Novel Horizontal Subsurface-Flow Constructed Wetlands For Acid Orange 7 And Nitrogen Removal
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Date
2014-07
Authors
Tee, Heng Chong
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Novel designed horizontal subsurface flow (HSF) constructed wetlands were developed incorporating baffles to allow horizontal and vertical flows sequentially along the treatment path. The design allows the treatment of pollutants under multiple aerobic, anoxic and anaerobic conditions sequentially in the same wetland bed. Four experimental-scale HSF constructed wetland units, two of which of novel design [NDP (planted baffled wetland unit) and ND (unplanted baffled wetland unit)] and the other two of conventional design [ODP (planted unbaffled wetland unit) and OD (unplanted unbaffled wetland unit)], were operated outdoors. One of each type of wetland units (NDP and ODP) was planted with cattail (Typha latifolia). The wetland units were initially fed with domestic wastewater until the cattail plants had attained maturity. The performances of the novel and conventional designed HSF constructed wetlands, planted and unplanted, in the removal of nitrogen and oxygen demand were compared at the hydraulic retention times (HRT) of 5, 3 and 2 days. They were then fed with domestic wastewater spiked with 300 mg/L of Acid Orange 7 (AO7) azo dye and their performances in AO7 removal were evaluated at HRT of 5, 3 and 2 days.
The results show that ammonia nitrogen removal efficiencies of 99, 96, 49 and 42 % were achieved in NDP, ODP, ND and OD, respectively, at 5-day HRT but deteriorated to 84, 70, 43 and 35 %, respectively, at 3-day HRT and further decreased to 74, 55, 35 and 26 %, respectively, at 2-day HRT. The mean values of first-order rate constant of ammonia nitrogen removal (1/day) were found to be 0.92 ± 0.13, 0.54 ± 0.04, 0.16 ± 0.01 and 0.12 ± 0.01 in NDP, ODP, ND and OD,
respectively, at the mean temperature of 27 oC. For COD removal, the novel designed units also showed better efficiencies with 79 % versus 69 % for NDP against ODP and 66 % versus 59 % for ND versus OD at 5-day HRT. Although all the wetland units exhibited a deterioration in COD removal efficiency as HRT decreased, the novel designed units always performed better than the conventional units. The removal efficiencies of AO7 in NDP, ODP, ND and OD were 100, 73, 57 and 26 %, respectively, at 5-day HRT but decreased to 88, 46, 37 and 9 %, respectively, at 3-day HRT and further decreased to 69, 30, 21 and 0 %, respectively, at 2-day HRT. The mean values of first-order rate constant of AO7 removal (1/day) were found to be 0.78 ± 0.22, 0.25 ± 0.04, 0.17 ± 0.03 and 0.05 ± 0.02 in NDP, ODP, ND and OD, respectively, at the mean temperature of 27 oC.
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Keywords
Novel horizontal subsurface-flow , constructed wetlands for acid orange 7