| To solve the problems of low efficiency, pore clogging and poor effect intraditional constructed wetland, we developed a new treatment technique ofhydroponic and extremely shallow hybrid constructed wetland, which waslow-investment, highly efficiency, stable and easy to run. On the basis of the formerstudy, we studied the stability of extremely shallow hybrid constructed wetland, theremoval efficiency of pollutants with different depth in each season and the feasibilityof CWs with Lolium perenne L. overwintering in northern areas.The pilot-scale treating system carried out in a wastewater treatment plant in Xi’anCity, the system is divided into three groups in accordance with the different waterdepth or deep-bed(0.1m,0.3m and0.6m), each group consist of hydroponic cultivation,horizontal flow and vertical flow constructed wetland. Wastewater come from theeffluent of primary sedimentation tank, the intermittent supplemental water loading inthe system is0.15m3/d for three times a day, and cultivated plants adopt Loliumperenne L. The system running for nine months and across three quarters. The mainresults and conclusions are shown as follows:（1）The hybrid process of hydroponic and constructed wetlands with Loliumperenne L. cultivated had good removal efficiency and stability for municipalwastewater treatment. In spring and summer, the pollutant concentrations in theeffluent from the three groups of system were lower than the second class specified inIntegrated Wastewater Discharge Standar（dGB18918-2002）.Among them, the removalefficiency in0.1m run（extremely shallow）hybrid process was significantly better thanthat in0.3m and0.6m run, especially in nitrogen and phosphorus removal.（2）The hydroponic cultivation ditch could be as pretreatment units of hybrid construction wetland. The results showed that the organic loading rate and the risk ofsubstrate clogging in constructed wetland were reduced effectively; the shallow waterdepth is beneficial to the growth and metabolism of Lolium perenne L., it not onlystrengthened the oxygen supply capability of root, but also provided more attachmentsites for the survival of microorganisms. Thereby, it strengthened the role of absorptionand degradation of plants and microorganisms.（3）The depth of substrate was closely related with the hydraulic loading rate,hydraulic retention time and volume load, and directly affects the removal efficiency ofpollutants in CWs. When the depth was reduced to0.1m, the DO and ORP in CWs wassignificantly increased. This is a effective solution to solve the problems of inadequateDO and too large anaerobic zone in traditional wetland.（4）The hydroponic cultivation ditch and constructed wetlands show a significantdifference in the removal efficiency before and after the winter ice. In the icing period,the surface ice greatly restricted reaeration, which led the removal rate significantlydecreased. A greater depth of water and substrate was conducive to insulation and the0.6m CWs were more stable in the icing period. Therefore, in the engineering, theextremely shallow CWs should pay attention to the insulation in the icing period ofwinter, or using the combination of CWs with different substrate depths.（5）The Lolium perenne L. was suit for hydroponic cultivation ditch andconstructed wetlands in the cold regions of winter. It can eliminates the trouble ofchanging the kinds of plants between the winter and spring. The Lolium perenne L. wasbetter than the control group on the land, the absorptive capacity of nitrogen was betterthan Canna, and the timely harvest was conducive to plant growth and pollutantremoval. |
PDF Full Text Request