Tag Archives: membranes

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.

Monitoring Hollow Fiber Membrane Breakage

Wu Q, Zhang Z, Cao G, Zhang X. Impact of polymeric membrane breakage on drinking water quality and an online detection method of the breakage. Journal of environmental science and health. Part A, Toxic/hazardous substances and environmental engineering. 2017 Jul 24:1-7. doi: 10.1080/10934529.2017.1342496.

Polymeric membrane has been widely used for the treatment of drinking water in China, and the total treating capacity has reached up to 3.8 million m3/d. However, the membrane breakage found in the membrane modules in many water treatment plants resulted in an increase in turbidity and bacterial amount in the membrane permeate. In this study, a membrane module running for 3 years in a full-scale application was examined in terms of the breaking positions and the numbers of the broken fibers. It was found that most of the breaking positions were mainly on the outlet side of the module and that the distance from these points to the outlet was about 1/10-2/10 length of the membrane module. The lab-scale tests showed that the increase of the numbers of the breaking fibers in the membrane module (the breaking fibers were from 1 to 4 of 75 fibers) resulted in the increase in turbidity, particle count and the amount of total bacteria and coliform bacteria. Meanwhile, the water quality after the filtration with broken membrane fibers was similar to the quality of the raw water, which indicated that once the membrane fiber breakage occurred in the membrane module, the quality of drinking water after membrane filtration was significantly affected. Furthermore, the breaking position closer to the outlet side of the membrane module exposed much higher microbiological risk than those in the middle or near the bottom side. A pilot scale test was conducted by using a membrane module with 6600 fibers, and the effect of the membrane breakage (1-4 broken fibers) on water quality was also investigated. The results indicated that periodical backwashing caused drastic fluctuation of turbidity, particle count and the bacterial amount in the permeate water, which might be due to the washing force and self-blocking action inside the hollow fibers. Moreover, there is a good quantitative relationship (R2 = 0.945) between particle count and the bacterial amount, which indicated that an online detection of particle count can be used to evaluate the bacterial risk. It was also suggested that the online detection of particle count after backwashing within 100 s would be a quick and precise method to identify any fiber breakage in time. These results are very important for the safety issue in the application of polymeric membrane to water treatment plants.

A Hybrid NF/RO System for Nitrate Removal

A hybrid NF/RO filtration scheme for nitrate removal is proposed and tested. Production of low salinity brines allowed to be discharged to sewerage systems. The new scheme can be applied in single or double NF stage modes prior to RO step. Appropriate NF membranes for the process should reject Cl better than NO3. The results show the process to be both technically feasible and energy efficient.

Epsztein R, Nir O, Lahav O, Green M. Selective nitrate removal from groundwater using a hybrid nanofiltration–reverse osmosis filtration scheme. Chemical Engineering Journal 1 November 2015 279:372-378

A novel and potentially cost effective filtration scheme for removal of nitrate from groundwater, characterized by production of low salinity waste brine that can be easily discharged to sewerage systems and high product-water recovery, is proposed. The inherent preference of particular NF membranes for rejecting chloride and sodium over nitrate ions is utilized in a preliminary NF stage to remove Na+, Cl+, Ca2+ and Mg2+ to a side stream. In a second stage, RO is applied to remove NO3 and the RO permeate is mixed with the side stream of the NF stage to create product water low in nitrate, yet with a balanced composition consisting all the required species and minerals. The number of NF stages depends mainly on the rejection efficiency of the NF membrane. Based on Israeli regulations for both drinking water and required composition of brines discharged to the sewage, a treatment scheme composed of a single and double NF stages followed by RO is shown to reach water recoveries of 91.6% and 94.3%, respectively. Each NF stage raises the energy cost by approximately 0.5cent/m3 product water. However, this cost is easily paid back by the inherent additional advantages of the combined scheme, i.e., less water treated by the RO, significant increase in total recovery ratio, no need in re-mineralization of the product water and minimization of calcium carbonate precipitation potential on the RO membrane. The principles for process design are described, making the specific treatment scheme proposed here easily adjustable to other regulatory requirements and other water characteristics. A provisional patent has been filed.

