HOT TOPIC – TEA BAGS!
Can I compost tea bags? There is something about this composting question – it keeps coming back – it was on the Radio’s 2 Simon Mayo Drivetime today. Here is an answer that deserves reading our a cup of tea!
You may remember the HOTBIN composter featured on Simon’s Drivetime innovation slot back in February last year.
Toby Buckland (BBC gardening expert) gave Simon a quick summary of ‘hot’ and ‘cold’ composting.
We were interested to hear Toby Buckland noted that some tea bags do not degrade because they have plastic fibres in so you should go for the more ‘expensive’ paper ones with strings.
HOTBIN composting checked composting out tea bags sometime ago. After checking several manufactuirng sites, we found most of the fibre used is paper. Some manufacturers add a small amount of polypropylene fibre to make the bags stronger and allow them to create a heat seal after the bag has been filled. This appears to be a minuscule amount of PP fibre.
In cold composting the bags tend to present in the final compost. In the HOTBIN composter and hot composting they are degraded fast and usually completely within 3 months. Occasionally a bag will need to go through again – more so with the pyramid bags!
In summary – the tea leaf and paper is composted, the inert PP fibres remain but are invisible within the compost and do not affect the soil.
The Guardian did a feature on this three years ago – A report published a few days ago by Which? Gardening reveals that teabags produced by top tea manufacturers such as Tetley, PG Tips, Twinnings, Clipper and Typhoo are only between 70-80% biodegradable. As a result, gardeners are finding the net part of teabags – caused by the inclusion of heat-resistant polypropylene – left on their compost heaps.
Which? Gardening contacted the major tea manufacturers to check the content of their products. PG Tips responded: “‘Like most of the teabags in the UK, our teabags are made with about 80% paper fibre, which is fully compostable along with the tea leaves contained in the bag. The remaining packaging includes a small amount of plastic which is not fully biodegradable.”
Tumbler versus HOTBIN
Tumbler compost bin versus HOTBIN with no turning
If you have landed on this page, you are probably trying to decide whether to buy a tumbler compost bin or the HOTBIN. We offer you a quick ‘expert’ recommendation and a more detailed list of items so you can evaluate the type of compost bin for yourself. Alternatively jump to over and read what HOTBIN customers say
Our expert recommendation: As soon as you set a goal to compost all food waste (including meat, leftovers, bread, pasta, etc), and you want to compost all year round (through winter), with no vermin, flies or odour, then you need to opt for a specialist ‘hot composting bin’. Many tumblers are not capable of hot composting. If you hot compost and use a bulking agent there is no need to turn your compost.
Decide for yourself (list of things you should review):
To establish if a product is “better” you need to take a step back and ask – ‘What am I trying to achieve?’
There are two sets of features to look at. The first group looks at whether you want to hot or cold compost, and the second group look at how easy the compost bin is to use.
Group 1 – Hot or cold composting?
Do you want to:
- Compost ALL food waste from a typical domestic home
- Compost all year round (i.e. through winter)
- Compost faster typically less than three months
- Compost difficult garden wastes (e.g. weed seeds, couch grass, etc.)
- Compost without rats, flies or odour
- Compost without turning (fork over the heap)
Vendors will try and persuade you their bin will do ‘a lot’ and you can ‘control things’. To a degree this is true – but there is a huge performance gap between a bin designed to hot compost and a tumbler that holds waste while it cold composts.
- Feed it the right mix of chopped up waste
- Retain heat – ie insulate it by using specialist insulating materials
- Aerate – harness the science of buoyant airflow to get air to each bacterium at microscopic level
- Control water – remove excess water from the mix
- Enclose the waste, remove odours and control vermin and flies
The items are connected – get all five right and it is a virtuous circle, get one wrong and it can quickly form a vicious circle, spiralling downwards out of control.
Feed it: Some materials compost faster than others. Feeding chopped up, ‘easy to digest’ waste allows fast digest and hence fast heat release.
Retain heat through Insulation:
All things compost faster as a function of temperature (read about the Q10 equation here)
. No compost heap will compost faster unless
it retains heat. Plastics are very poor heat insulators – do not get fooled by names like ‘thermo’ and a few extra mm of plastic. You need a top quality, waterproof insulated material/ Just like your loft insulation ask for U or R value rating! Most tumblers have no insulation of any significance so they do not retain heat. The HOTBIN is designed to control both conductive heat loss (via insulated walls) and convective heat loss (hot air flow). If your goal is to hot compost; walk away from non-insulated bins. If you goal is to compost typical amounts (2-5Kgs) of food waste through winter, check the insulation works – look for user endorsements offering time & temperature graphs using on known amounts of waste (Kgs/week). We are NOT aware of any insulated tumbler guaranteeing winter hot composting of 2-5Kgs per week.
Aerate the waste:
You can hot compost without turning! The science (ref in T Huag, Compost Engineering) states air introduced via turning will last only a short time. If you have twiggy/woody material that maintains ‘free air space’ structure and a temperature gradient, it will aerate via buoyancy air flow. To learn more about the theory of “no turning” visit our buoyancy airflow and free air space faq
Plus you need to take into account spinning or turning a compost tumbler is not always easy.
100 litres = 50 Kgs, 200 = 100 Kgs.
Even with levers this can be hard and it places huge stresses on plastic and metal joints.
Control moisture: This is critical to the composting process. Kitchen scraps are wet, as is grass clippings need to be balanced with dry materials. Some tumbler models have drain holes in the drum, and also a collection chamber in the base to receive the “compost tea”.
Wet waste: Wet waste tends to rise and then slumps to bottom – it churns into a solid sludge- the last thing you need! Wet waste is the norm when composting all food waste. This is really easy to handle in the HOTBIN – you just add shredded paper and bulking agent to balance the system.
N.B. Leachate: most of the excess water is driven off as steam in hot composting. Some excess will drain down. Look for a bin/tumbler that has some form of leachate collection
Control Odour: All composting produces odour. Aerobic composting avoids anaerobe pungent putrid odour – but it has a cabbage odour. You need to filter odour and reduce the any possible chance of attracting flies and vermin. Check if your tumbler has any odour filter mechanism – the HOTBIN does!
Pest control: Do not get sucked in by statements like “compost tumblers are 100% pest proof since they are fully sealed”. We believe no domestic compost bin is rat proof. Rat experts will tell you they will eat through all plastics (be it 3, 15mm PE or 50 mm EPP as in the HOTBIN) if there is any gap. Understand vermin – what attracts them (odour, warm and quite nesting sites), then look for design that makes the bin highly rat resistant. If you bins has ANY open holes of 0.5cm or larger and odour you will have problems sooner or later. Always look for off the ground, and look for a filter that removes residual odour to a very low non-nuisance level.
Group 2 – Usability factors
What are the key items that make it easy to use;
- Loading and unloading
Assembly: Bit of a preference – we suggest you look for bins that come ready assembled or at least require very little self assembly. HOTBIN requires none.
Loading and unloading: Small loading and unloading hatches panels are fiddle and difficult to use – it is a big issue for some composter. Some tumblers are good – others are hopeless. The HOTBIN is OK.
Batch or continuous: You can fill the HOTBIN to the top and leave a batch to mature (batch) or more commonly, you keep filling at the top and take out the compost from the bottom without stopping (continuous). With most tumblers there is the issue of when to stop adding new materials so that the whole composter can “finish” and the compost can be removed. Dual chambers are better than single so you can swap compartments, otherwise you may be looking at two bins. (This is a bigger issue if your goal is compost food waste over winter as you cannot stop for 2 months.
