Search

The tricarboxylic acid (TCA) cycle is a central metabolic pathway that is present in all aerobic organisms and initiates the respiration of organic material. The glyoxylate cycle is a variation of the TCA cycle, where organic material is recycled for subsequent assimilation into cell material instead of being released as carbon dioxide. Despite the importance for the fate of organic matter, the environmental factors that induce the glyoxylate cycle in microbial communities remain poorly understood. In this study, we assessed the expression of isocitrate lyase, the enzyme that induces the switch to the glyoxylate cycle, of the ubiquitous SAR11 clade in response to natural iron fertilization in the Southern Ocean. The cell-specific transcriptional regulation of the glyoxylate cycle, as determined by the ratio between copy numbers of isocitrate lyase gene transcripts and isocitrate genes, was consistently lower in iron fertilized than in high-nutrient, low chlorophyll waters (by 2.4- to 16.5-fold). SAR11 cell-specific isocitrate lyase gene transcription was negatively correlated to chlorophyll a, and bulk bacterial heterotrophic metabolism. We conclude that the glyoxylate cycle is a metabolic strategy for SAR11 that is highly sensitive to the degree of iron and carbon limitation in the marine environment., (© 2015 Society for Applied Microbiology and John Wiley & Sons Ltd.)

To study the effect of water quality and operating parameters on membrane fouling, a comparative analysis of wastewater (WW) and seawater (SW) fouled reverse osmosis (RO) membranes was conducted. Membranes were harvested from SWRO and WWRO pilot plants located in Vilaseca (East Spain), both using ultrafiltration as pretreatment. The SWRO unit was fed with Mediterranean seawater and the WWRO unit was operated using secondary effluent collected from the municipal wastewater treatment plant. Lead and terminal SWRO and WWRO modules were autopsied after five months and three months of operation, respectively. Ultrastructural, chemical, and microbiological analyses of the fouling layers were performed. Results showed that the WWRO train had mainly bio/organic fouling at the lead position element and inorganic fouling at terminal position element, whereas SWRO train had bio/organic fouling at both end position elements. In the case of WWRO membranes, Betaproteobacteria was the major colonizing species; while Ca, S, and P were the major present inorganic elements. The microbial population of SWRO membranes was mainly represented by Alpha and Gammaproteobacteria. Ca, Fe, and S were the main identified inorganic elements of the fouling layer of SWRO membranes. These results confirmed that the RO fouling layer composition is strongly impacted by the source water quality., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Water scarcity is one key challenge mankind is facing. Seawater reverse osmosis desalination is a promising technology to solve it. However, further innovation which needs to go beyond product specifications is needed to decrease the total cost of water while at the same time, improving sustainability footprint. This paper describes a breakthrough step-change in innovation within the desalination industry: transitioning from wet-tested seawater reverse osmosis (SWRO) elements to dry-tested SWRO elements. This new concept has been achieved by DuPont thanks to a cumulation of significant breakthrough in reverse osmosis technology: continuous advancements in membrane chemistry, automated precision manufacturing, single source manufacturing, a robust quality control, and enhancements in testing methods. Dry SWRO elements offer significant advantages over wet elements, given the requirement to monitor and eventually replace preservation solutions for wet membranes. Dry membranes enable longer storage times, lower labor costs and easier longterm warehouse planning. Dry membranes are safer to install due to a 4 kg weight reduction and are easier to handle. From the sustainability point of view, the dry-test SW concept also brings plenty of benefits: (1) Reduces fresh-water consumption as no wet testing is required; (2) Eliminates wastewater generated during wet testing; (3) Significantly reduces energy consumption by skipping wet testing; and (4) the lower membrane weight will significantly decrease the environmental footprint of dry elements, reducing by up to 20% the CO2 generation during transportation. In a large desalination installation supplied with dry SWRO elements, the greenhouse gas emissions reduction equals those generated by a passenger vehicle driving more than 500,000 km. Additionally, dry SWRO elements offer the same water productivity and permeate quality as wet elements. [ABSTRACT FROM AUTHOR]

Water scarcity is being recognized as one of the main threats that mankind is facing globally. Reverse osmosis membrane technology has developed as a promising technology to address this problem. This increase has been driven as materials are improved and costs dropped. This is especially relevant for Middle East countries (ME), where population is located in arid and semi-arid regions with limited rainfalls and a high degree of evaporation due to the high temperatures the region is exposed to. Therefore, getting a robust element that is able to offer a stable salt rejection even after multiple cleanings is of utmost importance to sustain the population and economic growth of the region. This paper aims at demonstrating the superior durability of FilmTec™ membranes compared to other manufacturers. This superior durability has been reported in a number of desalination plants where FilmTec™ membranes lifetime has exceeded more than 10 years, but a quantification and a reliable comparison of such superior durability compared to other manufacturers in a controlled environment has not been completed to date. In this paper, FilmTec™ SW30XLE elements are exposed together with equivalent commercially available membranes from other suppliers to a durability study to simulate long term operation and to determine the evolution of the membrane specifications over time. Particular focus is paid to the changes in salt rejection. Membrane durability plays a determining role in membrane replacement, which ultimately has a critical impact on the economics of any desalination plant. In this study, it was determined that after a number of cleanings, the salt passage increase over time of the membranes from other suppliers was close to 3.5 times larger than the value experienced by FilmTec™ membranes. More specifically, the salt passage increase experienced by FilmTec™ in the first study was 22%, while the membrane from another supplier showed a 73% increase; and in the second study, FilmTec™ had a salt passage increase of 43% while the membrane from the other manufacturer had a 140% salt passage increase. In a 100,000 m3/d desalination plant, this enhanced durability showed by FilmTec™ elements might represent a 5.5% cost of water decrease in the reverse osmosis stage, and total savings of 1.34 US ¢/m3 in the whole plant, which can be translated into savings of 488,000 USD/y. [ABSTRACT FROM AUTHOR]

