Composting Techniques E-Book

Rod Weston

• Herausgeber: The Crowood Press
• Kategorie: Lebensstil
• Serie: A Gardener's Guide to
• Sprache: Englisch

Seitenzahl: 340

Veröffentlichungsjahr: 2023

Beschreibung

It is widely accepted that composting benefits both the environment and the garden, as a means of reducing waste while contributing to a healthy soil. This practical guide offers a host of composting techniques for the home, allotment and community gardener, as well as indoor and balcony composting for those without access to a garden. It explains the processes behind aerobic composting and anaerobic fermentation, and the conditions necessary to compost effectively without mess or smell.

Leseprobe

CONTENTS

Introduction

1 Composting: History, Climate Change, Sites and Principles

2 Composting Techniques

3 Composting: Process and the Required Conditions

4 Phases of Hot Composting: Microorganisms, Macroorganisms and Pathogens

5 Entry-Level Composting

6 Mid- and Higher-Range Compost Bins

7 Composting for the Enthusiast and the Professional

8 Potential Problems

9 Compost Activators

10 Vermiculture: Composting with Worms

11 Bokashi Fermentation

12 Using Compost

13 Compost Teas and Liquid Feeds

Acknowledgements

Index

INTRODUCTION

In recent years there has been an increased interest in composting as an activity that can help to reduce greenhouse gas emissions and play a role in protecting the environment, while at the same time contributing to a healthy soil. The aim of this book is to make a small difference by encouraging householders to compost their organic waste and, most importantly, to continue composting. New composters may encounter various problems while trying to master the craft, and the drop-out rate tends to be quite high. It is hoped that detailing the different techniques and procedures to deal with any issues may help new recruits to persevere. As part of this approach, the photographs used to illustrate the text show less of the pristine bins and smart tidy gardens that often feature in books and more of the actual working bins, which can be untidy and in need of repair, and in some cases may look weedy and neglected. With a little help and knowledge, compost just happens. The composting area of a garden usually reflects the owner’s general approach to gardening; appearances can vary widely, from a well-managed and professional-looking set-up to a scruffy site tucked away in a corner of the garden, hidden from view. Both approaches can be effective. The key message is to keep composting, whatever style you adopt.

Like many of my generation, as I child I helped my father on his allotment. In those days, the allotment was an important piece of ground that played a major role in providing fruit and vegetables for the family. Compost heaps, along with manure from the local stables, provided essential nutrients and organic materials for the soil. I continued composting at home and, later, on my own allotment, but it was not until I joined the National Allotment Society that I became interested in composting as more than a way of disposing of garden waste and providing a soil supplement. In 2009, I became a Garden Organic Leicestershire County Council Master Composter. My desire to promote composting and encourage both gardeners and householders to adopt it as a means of reducing waste sent to landfill led to the establishment of a demonstration site at the County Council Museum and Discovery Park in Coalville, which showed a range of home composting techniques to visitors. I then became interested in promoting small-scale community composting on allotments, community gardens and in schools, and began to give talks to allotment societies and garden clubs. Over the years, the Coalville demonstration moved venue several times until settling at its present site at Stokes Wood Allotments in Leicester. This location has a ready supply of garden waste and access to catering waste as well as indoor and outdoor training facilities. The site now provides a community composting service to allotment plot-holders and continues to demonstrate different composting bins and techniques to the public.

It was my experience as Master Composter and as a member of the NAS that led to this book. My hope is to encourage people to start composting and, once they have got going, to develop their skills and techniques, and increase the range and volume of waste that they can divert from landfill. It is also aimed at encouraging groups to set up small-scale community composting on allotments, at schools and on community gardens. If garden and catering waste can be dealt with on site, the environmental costs of transporting it to a central location for processing can be avoided.

The advice in this book is intended to be taken as a guide. All the procedures and techniques that are described can be modified to suit your own particular circumstances. There are almost as many ways of composting as there are composters and, despite what might be read online, there is no single right way of doing anything. If what you are doing works, it must be right for you, although, of course, the method may be open to improvement. The main thing is to enjoy your composting in the knowledge that, while you are improving your soil to produce better crops, you are also, in a small way, helping to save the planet.

