Tag Archives: reverse osmosis

Predicting Fouling in RO Desalination Systems

Ruiz-García A, Melián-Martel N, Nuez I. Short Review on Predicting Fouling in RO Desalination. Membranes (Basel) 2017 Oct 24;7(4). pii: E62. doi: 10.3390/membranes7040062.

Reverse Osmosis (RO) membrane fouling is one of the main challenges that membrane manufactures, the scientific community and industry professionals have to deal with. The consequences of this inevitable phenomenon have a negative effect on the performance of the desalination system. Predicting fouling in RO systems is key to evaluating the long-term operating conditions and costs. Much research has been done on fouling indices, methods, techniques and prediction models to estimate the influence of fouling on the performance of RO systems. This paper offers a short review evaluating the state of industry knowledge in the development of fouling indices and models in membrane systems for desalination in terms of use and applicability. Despite major efforts in this field, there are gaps in terms of effective methods and models for the estimation of fouling in full-scale RO desalination plants. In existing models applied to full-scale RO desalination plants, neither the spacer geometry of membranes, nor the efficiency and frequency of chemical cleanings are considered.

Solar Powered NF/RO Systems, Tanzania

Owusu-Agyeman I, Shen J, Schäfer AI. Renewable energy powered membrane technology: Impact of pH and ionic strength on fluoride and natural organic matter removal. The Science of the total environment. 2017 Nov 23;621:138-147. doi: 10.1016/j.scitotenv.2017.11.111.

Real water pH and ionic strength vary greatly, which influences the performance of membrane processes such as nanofiltration (NF) and reverse osmosis (RO). Systematic variation of pH (3-12) and ionic strength (2-10g/L as total dissolved solids (TDS)) was undertaken with a real Tanzanian water to investigate how water quality affects retention mechanisms of fluoride (F) and natural organic matter (NOM). An autonomous solar powered NF/RO system driven by a solar array simulator was supplied with constant power from a generator. An open NF (NF270) and a brackish water RO (BW30) membrane were used. A surface water with a very high F (59.7mg/L) and NOM (110mgC/L) was used. Retention of F by NF270 was <20% at pH<6, increased to 40% at pH6, and 60-70% at pH7-12, indicating a dominance of charge repulsion while being ineffective in meeting the guideline of 1.5mg/L. Increase in ionic strength led to a significant decline in retention of F (from 70 to 50%) and electrical conductivity (from 60 to 10%) by NF270, presumably due to charge screening. In contrast, BW30 retained about 50% of F at pH3, >80% at pH4, and about 99% at pH >5, due to the smaller pore size and hence a more dominant size exclusion. In consequence, only little impact of ionic strength increase was observed for BW30. The concentration of NOM in permeates of both NF270 and BW30 were typically >2mg/L. This was not affected by pH or ionic strength due to the fact that the bulk of NOM was rejected by both membranes through size exclusion. The research is carried out in the context of providing safe drinking water for rural and remote communities where infrastructure is lacking, and water quality varies significantly. While other studies focus on energy fluctuations, this research emphasises on feed water quality that affects system performance and may alter due to a number of environmental factors.

Arsenic Removal Using Reverse Osmosis

Schmidt SA, Gukelberger E, Hermann M, Fiedler F, Großmann B, Hoinkis J, Ghosh A, Chatterjee D, Bundschuh J. Pilot study on arsenic removal from groundwater using a small-scale reverse osmosis system-Towards sustainable drinking water production. J Hazard Mater. 2016 Jun 11;318:671-678. doi: 10.1016/j.jhazmat.2016.06.005. 

Arsenic contamination of groundwater is posing a serious challenge to drinking water supplies on a global scale. In India and Bangladesh, arsenic has caused the most serious public health issue in the world for nearly two decades. The aim of this work was to study an arsenic removal system based on reverse osmosis at pilot scale treating two different water sources from two different locations in the State of Bihar, India. For this purpose two villages, Bind Toli and Ramnagar in the Patna District were selected, both located very close to the river Ganga. The trials were conducted with aerated and non-aerated groundwater. It is the first time that the arsenic removal efficiency for aerated and non-aerated groundwater by reverse osmosis technology in combination with an energy-saving recovery system have been studied. As the principle of reverse osmosis requires a relatively high pressure, its energy demand is naturally high. By using an energy recovery system, this demand can be lowered, leading to an energy demand per liter permeate of 3-4Wh/L only. Due to high iron levels in the groundwater and as a consequence the precipitation of ferric (hydr)oxides, it was necessary to develop a granular media filter for the trials under aeration in order to protect the membrane from clogging. Two different materials, first locally available sand, and second commercially available anthracite were tested in the granular media filter. For the trials with aerated groundwater, total arsenic removal efficiency at both locations was around 99% and the arsenic concentration in permeate was in compliance with the WHO and National Indian Standard of 10μg/L. However, trials under anoxic conditions with non-aerated groundwater could not comply with this standard. Additionally a possible safe discharge of the reverse osmosis concentrate into an abandoned well was studied. It was observed that re-injection of reject water underground may offer a safe disposal option. However, long-term hydrogeological studies need to be conducted for confirmation.

