The Composting Handbook: A how-to and why manual for farm, municipal, institutional and commercial composters

By Jane Gilbert

The Composting Handbook provides a single guide to the science, principles and best practices of composting for large-scale composting operations facing a variety of opportunities and challenges converting raw organic materials into a useful and marketable product.

Composting is a well-established and increasingly important method to recycle and add value to organic by-products. Many, if not most, of the materials composting treats are discarded materials that would otherwise place a burden on communities, industries, farms and the environment. Composting converts these materials into a valuable material, compost, that regenerates soils improving soils for plant growth and environmental conservation.

The Composting Handbook expands on previously available resources by incorporating new information, new subjects and new practices, drawing its content from current scientific principles, research, engineering and industry experience. In both depth and breadth, it covers the knowledge that a compost producer needs to succeed. Topics include the composting process, methods of composting, equipment, site requirements, environmental issues and impacts, business knowledge, safety, and the qualities, uses and markets for the compost products.

The Composting Handbook is an invaluable reference for composting facility managers and operators, prospective managers and operators, regulators, policy makers, environmental advocates, educators, waste generators and managers and generally people interested in composting as a business or a solution. It is also appropriate as a textbook for college courses and a supplemental text for training courses about composting or organic waste management.

• Created in conjunction with the Compost Research and Education Foundation (CREF)
• Includes the latest information on composting and compost, providing the first comprehensive resource in decades
• Written with focus on both academic and industrial insights and advances

• Language: English
• Publisher: Academic Press
• Release date: Dec 3, 2021
• ISBN: 9780323856034

Book preview

The Composting Handbook

A how-to and why manual for farm, municipal, institutional and commercial composters

Editor

Robert Rynk

Table of Contents

Cover image

Title page

Copyright

Dedication

Authors and Contributors

Preface

Acknowledgments and appreciations

Chapter 1. Why compost?

1. Introduction

2. Benefits and drawbacks of composting

3. Economic benefits of composting

4. Environmental benefits of composting

5. The drawbacks

6. Facts and fiction of composting and compost

Chapter 2. Enterprise planning

1. Introduction

2. Starting a composting enterprise

3. Assessing your resources

4. SWOT analysis

5. Defining success—start with the end in mind

6. Scoping out availability of feedstocks and markets for compost

7. Determine compost facility regulatory requirements

8. Planning human resource needs of a compost enterprise

9. Production planning—the business of manufacturing

10. Financial strategy—the business of business

11. Enterprise planning—case study

Chapter 3. The composting process

1. Introduction

2. What happens during composting?

3. Changes in the materials during composting

4. Factors affecting the composting process

5. Curing

6. When is it done?

7. Composting microbiology

Chapter 4. Compost feedstocks

1. Introduction

2. Feedstock value

3. Feedstock characteristics

4. Feedstock contaminants

5. Biodegradability

6. Combining feedstocks—amendments and recipes

7. Determining feedstock characteristics

8. Common feedstocks for composting

Chapter 5. Passively aerated composting methods, including turned windrows

1. Introduction

2. Passively aerated static piles

3. Techniques to improved passive aeration—passively aerated windrow system and natural aeration static pile

4. Turned windrow composting

Chapter 6. Forced aeration composting, aerated static pile, and similar methods

1. Introduction

2. Aerated static pile

3. Variations of aerated static piles

4. Methods combining turning and forced aeration of windrows and piles

Chapter 7. Contained and in-vessel composting methods and methods summary

1. Introduction

2. Basic principles

3. Agitated bays

4. Turned/agitated vessels

5. Aerated beds and bays in buildings and halls

6. Silos

7. Rotating drums

8. Tunnels

9. Moveable and modular aerated containers

10. Methods for on-site composting of food waste

11. Summary: comparing the composting methods

Chapter 8. Composting animal mortalities

1. Introduction

2. Mortality composting—basic principles

3. Pathogen elimination, risk management, and regulatory requirements

4. Feedstock characteristics and requirements

5. Methods and techniques

6. Sizing guidelines for passively aerated piles and bins

7. Other mortality composting methods

8. Managing mortality composting operations

Chapter 9. Composting operations and equipment

1. Introduction

2. Material handling equipment

3. Feedstock receiving and handling

4. Amendment handling and storage

5. Feedstock preprocessing

6. Composting operations

7. Curing

8. Postprocessing

9. Finished compost storage

10. Blending compost products

11. Bagging

Chapter 10. Site planning, development, and environmental protection

1. Introduction

2. Compost-site regulations

3. Environmental and community considerations

4. Site selection/evaluation

5. Site development

6. Site layout

7. Composting pad construction

8. How much space? Estimating the area for composting

9. Building—roofs and enclosures

10. Handling run-on/runoff

Chapter 11. Process management

1. Introduction

2. Odor

3. Temperature

4. Monitoring moisture content

5. Oxygen and carbon dioxide monitoring

6. Bulk density and free air space

7. Monitoring pH

8. Monitoring soluble salts (electrical conductivity)

9. Conservation of nitrogen and organic matter

Chapter 12. Odor management and community relations

1. Introduction

2. Odor regulations—All Over the Map

3. The nature of composting odors

4. The anatomy of an odor problem

5. The nature of the nuisance

6. Minimizing odors through site selection and management

7. Odor generation during composting

8. Strategies to reduce the generation of odors

9. Capture and control of odors once generated

10. Capture

11. Odor migration and dispersal

12. Neighbor and community relations—complaints and more

13. Odor characterization and measurement

Chapter 13. Safety and health principles and practices for composting facilities

1. Introduction

2. Hierarchy of controls

3. Safety and health regulations

4. Safety concerns at composting sites

5. Physiological health concerns

6. Biological and chemical health concerns

7. Prevention and preparedness

Chapter 14. Facility management

1. Introduction

2. Administrative functions

3. Managing the carbon footprint

4. Weights and measures

5. Materials analysis

6. Managing with the weather/seasons

7. Preventing and managing fires

8. Preventing and managing nuisance conditions

Chapter 15. Compost characteristics and quality

1. Introduction

2. Typical, and typically variable, compost product qualities

3. Compost performance characteristics

4. Aesthetic characteristics

5. Safety characteristics

6. Compost quality standards

7. Compost testing assurance

8. Laboratory analysis of compost products

Chapter 16. Compost use

1. Introduction

2. General considerations for compost use

3. Compost application rates

4. Equipment for spreading compost

5. Specific agricultural, horticultural, and forestry applications

6. Nursery and greenhouse applications

7. Turf and landscape applications

8. Erosion control and stormwater management

Chapter 17. Compost use for plant disease suppression

1. Introduction

Chapter 18. Compost marketing and sales

1. Introduction

2. Marketplace for compost

3. The Product(s)—compost(s)

4. Marketing concepts

5. Market options

6. Market planning

7. Compost sales

Chapter 19. Composting economics

1. Introduction

2. Economics overview

3. The big picture

4. Economics of compost use

Appendices

Sources of photographs and external graphics

Index

Copyright

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Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.