Durability: Choose carefully! Tumblers tend to be more heavily constructed since they need to be strong enough to hold the full weight of the composting materials. This does not always work – many fail at the joints and stands. Inspect the supporting legs and the central axis connection – they should be built to last years of use (Check for customer’s reviews after years of use!). The HOTBIN has no moving parts – and only a door to take on and off.
Size & Capacity: Avoid thinking bigger is better. Hot composting is typically 10-30 times faster – so you need vastly less capacity. When hot composting, match the size to the amount of waste – it is harder to get a big tumbler hot with a small amount of waste – the laws of physics do not support small amounts of waste getting or staying hot in large empty bins!
Price or rather value for money:
- The HOTBIN = £120-150
- Non-insulated tumblers = £70-500
- Insulated tumblers = £170-£450
HOTBIN composting supply a compost bin. If you are wondering how and why we are open about offering the secrets of buying the right bin – well its straight forward – our product is excellent, the customer’s reviews say it is excellent, we have used robust composting science and engineering for the design and operation. We have confidence you will choose the right product.
Jump back to HOTBIN products page. Jump back to your shopping cart
How to compost grass lawn mowing
To get fast superb results when composting grass lawn mowings in the HOTBIN:
Add 40 parts grass with 20 parts shredded paper and 1 part wood chip (bulking agent)
Typically this is a medium sized lawn mower collection box (40 litres) with a full carrier bag of shredded paper (20 litres) and 4 hands full (one 2-litre measuring jug) of bulking agent.
If you want to view a photographic sequence of grass compost stages, you can jump to our post on steps / stages of grass composting.
Below we explain why this recipe works, why just adding large amounts of grass can be problematic and offer 6 different options for handling large volumes of grass cuttings
The problem often seen when composting grass is you end up with a black slimy layer that stops the compost heap working.
In a HOTBIN you should get brown mulch in 7 days
Grass is one of the quickest materials to compost. In the HOTBIN you can typically convert grass to mulch within 7 days. Grass is so quick to heat up to 60-70C, the HOTBIN team recommend it to help accelerate and increase temperature quickly.
BUT! You can end up with a black anaerobic slime
In traditional compost heaps, it is one of the most troublesome materials to compost. Grass often heats up for 2 days and produces a very distinctive whiff (ammonia/urine). After 2-days it then ‘collapses’ into a cold, wet, slimy black mass that smells horrible (anaerobic mush).
Funnily enough we don’t have a picture of this as if you do it correctly in a HOTBIN it shouldn’t happen!
Composting grass successfully requires a little bit of extra composting knowledge but the real secret is matching the amount of grass you generate with the time and effort you have available.
Why does grass turn into a slimy putrid mess?
The ‘black slime’ is due to anaerobic conditions, i.e. excess water and too little airflow. Grass (lawn mowing) has a high water content (>80%) and no lignin (i.e. no woody stalk). As grass starts to decompose, the plants cells break down and become soft; water is released. The grass collapses and forms a thick impervious layer and airflow decreases. This in turn means the water is trapped, the process slows and a vicious circle is created where water is not removed, all oxygen stops flowing and aerobic bacteria cease to release heat. The heap cools and anaerobic bacteria take over releasing obnoxious odour and resulting in a ‘black slime’.
The golden rules for successfully composting grass are:
- Remove excess water
- Keep the grass aerated
- Balance the mix to avoid ammonia odour
So how do we get rid of excess water, keep the waste aerated and avoid both ammonia and or anaerobic odour?
- To remove excess water
You need lots of heat, i.e. you need to be ‘HOT composting’
- To keep the grass aerated (i.e. get air/oxygen into the grass layer)
You need buoyant airflow which requires a temperature gradient and a structure with spaces and gaps so the air can flow up.
Unless you have the means to force airflow (e.g. a pump / blower), or you can constantly turn/tumble (yes we mean constantly), then you are reliant on “buoyant airflow via the chimney principle” – and this requires the grass to maintain a structure with small air spaces (ie not a thick wet slimy mass!).
To get a structure that stops grass collapsing into a slimy heap, you need to add what we refer to as a bulking agent (typically this is wood chip). The bits of wood chip act like ‘stacking blocks’ and the air flows around them. Simple but essential!
- To avoid ammonia odour
To prevent excess ammonia, you need to be adding a fast/easy to digest carbon material like shredded office paper or chopped up corrugated cardboard.
The odour is caused because grass has an excess of nitrogen which the bacteria are unable to use as fast as it is released. So it forms ammonia gas and evaporates away. You are most likely to notice this when composting and/or turning large quantities of 1-2 day old grass lawn mowing. After 3 days things slow down and the nitrogen is no longer in excess. Turning grass heaps does not prevent the odour – it enables the trapped gas to escape ‘all in one go’. (If you have done this job, you may well come back inside the house and realise your clothes smell of ammonia!).
The HOTBIN does have an odour filter in the lid that does remove ammonia odour. But, when you add a whole box of grass in one go without anything else, the filter gets temporarily overload for 2-3 days. To prevent the odour during the initial 2-3 days you need to balance the carbon/nitrogen ratio.
You achieve this by adding a dry high carbon waste. The key here is to add ‘easy to digest carbon’ such as corrugated cardboard or paper shredding. Woody items like sawdust, shavings, wood chips are high carbon – but they are not easy to digest, so will not balance the C/N during the critical 2-days of intense activity. Here is the challenge – you need a lot of dry carbon! A 40L grass box (a typical mower box), needs 20L of paper – that’s a whole carrier bag full. It also needs to be mixed with the grass. Not everyone wants to do this, especially after cutting the grass. Below we outline a few options about different methods you might want to follow.
Large amounts of grass waste need extra steps to compost quickly, without ammonia and without turning putrid. Is the extra effort worth it? We think so! Each year fertilising grass lawns consumes considerable inorganic fertiliser – adding the nutrients back via compost is environmentally better.
Below are six options/choices for composting grass. Often you can ‘mix ‘n’ match’ routines at different seasons and times of the year to cater for the varying grass volumes.
1) Small to medium lawns – add grass into your HOTBIN each week
The HOTBINn will easily compost grass from a small-medium lawn (approx 40 litres/week or 1 large grass box per week, filling about a quarter of the bin each time).
This will generate some odour that you may well notice for 2 days. If this bothers you, there are a couple of methods to solve this:
- add shredded paper or corrugated cardboard in ratio 2 parts grass to 1 part paper
- Only add half a box, then return 3 days later add the other half
|Grass volume / Weight
||To Avoid wet slime
||To Avoid Ammonia
|40 litre (approx 20 Kg)
||Add 2 litre (a measuring jug) of bulking agent. Mix in well
||Add 20 litre (a full carrier bag) of shredded office paper or chopped up corrugated cardboard).
Results in approx 1.6 Kgs of compost in 30-90 days
2) Large lawn – use a dedicated HOTBIN for grass
If you have a large lawn and generate 3, 4 or more boxes each week, then you will need to consider a dedicated HOTBIN. It will cope with 2-4 boxes (about 60-80L) per week.
