Membrane oscillation and oil drop rejection during produced water purification A. Ullah a,b,⇑ , M. Habib b , S.W. Khan c , M.I. Ahmad b , V.M. Starov a a Department of Chemical Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK b Department of Chemical Engineering, University of Engineering & Technology Peshawar, Pakistan c Department of Civil Engineering, University of Engineering & Technology Peshawar, Pakistan article info Article history: Received 23 September 2014 Received in revised form 29 December 2014 Accepted 17 February 2015 Available online 23 February 2015 Keywords: Produced water Membrane oscillations Particle rejection Slotted pore membranes Deforming oil drops Microfiltration abstract Removal of crude oil droplets from produced water has been evaluated using a Nickel membrane with a slotted pore width of 4 lm and length of 400 lm. The membrane was oscillated at different frequencies that resulted in variable intensity shears at the membrane surface. The influence of membrane oscilla- tions on oil droplet rejection was investigated and reported in this work. Membrane oscillations gener- ated a lift for the surrounding particles which led the drops to move away from the membrane surface. Measurements have shown that the intensity of the droplet lift was linearly proportional to the intensity of the applied shear. Inertial lift velocity model reported in literature was used as a starting point which was coupled with the fluid’s convection velocity. The model predicted 100% cut-off points through the membrane at various oscillation frequencies. Without the applied shear rate, the static and drag forces balanced each other, which was assumed to be the 100% cut-off point. With the applied shear rate, the inertial lift and convection velocities become equal and this point was referred to as 100% cut-off point. Overall mass of crude oil droplets in permeate flow was calculated knowing the 100% cut-off point and interfacial tension between the dispersed and continuous phases. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction The occurrence of oil droplets in water is a severe environmen- tal problem posing significant threats to life within waters. The existence of oil in water is however attributed to various essential human activities such as the drilling and extraction of mineral oil and gas, food processing, and pharmaceutical manufacturing. Among all the activities the oil and gas industry is the biggest source of generating oil in water. Water coming from oil and gas platform contains oil droplets along with other chemicals, salts and metals. This oil contaminated water is commonly referred to as ‘produced water’ [1]. There are various disposal methods for this produced water, the common one being its discharge into the sea water or re-injection into the well for enhanced crude oil/gas pro- duction/recovery [2]. The reported maximum concentration of crude oil in produced water that is used for injecting into the oil wells and/or discharging into the sea is reported to be 10, and 30 ppm respectively [3]. Various physical, chemical, biological and membrane based techniques are currently available and are used for produced water treatment to remove the oil from water. However the high operational costs, usage of toxic chemicals, pro- duction of activated sludge has resulted in significant disadvan- tages for the use of chemical and biological treatment techniques due to their environmental un-friendliness and partially due to the requirement of comparatively big space for installation [2]. Physical separation techniques such as gravity separation and hydro-cyclones were found to be ineffective with oil drop sizes below 40 lm [2]. The use of membrane technology could be poten- tial benefit in comparison with other conventional techniques to remove oil droplets from the produced water mainly due to the fol- lowing distinct advantages [1]: a. Low space requirement for equipment installation. b. Physical separation thus requiring no chemical additives. c. Environment friendliness. d. Low input energy. e. High permeate quality. Various types of membranes are being investigated to remove the oil droplets from produced water. Studies on the use of ultra- filtration membranes were successful in the removal of oil from water however, the permeate flux was too low (100 lm 2 h 1 ), http://dx.doi.org/10.1016/j.seppur.2015.02.022 1383-5866/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Department of Chemical Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK. E-mail addresses: A.Ullah@lboro.ac.uk, asmatuet@gmail.com (A. Ullah). Separation and Purification Technology 144 (2015) 16–22 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur