Desalting in Australia : The development of a new process for brackish water

The present status of desalination in Australia, the world's driest continent, is reviewed. The well-established techniques of distillation, electrodialysis and reverse osmosis have been utilized to obtain potable water from underground sources or the sea. In remote areas where mining and tourism are major industries, about 30 plants with capacities of up to 900 m³/day have been installed.The future application of large scale desalting is likely to be for municipal purposes in more highly populated regions. The emphasis has been on the treatment of water of moderate salinity which may be of surface, underground, sewage or industrial origin.A new ion exchange desalination process is described which has been developed in Australia to upgrade mildly brackish water to potable or industrial standards. Developed jointly by CSIRO and ICI Australia, the process uses “Sirotherm” resins which are regenerated by hot water, in contrast to the conventional regeneration by chemicals. This uses low grade or waste heat, reduces operating costs compared with existing processes and saves adding extra regenerant chemicals to the environment.Operation of a 600 m³/day plant to remove 80% of the salinity in a 600 ppm municipal supply has recently commenced at a factory site in Adelaide, Australia. A 20 m³/day pilot plant has successfully demonstrated the removal of salt from reclaimed sewage in Tokyo, Japan, where water reuse is fast becoming mandatory. The resin is now available commercially throughout the world.     

海水淡化的热处理工艺技术综述

综述了海水淡化的主要热处理工艺：多级闪蒸(MSF)、多效蒸发(MED)和压气蒸馏(VC)。     

Novel chitosan-piperazine composite nanofiltration membranes for the desalination of brackish water and seawater

A novel chitosan (CS)-piperazine (PIP) composite nanofiltration (NF) membrane with satisfied characteristics for brackish water and seawater desalination was successfully developed. PIP was mixed with CS during the interfacial polymerization (IP) process to enhance the NF membrane permeate flux. The resultant NF membranes were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscope (AFM), contact angle. Effects of CS concentration, trimesoyl chloride (TMC) concentration, reaction time and the mixing ratio of CS/PIP on NF membrane performance were investigated thoroughly. When PIP in the aqueous phase monomers reached to 25% (w/w), the PWF (60.6 L·m^?2·h^?1) was synergistically improved by nearly 2 times without a significant reduction of Na₂SO₄ rejection (89.1%). Moreover, the NF membranes possessed excellent performance for the desalination of brackish water and seawater, which showed high potential to be applied in the desalination process for water treatment.     

Total desalination of brackish water

With desalination of brackish water far inland, the discharge of the concentrated brine which -is -inevitably produced as a by-product by all the desalination processes may pose a serious problem.

Deep well injection and discharge into rivers can be a solution in many cases. These methods however have serious disadvantages with respect to ecology and a pipeline to the sea can only be considered for shorter distances.

As an alternative, a hybrid plant consisting of a Reverse-Osmosis unit and a crystallization section has been studied. Such a combination converts brackish water into fresh water and a crystal sludge which can be either stored or treated for further use. Because of the scale-forming substances in brackish water, only modified crystallization processes can be employed as second stage of the hybrid plant. In this study, two versions are discussed: agitated thin-film evaporators and a modified MSF-process employing oil as a heat-carrier.

Cost figures for the total process will be given and the sensibility of the fresh-water-price to variations of the main parameters like capacity, fuel price etc. will be discussed.     

Flocculation,precipitation, sedimentation and flotation for use as pretreatment stages for brackish water and seawater in desalination plants

The increased application of ion exchange and membrane processes for producing drinking water from qualitatively poor sources of raw water necessitates the use of advanced mechanical and chemical technologies as well as combinations of these. Our immediate objectives are as follows: (a) Use of precipitation and flocculation reactions for removing inorganic and organic matter; (b) separation of the suspension by using flotation and sedimentation; (c) application of these processes in compact units to minimize investment costs, and (d) inclusion of sludge treatment in water processing using mechanical techniques of dehydration.     

Metabolic effects of drinking brackish water

Brackish water in the Arava Rift Valley in Southern Israel has a high sulphate and magnesium content. The inhabitants who drink this water have hypocalcaemia and hyperphosphataemia suggestive of parathyroid hypofunction. They also have a low urinary pH, massive urinary sulphate excretion, and a compensated metabolic acidosis. It is suggested that the low urinary pH may be one of the reasons for the high incidence of uric nephrolithiasis in the region.     

