the addition of harvested cattail and the growth of standing reed plant.The result of DGGE shows that the main bacteria existed in the reactor are Leptolyngbya and Escherichia with the similarity of 99%.