Mattheus F.A. Goosen

Fouling of Reverse Osmosis and Ultrafiltration Membranes: A Critical Review

Abstract Desalination by using reverse osmosis (RO) membranes has become very popular for producing freshwater from brackish water and seawater. Membrane lifetime and permeate flux, however, are primarily affected by the phenomena of concentration polarization and fouling at the membrane surface. The scope of the current paper was to critically review the literature on the fouling phenomena in RO and ultrafiltration (UF) membrane systems, the analytical techniques used to quantify fouling, preventive methods, and membrane cleaning strategies. The paper also makes specific recommendations on how scientists, engineers, and technical staff can assist in improving the performance of these systems through fundamental and applied research.

Thermodynamic and economic considerations in solar desalination

Abstract The thermodynamic efficiency of single-basin and multiple-effect solar water desalination systems was critically reviewed with special emphasis on humidification-dehumidification processes. Solar energy may be used, either directly or indirectly, to produce fresh water. The concept of using the humidification-dehumidification process in combination with the growth of crops in a greenhouse system, however, is relatively new. System economics was also covered since it affects the final cost of produced water. While a system may be technically very efficient, it may not be economic. The challenges and opportunities of solar energy were also briefly discussed. The paper closes with a summary of key factors affecting system performance and recommendations for future areas of investigation and development.

Feasibility of salt production from inland RO desalination plant reject brine: a case study

Abstract Production and disposal of rej ect brine are an integral part of an overall desalination process. For inland desalination plants, this poses a serious challenge to operators, as the option of ocean disposal of rej ect brine is not available. Various disposal options such as reinjection, lined and unlined evaporation ponds and natural depressions (lake) are currently being used. An alternative approach is to further process the reject brine to extract all the salts. This has the advantages of being environmentally friendly and producing commercial products (i.e., salts and fresh water). A desktop profeasibility study using data from Petroleum Development Oman (PDO), operating plants in Bahja, Rima, Nimr and Marmul, confirmed the technical feasibility of treating reject brines in simple processing routes using SAL-PROC technology. SAL-PROC is an integrated process for sequential extraction of dissolved elements from inorganic saline waters in the form of valuable chemical products in crystalline, slurry and liquid forms. The process involves multiple evaporation and/or cooling, supplemented by mineral and chemical processing. An analysis indicated that various types of salts including gypsum, sodium chloride, magnesium hydroxide, calcium chloride, calcium carbonate, and sodium sulphate can be produced from the reject brine of PDO desalination plants. These products have an approximate market value of US

Effect of feed temperature on permeate flux and mass transfer coefficient in spiral-wound reverse osmosis systems☆

895, 000 annually.

Simulation of fresh water production using a humidification-dehumidification seawater greenhouse

The objective of the present study was to analyze and model concentration polarization in spiral-wound seawater membrane elements. In particular, the influence of feed temperature, salinity and flow rate on permeate flow and salinity was evaluated. Membrane lifetime and permeate fluxes are primarily affected by the phenomena of concentration polarization (accumulation of solute) and fouling (i.e., microbial adhesion, gel layer formation and solute adhesion) at the membrane surface. Results show that the polymer membrane is very sensitive to changes in the feed temperature. There was up to a 60% increase in the permeate flux when the feed temperature was increased from 20 to 40°C. This occurred both in the presence and absence of solute. Surprisingly, the permeate flux appears to go through a minimum at an intermediate temperature. There was up to a 100% difference in the permeate flux between feed temperatures of 30 and 40°C. The differences were statistically significant (p<0.05). A doubling of the feed flow rate increased the permeate flux by up to 10%, but only at a high solute concentration. Membrane parameters were estimated using an analytical osmotic pressure model for high salinity applications. A combined Spiegler-Kedem/film theory model described the experimental results. The modeling studies showed that the membrane transport parameters were influenced by the feed salt concentration and temperature.

