Monitor provides early warning of tainted liquid

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Model HSA Indicator for Filter Use

A McNab Model HSA turbidity monitoring system was installed at a pigment manufacturer’s plant to monitor waste water and reduce water pollution.



A manufacturer of cadmium reds and yellows used for pigments for plastics must continuously monitor it waste water to prevent pollution of nearby tidal basins and to reduce loss of pigments.

A Baltimore, Maryland-based manufacturer of cadmium reds and yellows used as pigments for the plastics industry discharges its waste water into nearby tidal basins.  The company wanted to avoid polluting the basins and reduce its loss of pigments.

All plant waste water is collected and passed to two holding tanks. The tank contents are pumped through filter presses and the resultant filtrate is discharged.

The firm had been monitoring its filtrate with a scattered-light turbidimeter but this proved unsatisfactory because when pigment content was too high the particles would obscure the reception of the scattered light allowing for the possible discharge of contaminated waste water.


A continuously, on-line absorption turbidimeter system was installed to alert plant personnel to a potential problems and signal for re-circulation of the waste water.

The company supplemented the scattered-light turbidimeter with the McNab Model HSA turbidity monitoring system.  The new system consists of light source and a directly opposite-mounted photoelectric scanner within a flow cell.  Electronic signals are sent from the scanner to the cabinet containing an indicator/monitor and an alarm relays.

Suspended solids within the waste water affect the amount of transmitted light received by the photoelectric scanner.  The electronic signal transmitted by the scanner to the monitor varies in direct proportion to the solids contained.

The system's two alarm set-points are adjustable from 0-100% of scale, with measurement ranges of 0-10 through 0-1000 ppm (parts-per-million).  Maximum ambient temperature is 110º F

In this application, should the light source and/or photoelectric scanner be obscured, the system sounds an alarm to notify operators that a problem has developed and automatically reroutes the waste water back through the filter presses.

Since the installation of the HSA turbidity monitoring system, the only failure that has occurred was due to a faulty valve-positioning motor, which was subsequently replaced.  Officials from both the EPA and the U.S. District Attorney's Office have inspected the system and reacted positively.

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