Turbidity monitoring system helps reduce settleable solids to less than 40 ppm

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Model HSA Indicator/Controller for Centrifuge Use

A Model HSA turbidity monitoring system, to monitor settleable solids content, was installed on each clarifier at a dairy company to allow them perform automatic desludging.



Solids concentration levels of treated effluent exceeded the municipal sewer system's allowable levels. 

A large dairy company's milk and milk-products plant in Illinois would dispose of its treated waste water into the city sewer system. The small city, population of less than 12,000, is about an hour's drive northwest of Chicago.  Its sewer system required settleable solids content he no greater than 40 ppm.  The dairy's effluent was in excess of this amount.


The company installed three 3500-gph clarifiers to clarify the effluent from the final settling tank at a rate of between 200,000 and 250,000 gallons per day. The clarifiers operate twenty hours per day, five days per week.

A Model HSA turbidity monitoring system was also installed on each clarifier to allow them perform automatic desludging.

Consisting of a flow cell and an indicator/control cabinet, each turbidimeter system is in-line mounted on its clarifier's discharge line to continuously monitor effluent turbidity.

Mounted on the flow cell are two opposite-mounted housings: one containing the light source, the other a photoelectric scanner. A direct beam of light is shone through the effluent as it passes through the flow cell and received by the photo-electric scanner.

The amount of light received by the scanner is affected by the amount of suspended solids in the effluent. An electronic signal is sent by the detector to the indicator/control cabinet, where the signal is converted to turbidity measuring units and displayed. Also inside the cabinet are relay switches that activate when turbidity measurements exceed pre-set limits.

When pre-set concentration levels are surpassed, the relay activates, shutting off the feed line and discharging the sludge into a trough.  After sludge discharge, the feed line is reopened and the clarifier automatically returns to normal operations.

The sludge slurry from the three clarifiers is then pumped from the common trough to a storage tank, from where it is removed and used as fertilizer on nearby farm land.

Within one month of the installation of the clarifiers, the plant's effluent being discharged into the city sewer system contained well less than 40 ppm.

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