To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.

Library of Congress Cataloging-in-Publication Data

A catalog record for this book is available from the Library of Congress

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library

ISBN: 978-0-323-85602-7

For information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

About the covers. The large background photo on the front cover was provided by Karin Grobe. It shows a windrow composting facility handling discarded salad from a neighboring packing factory. The inset photos depict various composting methods and compost uses. From top to bottom, the sources are: Robert Rynk, Monica Ozores-Hampton, Cary Oshins, Judy Puddester, and Ji Li. The back cover shows selected posters promoting International Compost Awareness Week, including poster sponsored by the Composting Research and Education Foundation in the U.S., the Compost Council of Canada, and the European Composting Network.

Publisher: Charlotte Cockle

Acquisitions Editor: Nancy Maragioglio

Editorial Project Manager: Lindsay Lawrence

Production Project Manager: Paul Prasad Chandramohan

Cover Designer: Matthew Limbert

Typeset by TNQ Technologies

Dedication

This book is dedicated to Jerry Goldstein, and the Goldstein family, who fed a fledgling group of composters with knowledge and positivity, and nurtured us into an important industry.

Authors and Contributors

John Aber,     Professor Emeritus, University of New Hampshire, Durham, NH, United States

Ron Alexander,     R. Alexander Associates, Inc., Apex, NC, United States

Susan Antler,     Compost Council of Canada, Toronto, ON, Canada

Johannes Biala,     Centre for Recycling of Organic Waste & Nutrients, The University of Queensland, Gatton, QLD, Australia

Ginny Black,     Compost Research and Education Foundation (CREF), Raleigh, NC, United States

Anna F. Bokowa,     Environmental Odour Consulting Corporation, Oakville, ON, Canada

Jean Bonhotal,     Cornell Waste Management Institute, Cornell University, Ithaca, NY, United States

Nellie J. Brown,     Workplace Health & Safety Program, ILR, Cornell University, Buffalo, NY, United States

Sally Brown,     School of Forest Resources, University of Washington, Seattle, WA, United States

Michael Bryant-Brown,     Green Mountain Technologies, NE Bainbridge Island, WA, United States

Van Calvez,     Green Mountain Technologies, NE Bainbridge Island, WA, United States

Andrew Carpenter,     Northern Tilth, LLC., Belfast, ME, United States

Craig S. Coker,     Coker Composting and Consulting, Troutville, VA, United States

Leslie Cooperband,     Praire Fruits Farm and Creamery, Champagne, IL, United States

Matthew Cotton,     Integrated Waste Management Consulting, Richmond, CA, United States

Jeffrey A. Creque,     Rangeland and Agroecosystem Management, Carbon Cycle Institute, Petaluma, CA, United States

Gregory Evanylo,     School of Plant and Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States

Britt Faucette,     Filtrexx International, Decatur, GA, United States

Frank Franciosi,     U.S. Composting Council, Raleigh, NC, United States

Jeff Gage,     Green Mountain Technologies, Bainbridge Island, WA, United States

Scott Gamble,     Organic Waste Specialist, Professional Engineer, Edmonton, AB, Canada

Jane Gilbert,     Carbon Clarity, Rushden, Northamptonshire, United Kingdom

Thomas Halbach,     Extension Professor Emeritus, University of Minnesota, Minneapolis, MN, United States

James Hardin,     Associate Professor, SUNY Cobleskill, Cobleskill, NY, United States

Harry A. Hoitink,     Professor Emeritus, Ohio State University, Wooster, OH, United States

Harold Keener,     Professor Emeritus, Ohio State University, Wooster, OH, United States

Mark King,     Organics Management Specialist, Maine Dept. of Environmental Protection, Bangor ME, United States

Nanci Koerting,     Environmental Compliance, Grant County Mulch, Boonsboro, MD, United States

Nancy J. Lampen,     Associates for Human Resource Development, Pittsford, NY, United States

Tera Lewandowski,     Growing Media, The Scotts Miracle-Gro Company, Marysville, OH, United States

Ji Li,     Professor, Department of Ecology and Ecological Engineering, China Agricultural University, Beijing, China

Dan Lilkas-Rain,     Growing Media, Town of Bethlehem, Bethlehem, NY, United States

Lorrie Loder-Rossiter,     Revinu, Inc., Fleming Island, FL, United States

Pierce Louis,     Dirt Hugger, Dallesport, WA, United States

Frederick Michel,     Ohio State University, Wooster, OH, United States

Robert Michitsch,     University of Wisconsin–Stevens Point, Stevens Point, WI, United States

Deborah A. Neher,     University of Vermont, Burlington, VT, United States

Hilary Nichols,     U.S. Composting Council, Raleigh, NC, United States

Tim O'Neill,     Engineered Compost Systems, Seattle, WA, United States

Cary Oshins,     U.S. Composting Council, Raleigh, NC, United States

Monica Ozores-Hampton,     TerraNutri, LLC, Miami Beach, FL, United States

John Paul,     Transform Compost Systems, Abbotsford, BC, Canada

Tom L. Richard,     Pennsylvania State University, State College, PA, United States

Jonathan M. Rivin,     Materials Evaluation Specialist, Oregon Department of Environmental Quality, Portland, OR, United States

Nancy Roe,     Agricultural Consultant, Tucson, AZ, United States

Robert Rynk,     Professor Emeritus, SUNY Cobleskill, Cobleskill, NY, United States

Mary Schwarz,     Cornell Waste Management Institute, Cornell University, Ithaca, NY, United States

Ronda Sherman,     North Carolina State University, Raleigh, NC, United States

Stefanie Siebert,     European Compost Network, Bochum, Germany

Matthew Smith,     USDA National Agroforestry Center, Lincoln, NE, United States

Richard Stehouwer,     Pennsylvania State University, State College, PA, United States

Dan Sullivan,     Department of Crop and Soil Science, Oregon State University, Corvallis, OR, United States

Rod Tyler,     Green Horizons Environmental, Medina, OH, United States

Rudy Wentz,     Agricultural Equine Industry Economics, Formerly with the State University of New York, Cobleskill, NY, United States

Holly Wescott,     Heart Beet Gardens, Ashfield, MA, United States

Steven Wisbaum,     CV Compost, Charlotte, VT, United States

Jeff Ziegenbein,     Regional Compost Operations, Inland Empire Utilities Agency, Chino, CA, United States

Preface

The Composting Handbook began as an effort to produce a second edition of the On-Farm Composting Handbook (OFCH), which was originally published in 1992 by NRAES ¹ . This book is not, however, that anticipated second edition. Instead, it should be considered the OFCH's sequel; a much-expanded update that encompasses all applications of composting beyond the backyard—farm, commercial, institutional, and municipal. The Composting Handbook adopts the practical attitude of the original book, and it still retains a farm flavor. Indeed, readers who are familiar with the OFCH will recognize the connection. For me, there is some sadness in losing on-farm from the title. Personally, I continue to believe that farms offer the best situations for composting. Among other positives, the decentralized, and often remote, locations of farms pose many advantages. On-farm composting should be liberally encouraged, for almost all feedstocks.

