There are many applications requiring the detection and concentration of harmful substances in a fluid; for example, detecting the presence and concentration of a microbial pathogen in a source of drinking water such as a lake, reservoir, river, stream, storage tank, water main, or well. Some harmful substances may be difficult to detect using conventional methods at lower concentrations. Certain microbial pathogens may be harmful to human health at concentrations that are too low to accurately, reliably, and economically detect using conventional methods.
Furthermore, in some situations, the sample size used in conventional detection methods may not provide testing results that reflect the actual concentration in the source from which the sample was obtained with an acceptable level of accuracy or certainty. The concentration of a microbial pathogen in a few milliliters of water taken from a source of drinking water may not accurately represent the actual average concentration of the microbial pathogen in that source. As a result, analysis of multiple samples from a single fluid source may be required to determine the concentration of a harmful substance in the fluid source with an acceptable level of certainty.
For each of the above reasons, it has been proposed to concentrate a fluid sample taken from a fluid source by a known concentration factor to determine the concentration of a harmful substance in the concentrated fluid sample. Once the concentration of the harmful substance in the concentrated fluid sample has been determined, the concentration in the unconcentrated fluid sample can be determined using the known concentration factor by which the fluid sample was concentrated.
There remains a need for systems and methods that are portable, automated, that provide accurate and repeatable measurements, that provide acceptable concentration factors in acceptable amounts of time, and that minimize or reduce the risk of exposure of an operator to any harmful substance potentially carried by the fluid sample.
A concentrator system was used to detect low-level harmful substances in a large volume of fluid. The system comprises a concentrator system that produces a retentate and analyzes the retantate for the presence of at least one harmful substance. The system pumps at least 10 liters of fluid from a sample source through a filter, where a percentage of the fluid crosses the filter wall and is discharged; the remaining percentage of water is recycled back to the filter inlet. The filter prevents the passage of at least one harmful substance. While pumping, the concentrator system diverts retentate from the filter into a container. While pumping, the concentrator system recirculates at least part of the retentate in the container again through the filter. The concentrator system vents air to and from the container through an air filter, thereby preventing the release of at least one harmful substance out of the concentrator system.
The concentrator system also controls the speed of the pump with a control system that maintains a fluid pressure less than 25 psi during the pumping of the fluid, monitors the quantity of retentate within the container with a control system, and maintains a reduced volume level of retentate and a target volume of retentate. The system maintains the volume of retentate in the container so that it is within an operator-defined range. The method of maintaining a reduced volume level of retentate and a target volume of retentate consists of detecting a value at least relating to the volume or weight of the retentate, and controlling the amount of retenate diverted.