compost science and engineering
KEEPING THE HOTBIN HOT
How do I keep my HOTBIN composter working hot? My HOTBIN seems to have stalled – It won’t go above 40C any more…
Here at HOTBIN composting we are passionate about our brand promise that given the right volume and mix of waste everyone can hot compost at 40-60C.
We do not have many customers who struggle, and normally a combination of our Q&A database, email support or our unique composting photographic analysis service get their HOTBIN composting on track.
You can imagine therefore we get a bit hot under the collar when we find a customer where everything seems perfect, they have been hot composting for a while, all the settings are right (valve, door on, etc) the mix is right and there is nothing obviously wrong and yet the HOTBIN suddenly sticks persistently at 30-40C and will not rise. We have termed this “a stalled HOTBIN”.
Who is affected by stalling?
Firstly this is not to be confused with customers who have never reached 60C (if this is the case, please check out the FAQ: How to get to 60C check list. Stalled HOTBINs are where it has been working perfectly for months at 40-60 then suddenly it will not rise above 40C.
This is not a common occurrence and there are only a handful of reported cases. A dedicated customer (Andy U) wrote in and suggested an adaptation to help and this kicked off a summer of activity and research.
Why does it happen?
We have identified one central issue: restricted airflow through the base layer. (Think of the HOTBIN as a fire in the chimney, you add new waste onto the fire to fuel it. As the heat rises is ‘draws’ fresh cold air in at the base. This air is drawn up through the base layer. If not enough air flows, the bacteria are restricted and hence the heat produced is restricted.
What causes restricted airflow?
The HOTBIN works under many different waste conditions. However, we have identified the causes that can tip the balance and create restricted airflow:
- Base plate is ‘plugged’ (see below)
- Ultra compressed base layer
- Dense, compressed, wet layer of either paper or grass
Top tips for fixing A stalled HOTBIN
If you are suffering from a stalled HOTBIN, here are our tips for fixing it:
- Check to see if your base plate is ‘plugged’ (check this post to understand what we mean by plugged rather than normal operation where the holes are covered with compost).
- Sprinkle a couple of handfuls of wood chip on the base plate after each emptying to reduce the chance of plugging.
- Empty out the base layer at least every 6 months. Longer and it will lead to ultra compression of the base layer.
- Always add bulking agent – this is critical with Food waste, but it will also help prevent compression of any waste
- If stalled, stir the top half of bin to help aerate and break up any dense layers.
- Check for thick layers especially in lower half bin. – eg a solid layer of wet grass or compressed wet paper.
- Check mesh plate for leakage of water/leachate. If lots of leachate cross check to see if your real issues is that your waste is “too wet” for hot composting
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.
Can I add Autumn LEAVES to compost in my HOTBIN
Leaves can go in the HOTBIN and they make great humus.
If you have a lot of leaves (>10 litres, a bucket load), you need to tweak the recipe to ensure they HOT compost.
If you only add thick layers of leaves into the HOTBIN, it is unlikely they will rise above 20-30C as the woody nature means they are hard for bacteria to digest and hence heat is released slowly.
To HOT compost autumn leaves, see the recipe below:
How to HOT Compost Autumn Leaves
There are two parts to successful composting of autumn leaves.
1) Adding a nitrogen source to balance the high carbon in leaves
2) Ensuring that there is enough ‘easy to digest’ waste (e.g. greens, food waste, shredded office paper’ (which creates heat quickly) to keep things hot whilst the hard to digest woody material (in which heat is released slowly) are also digested. In some cases solving (1) & usually solves (2).
Here’s what you need to do to ensure you get the best out of your HOTBIN
Step 1: Shred leaves
Leaves tend to form a dense matted layer that restricts air and oxygen flow within the HOTBIN. We advise shredding the leaves (e.g. using mower or a hedge trimmer).
Step 2: Mix leaves with easier to digest materials like food waste
Many people simply will not have enough food waste to mix with high volume autumn leaf fall. You can cheat a little by adding another easy to digest waste to go with the leaves such as chicken poo, chicken pellets, or a sprinkling of blood bone meal.
The ideal waste to mix with autumn leaves is grass lawn mowing – unfortunately, it is rare in UK to be able to get the mower out in Autumn as it is too wet and compacts the lawn soil. If you have room storing leaves in a wire frame box ready for spring and first grass cut can work really well . (Avoid sealing in black bags – the leaves will go anaerobic (see below for anaerobic method).
Step 3 – Do not add too many each time – little and often is best
More than 10cm (20 litres) of cold wet leaves in one go will “stall” the HOTBIN. The cold leaves will lower the temperature of the HOTBIN below 20°C and the heat production falls below that needed to re-heat. So store the leaves in a pop up bag, protected from rain and add over a couple of weeks – you’ll be amazed how fast they compost.
