| Nitrogen (N) and phosphorus (P) in secondary effluent often cause eutrophication ofreiceiving water body. Constructed wetland and plant pond are the most effectivetechnologies for removal of N and P from secondary effluent. However, N removal rate byconstructed wetlands is low under low temperature, and a long hydraulic retention time(4-7d) is required. Substrates play an important role in P removal by constructed wetlands.While N removal by constructed wetlands is mainly governed by nitrification anddenitrification processes. Removal rates of N and P from secondary effluent are lower forplant pond under lower temperature. In this study, a combined ecological system wasdesigned and tested for enhanced removal of N and P in secondary effluent by constructedwetlands. The major results obtained from this study are summarized as follows.1.The maximum P adsorption obtained from the Langmuir model was 8914 mgP/kg forpeat, 2456 mg P/kg for zeolite and 5030mg P/kg for steel slag. Phosphate "adsorptiondecreased with, increasing temperature for both peat and zeolite, but increased withtemperature for steel slag through magnetic separation. Phosphate adsorption reached thehighest at pH 6.5 for peat, zeolie and at pH 3.5-10.5 for steel slag. Phosphorus removalgenerally increased with increasing adsorbent dose rate for peat, zeolite and steel slag. Thetests were also carried out on a continuous basis in peat, steel slag and peat+zeolitecolumns using secondary effluent. It was found that peat, steel slag and peat+zeoliteconlumn showed good P removal rates. The removal rates of dissolved P (DP) and total P(TP) from the secondary effluent were 94-99% and 76-95% by a peat column, 62-79% and71-82% by steel slag column, but reached 95-98% and 97-99%, respectively by a mixedcolumn of peat+zeolite (1:3, v/v). As compared with peat and steel slag alone, peatcombined with zeolite is more effective for removing P from wastewater, with additionalbenefits of NH4+-N removal by the zeolite.2. Zeolite had a greater ammonium adsorption capacity than peat or steel slag. Themaximum ammonium adsorption was 1318 mg P/kg for zeolite, 1020 mg P/kg for peatand 770 mg P/kg for steel slag. Peat and steel slag reached breakthrough point rapidly,while zeolite could maintain much longer for ammonium removal at different hydraulicretention time. Breakthrough time is 13h and 30h for zeolite at 20 min and 40 min hydrotic retention time, respectively.3. Hyperaccumulator-Sedum alfredii Hance could effectively remove Zn, Cd, Cu and Pbfrom the secondary wastewater. Its removal capacities for heavy metals, N and P areassociated with rhizospheric microbes. In addition, Sedum alfredii Hance could alsoeffectively take up N and P at various concentrations in the wastewater under lowtemperature. The results indicated that Sedum alfredii Hance can be used to effectivelyremove N, P (nitrate and phosphate) and heavy metals.4. The results from the experiments on the removal of N and P by beet on floating-bedsshowed that beet (Beta vulgaris var cicla)) was effective in removing TN, NH4+-N,NO3--N, PO43--P and TP from fishy pond, Huajia pond and secondary effluent under lowtemperature in winter. The average removal rates were 85.72％, 85.41％, 93.70％, 92.64％and 84.24％, respectively for TN, NH4+-N, NO3--N, PO43--P and TP from fishy pondand the corresponding values were 87.42％, 80.62％, 87.73％, 80.42％and 81.74％forHuajia pond. Even in high concentrations of N and P of secondary effluent, beet alsoshowed high removal rates for these nutrients. The average removal rate reached 49.93％,60.54％, 48.45％, 59.54％and 58.44％, respectively for TN, NH4+-N, NO3--N, PO43--Pand TP in secondary effluent. Moreover, beet could grow well in the three types ofeutrophicated water.5. Water fern (Azolla filiculoides lam.) has been assessed for nitrogen and phosphorusremoval at low temperature in outdoor experiments compared with different Pconcentrations in surface water. The results from showed that Azolla filiculoides lanm. hada good capability to remove NH4+-N, NO3--N, and PO43--P from water solutions atdifferent P concentrations. At the end of experiment, the removal rates of NH4+-N, NO3--Nwere 94.04％and 95.46％, respectively at 1.058 NH4+-N and 3.523 NO3--N mg/L. Theremoval rates of PO43--P also were 87.00％, 96.75％, and 99.00％, respectively at theconcentrations of 0.1, 0.4 and 1.6 mg P/L at the end of the experiment. Plant growthincreased at all the soluble P levels. Plant growth, total N and total P concentrations inplant increased with increasing soluble P concentrations in solutions.6. The combined ecological system was designed based on above research findings withdifferent substrates, microbe, and plants with respect to their removal efficiencies for N, Pand heavy metals and the properties of secondary effluent. The combined ecological systems were performed at short hydraulic retention time for five months. The resultsshowed the combined ecological systems had an excellent removal rates for CODCr,NH4+-N, TN and TP. The removal rate is＞91％for CODCr,＞98％for NH4+-N,＞90％forTN, and＞97％TP.
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