Performance evaluation of pipe circulating flocculation membrane system depending on kinds of coagulants

[Display omitted] •Application of two-stage coagulants addition by pipe circulating flocculation (PCF).•Humic acid fouling was controlled effectively by two-stage coagulants addition in PCF.•Difficulty to control reversible fouling from sodium alginate in coagulants addition.•PCF can be an alternative instead of conventional coagulation/flocculation. Coagulation followed by flocculation is commonly used to control membrane fouling. The objective of this study was to determine the effect of coagulation on membrane performance of pipe circulating flocculation with two-stage coagulant addition. This system makes it easy to add another coagulant. Moderate flocculating is expected with flocculation basin. In pipe circulating flocculation with a two-stage coagulant addition, the size of flocs inflowing the membrane was increased by 20–85% depending on coagulants and foulants compared to one-stage coagulation. While the system was ineffective for controlling fouling of fouled membrane with sodium alginate, membrane fouling caused by humic acid was well-controlled, resulting in considerable reduction of irreversible fouling. When synthetic wastewater containing single foulant of humic acid or sodium alginate was treated, removal rates of 64.5–69.1% and 38.9–47.0% were achieved depending on coagulants.