Coagulation of Oil in Water Using Sawdust and Bentonite and the Formation of a Floating Coagulated Material Tianlei Sun 1 and D. D. L. Chung 2 Abstract: The coagulation of oil in water is potentially cost-effective for removing oil from water. A coagulant consisting of sawdust (79.6% by volume), bentonite (15.8% by volume), and calcium hydroxide (4.7% by volume) gives coagulation efficiency of ≥94% and coagulation time of ≤ 45 s. The resulting coagulated material (a semisolid) floats on water. Its oil (liquid) content, which decreases with a decreasing amount of oil originally present in the water, ranges from 69–81% by volume. This paper provides the first identification of multiple forms of oil in a coagulated material that is made from a single form of oil. The oil consists of strongly bonded oil (16% by volume, with relative dielectric constant 32) and weakly bonded oil (84% by volume, with the same relative dielectric constant of 2.0 as the original oil). The maximum and minimum volumes of oil per unit area that can be coagulated by 0.022 cm 3 =cm 2 of coagulant volume per unit area are 0.116 and 0.052 cm 3 =cm 2 , respectively. Below the minimum amount of oil, the coagulated material sinks in water, thus hindering oil removal. DOI: 10.1061/(ASCE)EE.1943-7870.0000725. © 2013 American Society of Civil Engineers. CE Database subject headings: Coagulation; Oil spills; Water pollution; Bentonite. Author keywords: Coagulation; Bentonite; Environmental engineering; Spills; Backwashing (water treatment); Pollution; Fuels; Drilling. Introduction The removal of oil from water is relevant to oil-spill cleanups, water treatment, and water resource management. The coagulation of oil in water is an effective method for removing oil from water (Alther 1999; Badawy and Ali 2006; Canizares et al. 2008; Elosta and Shtewi 2011; Qiu et al. 1995; Tansel and Vilar 2005; Xu et al. 2001). In particular, bentonite is an attractive coagulant, due to its low cost and environmental friendliness (Alther 1999; Badawy and Ali 2006; Elosta and Shtewi 2011; Qiu et al. 1995; Tansel and Vilar 2005; Xu et al. 2001). However, bentonite suffers from its high density, which causes it to sink. It is desirable for the coagu- lated material to float on water so that it can be removed from above the water by methods such as scooping. Moreover, the sinking of the coagulated material is environmentally unfriendly; for example, in the case that the water source is an ocean, it may affect the ecology of the ocean floor. By the combined use of bentonite and sawdust, with sawdust being the vast majority, the coagulated material floats in the form of a semisolid sheet (Fu 2011; Fu and Chung 2011). The sheet has a continuous matrix involving oil, bentonite, and sawdust, and there is apparently no upper limit to the sheet size. Without sawdust, the aggregates (which take the place of the sheet) sink in water and the coagulation efficiency is low. The sawdust functions as a fibrous framework for the attachment of the coagulating oil and bentonite, thus facilitating the formation of a floating sheet, which may be conveniently removed. A number of questions need to be answered regarding the previously mentioned process of coagulation through using the combination of bentonite and sawdust: 1. The main component of the coagulated material is oil, which is also the component with a density less than that of water. What is the minimum amount of available oil required for the coagulated material to float? 2. What is the upper limit for the amount of oil that can be con- tained in the coagulated material? 3. What is the relationship between the amount of available oil and the structure of the coagulated material? 4. How fast does the coagulation occur? 5. What is the difference, if any, between the nature of the as received oil and that of the oil in the coagulated material? 6. Is all of the oil in the coagulated material the same in nature? If not, how do the different forms of oil differ? Prior papers used the method of microscopy to follow the pro- cess of coagulation, particularly in relation to the associated process of coalescence of the oil droplets (Tansel and Dimitric-Clark 2002). However, because of the wetness of the coagulated material and the fact that the coagulated material consists mainly of oil, with the solid component being a minority, it is difficult to observe the structure of the coagulated material by microscopy. Indeed, the mi- croscopic structure of the coagulated material is quite different after drying (Fu and Chung 2011). In contrast, this paper uses dielectric constant measurement to characterize the coagulated material. This method is suitable because • The dielectric constant differs between oil and the coagulant. • The dielectric constant depends not only on the proportions of the components but also on the continuity of the medium in which ionic or partially ionic species can move. • The dielectric constant of a given phase increases when the polarizability of the phase increases and the polarizability relates to the structure of the phase. 1 Graduate Student, Composite Materials Research Laboratory, Univ. at Buffalo, State Univ. of New York, Buffalo, NY 14620. E-mail: tianleis@buffalo.edu 2 Professor, Composite Materials Research Laboratory, Univ. at Buffalo, State Univ. of New York, Buffalo, NY 14260 (corresponding author). E-mail: ddlchung@buffalo.edu Note. This manuscript was submitted on July 23, 2012; approved on April 19, 2013; published online on April 22, 2013. Discussion period open until May 1, 2014; separate discussions must be submitted for individual papers. This paper is part of the Journal of Environmental Engineering, Vol. 139, No. 12, December 1, 2013. © ASCE, ISSN 0733-9372/2013/12- 1470-1481/$25.00. 1470 / JOURNAL OF ENVIRONMENTAL ENGINEERING © ASCE / DECEMBER 2013 J. Environ. Eng. 2013.139:1470-1481. Downloaded from ascelibrary.org by Suny At Buffalo on 05/06/14. Copyright ASCE. For personal use only; all rights reserved.