Automatic control system for energy optimization in membrane bioreactors Giuliana Ferrero a , Hector Monclús b , Gianluigi Buttiglieri a , Joaquim Comas b , Ignasi Rodriguez-Roda a,b, ⁎ a ICRA (Catalan Institute for Water Research), Scientific and Technological Park of the University of Girona, H2O Building, c/ Emili Grahit 101, E17003, Girona, Spain b Laboratory of Chemical and Environmental Engineering (LEQUiA), Environmental Institute, University of Girona, Girona, E17071, Spain abstract article info Article history: Received 10 August 2010 Received in revised form 1 October 2010 Accepted 7 October 2010 Available online 5 November 2010 Keywords: Aeration Automatic control Energy saving Membrane bioreactor The study presented in this paper involves the development and implementation of an innovative ‘performance-based’ control system for aeration optimization in membrane bioreactors. Permeability was appointed as key parameter for directly comparing temporary changes in membrane performance. Transmembrane pressure (TMP) and flux are gathered each 10 s and permeability values are automatically calculated; subsequently different mathematical algorithms are applied for the signal filtering of on-line data. The ‘current’ permeability trend is compared daily to the ‘reference’ permeability trend, and the control action applied is proportional to the ratio of the permeability comparison without exceeding the aeration flow recommended by membranes suppliers. Moreover, aeration is further reduced when permeate flux lower than the average design flux is detected, if the facility is operated under variable fluxes. The validation with different membrane configurations permitted to save up to 21% of the energy used for membranes aeration. © 2010 Elsevier B.V. All rights reserved. 1. Introduction MBR technology has passed from an emergent technology in the late 90s to currently reality all over Europe, where the number of municipal wastewater treatment plants with membranes has been multiplied by 4 from 2002 to 2005 [1] and, generally, in many countries affected by water scarcity problems. Its energy requirements are still higher than the ones required by conventional activated sludge with tertiary disinfection (sand filtration+UV or tertiary filtration with micro- o ultra-filtration) [2]. Since membrane aeration contributes significantly to the energy demand in membrane bioreactors, a large number of commercial solutions have been focusing on aeration reduction whilst maintaining membrane permeability [3]. Through the implementation of automatic control systems, optimal results are achievable regarding both energy optimization and fouling mitigation. Some of the most important publications can be found in the patent literature; however there is still a lack of robust control systems capable to reduce aeration requirements maintaining optimum filtration performances. EIMCO [4] proposed the optimization of MBR operation by automatically regulating cycles length and frequency, and decreasing the air scour requirements through aeration proportional to permeate flux, whereas ZENON [5] developed an on-line process control system that considers resistance values and adjust operational parameters such as membrane aeration frequency and membrane aeration flow in order to reduce operational costs related to fouling removal. Within the framework of the EU-project Amadeus, VITO (Flemish institute for Technological Research) developed the VITO fouling measurement [6,7], an on-line sensor that can be applied in an advanced control system for controlling membrane cleaning actions by measuring the reversible and irreversible fouling. The objective of this study was the development and validation of an innovative control system that determines a desired aeration rate to reduce costs using the information from process instrumentation and off-line data. It adjusts the aeration by measuring the performance of the system over a relatively short period of time and comparing the results with a longer period of time. 2. Materials and methods 2.1. UCT-MBR pilot plant An industrial scale pilot plant MBR with University of Cape Town (UCT) [8] configuration has been operated during nearly 2 years with two different membrane configurations (Table 1). It comprises a pre-screening system, a bioreactor (anaerobic tank, anoxic tank and aerobic tank), followed by a membrane compartment with submerged FS50 Kubota flat-sheet membranes unit during the first period of experimentation and submerged ZENON ZeeWeed 500a during the second period. The raw wastewater was collected after the pre-treatment (pre- screening and grit removal) in Granollers wastewater treatment plant (WWTP), North-East of Spain. One of the two centrifugal pumps Desalination 268 (2011) 276–280 ⁎ Corresponding author. ICRA (Catalan Institute for Water Research), Scientific and Technological Park of the University of Girona, H2O Building, c/ Emili Grahit 101, E17003, Girona, Spain. Tel.: +34 972 18 33 80; fax: +34 972 18 32 48. E-mail addresses: gferrero@icra.cat (G. Ferrero), hector@lequia.udg.cat (H. Monclús), gbuttiglieri@icra.cat (G. Buttiglieri), quim@lequia.udg.cat (J. Comas), irodriguezroda@icra.cat, ignasi@lequia.udg.cat (I. Rodriguez-Roda). 0011-9164/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2010.10.024 Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal