Membrane distillation plant effluent

Membrane Distillation (MD) is a hybrid thermal-membrane process that could be applied in produced water volume reduction applications while simultaneously augmenting sustainable water production in Qatar. A consortium of ConocoPhillips - Global Water Sustainability Center (GWSC), Qatar University (QU) and Qatar Electricity Water Company (QEWC), was formed to assess the suitability of MD to treat high salinity brines from thermal desalination plants similar salinity levels could be found in produced water. The pilot scale results showed that MD could operate at 50% recovery and achieve a stable flux of 5 L/(m. h) at when treating thermal brine at 70,000 mg/L TDS. The effluent produced contained < 10 mg/L TDS. 

Constmction of new power plants in the coal region of the western United States presents serious problems in states whose laws dictate zero effluent. In these plants, cooling-tower water withdrawn from rivers cannot be returned to them. In these situations, cooling-tower effluent is purified by distillation (vapor-compression plants have predominated) and by a combination of distillation and membrane technology. The converted water then is used as boiler feedwater the plant blowdown (effluent) is evaporated from open-air lined pools, and pool sediment is periodically buried back in the coal mine with the flue ashes. 

Ke and Regier [71] have described a direct potentiometric determination of fluoride in seawater after extraction with 8-hydroxyquinoline. This procedure was applied to samples of seawater, fluoridated tap-water, well-water, and effluent from a phosphate reduction plant. Interfering metals, e.g., calcium, magnesium, iron, and aluminium were removed by extraction into a solution of 8-hydroxyquinoline in 2-butoxyethanol-chloroform after addition of glycine-sodium hydroxide buffer solution (pH 10.5 to 10.8). A buffer solution (sodium nitrate-l,2-diamino-cyclohexane-N,N,N. AT-tetra-acetic acid-acetic acid pH 5.5) was then added to adjust the total ionic strength and the fluoride ions were determined by means of a solid membrane fluoride-selective electrode (Orion, model 94-09). Results were in close agreement with and more reproducible than those obtained after distillation [72]. Omission of the extraction led to lower results. Four determinations can be made in one hour. 

Despite of some technical and process limitations, membrane techniques are very useful methods for the treatment of different types of effluents. They can be applied in nuclear centers processing low- and intermediate-level liquid radioactive wastes or in fuel reprocessing plants. All the methods reported in the chapter have many advantages and can be easily adapted for actual, specific needs. Some of them are good pretreatment methods the other can be used separately as final cleaning steps, or can be integrated with other processes. Membrane methods can supplement or replace techniques of distillation, extraction, adsorption, ion exchange, etc. Evaluation of membrane processes employed for liquid radioactive waste treatment is presented in Table 30.17. 

Hybrid processes are also being considered more seriously than ever [84]. There are hybrid processes, such as pretreatment by UF and NF to provide RO feedwater and RO treatment of boiler water for the distillation process, and those are already in practice. Combining RO with the emerging membrane separation processes such as MD and forward osmosis (FO) will become more important to decrease the amount of effluent from the RO desalination plant. As drinking water production by the desalination of seawater and brackish water increases, iuCTease in the quantity of salty RO effluent will become more of environmental concern. The RO hybrid process with MD and FO may become the answer to solve the problem. 

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