A sequencing approach targeting the 16S rRNA gene unravels the biofilm composition of spiral-wound membranes used in the dairy industry

The influence of particles on biofouling behavior in spiral wound membrane elements

Spiral-wound new thin film composite membrane for a single-stage seawater desalination by reverse osmosis

Spiral-wound membrane reverse osmosis and the treatment of industrial effluents

The development of the spiral-wound reverse osmosis(RO) modules

Assessing the passage of particles through polyamide reverse osmosis membranes

To improve hydraulic conditions, periodic air/water cleaning (AWC) is applied to a nanofiltration (NF) spiral wound membrane (SWM) element under permeation conditions to control biofouling and particulate fouling. A pilot study was carried out for 212 days with a vertically positioned SWM element fed by tap water enriched with a biodegradable compound (60 mu g acetate-C l(-1)). Operational parameters were daily recorded, rinse water was collected and analysed and a membrane autopsy was performed at the end of the experimental run. Normalized pressure drop (NPD) increased as a result of biofouling and particulate fouling, and could be controlled by periodic AWC, while the membrane transport coefficient (MTC) and retention based on the conductivity remained constant. Rinsing water from AWC contained biomass and particulate matter (iron), predominantly during the first few minutes of AWC. Membrane autopsy revealed active biomass and inorganic deposits (mainly iron and copper) at the inlet and outlet of the membrane element. The use of AWC in (vertically positioned) NF/RO SWM elements under permeation conditions improved the control of membrane fouling (especially biofouling and particulate fouling) and did not compromise the integrity of the membrane element (until day 60).

The effect of spiral wound membrane element design characteristics on its performance in steady state desalination — A parametric study

One Step Membrane Filtration: A fundamental study

Nitrogen separation from domestic wastewater by reverse osmosis

Hydrogel-coated feed spacers in two-phase flow cleaning in spiral wound membrane elements: A novel platform for eco-friendly biofouling mitigation

Routine chemical cleaning with the combined use of sodium hydroxide (NaOH) and hydrochloric acid (HCl) is carried out as a means of biofouling control in reverse osmosis (RO) membranes. The novelty of the research presented herein is in the application of urea, instead of NaOH, as a chemical cleaning agent to full-scale spiral-wound RO membrane elements. A comparative study was carried out at a pilot-scale facility at the Evides Industriewater DECO water treatment plant in the Netherlands. Three fouled 8-inch diameter membrane modules were harvested from the lead position of one of the full-scale RO units treating membrane bioreactor (MBR) permeate. One membrane module was not cleaned and was assessed as the control. The second membrane module was cleaned by the standard alkali/acid cleaning protocol. The third membrane module was cleaned with concentrated urea solution followed by acid rinse. The results showed that urea cleaning is as effective as the conventional chemical cleaning with regards to restoring the normalized feed channel pressure drop, and more effective in terms of (i) improving membrane permeability, and (ii) solubilizing organic foulants and the subsequent removal of the surface fouling layer. Higher biomass removal by urea cleaning was also indicated by the fact that the total organic carbon (TOC) content in the HCl rinse solution post-urea-cleaning was an order of magnitude greater than in the HCl rinse after standard cleaning. Further optimization of urea-based membrane cleaning protocols and urea recovery and/or waste treatment methods is proposed for full-scale applications.

Scaling appears first in the tail spiral wound membrane (SWM) elements of desalination plants due to increased salt concentration in the retentate; in particular, membrane scaling starts locally when supersaturation of sparingly soluble salts (commonly CaCO3 and CaSO4) is attained. Reliable determination of the onset of membrane scaling in the tail elements (as a function of the local retentate physico-chemical properties) provides a threshold condition serving a dual purpose; i.e., it imposes essentially an upper limit to the degree of permeate recovery, and guides the selection of an appropriate anti-scaling program involving additives. Judicious use of the latter is important for reduction of desalination cost and environmental impact. The current practices for estimating incipient scaling within the spacer filled reverse osmosis (RO) membrane elements involve a great deal of uncertainty. In this study, slightly supersaturated in CaCO3 brackish waters were desalinated in a test section comprising a narrow gap spacer filled channel simulating local (constant flux) conditions in SWM modules. Detailed data on incipient membrane scaling were obtained leading to the following main conclusions: (a) minute quantities of very small particles, ever present in RO plants, apparently promote heterogeneous nucleation; moreover, under the conditions tested, induction period for membrane scaling is practically nonexistent. (b) the initial scale deposit rates measured by special techniques (but undetectable with common bulk flow measurements) are substantial, and if not mitigated would be detrimental to SWM performance over a relatively short operating time period. (c) accurate determination of supersaturation ratio at the membrane surface Sw can be a reliable criterion for the onset of scaling, instead of currently used indices (e.g. Langelier Saturation Index) or practical type recommendations; a reliable method has been employed to determine Sw under local retentate conditions. Based on these results, a novel system was developed for monitoring the scaling propensity of retentate, which involves combination of a limited number of measurements in key locations of a RO plant, reliable algorithms for local equilibria and supersaturation (Sw) calculations, and a modern wireless electronic system for plant wide monitoring.

Analysis of specific energy consumption in reverse osmosis desalination processes

Spiral-wound thin-film composite membrane systems for brackish and seawater desalination by reverse osmosis

The initial formation and spatiotemporal development of microbial biofilm layers on surfaces of new and clean reverse osmosis (RO) membranes and feed-side spacers were monitored in situ using flow cells placed in parallel with the RO system of a full-scale water treatment plant. The feed water of the RO system had been treated by the sequential application of coagulation, flocculation, sand filtration, ultrafiltration, and cartridge filtration processes. The design of the flow cells permitted the production of permeate under cross-flow conditions similar to those in spiral-wound RO membrane elements of the full-scale system. Membrane autopsies were done after 4, 8, 16, and 32 days of flow-cell operation. A combination of molecular (fluorescence in situ hybridization [FISH], denaturing gradient gel electrophoresis [DGGE], and cloning) and microscopic (field emission scanning electron, epifluorescence, and confocal laser scanning microscopy) techniques was applied to analyze the abundance, composition, architecture, and three-dimensional structure of biofilm communities. The results of the study point out the unique role of Sphingomonas spp. in the initial formation and subsequent maturation of biofilms on the RO membrane and feed-side spacer surfaces.