Some factors influencing the proportion of periplasmic hepatitis B virus pre-S2 antigen in the recombinant yeast Hansenula polymorpha.

A central composite design (CCD) was used to evaluate, for the purpose of future process optimization, the influence of pH, yeast extract and ammonium chloride concentrations on the proportion of periplasmic hepatitis B pre-S2 antigen in the recombinant yeast Hansenula polymorpha. Each factor was tested at five levels, and a second order polynomial model for the proportion of periplasmic antigen was fitted to the treatment combinations. pH showed the greatest effect: the proportion of periplasmic antigen was greatly increased at the higher pH levels. At the higher pH levels used, the proportion of periplasmic antigen was enhanced by a high concentration of ammonium chloride. Additional experiments have confirmed both the validity of the selected model and the optimal conditions found. A significant correlation was found between the proportion of periplasmic antigen and the total yield of antigen. These results indicated that it should be possible to modulate the distribution of the pre-S2 antigen between the periplasm and the cytoplasm of the yeast

Characteristics and Treatment of the Dental Waste Water Stream

Dental amalgam consists of approximately equal parts mixture of metallic mercury and an alloy powder consisting of silver, tin, copper and zinc. Amalgam has been used extensively as a tooth filling material, accounting for 75% of posterior restorations. The waste material from dental offices generated during restorative dental procedures contains amalgam. The uncontrolled discharge of this waste into the sewer system from a large number of dental units (i.e. dental clinics), will increase the mercury load to treatment facilities and could eventually contribute higher potential mercury exposure as well. The main objective of this project was to characterize the properties of the dental waste (DW) stream.published or submitted for publicatio

Development, analysis and comparison of models for respirometric biodegradation data

When continuous monitoring devices such as the electrolytic respirometer are used for performing biodegradation experiments, cumulative data are acquired. The structure of these observations limits the reliable application of existing methodologies for analyzing cumulative respirometric biodegradation trends, because the resulting error terms are likely to be highly autocorrelated. To overcome these limitations it is proposed that the Oxygen Uptake Rate (OUR) should be used as the data source for further analysis, because the dependence of the error terms is then removed. To model uniform reaction rate respirometric biodegradation OUR data trends, 1st and 2nd-order OUR models are proposed. Theoretical and practical assessment of these models in comparison with their cumulative counterparts indicates that (a) they are likely to have improved nonlinear behaviour, (b) their parameters will have more reliable confidence interval estimates, and (c) the optimal duration of an experiment performed to estimate the OUR model parameters is shorter compared to that required for estimating similar parameters in the case of cumulative biodegradation data. During respirometric biodegradation studies, data trends with distinct microbial growth periods often appear as well. In order to describe such observations a new diphasic OUR model is proposed, which provides valuable information for each phase in the form of 1st-order reaction rate coefficients and the duration of the first phase. Application of this model to a number of data cases indicates that this model can be regarded as a practical alternative for modelling diphasic respirometric data trends. A similar conclusion was drawn for a proposed two-stage respirometric biodegradation model. In the present study an approach is also suggested for performing statistical comparisons between biodegradation curves which have been obtained under different experimental conditions. This approach is based on the proposed OUR models,