Reverse-osmosis recovery system

Mohamed ES, Papadakis G, Mathioulakis E and Belessiotis V (2006), An experimental comparative study of the technical and economic performance of a small reverse osmosis desalination system equipped with an hydraulic energy recovery system , Desalination, 194,239-250. 

Membrane Pervaporation Since 1987, membrane pei vapora-tion has become widely accepted in the CPI as an effective means of separation and recovery of liquid-phase process streams. It is most commonly used to dehydrate hquid hydrocarbons to yield a high-purity ethanol, isopropanol, and ethylene glycol product. The method basically consists of a selec tively-permeable membrane layer separating a liquid feed stream and a gas phase permeate stream as shown in Fig. 25-19. The permeation rate and selectivity is governed bv the physicochemical composition of the membrane. Pei vaporation differs From reverse osmosis systems in that the permeate rate is not a function of osmotic pressure, since the permeate is maintained at saturation pressure (Ref. 24). 

The task of synthesizing an optimal RON can be stated as follows For a given feed flowrate, Qf. and a feed concentration, Cp. it is desired to synthesize a minimum cost system of reverse osmosis modules, booster pumps and energy-recovery turbines Chat can separate the feed into two streams an environmentally acceptable permeate and a retentate (reject) stream in which the undesired species is concentrated. The permeate stream must meet two requirements ... 

Reverse osmosis for concentrating trace organic contaminants in aqueous systems by using cellulose acetate and Film Tec FT-30 commercial membrane systems was evaluated for the recovery of 19 trace organics representing 10 chemical classes. Mass balance analysis required determination of solute rejection, adsorption within the system, and leachates. The rejections with the cellulose acetate membrane ranged from a negative value to 97%, whereas the FT-30 membrane exhibited 46-99% rejection. Adsorption was a major problem some model solutes showed up to 70% losses. These losses can be minimized by the mode of operation in the field. Leachables were not a major problem. 

The cost for companies in terms of cash, possibly scarce water resources, ever tightening discharge limitations and perpetual liability for landfilled waste, requires that firms seek other solutions. The ideal solution is to develop economic point of use recycling and reuse systems. A technology that offers the potential for on-site recovery of a broad range of electronics and metal finishing applications is Advanced Reverse Osmosis (ARO). 

A conventional wastewater treatment system with an average flow rate of 160,000 gpd produces effluent suitable for NPDES discharge. Metal hydroxide sludges are dewatered in a 15 cu. ft filter press producing more than one half ton of filter cake per day. The filter cake is further dewatered in a 7 cu. ft, batch-type sludge dryer. Based upon recommendations by their consultant, the firm also uses the sludge dryer to dehydrate nickel strip solutions. Two reverse osmosis systems are used for partial nickel recovery. Trivalent chromium is recovered by drag-out control and evaporation. 

Point-of-Source Recovery - in certain circumstances, it is possible to utilize reverse osmosis to effect a "zero discharge" electroplating rinse water recovery system. The rinse water from the first rinse is pumped to a reverse osmosis system that concentrates the salts and directs them back to the plating bath. The purified rinse water (permeate) is directed to the last rinse, and neither solute nor solvent is lost. in the united States there are approximately 150 reverse osmosis systems operating in this manner on nickel baths and 12 on acid copper. There are also a few installations operating on copper cyanide, hexavalant chrome, and acid zinc. 

The current ultrafiltration market is approximately US 200 million/year but because the market is very fragmented, no individual segment is more than about US 10-30 million/year. Also, each of the diverse applications uses membranes, modules, and system designs tailored to the particular industry served. The result is little product standardization, many custom-built systems, and high costs compared to reverse osmosis. The first large successful application was the recovery... 

Three different membrane processes, ultrafiltration, reverse osmosis, and electrodialysis are receiving increased interest in pollution-control applications as end-of-pipe treatment and for inplant recovery systems. There is no sharp distinction between ultrafiltration and reverse osmosis. In the former, the separation is based primarily on the size of the solute molecule which, depending upon the particular membrane porosity, can range from about 2 to 10,000 millimicrons. In the reverse-osmosis process, the size of the solute molecule is not the sole basis for the degree of removal, since other characteristics of the... 

A reverse osmosis unit has been proposed for the recovery of organic acids [4]. The plant under consideration was assumed to have a cellulose feed rate of 44,000 kg (dry) of municipal solid waste per hour. The flow to the unit consisted of 3 % short-chain organic acids (usually referred to as VFA for volatile fatty acids). It was also estimated that the unit would concentrate 36,500 kg of VFA to a 25 % solution. The total estimated capital cost for the reverse osmosis unit was 26.5 million dollars, assuming a membrane life time of 2 years. This estimated price was 0,378 per kg of concentrate leaving the system. 

It is to this topic of solute preferential sorption in reverse osmosis that this paper is dedicated. Specifically, this discussion will involve a description of solute preferential sorption, an overview of the literature in the area, and finally a presentation of some recent work on the removal of aromatic hydrocarbons from water. The significance of this work is at least two-fold. From a practical point of view the classes of solutes which demonstrate preferential attraction to the membrane material tend to be organic compounds and the removal and recovery of these solutes from water is environmentally and economically important. From a theoretical point of view an understanding of the phenomena involved is essential to the achievement of a fundamental description of the RO process. Although this paper deals solely with aqueous solutions and cellulose acetate membranes, it Is important to recognize that the concepts discussed can be extended to Include other membrane materials and non-aqueous systems. 

A wastewater stream at 25 °C is to be treated using a reverse osmosis system. The wastewater has a flowrate of 50 gal/min and a concentration of 5000 mg/L of sodium chloride. A 75% recovery rate is required. A reverse osmosis vendor has recommended a membrane with the following characteristics ... 

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