CHAPTER 1

COMPOSTING: HISTORY, CLIMATE CHANGE, SITES AND PRINCIPLES

Composting has a long history as an effective and environmentally friendly means of waste disposal. There has been a need to dispose of animal manure and used bedding since animals were first domesticated, so it was natural that animal (and human) waste would be used as one of the main sources of soil enrichment, until the introduction of modern sewage systems, science-based farming and chemical fertilisers. Composting has developed from an activity practised by individual farmers to being the key part of the waste management and environmental systems today. This introductory chapter will look at its history, as well as advising on the basic health and safety precautions that are required when working with compost.

A Brief History of Composting

The truism that there is ‘nothing new under the sun’ certainly applies to composting. Many of the techniques used today have their origins in those used by early farmers. One of the first written accounts of composting dates from between 2320 and 2120 BC, when the people living in the Akkadian Empire in Mesopotamia transitioned from being hunter-gatherers to farming. There is also evidence of small-scale cultivation in the Neolithic, Bronze Age and Iron Age in Scotland with midden heaps being ploughed into the land. By the first century BC, records show that the Chinese were enriching their soil with cooked bones, manure and silkworm debris. There are also references to the composting of manure and straw in an early Hindu text, and the Greeks, Egyptians and Romans are all known to have taken straw from animal stalls and buried it in cultivated fields. Similar practices are also mentioned in the Old Testament and the Hebrew Talmud, which records the enrichment of the soil using ashes, straw, stubble, chaff and grass, as well as the blood from animal sacrifices.

The Native Americans were active composters, using sheet and pit composting. They also composted while planting, burying uneaten fish and parts of animals as a nutrient source when sowing seeds. However, as in most areas, stable manure was more readily available than fish – evidence suggests that the early American farmers adopted a system using two loads of soil to one of farmyard manure.

Professor F.H. King of the U.S. Department of Agriculture toured China, Japan, and Korea in the early 1900s and published information on the use of manure (both animal and human), canal mud, green manure, and composts to maintain soil fertility. Sir Albert Howard took King’s writings into account when developing the Indore composting method on which many modern techniques are based. The Indore method used a mix of 3 parts plant matter to 1 part manure. These were initially piled up in sandwich fashion, with green layers of about 15cm (6in) thick followed by a 5cm (2in) layer of manure and then one of soil, ground limestone and rock phosphate. The layers were repeated until the heap was about 1.5m (5ft) high. The heap was kept moist and turned during decomposition providing aerobic conditions, and the resulting compost was ready in about three months.

Modern composting is often associated with the organic movement that began to grow in the early 1900s in response to the growth of industrial agriculture and use of synthetic chemical fertilisers and pesticides. Rudolf Steiner’s system of biodynamic agriculture, developed in 1924, included the use of compost preparations involving herbs. Some of these are still used today by home composters to make liquid fertilisers and as compost activators.

In the USA, J.I. Rodale continued Howard’s work and showed American gardeners the value of compost as a soil improver. In 1947 he established the Soil and Health Foundation, later to be renamed the Rodale Institute. In the UK, Lawrence D. Hills was so intrigued by the possibilities of the perennial hybrid plant Russian comfrey that he devoted much of the rest of his life to popularising its use. In 1954 Hills formed the Henry Doubleday Research Association (HDRA), which now trades as Garden Organic.

Compost bins at a National Trust estate. Materials are still being added to the bin on the left.

Compost: Reducing Waste

The standard definition of compost is that it is a soil conditioner produced through the aerobic biological decomposition of organic materials. Composting plays a key role in improving the structure and fertility of soil and encourages microbial activity (for more on this, seeChapter 12). The commercial product has usually undergone decomposition at mesophilic and thermophilic temperatures (hot composting), which reduces the viability of pathogens and weed seeds. At the domestic level, while both hot- and coldcomposting techniques may be used, cold composting is the more frequent choice.