If you have a large garden with lots of trees and mounds of leaves then possibly doing a little bit each week in the HOTBIN is impractical. Try the following – shred the leaves (e.g. using lawn mower), store in a wire frame or cold compost heap until spring. Mix with first grass cuttings in large volume piles. Turn occasionally.
Leaf Mould Versus Composting
If you are collecting leaves into a wire frame then you might go down the route of just leaving them in the box and waiting 1-2 years for leaf mould.
Leaf mould versus ‘bagging’ i.e. anaerobic digestion
Many compost sites note that ‘bagging’ leaves in black plastic and tying off will create a black slime that can be used as compost. What this really means is you are anaerobically digesting the leaves down to compost. To an extent this is ok, our point would be AD creates methane and you are releasing a GHG that is 24 times more harmful than CO2. And we hope you would agree that every little bit avoided helps.
Aerobic composing is carbon neutral. Also to be honest – the black bags absolutely stink when you open then!
You can now successfully compost large amounts of Autumn leaves in your HOTBIN.
This AUTUMN could be the time to RETHINK composting?
Autumn is coming – It’s will soon be time to start that big garden clear up again! Should you start to RETHINK your composting method now too?
You may well have wheel barrow loads of plant and weed being removed over the next few weeks.
What are you going to do with all your autumn garden waste?
1) Pile it all up as normal in that big heap – come back in spring hopeful of compost but most likely disappointed that you face the prospect of waiting another 12 months for your compost?
2) Take a different approach – join the HOTBIN composters and be sure of a fabulous batch of compost ready to dig in with you spring planting preparation?
3) Leave it out for the council green waste team to sort out – Oh dear! All that fuel, cost and effort to centrally reprocess it. Taking all that goodness from your soil this year, which means next year it has to be replaced by buying even more fertiliser, that takes even more energy and resources to make?
Composting during the cold autumn, winter and early spring months can usually be a very slow process. Especially when the temperature falls below 5C, the rate the bacteria work is almost nonexistent. The secret to fast composting is heat – and lots of it. Compost forms 64 times faster at 60C than it does at 10C. If you can keep your waste hot (between 40-60C), it will compost in 20 to 90 days!
There are many help sites that recommend building huge piles (minimum 1X1X1 m3), and then turning them regularly to keep them aerated and hot. But even this technique will struggle in winter as the heat produced by the bacteria is quickly lost to the cold air. (And it requires quite a bit of effort and space too)
This is why so many HOTBIN composters are happy – all the hard work to help support natural high temperature composting is provided by the HOTBIN. As long as you keep feeding it every week with enough waste – it will keep running at 60C. It has been tested and proven even with outdoor temperatures as low as -15C.
Not only can you get rid of all that garden waste, you will also be able to compost all your food waste over winter too.
Now if you were an early HOTBIN starter, your HOTBIN might be full already! If the bottom layer has been in there for 90 days, now is a good time to empty it to make room for your Autumn garden clear up.
It is always best to shred as much as you can (the smaller the pieces, the larger the surface area, the easier it is for the bacteria). Now if you don’t own a shredder then you can always use your lawn mower!.
Now you are ready to fill up HOTBIN to the top and get it back up to 60C .
If you have a large garden you may still have too much waste . So the best thing is to store it in pop up bag or on another heap. Remember to keep it covered to protect it from the rain. Where possible we suggest you store bags on stones/gravel so water drains out and some air can get in through the holes in the bottom.
You can add the excess waste every 4 days (about 20 litres 10 cms depth). As the ‘waste pile’ gets colder and older, reduce how much you add each week – But keep adding your food waste! (The bacteria need some easy to digest waste to keep the temperatures at HOT composting levels between 40-60C).
Keep going until all autumn waste is gone.
As soon as you start to collect a lot of autumn leaves – check out the ‘composting autumn leaves post’ as you need to tweak the recipe to hot compost leaves.
Remember the key to keeping it HOT is a BALANCE of ‘easy to digest waste’ made up of green stuff, food waste, plus shredded office paper’ (which creates heat quickly) with the hard to digest woody cuttings (heat released slowly), or partially composted waste (energy depleted).
Why not take up the challenge – find out what others have experience by visiting our ‘product reviews’ at www.hotbincomposting.com. Explore more about how it works by looking at our extensive ‘how to compost’ database, for example our ‘principles of hot composting’ article.
The HOTBIN is a simple design that helps maximise what nature does by bringing together the right conditions to make HOT composting easier. It does this by providing effective aeration between the bottom air inlet plate and the air outlet rotating valve, removing excess water through the valve as steam and allowing you to control the rate of heat loss.
Can you compost cigarette butts?
A number of composting advice sites indicate cigarette filters are made from synthetic plastics and do not decompose! We disagree – controlled hot Composting of cigarette butts is viable. Please read on to find out why!
