Remediation of acidic groundwater by way of permeable reactive barrier

Abstract

A permeable reactive barrier (PRB) was installed in the ShoalhavenFloodplain about 100 km south of Sydney (Australia), where acidic groundwater generation from pyritic soil poses a severe environmental and socioeconomic problem. Recycled concrete aggregates were a promising source of alkalinity-generating material and adopted as the reactive media for this PRB. The current study simulates the performance of the PRB through coupling geochemical reactions involved with recycled concrete and acidic groundwater with geohydraulics (transient groundwater flows). This is the first such attempt made for time-dependent modelling and performance verification of a PRB located in acid sulfate soil (ASS) terrain. The developed model describes the chemical clogging due to mineral precipitates and the associated reductions in porosity and hydraulic conductivity of the reactive medium. The governing equations of the model were incorporated into commercial software, MODFLOW and RT3D. The field results are in favourable agreement with the model predictions, confirming that the reduction in hydraulic conductivity due to mineral precipitation occurs predominantly at the entrance zone of the PRB and insignificantly in the middle and exit zones after 7 years of operation. Mineralogical analysis undertaken on sample specimens from the PRB also confirms that clogging is minimal at the entrance zone.Notation B aquifer thickness (m) C aqueous species concentration (mg/l) D hydrodynamic dispersion coefficient (m) h head (m) IAP ion activity product (depends on the reaction) K hydraulic conductivity at time t (m/s) Keq solubility constant (depends on the reaction) K0 initial hydraulic conductivity (m/s) kr effective rate coefficient ((mol/m 3 bulk)/s) Mk mineral molar volume (m 3 /mol) Nm number of minerals no initial porosity nt porosity at time t r reaction rate ((mol/m 3 bulk)/s 1 ) Re retardation coefficient Rk overall reaction rate for the mineral ((mol/m 3 bulk)/s) S storage coefficient T transmissivity (m 2 /s) t time (s) v seepage velocity (m/s) Fk volume fraction of mineral µ, C, D constants

Chemical clogging of granular media under acidic groundwater conditions

“…Recycled concrete aggregates were used in a pilot scale PRB installed in a low-lying sulfidic floodplain in Shoalhaven, Southeast Australia, for remediating acidic groundwater (Indraratna et al, 2014a) as shown in Figure 1. According to a pilot-scale PRB study conducted by Indraratna et al (2014b), formation of iron and aluminium oxy/hydroxides resulted in at least 4%, 3% and 0.5% reductions in porosity at the entrance, middle and exit zones, respectively.…”

Study on the Mechanical and Leaching Characteristics of Permeable Reactive Barrier Waste Solidified by Cement-Based Materials

“…Numerous studies have been conducted by various experts and scholars on the safe disposal of manganese associated with acid mine drainage [2,4,5]. Permeable reactive barrier (PRB) technology is the most visible and influential [6,7]. PRBs can be used as removable, semipermanent, or permanent devices [8].…”

Biogeochemical Clogging of Permeable Reactive Barriers in Acid-Sulfate Soil Floodplain

“…A Permeable Reactive Barrier (PRB) is frontier technology that can be used to neutralise groundwater acidity induced by pyrite oxidation in Acid Sulfate Soil (ASS) terrain (Benner et al 1999;Indraratna et al 2009;Indraratna et al 2014a). Low lying coastal acidic belts get exposed to the atmosphere due to lowering of phreatic surface in dry seasons and upon artificial draining during the course of ground infrastructure and agricultural development.…”