Under the standard definition, anaerobic decomposition by microorganisms that do not require oxygen to survive is not composting and does not produce ‘compost’ but anaerobic digestate. However, many home practitioners will refer to the process as ‘anaerobic composting’, and some of the techniques that are suitable for home and garden use are included here, as the digestate possesses some characteristics that are similar to those found in compost and is a nutrient-rich fertiliser.

Composting was once the preserve of horticulturists and gardeners, providing a useful way of converting garden waste into a ‘black gold’ that would improve their soil. However, the increasing interest in the environment, sustainability and climate change has attracted a new type of composter, who sees composting as a means of protecting the environment by repurposing waste material that might otherwise be sent to landfill, and of reducing the greenhouse gases released into the atmosphere. The practice is now being actively promoted by local councils and environmental bodies as a means of treating organic waste from homes and business premises.

Domestic waste chart showing approximate proportions by type. Food is typically the largest group and as such should form the main target for environmentally concerned composters. The figures may vary year on year.

The Waste and Resources Action Programme (WRAP) regularly reviews the statistics relating to household food and drink waste and publishes current information on its website (wrap.org.uk/resources). According to research, organic materials make up about 60% of household waste, so the benefits of increasing the amount that goes to be composted could be considerable. Rural households tend to home compost (or burn) a higher percentage of their garden waste than urban households. It has been estimated that less than half of the rural garden waste generated is collected by the authorities, while urban households strongly rely on kerbside collections.

Most compostable domestic waste is comprised of food. Cooked food can be composted with a bin designed for that purpose or in an entry-level bin if pre-treated with bokashi.

As councils have increased their charges for green waste collections, to help balance their books, there has been more interest in composting among urban households. However, showing an interest in composting is not enough. There is also a need to provide the right information to enable householders to compost successfully – and to continue composting. In 2004, for example, approximately 40% of householders who had bought a bin and started home composting gave up using it, because of a lack of knowledge. Almost two decades later, councils and others now produce leaflets, publish information online and train ‘Master Composters’ to provide support and advice. This has apparently resulted in a reduction in the drop-out rate to between 8 and 14%. In more recent years, this figure has reduced again, to 3.9%, which is probably about as low as it will go without further intervention.

The compost hierarchy showing the preferred order for dealing with compostable waste. Waste reduction may not be applicable to organic material from the garden, making home composting the first environmental choice.

The amount of food waste sent for composting and anaerobic digestion is only a small proportion of the total waste collected. Almost half of the food waste in the average rubbish bin could have been composted, although the amount collected should increase with the spread of separate food waste kerbside collections. Unfortunately, much of the publicity material issued to home composters still states that cooked food cannot be home composted when in fact it is compostable if the appropriate techniques are used. Everyone, even apartment dwellers, can help to reduce the amount of waste sent to landfill or other more costly forms of treatment by composting some food and garden waste at home. Treatment of compostable waste at source has much to recommend it as it avoids the financial and environmental costs of kerbside collection.

Composting and Climate Change

Waste disposal results in the direct and indirect emissions of greenhouse gases (GHGs). The main gases are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and non-methane hydrocarbons (NMHCs). Composting helps divert vegetable and other organic waste from landfill, in the process reducing the production of greenhouse gases, as well as helping prevent landfill disposal sites from filling up prematurely. When composting on the domestic front, nutrients found in organic material are recycled back to the soil, improving water retention and soil health. This leads to improved plant growth and sustainable food production.

The compost cycle.

Plant matter buried with other waste in landfill and open stockpiles, such as manure heaps, results in anaerobic decomposition, which releases significant amounts of methane into the atmosphere. While this gas can be collected and burnt to generate electricity, it is a significant contributor to global greenhouse gas emissions, being 26 times more potent than carbon dioxide. Global emissions from waste have almost doubled since 1970 and now produce 3% of anthropogenic (human origin) emissions. About half of these emissions come from the anaerobic fermentation of solid waste disposed of on land. The global warming effect of anaerobic decomposition can be mitigated where the methane is collected and used to produce electricity, with carbon dioxide as a by-product. Although it is still a greenhouse gas, CO2 has a weaker global-warming effect than methane. It is the primary gas given off during aerobic composting, but this is not considered to affect global warming, as the materials decomposing are from what is known as the short-term carbon cycle. However, some greenhouse gases will still be produced, particularly during hot composting, if there is insufficient oxygen in some areas of the bin. This will lead to anaerobic decomposition occurring, resulting in the production of methane and nitrous oxide. It can be prevented by maintaining airflow and air spaces in the bin by ventilation, aeration and avoiding the material becoming waterlogged.

