Foggy Situation

Ask an Expert From: Products Finishing, , from Hixson Inc.

Posted on: 1/1/2004

Question: We recently installed a five-stage iron phosphate washer to our facility so that we can clean, prep and paint our parts in house.

Question:

We recently installed a five-stage iron phosphate washer to our facility so that we can clean, prep and paint our parts in house. Expecting our wastewater to be fairly “clean” of regulated metals under the Metal Finishing Pretreatment Standards, we just pump the wastewater to a batch pH adjustment tank, check its pH, adjust its pH ( this is not a common action since wastewater is usually within our pH limits of 5 - 11) and then batch discharge. When we did our first self-monitoring, all the metals, cyanide, and total toxic organics concentrations were well below metal finishing limits as expected. However, when the city came in to perform their sampling, they analyzed for other pollutants regulated under their local ordinance. All were fine, except for fats, oils, and grease. Several samples were above the local limit of 50 mg/liter; these samples had FOG of 75-90 mg/liter. Now we have a notice of violation that we need to respond to. We have also taken several of our own samples and two of them were also above the limit. The parts going through our washer are quite clean and we see no oil sheen in our batch pH adjustment tank. Any ideas on what is causing the problem and how to solve it? J.B.

Answer:

You have an interesting FOG (fats, oils and grease) situation, and let me outline a suggested strategy that will not require you to further pretreat the wastewater. We have done so on several occassions.

First, is the FOG analysis performed on grab samples or composite samples? USEPA regulations only recognize grab samples, therefore, if the FOG analysis was performed on composite samples, they cannot be used for enforcement action based upon my non-legal experience.

Second, a critical issue is how FOG is defined in your city’s regulations. FOG is generally defined as any material that can be extracted from water by freon or hexane solvents. Total FOG, typically analyzed using Standard Methods 5520B, consists of non-polar and polar FOG. Non-polar FOG includes petroleum-based and mineral oils; that is, those materials that people usually think of as oils and greases in industrial applications. Non-polar FOG is typically analyzed using Standard Methods 5520F and is usually described as “petroleum hydrocarbons.” The polar FOG includes biodegradable animal fats, vegetable oils, some detergents, fatty acids and some waxes. Detergents, fatty acids and waxes can indeed be found in metal cleaning and preparation activities.

If you discover that your city’s FOG is defined as “petroleum hydrocarbons,” using Standard Methods 5520F, I strongly urge you to check with the testing laboratories regarding their procedure. When testing for “petroleum hydrocarbons,” the lab should first run Standard Methods 5520B to obtain total FOG and estimate how much silica gel (silica gel removes polar FOGs from the sample) must be added to the sample to remove all of the polar FOG, for any polar FOG remaining in the sample will show up as a “petroleum hydrocarbon.” If this solves your problem, great; if not, and you really do have “petroleum hydrocarbons” in excess of the city’s limits, you will likely have to pretreat further unless you can isolate the oil source.

If you discover that your city’s FOG is defined as “total FOG” using Standard Methods 5520B, I recommend that you take a number of samples and analyze them by both 5520B and 5520F. If you find that the “petroleum hydrocarbon” results of 5520F are comfortably below the city’s limits even when the “total FOG” concentrations are above the limit, you may consider approaching the city to discuss establishing a “special” FOG limit for your facility, although doing so with a notice of violation is not the best of time. But if the city is willing to consider it, you will want to show them that your wastewater basically contains biodegradable materials such as detergents, fatty acids and waxes. Material Safety Data Sheets can help as well as other analyses, such as biochemical oxygen demand (BOD5) and chemical oxygen demand (COD); a high BOD/COD ratio indicates a biodegradable material. For example, the BOD5/COD ratio of machine oil is 0.16 and, therefore, does not biologically degrade quickly and persists in the environment. If your city tells you that the state EPA will not let them consider this change, do not take their word and contact your state EPA directly. We have found that the state EPAs do not require stringent FOG regulations unless the city’s water reclamation plant ( aka sewage treatment) is violating its discharge permit.

If your city still demands that you meet their FOG limit of 50 mg/L, even recognizing that it is comprised of biodegradable detergents, fatty acids and waxes, there are a few fairly inexpensive technogies that could be used for small volumes of wastewater that contain somewhat low concentrations of FOG. Also, since you stated that you do not observe an oil sheen, we can assume that all of the FOG is emulsified or dissolved into the wastewater. Also, because you already pump your wastewater to the batch pH treatment tank, it would be quite easy to install pretreatment between sump and tank.

Both organoclays and activated carbon could be used in your application. I would first start with organoclays, which are bentonite clays modified with quaternary amines, remove oils up to 50% or more of their weight, have an oil absorption rate 2-7 times greater than activated carbon and, typically, have a cost half that of activated carbon. I would start with a system containing a bag filter (10-50 micron) followed by a filter vessel containing organoclay. If this system does not achieve consistent compliance, then consider installing an activated carbon filter after the organoclay filter; the activated carbon will “polish” the more soluble compounds that pass by the clays. Suppliers of such equipment can be found on PF Online supplier listing; search under Oil Skimmers, separators or Pollution-Control Equipment, water:sludge concentration/conversion.

It is very likely that both the spent organoclays and activated carbon can be disposed of as non-hazardous waste into a permitted sanitary landfill; appropriate testing is needed for final disposal determination. In one application, a facility significantly extended the life of its activated carbon by adding small doses of hydrogen peroxide (H2O2) into the wastewater. Hydrogen peroxide breaks down into water and oxygen, thereby keeping the dissolved oxygen content of the wastewater high. This encourages bacteria to grow inside the activated carbon and “eat” the FOG and other organics, thereby regenerating the activated carbon.

 



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