The same rules apply – but adding and mixing in large amounts of paper is intensive and requires a high degree of commitment – perhaps not what you want straight after cutting the lawn! Large lawns allow the HOTBIN to be located away from your seating area – so we suggest you save your effort of adding shredded paper to eliminate ammonia odour – just leave the HOTBIN down the garden and reap the benefit of fast compost without anaerobic slime.
|Grass volume / Weight
||To Avoid wet slime
||To Avoid Ammonia
|80 litre (approx 40 Kg)
||Add 4 litre (a measuring jug) of bulking agent
||Leave remotely and accept ammonia for 1-2 daysAdd 40 litre (a full carrier bag) of shredded office paper or chopped up corrugated cardboard).
Results in approx 1.6 Kgs of compost in 30-90 days
3) Leave the cuttings to compost on the lawn
Many gardening sites now actively promote leaving grass cuttings on the lawn. Normally you use an adapted/special mower blade that chops the grass into very small pieces (2-5 mm) and thoroughly spreads them. The method is to weekly trim of top third of grass and spread this evenly so it composts quickly, adding nutrients back to soil, but not creating thatch. If you have the grass ‘trail line’ down side of mower, then this will rot into mulch that blocks light and growth and does create thatch. Please refer to manufacturer for correct mower blades/settings. If you walk regularly on your lawn – you may find bits get on your shoes and are walked back into the house!
4) Best of both worlds’
Add the first few cuts of the year which tend to be large (say 3-4 boxes) into your empty HOTBIN. The bin is full for a week or so, and then rapidly becomes half-empty allowing ongoing use with food. After the spring cut, leave grass cuttings on lawn. Occasionally (e.g. when cutting hedges) add the grass box back on the mower and collect grass to complement garden ‘browns’.
5) Transfer grass to Local Authority
This is unlikely to interest HOTBIN users, but it is possible to have grass collected at the kerbside and taken to the council recycling centre. We are strong believers in home composting and believe in the environmental benefits of saving fuel and transport.
6) Allocate a large, remote area of garden to build smelly grass mounds
The mounds will tend to be smelly and go anaerobic, but it is fast to empty and dump lots of grass. We had rave reviews on how fast and efficient the HOTBIN is with grass – so maybe you do not need this option anymore!
So in essence it is easy to compost grass in your HOTBIN but depending on the amount you need to consider which methodology is best for you.
The Edible Garden Show
Hot Composting versus Cold Composting
What a brilliant turn out HOTBIN had in The Potting Shed at the Edible Garden show last weekend. There is definitely an appetite to learn more about the benefits of hot composting over cold composting and how it can contribute to reducing what each household sends to landfill.
If you didn’t get there you can read a PDF transcript of Tony’s presentation by clicking on the graphic below.
It essence he challenged the audience to consider during his talk whether Hot Composting was worthwhile or or just a lot of hot air!
He wanted them to reflect on these 5 key things:
- Time – is hot composting faster all year-round?
- Quantity – do you get any more compost if you hot compost?
- Endeavor – does hot composting take less effort?
- Quality – is the compost from hot composting any better?
- Planet – is hot composting good for the environment?
I think over the 3 presentation sessions that the only question mark remained was on whether it was more or less effort to hot compost! Well only you can decide whether the effort is worth it to achieve all the other benefits.
Our view is this…yes hot composting in a HOTBIN requires some active participation. This includes making sure you keep the bacteria happy with smaller pieces with a larger surface area and making sure you feed it approximately 1 caddy 2 times a week. But really the benefits of composting all food waste, more quickly, all year round to get a good quality compost whilst cutting your contribution to landfill is surely worth it!
You can read the full transcript of Tony’s talk below and let us know what you think.
Thank you to The Edible Garden Show for the opportunity to present and to Potty Innovations for the photography, we had a lovely time!
Remember you can also downlaod teh PDF form teh link above…
Hot Composting – Worth it or just a lot of hot air?
By Tony Callaghan, transcript of the Talk at the Edible Garden show 15-17th March 2013
Good morning, thank you for attending – when you volunteer for do talk, your worst nightmare is just 1 person in the audience, we have a full house and that is great!
My name is Tony Callaghan, I am the Inventor of a product called the HOTBIN. Today’s talk is about Hot Composting – is it worth it or just a lot of hot air.
I’d like to start at the end by asking, how are we going to judge if it is worth while? On the handout sheets you will see I have suggested 5 things we should ask and answer during this session:
- Time – is it faster, all year-round?
- Do we get any more compost?
- Does it take less effort?
- Is the compost any better?
- Is it good for the environment?
Keep these items in mind when we get to the summary!
I started my hot composting journey about 4 years ago. We had been in our new house 2 years, the black dalex cone had been filled with garden clippings and vegetable peeling from the kitchen, I had nailed together pallets to create a second bin and that was also full – it had carrot peelings over flowing from the top. One day the inevitable happened – the old rat popped its head out. I was politely informed to sort out the compost bin or stop composting!
Now all I really wanted was to find a compost bin online that worked and move on. I was looking for a 5-star review on Amazon etc that said this product works and customer really recommend it. I could not find it – I found instead was “it arrived on time / did not arrive on time, it was easy or hard to assemble – 1-5 stars, often with “I’ll let you know if it works in 12 months”. Of course no-one comes back to fill it the rating later. The more I looked the harder it became to find vendors that actually had case studies or evidence that the products worked. I got scared off and decided I would make my own. I had loads of attempts, kept reading website advice, adjusting, adding insulation, turning etc. They all work initially but then failed quite quickly. I soon released that something was amiss. Eventually out of frustration I bought a compost engineering book – 500 pages. Having read it cover to cover (I do have a science background!), I began to understand – some advice was out of context, other bits were just plain ‘myth’.
So let’s look at what hot composting is.
What is hot composting?
Could I ask for a show of hands – how many compost? (approx. 100/120 of audience); how many think they hot compost? (3-6 from 120); how many ever use a thermometer to check? (zero from 120)
In the UK, winter is around zero to 5C, spring 5-15C, summer 15-25C. The average over the year is 10C. Most UK compost heaps run at 10C. If you shower in the morning, that is normally around 35-40C. If you put your hand on a very hot radiator – that is about 60C. So when we say 40-60C is the hot composting range, it is very hot.
Why are we interested?
We will be looking at a number of benefits, but I want to focus on heat and speed first. I do not want to get too scientific, but there is a rule of nature called the Q10 equation. Very simply for every increase in temperature, the speed of reaction doubles. So if we take out UK compost heap as 10C, and say that is speed 1, then 20C = twice as fast, 30C 4 x times, 40C 8 x times, 50C 16 x times and 60C 32 x times faster. So a rough rule of thumb – if a material takes 12 months in a cold (10C) heap, it will take 12 days at 60C. Please do not go away thinking everything will compost in 12 days – it won’t – some things are faster than others.
How DOES it get hot?
People sometimes ask do we add heating rods and electric etc. The answer is no. The heat comes from the bacteria. As they work and reproduce they create heat. Think of it like going for a run – the faster you go, the more heat you make. There are two groups of bacteria we focus on the mesophilic who work up to 40C, and the thermophilic who work from 40-70C. Now the thing about the thermophilic bacteria is that other things do not survive above 40C. So flies get fried, worms make an exodus and come back in later as things cool down.
How do we make a hot compost heap?
We need to keep the bacteria happy. I’m going to look at 5 things. Think of them as linked circles – if they are all working, we get a virtuous circle and everything spirals up and we have success. If one of the links is broken, then we get a vicious circle that spirals down.