Although people may refer to anaerobic techniques as ‘composting’, strictly speaking the anaerobic process is more correctly described as anaerobic digestion or fermentation. Anaerobic fermentation in an enclosed anaerobic digester (AD) can be used to treat waste food, human effluent and livestock waste. The methane and other biogases produced in AD are collected and used for heating or power generation. Remaining bio-solids can be used as a fertilizer on farms. In hotter countries, small AD plants may be used to treat human waste from individual houses. Anaerobic composting on a bokashi system is used in agriculture and horticulture and can also be used in the garden and on a small scale in the home for kitchen waste (seeChapter 11).

Industrial composting practices that minimise anaerobic and maximise aerobic conditions are effective in reducing methane emissions from organic waste currently stockpiled or diverted from landfill.

Agriculture is a significant contributor to climate change, with at least 14% of global greenhouse gases (GHG) emitted as a result of farming activities, such as keeping livestock and ploughing, which releases carbon dioxide from the soil. The making and use of compost in farming, horticulture and home gardening contributes to the removal of atmospheric carbon through a process known as soil carbon sequestration. There is also an indirect contribution due to enhanced plant growth resulting from the use of compost on the soil. If as a result of applying compost fewer chemical fertilisers and pesticides are used, and the increased organic matter in the soil results in better water retention and a reduced need for irrigation, greenhouse gas emissions will be further reduced. Spreading compost and using a no-dig method can boost the carbon storage ability of the soil. While animal husbandry is a significant contributor to global warming it has been shown that, if compost is spread on grazing lands, it could capture a significant amount of greenhouse gas emissions with carbon storage utilising humus formation. The beneficial effect would continue into the future, resulting in an improvement of the overall greenhouse gas balance.

The Intergovernmental Panel on Climate Change and the European Commission have formally recognised carbon sequestration in the soil as one of the measures through which greenhouse gas emissions can be mitigated.

Table 1.1 Aerobic composting vs anaerobic digestion

Aerobic

Anaerobic

Requires oxygen for respiration

Does not require (or in the absence of) oxygen

Rapid decomposition

Slower decomposition

Produces heat (most noticeable in larger bins)

Generates little heat

Hot compost can kill pathogens, seeds and weeds

Insufficient heat to kill weeds or pathogens

No pungent gas produced

Pungent gas produced (for example, hydrogen sulphide)

Carbon dioxide is main gas released

Majority of energy released as methane

Produces compost

Produces sludge (digestate), which requires aerobic composting to complete process

Different Sites

Home and Allotment Composting

Aerobic home and allotment composting can make a valuable contribution to the reduction of the carbon footprint that is associated with the treatment of organic waste, by eliminating the road miles involved in collecting and taking the waste to the landfill tip or processing plant. Home composting also saves the road miles involved in transporting commercially produced compost to retailers and gardeners’ homes. Landfilling of domestic organic waste is increasingly being replaced by industrial composting. While this is a welcome development, the collection and transport of the waste still involves avoidable road miles. In addition, home composting produces fewer methane emissions than commercial composting.

A moulded plastic bin is often the first type acquired by a composter.

Individual householders, community gardens or schools may play only a small role in the processing of organic waste, with each using just one or two compost bins. However, it is likely that each plot-holder on an allotment, for example, will have at least one bin, with most having several, so an allotment site may be home to as many as 100 or even 200. The total area of land that could be involved in composting would be significantly increased if more gardens, lawns and parks were brought into use. Many county and city councils are responding to the climate emergency by actively promoting home composting, with subsidised compost bins and advice and training through Master Composter and similar schemes. Some are also adopting systems of composting and carbon sequestration in their parks and grounds, using the compost made from the green waste that they collect from households.

