Reverse osmosis | EPFL Graph Search

Reverse osmosis (RO) is a water purification process that uses a semi-permeable membrane to separate water molecules from other substances. RO applies pressure to overcome osmotic pressure that favors even distributions. RO can remove dissolved or suspended chemical species as well as biological substances (principally bacteria), and is used in industrial processes and the production of potable water. RO retains the solute on the pressurized side of the membrane and the purified solvent passes to the other side. It relies on the relative sizes of the various molecules to decide what passes through. "Selective" membranes reject large molecules, while accepting smaller molecules (such as solvent molecules, e.g., water). RO is most commonly known for its use in drinking water purification from seawater, removing the salt and other effluent materials from the water molecules. As of 2013 the world's largest RO desalination plant was in Sorek, Israel, outputting . History A p

Design of solar driven supercritical water desalination plant

Grzegorz Adam Koblanski

The objective of this master project is to develop model for the solar driven supercritical desalination plant. Furthermore we propose a possible system integration and examination of its performance in terms of energy and cost effectiveness. The model simulations and calculations are performed using Belsim Vali and in-house LENI developed program OSMOSE. Supercritical salt separation model was created based on the solubility models proposed by Leusbrock and research conducted by Khan and Rogak on salt mixture solubility. This allowed the creation of a salt separation model as a function of pressure and temperature in supercritical conditions. The proposed model is validated in certain range of pure water density and is characterized by 86% water recovery ratio for salts inlet concentration of 4%. During the simulation, a reactor was operated in fixed temperature of 660 K and 221 bar in order to fulfill potable water requirements in terms of TDS value. The simulations results show that through integration of recompression and steam network, a significant improvement in terms of energy usage and cost incurred can be obtain. Steam network integration with double steam step allows to eliminate electricity requirements and increase the exergy efficiency to 3.16%. The majority cost of the system is caused by the investment in the solar system due to linear behavior of costing function for solar installations. It is shown that 75% of overall investment cost is intended for hot utility. However, it was found that profitability can be obtain when secondary products income are taken into account. By possibility of selling industry salts that are separated in the reactor, it is possible to obtain cost of 0.96 CHF per cubic meter of generated potable water. Moreover, to achieve higher economic performance and fresh water recovery ratio hybrid, the “Reverse Osmosis – Supercritical Desalination Plant” system was investigated. It was found that joining two technologies led to significant economic savings together with drastic increase in water recovery ratio up to 91%. This shows that proposed integration not only increased profitability of the installation, but also increased water recovery ratio. Thus showing promising perspectives for possible future desalination systems.

2013

Pretreatment options for micropollutant abatement before aquifer recharge in drinking water production: Assessment of UV/H2O2 and dense membranes