And we all know where it leads – the stinking pungent heap that upsets the neighbours, attracts more vermin and flies – and sorting it out is a very unpleasant task.
As I talk through the 5 items, I will try and compare it to other advice, and try to help you with the context.
Number 1 – Retain the heat
So we know heat increases the compost speed and we get compost faster. To hot compost, you also need to retain the heat.
We all know hot moves to cold. If we place a compost heap in the outdoors, the heat will rapidly move to the cooler air. It is a fact of life, a law of science. You cannot prevent heat moving out and the heap cooling – that is why most heaps in the UK run “cold”.
To retain heat we need to insulate and reduce the rate of heat loss. There are two ways of doing this: use compost to create an insulation layer – a very large heap (at least 1XX1m, preferably 2m3) – the outer one metre of waste acts as insulation around the central hot core. This is why when you read books about hot composting they almost always say you need a big heap with lots of material. (They might not know why – but the experience shows it works!). Alternatively we can use a modern insulation material like EPP (expanded polypropylene. 50mm of EPP has the same insulation as 1 m of compost. Think of it like insulting your loft, you can leave it losing heat, add 200mm of fibre glass wool, or add a super 50mm insulation board.
Number 2 – small bits please!
Every time you chop things up you double the surface area. Think of it like this – you can fit one million bacteria on a pin head (apologies during the presentation I think I might have said 500 million!). Now add a whole potato into the heap. The bacteria have to eat through the peel (designed to protect it) and then all the potato. If you chop it they can get to more potato faster. Give the bacteria a break and chop things up.
In the kitchen this really is not that hard. We tend to chop vegetables and even the broccoli stalk does not take much effort to run the knife through. But if you are lucky enough to have a large garden, creating wheel barrows of waste, it takes a bit more effort with secateurs. If you have a hedge trimmer you can use it to chop waste, a rotary mower is good for leaves, and if you do not have a shredder you might be able to share one with a neighbour. Chopping and shredding makes a big difference to all composting.
Number 4 Oxygen / aeration
All the audience has heard about greens and browns and Carbon/Nitrogen ration of 30:1. I do not want to focus on these…they are important but are not high priority. After all we can compost grass (10:1) and compost wood (200:1).
I want to focus on how easy things are to digest. So I would like you to think about your diet! If you had consumed a bottle of coke (other fizzy drinks are available!), then you would be running around for an hour or so on a sugar high. You can digest glucose very easily. Now if you had porridge oats for breakfast, the theory is the more complex carbohydrates are harder to digest and energy is released more slowly – so you have less of a high, but keep going to lunch time. Bacteria are very similar – there are things they can digest easily and things that are hard. Sugars and carbohydrates are easy, cellulose (the main parts of plants) are in the middle – relatively easy and things like wood that contain lignin are very hard for bacteria to digest.
If you want to get your heap hot – you need to add some easy to digest materials! Grass and food waste are both very easy for bacteria to digest.
How many people add newspaper to the compost bin (a fair few) And how many add shredded office paper (less). Has anyone added newspaper (especially balled up) only to find in 6 months it is a small blob of non composted mush? Newspaper is “bits of wood” (hard to digest), but office paper goes through another step and is de-lignified – it is cellulose and much easier for bacteria to digest – Try them both and see who much faster one is…
Number 4 Oxygen / aeration
You all know we need oxygen/air to have aerobic composting. If we have no air we end up with anaerobic conditions, and all the odour issues.
Where do we need the air/oxygen? Well remember our tiny little bacteria trying to eat the waste. They need air on a microscopic level – everywhere in the heap. Getting air to all the heap is a big task. Often you will read the books and they state drill holes in the side for aeration, or that turning is essential. Others will describe complex ducting and airflow tubes. We researched loads of different designs. It turns out the compost engineers really know their subject. Turning does not really help – unless you want to turn it every second of the day! Most turning takes the outer none composted waste in to create a new central hot core of waste. Aeration holes in side of bins do not work – air has a particular way of flowing – it follows the path of least resistance – so through the wall and up and out. Tubes and central aeration is even worse the hot air rises up the pipe and out. After much failed experimentation we started to do what the industrial composters do – we added bits of wood chip. Think of this like building blocks – the bits stack on top of each other, they do not collapse and the air flows up and over. So add cold air in at the base, draw it up, keep it flowing up to all parts using wood chip. Because the structure does not collapse into a slushy mess – you will find you no longer need to turn. We have found no aeration system that gets even close to the success of using “buoyant airflow’ with wood chip.
Number 5 – water – We know as composters that if the waste is dry nothing happen. The bacteria need water to develop. But excess water is also a problem. It blocks all the holes around the food and wood chip and no air can flow. Food waste has a lot of water. So if you see advice to wet your material until wringing like a sponge, that might be ok for a cold heap where the water can drain away, but it is a ‘no-no’ for hot composting. We normally have to add dry materials (like shredded paper) to balance to excess water in food waste.
So the 5 things to keep bacteria happy: 1) Retain heat (insulation); 2) Small bits (shred/chop); 3) Waste mix (some easy to digest); 4) Oxygen to all bits (wood chip – bulking agent); 5) Water (need, but not too much). Get all five right and we have the virtuous circle. If one is wrong then a vicious spiral down.
What about other things
Manage residual odour – all composting produces odour! We want to avoid the putrid horrible anaerobic odours. But aerobic still produces odour – if it is released slowly you probably do not smell them. When you are hot composting and they are released quickly you do. We call it the boiled cabbage odour. It is preferable to filter hot compost odours before they leave the heap. We tend to call this a bio filter – and they are normally made form materials like charcoal and compost.
Protect from vermin and flies – you need to enclose the heap in a protective enclosure that that will prevent odour leaking out. If the odour is released then vermin and flies will be attracted. So you have to enclose the heap, and yet keep the aeration flowing through!
At the start we asked can we add more. Well if it is breaking down faster the bin will compost more. But there is another aspect – hot composting in a bin allows us to compost all food waste. Let me describe what we mean by “all” A couple of years ago, WRAP under the Love food, hate waste’ banner, did a huge study, It was something like 10,000 homes; they collected the black bag (general waste with food in) and took it away. A brave group of workers unloaded, took out, weighed and measured every piece of food waste to create a big long list. They found a huge 7.2 million tonnes of food waste was sent to landfill – about 250 Kgs for every household in the UK. Most of this was unnecessary waste (poor planning on sell by dates etc). Within the list of items we then went through and identified if it was recommend to add to compost heap (cold). About 65% of the items are on the “do not add” list – think about these items – meat, fish, bones, rice, pasta, bread, cakes – a vast amount of the food we waste is on the out list. With a correct hot composting bin, you can compost a whole lot more.
Now let us think about the garden waste. Has anyone dug up all the weeds, composted them used the compost only to find a lovely patch of weeds where the compost has been used? A few of you. Weeds seeds (and a few others seeds) tend not to be broken down in cold composting – so you replant them in natures best growing medium. In hot composting seeds breakdown – se we can add more weeds even difficult stuff like couch grass – as long as we get the high temperatures.
What about grass treated with weed killer herbicides? OK good to see not many using weed killer. If you read a lot of advice it says do not compost grass. People take it down the recycling centre – guess what they compost it! Herbicides break down in composting – faster in hot composting. So if the instructions say 12 months before using compost, you are on the safe side if grass composted at 60C and it has been in for 90 days.
