Process design of coal seam gas associated water treatment plants to facilitate beneficial reuse

Abstract

This study used computer simulation to select appropriate process designs to make coal seam gas (CSG) associated water comply with beneficial reuse regulations. The hypothesis was that computational simulation may predict the unit operations required for treatment of CSG associated water over a wide range of salinities. AqMB software facilitated complete analysis of water treatment from initial storage pond to final pH and sodium adsorption ratio (SAR) adjustment. Three samples of CSG associated water ranging from 3650 to 22123 mg/L total dissolved solids content were evaluated. Common to each process design was a settling pond, coarse & fine filtration, softening, anti-scalant addition, and reverse osmosis. When the water hardness was very hard, then a lime softening system may be required. Both microfiltration and ultrafiltration were considered, and in both cases the level of suspended solids was reduced to close to zero. Sodium exchanged WAC resin removed the majority of alkaline earth ions and inhibited downstream scale formation. The presence of substantial alkalinity was addressed by use of acid exchanged WAC resin in combination with an air stripper. However, process economics indicated this option was not favourable. A two-stage Reverse Osmosis system not only recovered from ca. 74–79 % water with all CSG associated water types but also the water quality was compliant with beneficial reuse regulations. The computer predictions mirrored actual data from operating industry sites.