Fouling and Cleaning of Ultrafiltration Membranes

Xiafu Shi, Galit Tal, Nicholas P. Hankins, Vitaly Gitis. Fouling and cleaning of ultrafiltration membranes: A review Journal of Water Process Engineering
Volume 1, April 2014, Pages 121–138

Ultrafiltration (UF) is one of the best options for both one-stage and as part of multi-stage water and wastewater purification. This review summarises the known facts about the fouling processes and cleaning procedures and details of the most successful physical and chemical cleaning combinations. The optimum cleaning is closely linked to the nature of the fouling. Precise knowledge of both the fouling type (organic, inorganic, or biological) and the fouling mechanism (gel formation, adsorption, deposition, pore blockage, or cake formation) is the key to success in UF membrane cleaning.

Paper is here (Open Access).

Ceramic Membrane Materials for Removing As(III) /As(V)

Sklari S, Pagana A, Nalbandian L, Zaspalis V. Ceramic membrane materials and process for the removal of as(iii)/as(v) ions from water Journal of Water Process Engineering April 2015 5:42-47

In this article, a hybrid process is described for the removal of As(III) and As(V) from drinking water, based on two ceramic membrane modules connected in series. The first module serves as an efficient distributor of ozone to the water stream and employs functionalized ultrafiltration membranes. The second module serves as an As(V) adsorber and employs microfiltration membranes with iron oxide nanoparticles deposited in the pores. The synthesis of the membrane materials and the evaluation of the process in treating a feed stream containing 70ppb As(III)+As(V) are described. As appeared from the results, complete removal of all Arsenic species could be achieved. Membrane regeneration and removal capacity recovery could be achieved by a membrane heat treatment at 110°C for 24h.

Click here for paper (Open Access).


Effect of Transmembrane Pressure on Ultrafiltration Virus Rejection

Elizabeth Arkhangelsky, Vitaly Gitis. Effect of transmembrane pressure on rejection of viruses by ultrafiltration membranes. Separation and Purification Technology Volume 62, Issue 3, 22 September 2008, Pages 619–628

Although partial penetration of ultrafiltration membranes by viruses and bacteria is well documented, there is no satisfactory explanation for the phenomenon. The current study seeks a possible explanation by studying the retention of viruses at different transmembrane pressures (TMPs). In contrast to previous predictions, higher TMPs lead to reduced virus retention levels. Based on indirect evidences it is proposed that the penetration occurs because of the formation during operation, rather than the initial presence, of abnormally large pores. It is therefore suggested that since pore enlargement is induced by high TMPs, high virus retention levels can be obtained only at low TMP values.

The paper is here (fee).

Membrane Technology Powered by Renewable Energy to Treat Drinking Water

Schäfer AI, Hughes G, Richards BS. Renewable energy powered membrane technology: A leapfrog approach to rural water treatment in developing countries? Renewable and Sustainable Energy Reviews. Dec2014, Vol. 40, p542-556.

Lack of access to safe drinking water remains a present concern in many developing countries, particularly in rural locations. Membrane water treatment technologies have the potential to remove microbiological and chemical contaminants reliably and simultaneously from a wide range of water sources. When powered by renewable energy, these systems are autonomous and have the ability to ‘leapfrog’ over installation of traditional infrastructure for electricity and water supply to reach remote communities. In this paper, current estimated costs for water, membrane plants and infrastructure are compared to indicate the window of opportunity for these exciting renewable energy powered membrane (RE-membrane) technologies. General estimated costs for decentralized membrane systems are within the range of some untreated water costs in developing countries. Specific system costs, however, are very process and location dependent. The appropriateness of a successful approach thus depends partially on careful examination of these parameters. In view of the comparisons made here, the biggest hurdle to adoption of the RE-membrane technology in a remote location may not be cost, but rather sustainability issues such as the lack of skilled personnel for operation and maintenance, service networks, availability of spare parts, socio-economic integration and adaptive capacity of communities to transfer and develop technology appropriate to local needs and circumstances.

Click here for paper (fee).