Theoretical considerations and modeling of chemical inactivation of microorganisms: inactivation of Giardia Cysts by free chlorine.

Chemical inactivation of microorganisms is a common process widely employed in many fields such as in treatment of water, preservation in food industry and antimicrobial treatments in healthcare. For economy of applications and efficiency of treatment establishment the minimum dosage of breakpoint in the chemical application becomes essential. Even though experimental investigations have been extensive, theoretical understanding of such processes are demanding. Commonly employed theoretical analyses for the inactivation of microorganisms and depletion of chemicals include kinetics expressing the rates of depletion of chemical and microorganisms. The terms chemical demand (x) and specific disinfectant demand (alpha) are often used in theoretical modeling of inactivation. The value of specific disinfectant demand (alpha) has always been assumed to be a constant in these models. Intracellular concentration built up within the cells of the microorganisms during inactivation could lead to possible weakening effects of microorganisms thereby requiring lower doses as disinfection proceeds makes the assumption of constant alpha inaccurate. Model equations are formulated based on these observations co-relating the parameters alpha and x with a progressive inactivation (N/N(0)). The chemical concentration (C) is also presented in terms of the inactivation time (t) and the survival ratio (N/N(0)) for given pH and temperature conditions. The model is examined using experimentally verified Ct data of Giardia Cysts/chlorine system. The respective values of x for different survival ratios were evaluated from the data using MatLab software. Proposed model correlating for the disinfectant demand (x) with the survival ratio (N/N(0)) fits satisfactorily with those evaluated from data. The rate constants for different pH and temperature conditions are evaluated which showed compatibility with the Arrhenius model. The dependence of frequency factors with pH indicated compatibility with accepted models. The Ct values regenerated with the kinetic data shows a very accurate fit with published data.

Continuous biosynthesis of biodiesel from waste cooking palm oil in a packed bed reactor: optimization using response surface methodology (RSM) and mass transfer studies.

This study aimed to develop an optimal continuous procedure of lipase-catalyzes transesterification of waste cooking palm oil in a packed bed reactor to investigate the possibility of large scale production further. Response surface methodology (RSM) based on central composite rotatable design (CCRD) was used to optimize the two important reaction variables packed bed height (cm) and substrate flow rate(ml/min) for the transesterification of waste cooking palm oil in a continuous packed bed reactor. The optimum condition for the transesterification of waste cooking palm oil was as follows: 10.53 cm packed bed height and 0.57 ml/min substrate flow rate. The optimum predicted fatty acid methyl ester (FAME) yield was 80.3% and the actual value was 79%. The above results shows that the RSM study based on CCRD is adaptable for FAME yield studied for the current transesterification system. The effect of mass transfer in the packed bed reactor has also been studied. Models for FAME yield have been developed for cases of reaction control and mass transfer control. The results showed very good agreement compatibility between mass transfer model and the experimental results obtained from immobilized lipase packed bed reactor operation, showing that in this case the FAME yield was mass transfer controlled.

Relevance of diffusion through bacterial spore coats/membranes and the associated concentration boundary layers in the initial lag phase of inactivation: a case study for Bacillus subtilis with ozone and monochloramine.

Disinfectants are generally used to inactivate microorganisms in solutions. The process of inactivation involves the disinfectant in the liquid diffusing towards the bacteria sites and thereafter reacting with bacteria at rates determined by the respective reaction rates. Such processes have demonstrated an initial lag phase followed by an active depletion phase of bacteria. This paper attempts to study the importance of the combined effects of diffusion of the disinfectant through the outer membrane of the bacteria and transport through the associated concentration boundary layers (CBLs) during the initial lag phase. Mathematical equations are developed correlating the initial concentration of the disinfectant with time required for reaching a critical concentration (C*) at the inner side of the membrane of the cell based on diffusion of disinfectant through the outer membranes of the bacteria and the formation of concentration boundary layers on both sides of the membranes. Experimental data of the lag phases of inactivation already available in the literature for inactivation of Bacillus subtilis spores with ozone and monochloramine are tested with the equations. The results seem to be in good agreement with the theoretical equations indicating the importance of diffusion process across the outer cell membranes and the resulting CBL's during the lag phase of disinfection.