Coagulants for removal of turbidity and dissolved species from coal seam gas associated water

This study demonstrated the value of coagulation approaches to the control of species in coal seam gas (CSG) associated water which can result in scaling of downstream membranes and equipment. The hypothesis was that coagulation can be effective at removing turbidity causing species, alkaline earth ions and dissolved silicates from a CSG associated water compositions. Both simulated and real CSG associated water were treated using a jar tester and addition of either aluminium chlorohydrate (ACH), aluminium sulphate (alum) or ferric chloride. All coagulants reduced the turbidity (> 95 %) and also removed alkaline earth ions and dissolved silicates (ca. 29 % for calcium; 0 % for magnesium; 60 % for barium; 21 % for strontium; 33 % for silica). Formation of a muscovite-like material was predicted using AqMB process simulation software to be responsible for silicate removal and barium sulphate precipitated when alum was used. Increasing turbidity and salinity did not appear to exhibit a significant impact upon coagulant performance. Notably, the co-presence of solution turbidity and organic matter in real CSG associated water samples promoted coagulant performance (ca. 75 % for calcium; 30 % for magnesium; 75 % for barium; 50 % for strontium; 48 % for silica). This observation was ascribed to the promotion of polymeric Alb and colloidal Alc species which were more effective materials for water clarification (compared to monomeric Ala species). Coagulation strategies appear prospective for the pre-treatment of CSG associated water samples to minimize fouling of downstream equipment and membranes employed for desalination.