Author: Simon Wang

Publisher:

Published: 2012

Total Pages: 200

ISBN-13:

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Bioretention devices are a Low Impact Design (LID) device primarily used to treat pollutants found in stormwater runoff. The filter media used in bioretention is important to ensure effective bioretention performance. Research has been carried out to assess combinations of materials readily available in the Auckland region which create physical and chemical properties to satisfy objectives for stormwater management. The investigation process included: establishing physical characteristics and performance criteria; investigation into available materials; particle size distribution testing; compaction assessment; hydraulic conductivity testing; and water quality testing. Compaction testing found water content to be related to mechanically compacted density if medias contained an organic fraction. A higher compacted density leads to a lower hydraulic conductivity by association. A target range for saturated hydraulic conductivity was set at 12.5 to 1,500 mm hr-1 to best meet hydraulic and pollutant removal objectives. Two commercial media (Daltons Rain Garden Mix, and Living Earth Rain Garden Mix)1 achieved the target hydraulic conductivity with light tamping compaction. Three mixes composed of fine sands (East Coast Sand, Woodhill Black Sand, Pumice Sand) with compost additions, showed the greatest potential to satisfy the hydraulic conductivity criteria with only wetting and settling compaction. These five media mixes were chosen to proceed to the water quality testing stage, primarily based on their hydraulic performance. Water quality testing involved dosing media to simulate filter media performance after 0, 5, 10, and 15 years of stormwater loading. Results indicate, for 15 years, the three sand based mixes are capable of removing copper and zinc in synthetic stormwater down to below 5 ug/L and 10 ug/L, and reduce mass loads by 60% and 70% respectively. Daltons Rain Garden Mix is able to remove copper and zinc in effluent down to 5 ug/L and 13 ug/L, and reduce mass loads by 36% and 46% over 15 years respectively. Living Earth Rain Garden Mix displayed copper leaching before eventually removing copper, and had inconsistent removal of zinc over 15 years. Over 15 years Living Earth Rain Garden Mix was estimated to reduce zinc mass load by 53%, but contribute 15% extra to copper loading. All five medias showed extreme phosphorus leaching over the simulated 15 years. Daltons Rain Garden Mix had the highest leaching concentrations (up to 3,200 ug/L), while Living Earth Rain Garden Mix had the lowest leaching concentrations (500 ug/L). The three sands were similar in phosphorus leaching levels (approximately 1,200 ug/L). The level of phosphorus leaching is a major concern and must be addressed before medias are considered for practical implementation.

Download or read book Bioretention Filter Media written by Simon Wang and published by . This book was released on 2012 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bioretention devices are a Low Impact Design (LID) device primarily used to treat pollutants found in stormwater runoff. The filter media used in bioretention is important to ensure effective bioretention performance. Research has been carried out to assess combinations of materials readily available in the Auckland region which create physical and chemical properties to satisfy objectives for stormwater management. The investigation process included: establishing physical characteristics and performance criteria; investigation into available materials; particle size distribution testing; compaction assessment; hydraulic conductivity testing; and water quality testing. Compaction testing found water content to be related to mechanically compacted density if medias contained an organic fraction. A higher compacted density leads to a lower hydraulic conductivity by association. A target range for saturated hydraulic conductivity was set at 12.5 to 1,500 mm hr-1 to best meet hydraulic and pollutant removal objectives. Two commercial media (Daltons Rain Garden Mix, and Living Earth Rain Garden Mix)1 achieved the target hydraulic conductivity with light tamping compaction. Three mixes composed of fine sands (East Coast Sand, Woodhill Black Sand, Pumice Sand) with compost additions, showed the greatest potential to satisfy the hydraulic conductivity criteria with only wetting and settling compaction. These five media mixes were chosen to proceed to the water quality testing stage, primarily based on their hydraulic performance. Water quality testing involved dosing media to simulate filter media performance after 0, 5, 10, and 15 years of stormwater loading. Results indicate, for 15 years, the three sand based mixes are capable of removing copper and zinc in synthetic stormwater down to below 5 ug/L and 10 ug/L, and reduce mass loads by 60% and 70% respectively. Daltons Rain Garden Mix is able to remove copper and zinc in effluent down to 5 ug/L and 13 ug/L, and reduce mass loads by 36% and 46% over 15 years respectively. Living Earth Rain Garden Mix displayed copper leaching before eventually removing copper, and had inconsistent removal of zinc over 15 years. Over 15 years Living Earth Rain Garden Mix was estimated to reduce zinc mass load by 53%, but contribute 15% extra to copper loading. All five medias showed extreme phosphorus leaching over the simulated 15 years. Daltons Rain Garden Mix had the highest leaching concentrations (up to 3,200 ug/L), while Living Earth Rain Garden Mix had the lowest leaching concentrations (500 ug/L). The three sands were similar in phosphorus leaching levels (approximately 1,200 ug/L). The level of phosphorus leaching is a major concern and must be addressed before medias are considered for practical implementation.