AWWA WQTC58928

An inability to reliably demonstrate log removal efficiencies in membrane systems withtypical water quality parameters such as turbidity and particle counting led to early regulatoryresistance in the use of membranes in the treatment of public drinking water supplies. Thischallenge is being primarily overcome through direct integrity verification of membrane systems.There is, however, a continued need for indirect system integrity verification through waterquality monitoring.The current limitations in water quality measurement strategies such as turbidity andparticle counting are due in part to the measurement of the contaminants (particles) in solution.In membrane systems that have only small but significant breaches, the contaminants are oftenso diluted by the contaminant free product water that they are virtually undetectable by currentwater quality parameters. In order to solve this engineering problem there either needs to be animprovement in current detection technologies such that the contaminants can be detected atextremely low concentrations, or there needs to be a strategy to dewater the dilute solution so asto detect contaminants at higher concentrations. It is currently being investigated thatquantification or detection of fluorescently labeled bacteria, present in a given source water,could be used as a rapid and sensitive indicator of water quality and log removal efficiency. Thiswork focuses on concentrating the particulate contaminants in the product stream andpreferentially detecting microorganisms through fluorescence probing.The filtrate water sample goes through three basic phases: particle separation, particlestaining, and laser scanning. Particle removal is performed by passing the entire sample volumethrough a small intact membrane filter, such that the particles (including all microorganisms) areretained on the surface of the membrane. If the membrane system is intact then there will betheoretically no particles captured on the surface of the sample membrane, but if there is sometype of breach in the system then particle breakthrough will occur and should be captured by thesample membrane. These captured particles will then be stained using a fluorescent stain thatbinds to nucleic acids. This fluorescent staining allows the prototype device to preferentiallydetect bacterial contaminants, thus allowing it to ignore any non-microbial surface bubbles orcontaminants. The optical design of the prototype device is similar in concept to an epiilluminatedfluorescence microscope. Scanning of the membrane is achieved through computercontrolled motorized stages and allows for the detection of stained microorganisms across theentire membrane surface.The prototype integrity device will be challenged with serial dilutions of a chosen sourcewater containing abundant microorganisms. These dilutions will give a detection threshold forthe integrity device and will establish meaningful engineering values. These values can then becorrelated to actual physical breaches in a membrane system. One potential area ofcompromised integrity exists in a membrane fiber module where one of the fibers has broken.This particular problem is important due to the abundant and increasing use of membrane fibersystems in drinking water treatment. A pilot has been constructed and measurements will betaken that will allow for the calculation of actual contaminant transport through a broken fiber.This developing technology has the potential to supplement existing indirect integrityverification techniques as used in membrane separation processes and might be used in otherapplications where on-line monitoring of bacterial quality of liquids or air is required. Includes 12 references, figures.

Product Details

Edition:

Vol. - No.

Published:

11/02/2003

Number of Pages:

12

File Size:

1 file , 670 KB