"Gigantic fatbergs clog London's sewers" – this headline appeared in the press. It refers to a rock-hard mass of cooled cooking fats in the sewer system resulting from the improper disposal of kitchen waste.

Cooking fats and oils, such as clarified butter or frying oil, are of animal or vegetable origin. Unlike in commercial establishments, where the fat in the wastewater is collected in grease traps, in private households it enters the domestic sewage pipes when dishes are washed and then flows through the sewer system to the sewage treatment plant. As temperatures in sewage pipes and sewers are usually below room temperature, the fats and oils that were initially dissolved with the help of detergent separate again. As a result, house connection pipes can become clogged and completely blocked over time.

To prevent narrowing of the public sewer system due to grease deposits, it is regularly cleaned with a suction flushing truck. During the wastewater treatment process at the sewage treatment plant, the grease must ultimately be extracted in the sand trap and transported to the digestion towers.

By not disposing of cooking oils and fats in the sink or toilet, you are making an important contribution to reducing the burden on sewer pipes and sewage treatment plants. There are also hygienic reasons for this, as grease deposits in the sewer attract rats.

How to recycle and dispose of cooking oils and fats correctly:

• Wipe small amounts of fat from pots and pans with kitchen paper and dispose of it in the residual waste. Treat margarine, salad dressings, etc., which contain other ingredients in addition to fat or oil, in the same way.
• Collect small amounts of old oil and fat in plastic bottles and dispose of them in the residual waste. Only fill the bottles when cold, as the plastic may melt otherwise. Only dispose of completely empty oil bottles in the glass recycling container. Wrap solid fat in newspaper and dispose of it in the residual waste.
• The vegetable oil from pickled vegetables, fish, or feta cheese, etc., is great for cooking.
• As fats should not get into the groundwater, they must not be disposed of in the compost.
• Olive oil without spices can be reused as massage oil or for hair care. Linseed oil, which has a short shelf life, is suitable for furniture care. Coconut oil can be used to care for leather products.
• Store cooking oil in a dark, cool place to prevent it from going rancid. The best-before date is only a guide. A smell and taste test will tell you whether your oil is still edible.

Larger quantities can be disposed of free of charge in Mainz at the hazardous waste collection vehicle (up to 5 liters) and at the hazardous waste collection point in Budenheim in normal household quantities. Make sure you do not mix different oils (contamination). Deliver waste in sealed, closed containers, which will then be disposed of.

Waste oil refers to used oil that no longer meets the requirements for lubrication or cooling. It is used oil from technical applications, e.g., motor oil, gear oil, or hydraulic oil. Waste oils consist entirely or partially of petroleum, synthetic, or biogenic oil. Petroleum is the same as mineral oil and, unlike edible oil, is extracted from underground deposits. Biogenic oils include lubricants such as organic chainsaw oil. They are produced partly or entirely from renewable raw materials, are classified as environmentally friendly, and are rapidly biodegradable.

Waste oil must never be disposed of in household waste, down the drain or even in the environment. The Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection (BMUV) warns that just one liter of waste oil can render up to one million liters of drinking water unusable. And so just a few drops in nature are enough to contaminate several liters of groundwater.

• Careful handling of waste oil is therefore advisable. Even small quantities should not be stored at home, e.g., in the garage, for long periods of time.
• Retailers are obliged to take back engine and transmission oil. Anyone who sells lubricating oil must also take it back. Upon presentation of the receipt, specialist retailers and gas stations must take back the same amount of waste oil that was purchased.
• If the purchase receipt has been lost, waste oil can also be handed in at a mobile hazardous waste collection point or a hazardous waste collection center.
• It does not always have to be classic lubricating oil. The BMUV recommends plant-based alternatives, which are more quickly biodegradable.
• Only change the oil when necessary. According to the BMUV, a car can travel 30,000 to 50,000 kilometers without an oil change, and a truck 100,000 kilometers. This automatically reduces the amount of used oil you have to dispose of.

Oils can only be recycled if they are delivered in pure form. This means that the oils must not be contaminated with solvents, other oils, brake fluid, or antifreeze. Containers that have contained oil, dirty cloths, oil cans, etc. must not simply be disposed of. Hand these items over to the dealer or dispose of them at the hazardous waste collection vehicle or hazardous waste collection point. In Mainz, the same quantities apply to waste oil as to cooking oils and fats.

When you drop off your used oils or oil residues at the collection point, they are sent for recycling or reused as fuel. High-quality motor oils in particular are a valuable resource. Mineral oils are sent for a second round of oil refining or other recycling. Edible fats and oils can be used in biogas plants and digestion towers at sewage treatment plants to produce biogas or digester gas. These gases are then used to generate heat and electricity. Specialized chemical plants can produce biofuel from cooking fats and oils. Vegetable cooking fats and oils are biomass within the meaning of the Biomass Ordinance for green electricity, biofuels, and bioheating fuels. The cooking fats, oils, and mineral oils (usually motor oil) collected in Mainz are delivered to various waste disposal companies and are initially stored in a temporary storage facility. Both types of waste are sent to the above-mentioned recycling facilities. If you have any further questions, please contact the Mainz Waste Advisory Team.