Today, more people live in cities or suburban areas than in rural areas, with limited outdoor space. Some urban dwellers may have a small garden with a lawn, or there will be a managed area of grass around an apartment block or commercial buildings and offices. In suburban areas, country towns and villages, the garden and grassed area will be larger. In both urban and rural areas, most householders who want access to more ground will live within a few miles of an allotment or community garden.

In terms of its environmental impact, the traditional garden lawn has not had a good press. Lawns can reduce biodiversity, and the pursuit of ‘perfection’ has tended to encourage the use of synthetic fertilisers and weedkillers. These can pollute the environment and have the unintended outcome of killing beneficial species. The mowing, fertilisation and general high level of maintenance necessary can result in a net emission of carbon dioxide and nitrous oxide, which are both contributors to global warming. However, the impact may be countered by the lawn’s capability for carbon sequestration, especially if it is managed environmentally.

Entry-level moulded bins. Composters will often use more than one type of bin.

Most composters start with one or two bins. Over the years they might expand to meet an increase in demand as their interest in composting develops.

Entry-level bins. A well-planned composting area can enhance the appearance of a working garden.

Community Composting

Concern for the environment and an increased sense of social responsibility have led to a significant growth in community composting schemes. These usually involve a community or group – an allotment, community garden, block of flats, community centre, café, village, workplace or school – coming together to turn the organic waste they produce into compost in a locally controlled, environmentally responsible, not-for-profit way. The resulting compost is then used locally. Community composters may also run education campaigns, promote home composting, and help others to establish new community composting schemes.

The reception bins on the small-scale site for 60 plots at Stokes Wood Allotments, Leicester. Community composting is becoming more popular in the UK, with schemes covering allotment sites, community gardens and schools. Larger schemes may incorporate kerbside collection or drop-off by club members at the site.

Community composting sites are covered by the waste regulations and need to meet the Environment Agency’s requirements under the Environmental Permitting (England and Wales) Regulations. In the UK, a licence or an exemption certificate will be required. The exemption application granted to small-scale schemes is simple to obtain via the completion of an online application form.

The requirement for a permit or licence or an exemption will depend on two factors:

• the quantity of material stored on site at any one time; and

• the type of material accepted for composting and the time the material is stored on site until it is ‘treated’ – in other words, composted.

Reception bin overflowing into working bins at the Stokes Wood allotment site – maintaining a tidy site while providing open access can be difficult.

In a smaller community scheme, for example, on an allotment site where the organic garden material is produced and the compost is used on site by plot-holders or community gardeners, the material is usually processed in pallet bins. Some allotment- and village-based schemes can be open access, but this brings with it the risk that the reception bins will be overfilled as people leave waste for composting. Sometimes, excess waste may be dumped into the wrong bin because of a lack of space. In such situations the working area may need to be fenced off from the reception bins to avoid unsorted waste being added to the working bins. Alternatively, the scheme may be enclosed, which means that it will be open to receive waste only at certain times and under supervision. Community composting sites may also seek to promote composting to the wider public, by providing tours and training, and perhaps holiday activities such as painting compost bins to attract and educate children.

Community sites often have space for education and children’s activities to promote composting.

A school or allotment that wants to make compost on site from its own garden waste and uncooked fruit and vegetables, including children’s snacks, for use on site, should be able to establish and operate the system at minimal cost. Usually, a series of low-cost domestic or pallet bins will be suitable. However, if a school or other workplace decides to compost catering waste from its kitchens, a more expensive composter such as the Ridan will be required, along with an increased level of planning and support. For more information on catering waste and food composting, seeChapter 6.

Where a community composting system is being established at a workplace, a tidy, more professional image may be important. In this case, more permanent bins made of sleepers, blocks or bricks may be used.

A tour of the community composting site, with interest being shown in the aeration system in the Aerobin.

Community sites may include bins suitable for cooked food. On most such sites the bins will be bigger than these domestic models.