But this book takes a much wider swipe and a deeper dive in its topics, applications, and geography. Unintentionally, the OFCH found readership among nonfarm and international readers. The Composting Handbook intentionally aims to serve nonfarm and international readers.

I submit that this book was written for the composting community by the composting community. Please look at the list of authors and contributors. I expect that you will be impressed by the length of the list and the talent represented. Also note the diversity of positions, perspectives, and locations of the contributors. Collectively, we are teachers, researchers, engineers, compost producers, facility managers, extension specialists, technical consultants, business consultants, compost users, public servants, nonprofit professionals, vendors of equipment and systems, soil scientists, horticulturists, and farmers. In addition, we authors benefitted from the good work of past and current colleagues. We borrowed knowledge from many published journal articles, guidelines, professional reports, presentations, books, and even graduate student thesis. I think that some of the more valuable elements of this book are in its references pages. At the end of every chapter, we itemized cited references, as required, but we also listed references that we authors relied on for wisdom and references that we consider potentially valuable resources for readers.

The Composting Handbook has a large and somewhat risky ambition. It seeks to serve nearly everyone in the composting community. It presents useful advice for new and prospective composters, as well as composting veterans. It targets composting practitioners, but professionals in any role within the composting industry should find it useful. While the emphasis is on compost production, there is ample advice for compost users too. The risk in trying to serve everyone is that no one will be satisfied. However, after reading and rereading the chapters, I am confident that we succeeded. Everyone will find some information of value. Most readers will find a lot of it.

The book also aims at a broad target geographically. The book is written with the expectation that it will be used internationally. It rightly draws from international publications and practices, regardless of the audience. But also, we consciously included international examples, photographs, rules, and regulations. I hope that we internationalized the book well enough. I apologize to those mostly non-English speaking citizens who I suspect we neglected.

Despite our efforts, there is no denying that the book has a US bias. This bias is an almost unavoidable consequence of the American genesis of the book. Conditions and regulations in the US steal much of the spotlight. The dollar values and spellings are also US (although a few odours and fertilisers might have slipped by).

Some balance is restored by the fact that metric (SI) measurement units are primary, and US (imperial) units are secondary. Having to acknowledge two sets of units throughout the book is annoying, and sometimes confusing, but it is currently necessary. Conversions between metric and US units are generally approximate throughout the book. For example, the difference between a US short ton (2000 lbs) and a metric ton, or tonne (1000 kg), is occasionally ignored. Either or both of these units are normally referred to as simply a ton, except where the situation requires more specificity. We can be approximate because composting is so forgiving. It usually permits approximations. The composting sage, Peter Moon of O2Compost, famously says, "There are no decimal points in composting." Peter is being poetic, of course, but his point is well taken—composting is such a robust process that it does not deserve a high degree of precision. Therefore, if you find a case where a metric dimension is coarsely converted to a round number in US units, please forgive us and move on. Sometimes onemeter can equal three feet. Sometimes 1123 kg can be a ton.

The information presented in The Composting Handbook—the principles and practices herein—are current to the time of its writing, circa 2021. The contents of this book will gradually become outdated. Some topics will soon become outdated. Therefore, we anticipate that you will continue to follow progress in the related scientific disciplines and in the practices within the composting industry. Please consult research journals and popular industry media, like BioCycle. Please join professional organizations associated with composting, and participate in their conferences and educational activities. Accurate knowledge will always be the best tool for success. Because regulations, best practices, and science will inevitably change, this book should not be regarded as a set of rules, or a surrogate book of regulations (the OFCH was sporadically used in that fashion). Instead think of The Composting Handbook a collection of guidelines, to be considered and applied according to the situation at hand, along with other information currently available.

Robert Rynk, Principal Editor

---

¹  

The On-Farm Composting Handbook was originally published by The Northeast Regional Agricultural Engineering Service (NRAES), a program of 13 land-grant universities in the northeastern US Electronic copies are available through Cornel University's e-commons system at https://ecommons.cornell.edu/handle/1813/67142.

Acknowledgments and appreciations

This book was a long time coming. In 2005, Marty Sailus, then manager of PALS ¹ (NRAES' successor) asked Leslie Cooperband and I to develop the second edition of the On-Farm Composting Handbook (OFCH). Leslie and I sat at her farm table in Illinois and mapped out a plan, including the contents, potential contributors, and timeline for the new edition. To save embarrassment, I will not reveal the timeline. Within a year, we even had a few authors complete a draft of several chapters. But then Leslie's farm enterprise began to flourish, and I started my job at SUNY Cobleskill. As it turns out, it is really hard to produce an ambitious book while running a farm or tending to a demanding day job. Although I attempted to keep up the momentum, the effort languished. In the meantime, PALS perished and composting science and practice evolved. As the project revived, we needed to find new content for the book, a new partner, and a new publisher. In the end, the editors and authors stepped up to revitalize the content. The Composting Research and Education Foundation (CREF) stepped forward to help produce the book. And Elsevier stepped in to publish it.

Given the book's history, this section is devoted to acknowledgments, appreciations, and a few apologies. In general, I would like to express my sincere and gratitude to everyone who contributed to the book and moved it forward. Specifically:

• Thank you to my patient co-editors, who put in many hours, and enlivened the work when it was floundering.

• Thank you to the book's authors and contributors for sharing their knowledge. Extra thanks (if that is a thing) to the long-suffering authors who have been with the project since the early years.

• Thank you, and sincere apologies, to Marty Sailus for his painstaking yet doomed efforts to motivate me to hurry the book toward its completion. Good try, Marty.

• Thank you to editorial assistant and counselor, Judy Puddester, for her patience, help, advice, and wagging forefinger (yes, her forefinger).

• My apologies to the many people who I naively told, over the years, that the book is nearly done and will be ready next year. Most of the time, I truly believed it myself.

• Extra special thank yous to the New York State Energy Research and Development Authority (NYSERDA) and Cornell University for financially supporting the project in its early stages. That early support was essential.

• An extra special thank you to the Kevin Tritz Memorial Fund (KTMF) for supporting the book in the later stages. Like Kevin himself, KTMF is dedicated to advancing the compost industry through sound scientific research and education. Kevin was a strong advocate for composting and a former president of the US Composting Council. Kevin would have been been all in with the book's development. http://www.mncompostingcouncil.org/kevin-tritz-memorial-fund.html

• Thank you to the original authors of the OFCH who laid the foundation for The Composting Handbook: Maarten van de Kamp, George B. Willson, Mark E. Singley, Tom L. Richard, John J. Kolega, Francis (Frank) Gouin, Lucien Laliberty, Jr., David Kay, Dennis W. Murphy, Harry A. J. Hoitink, and William F. Brinton. I am aware that Maarten, George, Mark, John, and Frank have passed on. They may have applied some divine guidance to the new book. Certainly, Maarten is chatting about it to others in the afterlife.

