Process evaluation of treatment options for high alkalinity coal seam gas associated water

Abstract

Both chemical amendment and ion exchange with cation resins were investigated in regards to remediation of coal seam gas (CSG) associated water characterized by relatively high concentrations of bicarbonate species. The aim of this study was to develop process engineering models using AqMB software which would accelerate selection of appropriate technologies to facilitate beneficial water reuse. Chemical amendment of CSG associated water was best conducted using sulphuric acid addition instead of hydrochloric acid due to cost considerations. However, the sulphate or chloride added to the CSG associated water restricted amendment processes to water samples comprising of <1000 mg/L bicarbonate ions. Use of weak acid cation (WAC) and strong acid cation (SAC) resin effectively remediated low salinity water samples (conductivity <650 μS/cm). For CSG associated water of higher salinity, SAC resin produced better water quality; albeit, less volume of WAC resin was required and this material is inherently easier to regenerate. Ion exchange was preferred to chemical amendment as acid addition detrimentally increased the amount of anions present in solution (sulphate or chloride) and thus limited the irrigation potential for the treated water. Regardless of the remediation strategy, dosing with a source of calcium was required to manipulate sodium adsorption ratio to meet regulatory guidelines. Future studies should consider cation/anion resin systems and also membrane based methods for CSG associated water treatment.