Larger community composting clubs and organisations may seek to set up a system whereby materials are collected and dropped off by members or acquired via kerbside collections. The finished compost may then be sold to members or to the public for off-site use. Many of these larger schemes will be grant-funded to cover ongoing operational or staff costs. However, the funding model does carry some risk as the income cannot usually be guaranteed in the long term.

Where a scheme is being set up to take waste from the local community, a Community Interest Company (CIC) should be formed to manage it, if the organising society does not already have that status. Advice should be taken in advance to ascertain whether use as a composting site will require planning permission.

Leaves deposited in community composting bins at a County Council site; the bins were originally used to compost waste from the offices.

Biochar

Charcoal will be familiar to most people as a product of heating wood in the absence of oxygen. The term ‘biochar’ refers to the solid residue of plant material that has been pyrolysed, that is to say, carbonised under a high temperature. Biochar can be produced from almost any material, including bamboo, coco, straw, softwoods, hardwoods. The source of the organic content should be checked to ensure that it has not been grown or harvested in a way that damages the environment.

Biochar incorporation into soil can result in the removal of carbon dioxide from the atmosphere by terrestrial carbon sequestration. Biochar can be mixed with compost during the maturation period six to 12 weeks before it is applied to the soil. However, for the home composter, the main environmental benefits occur if biochar is mixed with a source of greens and introduced at the start of the composting process. This can result in reduced emissions of the greenhouse gases, methane, nitrous oxide and ammonia. The compost incorporating the biochar can be added to the soil when the composting process is complete, after three to 18 months.

Used in this way, biochar also acts as a bulking agent, helping to keep the compost aerated. It also results in an increase in temperature, leading to a consequent reduction in the time taken to produce finished compost.

Country-House Composting

Allotment and community garden sites may be operated on a similar scale and use similar methods to professional gardeners caring for a large country-house or estate gardens. Traditionally, such sites would be based as a large-scale hot-composting system with three to five bins, either turning to aerate or operating on a non-turn system. It is well worth looking at such systems and the vegetable gardens when visiting National Trust houses and other similar properties. In most cases the gardeners are only too happy to explain the techniques used.

Bank of traditional bins on a soil base at a National Trust estate.

Part of a new composting facility at Blickling Hall in Norfolk, developed as part of a green initiative.

Principles

Composting: Aerobic and Anaerobic

Composting need not be complicated. Under the right conditions, it just happens. If left alone, all organic matter will naturally decompose, but composting means that the time taken can be reduced. The finished product will be in a form that allows the organic material and nutrients to be returned to the soil while minimising damage to the environment. There are some who define composting more narrowly as the aerobic decomposition of organic material and label the anaerobic process as digestion or fermentation. As a matter of convenience, the wider definition will be used here.

Aerobic composting using a traditional heap.

There are three different approaches to the home ‘composting’ of organic wastes: aerobic composting, vermicomposting and anaerobic digestion. (For more detail on aerobic and anaerobic respiration, seeChapter 3.)

Aerobic composting in entry-level moulded compost bins.

•Aerobic composting: in this process, the waste is continually aerated by air flowing through the organic material and, optionally, by intermittent physical turning of the waste by the composter. There are two forms of composting, described as ‘hot’ or ‘cold’, depending on the temperatures reached during the process of decomposition.

•Vermicomposting: in this aerobic composting system, the organic material is eaten by worms and is turned into compost as it passes through the worm’s digestive system. The composting material is at, or about, ambient temperature with little temperature variation in the heap.

•Anaerobic fermentation/digestion: this process is carried out in an oxygen-deprived environment. It is used less frequently to deal with garden waste, but a bokashi system is often used as an indoor pre-composting treatment for food waste. The material being digested shows only a very slight increase in temperature.

Composters should be encouraged to try a variety of methods and techniques across the three approaches, to increase the range of materials composted. However, aerobic composting is the most popular of the three and the majority of this book will be devoted to the different techniques relating to this particular process. The advice on methods and techniques is intended to give guidance, but it is important to experiment using different methods and mixes of materials to determine those most suited to the waste available. In basic terms, if it works, it is being done right, no matter what others might say. It is also important to remember that working bins do not need to look pretty or smart in order to function, although keeping the site tidy does give a much more professional impression.