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¹  

Plant And Life Sciences (PALS) Publishing was a program of the Dept. of Horticulture at Cornell University. PALS was the successor to NRAES the publisher of the original OFCH. PALS ceased operation in 2018. Its publications are still available through Cornell University. https://www.cornellstore.com/pals-publishing

Chapter 1: Why compost?

Authors: Robert Rynk ¹ , and Leslie Cooperband ²       ¹ SUNY Cobleskill, Cobleskill, NY, United States      ² Praire Fruits Farm and Creamery, Champagne, IL, United States

Contributors: Cary Oshins ³ , Holly Wescott ⁴ , Jean Bonhotal ⁵ , Mary Schwarz ⁵ , Ronda Sherman ⁶ , and Sally Brown ⁷       ³ U.S. Composting Council, Raleigh, NC, United States      ⁴ Heart Beet Gardens, Ashfield, MA, United States      ⁵ Cornell Waste Management Institute, Cornell University, Ithaca, NY, United States      ⁶ North Carolina State University, Raleigh, NC, United States      ⁷ School of Forest Resources, University of Washington, Seattle, WA, United States

Abstract

This chapter addresses the question Why compost? as a way to familiarize the reader with the many benefits of composting and its associated drawbacks. In doing so, it introduces the content of the ensuing chapters of the book. Topics touched on are the economic and environmental benefits of composting, and the challenges of operating a composting facility. More detailed information is found in the remaining chapters.

Keywords

Benefits; Climate change; Drawbacks; Fact; Fiction; Greenhouse gas emissions; Introduction; Vermicomposting

1. Introduction

"Composting" is the aerobic, or oxygen-requiring, decomposition of organic materials by microorganisms under controlled conditions. It has been practiced for eons, on wide-ranging scales of operation, from backyard piles to huge automated systems contained in warehouse-like buildings. Similarly, composts, made from a long list of feedstocks, have long been appreciated and used to the benefit of farmers, gardeners, and landscapers in a variety of applications (Platt et al., 2014). It is a means to conserve resources, preserve the environment, and create value (U.S. PIRG 2019). It yields useful natural products from less useful, and often wasted, organic ingredients. In so doing, composting opens opportunities for:

• farmers to improve handling and enhance the value of manure and crop residues,

• municipalities and other public entities to better use the organic materials that generally fall under their purview, including leaves, yard trimmings, biosolids¹, and solid waste,

• industrial, commercial, and residential food waste generators and collectors to dispose of food in an environmentally benign manner through recycling,

• operators of anaerobic digestors to create added-value outlets for digester effluents,

• generators of organic materials to become recyclers of organic materials,

• farmers, ranchers, horticulturalists, gardeners, and other plant growers to enrich their soils and improve their methods and products,

• environmental managers to help offset the climate impacts of greenhouse gases by sequestering carbon in soils, and,

• businesses, farms, and small entrepreneurs to earn money through composting services and the production and sale of compost.

The ingredients, or feedstocks, for composting are organic residuals—manure, leaves, yard trimmings, wood and paper products, food residuals, biosolids, and variety of other organic materials (Chapter 4). These residuals inherently possess utility and value. They contain resources in the form of organic matter, energy, nutrients, minerals, and microorganisms that can benefit soils, crops, the landscape, livestock, people, the atmosphere, and the environment. Composting retains the nature of these resources and transforms them into soil-building products. The value of the composted products nearly always exceeds that of the original feedstocks.

Composting is only one of many alternatives for managing organic residuals. Many types of residuals can be applied to farmland directly as a source of organic matter and nutrients, as they have been used traditionally. Some residuals can be applied directly in the landscape as mulch. They can be processed for energy production or livestock feed. Other biological conversion options include vermicomposting and anaerobic digestion, neither of which is covered in detail in this book. Although vermicomposting shares many features with conventional composting, the processes are different enough to merit separate coverage (see Box 1.1).

So, with these options for recycling organic residuals, the question that needs asking is: Why compost?

Box 1.1

Vermicomposting

Author: Rhonda Sherman.

Vermicomposting is a controlled biological process that relies on earthworms and microorganisms to decompose and stabilize organic materials. The earthworms ingest organic particles and resident microorganisms to obtain sustenance. The digested particles that they excrete are called castings. The resulting product, a mixture of castings and otherwise-decomposed feedstocks, is called vermicompost or vermicast.

It is crucial to understand the differences between thermophilic composting and vermicomposting. They are two separate methods of managing organic materials and have diverse outcomes. Vermicomposting takes place at lower, mesophilic, temperatures. Vermicomposting worms thrive at temperatures in the range of roughly 15–28°C (about 60–80F) and do not tolerate temperatures above 35°C (95F). Temperatures are kept low by using shallow windrows, beds, and bins and by adding feedstocks gradually, as needed by the worms. The absence of high temperatures means that the vermicast is not heat-sanitized, although pathogens numbers are greatly reduced by the worms' digestion and the competing microorganisms (Sawati and Hait, 2018). Precomposting of feedstocks is encouraged to destroy pathogens and seeds with more certainty, make the worm feed homogenous, decompose potential toxins, reduce ammonia levels, and to reduce the weight, volume, and heat in feedstocks.

Earthworms can process food residuals, animal manures, crop wastes, paper products, industrial organic byproducts, and brewery wastes. They can also consume biosolids and sludge produced from paper and pulp mills, and milk processing plants. Manure produced by cows, pigs, horses, goats, llamas, alpacas, sheep, and rabbits is commonly vermicomposted. Chicken manure is an exception because it is too high in ammonia.

Vermicomposting does not require specialized training or equipment. Many farmers utilize unused animal housing for their vermicomposting operations. Worm beds or windrows can be set directly on the ground, in pits or trenches, or in bins. Bins are typically made of lumber, concrete blocks, bricks, poured concrete, or clay tile. Discarded items may also be repurposed as worm bins. For larger operations, many choose to build or buy continuous flow-through digesters that automate feeding and harvesting of vermicompost.

Although vermicomposting does not necessitate advanced schooling, there are several key points of knowledge that are required to be successful. Many people initially focus on bins and equipment and miss the point that earthworms are doing the majority of the work, not machines. Therefore, it is essential to master earthworm animal husbandry skills on a small scale before expanding an operation. Vermicomposters must use the appropriate earthworm species and provide their needs to help them thrive.

There are more than 9000 species of earthworms, but only seven species are suitable for vermicomposting. Most earthworms live underground and consume soil. Earthworms used for vermicomposting live on top of the ground in decaying organic materials such as manure and leaf piles. Most people use one species of earthworm for vermicomposting. It has many common names, such as red wiggler, red worm, brandling worm, tiger worm, or California red worm, but these are all nicknames for the species Eisenia fetida.

