Recovery of calcium carbonate from steelmaking slag and utilization for acid mine drainage pre-treatment.

The conversion of steelmaking slag (a waste product of the steelmaking process) to calcium carbonate (CaCO(3)) was tested using hydrochloric acid, ammonium hydroxide and carbon dioxide via a pH-swing process. Batch reactors were used to assess the technical feasibility of calcium carbonate recovery and its use for pre-treatment of acid mine drainage (AMD) from coal mines. The effects of key process parameters, such as the amount of acid (HCl/calcium molar ratio), the pH and the CO(2) flow rate were considered. It was observed that calcium extraction from steelmaking slag significantly increased with an increase in the amount of hydrochloric acid. The CO(2) flow rate also had a positive effect on the carbonation reaction rate but did not affect the morphology of the calcium carbonate produced for values less than 2 L/min. The CaCO(3) recovered from the bench scale batch reactor demonstrated effective neutralization ability during AMD pre-treatment compared with the commercial laboratory grade CaCO(3).

Identification of informative metabolic responses using a minibioreactor: a small step change in the glucose supply rate creates a large metabolic response in Saccharomyces cerevisiae.

In this study, a previously developed mini-bioreactor, the Biocurve, was used to identify an informative stimulus-response experiment. The identified stimulus-response experiment was a modest 50% shift-up in glucose uptake rate (qGLC) that unexpectedly resulted in a disproportionate transient metabolic response. The 50% shift-up in qGLC in the Biocurve resulted in a near tripling of the online measured oxygen uptake (qO2) and carbon dioxide production (qCO2) rates, suggesting a considerable mobilization of glycogen and trehalose. The 50% shift-up in qGLC was subsequently studied in detail in a conventional bioreactor (4 l working volume), which confirmed the results obtained with the Biocurve. Especially relevant is the observation that the 50% increase in glucose uptake rate led to a three-fold increase in glycolytic flux, due to mobilization of storage materials. This explains the unexpected ethanol and acetate secretion after the shift-up, in spite of the fact that after the shift-up the qGLC was far less than the critical value. Moreover, these results show that the correct in vivo fluxes in glucose pulse experiments cannot be obtained from the uptake and secretion rates only. Instead, the storage fluxes must also be accurately quantified. Finally, we speculate on the possible role that the transient increase in dissolved CO2 immediately after the 50% shift-up in qGLC could have played a part in triggering glycogen and trehalose mobilization.

The dissolution characteristics of calcium sulfide and utilization as a precipitation agent in acidic wastewater effluent treatment.

The dissolution characteristics of CaS in the presence of CO2 has been investigated by monitoring sulfide speciation, solution conductivity and pH during dissolution. The sulfide speciation associated with CaS dissolution was utilized for metal precipitation from acidic wastewater effluents. The mechanism involved in the dissolution process was observed to be pH-dependent, characterized by increased solution conductivity as the HS(-) species becomes dominant in solution in the form of the Ca(HS)2 complex. The replacement of HS(-) by CO3(2-) in the Ca(HS)2 complex triggered CaCO3 precipitation and H2S stripping and this was characterized by decreased solution pH and conductivity. The sulfide to total metal molar ratio was observed to have an effect on the pH and therefore sulfide speciation as well as extent of metal removal. The utilization of CaS in the treatment of acidic wastewater effluents demonstrated complete metal removal, with the potential of a pH-controlled selective metal removal and recovery.

High AIDS-related mortality among young women in rural KwaZulu-Natal.

OBJECTIVE: To establish mortality rates and cause of death in a rural community in KwaZulu-Natal. This study was conducted as part of a demographic and health survey to assess the impact of HIV infection in this community. METHODS: A cross-sectional survey was conducted between February and July 2004. The survey made use of structured questionnaires and verbal autopsies, which yielded detailed information at household level, including the demographic profile of residents, mortality rates and cause of mortality between February 2003 and February 2004. RESULTS: The overall mortality rate in this community was 2.9 deaths per 100 person-years (95% confidence interval (CI): 2.5 - 3.3 per 100 person-years). The highest mortality rate among women occurred in the 30 - 34-year age group, while among men it occurred in the 35 - 39 and > 60-year age groups. Of the 185 verbal autopsies reported, 77 deaths (42%) were attributable to AIDS. The survey revealed that women aged 20 - 24 and men aged 35 - 39 years were bearing a disproportionately large burden of AIDS-related mortality in this community. CONCLUSION: AIDS-related mortality was found to be disproportionately high in young women in this small rural community, and the majority of deaths resulted from pulmonary tuberculosis. The need to strengthen prevention and treatment efforts in this and similar settings is highlighted.

