Improved calcium sulfate recovery from a reverse osmosis retentate using eutectic freeze crystallization.

A novel low temperature crystallization process called eutectic freeze crystallization (EFC) can produce both salt(s) and ice from a reverse osmosis (RO) stream by operating at the eutectic temperature of a solution. The EFC reject stream, which is de-supersaturated with respect to the scaling component, can subsequently be recycled back to the RO process for increased water recovery. This paper looks at the feasibility of using EFC to remove calcium sulfate from an RO retentate stream and compares the results to recovery rates at 0 and 20 °C. The results showed that there was a greater yield of calcium sulfate obtained at 0 °C as compared with 20 °C. Operation under eutectic conditions, with only a 20% ice recovery, resulted in an even greater yield of calcium sulfate (48%) when compared with yields obtained at operating temperatures of 0 and 20 °C (15% at 0 °C and 13% at 20 °C). The theoretical calcium recoveries were found to be 75 and 70% at 0 and 20 °C respectively which was higher than the experimentally determined values. The EFC process has the added advantage of producing water along with a salt.

Antimicrobial susceptibility of Neisseria gonorrhoeae isolated from maternal and child infections in Harare. The Puerperal Sepsis Study Group.

The in vitro antimicrobial susceptibilities of 29 PPNG and 26 non-PPNG isolated from women and neonates in Zimbabwe were investigated. There was evidence of chromosomal resistance to penicillin in many of the non-PPNG strains, with over 60 percent of all isolates having an MIC greater than 1 mg/litre. Reduced susceptibility to tetracycline was evident in about 20 percent of PPNG strains, particularly those containing the 4.4Md plasmid, while over 10 percent of non-PPNGs showed partial resistance to cefuroxime. Less than half of the strains were susceptible to erythromycin (MIC50 greater than 0.5 mg/litre) while all were susceptible to kanamycin and spectinomycin. PPNG containing the 3.2 Md plasmid were very susceptible to thiamphenicol (MIC50 0.25 mg/litre), while other strains were only moderately susceptible (MIC50 2 mg/litre). These findings suggest that penicillin, tetracycline or erythromycin may no longer be relied on for the successful treatment of gonococcal infection in women and babies. Thiamphenicol, Blactamase stable cephalosporins, kanamycin or spectinomycin may be useful alternatives, effective against most strains of both PPNG and non-PPNG. Continued surveillance is recommended to monitor changes in this susceptibility pattern.