Vermicast is a premium product, generally superior to conventional compost. It is rich in nutrients that are readily available to plants. It also contains massive numbers and varieties of microorganisms that benefit soil and plant health. Because vermicast is not subject to thermophilic temperatures, it has higher numbers and greater varieties of microorganisms compared to conventional compost. Plant growth hormones and humic and fulvic acids in vermicast increase plant growth and crop yields. Phenolic compounds repel insects that eat plants. Vermicast and its liquid extracts have been found to suppress plant diseases (see Chapter 17). Because of its beneficial effects on soil and plants, vermicast sells for a premium price, in the range of $250 to $1300 per cubic meter ($200 to $1000 per cubic yard).

Only a small amount of vermicast can provide the benefits to plants described earlier. Mixing 10% to 20% volume of vermicast with soil significantly increases plant growth and yields and suppresses pests and diseases. Vermicast is commonly added to soils in gardens, vineyards, golf courses, nurseries, farm fields, lawns, and in potted plants. Some thermophilic compost manufacturers and soil blenders mix vermicompost into their products to provide added benefits.

Thousands of people all over the world are vermicomposting to manage organic waste and generate part or all of their income from gate fees or sales of vermicast or earthworms. The Worm Farmer's Handbook (Sherman, 2018) provides detailed descriptions of two dozen vermicomposting operations taking place at farms, institutions, municipalities, schools, and businesses. The book also provides information about earthworm biology, vermicomposting methods, and management practices. Additional resources, including videos, are available at the website, https://composting.ces.ncsu.edu/.

Composting performs two fundamental functions—it converts difficult materials into a valuable commodity and an easily handled material. A composter benefits from both functions, regardless of whether composting is practiced primarily to manage organic residuals or primarily to produce compost (Fig. 1.1). For instance, a landscaping business might compost yard trimmings from the surrounding community to obtain the resulting compost for its own use but, in doing so, also collect fees for recycling the yard trimmings.

Figure 1.1  Composting offers the potential to generate two revenue streams: services for recycling waste materials and sales of compost products. Source: Brendon Mallia.

The first of these functions reflects a waste management goal, which has been the primary driver for composting for several decades. The second function is manufacturing, and it is becoming more prevalent as growing numbers of users recognize the value of compost. In fact, many composting experts and practitioners have embraced the manufacturing model as the new paradigm for composting (USCC, 2020). As a manufacturing process, the emphasis of composting is producing specific compost products with specific characteristics for particular uses or markets. Like any manufacturing enterprise, composters have to ensure that the revenues and benefits outweigh the costs and drawbacks.

Practitioners have developed their own notions about composting and compost that seem true, perhaps even obvious. However, some of these notions do not hold true for every situation. The prominent facts and fictions of composting and compost are addressed in Section 5 of this chapter.

2. Benefits and drawbacks of composting

Composting offers a variety of economic and environmental benefits. When considering the benefits of composting, it is important to distinguish between composting, the process and compost, the product.

Although the benefits are numerous, composting can be a major undertaking, with associated costs and drawbacks (Table 1.1). One cannot simply dump leaves on a hillside or pile manure behind the barn and expect to have compost several weeks later. A successful composting operation deserves the same planning and commitment given to other functions, like crop production or landscape maintenance. Although it is often integral to the other operations, composting should be viewed as an enterprise in its own right. Like any enterprise, a composter needs to consider the labor, physical infrastructure, financial resources, and time available to compost properly.

Table 1.1

3. Economic benefits of composting

There are direct and indirect economic benefits to composting. Direct benefits result in revenue from processing organic residuals and/or selling finished products derived from composting (Chapter 18). Indirect benefits arise from cost savings associated with purchasing, handling, storing, transporting, and dispersing the organic residuals in other ways. Together these benefits can increase the efficiency of a manufacturing or farming system by reducing handling and transportation costs and/or capturing revenue from resources that might otherwise be wasted.

3.1. Revenue from processing or gate fees

Many municipalities, institutions, commercial enterprises, and industries that generate organic wastes do not have the capacity to process those materials properly, let alone compost them. This situation creates an opportunity for composters to collect processing fees by composting organic residuals generated by someone else. The fee collected for accepting waste materials is commonly referred to as a tipping fee or gate fee. This book uses the term gate fee.

Other people's residuals can be primary feedstocks for a composting operation, or they can supplement existing feedstocks. In the latter case, the off-site feedstocks can improve a composting mix. For instance, on-farm composters often need to mix manures with relatively dry materials that are good sources of carbon. Examples are leaves, newspaper, cardboard, sawdust, bark, and wood shavings. Conversely, municipal composters frequently need to mix their high carbon feedstocks with high nitrogen materials such as manures from farms or food waste from curbside collection programs.

Compost feedstocks generated by others must be considered with a measure of caution. First, gate fees can be difficult to capture. Alternative uses for organic residuals often exist, and the competition for the generator's dollar can be strong. Second, some of these unwanted residuals are unwanted for a reason. They can be difficult to handle or have the potential to create nuisances (e.g., odors, trash).

Composting off-site wastes might lead to extra processing at the composting site, odor problems and odor control measures, resistance from neighbors, and more restrictive environmental regulations. For instance, adding just one additional feedstock to a mix can double or triple materials handling efforts prior to composting. The impact on the quality and value of the compost product also must be considered since the feedstocks influence the compost's market value and use, and the concentration of contaminants (such as plastic, glass, or heavy metals) reduce the compost market value.

3.2. Saleable product

One of the most attractive features of composting is that there is a market for the product (Fig. 1.2). Potential buyers include home gardeners, landscapers, developers and construction contractors, public transportation (e.g., highway) agencies and their contractors, vegetable farmers, turf growers, vineyards, operators of golf courses, and ornamental crop growers (Chapter 18). The price of compost varies considerably depending on the quality of the finished product and the markets available and their level of awareness and appreciation of the value of using compost. The price range is large and variable. The current price of bulk compost typically ranges roughly from $10 per cubic meter (or cubic yard), for high volume users that are not discriminating about compost qualities, to over $70 per cubic meter for premium markets interested in specific compost characteristics. As an example of the extreme high value of compost, aggregated, aged leaf compost used to filter out pollutants in storm water sells for over $300 per cubic meter. At the other extreme, some municipalities allow citizens to take a limited amount of compost for free.

Figure 1.2  Compost has value; at least as much value as topsoil. (Note: prices are circa 2006 in New Zealand dollars).

3.3. Useable product

Compost that is not sold still has economic value for the composter, if the composter has good uses for the compost (Chapter 16). The monetary benefits can be realized through better crop yields or plant quality, or more directly as savings in the cost of purchased compost, topsoil, mulch, and fertilizer. Many composters have become composters simply to produce compost for their own use.

