Carbon attrition during continuous electrolysis in carbon bed based three-phase three-dimensional electrode reactor: Treatment of recalcitrant chemical industry wastewater Nitin Gedam, Nageswara Rao Neti * Wastewater Technology Division, CSIR-National Environmental Engineering Research Institute (CSIR-NEERI), Nagpur, Maharashtra 440020, India A R T I C L E I N F O Article history: Received 23 May 2014 Accepted 28 June 2014 Keywords: Three-phase three-dimensional electrode Granular activated carbon Carbon attrition Chemical oxygen demand Recalcitrant wastewater treatment A B S T R A C T The performance of a carbon bed based three-dimensional electrode reactor (TDR) in terms of chemical oxygen demand (COD) removal from recalcitrant chemical industry wastewater was assessed. The pH and temperature changes in the TDR during electrolysis were correlated with COD removal efficiency. The carbon weight loss and particle size reduction due to erosion of carbon particles during electrolysis was also examined. Two cases of experiments were performed; ‘case I’ employed a high surface area Indcarb- 60 GAC, whereas a low surface area carbon (GAC-10) was used for ‘case II’. The other experimental variables are, initial COD concentration, hydraulic retention time (HRT) and the duration of electrolysis. The experimental results showed that TDR could remove COD efficiently (49  7%). The apparent Faradic efficiency and specific electrical energy consumption were estimated to be 3.42% and 6.59 kW h kg 1 COD for case I and 0.78% and 28.65 kW h kg 1 COD for case II. Use of high surface area carbon in TDR is inferred to be beneficial. However, the GAC particles in TDR were found to undergo slow attrition during electrolysis. It is inferred that carbon attrition may prove to be a major setback for scale up attempts as it can lead to gradual loss in liquid holding capacity of carbon bed due to stratification and filling of voids in the carbon bed with carbon fine dust. ã 2014 Elsevier Ltd. All rights reserved. 1. Introduction High strength chemical industry wastewater requires high degree of treatment before being discharged into the water bodies. The conventional treatment incorporating chemical and biological treatments alone is not adequate. More recently, advanced oxidation processes such as electrochemical oxidation (EO) treatment are being increasingly viewed as capable of providing necessary treatment [1–4]. A variety of design options for setting up an electro oxidation reactor are available, viz., cell configuration (divided and undivided), electrode configuration (two-dimension- al and three-dimensional) and flow-types (plug flow and continuously stirred tank type) [5]. Our group has been working towards the development of three-phase three-dimensional carbon bed electrochemical reactor (TDR) with the aim of treating recalcitrant effluents from chemical industries [6–10]. Thus, leachate from a toxic solid waste disposal facility could be treated effectively i.e., 60–64% COD removal with >80% mineralization efficiency using TDR in 6 h [7]. On the other hand, caprolactam wastewater underwent poorer degradation in TDR with only 18% COD removal in 7 h [8]. While the above research clearly demonstrates that electro oxidation of recalcitrant effluents in TDR is feasible, there is need for optimizing the operational parameters (pH, flow rate etc.). Moreover, the electrochemical degradation of wastewater using such TDR in continuous mode is not comprehensively investigated, particularly with reference to stability of carbon surface on long term use. In this study, continuous electrolysis of chemical industry wastewater in the TDR was investigated. The performance of the reactor for consistent removal of pollutant (COD) was aimed at, while the other related issues viz., stability of carbon particles, changes in pH, and temperature were also investigated. 2. Material and methods 2.1. Effluent The segregated high strength chemical industries wastewater used in this study was obtained from a common effluent treatment plant (CETP) site in Gujarat (India). The dark brown effluent with pH 8.1 contained high COD in the range 5–10 g L 1 , 1.1–2.4 g L 1 * Corresponding author. Tel.: +91 712 2249885 88/2249970 72; fax: +91 712 2249900. E-mail addresses: nn_rao@neeri.res.in, nnrao.neeri@gmail.com (N.R. Neti). http://dx.doi.org/10.1016/j.jece.2014.06.025 2213-3437/ ã 2014 Elsevier Ltd. All rights reserved. Journal of Environmental Chemical Engineering 2 (2014) 1527–1532 Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering journal homepage: www.else vie r.com/locat e/jece