An inability to reliably demonstrate log removal efficiencies in membrane systems with
typical water quality parameters such as turbidity and particle counting led to early regulatory
resistance in the use of membranes in the treatment of public drinking water supplies. This
challenge is being primarily overcome through direct integrity verification of membrane systems.
There is, however, a continued need for indirect system integrity verification through water
quality monitoring.
The current limitations in water quality measurement strategies such as turbidity and
particle 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 often
so diluted by the contaminant free product water that they are virtually undetectable by current
water quality parameters. In order to solve this engineering problem there either needs to be an
improvement in current detection technologies such that the contaminants can be detected at
extremely low concentrations, or there needs to be a strategy to dewater the dilute solution so as
to detect contaminants at higher concentrations. It is currently being investigated that
quantification 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. This
work focuses on concentrating the particulate contaminants in the product stream and
preferentially detecting microorganisms through fluorescence probing.
The filtrate water sample goes through three basic phases: particle separation, particle
staining, and laser scanning. Particle removal is performed by passing the entire sample volume
through a small intact membrane filter, such that the particles (including all microorganisms) are
retained on the surface of the membrane. If the membrane system is intact then there will be
theoretically no particles captured on the surface of the sample membrane, but if there is some
type of breach in the system then particle breakthrough will occur and should be captured by the
sample membrane. These captured particles will then be stained using a fluorescent stain that
binds to nucleic acids. This fluorescent staining allows the prototype device to preferentially
detect bacterial contaminants, thus allowing it to ignore any non-microbial surface bubbles or
contaminants. The optical design of the prototype device is similar in concept to an epiilluminated
fluorescence microscope. Scanning of the membrane is achieved through computer
controlled motorized stages and allows for the detection of stained microorganisms across the
entire membrane surface.
The prototype integrity device will be challenged with serial dilutions of a chosen source
water containing abundant microorganisms. These dilutions will give a detection threshold for
the integrity device and will establish meaningful engineering values. These values can then be
correlated to actual physical breaches in a membrane system. One potential area of
compromised 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 fiber
systems in drinking water treatment. A pilot has been constructed and measurements will be
taken that will allow for the calculation of actual contaminant transport through a broken fiber.
This developing technology has the potential to supplement existing indirect integrity
verification techniques as used in membrane separation processes and might be used in other
applications where on-line monitoring of bacterial quality of liquids or air is required. Includes 12 references, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 670 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 12 |
| Published : | 11/02/2003 |
