Sixteen small scale Subsurface vegetated beds (SVB) were installed down slope of the
residence at the Whitethorne Planation (WP) site. Treatments included three detention times
(2.6, 3.9, and 5.9 days), two recirculation ratios (0 and 0.5), and two plant species [woolgrass
(Scirpus cyperinus) and cattail (Typha latifolia)]. Twelve larger scale SVBs were
constructed at the Powell River Project (PRP) site, Wise County, VA. Treatment consisted
of three detention times (4, 8, 12 days) with the same plant species (cattail and woolgrass).
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.
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