Electrocoagulation for the purification of highly concentrated brine produced from reverse osmosis desalination of coal seam gas associated water

Abstract

The ability of electrocoagulation (EC) at facilitating salt recovery from brine resultant from reverse osmosis (RO) desalination of coal seam gas (CSG) associated water is described. The aim was to reduce the presence of high concentrations of dissolved silicate which inhibit salt recrystallization by forming precipitates on equipment. The hypothesis was that EC could operate effectively in brine solutions and provide high silicate removal; thus facilitating a zero liquid discharge strategy. A benchtop EC unit equipped with either aluminium, iron or mixed iron-aluminium electrodes was used to treat simulated brine from a high recovery RO process. Up to 98.9% of silica was removed when aluminium or aluminium-iron electrodes were used. Significant reduction in concentrations of alkaline earth ions were also recorded (Ba > Sr > Ca > Mg) especially with iron electrodes. It appeared that silicate removal was via aluminosilicate formation. Hydraulic retention time was a key variable with 20 s recommended on the basis of performance/cost trade-off. Polarity reversal did not substantially change removal performance but impacted power consumption. For iron and iron-aluminium electrodes 1 min polarity reversal was preferred whereas for aluminium electrode 5 min was optimal. However, a thick coating was formed on the electrode surface and this may inhibit performance if longer tests are conducted. All flocs formed settled relatively rapidly (<20 min) which was in a time frame suitable for industrial application.