Chemical Engineering Journal 178 (2011) 50–59 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal jo ur n al homep age: www.elsevier.com/locate/cej Characterization and coagulation–flocculation behavior of polymeric aluminum ferric sulfate (PAFS) Guocheng Zhu a , Huaili Zheng a,∗ , Zhi Zhang a , Tiroyaone Tshukudu a , Peng Zhang a , Xinyi Xiang b a Key Laboratory of the Three Gorges Reservoir Region’s Eco-Environment, State Ministry of Education, Chongqing University, Chongqing 400045, China b School of Geographical Sciences, Southwest University, Chongqing 400715, China a r t i c l e i n f o Article history: Received 23 June 2011 Received in revised form 1 October 2011 Accepted 4 October 2011 Keywords: Individual coagulant Composite coagulant Polymeric aluminum ferric sulfate Coagulation–flocculation behavior Wastewater treatment a b s t r a c t Recent advance on the application of the composite coagulant in the coagulation–flocculation process has attracted a widespread interest. Previous research has demonstrated that iron-based composite coagulant could enhance the performance of the coagulation–flocculation. In this research, results of an experimental study using polymeric aluminum ferric sulfate (PAFS) as a modified coagulation reagent for treating wastewater was presented. The structure and morphology of PAFS were investigated using some conventional methods, and response surface method (RSM) was employed to optimized the coagulation–flocculation process while the evaluation of treatment efficiency was determined by measuring both the reduction of turbidity and chemical oxygen demand (COD). In addition, parameters affecting coagulation–flocculation behavior such as coagulant dosage, wastewater initial pH, were also examined. The results showed the structure of PAFS as a non-stoichiometric basic iron sulfate salt taking the shape of a compact network and exhibited better coagulation–flocculation performance when the species distribution of (Fe–Al) a , (Fe–Al) b and (Fe–Al) c in PAFS were 37.4%, 3.79% and 59.08%, respectively. Compared with PFS, PAFS showed a superior flocculation performance with the maximum COD removal efficiency of 83.6% and the lowest residual turbidity of 0.96 NTU at the coagulant dosage of 45 mg/L. In the coagulation–flocculation process, the adsorption-bridging and charge neutralization mechanisms played an important role in colloidal destabilization and aggregation. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The coagulation–flocculation process does not only separate suspended solids from water, but also reduce color and certain organic compounds from different sources of wastewater such as dyes wastewater, municipal sewage, micro-polluted water, oily wastewater, paper industry wastewater [1–5]. On the other hand, continued population growth and industrialization have resulted in the degradation of various ecosystems, which human life relies on. Hence, studies on improving the performance of the coagulation–flocculation process have attracted a lot of attention [1–4]. The performance of the coagulation–flocculation process is largely affected by the coagulants type that enhance the aggrega- tion of particles to form large, rapid-setting flocs either through charge neutralization or chain-bridging mechanisms. Therefore, research on wastewater treatment has been focused on the syn- thesis of new coagulant to improve the coagulation–flocculation process [5–7]. These novel coagulants include inorganic, organic and composite coagulants. However, composite coagulants have ∗ Corresponding author. Tel.: +86 23 65120827; fax: +86 23 65121769. E-mail addresses: zgc945ahhn@163.com (G. Zhu), zhl6512@126.com (H. Zheng). attracted more research attention due to excellent coagulation performance and have been widely used in many wastewater plants [8]. The most common coagulants used during the coagulation– flocculation process are hydrolyzing metal salts of aluminum and iron such as AlCl 3 , Al 2 (SO 4 ) 3 , FeCl 3 , and Fe 2 (SO 4 ) 3 [9,10]. Their major drawbacks are that the coagulant species form rapidly dur- ing dilution, and the formation of hydrolysis species cannot be controlled. However, for Al-based coagulants this may result in a high residual concentration of Al in the treated water [11,12]. Recently, concerns have been raised about the potential toxicity of residual aluminum and therefore, a threat to human health and the environment [17]. To overcome this problem, a relatively new type of coagulants commonly known as inorganic polymer coag- ulants/flocculants (IPCs/IPFs) such as poly-ferric chloride (PFC), poly-ferric sulfate (PFS) have been developed worldwide since the 1960s [13]. They are applied in the treatment of both municipal and industrial wastewater [14,11,15]. The iron-based coagulants are synthesized by oxidation of ferrous sulfate to ferric sulfate, and then carrying out a controlled partial hydrolysis of ferric sulfate to produce a heterogeneous mixture of ferric (Fe(III)) ion hydrolysis species. The species reacts with many chemical additives forming a high polymer that enhances the aggregating power of flocculants 1385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2011.10.008