Residence time distribution (RTD) profiles were investigated in a standard oscillatory baffled reactor (OBR) as a function of oscillatory and bulk flow components using a design of experiments (DoE) approach. A second-order, polynomial model (R2=92.1%) was fitted to N values estimated from concentration profiles and used to maximise plug flow conditions. The velocity ratio (Ψ) required to maximise plug flow was 1.9, agreeing well with the range previously identified by Stonestreet and van der Veeken (1.8 < Ψ < 2.0), suggesting that the approach used here is valid. This method could be used to rapidly quantify and maximise plug flow in various OBR designs in a simple and robust manner which could prove valuable for the operation and design of continuous processes using OBR technology.
Recent implementation of the EU Water Framework Directive necessitates addressing water quality issues at the catchment scale. In this study, contaminant loading of all point discharges have been measured, establishing the overall impact of mine waters within the catchments, and allowing the derivation of contributions of diffuse mine water pollution to these totals. The results of two ongoing case studies of mine-impacted river catchments in the northeast of England are presented. The Allen catchment, Northumberland, is impacted by discharges from abandoned Pb/Zn mines with up to 6 mg/l Zn and 0.2 mg/l Pb, which significantly exceed European ecotoxicological standards by up to a factor of 75 and 20 respectively. The Gaunless catchment, County Durham, receives uncontrolled discharges of coal mine waters with up to 8 mg/l Fe. Preliminary findings show that during both low and high flow conditions diffuse iron pollution contributes significantly to in-stream iron loadings. Probable pathways include direct groundwater input and remobilisation due to scouring of streambed sediments.
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