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A wetland used for wastewater treatment should be incorporated with oxygen. One method to improve oxygen concentration in wetland is flow modification. In this study the effect of pulsed sewage water feed on treatment efficiency of free-surface-flow constructed wetlands was studied. This research was conducted in two phases from January to June and June to September in 2006. Two wetland units (L1 and L2) were planted with Scirpus grossus ; L1 received a continuous wastewater feed (CF) and L2 a pulsed feed (PF; five days of feed followed by two days of no feed). The removal of biological oxygen demand (BOD 5 ), ammonium nitrogen (NH 4 -N), and nitrate nitrogen (NO 3 -N) were analysed for effluent, and total Kjeldahl nitrogen (TKN) and total phosphorous (TP) in the substrate of both units were compared. Plant growth was monitored continuously for both systems. BOD 5 removal was increased by 14% by the pulsing application compared to the CF application. The average removal rate of NO 3 -N was 36% and 45% in CF and PF respectively and the differences were statistically significant. The average removal of NH 4 -N was 27.5% and 24.0% in CF and PF, which were not significantly different. The TKN near the outlet was ~5 mg per 100 g soil in both units. However, TP was higher (~22 mg per 100 g soil) at the outlet of the PF unit compared to the CF unit (~12 mg per 100 g soil). The maximum plant height was 220 cm in both systems, and no significant difference was observed. In contrast, the PF unit showed a significant reduction in shoot density and biomass production of S. grossus compared to the CF unit. The results of this study indicate that the pulse feeding strategy improved the removal of BOD 5 and reduced the above ground biomass production compared to the continuous feeding system. However, no clear improvement in ammonium removal was observed in the PF system in comparison to previous studies. DOI: 10.4038/tar.v21i2.2596 Tropical Agricultural Research Vol. 21(2): 147-156 (2009)

tropical agricultural research

Comparison Study of Pulsing and Continuous Flow for Improving Effluent Water Quality and Plant Growth of a Constructed Wetland to Treat Domestic Wastewater