EWRE: Jan. 10, 2014, 12:20pm

Seminar Location: USF Tampa campus - ENG room 4
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University of South Florida – Civil & Environmental Engineering

Environmental and Water Resources Engineering Graduate Seminar – Spring 2014

Performance of Modified Bioretention Systems

Thomas J. Lynn, P.E.

Civil & Environmental Engineering, University of South Florida

Friday, January 10, 12:20-1:10

Room 4 ENG Building

Abstract. Urbanization increases nitrogen loadings from stormwater runoff, which promotes eutrophication in downstream surface waters.  Eutrophication can be managed using Low Impact Development (LID) technologies, such as bioretention systems.  However, total nitrogen removal is often limited by low nitrate (NO3⁻) removal efficiencies.  A modified bioretention system is a relatively new LID technology that incorporates a submerged carbon-containing medium to support denitrification.  Little is known; however, about the factors controlling NO3⁻ removal in these systems.  In this research, microcosms were used to investigate NO3⁻ removal performance using mixtures of wood, sand and gravel media during initial start-up and after acclimation.  Column studies were used to investigate NO3⁻ removal performance at varying storm event flow rates and number of days between storm events, or antecedent dry conditions (ADCs).  Microcosms were observed to have poor NO3⁻ removal during start-up (-39 to 28%) and production of Total Kjeldahl Nitrogen (TKN) (11 mg/L), phosphate (15 mg/L) and dissolved organic carbon (DOC) (130 mg/L).  After acclimation, the wood-containing media removed up to 100% NO3⁻ within six hours, and produced low amounts of TKN (<0.1 mg/L) and DOC (2 mg/L).  Column studies showed that increased detention times and ADCs improve NO3⁻ removal.  During ADCs, water retained in the system becomes supercharged with DOC.  During a storm event, the initially high DOC concentrations support high denitrification rates; however, over time, NO3⁻ removal decreases as DOC is washed out of the system.  This study describes how modified bioretention systems operate in harmony with natural biological processes to reduce eutrophication.  The results provide practical guidelines for designing modified bioretention systems.  In addition, data from microcosm tests were used to estimate that eucalyptus wood based modified bioretention systems will support NO3⁻ removal for at least 20 years.

 

  Biosketch. Thomas J. Lynn is a doctoral candidate in the Civil and Environmental Engineering Department at the University of South Florida, Tampa, Fla.  He earned his bachelor of science in civil engineering and a master’s degree in environmental engineering from the University of South Florida.  He has four years of professional experience working as a surface water regulator for the Southwest Florida Water Management District and as a land development consultant in Ocala, FL.  He is a registered professional engineer in the state of Florida.  His current research focuses on how nitrate is removed in the internal water storage zone of bioretention systems.

Spring 2014 Semester Seminar Schedule 

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