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CRC PUBLICATIONS |
Removal of Suspended Solids and Associated Pollutants by a CDS Gross Pollutant Trap
Tracey Walker,
Robin Allison,
Tony Wong,
Rick Wootton
Publication Type:
Technical Report
This is a publication of the initial CRC for Catchment Hydrology
CRC Program:
Urban Hydrology (Previous CRC)
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Publication Keywords:
Storm Sewage
Trap
Pollutants
Suspended Solids
Flow Rates
Phosphorus
Nitrogen
Water Quality (Natural Waters)
Water Quality Monitoring
Urban Areas
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Abstract / Summary:
Abstract
Pollutants carried by urban stormwater runoff are considered a significant contributor to the degradation of receiving waters. Gross pollutants are often targeted first for removal and many structural measures have been applied with varying results. In a previous CRC study, Continuous Deflective Separation (CDS) units were found to be an effective gross pollutant trap. However, the removal of pollutants <5 mm is less well understood although field observations suggest the CDS unit does retain a portion of this material. This report investigates the performance of a CDS unit installed at Coburg in Melbourne, Australia. The removal efficiencies for Total Suspended Solids (TSS), Total Phosphorus (TP) and Total Nitrogen (TN) were estimated for storm and dry weather flow conditions.
During storm flow conditions, water samples were collected using automated samplers and inflow TSS, TP and TN concentrations from the Coburg catchment were observed to be as high as 570 mg/L, 4.3 mg/L and 6.0 mg/L respectively. In the case of TSS, the CDS unit effectively reduced concentration levels above 75 mg/L, with a mean removal efficiency of approximately 70%. For concentration levels below 75 mg/L TSS removal was highly variable. This is thought to be due to flow turbulence maintaining a larger fraction of the inflow particles in suspension. Removal rates for TP were found to be approximately 30%, although there were occasions when downstream concentrations were found to be higher than the inflows. Removal rates for TN were found to be highly erratic.
During dry weather flow conditions, the data suggest that the CDS unit has a small effect on the TSS, TP and TN concentrations. The CDS unit was found to have consistently removed TN under dry weather flow conditions. However, statistical analysis of dry weather samples show a consistently higher concentration of TP at the outflow compared to inflow, in contrast to TN which showed the reverse trend. TSS showed no significant trend although there is a tendency for the unit to slightly increase TSS concentrations at the outflow. During dry weather flows, it is possible that a high proportion of TP discharged from the CDS unit is in the soluble form resulting from sediment desorption in the CDS separation chamber.
This report is available for downloading here. Printed copies can be purchased from the Centre Office.
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Centre Office:
CRC for Catchment Hydrology
Dept of Civil Engineering
Building 60
Monash University Vic 3800
Tel: +61 3 9905 2704
Fax: +61 3 9905 5033
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