The last item on our list was – is it better for the environment? Well if we have anaerobic digestion we get methane and that is 24 times worse than CO2 for the environment. It is great if we have large scale AD where the plant collects all the methane and uses it for energy, but not if we have anaerobic piles or landfill piles.
If we can compost all food waste we no longer have to collect – so we save on fuel and transport and landfill.
Summary – is it worth it
It is not easy to create via DIY techniques a domestic hot composting system that controls all 5 virtuous items and stays hot with relatively small amount of food waste through winter. If you have lots of garden waste (not food waste) you can create big hot heaps, but it takes a lot of effort to turn it.
Most food waste comes in small amounts each week all through the year. We think you need a specialist hot composting bin to handle this. The HOTBIN was specifically designed to achieve HOT composting to allow ALL Food Waste to be composted.
Have you got an insulated compost bin?
How to challenge the marketing waffle and avoid buying a duff ‘hot composter’
This post is one of a series that help explain hot composting and how to choose a hot composting bin that performs in a domestic environment.
We are seeing an increasing number of articles on hot composting and more and more compost bin suppliers describing their compost bin as ‘insulated’ or ‘heat retaining’ to help you achieve faster composting and even hot composting. There is good news and bad in this – good that there is an increasing recognition that hot composting can be achieved at home in your back yard, but also a worry that some of the claims on hot bins are ludicrously misguiding buyers. The basic laws of nature (Newton’s law on cooling and the biological rate of heat production per kilo of food/garden waste) do not support most compost bin designs ever retaining enough heat to rise above ambient (air temperature) never mind get into the hot composting 40-60C range.
If you want to hot compost we suggest you read below and familiarise yourself with science and choose your hot bin carefully. Look for one with a clear application of science to create a design that works. If you do not have the time or expertise to do this then read the article below as our advice is simple. Search for customer reviews and testimonials – but look beyond the ‘it arrived and I have set it up’ type review that appear on many shop sites, search explicitly for “compost reviews 60C”, “compost bin that works at 40-60C”, “I am hot composting” “my temperature gauge reads above 40C”, “I have reached 60C”, i.e. hot temperature in my compost bin”
The HOTBIN team spent 2 years analysing why various compost bin designs failed to deliver hot composting. Once we had the engineering solution for what would work we set about figuring out how to make it cost effectively. There are over 200 compost bins on the market. To date we still have only found 5 domestic compost bins worldwide we believe genuinely offer a realistic chance of hot composting in a domestic environment. They cost respectfully: £900, £550, £250, £185 and £175. Prizs for which is the HOTBIN!
Here’s the science and engineering you need to choose a hot compost bin:
Newton’s law of cooling – hot moves to cold until a balance (equilibrium) is reached. A cup of hot tea always cools to your room temperature. Leave it outside in the snow and it will eventually freeze. A compost heap follows the same law – all heat produced by the bacteria moves from the hot centre out to the cooler outside air. You cannot stop this, all that can be changed is the speed at which the heat lost occurs. Put your tea in a well insulated thermos flask and it will stay warm all day. Forget to drink it and return next day – at best it will be luke warm.
A very thick insulated material will slow heat loss – but this is very different to using the term “insulated” because it uses a thin insulating material (plastic). Know your facts – challenge the supplier – as for their scientific evaluation (evidence) and ask for customer reviews that prove they are hot composting (i.e. achieving 40-60C)
Here’s a quick comparison of several compost bin materials and how thick they need to be to have equal insulation value:
|U ValveMeasure of resistance to heat flow per m2
U valve is used by the building industry to stop you getting ripped off when buying roof insulation
|50 mm wall of expanded polypropylene (EPP)
||This is what the HOTBIN is made from – 50mm thick EPP walls
|To achieve the same insulation (U Value) – ie to slow conductive heat loss to the same level –below we compare how thick the walls of other compost bin materials would need to be
| 500mm thick of wet wood
||That’s about 5 railways sleepers wide! Pallets are 20mm thick wood.
|= 700mm of compost
||A pallet frame is about 1m wide. 500mm each side of a really big heap. Only the very small centre is likely to stay warm. Be prepared to turn all the outer compost into the middle!
|= 600mm of High density polyethylene
||Most compost bins have HDPE walls 2-3mm thick). Image a bin with 0.6mm thick plastics wall!! (Plastic dalexs keep the waste together and offer some protection against wind and rain. They do not “thermally insulate” your compost heap.
|= 50mm of foamed LDPE
||LDPE foam insulates as well as EPP. Most PE foam is floppy and costs significantly more to mfg. Rigid foamed PE board is available – we have only found compost bins with 15mm thick walls – i.e. 5 times less insulation than the HOTBIN.
|= 50mm of PU foam
||Most PU foam boards are ‘open cell’ which means they absorb rain water or steam/water from compost. They will be wet and cease to insulate within a few days.
If you have a very big garden with lots of waste – build a big compost heap (>2m*2m*2m). It will stay warm in the middle for a period of time. Turn occasionally to move the outer cold, non composted waste into the middle. This is what industrial composters do in their ‘windrows’ composting and it is the system largely designed by Sir Howard back in 1930s that forms the backbone the ‘New Zealand 3 bin rotation system’. Not many have this amount of waste, or the time and energy to turn this much material.
Now you know you need to look at thickness and the thermal insulation of the walls (i.e. obtain the U value). However heat is also lost by convection. Air moves within the compost (at last we hope it does otherwise it will go anaerobic and smelly very quickly!). Moving air transfers heat very fast. Winds can cool things 100 times faster than still air. Go out in a cold wind with no clothes on and you will suffer hypothermia very quickly due to ‘wind chill’. Your compost heap is the same, it loses heat as cool air flows over it and carries warm air out.
We have discussed conductive and convective heat loss and the need to minimise it to have a reasonable chance of achieving hot composting by using insulated walls, sealed lids and airflow valves. There is one other important piece of science we have to adhere to – the first law of thermodynamics: energy and matter can neither be created nor destroyed, all we do is change the form. Focusing this down to the relevant bit; the total energy (heat) going in (from food as calories) must equal the total energy going out (i.e. heat lost).
There is a bit of chemical engineering science that looks at amount of energy available from bacteria composting each Kg of food waste, how much is lost as heat due to convection and conduction. It also defines how much needs to be retained to keep the compost above ambient (i.e. at 60C rather than air temperature at 10C. This law is the bit most compost bin designs convientely ignore and or fail to explain. Most households do not have enough waste (i.e. energy going in) to keep warm due to the amount of heat being lost.
The average house produces 5Kg of food waste a week (and maybe 10Kg -20Kg of green waste during the summer gardening season). The HOTBIN will stay hot with 5-10Kgs of waste a week. The maths are straight forward – most other compost bins lose heat so fast they need 50-100Kgs per week going in to keep warm. If you have this much waste, you can copy the hot system used by industrial composting – build big heaps 2mX2m, get a tractor and turn the waste.
Even the very best hot composting systems designs have a minimum amount of waste that needs adding each week to keep things hot. We find around 20% of HOTBIN customers struggle to hot compost and by far the biggest issue is these users who do not have the minimum amount of waste to hot compost. Garden Organic tested the HOTBIN against a leading plastic compost bin claiming to hot compost. The science explains why many compost bins can be loaded with 200-400 litres of waste in one go, they get hot for a few days and then cool. The science also explains why such bins are unable to heat up or stay warm when 5Kgs per week of food waste is added.