This paper discusses the feasibility of using reverse osmosis concentrate to backwash ultrafiltration membranes in the seawater reverse osmosis desalination space. Brine is produced through DOW FILMTEC™ reverse osmosis elements and it backwashed every 90 min to DOW™ ultrafiltration membranes. A side-by-side validation is done for 15 d using two parallel ultrafiltration and reverse osmosis integrated systems. One line uses brine for backwashing, while the other uses conventional filtrated water. The optimization is proven to have the same cleaning efficiency than the conventional backwashing methods and no precipitation is observed in the fibers. An additional validation period that uses reverse osmosis brine during backwashes and only two backwash steps is also carried out successfully. These steps are the previously identified backwash top with air scour and forward flush. Fibers also show an excellent integrity after the whole experimental period. A model is built in order to analyze the backwash efficiency of the optimized conditions and the transmembrane pressure increases during the filtration cycle. The results show the same fouling tendency for the line operating with brine and the line operating with filtrated water. The efficiency of the ultrafiltration process is improved from 88 to 98% thanks to this optimization together with the previous researches. This represents filtrating 96 min extra per day and a reduction of 100% in the filtrated water used during backwashes. The chemical equivalent concentration is also optimized from 0.28 to 0.06 mg/L NaClO thanks to the adjustment of the chemically enhanced backwash frequency. This accounts for a 7.1% savings in the ultrafiltration step and for a 1.2% savings in the whole desalination process. [ABSTRACT FROM PUBLISHER]

This paper is part of a global research project conducted by Dow Water & Process Solutions to optimize the efficiency of ultrafiltration processes. After an initial identification of the backwash as the key opportunity to increase the efficiency of the process, a study based on its optimization is developed. Main emphasis is given to the sequence and subsequent number of steps involved in the backwash. The ultimate goal is thus to increase the availability and recovery of the process while still attaining a high cleaning effect during the backwash. This optimization is done through the realization of various experiments using DOW™ Ultrafiltration SFP-2660 outside-in polyvinylidene difluoride (PVDF) membranes following an exhaustively planned factorial design of experiments. The factors being assessed are the steps normally performed during a backwash. These are the air scour (AS/D), the draining (D), the backwash top (BWT) with or without air scour, the backwash bottom (BWB) and the forward flush (FF). The responses analyzed are the calculated efficiency of the process and the experimentally obtained transmembrane pressure, which represents the fouling rate of the membrane. The results are analyzed through a formal statistical study of the analysis of the variance and are validated through 25 days of stable operation. The results show that the backwash can be simplified from an original sequence of five steps to only two steps, which are the backwash top with air scour and the forward flush without impairing the effectiveness of the cleanings. This leads to an increase in efficiency higher than 5%, which represents a decrease of 50% in the filtration inefficiency. This is achieved thanks to the reduction of the time invested for the cleanings and the decrease in the amount of water consumed. [ABSTRACT FROM AUTHOR]

Desalination market growth has triggered significant development in SWRO membrane and process development and the new extra high rejection and ultra low energy membranes from Dow, FILMTEC™ SW30XHR-400i and SW30ULE-400i, as well as the internally staged design concept, have been validated in extensive field testing and various commercial plants over the recent years and are now commercially available. These solutions from Dow can be used to increase membrane flux and system recovery and / or to reduce feed pressure. This yields capital cost and /or energy savings. These savings have been assessed in 4 different situations / geographies, using a thorough and validated cost model. These geographies are South Pacific (Australia), Persian Gulf (Saudi Arabia), with very different feed water qualities (in terms of feed salinity and temperature range) and product quality requirements (in terms of bromide, boron and salinity). Depending on the cost savings route chosen, there are strong differences in the consequences with regards to size of the RO stage (17-26% smaller), size of the pretreatment (9-12% smaller), and/or the feed pressure (2-6 bar lower). These cost savings are in the range of US cent 0.4-4.1/m³ water produced. This is equivalent to 0.7-6.5% water cost saving. Considering that these considerable cost savings are readily available since 2008 from Dow Water Solutions, the industry should start to significantly benefit from these in the coming years. [ABSTRACT FROM AUTHOR]