Rapid, online detection of enterococci and of the total microbial activity in water

Technology

Certain microorganisms in drinking water, surface water and cooling-tower water (e.g., faecal pathogens, Legionella pneumophila) can present a threat to public health. For this reason the microbial quality of drinking water, surface water and recreational water is monitored – for instance, by determining the number of enterococci and Escherichia coli as indicators of faecal contamination. Drinking water and cooling water are monitored, among others, through an analysis of the total bacteria numbers as an indicator of the extent of the growth in the system.

The conventional microbial culture methods are however relatively lengthy: one day (E. coli), two days (enterococci) or three days (total bacterial count). The drawback of all these methods is that they still require the intervention of a sample taker, analyst or other technician. Because of the lengthiness of these methods, and the fact that the measurements can’t be conducted fully automatically and online, there has long been a desire on the part of the drinking water companies, waterboards and industrial water users for rapid methods to determine microbial water quality without the need for a technician’s intervention. It is expected that such methods would allow for the more rapid detection of microbial water-quality problems and, after actions are taken, for the more rapid determination of whether the water is safe again. This would both increase water quality and cut costs.

Currently, the rapid methods for the detection of E. coli are only applied to a limited degree, because it is the culture of enterococci that now constitutes the rate-determining step. To address this, a rapid detection method for enterococci was developed in a previous TKI project. The initial results show that the measurement principle works, but further development is needed.

The drawbacks of the current monitoring (culture method) of the total number of bacteria in water are that it: (i) detects only ~1-10% of the bacteria present, (ii) takes one to three days to produce results, and (iii) only provides a snapshot in time. The BACTcontrol and the Grundfos BACMON are new, rapid, online methods to determine total bacteria numbers. These methods are possibly suitable for the online monitoring of any microbial disturbances in drinking water and cooling water, and/or of the effect of control measures on water quality. However, before they can be reliably implemented, supplementary experimental research is needed.

Challenge

This project intends to develop, for several water types, a rapid detection method for enterococci (drinking water and surface water) and of total microbial activity (drinking water, groundwater, surface water and cooling-tower water). The enterococci analysis and the total microbial activity will be done using the BACTcontrol system; the Grundfos BACMON system will only be used to determine the total microbial activity. These systems will be compared with the current methods and then validated. They can subsequently be applied in water practice as early-warning systems for contaminations and/or bacterial growth in water.

Solution

At the end of the project the enterococci analysis will have been further developed and optimised, for subsequent use in water practice. The two online methods to determine total microbial populations will have been compared in various water types with other biomass parameters, thereby providing a reliable underpinning of the performance characteristics of both methods.