RO Membranes for Desalination

Seema S. Shenvi, Arun M. Isloor, A.F. Ismail. A review on RO membrane technology: Developments and challenges. Desalination Volume 368, 15 July 2015, 10–26

Reverse osmosis (RO) based desalination is one of the most important and widely recognized technologies for production of fresh water from saline water. Since its conception and initiation, a significant development has been witnessed in this technology w.r.t. materials, synthesis techniques, modification and modules over the last few decades. The working of a RO plant inclusive of the pretreatment and post-treatment procedures has been briefly discussed in the article. The main objective of this review is to highlight the historical milestones achieved in RO technology in terms of membrane performance, the developments seen over the last few years and the challenges perceived.

The material properties of the membrane dominate the performance of a RO process. The emergence of nano-technology and biomimetic RO membranes as the futuristic tools is capable of revolutionizing the entire RO process. Hence the development of nano-structured membranes involving thin film nano-composite membranes, carbon-nanotube membranes and aquaporin-based membranes has been focussed in detail. The problems associated with a RO process such as scaling, brine disposal and boron removal are briefed and the measures adopted to address the same have been discussed.

Fluoride and Uranium Removal by NF and RO

Junjie Shen, Andrea Schäfer. Removal of fluoride and uranium by nanofiltration and reverse osmosis: A review. Chemosphere. Volume 117, December 2014, 679–691

Inorganic contamination in drinking water, especially fluoride and uranium, has been recognized as a worldwide problem imposing a serious threat to human health. Among several treatment technologies applied for fluoride and uranium removal, nanofiltration (NF) and reverse osmosis (RO) have been studied extensively and proven to offer satisfactory results with high selectivity. In this review, a comprehensive summary and critical analysis of previous NF and RO applications on fluoride and uranium removal is presented. Fluoride retention is generally governed by size exclusion and charge interaction, while uranium retention is strongly affected by the speciation of uranium and size exclusion usually plays a predominant role for all species. Adsorption on the membrane occurs as some uranium species interact with membrane functional groups. The influence of operating conditions (pressure, crossflow velocity), water quality (concentration, solution pH), solute–solute interactions, membrane characteristics and membrane fouling on fluoride and uranium retention is critically reviewed.

Minimizing Costs and Energy Consumption; Arsenic Removal by Reverse Osmosis

A. Abejón, A. Garea, A. Irabien. Arsenic removal from drinking water by reverse osmosis: Minimization of costs and energy consumption. Separation and Purification Technology Volume 144, 15 April 2015, Pages 46–53

Arsenic is one of the most serious inorganic contaminants in drinking water on a worldwide scale. To comply with the MCL (maximum contaminant level, 10 μg/l arsenic in drinking water) established by the World Health Organization, numerous techniques have been studied, such as ion exchange, coagulation and flocculation, precipitation, adsorption and membrane technologies. Among the available technologies applicable to water treatment, membrane filtration has been identified as a promising technology to remove arsenic from water.

The goal of this study is to demonstrate the technical and economic viability of removing arsenic (V) using an optimized reverse osmosis process, with minimization of the total cost as the objective of the optimization strategy. The optimization results showed that the total costs of a two-stage membrane cascade used for the removal of arsenic (V) from drinking water for a population of 20,000 inhabitants were 1041 $/d and 0.52 $/m3 of drinking water produced. Energy consumption was the most relevant cost, corresponding to 35% of the total cost. Sensitivity analysis was performed to determine the total costs of the installation for different scenarios in terms of drinking water production: (i) 0.44–0.56 $/m3 for electricity prices of 0.05–0.10 $/KW h; (ii) 0.88–0.45 $/m3 for populations ranging from 5000 to 50,000 inhabitants; and (iii) 0.52–0.61 $/m3 when the membrane lifetime was reduced from 3 to 1.5 years. The multiobjective optimization solutions, which consider the best compromises among the quality and cost objectives, indicated that the concentration of As (V) in the permeate water can be reduced to 0.5 μg/l at a feasible cost.

The paper is here (fee).

Fluoride, Uranium Removal Using High-Pressure Membranes

Shen J, Schäfer A. Removal of fluoride and uranium by nanofiltration and reverse osmosis: A review. Chemosphere. 2014 Nov 1;117C:679-691. doi: 10.1016/j.chemosphere.2014.09.090.

Inorganic contamination in drinking water, especially fluoride and uranium, has been recognized as a worldwide problem imposing a serious threat to human health. Among several treatment technologies applied for fluoride and uranium removal, nanofiltration (NF) and reverse osmosis (RO) have been studied extensively and proven to offer satisfactory results with high selectivity. In this review, a comprehensive summary and critical analysis of previous NF and RO applications on fluoride and uranium removal is presented. Fluoride retention is generally governed by size exclusion and charge interaction, while uranium retention is strongly affected by the speciation of uranium and size exclusion usually plays a predominant role for all species. Adsorption on the membrane occurs as some uranium species interact with membrane functional groups. The influence of operating conditions (pressure, crossflow velocity), water quality (concentration, solution pH), solute-solute interactions, membrane characteristics and membrane fouling on fluoride and uranium retention is critically reviewed.

Click here for paper (fee).