CORRECTED PROOF Please cite this article in press as: A. Vargas, et al., Controlled backwashing in a membrane sequencing batch reactor used for toxic wastewater treatment, J. Membr. Sci. (2008), doi:10.1016/j.memsci.2008.03.073 ARTICLE IN PRESS G Model MEMSCI 8529 1–6 Journal of Membrane Science xxx (2008) xxx–xxx 1 Contents lists available at ScienceDirect Journal of Membrane Science journal homepage: www.elsevier.com/locate/memsci Controlled backwashing in a membrane sequencing batch reactor used for toxic wastewater treatment 1 2 Alejandro Vargas ∗ , Iv ´ an Moreno-Andrade, Germ ´ an Buitr ´ on 3 Laboratory for Research on Advanced Processes for Water Treatment, Instituto de Ingenier´ ıa, Unidad Acad´ emica Juriquilla, Universidad Nacional Aut´ onoma de M´ exico, Blvd. Juriquilla 3001, Quer´ etaro 76230, Mexico 4 5 6 article info 7 8 Article history: 9 Received 6 February 2008 10 Received in revised form 26 March 2008 11 Accepted 29 March 2008 12 Available online xxx 13 14 Keywords: 15 Sequencing batch reactor 16 Submerged membrane 17 Microfiltration 18 Fouling 19 Backwashing control 20 abstract A new control algorithm for performing filtration in a membrane sequencing batch reactor (MSBR) to prevent fouling is presented. Based on continuous measurements of the transmembrane pressure (TMP) and the permeate flux, the algorithm decides when to initiate backwashing. The algorithm was tested on a laboratory scale bioreactor treating synthetic wastewater containing 4-chlorophenol (4CP) as model toxic compound and filtration was carried out using a submerged tubular membrane module and a diaphragm pump. Several controller configurations were tested for different MSBR cycles. The results showed that the proposed algorithm was robust against the highly varying mixed liquor characteristics and was able to keep the TMP below critical values and maintain the flux at a maximum for most of the filtration time. Therefore, despite possible frequent backwashes, the total filtration time was minimized. © 2008 Elsevier B.V. All rights reserved. 1. Introduction 21 Membrane technologies have gradually become more preva- 22 lent in wastewater treatment processes due to the high quality of 23 the effluent obtained, the smaller footprint of the treatment plant, 24 and the decreasing costs associated with its implementation. Most 25 membrane bioreactors (MBR) for wastewater treatment eliminate 26 the sedimentation tank and use a submerged membrane module 27 in some part of the reaction basin. The process is therefore still 28 continuous and may suffer from some of its drawbacks, such as a 29 limited flow capacity or a low resistance to toxic wastewaters or 30 high concentration peaks [1]. In contrast, sequencing batch reactor 31 technology (SBR) is more versatile. All phases occur in one tank, 32 namely fill, react, settle, draw, and idle, and the conditions can 33 be readily modified for improved process control [2]. Furthermore, 34 SBR technology is quite appropriate for industrial or semi-industrial 35 applications, due to its higher capacity to support changes in the 36 flows and concentrations of toxic compounds. The technology has 37 demonstrated high efficiency in the removal of organic matter and 38 nutrients if properly designed [3]. There exists recent interest to 39 combine both technologies in what has been called a membrane 40 sequencing batch reactor (MSBR) [4]. 41 ∗ Corresponding author. Tel.: +52 55 56234266; fax: +52 55 56234285. E-mail address: avargasc@ii.unam.mx (A. Vargas). In a MSBR the sedimentation and decantation phases of a typi- 42 cal SBR cycle are replaced by membrane filtration, while the fill and 43 reaction phases are usually kept unmodified. Furthermore, clear 44 water can also be extracted during the reaction phase [5]. The 45 separation of biological sludge from the permeate using the sub- 46 merged membrane allows a higher mixed liquor suspended solids 47 (MLSS) concentration, so that a very high treatment capacity can be 48 achieved. In addition, prolonged relaxation periods for membrane 49 filtration occur naturally and may help mitigate fouling. Further- 50 more, a bottleneck of the SBR process is the problem of clarification; 51 the use of a membrane therefore increases the robustness of the 52 process when poor settleability conditions exist. 53 A common problem in membrane bioreactors is fouling. It is 54 caused by the deposition of soluble and particulate materials, not 55 only on the membrane surface, but also inside its pores. There has 56 been extensive research both on the membrane fouling mecha- 57 nisms – including its mathematical modelling – and on strategies 58 to reduce this phenomenon and thus extend the membrane oper- 59 ation before chemical cleaning is needed [6]. Membrane fouling 60 seems to depend on several factors, including the operating condi- 61 tions, the sludge characteristics, the substrates treated, the type of 62 membrane, etc. [6]. 63 In order to prevent or mitigate fouling, several actions can be 64 taken, from the use of new materials for the membrane itself, 65 to some optimization of the operating conditions [6]. Other pos- 66 sibilities include encouraging floc formation or the addition of 67 adsorbents such as granular activated carbon [7]. In submerged 68 0376-7388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2008.03.073