3.4. Animal bedding substitute

Compost has been used for poultry litter and bedding in livestock barns. Research and experience have shown that compost is generally a safe and effective bedding material. Increasingly, the solid manure fraction, mechanically separated from liquid manure, is recycled as bedding after a short period of composting, which kills pathogens and drives off moisture (Fig. 1.3). Bedding is also recovered from the effluent of anaerobic digesters after separation and subsequent composting.

Figure 1.3  Windrow composting of manure solids for the production of recycled livestock bedding. Source: M. Schwarz.

3.5. Destruction of weed seeds, pathogens, and reduced pesticide costs

The high temperature achieved during composting effectively destroys weed seeds contained in grass, leaves, yard trimmings, manure, crop residues, and other vegetation. Applying compost versus the raw feedstocks (e.g., manure or leaves) greatly decreases weeds, reducing, if not eliminating, the need to apply herbicides. Crop and plant producers can achieve savings in both chemical costs and application costs (labor and fuel). Similarly, the destruction of plant pathogens during composting, the disease suppressive nature of compost and the increased plant vigor can reduce the disease and insect pressure on crops, leading to savings in application of other crop chemicals.

3.6. Reduced disposal costs

Composting can be a cheaper alternative to waste collection and disposal, especially where the associated fees are high or the disposal site is a great distance away. In such cases, the generator can compost the material on-site or contract with a local composter to process the material. The on-site approach is practical on a small scale and for larger waste generators that have the land base, equipment, and skill set to carry out large-scale composting. Examples include municipal public works agencies, farms, vineyards, nurseries, greenhouses, food processing companies, brewers, and lumber yards. Numerous institutions, including schools and hospitals compost food waste in on-site systems. Specific on-farm examples include composting of poultry and livestock mortalities and composting of grass seed straw in locations where field burning has been prohibited.

3.7. Reduced handling costs

Composting reduces handling costs by making the organic residuals easier to manage. Compost is typically drier and substantially reduced in weight and volume compared to the raw feedstocks. The volume reduction typically falls in the range of 50% to 75%, depending on the feedstocks. The reduced weight and volume can significantly lower the cost to load, unload, store, and transport materials. In some cases, the savings can offset the compost production costs.

3.8. Expanded outlets for organic residuals

In addition to decreasing the volume and weight of raw feedstocks, composting also changes their character. The compost has a low rate of decomposition, little or no odor and less moisture. As a result, the compost is acceptable for a broader spectrum of uses than the raw feedstocks. Although some other organic residuals can be directly land-applied in their raw state, certain conditions can limit the practice. For example, wood and paper residuals are limited by nitrogen immobilization. Direct land application of leaves is discouraged by their low bulk density and weed seeds. Biosolids are constrained by community resistance and harvest waiting periods. Composting these residuals opens up other options.

3.9. Improve manure management

Farms have reported reductions in manure handling expenses due to composting, including savings in the cost of transportation, labor, storage, and fly control chemicals (Chapter 18). Compost is easier to handle than manure and stores well without odors or fly problems. Spills of compost during road transport are a much smaller concern compared to raw manure. Because of its storage qualities, compost can be applied at convenient times of the year. This advantage minimizes runoff and nitrogen loss in the field and reduces the need for extended storage of raw manure. Also, composting manure with a large amount of bedding lowers the carbon/nitrogen ratio to acceptable levels for land application (minimizing the potential for nitrogen immobilization when mixed with the soil). In organic farming applications, composting manure can effectively shorten the waiting period between land application and crop harvest.

On farms with insufficient or no cropland for land spreading, direct application of manure to cropland is constrained or simply not an option. In some cases, many years of manure and fertilizer applications have saturated the soil with nutrients, particularly phosphorus, creating conditions for nonpoint source pollution of surface and ground waters. In some regions with excessive soil nutrient loads, regulations have either curtailed or eliminated the application of manure to cropland. Composting makes it easier to export nutrients off the farm or to fields farther from the barn. In general, composting expands the outlets for manure, increasing the distance at which it can be economically transported and the number of neighboring farmers, and other users, willing to accept it.

4. Environmental benefits of composting

Both composting and compost offer environmental benefits. The benefits from composting derive from the diversion of feedstocks from less desirable alternatives (e.g., landfills) from the conversion of waste and from the ability of the process to destroy pathogens and decompose worrisome organic compounds (e.g., antibiotics). The use of compost supplies a wide range of environmental benefits resulting from improved plant growth and healthier soils (Bell and Platt, 2014; Gilbert et al., 2020; Soils for Salmon, 2020).

4.1. Soil health and plant vigor

Compost is an excellent soil conditioner. Compost adds decomposed organic matter, which improves soil structure, improves soil water balance, and increases the soil nutrient reserves, particularly the cation exchange capacity. The organic matter benefits of compost translate to reduced potential for soil erosion, runoff, and the subsequent nutrient and sediment losses. The soil improving effects of compost encourage extensive root growth and generally increases plant vigor. The more vigorous plants are better able to withstand stresses such as drought, insects, and disease (Fig. 1.4).

4.2. Nutrient retention

Compost contains both major plant nutrients (N, P, K) and minor nutrients or trace elements. Applying compost to farm fields, landscapes, and gardens reduces the need for commercial fertilizers. Compared to commercial fertilizers and raw manure, the nutrients in compost are less water-soluble, especially nitrogen (N). As a result, the nutrients are less likely to be lost through leaching and runoff. Regular applications of compost increase the reserve of nutrients stored in the soil. In addition, the soil-building qualities of compost increase the soils ability to hold soluble nutrients in place. Replacing fertilizers with compost reduces the negative environmental impacts associated with manufacturing those fertilizers as well as reducing the potential to overload soils with nutrients that could then be lost to the environment.

Figure 1.4  The soil-improving benefits of compost typically result in vigorous plants with healthy root systems. Source: R. Alexander.

4.3. Water conservation

Compost application to soils adds organic matter that improves soil water holding capacity and water balance in the soil. The resulting benefits include increased efficiency in water usage, increases drought tolerance, and decreases reliance on irrigation. The water conserving benefits depend on the existing soil texture. The potential to conserve moisture is greatest in sandy soils. In clayey soils, the compost may have little or no effect on available moisture holding capacity. However, compost still improves the structure and aggregation of clay soils, creating greater soil porosity and greater range of pore sizes. This effect makes soils more amenable to increased water infiltration, thereby reducing runoff. Increased water infiltration means that plant roots can access more water and that plants are better able to extract water under drought conditions. The improved water holding capacity through application of compost is further discussed in Chapter 15.

4.4. Plant disease suppression

Generally, compost has been found to reduce soil-borne plant diseases. The effect is not consistent among all composts and all diseases, but it is well documented. If composts can be used as alternatives to fungicides, fumigants, and other pesticides, this benefit reduces or eliminates the environmental impact of such pesticides (alteration of soil properties, loss to atmosphere or water bodies) and the human health issues associated with worker application of such pesticides. The disease-suppressing qualities of compost are discussed in greater detail in Chapter 17.

