Turbidity monitoring system aids in the removal of solids as small as 0.5 microns

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Model HSB Turbidity Monitoring System

A steel company installed an automatic diatomite filtration system to remove solids from its liquid waste. To monitor the effectiveness of the filtration process, the company installed a McNab Model HSB turbidity monitoring system in the line immediately after the diatomite filter.

Problem

A steel company wanted to prevent the formation of porous rock formations in its acid disposal well.

Hydrochloric and sulfuric acids are used to clean iron from the surface of steel during its manufacture. This Indiana-based steel company invested thousands of dollars to build a deep ground well to dispose of its spent acids. Solids contained in the spent acid will cause formations of porous rock to develop, clogging the well.

Solution

The company installed an automatic diatomite filtration system to remove solids from its liquid waste. To monitor the effectiveness of the filtration process, the company installed a McNab Model HSB turbidity monitoring system in the line immediately after the diatomite filter.

The spent hydrochloric and sulfuric acids, along with iron salts and other suspended particles, are pumped from the process to one of two 100,000 gallon above-ground storage/settling tanks.

After preliminary settling, the waste effluent is pumped into one of two 300 square-feet pressure-leaf filters, each containing 14 vertical leaves and an internal cake sluicing device. Cake that accumulates is cleared using a water jet, and the resultant slurry is sent to the company's waste treatment plant.

A 50-lb. bag of diatomite is used to pre-coat the leaves of the pressure filter, which operates for 36 hours or until turbidity levels as indicated by the McNab Model HSB turbidimeter exceed 5 ppm (typical turbidity is 1 ppm), at which point the filter is removed and replaced.

The McNab Model HSB turbidimeter consists of a flow cell with four waterproof housings mounted thereon. The flow cell is connected to an indicator/control cabinet housing the electronics and a meter.

One flow cell housing contains the light source. Two housings are mounted at 90º angles from the light source: one holding the measuring detector and the other containing a test lamp and light trap. The fourth housing, mounted directly opposite the light source, serves as a reference detector and is used to measure transmitted light so as to provide a ratio to compensate for variations in color, bulb deterioration and/or the fouling of optical surfaces.

Light striking a particle is reflected at various angles from the light beam.  The Model HSB continuously gauges solids content by measuring the light scattered off of particles at a 90º angle from the direct light beam.

Light striking a particle contained in the effluent will "scatter" when it comes in contact with the particle. This light deflects in many angles from the direct beam.  Light scattered 90º from the source is detected by the photoelectric scanner, which sends electronic signals to the indicator control box. This signal is converted to a turbidity ppm value and indicated on the monitor's display, which sounds an alarm when turbidity levels exceeds the preset level of 5 ppm.

The filtered liquid is transferred first to a buffer tank, and then injected into the deep ground well.

The use of this filter system and turbidity monitoring system has allowed the company to remove particles as small as 0.5 microns prior to well injection.  This decreases the chances of porous rock development and well clogging. The company is able to dispose of its acid waste at a rate of 150 gpm.

Questions? Contact McNab

A92-42a

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