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Oil & Grease In Wastewater - What To Do?

January 9, 2015

One of the most common concerns for water discharge is the presence of oil and grease in the treatment system. Oil and grease in its natural state is found floating on the surface or observed as an ‘oil sheen.’ Synthetic oils are also problematic. When a murky or hazy water is observed, the synthetic oil is ‘emulsified’ and soluble within the wastewater solution.

Both natural oils and synthetic oils need to be addressed for wastewater treatment. Oils and grease within an industrial wastewater discharge can create problems for the following regulated parameters: heavy metals (like zinc and nickel) and organic loading (like BOD and COD) and turbidity (water is murky) and also TSS (total suspended solids). Adding to all of these concerns is the fouling of pH probes and possible toxicity problems with the discharge water.

Coventya WaterCare has been treating wastewater solutions with oil and grease concerns for over 20 years.

SO WHAT TO DO WITH OILY WASTEWATER? 

Here are a few helpful treatment steps to consider if you find oil and grease to be of concern.

Floating oil and grease (natural oils) can be ‘cracked’ or separated from the water phase by a pH adjustment as well as the use of a cationic polymer. By dropping the pH of the solution to 2 to 3 units, natural oils tend to ‘crack’ or separate to the surface. To enhance this process, sometimes the use of a cationic polymer, like OMEGA CP-1154 or OMEGA CP-1169 can greatly assist in the separation process. Once the oil is separated, a skimmer or decanting process can keep the clear water away from the oily layer. Upon removing the oily layer, the pH can be adjusted (usually with lime or sodium hydroxide) and the wastewater can proceed with further treatment as needed.

Emulsified oils and grease (a murky solution) are more difficult to deal with. The best option is to try and agglomerate all of the soluble oily solids into a reaction with a coagulant. This usually works best if the pH is depressed first (2 to 3 range) and then a coagulant is added such as OMEGA C-3113, OMEGA C-3112, or OMEGA C-3114 [Note: all aluminum based products.] We also have had good success with OMEGA BP-4123 [iron/polymer based] and OMEGA BP-4188 [calcium/aluminum/polymer]. After the coagulant is added, the pH is raised to neutral to alkaline levels (a range of 7 to 10 with lime or sodium hydroxide). It is common to add an anionic polymer flocculant, as a final step, to agglomerate the oily-coagulant formation into a larger mass for solids settling or solids floatation. Try using OMEGA AP-2140 for this step.

HOW DOES ONE KNOW IF THE WASTE TREATED EMULSIFIED SOLUTION WILL FLOAT
OR SINK? 

The amount of emulsified oil and grease within the solution will be consumed by the coagulant in the reaction. Since oil and grease is normally lighter than water, sometimes the solution will float after treatment. If this is the case, then a skimmer or decantation process will be needed as a final step.

If the coagulant is applied at a dosage which creates a mass of solids (oils and coagulant) which is heavier than water, then the agglomerated solids will most likely sink and precipitate.

A simple answer to this question is: It all depends on the concentration of the emulsified oils and greases in the solution.

Coventya WaterCare can assist in your treatment investigations. If you would like assistance, please submit an untreated sample along with a survey form to our laboratory. Our personnel will do the treatability testing and report back to you with our recommendations.

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