Microfiltration of algae: Impact of algal species, backwashing mode and duration of filtration cycle Mayank Shekhar, Amritanshu Shriwastav ⁎ ,1 , Purnendu Bose, Shemeera Hameed Environmental Engineering and Management Program, Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016, India abstract article info Article history: Received 13 September 2016 Received in revised form 28 January 2017 Accepted 31 January 2017 Available online xxxx The objective of this study was to investigate and compare the microfiltration characteristics of mixed algal cul- tures containing two species of green microalgae: Chlorella vulgaris and Chlamydomonas reinhardtii. Submerged membrane filtration experiments with 300 mg L -1 suspensions of pure algal cultures indicated that while mem- brane fouling potential was comparable in both cases, Chlorella vulgaris had a lower cake formation potential. Fil- tration experiments were carried out with 1000 mg L -1 suspensions of mixed algal culture over several 12-h cycles with backwashing, either in the on-line or off-line mode. While on-line backwashing caused more fouling, this did not significantly affect the flux through the membrane, which was controlled by the cake formation on the membrane. The algal mixed culture was also filtered over many 3-h cycles with on-line backwashing. Lower cycle duration resulted in lower average cake resistance and hence allowed more membrane throughput, but at the cost of more frequent backwashing. Chemical washing of the membrane could remove the fouling re- sistance only partially. Thus, despite periodic chemical washing, the intrinsic membrane resistance increased consistently with cumulative throughput through the membrane. © 2017 Elsevier B.V. All rights reserved. Keywords: Microalgae Submerged membrane Fouling potential Cake formation Backwashing Chlorella vulgaris Chlamydomonas reinhardtii 1. Introduction The algal based technologies have garnered increasing attention in past decade or so because of their dual applications in wastewater treat- ment and biofuel production [1–3]. However, the simultaneous achieve- ment of these objectives is critically dependent on the efficiency of algal harvesting and dewatering [4]. This is often a complex proposition be- cause of the very nature of algal cells, viz. small cell size, low density and concentrations in growth medium [5]. Due to these inherent chal- lenges with microalgal cultures, conventional processes for harvesting, such as centrifugation and flocculation, are highly energy intensive, and often control the economics of biofuel production and other down- stream utility for valuable compounds, viz., proteins, pigments, etc. [4]. The recent investigations into algal biorefinery are predominantly fo- cused on maximizing the product output from harvested algal biomass in order to achieve sustainability and offset the higher harvesting and dewatering costs [6–8]. Recent efforts on membrane microfiltration of algal cultures have demonstrated this to be a feasible alternative due to relatively low ener- gy inputs and simplicity, while achieving nearly 100% biomass recovery [9,10]. The role of membrane technology for harvesting the algal bio- mass has also been investigated by various researchers in algal biorefineries [11]. These also allow for recirculating of permeates with- out any chemical build-up [5]. Gerardo et al. reduced the energy re- quirements and associated cost of membrane microfiltration of Scenedesmus sp. from 2.23 kWh m -3 and $0.282 kg -1 of harvested microalgae to 0.90 kWh m -3 and $0.058 kg -1 of microalgae harvested by optimizing the process itself [9]. Similar process optimization for Chlorella minutissima reduced the energy consumption to 1.27 kW kg -1 biomass from initial 2.86 kW kg -1 biomass [12]. Also, Chu et al. demonstrated long term applicability of dynamic membrane for Chlorella pyrenoidosa [13]. Similar investigations have been carried on applicability of membrane microfiltration with other microalgal spe- cies, viz. Chlorella vulgaris [14], Chlorella sorokiniana [15], Scenedesmus sp. [16], Nannochloropsis oculata [17]. The roles of different process parameters, such as critical flux, trans- membrane pressure, membrane characteristics, mode of operation, etc., have also been investigated by various researchers [4]. Recently, Marbelia et al. investigated the role of membrane porosity and surface charge on the membrane fouling by many algal species [18]. Their re- sults show increase in fouling with increasing porosity. Also, negatively charged membranes showed reduced fouling for many algae and was found to be dependent on exopolymer particles [18]. The effect of tem- perature on membrane fouling was investigated by Chu et al. who re- ported higher critical flux with higher operating temperature [19]. The lowering in water viscosity was partly suggested to be the reason for Algal Research 23 (2017) 104–112 ⁎ Corresponding author. E-mail address: amritan@iitb.ac.in (A. Shriwastav). 1 Present address: Centre for Environmental Science and Engineering, Indian Institute of Technology Bombay, Mumbai - 400 076, India. Tel.: +91-22-2576-7858; fax: +91-22- 2576-4650 http://dx.doi.org/10.1016/j.algal.2017.01.013 2211-9264/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Algal Research journal homepage: www.elsevier.com/locate/algal