Aerobic composting in pallet bins with a lid and sliding hatch.

Microplastic Pollution

Pollution by microplastic particles is being recognised as an increasing environmental problem. Considerable publicity has been given to the issue of plastics in teabags contaminating the soil and watercourses. Also implicated are some of the materials used in gardening and composting, including woven polypropylene ground-cover fabric and old sheets of polythene that often serve to line and cover compost bins, heaps and windrows. The breakdown of such materials can cause environmental contamination, and this may also occur when waste materials are not sorted properly. Care should always be taken not to allow plastic-coated containers or food wrappings to end up in food waste and subsequently in the compost.

Some teabags still contain plastic and do not decompose properly when composted.

Magnification of a teabag after composting.

Health and Safety

Composting is a relatively low-risk activity and the risks that are present can be reduced to acceptable levels by a sensible assessment and the use of simple control measures. The hazards most likely to cause injury or ill health during composting, as with all gardening activities, will be those resulting from slips and falls, manual handling and the use of hand tools. However, the issue that probably causes the most concern in composting is the risk of infection. A number of disease-causing microorganisms may be found in manure, compost and soil, and these could present a risk of infection – albeit relatively small – to the composter. These include the food-poisoning bacteria that are often featured in the press following an outbreak, such as salmonella, campylobacter, Clostridia perfringens, E. coli, and Staphylococcus aureus, as well as other pathogens present in the environment.

Compost bins on an allotment site. Trips, falls and manual handling incidents are the most likely cause of injury.

The risk from material from the domestic kitchen or garden is relatively low as it is less likely to be contaminated with animal and faecal waste than materials from some other sources. Luckily, most of the pathogenic bacteria, if present, will not be present in large enough numbers to cause disease in humans and in most cases the hot-composting process will kill those remaining. More details of these organisms are given in Chapter 4.

Bioaerosols (airborne microorganisms including bacteria and fungi spores) have been implicated in cases of infection in industrial composting plants, with rare cases associated with home gardening with compost. The number of bioaerosols will be dependent on the degree of contamination of the initial organic material, the growth of the organisms while awaiting composting, multiplication during the composting process and the actual activity being undertaken. Higher-risk activities include turning and sieving compost and any process that involves disturbing compost on which mould is growing or when the compost smells mouldy.

The risks of infection when working with compost are small and a few simple precautions will reduce the likelihood to an acceptably low level:

• Wear gloves, either gardening gloves or nitrile/latex gloves for more delicate tasks. Wash or dispose of gloves after use.

• Wash hands and/or use hand sanitiser (if washing facilities are not available).

• Do not store compost in a greenhouse; it will warm up during the summer, allowing microorganisms to multiply.

• Open bags of compost slowly and in a well-ventilated space. When disturbing compost, do not hold the head directly over the bag or bin, to avoid breathing in any aerosols or spores that might be released.

• Moisten compost to reduce bioaerosols during turning (aeration) and consider wearing a dust mask (particularly if the compost smells musty).

• To avoid inhaling airborne particles when turning compost outdoors, stand up-wind so that they are blown away from the face.

• Anyone with a weakened immune system or lung diseases should wear a suitable face mask (FFP2 or N95 standard).

• Shred woody material in a well-ventilated area.

CHAPTER 2

COMPOSTING TECHNIQUES

With the range of different composting techniques available, the potential composter will need guidance when trying to select those that best suit their needs and lifestyle. The various aerobic composting systems all have their own pros and cons, and the information given here will help with choosing the most appropriate method for each situation. Details of anaerobic fermentation or digestion techniques are also given as, although these are not strictly speaking methods of composting, they do have their uses in treating kitchen and garden waste. More detailed information follows on entry-level methods for those new to composting, the use of more expensive bins and on hot composting and food-waste composting for those who wish to extend their activities, as well as more specialised techniques such as bokashi fermentation and composting with worms.

Options for composting garden waste.

Options for composting food waste (including cooked food).

