Biological sensors for online monitoring of drinking water pipes

Clean drinking water is vital for man. Water pipes are in permanent danger of being contaminated. In addition, drinking water supply constitutes a potential target for terrorist attacks. Thus, it is essential that threats to public health are recognized at an early stage.

The German drinking water ordinance requires regular checks for certain pathogens and chemical substances. This is normally done by taking samples and examining them in a laboratory. Standard analysis methods used are protracted and limited to certain parameters: unknown or unexpected toxic substances are therefore not detected in a timely way making these methods unsuitable for use as warning systems which can indicate the presence of chemical or biological substances at an early stage.

Objective: Online monitoring with bio-sensors

In the present project “AquaBioTox” the Fraunhofer IGB together with its project partners Berliner Wasserbetriebe (a water provider), bbe Moldaenke and the Fraunhofer IOSB are developing solutions for continuous online monitoring of drinking water pipes. The aim is to establish a biological broadspectrum sensor which reacts immediately and reliably to hazardous substances in the water, and indicates their presence by means of automatic image analysis.

Results

Fig. 1: Measuring cell with microbial test organisms and bbe probe for measuring fluorescence intensity.

Fig. 2: Fixed-bed reactor covered with E. coli RFP before (left) and after addition of glutardialdehyde (right).

The contribution of the Fraunhofer IGB to the AquaBioTox project is the development of microbiological and mammal cell systems which react quickly to the presence of toxic compounds through a reduction in the fluorescence. They can, therefore, be utilized as biological sensors. Currently fluorescence levels are recorded by means of a probe developed by bbe Moldaenke.

Comprehensive screening led to the choice of two strains of bacteria (Caulobacter crescentus, Escherichia coli) and two mammalian cell lines (HEK 293, CHO). The test organisms are kept immobilized in the measuring cell on a substrate in small bioreactors with test fluid circulating around them (Fig. 1). In addition, these biological sensors are used in combination with a daphnia toximeter established by bbe Moldaenke to increase the spectrum of the detection system. Table 1 summarizes the currently established reactions of the biological systems used in AquaBioTox. The chart shows the stability of the bio-sensor in drinking water under conditions which meet the relevant applicable regulations, respectively and demonstrates the impact of a toxic compound on the test organisms. Fig. 2 shows a noticeable color change of the microbial system after addition of a toxic substance.

Outlook

After completion of the ongoing research project it is intended to transfer and adapt the measuring principle to other areas of application. Amongst other environmental issues the Fraunhofer IGB is concerned with research into semi-decentralized water and wastewater infrastructure systems. The expected increase in these ideas such as the utilization of processed rainwater requires different solutions for online monitoring. Similar functional principles have been validated in the AquaBioTox project and after necessary specific adaptations have been made, online monitoring could replace the currently used complex and very expensive analysis methods which mainly only provide summary parameters.