Linkage of pipeline blockage to coagulation-flocculation process: effect of anionic polymer and pH

Abstract

Abstract This study investigated the frequent blockages observed in the discharge pipeline in the chemical mechanical polishing wastewater treatment plant. Preliminary analyses indicated that blockages were predominantly consisted of residual organically-bounded Al due to overdosage of polyaluminum chloride (PACl) and anionic polymer during coagulation-flocculation process. To minimize the recurrence of blockage, jar test experiments were conducted in this study to identify optimum dosages of PACl and anionic polymer as well as optimum pH value. According to the model derived from jar tests, the optimum PACl dosage was dependent on the soluble Cu concentration of wastewater with low initial turbidity [ 1000 NTU), while the optimal PACl dosage was 30 mg L−1 when initial turbidity around 7000 NTU. The change of pH in the range of 8 to 9.5 did not significantly affect the turbidity or Cu removal, however, higher pH increased the deposition of residual monomeric Al species which might lead to blockage. In summary, controlling PACl dosage at optimum dosage under the conditions of pH 8.5 ± 0.5 and 1 mg L−1 polymer could reduce the blockage occurrence as well as maintain the effluent quality to meet the standards.

Keywords

• Pipeline blockage, Polyaluminum chloride
• pH
• Anionic polymer