Effect of OH-/Al3+ ratio on the coagulation behavior and residual aluminum speciation of polyaluminum chloride (PAC) in surface water treatment

The coagulation behavior, residual aluminum ratio of three PAC coagulants as well as content and proportion of different residual Al speciation during the treatment of a specific surface water were investigated in this paper. Experimental results suggested that surface adsorption and entrapment effect worked effectively in turbidity removal regarding this specific water. PAC(20) was appropriate to remove hydrophilic natural organic matter (NOM), while PAC(15) and PAC(23) were appropriate to remove hydrophobic fraction NOM. PAC, especially PAC(20), could reduce the content of total dissolved Al and dissolved monomeric Al with comparatively higher toxicity. PAC(20) showed lower concentration for every residual Al species. The majority of total residual Al existed in the form of unsoluble particulate Al (about 62-93% for PAC(15), 65-92% for PAC(20) and 54-78% for PAC(23)). Among total dissolved Al in the effluent treated with PAC(15) and PAC(23), dissolved organically-bound Al was almost the major speciation (about 40-92% for PAC(15) and 37-86% for PAC(23)). There existed no dissolved organically-bound monomeric Al in purified water treated with three PAC samples. Residual Al ratio of PAC varied in the following order: PAC(15) > PAC(23) > PAC(20). Besides, Al speciation in coagulants likely remained in treated water at lower dosage. (C) 2011 Elsevier B.V. All rights reserved.