Evaluation of the subsurface vegetated bed form of constructed wetlands for domestic wastewater treatment
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At the WP site, pollutant removal incresed with detention time for 5-day biochemical oxygen demand (BODs), total Kjeldahl nitrogen (TKN), ammonium (NH4-N), phosphates (PO/--P), redox potential (Eh), and total dissolved solids (IDS). The pollutant removal rates, based on 23 data sets, were: BODs (54-70%); NH/-N (30-61%); TKN (33-52%); PO/--p (7-28%); fecal coliforms (FC) (>99%) and coliphages (>95%). Recirculation appeared to have no apparent benefit. There were no differences in P, S and secondary and trace metals concentrations in the SVBs planted to cattail and woolgrass. Plants could remove 2 -10% of the total N applied and 13-57% of the total P applied to the SVBs if harvested once a year during the growing season.
At the PRP site, differences were obselVed among the detention times for BODs, TKN, NH4-N, P04-P, TDS, pH, EC and Eh. The pollutant removal percentages were: FC (>99%); BODs (30-75%); NH4-N (27-88%); TKN (27-81%); PO4 3-P (24-46%); and TDS (12-73%). Samples collected from shallow wastewater column exhibited a higher level of treatment. There were no differences in FC, BODs, TKN and NH/ -N concentrations between s VB s planted to cattail and woolgrass, and there were no differences in tissue N content between cattail and woolgrass at both sites.
The average NH3 volatilization rate was 236 mg N/m2/day, and accounted for 7-37% of total N applied to the SVBs. Average measured denitrification rates ranged from 3.87 to 6.69 mg N20 / m2 / h, and accounted for 2-17% of total N applied.
- Doctoral Dissertations