4.5. Erosion control

Compost can be used as a surface mulch on slopes and bare ground to reduce erosion from rainfall and runoff. In addition, erosion control techniques have been developed that use compost installed in berms or within filter socks (compost filled mesh cylinders). In these instances, the compost serves to slow or eliminate runoff, remove sediment and filter contaminants. A wider choice of application equipment for compost has increased the uses for compost in erosion control and other environmental applications. This topic is discussed in greater detail in Chapter 16.

4.6. Pathogen destruction

The high temperatures generated during composting, plus the vigorous biological activity, destroy pathogenic organisms that can infect plants, livestock, and humans. Thus, compared to direct land application of fresh organic residuals, composting reduces the risks of spreading disease to plants and animals. The effects of composting on pathogen destruction have been studied for a large variety of pathogens including pathogenic viruses (e.g., avian influenza), bacteria (e.g., Salmonella, e-coli), fungi and protozoa (e.g., Giardia and Cryptosporidium parvum). While a few plant pathogens (e.g., tobacco mosaic virus) survive in lower numbers, the studies have shown that composting effectively sanitizes the compost of nearly all pathogens of concern (Ryckeboer et al., 2002). To date, little is known about composting's effect on the destruction of prions, the agents responsible for livestock diseases like BSE (cattle), scrapie (sheep), and chronic wasting (deer). Current and future research in this area should provide guidance about the efficacy of composting for prion destruction (see Chapter 8). Chapters 3 and 8 provide more information about the fate of pathogens during composting.

4.7. Destruction of hormones, antibiotics, and pesticide residues

Recent studies evaluating water quality of rivers and streams flowing have discovered the presence of hormones, antibiotics, and pesticides in waterways. Many of these xenobiotic compounds are human introduced, nonnaturally occurring compounds, and from farms where hormones and antibiotics are fed routinely to livestock or used in livestock or crop production. Pesticides, particularly herbicides like atrazine, tend to persist in the environment and make their way to surface or ground waters. Other studies associated similar xenobiotic compounds with municipal wastewater treatment facilities. Composting of biosolids, manures, yard trimmings, and crop residues that often contain these synthetic organic compounds is an effective means to degrade them, so they are less susceptible to be lost to the environment. Most pesticides readily decompose to safe levels during composting, with the notable exception of a few persistent compounds, like the herbicides clopyralid, aminopyralid, aminocyclopyrachlor, and picloram (see Chapter 15).

4.8. Treatment of animal mortalities

Although not universally accepted, composting is widely practiced to treat carcasses from animals that have died routinely on farms, along roads, on beaches, and in catastrophic situations that result in mass mortalities, such as disease outbreaks in poultry barns. In many cases, composting is the preferred method of treatment. The resulting compost is typically used on-site.

The emergence and growth of animal mortality composting is largely driven by the reduction of local rendering facilities. However, regulations restricting burial and incineration have also been a factor. Composting of dead animals is not approved in all states, provinces, and countries, particularly outside of the United States. Even within the United States, there are restrictions. Chapter 8 covers this topic in detail.

4.9. Low risk of environmental impacts from compost use

When compost is used or land-applied, it presents a low overall risk of air, soil, and water pollution. The environmental impacts of using compost are much lower than the raw feedstocks from which it is made, and products that it might replace, like chemical fertilizer.

Composting greatly reduces the risk of odors and airborne contaminants associated with land application and storage of manure, biosolids, and other odor-prone raw materials. At the time of application, mature compost does not emit strong odors. Composting requires a moderate moisture content (between 45% and 65% by weight) and relatively high carbon to nitrogen ratio (>20:1). These moderate moisture conditions greatly reduce the degree of nitrogen loss, either dissolved in water or as a gas, thus reducing the risk of odors.

As noted above, composting converts water-soluble nutrients, including most nitrogen and some phosphorus compounds, to more stable forms, making them less likely to be dissolved in runoff and leachate from fields and storages. The increased portability of compost, compared to raw feedstocks, evens out soil nutrient imbalances at the landscape or watershed scale that may have developed from long-term high-rate applications of manures, fertilizers, or other nutrient-rich soil amendments. The relative homogeneity and stability of compost compared to raw feedstocks also increases the windows of opportunity for timing of land application.

The lower impacts of compost use must be weighed against the potential environmental impacts of converting the feedstocks into compost. Nevertheless, if composters follow best management practices in making compost, there is likely to be a net environmental benefit.

4.10. Reduction of greenhouse gas emissions

Recent studies comparing gas emissions from static manure piles and actively composted (high temperature composting) manure piles show significant reductions in emissions of greenhouse gases like methane and nitrous oxide from composting manure piles (Brooksbank, 2018). Diversion of organic wastes such as food wastes and industrial organic wastes from landfills also has the potential to reduce fugitive greenhouse gas emissions.

Additional reductions in greenhouse gases can result from the use of compost in agricultural and horticultural settings. Since compost use reduces the need for synthetic fertilizers, fungicides, and herbicides, there is potential for reduced greenhouse gas emissions associated with input manufacturing. At present, the impact of composting on greenhouse gases and global warming is still being determined because methane and nitrous oxide gases can be emitted from composting piles. However, current information suggests that composting overall has a positive impact, especially when taking into account compost use as a soil amendment and nutrient supplement (Box 1.2).

Box 1.2

Climate, carbon, and composting

Author: Sally Brown.

Composting can impact carbon emissions and carbon storage in multiple ways. Much of the focus on carbon accounting for composting has been on avoided greenhouse gas emissions when organics are diverted from a landfill and composted under controlled conditions. There has also been work to characterize greenhouse gas emissions during the composting process. What is also critical to consider is the impact of compost use both in terms of carbon accounting and in the range of ecosystem benefits that compost provides when used to improve soils.

Avoided emissions

When highly putrescible organics such as food waste are landfilled, they have sufficient moisture and nutrients to start degrading quickly. Most of the landfills in the developed world are sanitary landfills. That means that waste is deposited in lined landfill cells and compacted so that oxygen is limited. Methane (CH4) gas is formed when microbes decompose the organic waste where oxygen is limited. While valuable as a fuel, when CH4 is released to the atmosphere it has 23 times (23×) the impact of carbon dioxide (CO2) over a 100-year time frame. When the cell is full, it is closed, and methane gas is collected to be flared or used as natural gas. It typically takes two to five years between the time a cell starts receiving waste and cell closure. However, methane generation often starts within months after organic waste is put into a cell. Because food waste is so putrescible, it creates methane even faster. Much of the methane generated by the decomposing material is released to the atmosphere before gas capture is functional.

The US EPA WARM (Waste Reduction Model) recently revised its estimates of methane release from food waste in landfills. According to the WARM model, about 1 ton of carbon dioxide equivalent (CO2e) is released from landfilled food waste in the form of methane. That estimate is on a wet weight basis, which means that taking food waste out of landfills and to compost piles yields huge greenhouse gas savings.