Whether a material IS or IS NOT compostable (i.e. biodegradable) is a matter of scientific fact. We like to check the science and leave you better informed. It is rare for us to re-mind our readers our FAQ advice is provided on ‘without guarantee or indemnity’ – but on this occasion, as the topic is going to get people ‘hot under the collar’, a reminder that this is our reading of the science – we are only seeking to help inform your decision.
Searching the literature, we found that cigarette butts (the white filter bit) is made of ‘synthetic cellulose acetate’. That may sound non biodegradable but this is not the case. You can evidence this very quickly – a staggering 4.5 trillion butts are discarded each year (We can’t find a source for this number, but it is used widely on many sites, so let’s assume it is accurate). If these butts are not biodegradable – where are they now? Mass consumption Smoking has been around for 100 years or so. Despite the efforts of our Councils, if they did not decay, our sewers would be blocked and our streets piled high with cigarette butts. Now for the science proof!
The filters are mainly made from a synthetic polymer called cellulose acetate. All sounds a bit scary, but not really.
Acetic Acid (vinegar) is one of nature’s building blocks – life on earth needs it. Cellulose acetate is just lots of vinegar molecules joined together into a chain. Cellulose acetate is a short step away from cellulose (i.e. wood!). Most cigarette butts apparently still use natural cellulose acetate (i.e. tow from the wood pulp http://www.bat.com/group/sites/UK__3MNFEN.nsf/vwPagesWebLive/4572237B0C2D456CC1257314004EF667
). Even if they do not, synthetic (i.e. man made) cellulose acetate is man’s copy of nature’s science. It is used all around you – wrapped a present with cellotape recently, kept any photographic film (pre digital!) – that’s all cellulose acetate.
How fast cellulose acetate decays is directly related to the composting conditions – and principally the temperature of the heap (Q10 equation). You will often see quotes of 3,10 or 50 years as estimates for cigarette butt decomposition time. This is directly comparable the time it takes to decompose lignin (i.e. wood). Most of these tests are done outdoors (so an average of 10C is the temp for most tests). If you increase the decomposition temperature to 60C, you can divide this number by 32 and you’ll get the time it takes to hot compost it. So 10 years at 10C = 4 months at 60C (Again this is directly comparable to wood in an outdoor heap and wood in an IVC composting plant.
Even if we agree it is biodegradable, surely we do not want cigarette butts in our compost bins – they are full of toxic, carcinogenic tar chemicals the list of additives runs into 600 approved of by FDA for addition to cigarettes. If you really want to see some serious chemical names have a look at Wiki – http://en.wikipedia.org/Wiki/List_of_cigarette_additives
. Yes there are carcinogens in butt filters, but don’t forget – burning wood, fire smoke, the original tobacco plant, and much of nature – also has these nasty chemicals. Someone may have tested every single item and may challenge back, but looking through the list, from our knowledge of composting bacteria, they all look like readily biodegradable organic chemicals (i.e. bacteria food). These chemicals are built up in plants and broken down by bacteria all the time. (Take the logic to the extreme – if the carcinogenic chemicals made in plants were not biodegraded, then over the millennia they have been made by plants, they would have built up in soils – maybe even to a level that would have made soil toxic to humans?
What about the risk from “TMV – tobacco mosaic virus”. From our reading on the subject, claims are made that small fragments of tobacco carry the virus over from the tobacco leaf into the cigarette and onto the filter. TMV is known to be resistant to low temperature composting. However read wiki: http://en.wikipedia.org/wiki/Tobacco_mosaic_virus
. If your heap is hot (60C), the virus is going to outcompeted, die and be eaten by the thermophilic bacteria. If you add in the fact that remote chance TMV survives the burning process at 200C, a small chance a tiny fragment gets into filter and that a tiny fragment is not then eaten by bacteria – TMV from composting butts looks a really low risk.
Only you, as the composter, can make the decision whether to compost your cigarette butts. I do not smoke, but if I did, I’d be more worried about smoking than composting cigarette butts!
So finally – what’s the alternative? Leave them lying around, hope someone cleans them up and takes them to landfill! Then what? Well they will just decompose anaerobically and release methane!
Proper HOT Composting of cigarette butts looks sound!
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.
A text book start for the HOTBIN
The Compost Woman, who knows an awful lot about composting, reviews the HOTBIN! And I’m pleased to announce she has had a text book start as she has already reached 60C!
She started with an very full HOTBIN having plenty of material available for her base layer.
After 24 hours there was already a noticeable difference as the the material started to decompose.
She is a freelance Forest School Leader and Environmental Educator who works with both adults and children on all sorts of things. As well as a volunteer Master Composter and Master Gardener, helping people make compost and grow veg at home or at school.
There is more than ONE alternative to sending food waste to Landfill
Ban food waste from Landfill?
Collect and reprocess it via anaerobic digestion (AD) instead? Well yes and no!!