Influence of spacer thickness on permeate flux in spiral-wound seawater reverse osmosis systems

A thermodynamic simulation study was performed on the influence of greenhouse-related parameters on a desalination process that combines fresh water production using humidification-dehumidification with the growth of crops in a greenhouse. With the system under study, surface seawater trickles down a porous front wall evaporator through which air is drawn into the greenhouse. The saturated air passes through a condenser, which is cooled using cold deep seawater or cool seawater coming out of the evaporators. Thermodynamic modeling of the seawater greenhouse system in our laboratory has shown that the dimension of the greenhouse had the greatest overall effect on water production and energy consumption. A wide shallow greenhouse, 200 m wide by 50 m deep gave 125 m3.d−1 of fresh water. This was greater than a factor oftwo compared to the worst-case scenario with the same area (50 m wide by 200 m deep), which gave 58 m3.d−1. Low power consumption went hand-in-hand with high efficiency. The wide shallow greenhouse consumed 1.16 kWh.m−3, while the narrow deep structure consumed 5.02 kWh.m−3 . The benefits of the development of the seawater greenhouse for arid regions are discussed.

Electrostatic Droplet Generation for Encapsulat ion of Somatic Tissue: Assessment of High‐Voltage Power Supply

A primary reason for flux decline during the initial period of a membrane separation process is concentration polarization of the solute at the membrane surface. The objective of the present study was to analyze and model concentration polarization in spiral-wound seawater membrane elements. In particular, the influence of spacer thickness in the membrane units on permeate flow and its salinity was evaluated. Membrane parameters were also estimated using an analytical osmotic pressure model for high salinity applications. The effects of spacer thickness on permeate flux suggest that the observed flux decreases by up to 50% in going from a spacer thickness of 0.1168 to 0.0508 cm. The different geometry/configuration of the spacer may influence turbulence at the membrane surface that in turn affected concentration polarization. This suggests less turbulence with the smaller spacer thickness. The membrane module with an intermediate spacer thickness of 0.0711 cm was found to be the best economically since it gave the highest water production rate (L/h).

Electrostatic Encapsulation and Growth of Plant Cell Cultures in Alginate

The production of alginate microbeads with and without somatic tissue was investigated using an electrostatic droplet generator with a custom‐made fixed (5.7 kV) and variable (0–20 kV) high‐voltage power supply. The effects of applied potential, needle size, and alginate concentration were assessed as well as the immobilization of carnation callus cells. The high‐voltage output from the power supply depended on whether the low‐voltage input was increasing or decreasing. This hysteresis effect may be due to the electrical properties of the oscillator in the high‐voltage source. While a short electrode distance and a high needle gauge were important for producing small alginate bead diameters (e.g., 100 μm), alginate concentration in the range 1–3% (w/v) was not a key factor. Somatic tissue encapsulated using 2% sodium alginate retained viability over a 2‐month culture period.

Today's and Future Challenges in Applications of Renewable Energy Technologies for Desalination

The growth of callus tissue from African Violets, encapsulated in alginate using electrostatics, was investigated as well as the mechanism of alginate droplet formation. Alginate microbeads as small as 500 (±50) microns in diameter could be produced by electrostatic extrusion directly from a plastic syringe (1900 micron extrusion orifice), in the absence of a needle. Video analysis of the mechanism of electrostatic alginate droplet formation from the syringe showed the development of a Taylor cone‐like droplet which extended to form a thin strand that then broke up into droplets. Autoclaving of the alginate/medium solution significantly reduced its viscosity, giving smaller beads. Calculated microbead diameters agreed well with experimental values. Callus tissue from leaf explants was successfully immobilized and cultured using electrostatic extrusion. Tissue immobilized using 4% alginate in medium and cultured on agar grew best, producing a complete plantlet within four months. The long‐term aim is to develop an effective method for large production of artificial seeds.

Physico-chemical and mass transfer considerations in microencapsulation.

Recent trends and challenges in applications of renewable energy technologies for water desalination are critically reviewed with an emphasis on environmental concerns and sustainable development. After providing an overview of wind, wave, geothermal, and solar renewable energy technologies for fresh water production, hybrid systems are assessed. Then scale-up and economic factors are considered. This is followed with a section on regulatory factors, environmental concerns, and globalization, and a final segment on selecting the most suitable renewable energy technology for conventional and emerging desalination processes.