Studies on Oilfield Wastewater Purification with PACL and DMDAAC Polymer Flocculant

Polyaluminum chloride (PACl) coagulant and poly (dimethyl diallyl ammonium chloride-AM) flocculants were applied to purify the wastewater from Zhanazhol oilfield, Kazakhstan. Water quality measurement showed that suspended solids content (SS) and particles size in wastewater were in excess of the reinjection standard for Kazakhstan. The SEM–EDX analysis indicated that suspended solids consisted clay particles and iron compounds. The latter could be generated from mental corrosion due to high concentration of salinity, hydrogen sulphide (H2S) and chloride ion. Jar test was conducted to investigate the effects of chemical agents dosage, settling time and Ca2+ ion concentration on removal of suspended solids from oilfield wastewater. Test results showed that PACl coagulant and DMDAAC polymer flocculant could significantly improve the separating velocity and removal rate of suspended solids. Their synergistic effect could strengthen the electric neutralization and increase the particles size. The flocculation effect increased through extending settling time. But Ca2+ concentration increase could reduce flocculation effect to a certain extent. Compared to raw wastewater, the SS content in treated wastewater could be reduced by 89.3% at optimal dose. Meanwhile, the particles size decreased from 8 microns for raw wastewater to less than 3 microns for treated wastewater. This paper had implied the characteristics of suspended solids in Zhanazhol oilfield wastewater with high salinity and hydrogen sulphide (H2S). Moreover, this study provides further understanding of the performance of poly(dimethyl diallyl ammonium chloride-acrylamide) flocculant for purifying oilfield wastewater. The results laid a good foundation for subsequent wastewater treatment to achieve the quality standard of injection water.