Respect the 3Rs: we should reduce food waste. Accepting there is always going to be some waste to treat…
There have been renewed calls to ban food waste from landfill in the Guardian today . The report’s co-author Quentin Maxwell-Jackson is reported by the Guardian to state: “Anaerobic digestion technology has so many clear advantages over other waste treatment and energy generation options that it is very surprising it has not taken off in a big way yet in the UK.”
Calls to ban food waste have been made before. The Government’s stated policy is collection and reprocessing food waste via AD.
It is still probably still too early for the policy makers to ban food waste from landfill as the UK does not have the capacity ‘coming on stream’ to reprocess it via alternative means.
Every new AD plant takes time to get planning permission, to build and commission. At out last reckoning, about 3 major were due to come on stream next year and we estimated the UK needed 300 to divert food waste from landfill – it is going to be a huge cost and long path.
AD makes a lot of sense – we need a collection/reprocessing technology that caters for the majority and we know only about 15-20% of the UK population does (or will) home compost and traditional home composting has never been appropriate for all food waste.
We should not let the historic issues of home composting all food waste (including cooked food, meat, fish, bread, cakes, rice, pasta etc) that create a stinky odour that deters people and attracts rats, flies from continually reviewing technology for home composting. The HOTBIN team has real factual evidence that the HOTBIN has changed home composting of food waste for the better. Users have changed behaviour and are diverting all food waste from landfill. We estimate 5m current home composting households could divert all food waste and make a contribution – immediately.
100,000 HOTBIN users would equate to 1 new big AD plant. Delivering a million units a year (we wish!) is a logistics co-ordination issue – the capacity can be made available very quickly. We understand home composting is not for everyone – but we need to make a dent in landfill now and it can be done now.
There are other reasons why AD is not the ‘be all and end’ of reprocessing food waste. Reprocessing is a complex combination of user behaviour, logistics and technical facts. Yes AD has advantages, but so does home composting. Home composting removes the need for collection and transport, the compost can be used in the garden (reducing fertiliser and peat consumption) and adding organic matter and humus back to into soil is essential to soil fertility.
Help us win government support – HOTBIN composting diverts domestic food waste.
[At present we are pushing water up a hill and knocking on closed doors.]
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
The HOTBIN composting the whole takeaway!
Composting ‘Vegware’ ™ & Biodegradable bags and containers in the HOTBIN
The HOTBIN was developed to compost all food, garden and grass in the home and garden. We were contacted by Lucy Frankel at the foodwastenetwork.org.uk who is building a food waste network www.foodwastenetwork.org.uk to help commercial business do more to divert food waste from landfill.
We got to talking about using the HOTBIN for small cafes, restaurants and hotels (noting a limitation under ABPR that each commercial site would need to have its own garden/land to use any compost made). Lucy wanted to know if the HOTBIN could handle things like compostable takeaway packaging and asked if we would try some specific tests for her. Lucy works for Vegware Ltd who offer compostable products like cups, tableware, fast food containers and the like.
We were keen to give it a go, confident the HotBin would eat them fast and furious!
What are the composting objectives?
- If the HOTBIN composts them, users can use these containers at home
- If HOTBIN eats them, then possible use of Vegware + HOTBIN at summer events that are semi permanent (ie weeks rather than days) over summer.
We are not suggesting homes will use all these items but on the other hand isn’t it good to know if your Vegware fish & chips, pizza or deli container can be composted at home.
Setup and methodology
- A range of items were received. These were chopped up with scissors.
- The HOTBIN was running at 50C, and the items were just tossed in.
- Each weekend more food waste was added above the Vegware and stirred in
Progress at end of week 2
- Well as expected the more ‘cardboard’ like containers had gone!
- The ‘clear plastic’ (PLA) pots has started to compost (turn white, curled edges)
- Spoons and forks (CPLA) – a lot tougher and will take longer
- There has been no noticeable affect good or bad on the temperature of the HotBin
Progress at end of week 6
- Only one fragment of ‘clear plastic’ (PLA) remains
- Spoons and forks (CPLA) – all but two fragments gone
Looking at the small fragments left – they are soft and have been well attacked. It is most likely that these fell to side and dropped to lower colder zone during stirring.
The HOTBIN eats PLA containers – no problems. The thicker spoons and forks (CPLA) are also eaten – it just takes a little longer and you might need to pass a few bits back through.
Notes on what the materials are made from:
PLA is made from corn starch by Natureworks LLC, and is an ideal replacement for oil-based plastic in a multitude of applications. These include films, thermorformed products such as cups and deli pots, and also injection-moulded products.
CPLA is a proprietary combination of PLA, chalk and other biodegradable additives. CPLA is suitable for high-heat applications such as making cutlery and hot cup lids, as it can take temperatures of up to 85°C without any deformation.