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14The removal of the trace inorganic contaminants boron (B(OH)

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Endosulfan (ES) is a micropollutant found in reverse osmosis concentrates from water reuse applications. Electrodialysis (ED) can remove and recover charged solutes from such concentrates.While polar compounds cannot normally be removed, their fate in ED is important as they can contribute to membrane fouling/poisoning and be released during cleaning. High adsorption of ES to ED membranes was observed. Consequently, the influence of solution pH and presence of humic acid (HA) on sorption mechanisms of ES to ion-exchange membranes during batch sorption isotherm and ED experiments were investigated systematically. ES-membrane partition coefficients * Current address: Faculty of Engineering, University of Wollongong, Wollongong NSW 2522, Australia 2 (log K AEM/CEM ) quantified through sorption isotherm experiments suggested that ES sorption was resultant of membrane catalysed ES degradation, hydrogen bonding and cation-π interactions between ES and membrane functional groups. ES sorption at pH 7 (550 µg/cm 3 ) was greater than sorption at pH 11 (306 µg/cm 3 ) due to alkaline hydrolysed ES and resultant decrease in bonding capacity with the membranes at high pH. The presence of HA reduced sorption at pH 7 (471 µg/cm 3 ) and 11 (307 µg/cm 3 ) due to HA competitive sorption. Partial membrane desorption was noted in isotherm (≤ 20%) desorption experiments and was dependent on the initial mass sorbed, solvent pH and resultant membrane interactions.

This study focuses on coupling geochemistry with geo-hydraulics to enable time-dependent modelling of the remediation of acidic groundwater using an alkaline permeable reactive barrier (PRB). Chemical clogging due to secondary mineral precipitates reduces the porosity and hydraulic conductivity of the reactive medium. The governing equations are incorporated into commercial numerical codes, MODFLOW and RT3D. An original algorithm was developed for RT3D to simulate geochemical reactions occurring in the PRB. The results and the model predictions are in agreement, confirming that the hydraulic conductivity reduction due to mineral precipitation occurs at the start of permeation and continues until halfway through the testing phase. This study focuses on coupling geochemistry with geo-hydraulics to enable time-dependent modelling of the remediation of acidic groundwater using an alkaline permeable reactive barrier (PRB). Chemical clogging due to secondary mineral precipitates reduces the porosity and hydraulic conductivity of the reactive medium. The governing equations are incorporated into commercial numerical codes, MODFLOW and RT3D. An original algorithm was developed for RT3D to simulate geochemical reactions occurring in the PRB. The results and the model predictions are in agreement, confirming that the hydraulic conductivity reduction due to mineral precipitation occurs at the start of permeation and continues until halfway through the testing phase.Keywords: acidic groundwater, chemical clogging, permeable reactive barrier, mineral precipitation, transport modelling 2 IntroductionAcidic groundwater generated from acid sulfate soil (ASS), which occupies over 200,000 This head will be the input into MODFLOW which in return will be used to couple the groundwater flow with reaction kinetics in RT3D. User-defined module facilitated in RT3D was used to feed the geochemical algorithm into the numerical codes. This model is beneficial for practising engineers and scientists who have to deal with ASS especially in coastal areas of Australia. Laboratory column experiments were carried out under constant flow of 1.2 mL/min (millilitres per minute) using a Masterflex peristaltic pump (Fig. 2). Two simultaneous column experiments were run as suggested by [29] one for sampling and one to take pressure readings. The purpose of running two simultaneous columns instead of one column was to eliminate the impact of sampling activities on the pressure in the column [29]. The pressures at the onset were measured for both columns using pressure transducers at both ends which were almost the same. The input and environmental conditions were maintained the same for both columns, so the pressure readings calculated at each port was assumed similar to the respective sampling port at the same height in the other column. Methodology Laboratory column experimentsThe crushed recycled concrete used in this study was a waste material discarded after the demolition of old concrete structures. The particle size of crushed concre...