Enhanced biofilm solubilization by urea in reverse osmosis membrane systems

Abstract

Chemical cleaning is routinely performed in reverse osmosis (RO) plants for the regeneration of RO membranes that suffer from biofouling problems. The potential of urea as a chaotropic agent to enhance the solubilization of biofilm proteins has been reported briefly in the literature. In this paper the efficiency of urea cleaning for RO membrane systems has been compared to conventionally applied acid/alkali treatment. Preliminary assessment confirmed that urea did not damage the RO polyamide membranes and that the membrane cleaning efficiency increased with increasing concentrations of urea and temperature. Accelerated biofilm formation was carried out in membrane fouling simulators which were subsequently cleaned with (i) 0.01M sodium hydroxide (NaOH) and 0.1M hydrochloric acid (HCl) (typically applied in industry), (ii) urea (CO(NH 2 ) 2 ) and hydrochloric acid, or (iii) urea only (1340 g/L water ). The pressure drop over the flow channel was used to evaluate the efficiency of the applied chemical cleanings. Biomass removal was evaluated by measuring chemical oxygen demand (COD), adenosine triphosphate (ATP), protein, and carbohydrate content from the membrane and spacer surfaces after cleaning. In addition to protein and carbohydrate quantification of the extracellular polymeric substances (EPS), fluorescence excitation−emission matrix (FEEM) spectroscopy was used to distinguish the difference in organic matter of the remaining biomass to assess biofilm solubilization efficacy of the different cleaning agents. Results indicated that two-stage CO(NH 2 ) 2 /HCl cleaning was as effective as cleaning with NaOH/HCl in terms of restoring the feed channel pressure drop (>70% pressure drop decrease). One-stage cleaning with urea only was not as effective indicating the importance of the second-stage low pH acid cleaning in weakening the biofilm matrix. All three chemical cleaning protocols were equally effective in reducing the concentration of predominant EPS components protein and carbohydrate (>50% reduction in concentrations). However, urea-based cleaning strategies were more effective in solubilizing protein-like matter and tyrosine-containing proteins. Furthermore, ATP measurements showed that biomass inactivation was up to two-fold greater after treatment with urea-based chemical cleanings compared to the conventional acid/alkali treatment. The applicability of urea as an alternative, economical, eco-friendly and effective chemical cleaning agent for the control of biological fouling was successfully demonstrated.

Pilot-Scale Assessment of Urea as a Chemical Cleaning Agent for Biofouling Control in Spiral-Wound Reverse Osmosis Membrane Elements

“…Confirming the previous lab-scale studies [23], the results of this pilot-scale study show that urea cleaning and the standard acid/alkali cleaning are equally effective with regards to restoring the normalized feed channel pressure drop. Both cleaning strategies fulfilled the aim of chemical cleaning i.e., to restore the feed channel pressure drop of the membrane element when it exceeds 10–15% of the start-up value.…”

“…Cleaning of the membrane modules at the DECO plant with chemicals such as NaOH and urea is therefore a suitable cleaning strategy, since the reaction mechanism of both the cleaning agents results in the removal of organic fouling [19,38]. Preliminary laboratory studies confirmed the compatibility of urea with the polyamide membranes [23], where urea was not found to damage the polyamide layer of the membrane.…”

“…The ability of urea to dissolve biofilm proteins has been discussed briefly in the literature [20,21,22]. Recently, controlled laboratory experiments have been conducted using membrane fouling simulators to assess the efficiency of concentrated urea as a chemical cleaning agent for RO membranes [23]. These studies demonstrated considerable potential of urea to enhance biofilm solubilization and removal.…”

“…This study examined the efficiency of urea as a chemical cleaning agent in contrast to the conventional acid/alkali cleaning protocol, applied to 8-inch diameter spiral-wound RO membrane elements taken from a full-scale installation and cleaned in a pilot test facility. To fulfil this objective, performance data of the membrane modules was assessed and a subsequent autopsy of the membrane modules was carried out, enabling detailed laboratory analysis using advanced analytical techniques which had not been incorporated in our previous lab-scale studies [23].…”

Effect of phosphate availability on biofilm formation in cooling towers

“…Discussion P-limitation restricts microorganism growth but not biofilm formation in cooling tower systems A goal of this study was to investigate the efficiency of phosphate limitation as a preventive method for biofouling control in CTs. The applied short-term approach, based on nutrient dosages in the feed water, has been shown to be suitable for prediction of long-term biofouling (Sanawar et al 2017) and has been used to study membrane filtration systems (Siddiqui et al 2017;Sanawar et al 2018). The pilotscale experiment showed that: (1) active biomass growth in the CT was strongly inhibited under P-limited conditions compared with conditions with additional phosphate supplied (Figures 3 and 4); (2) the overall accumulation of organic matter was similar when all nutrients were supplied or under P-limited conditions with only organic carbon supplied ( Figure 3); (3) P-limitation caused a shift in bacterial community structure ( Figure 6) and seemed to promote the production of carbohydrates over proteins by the microorganisms in the extracellular matrix and to result in a more homogeneous biofilm (Supporting Information Figures S1 and S3).…”