Jean Claude Block

Indigenous bacterial inocula for measuring the biodegradable dissolved organic carbon (BDOC) in waters

A collaborative study was carried out in order to compare the biodegradable dissolved organic carbon (BDOC) analysis using different indigenous mixed bacterial populations as inocula. The variables examined in the study were the laboratories, the water samples (raw, ozonated or finished water), the origin of the inoculum: suspended bacteria from river waters and attached bacteria onto sand taken from drinking water treatment plants. Variances associated with individual components of this study were isolated: the laboratories represented the highest source of variation (56.6–70.7%), while the inoculum origin contribution to the increase of variance is lower (12–26%). As a conclusion, indigenous mixed bacterial populations (suspended or attached bacteria) may be used reliably as standard inocula in BDOC determinations without introducing excessive variability.

Dynamic modeling of bacteria in a pilot drinking-water distribution system

Computer modeling can be a useful tool in understanding the dynamics of bacterial population growth. Yet, the variability and complexity of biological systems pose unique challenges in model building and adjustment. Recent tools from Bayesian statistical inference can be brought together to solve these problems. As an example, the authors modeled the development of biofilm in an industrial pilot drinking-water network. The relationship between chlorine disinfectant, organic carbon, and bacteria concentrations was described by differential equations. Using a Bayesian approach, they derived statistical distributions for the model parameters, on the basis of experimental data. The model was found to adequately fit both prior biological information and the data, particularly at chlorine concentrations between 0.1 and 2 mg/liter. Bacteria were found to have different characteristics in the different parts of the network. The model was used to analyze the effects of various scenarios of water quality at the inlet of the network. The biofilm appears to be very resistant to chlorine and confers a large inertia to the system. Free bacteria are efficiently inactivated by chlorine, particularly at low concentrations of dissolved organic carbon.