By Ian L. Pepper, University of Arizona Environmental Research Lab, and Daniel Quintanar, City of Tucson Water Department
The security of potable water within distribution systems is the goal of continuing research in industry and academia. Such systems can be compromised by intrusion events that can be accidental or deliberate. Accidental intrusion of contaminants can occur due to inadequate treatment, or due to broken pipes within the distribution system that subsequently allow contaminants to enter. Deliberate intrusion could occur due to terrorist activities or disgruntled consumers or employees. Contaminant intrusion of any form can be chemical or microbial in nature. In addition to chemicals introduced through accident or deliberate action, non-regulated chemicals of concern may be detected in water distribution systems. These may be pharmaceuticals and personal care products or PPCPs, which include hormones such as estrogen and testosterone. Many PPCPs are known endocrine disrupting compounds that interfere with endocrine glands, their hormones or the activities of hormones. Microbial contaminants of concern include bacterial, viral and protozoan pathogens that cause a variety of illnesses ranging from gastroenteritis and meningitis to hepatitis.
Contamination of water due to intrusion could have serious implications for a community, regardless of how the intrusion occurred. Also, the impact of an intrusion event is time-dependent. The longer the duration of time needed for detection, the more people are exposed. Therefore realtime detection would be the ideal solution to minimizing the number of people exposed to the contaminated water. We define real-time detection as less than one minute, whereas near-real-time can take up to two hours. Laboratory analyses of water typically take several hours to complete from start to finish, due to the time needed to take the sample, transport it to a lab, and then actually conduct the analysis. In contrast, sensors that monitor continuously have been developed that are typically in-line and can monitor water quality 24/7. The University of Arizona, with help from Tucson Water, has developed a Real-Time Sensor Lab that is the envy of the world.
Several in-line chemical sensors have been developed commercially to monitor routine water quality parameters such as chlorine, turbidity and pH. In addition, in-line sensors are available for the detection of nitrate, fluoride and arsenic. More sophisticated real-time chemical sensors utilize multiple sensors in combination. One example is the Hach Event Monitor, which monitors several parameters including chlorine residual, turbidity, pH, electrical conductivity and total organic carbon. Software then utilizes algorithms to convert all collected data into a single value, which is used in a decision making process to evaluate whether or not an intrusion event has occurred. A technology named S::CAN utilizes ultraviolet spectroscopy to evaluate the presence of chemical species in solution. Finally, fluorescence spectroscopy sensors can be used to evaluate dissolved organic carbon.
Inline microbial sensors that detect the presenceof microorganisms in real-time are limited in number.Currently, technologies have relied on multi-angle light scattering (MALS), which occurs when laser light interacts with particulates within the water. Instant BioScan utilizes laser light scattering plus fluorescence emissions, which in combination gives an estimate of the number of viable bacterial cells in the water.
An important overall concept with respect to continuous sensing of contaminants is that it is not always necessary to know the identity of the contaminant, regardless of whether it is a microbial or chemical contaminant. Rather, a trigger is needed that indicates in real-time whether or not there is a change in the water quality that could indicate an intrusion event. Once an alert is raised, near-real-time technologies can be used to determine the identity of the contaminant, and indicate the appropriate strategy to eliminate the contaminant.
SCADA, which stands for Supervisory Control and Data Acquisition System, is the software and hardware technology associated with data acquisition and operational control of a water distribution system. Tucson Water’s current system uses the SCADA Master Station equipment to monitor and control the quantity, quality, flow rate and pressure levels of the water in the drinking water system. An upgraded Operations Management Center will plan, schedule, control and monitor water system operations by accessing multiple software tools, and applications of optimized business process and decision support systems. In concept, the SCADA would collect data from real-time monitoring technology associated with the distribution system.
The Real-Time Sensor Lab will soon move to a new center, which is currently being developed. This center, the Water and Energy Sustainable Technology Center (WEST) will be located within a newly constructed building, via a partnership within Pima County Wastewater’s new Water Reclamation Campus (see Announcements). WEST will officially be launched in 2014.