The objective of present study was to evaluate the removal efficiency of high strength organic wastewater using experiment scale of constructed wetlands by comparing the free water surface flow (FWS) and subsurface flow (SF) systems. The emergent plant employed was Cyperus sp. The average removal efficiencies for both systems were 57.8-61.4%, 79.9-86.8%,88.6-92.0%, 46.9-58.1 %, and 79.9-91.2% for BOD5, COD, TKN, NO·3-N and TP, respectively. High removal efficiencies for both wetland systems were TKN and TP whereas N03-N removals were lower than other parameters. Mean removal efficiencies indicated that the SF systems were higher than the FWS constructed wetlands. Based on the t-test analysis, the average removal efficiencies of COD, TKN and TP for SF were significantly higher than FWS. In addition, relationships between BOD5 removals and initial BOD5 concentrations indicated a fairly significant linear relationship for the SF systems (R2 = 0.59) and the FWS (R2 = 0.54). Furthermore, COD removal were significantly influent by inflow COD concentrations as indicated by a strong significant linear relationship for SF (R2 = 0.89) and FWS systems (R2 = 0.90).
This study was conducted to quantify emissions of greenhouse gases (GHGs), methane (CH 4 ) and Nitrous Oxide (N 2 O), from free water surface constructed wetlands used for domestic wastewater treatment. All constructed wetlands were monoculture and each plot was planted with Phragmites sp., Cyperus sp., or Canna sp. The average CH 4 and N 2 O emissions were in the range of 5.9-11.2 and 0.9-1.8 g/m 2 /h, respectively. Seasonal fluctuations of CH and N 2 O emissions were observed. The highest fluxes of both GHGs occurred during hot rainy season (July-October) followed by summer and the lowest found in cool season. The mean of CH 4 and N 2 O emissions from different plants species were significantly different (p<0.05). Average CH 4 emissions from constructed wetlands planted with Phragmites sp., Cyperus sp. and Canna sp. were 11.2, 6.0 and 5.9 mg/m 2 /h, respectively, while mean N 2 O emissions were 0.9, 1.0 and 1.8 mg/m 2 /h, respectively. Calculated of Global Warming Potential (GWP) found that GWP of CH 4 and N 2 O flux from constructed wetlands planted with Cyperus sp., was the highest (669 mg CO equivalent/m 2 /h), followed by Phragmite sp., (524 mg CO 2 equivalent/m 2 /h) and Canna sp., (434 mg CO equivalent/m 2 /h), respectively. These results suggested that municipal wastewater treatment by constructed wetlands planted with Canna sp. and Phragmite sp., had potential of lower GHGs emissions into the atmosphere and Phragmite sp., provided the highest removal rate of Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD).
One hundred and thirty-seven samples of agricultural residue were taken from the study area of forty subdistricts in twenty districts of ten provines in the Northeastern region of Thailand. The samples were analyzed for major physical and chemical properties and subjected to simulated burning. Rice straw had the highest dry weight and bagasse the lowest. Bagasse had the highest moisture content and the highest carbon content. Results from simulated burning found that sugarcane leaf emitted more CO2 than the other residues. Weight loss on combustion was in the range of 75-92 %, and the simulated burn of agricultural residues showed CO2 emission values at 67% of the IPCC values.
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