Membrane Fouling and Chemical Cleaning in Three Full-Scale Reverse Osmosis Plants Producing Demineralized Water

Abstract

Membrane fouling and cleaning were studied in three reverse osmosis (RO) plants. Feed water was secondary wastewater effluent, river water, and surface water. Membrane autopsies were used for fouling characterization. Fouling layer measurements included total organic carbon (TOC), adenosine triphosphate, polysaccharides, proteins, and heterotrophic plate counts. In all locations, membrane and spacer fouling was (bio)organic. Plant chemical cleaning efficiencies were evaluated from full-scale operational data and cleaning trials in a laboratory setup. Standard cleaning procedures were compared to two cleaning procedures specifically adapted to treat (bio)organic fouling using commercial blend cleaners (mixtures of active substances). The three RO plants were impacted by irreversible foulants causing permanently decreased performance in normalized pressure drop and water permeability even after thorough chemical cleaning. The standard plant and adapted cleaning procedures reduced the TOC by 45% on average, with a maximum of ∼80%. In general, around 20% higher biomass removal could be achieved with adapted procedure I compared to adapted procedure II. TOC measurements and SEM showed that none of cleaning procedures applied could remove foulants completely from the membrane elements. This study underlines the need for novel cleaning approaches targeting resistant foulants, as none of the procedures applied resulted in highly effective membrane regeneration.

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

“…A similar finding was reported by Beyer et al, (2017). In this study [19], examining chemical cleaning at three full-scale RO plants, feed channel pressure drop improved by 10%, but permeability decreased by 5% and salt rejection remained unchanged, indicating a compaction of the fouling layer. It is also plausible that NaOH requires a longer contact time than urea to effectively restore membrane permeability.…”

“…The analysis of the membrane surface morphology (SEM) and biofilm composition (EDX and FTIR) confirmed the presence of biological materials (biofouling) on the membrane modules. 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.…”

“…Chemical cleaning of membrane modules is routinely carried out at full-scale installations to restore membrane performance. Several studies have highlighted the need for new chemical cleaning strategies since the conventional cleaning by NaOH and HCl fails to provide highly effective membrane regeneration [16,17,18,19]. The ability of urea to dissolve biofilm proteins has been discussed briefly in the literature [20,21,22].…”

Impact of the Raw Water Seasonal Variations on the Reverse Osmosis Performance: Khenifra Plant, Morocco

“…To restitute the initial performance of RO unit and control the fouling phenomenon [47], the Dow FilmTec TM company recommended to carry out a standard chemical cleaning, applying basic (1% 4Na-EDTA + 0.1% NaOH) and acidic (0.2% HCl) chemical solutions [26,31,48].…”

“…Basic chemical agents including sodium hydroxide (NaOH) clean off organic fouling and biofouling by hydrolysis and solubilization; instead, acid agents including hydrochloric acid (HCl) disperse inorganic fouling, break up the composition of the bacterial cell wall and promote precipitation of proteins [24,32,47,49]. Concerning RO membranes, cleaning procedures involve various steps of high flow recirculation and soaking [31], enduring all over between 6.5 to 24 hours in period at a usual temperature of 35°C [32,47].…”