The influence of coal seam water composition upon electrocoagulation performance prior to desalination

Abstract

EC was investigated to ascertain its applicability to remove dissolved species from a variety of associated water samples typical of coal seam gas (CSG) operations. The hypothesis was that the CSG water composition may impact EC performance for the removal of problematic species such as alkaline earth ions and dissolved silicates. Bench top studies of a range of CSG associated water samples revealed that the greater total salinity (conductivity from 5290 to 15680 μS/cm) the less alkaline earth ions were removed. However, dissolved silicate remediation maintained high efficiency (89.5 to 98.0%) regardless of water salt content. Residual aluminium was present in treated water when aluminium electrodes were employed (4.6 to 39.0 mg/L) and correlated with increasing solution pH. In contrast, steel electrodes did not result in notable residual iron. Whether steel or aluminium electrodes were optimal depended upon the CSG water salinity. Aluminium based flocs were discovered to settle significantly slower than iron based flocs, with salinity influencing aluminium flocs properties more than iron flocs. Differences in the presence of amorphous species and crystalline gibbsite may in part explain the floc settling behaviour. In either case, dewatering of flocs represents a technical challenge. The major cost in terms of economics was electrode consumption whether iron or aluminium electrodes were used. The system with lowest operating cost was always iron (A$2.50 to 2.68 per kL compared to A$2.70 to 4.32, per kL for aluminium) regardless of water salinity.