Daily Archives: October 5, 2014

Vacuum Membrane Distillation for Drinking Water Production

Naidu, Gayathri, Jeong, Sanghyun, Choi, Yongjun, Jang, Eunkyung, Hwang, Tae-Mun, Vigneswaran, Saravanamuthu.Application of vacuum membrane distillation for small scale drinking water production. Desalination 2014-12-01 354:53-61 

This study evaluated the applicability of a modified design vacuum enhanced-multi effect membrane distillation (V-MEMD) for drinking water production with feed solution containing NaCl and CaSO4. The applicability was studied in terms of flux, scale formation and ease of cleaning. A slight flux decline (18–20%) was observed with loosely deposited crystals in the membrane module during the 920min of the operation. Larger formation of crystal (volume weighted mean size, D[4,3]) was observed in the final feed brine (D[4,3]brine feed=455.96μm) compared to that inside the module (D[4,3]brine module=62.68μm). The loose crystal deposition was attributed to the absence of hydraulic pressure, low feed temperature, high turbulence (Re=5665.6) and short membrane retention time (21.6s). The crystal formation in the membrane module, D[4,3]brine module increased with reduced permeate side vacuum and lower feed velocity. Periodic DI water flushing was found to be efficient to remove the scaling. The feed component mass balance showed that most of the components were able to be removed with 2L DI water flushing. A 70% recovery ratio was projected for a scaled-up unit, highlighting the suitability of the V-MEMD as a small scale system for drinking water production.

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Chronic Effects Benchmark for Freshwater Aquatic Life

McPherson CA, Lee DH, Chapman PM. Development of a fluoride chronic effects benchmark for aquatic life in freshwater. Environmental toxicology and chemistry. 2014 Aug 16. doi: 10.1002/etc.2724.

Canada has an interim water-quality guideline for fluoride for protection of freshwater aquatic life that dates from 2002, and 1 Canadian province has a different interim water-quality guideline for fluoride that dates to 1995. The United States does not have a national benchmark for fluoride in freshwater, and only 1 US state has such a benchmark. There are no other national or regional benchmarks for fluoride chronic toxicity in freshwater. In the present study, available data on the acute and chronic toxicity of fluoride to freshwater aquatic life were compiled and reviewed. Acute toxicity was reported to occur at concentrations ranging from 11.5 to >800 mg/L fluoride (F ). The majority of chronic effects occur at concentrations between 1.8 mg/L and 195 mg/L. A total of 10 chronic studies representing 16 species (5 fish, 7 invertebrates, and 4 algae/aquatic plants) were used to derive a chronic effects benchmark of 1.94 mg/L F , applying the species sensitivity distribution approach.