P. Niquette

Impacts of pipe materials on densities of fixed bacterial biomass in a drinking water distribution system

Densities of fixed bacterial biomass were measured on different pipe materials (PVC, PE, cemented steel, asbestos-cement, cemented cast iron, tarred steel and grey iron) incubated in drinking waters from different sources (ground waters and a surface water) which had different characteristics (temperature, concentration of residual oxidant and content of biodegradable organic matter). Results showed that the densities of bacterial biomass fixed on plastic-based materials (PE and PVC) were the lowest. Densities of bacterial biomass fixed on gray iron were from 10 to 45 times higher than those measured on plastic-based materials. Cement-based materials had intermediate values. Pairs of cement and PVC coupons were incubated at 15 different locations in a distribution system, and there was a strong correlation between the amount of fixed bacterial biomass on these coupons, with the cement containing 2.6 times more biomass.

Bacterial Dynamics in the drinking water distribution system of Brussels

Water samples and pipe coupons were collected from the Brussels drinking water distribution system (DS). A treated surface water and various groundwaters feed this DS. Parameters related to bacterial regrowth have been measured on these samples: temperature, concentrations of free residual chlorine, concentration of biodegradable dissolved organic carbon (BDOC), abundance of suspended bacteria, densities of fixed bacteria and levels of bacterial activity. Results showed that groundwaters were less susceptible to favor bacterial regrowth in the DS pipes. Treated surface water and mixed waters had the highest potential of bacterial regrowth in the DS dead ends. Results also showed that the potential regrowth induced by the distribution of a treated surface water could be reduced if: (1) the BDOC levels were below 0.25 mg C/l at the outlet of the surface water treatment plant; (2) a significant free chlorine residual was present within the whole DS. Second-stage biological filtration using granular activated carbon is now under construction at the surface water treatment plant feeding a part of this DS. This treatment implementation should reduce BDOC levels and chlorine demand of the treated surface water and will further reduce the slight regrowth phenomena observed in this DS.

Biodegradable organic matter removal in biological filters : Evaluation of the CHABROL model

The implementation of biological filtration on granular activated carbon under various operating conditions has revealed that biodegradable organic matter (BOM) removal performance is not easily predicted. In this context, the statistical analysis of the differences between experimental data and data calculated by a deterministic model may provide insight into the source of prediction errors. The CHABROL model, developed by Billen et al., (1992), relates BOM consumption to biomass densities in order to predict BOM removal profiles in biological activated carbon filters (BAC) and rapid sand filters. This work presents the results of testing the CHABROL model using a large database from pilot and full-scale filters located in two Canadian cities: Laval and Montreal. This database includes data from two different water sources and three biological filtration configurations (direct filtration, first-stage dual-medium sand-BAC filters and second-stage mono-medium BAC filters). Since nearly half of all experimental data were obtained at very low temperatures (≤1°C), the impact of prolonged acclimation to very cold temperatures was investigated to ensure accurate prediction by the CHABROL model. Experimental results have shown that modifications in the CHABROL model have to be made to account for the acclimation to very cold temperature and to prevent under estimations of the BDOC removals. The results of the model testing show overall satisfactory results in the ability to predict BDOC removals in various types of filters, except for the sampling campaigns completed just prior to backwash. This comparison shows the interest of using a predictive model to predict performance in dynamically operated filters which may be used for design and operation.

Evaluating the Performance of Continuous Flow Biofilm Reactors for the Rapid Determination of Biodegradable Dissolved Organic Carbon in Drinking Water

This study was undertaken to evaluate the newly developed biofilm reactor for the measurement of biodegradable dissolved organic carbon (BDOC) in drinking water. This method enables rapid BDOC determination which would be ideally suited for the dynamic measurement of treatment plant BDOC variations in cases where reactor performance is stable with changing water quality. The biofilm reactors were found to best operate at constant temperature (19–23 °C). BDOC performance was found to be unhindered in low substrate, oligotrophic waters. BDOC values obtained using a suspended-inoculum BDOC measurement technique correlated positively with biofilm reactor BDOC values, although significant scatter was observed.