Removal of Oil and Cr(VI) from Wastewater Using Modified Pectin Flocculants Kun Yang, S.M.ASCE 1 ; Yujing Li 2 ; and Yucheng Chen 3 Abstract: This study examined the effects of pH, dosage, and stirring time on the removal of oil and Cr(VI) from simulated wastewater by pectin obtained from citrus byproducts. After pectin modification by etherification and polyaluminum chloride (PAC) impregnation, the extract removed highly concentrated oil and Cr(VI) from wastewater. Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction were used to characterize the flocculants and confirm modification of the pectin. An orthogonal factorial experiment with factors of stirring time, dosage, and pH was used to optimize the conditions for contaminant removal by the modified pectin. The average removal rates were 79 and 77% for oil and Cr(VI), respectively. A central composite design with factors of PAC, zinc sulfate (ZnSO 4 ), pH, and microwave irradiation time showed that PAC and ZnSO 4 intensified the flocculation effect. The actual optimum removal rates for oil and Cr(VI) were 95.0 and 98.4%, respectively. Binomial regression adequately predicted the experimental results. DOI: 10.1061/(ASCE)EE .1943-7870.0000793. © 2013 American Society of Civil Engineers. Author keywords: Modification; Oil; Cr(VI); Flocculation. Introduction The treatment of municipal effluents has become a global problem, attributable in part to high concentrations of oils and toxic heavy metals. Approximately 5.0–50.0 million tons of oil are discharged into sewage systems from various sources each year (Rios et al. 1998). Research has indicated that the oil concentrations in munici- pal wastewaters could approach more than 1,000 mg=L. Detergent use complicates water treatment by emulsifying the oils. Oils and animal fats contain multiple unsaturated and saturated fatty acid glycerides, and impart high chemical (COD) and biological oxygen demands (BOD). Such wastewater, if used for irrigation, would severely damage crop production. Furthermore, wastewater oil con- centrations higher than 50 mg=L can strongly impact the growth of active sludge and biofilms and decrease treatment efficiency. Heavy metal contamination is also a major problem in waste discharge. The leather tanning and dye industries discharge in- effectively treated effluents that contain high concentrations of chromium, including Cr 2 O 2− 7 , which results from the use of potas- sium dichromate (K 2 Cr 2 O 7 ). For example, in the production of one ton of leather, a factory may discharge 50–60 tons of wastewater with a Cr(VI) concentration of 410 mg=L(Gong et al. 2010). Of chromium’ s two most common oxidation states, Cr(VI) is more harmful to humans than Cr(III), and is known to cause liver and respiratory failure. The Cr(VI) in drinking water is also becom- ing a significant carcinogen. Moreover, other heavy metal salts in aqueous phases, for example, MnO − 4 , tend to oxidize Cr(III) to Cr(VI), which may be discharged into municipal systems in anionic form (Rollinson 1973). Finally, the local temperature, pH, and presence of organic materials can affect the migration and transfer of Cr(VI), making it difficult to remove (Rollinson 1973). Various approaches to wastewater treatment have been devel- oped, including coagulation, biochemical processing, electrodialysis, adsorption, chemical oxidation, and ion exchange methodologies (Gao and Xu 2012). Among these, coagulation and flocculation are processes that are widely used in feedwater and wastewater treatments. Upon adding flocculants to wastewater, small colloids aggregate into large flocs, and can be removed by forming con- densed filter cakes (Gao and Xu 2012). This process can reduce the BOD by 90%, and remove more than 40% of the heavy metals and a portion of the phosphorus in waste streams. However, the behavior of flocculants is very sensitive to the flocculation reaction conditions. For example, Vik et al. (1984) suggested that the de- stabilization regimes of alum coagulation in humic solution did not correspond to previous findings. Thus, it is impossible to apply a general method to determine the appropriate dose for all waters, because floc formation is largely dependent on physicochemical conditions, including pH, dosage, and stirring time. Any fluctua- tions in these factors would lead to different experimental results (Wang et al. 2002). Therefore, preliminary studies are an important operation prior to the industrial use of flocculants. Considering the important role flocculants can play in waste re- moval, researchers have developed numerous kinds of flocculating agents. Traditional flocculants include inorganic flocculants (ferric and aluminum salts) and manufactured organic high-polymer floc- culants such as polyacrylamide (PAM) and sodium polyacrylate (PAAS). Recently, the use of traditional flocculants has been ques- tioned because of their low efficiency, high cost, and their harmful intermediate degradation products. For example, the inappropriate use of the inorganic flocculant polyaluminum chloride (PAC) was associated with neurological illnesses, specifically Alzheimer’ s disease (Huang et al. 2012). Therefore, developing novel organic- inorganic hybrid flocculants that exhibit improved safety, high 1 Research Assistant, Chongqing Key Lab of Agricultural Resources and Environment, College of Resources and Environment, Southwest Univ., Chongqing 400715, China (corresponding author). E-mail: kunyan68@ hotmail.com 2 Research Assistant, Chongqing Key Lab of Agricultural Resources and Environment, College of Resources and Environment, Southwest Univ., Chongqing 400715, China. E-mail: mentee@yeah.net 3 Professor, Chongqing Key Lab of Agricultural Resources and Envir- onment, College of Resources and Environment, Southwest Univ., Chongqing 400715, China. E-mail: chenyucheng@swu.edu.cn Note. This manuscript was submitted on May 17, 2013; approved on October 3, 2013; published online on October 5, 2013. Discussion period open until April 8, 2014; separate discussions must be submitted for individual papers. This paper is part of the Journal of Environmental Engineering, © ASCE, ISSN 0733-9372/04013004(10)/$25.00. © ASCE 04013004-1 J. Environ. Eng. J. Environ. Eng. 2014.140. Downloaded from ascelibrary.org by LEHIGH UNIVERSITY on 02/22/14. Copyright ASCE. For personal use only; all rights reserved.