Reverse osmosis plant | EPFL Graph Search

A reverse osmosis plant is a manufacturing plant where the process of reverse osmosis takes place. Reverse osmosis is a common process to purify or desalinate contaminated water by forcing water through a membrane. Water produced by reverse osmosis may be used for a variety of purposes, including desalination, wastewater treatment, concentration of contaminants, and the reclamation of dissolved minerals. An average modern reverse osmosis plant needs six kilowatt-hours of electricity to desalinate one cubic metre of water. The process also results in an amount of salty briny waste. The challenge for these plants is to find ways to reduce energy consumption, use sustainable energy sources, improve the process of desalination and to innovate in the area of waste management to deal with the waste. Self-contained water treatment plants using reverse osmosis, called reverse osmosis water purification units, are normally used in a military context. Reverse osmosis plants require a variety of pre-treatment techniques including softening, dechlorination, and anti-scalent treatment. Following pre-treatment, high levels of pressure send water through a semi-permeable membrane, which retains all contaminants but lets pure water pass through. Energy requirements depend on the concentration of salts and contaminants in the influent water; higher concentrations requires more energy to treat. In 1977 Cape Coral, Florida became the first municipality in the United States to use the RO process on a large scale with an initial operating capacity of 11,356 m3 (3 million gallons) per day. By 1985, due to the rapid growth in population of Cape Coral, the city had the largest low pressure reverse osmosis plant in the world, capable of producing 56,782 m3 (15 million gallons) per day. In Israel at Ashkelon on the Mediterranean coast, the world's largest reverse osmosis plant is producing 396,000 m3 of water a day at around possibly US$0.50 per m3. In western Saudi Arabia at Yanbu, production started in 1999 at 106,904 m3 of water a day.

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 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