Small-angle neutron scattering studies of alginate as biomineralizing agent and scale initiator Y.N. Dahdal a , V. Pipich b , H. Rapaport c , Y. Oren a , R. Kasher a , D. Schwahn d, * a Zuckerberg Institute for Water Research, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus, 84990, Israel b Jülich Centre for Neutron Science JCNS-FRM II, Outstation at FRM II, D85747 Garching, Lichtenbergstrasse 1, Germany c Department of Biotechnology Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel d Technische Universit€ at München, Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II), D-85748 Garching, Germany article info Article history: Received 27 November 2015 Received in revised form 2 January 2016 Accepted 4 January 2016 Available online 11 January 2016 Keywords: Alginate RO-Desalination Membrane fouling and scaling Small-angle neutron scattering abstract Alginate is an important part of the extracellular polymeric substances excreted by microorganisms giving rise to biofouling on reverse osmosis membranes in desalination plants for water treatment. We present a small-angle neutron scattering study on aggregation of alginate when exposed to an aqueous salt solution simulating the reverse osmosis concentrate of a wastewater reclamation plant. We explored the behavior of alginate as dissolved molecule and as grafted to the surface of gold nanoparticles thereby simulating the condition of alginate attached at the surface of a membrane. The behavior of dissolved and grafted alginate was different when exposed to the simulation solution. The dissolved alginate ag- gregates to a gel like structure whereas the grafted alginate induces formation of 0.2 mm large particles. These particles form stable composites within few seconds with volume fraction of about half mineral and half gold nano-particles. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Reverse osmosis (RO) technology of producing potable water from pretreated wastewater and seawater has to overcome the severe problem of membrane biofouling and scaling. In the course of operation the permeability of membranes declines thereby limiting the economic feasibility of the process. Unlike seawater, scaling of calcium phosphate during wastewater effluent desali- nation is a particular problem as no effective antiscalant is pres- ently available. Quite generally RO desalination permits gaining potable water with yields of about 80% and 50% from wastewater and seawater, respectively [1,2]. The feed for RO treatment contains salt molecules as well as biomolecules excreted from microorgan- isms as extracellular polymeric substances (EPS). These extracel- lular polymeric substances are proteins and polysaccharides forming a biofilm at the surface of the membrane, which induces the inorganic salts to formation of minerals such as calcium phos- phate and calcium carbonate. This type of fouling is considered the “Achilles heel” of the membrane process because microorganisms multiply and produce the EPS over time [3]. We systematically studied the interaction of EPS organic and salt molecules in a simulated secondary effluent (SSE) solution using the technique of small-angle neutron scattering (SANS). The SSE solution is modelling the concentrate of secondary-treated do- mestic wastewater effluents at 80% stage of recovery; the ionic profile of the SSE solution was designed based on the chemical composition of secondary treated effluents of the Shafdan waste- water plant in Israel and was described previously [4]. The con- centrations and activities of the ions in SSE solution are presented in the Appendix A2 (Table A2), and preparation of SSE solution was described previously [4]. SANS studies on two prominent members of EPS, namely the proteins BSA and lysozyme in SSE solution were already published [5,6]. The main result of these studies is that both proteins induce instantaneously a mineral formation of mm large composite colloids of mineral and protein. The mineral part con- sisted of calcium phosphate as well as of calcium carbonate. Ac- cording to [6] the surface of a 30 Å large gold nanoparticle (GNP) was coated by BSA in order to better mimic the biofouling at the surface of a membrane. We found an immediate (within a few seconds) mineralization of 0.2 mm large composite colloids when mixing the coated GNPs with the SSE solution. The BSA coated onto GNPs induces a smaller amount of precipitated mineral compared * Corresponding author. E-mail address: d.schwahn@fz-juelich.de (D. Schwahn). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer http://dx.doi.org/10.1016/j.polymer.2016.01.012 0032-3861/© 2016 Elsevier Ltd. All rights reserved. Polymer 85 (2016) 77e88