The HOTBIN does what is says on the BIN – it will stay hot all year at 40-60C with typical volumes of waste from a 4 person household (i.e. 5Kgs per week).
HOTBIN – it does what is says on the BIN
HOTBIN believes it has used nature’s laws of science to design a compost bins that work and explain why many others will more often than not fail to warm compost never mind hot compost. We neither want to overstate (or understate!) how the HOTBIN or any other product works.
Urine on Compost – to pee or not to pee that is the question
Can I add urine to my Compost?
Many gardening and composting sites recommend adding urine onto compost heaps to help speed things up. This basically means ‘taking a pee on the compost heap’. Here at the HOTBIN composting, we agree urine works well for cold (traditional) composting, but it is a definite No for the HOTBIN due to the nature of excess water – we go into a bit more detail below.
(Jump to this post if you are looking for advice on composing baby nappies).
Why is it recommended for cold composting?
Urine is about 98% water and the rest is mainly a chemical called urea. Urea is a source of ‘food’ and nitrogen for bacteria – they eat it. Because it is small molecules in a water solution – the bacteria can digest it very quickly which means heat is released quickly – this is good news so far!
Why is the HOTBIN different?
There are two main home composting methods – hot and cold. Almost all the advice regarding urine is for cold composting. All composting releases water from the plant tissue. There are two places the water can go – it can drain into the soil or evaporate into the air.
In hot composting (and specifically in the HOTBIN), heat from the bacteria working (digesting) is used to remove this excess water from food waste. Adding more water (via urine) should therefore be avoided because you are just adding water to get a few grammes of urea (food). The extra water in urine is a huge negative in the HOTBIN – you end up needing to add another dry material to balance things – so a bag of shredded paper per half pint of urine.
In cold composting, you are accepting the water will drain in to the ground, and hence you are adding 2% (a few grammes) of nitrogen.
I read somewhere you cannot use female urine or urine if taking medication?
There are sometimes small amounts of antibiotics (if you are taking medication for urinary tract infections) or hormones (if you are taking contraceptive pills). Antibiotics and hormones are proteins. We are confounded by sites that state you cannot compost them – bacteria rapidly digest proteins!
Can I add cat pee or pet urine?
The above applies for human pee, cat pee, dog pee and any other animal pee!
If you have pet bedding soaked in urine, it is OK to add in the HOTBIN because the exceptionally dry bedding (eg straw, saw dust, paper) balances the water in the urine.
How Do I get the HOTBIN working fast?
If you are struggling to get your waste hot, we have a number of posts on this topic – try how to get to 60C. It can be a little harder in winter as there is less waste, your best bet is to try a handful of chicken pellets rather than pee. You will add more nitrogen and more food (poo) for the bacteria and as pellets are dry so it avoids the issue of excess water. You can also kick start it in winter using the hot water bottle.
Preventing a wet HOTBIN
How and why do I use corrugated cardboard and shredded paper in the HOTBIN?
Dry corrugated cardboard and shredded paper is easy for composting bacteria to digest (see table below).
Because they are also very ‘dry’, i.e. have very low water content (typically less than 5% water), they are the best materials to add to wet food waste to balance things out and ensure there is enough heat to drive off excess water as steam.
By the way this use has nothing to do with aeration and very little to do with balancing carbon/nitrogen ratios!
(Please note – Ignore the advice on many cold composting sites that scrunched up newspaper and or cereal packet cardboard will provide aeration – in the HOTBIN they WILL NOT create aeration pockets – quite the reverse – the paper and card will be soaking wet within hours and form a matted impervious layer to airflow. It is highly likely the newspaper will come out when you empty the bin as a flattened blob of soggy newspaper.)
It is essential you mix both the paper and the cardboard into the waste rather than just add it in as a layer on the top. When adding food waste ALWAYS also add bulking agent. The bulking agent will form a supportive structure (think building blocks) around which air can flow.
Why will paper and corrugated paper compost quickly but not newspaper?
It is easy to think all paper products come from wood so they should all decompose at the same rate.
We know that thin high surface area materials will decompose faster – so cardboard is faster than a wood branch piece as the bacteria have more surface area to attack. If we assume and example where surface area is the same and the temperature is the same, the speed at which wood products compost is directly related to the amount of lignin contained – so hard wood decompose slower than soft woods.
We can take this analogy a little further to explain newspaper and white office paper – the comparison is made in the table below.
|White paper (e.g. office, A4 copier, coffee filters)
||The caustic part of the Kraft paper pulping process removes lignin to leave only cellulose fibres.Shredded it rather than crunch it up. Sprinkle in little and often – thick layers will quickly get wet and form an impervious mush that prevents airflow.
|Corrugated brown cardboard boxes, egg cartons
||Although processed, about 5-10% lignin remains.Corrugated cardboard has the advantage of trapped air/air channels. Shredded or tear up – large sheet will block airflow
|This is low cost paper – the expensive lignin removal stage is not undertaken – it is small wood fibres. (Compare to white office paper above).Ensure shredded or scrunched up. It will compost far more slowly than food, grass and most other wastesDo not add whole cereal boxes – tear up and spread / mix into waste. Add sparingly – if attempting to dry wet waste, much better to use office paper or corrugated cardboard.
|Wax coatings are slow to decay. Higher temperature allows addition in HOTBIN
How do I create lots of chopped up cardboard quickly?
Everyone tends to have corrugated cardboard boxes, but tearing them up can be tiresome. You can quickly cut into strips using a craft or Stanley knife – but you need to take care and do this correctly to avoid taking your fingers of! A safer way is to see if your office shredder is a ‘multi sheet’ unit. If it is it will shred 8 sheets of paper at a time and you will find it will shred most cardboard boxes. See photo’s below. Please keep in mind if you put too much strain on a low sheet feeder it will just overheat and conk out!
A useful post on dealing with excess water in the HOTBIN can be found on our online FAQ : Excess Water Post
Compost – What Should it Look Like? Looks can be deceptive!
Compost from you compost heap, compost bin and indeed your HOTBIN composter can vary an awful lot.
With many HOTBIN® composters coming up to their first autumn, there will be a lot of hot compost being taken out and used in the garden. We thought it would be good idea to let you know what to expect as ‘looks can be deceptive’!
To do this we will look at several batches of compost alongside some HOTBIN composts. Suggest how they might be graded based on common expert visual assessments. Then we will take you on a journey beyond the first look to give you some insight into compost stability and maturity tests (we’ve done them for you!), discuss what happens when you dry and sieve HOTBIN compost (don’t worry no-one is suggesting you need to do this) and finally do a bit of mud pie play to demonstrate a property called ‘colloidal behaviour’’. Finally we will tie these properties back to humeric substances and suggest that what you really need to look for in fabulous compost is high humeric substance content.
This blog is a little more scientific in nature than some of our others – so if you want the headline without the science it is this:
What a compost looks like can be deceptive. HOTBIN compost is often very sticky and very moist/wet and looks lumpy and perhaps even needing further composting. Tests show rather than it being ‘poorly’ composted, quite the reverse – it appears to have a very high humeric substance content and this is good news for your soil and plants – humeric substance is known as ‘black gold’ for a reason!
If your compost looks like (Fig 4&5), or even (Fig 6) below it is OK to dig in to your soil and does not need ‘more composting’. If you only want ‘fine’ particles of compost e.g. looking like (Fig 1) or (Fig 2) – the solution is fairly simple – dry your compost and then sieve it – you will surprised by how much fine material there is in HOTBIN Compost.
