Geotextile dewatering of flocculated, fiber reinforced fly-ash slurry B.W. Maurer a,⇑ , A.C. Gustafson a , S.K. Bhatia a , A.M. Palomino b a Department of Civil and Environmental Engineering, Syracuse University, Syracuse, NY 13244, USA b Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, TN 37996, USA article info Article history: Received 18 August 2011 Received in revised form 4 February 2012 Accepted 6 February 2012 Available online 19 February 2012 Keywords: Fly ash Geotextile tube dewatering Filter cake Polymer flocculants Fibers abstract Coal-based thermal power plants are a principal source of power generation in many industrialized coun- tries. Consequently, fly ash and other coal combustion residuals are produced in significant quantities and must be appropriately managed, most commonly using wet-storage impoundments. Concurrent with diminishing impoundment capacity and increasing beneficial reuse of coal residuals worldwide, legisla- tion is proposed in the US to close or liner retrofit all existing impoundments. Each of these progressions necessitates an increase in the dredging, dewatering, and transport of wet-disposal ash sludge. In recent years, geotextile tubes have increasingly been used to efficiently and economically dewater a number of low percent-solids sediments, by-products, and wastes. A laboratory investigation was conducted for studying the efficacy of geotextile tubes for dewatering hydraulically transported fly ash slurry. The dewatering behavior of unmodified fly ash was compared with that of specimens reinforced with ran- domly dispersed flexible PVA fibers and/or flocculated with optimized polyacrylamide. Results indicate that geotextile tubes can be effectively used for dewatering flocculated fly ash slurries and that the strength of retained fly ash can be significantly improved by adding reinforcement fibers at 1% of dry sol- ids mass. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Coal-based thermal power plants (TPP) are a principal source of power generation in many industrialized countries. In 2009, coal- fired production accounted for approximately 48% of all electricity generated in the United States [1]. In the US alone, more than 134 million tons of coal combustion residuals (CCRs) were generated in 2009, including approximately 63 million tons of fly ash [2]; simi- lar magnitudes of fly ash production have been estimated else- where, including China, Europe, India and Russia [3]. The fly ash generated by a TPP is managed in one of two fundamental ways: (1) fly ash is removed in dry-form for beneficial reuse or disposal in on-site or off-site landfills or (2) fly ash is mixed with 70–80% water, transported in slurry form, and discharged into large surface impoundments. This second method, termed wet-disposal, has his- torically been the most common and inexpensive management practice worldwide [4–6]. In the US, there are an estimated 1600 coal waste impoundments currently in operation and an additional 670 impoundments which are inactive or abandoned but still con- tain coal ash slurry [7]. Ash impoundments are typically con- structed near the power plant either by constructing a concrete or earthen embankment enclosure or by damming the open end of a natural valley. Given the large volume of ash produced, such impoundments require considerable land area for storage. The ever-increasing need for wet-disposal storage capacity and con- cerns over fly ash leachate [8], groundwater contamination [9], and impoundment failures [10] present environmental and logisti- cal difficulties. As a result, the management, handling, and re-use of fly ash are a growing challenge and of great interest to coal- based energy industries worldwide. Due in large part to the well-publicized failure of an impound- ment at the TVA’s Kingston, TN plant in 2008 and the resulting ash slurry spill into the Clinch River, the US. Environmental Protection Agency (EPA) proposed new legislation regulating coal ash man- agement. The legislation could principally either force closure of all wet-disposal surface impoundments or require liners for both existing and new impoundments and provide minimum safety cri- teria. Thus, for the latter option, surface impoundments could re- main in operation if they are currently lined or if the owners choose to liner-retrofit. While the future of coal ash regulation in the US is uncertain, management of wet-disposal fly ash is under rigorous observation, and it is apparent that future regulatory and/or voluntary safety measures are forthcoming. For either reg- ulatory action, some impoundment owners would be faced with dredging and handling significant volumes of wet-disposal ash slurry. In addition to the potential needs brought on by regulatory action in the US, ash pond owners commonly employ cyclic dredg- ing to restore impoundment capacity, to perform maintenance, and to remove ash for beneficial re-use [11]. In developing countries such as India, beneficial re-use rates are very low [9] relative to 0016-2361/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2012.02.013 ⇑ Corresponding author. Tel.: +1 315 521 1054; fax: +1 315 443 1243. E-mail address: bwmaurer@syr.edu (B.W. Maurer). Fuel 97 (2012) 411–417 Contents lists available at SciVerse ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel