Problem Solving Article: A Million Gallons A Day 

Third Article in a Series of Problem Solving Articles in an Industrial Setting

First I would like to explain the waste water treatment process leading up to the oil filtration. You will read how I decided that there was a more efficient way to do the oil filtration that would also reduce our waste water discharges into the County system. 

At the olive cannery where I worked, the waste and cleanup water was collected in a series of floor drains and then gravity-flow, piped out to a 20 feet deep tank capable of holding 20,000 gallons of water.

Two electric motors at 20 horsepower each drove a vertical pump on the bottom of the tank through a drive line. The pump discharge was piped up to the top of a set of stainless steel filters.

The water cascaded down the curved face of the filters and ran through holes into a trough. The larger solids in the water remained on the filter and were carried down to another trough.

The waste water in the trough was then cascaded over a set of filters with much smaller holes and more of the solids were removed. All the solids were thrown into an augur where they were transported to a dump into a collection bin.

The filtered water dumped into a larger tank abutting the first tank. The final tank held 100,000 gallons of plant waste water. No sewer water was included in the waste water. During a normal 24 hour workday, about 1.3 million gallons of plant waste water a day passed through the system and then into the Tulare County waste water system.

At the discharge end of the tank, a concrete barrier was built into the tank from side to side extending from the top of the tank to three feet from the bottom end of the tank wall was lowered about two feet from the sides This allowed the water to pass into a metering flume and from there into the County piping system.

Attached to the barrier and also spanning the tank (20 feet) was a rotary skimming wheel which attempted to scrape floating olive oil off the surface into a trough containing an augur. The augur dumped the oil into a container and the oil was then pumped into the storage tank for further processing into livestock feed.

I decided that there was a more efficient way to collect the oil that would also reduce our waste discharges into the County system. We would be able to reduce the charges for disposal of the wastes and also sell the processed oil for livestock feed.

The primary design change would be to the rotary scraper. By elongating the plane of the scraper to twelve feet long by 20 feet wide, one end of the scraper would be in the water and as the paddles exited the water and rode up the stainless steel plates they would be able to capture more of the floating oil.

The scraper body would have two shafts, one at each end, and each shaft would have three bearings with a supporting bearing in the middle of the shaft. The middle bearing would be a split type so it could be installed and replaced without having to remove the whole shaft.

Each paddle would be further apart than on the rotary wheel and this would allow more time for the oil to collect. Each paddle was tipped with two ten feet long pieces of UHMW. The UHMW was bolted to a two inch by 3/16 inch by ten feet long piece of stainless steel flat plate that was in turn bolted to the paddle wheel.

The UHMW was flexible enough to give a little as it scraped the collection plates. Through being bolted on, they were easily adjusted or removed for replacement.

The plant contractor built the framework alongside the waste water tank. He used a laser leveling device to ensure that the framework was level and plumb. The drive end would rest on the barrier and be bolted to the barrier through leveling bolts.

The opposite end would be supported by stainless steel supports up the sides of the tanks to the top edge. The supports would rest on the top tank edge and bolts were threaded through the support and against a steel plate resting on the concrete edge. 

The support could be raised or lowered the length of the large one inch by nine inch bolts. The weight of the scraper and the bolted drive end held the supports in place.

I contracted with a waste water engineering consultant to design a waste water aeration array to sit on the bottom of the main tank and pass air bubbles into the water. The array would be fifteen feet wide by five feet long and be positioned at the end of the tank opposite the scraper.

The plant contractor built the array at the same time as the scraper. All parts of both pieces of equipment were built of stainless steel, plastic or cast iron to reduce or eliminate as much as possible corrosion from the salty waste water environment.


When the scraper was completed, two fork lifts with slings were used to put the scraper on the tank. The tank was empty so it could be put into place easier than if full of water. The augur and augur drive motor were still in place and connected.

The scraper drive motor was connected as the scraper was levered into position. The positioning bolts had to be shimmed hire, but they worked great.

The tank was filled and the scraper turned on. It worked good. The bubbler array was completed, tested and installed. The array was lowered on a semi-permanent hoisting device so the array could be pulled out for repairs.

The bubbler was turned on and the air adjusted for maximum bubbles. Soon, more oil was floating to the surface and the scraper was pushing it into the augur. Success.

The whole project had been carried out for less than $15,000 total for parts and labor. I checked our bill from the County and we saved more than that within the first three months. After that, we were making money.

Feel free to copy this article in it's entirety as long as you include the credits below. Thank you for spreading the knowledge.

Author: Larry Bush 
Profile: Electrician in industrial, construction, marine, and food industries for 47 years, with 22 of those years in management.
URL: http://www.reliability-consultant.com