Table 2.1 Practical aspects of the different techniques

Spreading or Burying, Mounds and Heaps

Sheet Composting, Trench and Post-Hole Techniques

Some methods require no expenditure or special equipment as the compost is made simply by spreading or burying the organic waste over the ground or adding it to a trench or post holes dug in the garden. As it is free and requires no equipment, it might be expected to be more popular than it is, but in fact these techniques are used only by a small minority of composters.

Trench composting is often used as a seasonal technique during the late summer and autumn, with the waste being allowed to compost over a few months in preparation for spring planting.

Sheet composting is best used for garden rather than kitchen waste. It can look untidy, but it is an effective way of adding organic material to large vegetable or allotment gardens and where no-dig techniques are being used. Trench composting is often used to provide a means of preparing the ground in the autumn for planting runner beans in the spring. Post-hole composting can be used to add organic material to small empty spaces or an already planted bed.

Pros: Inexpensive, no turning or aeration required. It is not visible once covered and feeds garden in situ. Post-hole composting can be used in permanent beds between plants.

Cons: There is a need to plan for future use of ground to ensure that space is available for the composting and growing. Digging is required. The waste can take a long time to break down, and there is no compost to harvest. May be difficult to compost during winter months. Might attract rats and vermin if materials are not well buried. Composting meat or dairy products is not recommended.

Time required: 6–12 months

Lasagne Composting and Hügelkultur

Lasagne composting is a no-dig technique using layers of greens and browns and can also be used to fill raised beds.

Lasagne composting in rows in a National Trust garden.

The Hügelkultur method is a permaculture technique, with large pieces of decaying wood being used as a base and layers of compostable organic material added to form a mound up to several feet high. The wood and other materials are left to decompose below ground, while allowing the cultivation of plants on the raised mound, or less commonly a sunken bed. It may be considered as a combined raised (or sunken) bed and compost heap and is said to remain fertile for up to six years. The technique may be used to deal with tree stumps. There are more details of this technique in Chapter 5.

Small Hügelkultur mound being built on a decaying wood base covered with layers of greens and browns. It will be topped with soil and ultimately planted up.

Pros: Provides an additional level on which to grow plants and a means of utilising rotting wood.

Cons: Forms a permanent mound so needs advance planning.

Compost Heap or Pile

The use of the traditional compost heap or pile has fallen out of fashion in the UK, as gardens have become smaller and many gardeners prefer to keep them neat and tidy. In these cases, a bin is a better option. However, a heap requires no expenditure, just a space in a less frequently used part of the garden that is suitable for a large pile of decomposing material that may spread sideways in use. The pile may be extended to make a long pile or ‘windrow’. Windrows of up to 5 or 6 feet in height and 8 or 10 feet at the base are often used to compost municipal organic waste. A heap can be used for both cold and hot composting and can be constructed using layers of browns and greens to give the correct ratio of carbon to nitrogen in the material being composted. This is referred to as the C:N ratio. Unfortunately, they also provide a readily available source of food and shelter for rats and other creatures, although regular turning may reduce the likelihood of them inhabiting the pile.

A traditional compost heap composting grass and leaves.

Pros: Inexpensive. No preparation required unless a concrete base is to be used. Easy to turn and aerate. Suitable for hot or cold composting. A heap is easy to monitor in terms of condition and the compost is easy to harvest.

Cons: May look messy and requires space as it may spread. Might attract rats and vermin. May be difficult to compost during winter months. Requires covering to prevent compost becoming waterlogged during wet weather. Not recommended for meat or dairy products.

Time required: 6–12 months

Traditional heaps have often been replaced by plastic and pallet bins.

A badly maintained heap spreading over the garden.

Containers for Outdoor Composting

Moulded Plastic Bins

Plastic bins can be purchased in a range of shapes and sizes, the most popular of which (in the UK) are the 220- and 330-litre ‘Daleks’, sometimes available through subsidised local council schemes. Most of these bins will include a hatch for removing the finished compost. A base plate may also be available to help prevent entry of vermin.

Compost in a wire bin. This type of bin is frequently used for making leaf mould.