Bulletin 80

Bulletin 80

Ozone Treatment of Microbially Contaminated Cooling and Lubricating Oils

The biological instability of oil/water emulsions used for various cooling and lubricating functions poses an environmental problem.

 Inside plants, these liquids are generally contained in small vats near each machine or in large common vats serving many machines.  The liquids are subject to unwanted fermentation by microorganisms that abound in the air.  Most of these are harmless to man, but do degrade the emulsions making it necessary to replace them from time to time.  This is a costly program.  New lubricant must be purchased and extra payments are required for proper disposal of the old.  Pathogenic bacteria often gain a foothold in the solutions and are carried to the machine work stations where workers are exposed to possible infection.  Much of the dermatitis conditions found among machine tool workers is traceable to this source and has been clarified when the solutions are kept biologically clean.  Other known diseases including salmonella, typhoid, and legionnaires disease have been isolated from such tanks.

 Foul odors are inevitably produced causing "Monday morning stench" that often causes delays in getting the labor force started to productive work - waiting for the odors to dissipate after the circulation has been operating awhile.  These odors are proof of the damaging work of the microorganism.

 Action by microorganisms can be partly controlled by the addition of biocides to the coolubricant.  Such chemicals are costly and often contribute to the irritability of the solution in contact with skin.  The FDA and EPA have eliminated the use of mercurials and chlorinated phenols that were early favorites.  Today we must rely upon the weaker formaldehyde releasing agents which are also irritants.  Biocides are consumed in the process causing them to be replaced at more expense.  Many plants discard the contents of the smaller tanks frequently rather than face the expense of adding biocides.  The rationale is that so little coolant is lost that it is less costly to replace the solution.  Larger tanks are changed less frequently because of the greater cost, but very few of these last longer than two or three months unless more effective means are taken to preserve them.

 Ozone, ultraviolet energy and hydrogen peroxide have been effective in combating bacterial growth without the addition of irritant factors to the material being treated.  At times two or more of these agents may be economically applied to prolong the usefulness of coolubricants.  Ozone is the most effective of these and is generally the first choice.  The others may be added if necessary.

 Ozone is an active, yet unstable, form of oxygen that is the most powerful oxidizing biocide available.  It is stronger than chlorine or bromine and provides a cascading action in that it sterilizes at each of several steps during its decomposition.  It is most conveniently applied by bubbling a dilute concentration of the gas into the holding tank or existing purifying system near the clean discharge port.  Ozone is generated as needed near the point of treatment and is generated only so long as it is being used.  There is no need to store it.  It is made safely, and no ozone escapes from the system to enter the work space atmosphere.

 Ozone generators are sized to the application. A tank holding 20,000 gallons or more will have its own generator. A single generator might, however, supply the ozone for treating several tanks with individual capacities of  between 30 and 1000 gallons.  When several tanks are treated by a common generator, they should be within 50 feet of each other and must be balanced hydraulically.  It is simpler to treat several tanks in sequence rather than to balance the feeds.  Generators may also be moved from site to site in a plant to service more tanks because constant ozonation is seldom required to gain the purpose.

 The use of ozone will:

 1.      Prolong the useful life of coolubricants

2.      Save money on replacement of oils used

3.      Save money through reduced amount of biocide used

4.      Save money on extra charges for waste disposal

5.      Reduce odors in the work space - more pleasant conditions

6.      Reduce bacteria in the cooling bath contacting workers

7.      Reduce incidence of dermatitis among workers

8.      Reduce other microorganisms capable of growing there

USE IN WASTE STREAMS

The same equipment may be used to destroy many toxic substances and to reduce the BOF and COD values of various effluents throughout the plant before emptying them for sewerage.  In such uses, it is more common to allow the entire output of the ozone generator to flow into a single treating point rather constantly and to not divide its use. 

 We have installed ozone treatment for large coolubricant tanks since 1972.  Many of these hold in excess of 10,000 gallons.  In each case bacterial development has been controlled, dermatitis has been reduced or eliminated, and life of the system has been materially lengthened.  There are several documented periods of more than a year between changes of coolubricant.

 We have now developed smaller ozone generating units that may be applied economicaly to smaller tanks with capacities down to and including 30 gallons.  Because it is seldom necessary to ozonate continuously, these small generators may be moved from tank to tank, or several tanks may be served from a common generator.  These generators utilize photochemical rather than corona sources.  As a result, they do not require the dehydration of the air stream feed-stock nor do they require the high voltage.

 The basic generator consists of photochemical ozone generator tube assembly mounted on board with provisions for air filters, timers, switches, and valves.  Means are provided for attachment to plant air supply and a check valve protects the output.  Equipment as provided may be plumbed (by plant maintenance) to the application points using either plastic tubing or pipe.  Diffusers are supplied as needed in each tank to be treated.

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