Desalination and Power Generation of Caspian Sea by Applying New Designed Microbial Desalination Cells in Batch Operation Mode Laleh R. Kalankesh , a Susana Rodríguez-Couto, b,c,d and Mohammad Ali Zazouli e a Department of Environmental Health Engineering, Faculty of Health and Health Sciences Research Center, Student Research Committee, Mazandaran University of Medical Sciences, Sari, Iran b Universidad de Navarra, San Sebastian, Spain c TECNUN, San Sebastian, Spain d IKERBASQUE, Basque Foundation for Science, Bilbao, Spain e Department of Environmental Health Engineering, Health Sciences Research Center, Faculty of Health, Mazandaran University of Medical Sciences, Sari, Iran; mzazouli@mazums.ac.ir (for correspondence) Published online 00 Month 2019 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ep.13205 The Caspian Sea is one of the largest water sources located in the north of Iran; so this research was carried out to investigate the new design of microbial desalination cell (MDC) (double layer) efﬁciency in water desalination and power generation of the enormous saline water source in the north of Iran. Actual (i.e., Caspian Sea) and artiﬁcial seawater with different initial salt concentrations (5, 25, and 35 g/L NaCl) and, different hydraulic retention times (24, 48, and 72 h) in batch and open circuit voltage (OCV) mode were examined. In addition, the oxi- dation and reduction processes during desalination of each stage were monitored at 10 min intervals for 60 min. According to the obtained experimental data, both the desalination efﬁ- ciency and the power generation decreased from 65  1% to 41  1% and 80  4.5 mW/cm2 to 51.20  2.5 mW/cm2 by increasing the retention time from 24 to 72 h for Caspian Sea water and 5 g/L NaCl, respectively. Maximum and minimum desalination efﬁciencies were 48  1% and 65  1% for Cas- pian Sea water and 5 g/L NaCl, respectively. Moreover, the maxi- mum power densities were 72.83  3.36 mW/cm2 and 80.00  4.00 mW/cm2 for 35 g/L NaCl and seawater, respec- tively. As far as the authors know, this is the ﬁrst study on the application of the new designed stacked MDC for power genera- tion and desalination of water from the Caspian Sea. © 2019 American Institute of Chemical Engineers Environ Prog, 2019 Keywords: Caspian Sea, desalination, power generation, saline water INTRODUCTION Water scarcity is one of the serious global issues [1]. Although water is an abundant natural resource, today, millions of people worldwide do not have access to fresh water [2]. Sea (with 35 g/L salinity) is one of the most important parts of the global water resources. Geological studies show that most regions facing water scarcity have huge saline water resources. Therefore, an adequate management of such water resources can provide most of the demand of fresh water [3]. The desalination technologies currently used include thermal and membrane methods. How- ever, such methods are under question due to their high energy consumption and environmental impact [4], emitting green- house gases and, thus, contributing to the climate change. Hence, cost efﬁciency desalination technology is needed. In recent decades, research based on the use of microbial desali- nation cells (MDCs) as a suitable alternative for water desalina- tion has increased dramatically [5]. A microbial desalination cell (MDC) is a novel technology developed for wastewater treat- ment, desalination of saline water, and bio-electricity production simultaneously [6]. So far, most studies conducted on MDCs investigated the effect of the number of the MDC chambers on water desalination [7–9] while few studies considered the effect of multiple pairs of ion exchange membranes (IEMs) without distance between them and with no additional chamber. Research showed that in using stacked MDCs, the internal resis- tance and the simultaneous desalination rate increased [8–10]. However, the effect of the space between the anion exchange membrane (AEM) and the cation exchange membrane (CEM) on the desalination and power generation is not deniable as well as the desalination efﬁciency on the middle chamber and the chemical production on the cathode and anode chamber [4]. Moreover, MDCs’ operation mode affects the desalination and bioelectricity generation efﬁciency [11]. Literature has reported three different operating modes of MDC (batch, cyclic batch, and continuous) each of them performing a different efﬁ- ciency. Thus, operating in cyclic mode showed better perfor- mance than operating in batch mode due to maximum power density generation while, in continuous circulation pH ﬂuctua- tions are removed through homogeneous distribution of the substrate, thereby increasing the desalination efﬁciency and the produced power density simultaneously [12] but it is energy consumer mode. Thus, several studies carried out in recent years which have using Stacked Microbial Desalination Cell (SMDC) and MDCs and have achieved >90% of salt removal efﬁciency operating in continuous mode at different initial salt concentrations [6,9,10,12]. In addition, some studies investigated © 2019 American Institute of Chemical Engineers Environmental Progress & Sustainable Energy DOI 10.1002/ep 1