Effect of granular activated carbon filter on the subsequent flocculation in seawater treatment

In this study, a granular activated carbon (GAC) filter was used to remove organics from seawater. The effect of GAC filtration on the subsequent treating of seawater by flocculation was evaluated through Jar test experiments and submerged membrane coagulation hybrid system (SMCHS). GAC filtration removed 70% of low molecular weight (LMW) neutrals and acids from seawater which helped to reduce the biofouling of membrane. GAC filtration also helped to reduce flocculant dose significantly. Relatively high doses of ferric chloride (FeCl3 3 mg/L) and poly-ferric sulfate (PFS 2 mg/L) were normally needed to obtain high organic removal when flocculation was used without the pretreatment of GAC filter adsorption. The use of GAC filtration prior to the application of SMCHS reduced the flocculant dosage to 1 mg/L to achieve the same removal. The subsequent flocculation by different flocculants such as ferric chloride (FeCl3) and poly-ferric sulfate (PFS) was found to be able to remove biopolymers which were not effectively removed by the pretreatment (GAC filtration). The technical and cost analyses made showed that a combination of GAC filtration and flocculation with low flocculant dose can be a superior technical and economical solution for seawater pretreatment.