Opportunities for treating sexually transmitted infections and reducing HIV risk in rural South Africa.

AIM: This paper is a report of a study to determine the aetiological distribution of sexually transmitted infections and prevalence of human immunodeficiency virus infection in selected primary health care clinic attendees. BACKGROUND: South Africa has a high prevalence of human immunodeficiency virus and other sexually transmitted infections. Sexually transmitted infections are managed syndromically in the public sector as part of the essential nurse-driven primary care services provided at no cost to the client. METHOD: This cross-sectional study was conducted in a rural community in South Africa between September and November 2002. A total of 277 consenting women were recruited. Vulvo-vaginal swabs were collected for screening for Neisseriae gonorrheae, Chlamydia trachomatis and Trichomonas vaginalis using DNA amplification methods and Gram stain with Nugent's score for the diagnosis of bacterial vaginosis. Seroprevalence of syphilis and human immunodeficiency virus infection were determined. FINDINGS: The overall prevalence of human immunodeficiency virus in the study was 43.7% (95% confidence interval 37.6-50.0) with the prevalence in family planning clinic attendees 45.5% (95% confidence interval 38.9-52.3) and antenatal clinic attendees 33.3% (95% confidence interval 19.6-50.3). The prevalence of sexually transmitted infections amongst both the antenatal clinic and family planning attendees accounted for at least 70% of cases. Fifty per cent of women had one recognized sexually transmitted infection with 17.9% of the family planning and 14.5% of the antenatal clinic attendees having infections from two recognized pathogens. All infections were asymptomatic. CONCLUSION: Nurse-driven antenatal and family planning services provide a useful opportunity for integrating reproductive health services, human immunodeficiency virus voluntary counselling and testing and treatment of sexually transmitted infections.

MIRACLE: mass isotopomer ratio analysis of U-13C-labeled extracts. A new method for accurate quantification of changes in concentrations of intracellular metabolites.

First, we report the application of stable isotope dilution theory in metabolome characterization of aerobic glucose limited chemostat culture of S. cerevisiae CEN.PK 113-7D using liquid chromatography-electrospray ionization MS/MS (LC-ESI-MS/MS). A glucose-limited chemostat culture of S. cerevisiae was grown to steady state at a specific growth rate (mu)=0.05 h(-1) in a medium containing only naturally labeled (99% U-12C, 1% U-13C) carbon source. Upon reaching steady state, defined as 5 volume changes, the culture medium was switched to chemically identical medium except that the carbon source was replaced with 100% uniformly (U) 13C labeled stable carbon isotope, fed for 4 h, with sampling every hour. We observed that within a period of 1 h approximately 80% of the measured glycolytic metabolites were U-13C-labeled. Surprisingly, during the next 3 h no significant increase of the U-13C-labeled metabolites occurred. Second, we demonstrate for the first time the LC-ESI-MS/MS-based quantification of intracellular metabolite concentrations using U-13C-labeled metabolite extracts from chemostat cultivated S. cerevisiae cells, harvested after 4 h of feeding with 100% U-13C-labeled medium, as internal standard. This method is hereby termed "Mass Isotopomer Ratio Analysis of U-13C Labeled Extracts" (MIRACLE). With this method each metabolite concentration is quantified relative to the concentration of its U-13C-labeled equivalent, thereby eliminating drawbacks of LC-ESI-MS/MS analysis such as nonlinear response and matrix effects and thus leads to a significant reduction of experimental error and work load (i.e., no spiking and standard additions). By coextracting a known amount of U-13C labeled cells with the unlabeled samples, metabolite losses occurring during the sample extraction procedure are corrected for.

Critical evaluation of sampling techniques for residual glucose determination in carbon-limited chemostat culture of Saccharomyces cerevisiae.

In this paper, three sampling techniques for rapid quenching of cellular metabolism and subsequent separation of cells from fermentation broth are compared: (i) quick freezing of fermentation broth directly in liquid nitrogen; (ii) quenching metabolism by exposing the fermentation broth to stainless steel beads (4-mm diameter) in a filter syringe precooled to -18 degrees C; and (iii) withdrawal of the filtrate through a 0.45 microm filter attached to a syringe and a needle inserted directly into the fermentor. It was concluded that use of liquid nitrogen as a quenching method to rapidly arrest cellular metabolism, for quantitative analysis of extracellular glucose, is not a very reliable method and that the filter syringe steel beads work very well.