Desalination of brackish water by electrodialysis

The performance of an electrodialysis unit comprising interpolymer type cation and anion-exchange membranes developed in this institute in single-stage and two-stage operation for desalting of brackish waters having different total dissolved solids has been studied highlighting the energy requirement and pressure drop under different conditions. For higher salinity waters, a two-stage reduction is advantageous with lower power requirements and power index. The results will be useful for design and installation of ED plants in brackish water sectors.     

Characteristics of RO foulants in a brackish water desalination plant

This study identified the membrane fouling of a two-stage RO process of the Bai-sha brackish water desalination plant facing serious fouling problems. Two membrane modules, one from each stage, were autopsied and diagnosed for the cause for the failure of the RO system. Different morphologies were exhibited on the fouled membrane. Results suggested that the fouling on the first-stage membrane tended to be organic and biological, while that on the second-stage membrane appeared to be scaling. Higher than 85% of the foulants on the first stage membrane were organic substances in opposed to the 5 to 8% of those on the second stage membrane. However, the total organic matter on the second stage membrane was more than that on the first stage one. The thick layer of scalants on the surface of the second-stage membrane was identified to be calcium carbonate of which the crystal was clearly seen in the SEM images. The scaling was thickest at the outlet of the membrane. Huge amount of microbes were found on both membranes. The FTIR results also suggested the existence of extracellular polymeric substance (EPS) on the first stage membrane. This study recommended that the recovery rate, pH and the potential for bio-fouling should be defined at the real operation.     

Desalting 36,000 ppm well water with electrodialysis — a 5-year report

The author reported on the design and initial operation of this unidirectional electrodialysis plant in July 1977. The 36,000 ppm TDS well water is saturated with calcium sulfate and contains high levels of hydrogen sulfide (reported as high as 190 ppm). The 42,000 USGPD plant has now been in service for nearly 5 years and has never failed to provide the potable water needs of the desert camp that it serves.The operation of the pretreatment section of the plant has been modified to reduce the amount of lime fed to the solids contact clarifier thereby reducing the quantity of acid required for pH reduction of the feed water.The only major modification to the electrodialysis portion of the plant has been the installation of new type anion membranes. The membrane stacks are now primarily equipped with two types of anion membranes, both of which operate at a lower electrical resistance and higher ion transfer efficiency. The result of these more efficient anion membranes is a lower power consumption and higher production rate. Improvements to the electrode system have resulted in continuous membrane stack operating periods of over 6000 hours between disassemblies.Equipment to increase the capacity of the plant by 50% is scheduled for installation and start-up in 1981.     

Reverse osmosis in the desalination of brackish water and sea water

To make RO an economical process, plant and operating costs have been reduced by developing compact modules, led by polyamide hollow fibre modules which recover energy from the reject when desalinating highly saline brackish water and seawater. Such plants only start to pay their way at product rates of around 400m³ /d +. Energy costs for desalination systems with lower capacities can also be reduced considerably by operating the RO plants at conversion rates of more than 30%. To what extent the required higher conversion rates can be obtained for a particular application depends on concentration of scales-forming content matter (calcium sulphate, strontium sulphate, barium sulphate and calcium carbonate), salt content of the raw water, concentration of fouling substances such as iron, manganese, anorganic and organic matter, risk of biological growth due to algae, shells and bacteria. The scope and type of conditioning and pre-treatment are based on these factors.     

Evaluation of an ion exchange system regenerated with seawater for the increase of product recovery of reverse osmosis brackish water plant

An experimental ion exchange unit was operated on the Red Sea shore. Softening of the reject containing 1,400 ppm calcium from a nearby RO brackish water plant was performed using seawater as regenerant. The ex- perimental results reported show that the calcium concentration in the softened reject was reduced to a level which enables further RO desalting of the reject at 50% product recovery. A preliminary economic evaluation of 4,000m³/day RO plant indicates that desalting of softened reject would be more economically advantageous than the continued operation of the existing thermal seawater desalting plants and should precede the commercial RO seawater desalting at this location.     

Optimizing design and cost of seawater reverse osmosis systems

The influence of design parameters, such as raw water temperature and total dissolved solids content (TDS), design pressure, and recovery, on total unit cost for the production of desalinated water from the Arabian Gulf in Saudi Arabia by means of reverse osmosis is presented for plant capacities ranging from 75,000 m³/d to 700,000 m³/d. It is concluded that total unit water cost is significantly influenced by raw water TDS, design pressure and design recovery. It is recommended to investigate the feasibility of operation at increased pressure. Finally, total water costs for reverse osmosis desalination are presented also as a function of salinity, with TDS levels ranging from 3000 mg/l to 55,000 mg/l.     