Our analysis tour includes;
1. Visual inspection
2. Carbon / nitrogen maturity test
3. Visual after drying and sieving
4. Pliability / colloidal behaviour
5. Humus test
6. Result to quality – is it fabulous?
1. Visual inspection – Below are 6 samples of compost
- (Fig2) Garden centre compost laid out dry
(Fig 3) Typical cold compost
- (Fig4) HotBin compost at 3 Months
(Fig5) HOTBIN compost that is it too wet
(Fig6) HOTBIN compost that has gone
anaerobicNow in our earlier blog (good, bad or fabulous compost) we outlined details on how different experts defined good compost. If we asked this group of experts to visually judge the samples above here is what we would expect:
(Fig1) Vermicompost – looks fine and rich, super
(Fig2) Garden centre compost laid out dry – looks very fine and free flowing, uniform and has probably been sieved
(Fig 3) Typical cold compost – looks mature, maybe 2 years old and as expected,
(Fig4) HotBin compost at 3 Months – looks ok, dark brown and a little lumpy
(Fig5) HOTBIN compost that is it too wet – looks water logged, lumpy, immature and soggy
(Fig6) HOTBIN compost that has gone anaerobic – definitely looks anaerobic, it’s black sludge not compost
2. Carbon / nitrogen maturity test
Industrial producers of compost (i.e. compost sold in garden centres) do a check to establish how active the bacteria are. Above a certain level and the compost is too active (i.e. not mature & stable) it needs to be left longer otherwise it can draw nitrogen from the soil as bacteria continue to use the carbon in the remaining compost. The maturity and stability test can be undertaken via the Solvita compost test method. You can do these at home, although it gets expensive!
Garden centre compost (Fig2) would not have gone on sale without passing the C/N maturity and stability tests. How did HOTBIN (Fig4&5) compare? Well they both fall in the stable and mature range. This will surprise a lot of experts as they look lumpy and lumpy normally means large pieces of non-composted material which is highly likely to result in an ‘active’ rather than stable result.
3. Visual after drying and sieving
We recently tested a range of compost sieves (see guide to compost sieves post). We know wet and sticky compost is a complete pain to sieve. When testing the Compostsifter it failed to sieve any of HOTBIN (Fig5). So we dried the compost and tried again. This reminded us of an old saying – ‘looks can be deceptive’. Below is the result of the sieving test.
HOTBIN compost sieved
The result was about 80% of all the compost went through the fine (8mm mesh) sieve. There is about 15% of wood chip pieces (0.8-1.5mm), and 5% oversize non-composted items (notably pampus grass roots – these are possibly going to take the record for the hardest most difficult material to compost – but that’s another blog!). I’d just like to say this sieve result is not a one off – we have seen it many times, same results.
If we visually compare the sieved HOTBIN compost with the sieved garden centre compost they now look very similar. So was the problem just that the HOTBIN sample has been stuck in the base and got wet? Is the difference just about one compost being very wet and another compost being dry? No!
4. Pliability / colloidal behaviour
When we sieve and handle HOTBIN compost we notice something else – it is very sticky. It rolls into balls in the sieves, when you grab a handful you can make a ball. It is ‘pliable’ just like a potter’s clay or children’s plasticine.
HOTBIN Vs Garden Centre on compost pliability
There are two common substances in soils and composts that create a pliable mix – clay and humeric compounds. Both these are ‘colloidal’ materials and it is this property and the resultant way they hold water that leads to the pliability.
We can take the pliability test a little further. If we make a ball of moist compost from Garden centre compost and HOTBIN compost (Fig5) and leave then to dry in the sun for 4 days. Now what happens when we try and squeeze each ball?
HOTBIN Vs Garden Centre – compost pliability after drying
The garden centre compost sample behaves more like peat – it sticks when wet, dries fast (i.e. looses water 2-4 times faster) and then the organic material falls apart when the dry ball is pressed. Whilst the HOTBIN sample is still damp and pliable, it forms a very hard solid outer layer material with soft inner. Even after 100% drying and re-wetting the pliability returns.
At this stage we should mention that HOTBIN composting (and certainly the batch of HotBin compost above ) had no soil added – hence the pliability is not believed to be due to soil clay.
5 Humus test
We think (and we mean ‘think’ because we have no laboratory proof) that it is possible that HOTBIN compost has more humeric substances than many other composts.
HOTBIN compost – Pliable humus
Can we test for humeric substances? The answer is yes but not easily outside a fully operational soil testing lab. There is a relatively simple humus soil test – targeted at measuring the concentration of humeric substances in soils. The HOTBIN samples are off the scale – but a note of caution – the test aims to give a reliable field test for soils with 0.5-6% humeric substances. It cannot be relied on for concentrations well above this.
6 Result to quality – is it fabulous?
We believe there is a real difference between compost and compost that contains very high amounts of humeric substances. Partly decomposed material (compost) will continue to decompose when added to the soil and eventually the carbon cycle completes and it is returned to carbon dioxide and a small amount of recalcitrant humus in the soil. Humeric substances do not decompose in the soil (to any great extent) so adding a concentrated form will improve your soil faster.
HOTBIN compost – drying out
As a company we are not into making claims about our products we can’t substantiate – to be clear – we believe we can explain the appearance and behaviour of HOTBIN compost. We believe we can trace (but not prove it yet!) this back to higher humeric substance content in HOTBIN compost. One day we will have the evidence – until then we believe our logic and science has merit, you can do your own testing, contribute to the debate or ignore our findings as just marketing waffle!
HOTBIN investigates an interesting composting method
We had an interesting question come in last week!
Was Black Soldier Fly (BSF) composting the most efficient composting system ever?
After many years in composting, we had not come across BSF before, intrigue and a hint of competiveness that any system might be better than the HOTBIN, we did a bit of googling. You learn something new every day!
- BSF (Hermetia_illucens) is a species of fly with native to America (with a cousin down in Australia). There will be a UK entomologist who will no doubt identify a cousin in UK, but so far not aware – and hence possible reason we have not come across them in UK)
- It has a niche habitat – rotting food/manure. The fly lays eggs in compost and the larvae (some would say maggots) eat the food waste – and they appear pretty good at it. (This is no different to house flies and or vinegar/fruit flies – BSL are much bigger and eat more!)
- The larvae are not meant to be allowed to hatch into flies (ie pupate), they are collected and used as chicken feed and/or fishing bait
- There are a number of specialist bins designed to house, retain and harvest the larvae. As a food waste disposal system, it more closely resembles worm composting.
What about claims to be the “most efficient”? We are always suspicious of ‘fastest and best’ and try and uncover the scientific facts. There was no reference to a specific quote and we did not see the claim on sites listed below. It looks like there is enthusiasm for BSF, as highly efficient and this enthusiasm comes from the visible disappearance of food waste as BSF larvae eat food within 2-4 days. If you compare 4 days to “composting” even hot composting at 30 days – you might think it’s more efficient. But decomposition (eating waste food) is just a set of biochemical reactions involving enzymes – the rules are fixed: the rate at which reactions take place is governed by the Arrenhenius equation – which basically boils down to temperature. BSF Larvae die at 40C, thermophilic bacteria operate at 60C and in many cases 70C.
In simple terms, larvae at 40C work at the same speed as bacteria at 40. If we say composting at 10C is rate X1, then larvae and bacteria at 40C are X8 times faster, but bacteria at 60C are 32 times faster – speed wise, we think no contest!
