Miloslava Prok š ová, Marianna Cíchová and Lívia Tóthová
3.5 NEW APPROACH OF ONLINE CONTAMINATION MONITORING DEVICE (OCMD)MONITORING DEVICE (OCMD)
Common cultivation methods of microbiological contamination monitoring rely on periodic water sampling and analysing that take hours or days to evaluate. These methods are usually sufficient for compliance monitoring but are inadequate for early warning systems because by the time the results are known a considerable portion of the contaminated water could be consumed. New technologies of pathogen detection differ significantly from those currently used for conventional water quality monitoring. In developing pathogen detection systems, efforts have mainly focused on the detection of pathogen genome with high sensitivity and accuracy. Polymerase chain reaction (PCR)-based methods are applied most frequently to detect and identify pathogens according to unique genomic DNA. However, the conventional PCR approach typically involves a minimum of 6 h of tedious labour in carrying out the sample processing, DNA extraction, DNA amplification and agarose gel electrophoresis. In the past decade, the development of micro-fabrication technology has prompted significant advances in many fields, particularly in the miniaturization of chemical and genomic analysis devices. The micromachined analytical system, which integrates sample collection, sample concentration and pretreatment with the DNA extraction, amplification, hybridization and detection, can be realized by combining functional microfluidic components. Many such devices for different types of environmental samples have been reported in the literature, including micro-PCR chips (Northrup et al. 1993), micro-DNA chips (Fan et al.1999), micro-DNA biosensor (Kwakyeet al.2006) and so on.
Technical specifications of new OCMDs should be specifically designed for the detection water contamination during treatment and distribution to consumers. Some important factors should be considered in connection with preparatory procedures, water sampling or water intake, filtration, purging of captured microorganisms, lysing and DNA extraction methods, detection of microorganisms, measurement and signal evaluation by a sensor.
Service reservoirs or water towers are regarded as the most vulnerable parts of water supply systems. It can be reasonably assumed that they would be the most probable targets of a terrorist attack. Design of a water sampling part of the OCMD should take into consideration specific construction and operating conditions of service reservoirs/water towers (or other sampling points). Two possibilities could be considered for water sampling from reservoirs, sampling from under the water level, or sampling on the discharge from the reservoir.
Usually, at neither of these sampling points there is a pressure sufficient for the filtration of required water volume in reasonable time through membrane filters (or an other chosen filtration device). Therefore, it would be necessary to use a pressurized sampling device.
Sample collection procedures for Online Contaminant Monitoring System 43
The requirements for the filtration arise from the size differences of used microorganisms (viruses, bacteria, protozoa). The filtration could be made by three ways depending on the necessity to separate different types of microorganisms:
• Set of three separate membrane modules for each filtration membrane with a specific pore size;
• One filtration module with a membrane with the smallest pore size;
• Microfiltration or ultrafiltration membrane units for separation of particles from 0.10 µm and 0.005 µm, respectively.
If mutual separation of captured microorganisms is required a one-step filtration can be sufficient that would be optimal for the minimization of a handheld device. A membrane with the pore size 0.22 µm or a microfiltration or ultrafiltration membrane unit can be used for the filtration (Clancyet al.1998; Schaub et al.1993).
It is important to know that microfiltration and ultrafiltration technique requires higher operating pressures (0.03–0.3 MPa and 0.1–0.6 MPa, respectively).
3.5.1 Location of OCMD in water system
Contamination events, whether accidental or deliberate, can affect any part of a water system. OCMD should provide coverage of all parts of the system in which contamination presents a risk. OCMD should provide detection of contamination events, location information and necessary laboratory analyses to identify and measure specific contaminants. An ideal but very expensive solution (number of samples, contaminants, equipment of instruments) would be to locate sampling sites at all important nodes of a distribution system vulnerable to contamination. Parts of a water supply system where a monitoring device can be located are presented in the Table 3.3.
Table 3.3 Parts of a water supply for potential locations of monitoring devices.
Location Threat of intentional
Source waters Relatively low Large quantities of contaminant needed– therefore it is easy to detect
Covers large part or all of system
Raw water transport Slightly higher than for sources
There are several locations on a water supply system that have a higher risk of a terrorist attack and are more proper for the location of monitoring device, among them especially:
• Incoming water supply line where there is a greater certainty of impact and economy of use of a likely contamination (typically a high security government facility or a target of high iconic value);
• Pump station discharges where there is the greatest assurance of having the contaminant effectively and broadly distributed. Pump stations have also some advantages as places for monitoring device location in terms of power supply, telecommunication and other infrastructure needed to support a device;
• Storage facilities (service reservoirs and/or water towers) where water is usually not under pressure and contaminant introduction would be easier. However, its effect is less certain, particularly if the water exchange from the storage facility is slow.
In selecting sites for online contamination monitoring device location it is useful to identify as many candidate sites as practical. It includes identification of points with the highest vulnerability to contamination using the risk analysis methodology. The assessment should include evaluation of accessibility of the insertion point as well as the sensitivity of the affected population. If a utility is not restricted in its resources, best locations can be selected by a hydraulic analysis of a water supply system. A functional and well-calibrated network model can be useful for the determination of dominant contaminant pathways. Alternatively, when a model is not available, knowledge of the system and educated guesses on dominant pathways and device locations might be used.
An assessment of the parameters discussed above leads to the identification of the following main factors for consideration in selection of type of instrument and its location:
• Minimize contamination detection time for a given number of sensors,versusminimize the number of sensors for a specified time of detection;
• Maximize monitoring coverage for all consumers versus maximize coverage for vulnerable (at risk) consumers such as populations at schools, nursing homes, hospitals, and so on;
• Continuous monitoring versus periodic monitoring;
• Automated sampling versus manual sampling;
• Instrument life cycle costs;
• Instrument ease of use and maintenance by utility.
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Table 3.3 Parts of a water supply for potential locations of monitoring devices (Continued).
Location Threat of intentional
Moderate to little Multiple locations to get full coverage
Sample collection procedures for Online Contaminant Monitoring System 45
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