电渗析苦咸水淡化技术研究进展

电渗析苦咸水淡化技术具有脱盐效果好、成本较低、绿色环保等优点,但存在制膜工艺繁琐、传质模型不够精确、能效有待提升等问题。本文首先分析了苦咸水电渗析用离子交换膜的制备及改性方法,对膜材料存在的问题进行了探讨。综述对比了苦咸水电渗析在简化模型、理论模型、半经验模型方面的原理及最新进展,系统总结了常规苦咸水电渗析过程的运行方式和工艺优化策略,并进一步介绍了以新型电去离子、冲击电渗析、可再生能源驱动电渗析为代表的新型电渗析过程在苦咸水淡化方面的原理及应用。在此基础上,提出了今后的研究方向集中于降低制膜成本、优化传质模型、探究集成膜法淡化工艺以及新型电渗析过程等方面。     

Desalting sea water to less than 4 ppm by electrodialysis

In designing a continuous (single pass) electrodialysis plant to desalt water from a sea water salinity of 35,000 ppm to less than 4 ppm, or approximately 10,000 fold reduction in concentration, the number and mix of hydraulic and electrical stages are key design variables to maximize the cut achieved by each electrodialysis stack and therefore to minimize the number of stacks in the plant. The total number of stages in the plant and the flow rate per stage determine the plant's specific production while the pressure drop per stage sets the requirement for interstage pumping. The number of electrical stages limits the total current density applied and also determines the specific energy consumption of the plant. The design analysis is applied, using experimental data, to a plant application requiring minimum investment and simplified plant operation.     

Conceptual design and cost study for a dual-purpose nuclear-electric reverse osmosis seawater conversion plant

This paper presents the results of a study to develop a conceptual design, and cost estimate for a 25 million gallon per day seawater reverse osmosis desalting plant operating at both Caribbean and Persian Gulf sites. The plants operate in conjunction with a 1000 MWe nuclear power plant. Four seawater membrane manufacturers were supplied with feedwater analyses and a simplified cost estimating procedure so that they could recommend an optimum membrane system. From this information, plant designs and cost estimates were developed. For both sites, a two-stage system was selected for the conceptual cost estimate. The product water cost was determined, based- upon 1978 construction costs, for both the Caribbean, and Persian Gulf sites. In addition, areas of potential cost reduction were discussed.     

Optimal design of an electrodialysis brackish water desalination plant

This paper considers the optimal design and operation of electrodialysis (ED) desalination plants. In general an ED plant aims to produce potable water from a high salinity source, like brackish water or high salinity water. The system is modelled mathematically as mixed-integer non-linear programming (MINLP) optimization problem, determining the number of desalination stages, the membrane area, the total required energy so as to minimise the total annualised cost of the investment accounting for both infrastructure and operating costs. Two examples from the literature illustrate the applicability of the proposed approach and evaluate the quality of the results obtained.     

RO membrane autopsy of Zarzis brackish water desalination plant

Tunisia, located in a semi-arid zone, has limited water resources. The shortage of good water quality in particular at the south regions required a brackish water desalination to supply these regions with potable water. Zarzis desalination plant, working since 1999, has revealed difficulties related to the loss of membrane performances. In the aim to determine the reason of membrane fouling, foulant layer were analysed. The membrane autopsy has achieved by different methods, such as TOC (total organic carbon) measurement, SEM (scanning electron microscopy), AFM (atomic force microscopy), FTIR (fourier transform infrared spectroscopy) analysis, diffraction by X-ray. Results show that the foulant layer composed mostly of SiO₂, clay, organic matter (polysaccharide, protein), CaSiO₃, Fe₃O₄, AlPO₄, and CaSO₄. The characteristics bonds obtained by IR indicate the presence of polysaccharides and proteins that constitute a source for further microbiological growth; this is the problem of biofouling. The metallic elements results of corroded stainless steel and internal coating of cartridges filter that are damaged by the silica particle rejected by sand filters. The scale of CaSO₄ and CaSiO₃ deposition is owing to the bad antiscaling efficiency. The results are presented and discussed in the light of new trends in material.     

Optimization of fluoride removal from brackish water by electrodialysis

The study showed that desired potable water can be easily obtained by electrodialysis from fluoride-rich brackish water. Studies have been performed to defluoridate brackish water containing 3000 ppm of total dissolved solids (TDS) and 3 ppm of fluoride using electrodialysis. The behaviour of water parameters (ion contents, TDS, pH, total hardness) with electrodialysis parameters (duration, flow rate, temperature, voltages) is followed. Optimal operational conditions for obtaining desired potable water have been proposed.     

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

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.