But is speed what we need to focus on? What are we trying to accomplish? Are we seeking to dispose of food waste fast, make fish bait or make great humus with high nutrient and water holding capacity that dramatically improves soil fertility? (With the added plus of diverting food from landfill).
Nature eventually recycles all plant and animal matter back to carbon dioxide and water. Does it matter if the larvae eat food, then the chickens eat the larvae and then the bacteria eat the chicken poo? Or that the bacteria eat the food (and release carbon dioxide), but leave some residual waste (compost) that gets eaten much later and then finally becomes carbon dioxide. Both routes are carbon neutral and better that sending it to landfill where it will decompose anerobically releasing methane. BSFL larvae eat the food and produce a small amount of residual compost like material. Composting and hot composting produces a lot of compost for the garden. Compost is beneficial to the soil before it is finally returned to carbon dioxide.
We should perhaps note that for many humans, the reaction (rightly or wrongly) to flies, larvae & maggots are negative. Even though BSF appear as good guy (does not bite, sting or carry diseases problematic to humans), we know from experience (backed up by surveys), that one of the biggest reasons people stop composting is flies and maggots. The prospect of actively promoting lots of maggots in waste food seems at best destined as a specialist area.
How to compost ALL food waste
Below we explain how to Compost ALL domestic food waste
(i.e. at home, in a garden, or via backyard composting).
Why do we need this blog?
Surely food waste is just like other waste for composting – we just add it to the compost heap and it breaks down?
What’s the big problem? Well to a degree this is true, food waste is carbon/organic and will compost. The problem is NOT that food waste does not compost, it’s just that more often than not, it creates a putrid stinky mush that attracts rats and flies.
What are the specific issues with food waste composting
Here at HOTBIN Composting we talk to a lot of people who compost – from Master Composters, Council Recycling Officers, expert gardeners to complete novices and we have also read hundreds of composting forums and blogs: the advice is near universal: ‘do not add meat, fish, cooked food waste, mouldy bread, left over bones, cakes, bits pizza, chip boxes, dairy products, gone off fruit, out of date fridge contents to your compost heap. If you do, they will rot, produce putrid odour which in turn will attract vermin and flies. Only add kitchen peelings and tea bags,coffee grinds’.
Kitchen peelings,tea bags, coffee grinds only account for 40% of domestic food waste.
The other 60% falls into the “do not” add to a compost heap.
[We know this because very detailed waste analysis of what goes in our disposal bins and onto municipal refuse collection and landfill was undertaken by the Love Food Hate Waste campaign in 2011 (recycle Now, WRAP) . Teams of people sifted and weighed the contents of 1000’s of household waste bins over many months (nice job!). So we know on average, a UK household produces 250Kg/year of food waste. Every item wasted was listed and weighed (what they call a composition analysis), so it is easy to look at the list and reclassify per the compost “in/out” list.]
So even those with a compost bin, will most likely still be sending food waste to landfill.
They might still have stinky food waste sitting in a kitchen or wheelie bin for two weeks. (We accept there is a growing number of councils rolling out kerbside collection to be used in AD/EfW recovery plants – but this is a small part of the total).
Millions of home composters want to add ALL food waste to their compost bins.
This is what why the HOTBIN was invented: ‘to create a compost bin and method that enables millions of existing home composters to compost ALL food waste without the inherent problems of odour, vermin and flies’
Why does food waste rot and go putrid
As food waste starts to breakdown it forms a thick slimy mush. This soft mush prevents airflow and so the waste quickly turns anaerobic. As soon as anaerobic bacteria take over, the waste releases putrid gut wrenching odours. From here it is all downhill – the smell attracts vermin and flies and everything becomes unpleasant. As food is composted, the structure/fibre of the food weakens and water is released. There are three places the water can go – it can drain to the ground, it can be driven off as steam (water vapour) or it can remain in the waste. Under most composting conditions the water stays in the waste until it becomes saturated and then it will start to drain into the ground. Composting soft food waste naturally produces a mushy slime.
The alternative is to use heat produced by the bacteria to drive of water as steam vapour. This happens when we hot compost.
The golden rules for successfully composting ALL food waste are:
- Remove excess water
- Keep the waste aerated
What is composting?
The biggest part of the composting process relies on bacteria and if you refer to our post So What is Composting? you will note their requirements are not dissimilar to what humans need to survive and grow!
So how do we get rid of excess water and keep the waste aerated?
We take a lead from industrial composting and apply the science and engineering they use to a domestic compost bin.
(If you want to look up the science and engineering, have a read through Haug – Practical Handbook of Compost Engineering) on Amazon book review.
Let’s cut to the chase
- To remove excess water
You need lots of heat i.e. you need to be ‘HOT composting’
- To aerate you need to keep adding lots of oxygen/air
Unless you have the means to force airflow (e.g. a pump / blower), or you can constantly turn/tumble (yes we mean constantly), then you are reliant on “buoyant airflow’ or 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 – i.e. you need heat.
- To maintain buoyant airflow (even with heat)
You need to a heap structure that maintains buoyant airflow. To get a structure that stops food waste collapsing into a mush you need to add what we refer to as a bulking agent (typically this is wood chip).
In summary to compost food waste, you need to get the waste hot, aerate it (via buoyancy airflow) and ensure it stays aerated by adding a bulking agent. It sounds technical and it would be easy to achieve where it not for nature’s laws on heat production and heat loss!
Nature has a law on how much heat is produced
Bacteria release heat as a by-product when they ‘eat’ the waste– just like humans release heat when we eat and exercise. The amount of heat is capped by the calorific value – the more calories the more energy and potential heat. The rate of heat released varies by food type.
Think of it like this human analogy – eat coke and sweets (sugar!) for breakfast and you’ll be on a sugar high for a few hours, then hungry again. East oats/muesli and it will be digested more slowly but over a longer period – you’ll make it to lunchtime.
Bacteria are the same – they digest and release heat from sugars and carbohydrate food very fast, from cellulose (plant material) slower, and from lignin (wood) even slower. The amount and rate of heat generated is determined by what goes in and how much goes in. For most households – it is a challenge to create a hot compost heap, you need about X10 more food waste than most households create.
Nature has a law on how much heat is lost
Heat transfers from a hot place to a cold place until they both reach equilibrium, i.e. the same temperature. This law is scientifically defined by Newton’s law of cooling. Let’s simplify it for a compost heap – even in summer (25C), a compost heap will not stay hot (40-60C) for long as the heat rapidly moves to the cool air. 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 – by having a large heap so the outer metre of waste acts as insulation or use a specialist insulation material.
Oh, one last thing – odour, vermin and flies
Lets assume we are now hot composting away. All composting creates odour and food odour attracts rats and flies. Unless you want a heap infested with rats and flies then you are going to need to control odour so it does not attract vermin and control access the compost heap just in case. In other words, compost in a container that won’t attract rats or let flies in.
Successful food waste composting needs heat (for water removal), oxygen (to ensure aerobic bacteria active), which in turn needs a heat gradient, which needs bulking agent to allow airflow. We need to balance the heat produced with the rate of heat loss (insulation, protection from wind) to keep the bacteria warm and composting fast and then protect the whole operation from infestation with rats and flies.
Achieving the above without a specialist bin is very hard.
The HOTBIN was specifically designed to achieve HOT composting to allow ALL Food Waste to be composted. To find out more please visit our extensive FAQ