Industrial wastewater is like a cocktail you don't want to order. They contain oils, fats, and solid particles that settle out during treatment and form difficult-to-treat grease or oil sludges. Their disposal is not cheap, easy, or environmentally sound. Yet there is a way to turn this ‘stowaway’ into a relatively cleverly managed by-product.

So the question is: Why is oil sludge a challenge? How can you handle it properly? What results can you expect if you choose the right solution? But let's start at the beginning, so it has a head and a tail.

What is oil (grease) sludge and where is it produced?

Imagine a mixture like thin mayonnaise - water, fat, oil, and solid particles held together in an emulsion. This mass is produced in many industries:

• Food processing - from meat, milk, oil and fat processing

• Petrochemical - from oil refining and fuel production

• Shipping - from tanker and marine engine cleaning

• Chemical industry - from plastics, cosmetics, and detergent production

• Recycling - especially rinse water

• Metal fabrication and machining - from emulsions and coolants

• Dry cleaners connected to chain stores or car washes

• Leather and textile industries

Fatty sludge can be erratic. One day they contain more oil, the next day more water or insoluble substances. This variability makes them a tough nut to crack with a one-size-fits-all solution.

So it's always a question for an expert to assess the situation and propose a solution that works.

Why is fatty sludge a problem?

Imagine trying to pour the oil out of a soup - you know it's there, but it keeps mixing with the water. Fats and oils often form stable emulsions that make it impossible for the water to separate easily. And because mechanical dewatering (e.g., using a press) is all about displacing water, the result can be only slightly “displaced” waste and a lot of frustrated field technicians.

Another complication is the high viscosity and the presence of insoluble particles. Without thorough preparation, dewatering becomes a lottery bet.

What is the solution?

The processing of fat sludge is best done where chemical pre-treatment is combined with mechanical dewatering - like baking bread: flour alone is not enough, you have to knead it, let it rise and bake it properly.

• Chemical pre-treatment - the basis for success

The use of suitable flocculants, coagulants or enzymatic treatment helps to break down emulsions and separate water. In some cases it is necessary to adjust the pH, add additives such as bentonite or use flotation technology.

We like to use an analogy to explain this, and for this one we would say that this stage is like “combing out matted hair” - you prepare the sludge to be processed mechanically.

• Mechanical dewatering - effective with screw presses

Screw presses are the ideal solution for continuous dewatering of oil sludge. They can handle the variable consistency, plus the sludge acts as a “lubricant” that reduces mechanical wear on the equipment.

Achievable dry solids typically range between 18-25%, in some cases even more. This results in a significant reduction in waste volume of 60-80%, which immediately translates into lower disposal costs.

Results from practice, or the numbers speak for themselves

Meat processing - Prague

Sludge type: flotation foam

Input dry matter: 1.5%

Output dry matter: 16%

Flow rate: 3.5 m³/h

Poultry slaughterhouse - France

Sludge type: high fat primary

Input dry matter: 7.4%

Output dry matter: 23%

Flow rate: 3.8 m³/h

Used Frying Oil Processor - Czech Republic

After deploying the screw press, we managed to:

Reduced waste volume by 60%

Reduced annual disposal costs by 35%

You may be wondering - why screw presses?

They have several advantages that make them the perfect choice for investors and WWTP operators:

- They are compact - they can be integrated even in confined spaces or as container solutions.

- They are energy efficient and have low operating costs.

- They are also suitable for sludge with a high fat content thanks to the self-cleaning mechanism (dewatering rings).

- Simple operation without the need for continuous service.

And what about the dewatered sludge?

In some cases, the dewatered material can be further used - for example, as raw material for biogas production or as an alternative fuel. This turns sludge from waste into a valuable source of energy.

4 tips for the end - how to get the most out of oil sludge?

✔ Pre-treatment of sludge with chemistry (flocculation, enzymes, pH correction)

✔ Correctly selected mechanical dewatering technology (e.g. screw presses)

✔ Recycling of the resulting material possible

✔ Long-term cost savings and greener operation

Looking for a solution for oil and grease sludge?

If you have a build-up of difficult-to-treat sludge in your operation, it pays to look for a solution that not only works, but also makes sense as an investment in the long term. The right technology will save you costs, space and hassle.

Try a solution that is already helping dozens of plants across Europe.