Assessment Of Pollutant Removal Performance In A Bio-Filtration System - Preliminary Results

Author: Lloyd, S.D. , Fletcher, T.D. , Wong, T.H.F., Wootton, R. M.

Citation: Lloyd, S.D., Fletcher, T.D., Wong, T.H.F. and Wootton, R.M. (2001), Assessment of Pollutant Removal in a Newly Constructed Bio-retention System, proceedings of the 2nd South Pacific Stormwater Conference, Auckland, New Zealand, 27 ? 29 June 2001, pp.20-30.

Year Of Publication: 2001

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Theme: Catchment Modelling, Ecology & Restoration, Monitoring & Assessment, Urban Water, River Management

Abstract: This paper presents the preliminary findings of a series of controlled field experiments investigating the pollutant removal effectiveness of a newly constructed bio-filtration system. A bio-filtration system consists of an infiltration system (e.g. gravel infiltration trench) overlain by a vegetated (normally grass) swale. Flow conditions corresponding to the peak discharges of the 3 month, 1 yr and 5 yr ARI events were simulated. In addition, experiments involving the operation of the swale by itself were undertaken, by discharging flows directly into the swale, with inlets to the underlying infiltration trench blocked. In essence, the system operated as a swale with a relatively high infiltration capacity due to the underlying trench. Pollutant removal efficiency was investigated by dosing of the system with pollutants of known characteristics and mass. Two pollutant sets were used (differing in mass, to achieve two different concentrations for each flow rate) consisting of Bromide, TSS, PO4, and NOX. Bromide (Br) has been used as a conservative tracer, allowing the mass balance of the pollutographs to be calculated. The results presented in this paper are for the 3 month ARI simulation (~2.5 l/s) for the full bio-filtration system, and the simulation whereby flows were discharged to the swale component of the system only, at a rate of approximately 2 l/s. The results show TSS removal of between 55% and 74%, and TP removal of between 24% and 55%. The relatively low phosphorus removal may in part be attributed to the exclusive use of soluble reactive phosphorus in the dosing mix. While a reduction in NOX was observed, no effective removal of TN was found.

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