Not all materials generate as much methane as food waste. For example, woody materials are relatively inert in landfills. Yard trimmings decompose moderately well to slowly in landfills, depending on the mix of wood and fresh plant debris. Animal manures are rarely landfilled, but they generate abundant methane when stored in moist piles or lagoons prior to land application. These materials make excellent compost and can also provide carbon credits when composted instead of improperly stored.

Emissions during the composting process

Composting is a predominately aerobic process. Access to sufficient oxygen lets the range of microorganisms involved rapidly decompose the composting feedstocks. This decomposition releases a lot of CO2, heat, and transforms the organics into a stable soil amendment. However, composting is not entirely aerobic. Micro sites even within a well-aerated compost pile can be anaerobic. A well-aerated compost pile generates fewer odors and reaches sufficient temperature to kill all pathogens and weed seeds. Good aeration also limits the release of greenhouse gases during composting.

There are three types of gas that can be emitted during composting that qualify as carbon emissions—carbon dioxide, methane, and nitrous oxide (N2O).

CO2—Carbon dioxide is produced from oxidizing carbon compounds. As we eat and digest the carbon in our food, we breath out carbon dioxide. The same thing happens as microbes eat the materials in a compost pile. Although CO2 is a primary culprit in carbon emissions from burning fossil fuels, it is not a factor in carbon emissions during composting. The CO2 released from burning fossil fuels is from the long-term carbon cycle. The CO2 released from decomposition is considered biogenetic. It comes from the short-term carbon cycle, the annual cycle of growth and decay of living things. However, composting does generate some nonbiogenic CO2 emissions through equipment use, transportation, electricity consumption, and any other input that consumes fossil fuel.

CH4—Methane is produced by specialized microorganisms that decompose organics in cases where oxygen is limited. It only lasts in the atmosphere for 12 years but is a highly potent greenhouse gas. It can be produced during composting when oxygen is scarce. Methane is most commonly detected when the composting process first starts and feedstocks are cool and wet. As pile heats up, moisture evaporates and allows for greater air flow and oxygen penetration. Emissions from composting are best controlled by making sure piles stay aerobic throughout the process.

N2O—Nitrous oxide is a highly potent greenhouse gas with 296× the impact of CO2 over a 100-year time frame. It can be formed as ammonia converts to nitrate. However, it is most commonly formed as nitrate is transformed back to nitrogen gas in the absence of oxygen, a mostly biological process called denitrification. In the initial stages of composting, most of the nitrogen is present as organic nitrogen. As the carbon is mineralized, the nitrogen is converted first to ammonia and then to nitrate. Nitrous oxide can be detected during composting. It typically is seen after a portion of the nitrogen in the feedstocks has been converted from organic nitrogen. Although the quantities detected are generally low, it merits concern because of the high potency of this gas. Sufficient aeration is one tool to limit formation of N2O. Selecting feedstocks with a sufficiently high carbon to nitrogen ratio (e.g., greater than 30:1) also discourages N2O formation.

There are cases where composting can emit significant quantities of CH4 and N2O; for instance, with quickly degrading and/or nitrogen-rich feedstocks that are poorly aerated. However, these cases are the exception, not the rule. In addition, the CO2e is almost always much lower than would be emitted if these same materials were landfilled or improperly stored.

Carbon sequestration from using compost

Studies have shown that adding organic matter to soils can increase the quantity of carbon stored in the soil. By increasing soil carbon, the compost is effectively taking CO2 out of the atmosphere and storing it in the soil. The EPA WARM model gives a credit of 0.2 tons of CO2e per ton of feedstock composted for soil carbon sequestration. The actual amount of carbon stored varies, depending on how disturbed the receiving soil is, whether the soil is cultivated and the climate where the compost is used. When the compost is used to replace fertilizers, there is an additional benefit as fertilizers require a great deal of fossil energy to produce.

Table 1.2 provides estimates of the net CO2e emissions from landfilling and composting food scraps, yard trimmings and a 50/50 mix of each. On balance, composting is the superior CO2e option when food is a prominent feedstock. Landfilling and composting perform nearly the same with 100%-yard trimmings, owing to the assumption that the carbon in the woody yard trimmings remains sequestered within the landfill.

Counting carbon credits and demerits is an inexact exercise. It involves broad assumptions, imperfect data, and generalized conditions. A well-run composting operation will minimize emissions from composting. Composting feedstocks that would otherwise produce CH4 will provide significant emissions reductions. If the compost is used as a soil amendment, soil carbon storage will provide additional benefits, and possibly the largest advantage. The magnitude of the soil-sequestration benefit will vary based on how healthy the receiving soil is already. There is no argument, however, about the general environmental benefits of using compost. Adding compost to soils is an excellent way to improve soil health. Healthy soils are the basis for a broad number of ecosystem services including improved rainwater infiltration, reduced soil erosion, moisture and nutrient retention, disease suppression, and carbon sequestration.

References cited

3. Brown S. Greenhouse gas accounting for landfill diversion of food scraps and yard waste.  Compost Sci.  2016;24(1):11–19.

4. U.S. EPA, . Solid Waste Management and Greenhouse Gasses Documentation for Greenhouse Gas Emission and Energy Factors Used in the Waste Reduction Model (WARM). 2014. http://epa.gov/epawaste/conserve/tools/warm/SWMGHGreport. Html.

Table 1.2

Data from Brown, 2016. Greenhouse gas accounting for landfill diversion of food scraps and yard waste. Compost Sci. 24 (1), 11–19 and U.S. EPA, 2014. Solid Waste Management and Greenhouse Gasses. Documentation for Greenhouse Gas Emission and Energy Factors Used in the Waste Reduction Model (WARM). http://epa.gov/epawaste/conserve/tools/warm/SWMGHGreport. Html.

5. The drawbacks

Although composting harnesses natural biological processes, nevertheless, it can pose challenges. Composting deals with a diverse collection of actively decomposing organic materials that can be wet, dry, bulky, particulate, potentially odorous, and attractive to pests. Materials handling, space, and equipment are major elements of composting. In addition, composting is normally practiced outdoors, and year-round, at the perils of bad and changing weather. Trouble-free operation and the production of quality compost require investment, resources, effort, and diligence.

5.1. Time and money

Like any other manufacturing system, composting requires equipment, labor, and management (Chapter 19). The initial investment for a composting operation can be very low, if existing equipment and facilities are used. This approach is fine where the volume of material is relatively small. However, most medium to large-scale operations have found that only adapting existing equipment requires too much labor and restricts composting process management and quality control. Many composters have found it necessary to purchase special composting equipment, develop a separate infrastructure, and hire one or more employees dedicated to the composting operation. When the sale of compost becomes a major objective, the composting operation can become a business in itself (Chapter 2). The investment needed is inherently tied to the scale of operation. With special equipment, currently it could cost as little as