Environmental Engineering Reference
In-Depth Information
Based on this information, the most suitable media for a denitrification PRB
at the Damplands site was assessed to be sawdust or woodchips as they
• Are relatively degraded carbon sources in comparison to straw,
alfalfa, or other organic matter commonly used
• Have been shown to be a relatively long-lived source of carbon
(Vogan 1993)
• Have been shown to be effective in removing nitrates in field trials in
Western Australia (Fahrner 2002, Water Corporation 2004, GHD 2007)
• Have been shown to potentially remove DOC from groundwater
(GHD 2007)
Laboratory bench-scale tests were conducted to predict how potential car-
bon material may perform in the proposed denitrification PRB at the WCS.
The column for the apparatus was constructed of polyvinyl chloride (PVC)
tubing with a length of 100 cm and a diameter of 10 cm. The column appara-
tus allowed for the collection of samples from the influent and effluent solu-
tion. There were also four sampling ports along the length of each column; at
distances of 5, 20, 40, and 65 cm from the base of the column. These sampling
ports were used to quantify denitrification rates of the solution as it flowed
through the carbon media.
The porosity of the mixture was determined gravimetrically. To ensure
a homogenous mixture, the materials were mixed thoroughly before place-
ment into the column. The tests were performed at ambient room tempera-
ture in the laboratory.
Samples of groundwater were collected from a well in the vicinity of the
proposed PRB, which would be expected to be representative of groundwater
entering the treatment zone. During previous groundwater sampling events,
this well exhibited elevated levels of nitrate and, during the experiments, the
average influent nitrate concentrations was determined to be approximately
12 mg/L NO
3
-N.
The groundwater obtained from the site was pumped upwards through
the columns at a constant flow velocity using a precision variable-speed-
drive peristaltic pump. A range of flow velocities were selected during the
testing to mimic the flow velocity expected in the PRB.
Samples were collected from the sampling ports in appropriate containers
and transported to a National Association of Testing Authorities (NATA)-
accredited laboratory for analytical analyses. The samples were analyzed for
nitrate as nitrogen, nitrite as nitrogen, total nitrogen, total Kjeldahl nitrogen,
ammonia, DOC, and TOC.
The first round of four column experiments included four locally sourced
materials:
1. 100% Sand—as a control
2. 100% Shredded aged native tree (Karri) bark
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