TREATMENT OF LANDFILL LEACHATE BY INTEGRATED HORIZONTAL-FLOWCONSTRUCTED WETLANDS

Lei Yang, Yi-Lin Chen, National Sun Yat-sen University, Kaohsiung, Taiwan

Landfill leachate treatment can be expensive and energy-intensive achieved in advanced wastewater treatment plants. One possible method to reduce cost and energy requirements is to treat the leachate on-site using constructed wetlands. In this study, we investigated the feasibility of treating the leachate from a ten-year old landfill site, with high ammonia levels and low BOD/COD ratio, by pilot-scale constructed wetlands. An integrated horizontal-flow constructed wetland system fed by original landfill leachate was used in this study. The integrated constructed wetland system contained two basins connected in series: one installed as free water surface (FWS) constructed wetland, and the other as subsurface flow (SSF) one, both of which were in the same size of 2 m(L)x1 m(W)x1 m(H). The FWS system was planted with reeds (Phragmites australis), while the SSF system was planted with evergreen (Dracaena sanderiana cv.). After one-year operation, the experimental results showed that this constructed wetland system performed better in the condition of hydraulic retention time (HRT) controlled at 5 days than that at 10 days for both nitrogen removal and BOD, while almost half of COD was removed in both controlled HRT conditions in the experiment. According to the analytical results, the removal efficiencies of total nitrogen (TN) and ammonia (NH₃-N) were measured equal to 62% and 79%, respectively in HRT of 5 days, while the values were measured equal to 52% and 74%, respectively for HRT controlled in 10 days. For BOD removal efficiencies, the condition of 5-day HRT presented 67%, while it was measured equal to 28% for HRT controlled in 10 days. Meanwhile, the removal efficiency of COD was found equal to the same value of 46% in both HRT conditions controlled in this study. However, we found that both total phosphorous (TP) and phosphate (PO₄^-3) exhibited higher removal efficiencies in the test run of HRT controlled in 10 days than that in 5 days, which was because PO₄^-3was removed mainly by chemical adsorption onto the medium surface used in constructed wetland systems. The media might have been saturated in the second stage of test run with HRT controlled in 5 days. The reason why the removal efficiencies of TN were lower than NH₃-N was believed due to less active for denitrifying bacteria in systems. It was believed that lack of organic carbon source in the secondarily treated leachate would result in insignificant denitrification to make nitrate build-up in the system. There are two conditions required for denitrification: one is anoxic environment, and the other is sufficient organic carbon sources. In constructed weland systems, the medium surface could provide an anoxic sites to achieve denitrification occurring. Hence, deficient of organic carbon source was the only reason to depress denitrification in wetland system to treat aged landfill leachate. Therefore, we tried to add extra organic carbon sources (fructose and molasses) into the wetland systems to verify this hypothesis in the final stage of test run. The experimental results showed that the higher the amounts of BOD were added into the wetland system, the higher the amounts of TN were found removed. These experimental results surely confirmed that adding BOD into a wetland system could help to achieve complete denitrification.

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Lei Yang, prof., Department of Marine Environment and Engineering, National Sun Yat-sen University, 70 Lien-Hai Road, Kaohsiung 804, Taiwan. Tel. (7) 525-20-00 (ext 50-68), fax (7) 525-50-68. E-mail

Последние изменения внесены 10.07.07