Sarah Christine Boesgaard Christensen

A novel, optical, on-line bacteria sensor for monitoring drinking water quality

Today, microbial drinking water quality is monitored through either time-consuming laboratory methods or indirect on-line measurements. Results are thus either delayed or insufficient to support proactive action. A novel, optical, on-line bacteria sensor with a 10-minute time resolution has been developed. The sensor is based on 3D image recognition, and the obtained pictures are analyzed with algorithms considering 59 quantified image parameters. The sensor counts individual suspended particles and classifies them as either bacteria or abiotic particles. The technology is capable of distinguishing and quantifying bacteria and particles in pure and mixed suspensions, and the quantification correlates with total bacterial counts. Several field applications have demonstrated that the technology can monitor changes in the concentration of bacteria, and is thus well suited for rapid detection of critical conditions such as pollution events in drinking water.

Distribution of Asellus aquaticus and microinvertebrates in a non-chlorinated drinking water supply system - Effects of pipe material and sedimentation

Danish drinking water supplies based on ground water without chlorination were investigated for the presence of the water louse, Asellus aquaticus, microinvertebrates (<2 mm) and annelida. In total, 52 water samples were collected from fire hydrants at 31 locations, and two elevated tanks (6000 and 36,000 m(3)) as well as one clean water tank at a waterworks (700 m(3)) were inspected. Several types of invertebrates from the phyla: arthropoda, annelida (worms), plathyhelminthes (flatworms) and mollusca (snails) were found. Invertebrates were found at 94% of the sampling sites in the piped system with A. aquaticus present at 55% of the sampling sites. Populations of A. aquaticus were present in the two investigated elevated tanks but not in the clean water tank at a waterworks. Both adult and juvenile A. aquaticus (length of 2-10 mm) were found in tanks as well as in pipes. A. aquaticus was found only in samples collected from two of seven investigated distribution zones (zone 1 and 2), each supplied directly by one of the two investigated elevated tanks containing A. aquaticus. Microinvertebrates were distributed throughout all zones. The distribution pattern of A. aquaticus had not changed considerably over 20 years when compared to data from samples collected in 1988-89. Centrifugal pumps have separated the distribution zones during the whole period and may have functioned as physical barriers in the distribution systems, preventing large invertebrates such as A. aquaticus to pass alive. Another factor characterising zone 1 and 2 was the presence of cast iron pipes. The frequency of A. aquaticus was significantly higher in cast iron pipes than in plastic pipes. A. aquaticus caught from plastic pipes were mainly single living specimens or dead specimens, which may have been transported passively trough by the water flow, while cast iron pipes provided an environment suitable for relatively large populations of A. aquaticus. Sediment volume for each sample was measured and our study described for the first time a clear connection between sediment volume and living A. aquaticus since living A. aquaticus were nearly only found in samples with sediment contents higher than 100 ml/m(3) sample. Presence of A. aquaticus was not correlated to turbidity of the water. Measurements by ATP, heterotrophic plate counting and Colilert(®) showed that the microbial quality of the water was high at all locations with or without animals. Four other large Danish drinking water supplies were additionally sampled (nine pipe samples and one elevated tank), and invertebrates were found in all systems, three of four containing A. aquaticus, indicating a nationwide occurrence.

Influence of Asellus aquaticus on Escherichia coli, Klebsiella pneumoniae, Campylobacter jejuni and naturally occurring heterotrophic bacteria in drinking water.

Water lice, Asellus aquaticus (isopoda), frequently occur in drinking water distribution systems where they are a nuisance to consumers and water utilities. Whether they are solely an aesthetic problem or also affect the microbial water quality is a matter of interest. We studied the influence of A. aquaticus on microbial water quality in non-chlorinated drinking water in controlled laboratory experiments. Pure cultures of the indicator organisms Escherichia coli and Klebsiella pneumoniae and the pathogen Campylobacter jejuni as well as naturally occurring heterotrophic drinking water bacteria (measured as heterotrophic plate counts, HPC) were investigated in microcosms at 7 °C, containing non-sterilised drinking water, drinking water sediment and A. aquaticus collected from a non-chlorinated ground water based drinking water supply system. Concentrations of E. coli, K. pneumoniae and C. jejuni decreased over time, following a first order decay with half lives of 5.3, 18.4 and 1.3 days, respectively. A. aquaticus did not affect survival of indicators and pathogens substantially whereas HPC were influenced by presence of dead A. aquaticus. Growth rates increased with an average of 48% for bacteria grown on R-2A agar and an average of 83% for bacteria grown on yeast extract agar when dead A. aquaticus were present compared to no and living A. aquaticus present. A. aquaticus associated E. coli, K. pneumoniae and C. jejuni were measured (up to 25 per living and 500 per dead A. aquaticus) and so were A. aquaticus associated heterotrophic bacteria (>1.8*10(4) CFU per living and >6*10(4) CFU per dead A. aquaticus). A. aquaticus did not serve as an optimised habitat that increased survival of indicators and pathogens, since A. aquaticus associated E. coli, K. pneumoniae and C. jejuni were only measured as long as the bacteria were also present in the water and sediment.

GISMOWA: Geospatial Risk-Based Analysis Identifying Water Quality Monitoring Sites in Distribution Systems

AbstractMonitoring water quality in drinking water distribution systems is the basis for proactive approaches to prevent or manage emerging water quality issues, and such a monitoring requires a st...

Asellus aquaticus as a Potential Carrier of Escherichia coli and Other Coliform Bacteria into Drinking Water Distribution Systems

Individuals of the water louse, Asellus aquaticus, enter drinking water distribution systems in temperate parts of the world, where they establish breeding populations. We analysed populations of surface water A. aquaticus from two ponds for associated faecal indicator bacteria and assessed the risk of A. aquaticus transporting bacteria into distribution systems. Concentrations of up to two E. coli and five total coliforms·mL−1 were measured in the water and 200 E. coli and >240 total coliforms·mL−1 in the sediments of the investigated ponds. Concentrations of A. aquaticus associated bacteria never exceeded three E. coli and six total coliforms·A. aquaticus−1. During exposure to high concentrations of coliforms, concentrations reached 350 coliforms·A. aquaticus−1. A. aquaticus associated E. coli were only detected as long as E. coli were present in the water and sediment. The calculated probability of exceeding drinking water guideline values in non-disinfected systems by intrusion of A. aquaticus was low. Only in scenarios with narrow pipes and low flows, did total coliforms exceed guideline values, implying that the probability of detection by routine monitoring is also low. The study expands the knowledge base for evaluating incidents with presence of coliform indicators in drinking water by showing that intruding A. aquaticus were not important carriers of E. coli or other coliform bacteria even when emerging from faecally contaminated waters.