How To Compost All Food Waste - And Save The World
It is easy to home compost vegetable peelings, tea bags, coffee grinds - but they typically only account for 35% of domestic food waste. The other 65%* (meat, fish, cooked food leftovers, mouldy bread, plate scrapping, chicken bones, cakes, bits pizza, chips, etc) falls into the "do not" add to your compost bin list. (*calculated from the 2011 Recycle Now, WRAP waste analysis figures) It is not that easy to compost all food waste. As food breaks down, the cell structure weakens and water is released. The food collapses into a thick slimy mush. This mush prevents airflow and the waste quickly turns anaerobic. As soon as anaerobic bacteria take over, putrid gut wrenching odour is released. From here it is all downhill - the smell attracts vermin and flies and everything becomes unpleasant.
Millions of home composters want to compost all food waste. Not only will this divert it from landfill, it will produce more quality compost to grow more healthy plants and vegetables.
Top tips for successfully composting ALL food waste
Keep it hot - insulate you waste - bacteria release heat as a by-product when they 'eat' the waste. Heat transfers from a hot to a cold until equilibrium (same temperature) is reached. Even in summer when the air temperature might hit 25C (80F), a compost heap will not stay hot (40-60C, 100-140F) for long as the heat rapidly moves to the cooler air. A simple rule of thumb: if it takes 12 months at 10C, it would take 12 days at 60C. (I am not implying everything will compost in 12 days! This is just a rough way to compare 'cold' and 'hot' composting times). OK, if you want to keep your waste hot, you need to reduce the rate of heat loss ie you need to insulate it. There are two ways of doing this: a very large heap (at least 1XX1m (1 cubic Yard for US!) where the outer metre of waste acts as insulation around a small hot core, or by using a bin made from a highly insulating man-made material like expanded polypropylene. If insulating your compost heap were easy we would all be wrapping the heaps in bubble wrap. It is hard as you have to insulate against conductive (solid/solid) and convective (solid/gas) heat loss. The later means controlling the hot air leaving the heap and that bit is hard to do as a DIY task - as an analogy, think of a pressure cooker + lid and valve - it is a sealed container than releases a fixed amount of steam!
Feed & Shred -most composters will be aware of Green/Browns and the 30:1 carbon to nitrogen ratio. They have a part to play, but I prefer to ask people to think about a the bacteria diet. Just like humans, they can digest some things quickly (sugars, glucose), something at a medium rate (carbohydrates, fats, proteins and cellulose), and some things very slow (wood containing lignin). To keep the compost hot, you need enough "easy to digest" items in the mix. You also need enough Kgs (lbs) in weight to ensure the energy released as heat is greater than the energy lost to the atmosphere by cooling. It is often said that one million bacteria can fit on a pin head. Give them a break! A whole potato wrapped in a protective peel is a gargantuan challenge. Chop things up - let them get into to the soft easy to digest stuff inside - this will raise the temperature making the harder items faster to digest.
Remove (or manage) excess water - you need lots of heat to drive off excess water as steam in 'HOT composting'. You will almost certainly need to add dry shredded office paper or corrugated cardboard (not newspaper!) to balance 'wet' food waste.
Aerate - you need to keep pulling lots of oxygen/air into the waste - unless you have the means to force airflow (e.g. a pump / blower), or you can constantly turn/tumble (I mean constantly), then you are reliant on "buoyant airflow' - the chimney principle of hot air rising creating a pressure drop that pulls cold air through from below. You only get buoyant airflow if there is a temperature gradient (ie hot) and a structure through which the air can move.
Add a 'Bulking Agent' to maintain buoyant airflow - to get a structure that stops food waste collapsing into a mush you need to add what we refer to a bulking agent - typically wood chip. (Turning, no turning and using bulking agents to create free airspace can be quite technical - so visit our web site (see below) to get more in depth information).
Manage residual odour - all composting produces odour. To dramatically reduce and prevent attracting vermin and flies, you need a filter and reduce the odour leaving the compost heap. This can be achieved by a layer of compost or a specialist "bio filter". But you do need to filter all air leaving the heap! (PS the odour from a hot compost heap is what we call "cabbage" like, and not to be confused with the putrid odurs from anaerobic heaps. Unless you want a heap infested you need to enclose it, filter the gases and do both without cutting off the flow of new air/oxygen into the heap.
I spent 2 years attempting to build a food waste hot composting system. I followed numerous online advice sites. I went from cold too hot, too stalled to anaerobic. I lost count of the number of stinky, pungent 'test' bins I had to sort out. Eventually in frustration (I don't like to lose!) I purchased a mega composting engineering handbook (T. Haug - great book if you have a strong chemical engineering bent). I finally learnt where pieces of advice were out of context and why they worked for some situations but not others.
It is not easy to create a domestic hot composting system to cope with food waste through the winter months. Look carefully and most descriptions of hot composting and they almost all refer to very large (+500 Kg, 1 cubic metre (yards) of material). These large piles of garden waste take a lot of turning. Most food waste comes in small amounts - 2-5Kg per week, and all through winter (when garden waste is not around).
Composting food waste without a specialist bin is hard. With a specialist bin - easy!
What about saving the world! If you are unsure how humus (the important ingredient in compost) will save the world - then research the following: no compost means no humus, no hums means no soil fertility, which means no plants, which means no food, which equals a whole heap of trouble for us all. Then double back and look up what causes soil erosion, desertification, acidification and the current health of the world's arable farm land bank (hint: lack of humeric substances). Let me know if you agree!
Thanks for reading.
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The HOTBIN was specifically designed to HOT compost ALL Food Waste. Visit us: http://www.hotbincomposting.com.