Hybrid coagulation/membrane process treatment applied to the treatment of industrial dyeing effluent

A combined system of coagulation and membrane processes was investigated in this study for reactive dyeing wastewater treatment. Microfiltration (MF) and ultrafiltration (UF) membranes were tested in order to study the effect of the membrane type on the hybrid system performances. Additionally, membrane resistance analyses were conducted in order to understand the membrane fouling mechanism. Two different coagulants were used: Al-2(SO4)(3)(Alum) and Amerfloc445. The influence of the coagulation conditions including coagulant nature and shear rate and duration on the UF behavior was studied. Indeed, a procedure of flocs breakage-reformation under different shear intensities was followed in the coagulation step, during these tests, flocs size and sensitivity to breakage as well as their regrowth ability were examined. The filtration results indicated that the coagulation step did not enhance the MF performances. The coagulation/ultrafiltration system was found to be better not only in term of permeate quality but also in fouling minimization. Although, Amerfloc445 generated the largest flocs with the best regrowth ability, but these flocs were more sensitive in increasing shear rate. As a result, the flocs breakage dropped the UF normalized flux by at least 22% with Amerfloc445 against a maximum of almost 12% with Alum. The extension of the shear duration from 5 min to 10 min affected the UF behavior especially in the presence of Amerfloc445; indeed the normalized flux decrease reached 14% against just 3% for pre-coagulated effluent with Alum.