Robin Wünsch

Micropollutants (MP) such as residues of pharmaceuticals, industrial chemicals or pesticides can be detected in almost all water resources. Various processes can be used to abate them in drinking water treatment, e.g., ozonation, advanced oxidation processes (AOP), adsorption on activated carbon or membrane filtration. The selection of a suitable process combination is a complex task for water suppliers.This thesis compares two process chains in the context of a multi-barrier system including managed aquifer recharge (MAR). To protect soils and aquifers from MP in the future, an additional barrier against MP upstream of the MAR was investigated: (1) a full-stream treatment using the AOP UV/H2O2, and (2) a side-stream treatment with low-pressure reverse osmosis (LPRO) or nanofiltration (NF) and ozonation of the retentate to treat the concentrated MPs.Pilot-scale experiments were conducted to determine the relative abatements of MP by UV/H2O2 treatment and by a subsequent soil column treatment. Compared to a soil column fed with water without UV/H2O2 pretreatment, the performance of the combined process (UV/H2O2 + soil column) was more efficient. However, this could be explained by an additive effect of the individual processes.Relative abatements in the UV/H2O2 process are mainly based on the introduced UV fluence and hydroxyl radical exposure. These parameters could be calculated with a model based on the measured relative abatements of two MPs (probe compounds) and their kinetic data (second-order rate constants for the reactions with hydroxyl radical, absorbance and quantum yield).With this information, the relative abatements of other MPs could be predicted with an accuracy of ±20%. A sensitivity analysis of the model showed that the relative abatements of the selected probe compounds should be >50%. In this case, the accuracy of the calculated parameters depends mainly on the precision of the kinetic data.In the case of membrane-based treatment of water by LPRO or NF, a concentrate is produced. Ozonation to treat MP in the concentrate is accompanied by a formation of the possibly carcinogenic bromate by oxidation of bromide. To achieve the highest possible MP abatement with simultaneously low bromate formation, both membrane selection and subsequent concentrate ozonation were investigated. In laboratory tests with standardized concentrates, neither the water source nor the membrane type caused a change in bromate yield for similar relative MP abatements. However, NF membranes have lower relative retentions of bromide and MP than LPRO membranes, making NF concentrates more suitable for ozonation with limited bromate formation.A comparison of UV/H2O2 with membrane treatment showed that full-stream treatment with UV/H2O2 has about four times lower costs and an about five times lower environmental impact. In addition it achieves significantly higher disinfection. In contrast, side-stream treatment with LPRO causes up to two times lower impacts for the environment when the electrical energy source is wind or hydropower. This study thus contributes technical, economic, and environmental aspects to a holistic evaluation of the two process options.

EPFL2022

Design approach for the improvement of the economic and environmental performances of potable water supply

François Vince

Triggered by the Kyoto Protocol and by the aggravation of freshwater scarcity, environmental impacts should soon become key decision criteria for the planning of potable water supply projects, especially when advanced systems such as seawater desalination are at stake. In order to foster the transition of the water industry towards sustainable practices, the present work proposes an integrated design approach dedicated to potable water supply that targets both economic and environmental objectives. At first, the current industrial practices (Chapter I) and the technical characteristics of potable water supply systems (Chapter II) are analyzed via the modeling of the process units used for potable water supply: pumping systems, conventional water treatment processes (e.g. clarification, filtration, disinfection) and advanced water treatment processes (e.g. membrane processes, thermal processes). Using the ISO 14040 standardized Life Cycle Assessment (LCA) method, Chapter III presents the development of a performance indicator that assesses the environmental impacts generated through all stages of the life cycle of potable water supply (i.e. from "cradle to grave"): from the construction of the potable water treatment plant, to its operation and decommissioning. This LCA-based indicator provides a holistic overview of all potential environmental impacts (e.g. green house gases (GHG) emissions, impacts on ecosystems and on human health). It allows to stress out the impact sources and the penalizing steps within potable water supply (Chapter IV): The production of electricity and chemicals required by the potable water treatment plant is highlighted to generate respectively 75% and 15% of the total impacts generated during the life cycle of potable water supply. Different potable water supply scenarios (e.g. potable water supply from ground water, from surface water, seawater desalination, water import from distant water resources) are benchmarked, in order to identify the best solutions as a function of the local context (e.g. type of electricity supply, topographic conditions, feed water quality). Based on the results of the environmental assessment, Chapter V proposes measures for the improvement of the industrial practices of the water sector, targeting energy and chemicals management, electricity sourcing and effluent disposal. Within the same perspective, Chapter VI details an optimization method for the design of the reverse osmosis (RO) membrane process, i.e. the key treatment process for desalination and wastewater reclamation. This method systematically synthesizes RO process configurations and evaluates their performances on economical (total annualized costs), technical (energy requirement, water conversion rate) and environmental criteria (GHG emissions). Evolutionary algorithms are then used to optimize the design of these configurations (process layout and operating conditions) and to identify those featuring the best trade-offs between economical costs and environmental impacts. As case study, the optimization method is applied on a brackish water reverse osmosis (BWRO) desalination project. The characteristics of the optimal BWRO process configurations are calculated as a function of the project constraints (e.g. economical and technical settings, minimum potable water quality), in order to illustrate how this method may support process engineers for the design of desalination plants.

EPFL2008