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I have recently wondered what I should be doing with my used kitchen oils having seen a news article about an enormous fatberg clogging the sewer in London.

Obviously putting it down the sink really doesn't do anyone any good for the above reason. I've tried to look around online for answers and most articles suggest reusing it, taking it to a collection center, making soap or bird feed balls or just throwing it in the trash (in a container).

None of these feel like a real solution to me. Throwing it in the trash is obviously damaging for the environment, especially if you have put it in a plastic or other non-biodegradable container. Making bird feeds or soap is good and all but people don't have time for this and how much soap and bird feeds do you really need? I believe that after oils are taken to collection points, it is then processed into biodiesel which is also going to be bad for the environment in the long-run. Biodiesel produced from cooking oils does in fact produce 45-65% less greenhouse gas emissions than petrodiesel. This is great, don't get me wrong and I agree that this is probably the best option for now. It does however rely on you're local government providing this service or on you personally owning a diesel vehicle if you wanted to do some DIY production. In an age where electric cars seem to be the future, this really only seems like a stopgap solution as I envisage combustion engines will only decline in popularity as electric cars become more financially viable.

What I'm wondering is whether there is a scientific way to actually break the oil down into something that isn't damaging so that it no longer poses any sort of environmental threat. I've tried to have a look around for any information/research/products related to this but have found very little.

I have read that there are enzymes that can break down oils but would this be suitable in a residential environment? Perhaps not if it doesn't already exist as a solution? What would the reasons for this be?

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    Why do you feel conversion to bio-diesel is bad for the environment? Presumably it will replace conventional diesel. – LShaver Nov 21 '17 at 3:02
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    Putting oil and grease down the drain has never been a good idea whether connected to proper sewers or to a septic tank. Kitchen oils are biodegradable since they are of animal or vegetable origin. I think the first course of action is to reduce the use of oils by changing the way you cook. It might be healthier as well. I mostly sautee with small amounts of oilive oil so I end up eating most of it and wiping the pan out with a paper towel before washing up to remove any remainder. I doubt biodiesel is any worse for the environment than petroleum. – Richard Chambers Nov 21 '17 at 4:07
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You can compost the oil / grease if you have the room. It's just not as easy to do as most kitchen waste. Oil tends to make your compost pile anaerobic, so its gets smelly and can attract vermin. But if you have the space for a second (or more) composter / compost pile, and can control the vermin, it will work. Since the pile will likely be anaerobic, just expect it to take a couple years to break down. I, for example have one aerobic system breaking down my regular green and brown material every couple of months for the garden, then I have another "digester" for pet waste, and a third for the other hard to break down stuff and things that need more time, like oils, dairy, and diseased plants I don't want in the regular bin.

  • Thanks Adam, I didn't realise oil could be composted. Would composting oil differ from composting plant matter in any way, in terms of how you do it? As you yourself have a specific composter for oils, do you have any advice for keeping vermin away? – Andy Furniss Nov 23 '17 at 9:51
  • I found this page which was quite helpful - planetnatural.com/composting-101/compost-digesters/anaerobic – Andy Furniss Nov 23 '17 at 10:02
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While you have dismissed it in your question, I'd say that the best way to dispose of old oil is to convert it to Bio-Diesel and burn it - that reduces the amount of conventional Diesel that is dug from the ground, or made from virgin plant oil (which has the associated issues of using fertile ground for fuel instead of food).

Oil-fuelled vehicles are going to be around for quite some time yet, so why not use a better fuel in the same vehicle in the interim?

  • I listened to an interesting discussion on the "fuel vs food" debate a while ago, and learned that this isn't the real issue. The root cause of malnutrition in the world is not a lack of food production, as evidenced by how much food is wasted in rich nations. However, converting virgin forest to cropland, or not allowing farmland to lie fallow periodically, is a serious environmental issue. – LShaver Nov 21 '17 at 14:18
  • Biodiesel produced from cooking oils does in fact produce 45-65% less greenhouse gas emissions than petrodiesel. This is great, don't get me wrong and I agree that this is probably the best option for now. It does however rely on you're local government providing this service or on you personally owning a diesel vehicle if you wanted to do some DIY production. In an age where electric cars seem to be the future, this really only seems like a stopgap solution as I envisage combustion engines will only decline in popularity as electric cars become more financially viable. – Andy Furniss Nov 22 '17 at 10:57
  • Agreed, but that will take decades - and hopefully by then there will be other technologies to make use of the old oil (perhaps turning it into some kind of plastic by rearranging the hydrocarbon chains or something) – Nick C Nov 22 '17 at 11:33
  • Maybe your response is something that you could use in your question to clarify why you consider "Bio-Diesel" an invalid Option, @AndyFurniss? – T-Saurus Nov 22 '17 at 14:51
  • Good point @T-Saurus. I will add it in. – Andy Furniss Nov 22 '17 at 15:29
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In your question you assume that it is then processed into biodiesel. This is not always the case, for example it can be converted in lubricating oil and glycerol to make soap. In the abstract of the paper Applications of Waste Cooking Oil Other Than Biodiesel: A Review many examples of applications apart from biodiesels are listed.

It can be processed to obtain pyrolytic oil, hydrogen gas, biodiesel or electricity production by direct burning. Applications like combined heat and power generation (CHP) can utilize WCO with utmost efficiently. It can also be processed chemically to obtained biodegradable polyurethane sheets, greases, biolubricants, soaps and alkyd resins. Properly purified and sterilized WCO can be used as a carbon source in fermentation processes for the production of rhamnolipid biosurfactant and polyhydroxybutyrate (PHB).

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A: Reexamine your life style. How are you producing this fat? Can you produce less? Looking at our life, we probably produce about 4-5 tin cans of fat a year. When the can is full, it goes in the food garbage if it didn't get sidetracked to the dog dishes. (We have 3 garbage streams -- anything with food; recyclables -- paper, plastic, metal all meeting certain standards; dry goods -- dirty cardboard, construction waste, lawn waste.

B: Another use for small amounts of fats is to add it to your pet's food. We have 3 border collies and they quite like any flavourings we add to the kibble. In this sense the tin can becomes a holding spot so they don't get too much at once.

C: If it's liquid fat, you can mix it about 1:20 with dirt or kitty-litter and put onto the compost heap. You can do this with solid fat too if you melt it first. Chunks of fat are more likely to attract mice and rates. Bacteria will eat it over the course of a year.

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We S Pacific. Use this way. Before our holding tank. We have a grease pit. The oil floats to the top there. Or most. Before going to the holding tank. Once a year we have both removed. The grease pit is opened. It stinks! The grease removed bagged. Took to the candle factory for use. The pit or holding tank pumped out for use on the rice fields. This presents some other problems. As food is raised in human manure. We don't eat salads but steam vegetables.

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