Journal of Water Process Engineering 10 (2016) 188–199 Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe Recovery of cooling tower blowdown water for reuse: The investigation of different types of pretreatment prior nanoﬁltration and reverse osmosis Mohammad Hossein Davood Abadi Farahani a , Seyed Mehdi Borghei a,∗ , Vahid Vatanpour b a Department of Chemical and Petroleum Engineering, Sharif University of Technology, PO Box 11155-9465, Azadi Ave, Tehran, Iran b Faculty of Chemistry, Kharazmi University, Tehran, Iran a r t i c l e i n f o Article history: Received 10 November 2015 Received in revised form 18 January 2016 Accepted 19 January 2016 Keywords: Water reuse Cooling tower blowdown Nanoﬁltration Reverse osmosis Coagulation a b s t r a c t The suitability of two different pretreatment methods, i.e., coagulation-ﬁltration and ultraﬁltration (UF), and two ﬁnal membrane treatment technologies, namely nanoﬁltration (NF) and reverse osmosis (RO), for desalination of a cooling tower blowdown (CTBD) was investigated. Particular attention was paid to ensuring that the best pretreatment method could enhance the permeate ﬂux and lifespan of the NF and RO membranes and decrease the membranes’ fouling characteristics. Furthermore, the difference of NF and RO performances in CTBD treatment was investigated. In order to ﬁnd the most appropriate type of coagulant, coagulant dosage, pH and co-coagulant dosage, 21 jar tests were performed. The results showed that 50 mg/L of Polyaluminium chloride (PACl) in the presence of 0.5 ppm co-coagulant in pH of 6.5–7.5 has the best treatment performance. Silt density index (SDI), chemical oxygen demand (COD), turbidity, electrical conductivity, and membrane permeate ﬂux tests were performed for both pretreatment and treatment stages. Both pretreatment methods produced appropriate feed for NF and RO in terms of SDI and turbidity. Using the coagulation–ﬁltration pretreated water instead of raw water as a feed for NF and RO membranes showed about a 25 and 33 percent improvement in permeate ﬂux after 100 min in 10 and 15 bar applied pressure for NF and RO, respectively. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Petrochemicals, reﬁneries and power plants are among the biggest water-consuming industries. Cooling tower systems con- sume the most water of all systems such that the feed water of cooling towers accounts for the largest portion of water demand. Since a signiﬁcant amount of water is lost due to evaporation, wind action, leakage, and drainage, a large amount of make-up water is needed to maintain the water balance and keep cooling water Abbreviations: P, operation pressure (MPa); t, permeation time (h); A, mem- brane effective area (m 2 ); Alum, aluminum sulfate; BOD, biological oxygen demand; COD, chemical oxygen demand; CTBD, cooling tower blowdown; DOC, dissolved organic carbon; EC, electrical conductivity; FeCl3, ferric chloride; GAC, granulated activated carbon; J, permeate water ﬂux (kg/m 2 h); M, mass of permeated water (kg); MF, microﬁltration; NF, nanoﬁltration; PAC, powdered activated carbon; PACl, polyaluminum chloride; RO, reverse osmosis; SDI, silt density index; SiO2, silicon dioxide; TDS, total dissolved solids; UF, ultraﬁltration. ∗ Corresponding author. E-mail addresses: mborghei@sharif.edu, mborghei2@yahoo.com (S.M. Borghei). operation at a steady state. The amount of lost make-up water is relative to climate conditions and the conﬁguration of cooling sys- tem equipment. In this regard, drainage loss (blowdown), which constitutes the biggest portion of feed water loss, varies greatly with changes in source water quality and cooling water treatment [32]. For a long time, cooling tower blowdown was discharged directly to surface water bodies and was not reused as treated make-up water in many countries. Environmental contamination and an increase in wastewater were two of the dire consequences of blowdown water discharging [32]. Scarcity of water, large quan- tities of cooling tower blowdown water, and an increase in water prices have been the primary motivations driving recent studies and researches on blowdown water treatment and reuse [32,27,30]. Also, new multiple technologies for water conservation, in par- ticular high-concentration circulation water treatment technology, have been progressively used in circulating cooling water systems to utilize water more efﬁciently, [31,33,23,17,11]. Both scale and corrosion inhibitors are the main pollutants of the blowdown water of cooling systems. Blowdown water is a suitable resource to use as http://dx.doi.org/10.1016/j.jwpe.2016.01.011 2214-7144/© 2016 Elsevier Ltd. All rights reserved.