Researrch data

Making sense of research data: organic waste management and composting cost comparisons

When personal expertise is lacking, people place their trust in experts to facilitate decisions about everything from home additions to medical care.  Governing boards are no different.  They rely on the knowledge of utility directors, staff engineers, and consultants to help them make informed decisions.

But when presented with an avalanche of numbers – from scientific data to cost and operating projections – how do members of city councils and county commissions know if the information contained in that mountain of reports is accurate and unbiased?  How do they know they’re comparing apples to apples and not apples to oranges?

Placing value on studies specific to waste management can be complex.  One report might compare landfilling, incineration, and anaerobic digestion, but leave composting out of the mix.  Another may include composting, but base assumptions on an antiquated window system and not a modern, high-rate technology.  Research could unearth reports about a costly public project but never discover a more efficient, cost-effective commercial system.

This is not to suggest such errors or omissions are intentional.  Sometimes, it’s simply a case of “you don’t know what you don’t know.”  But when combined with the fact that detailed financial or operational data from private-sector owners is rarely made available in public spaces, one begins to understand the difficulty in obtaining good data on which to base conclusions and recommendations when doing composting cost comparisons.

The takeaway?  Assume all research is flawed in some way.  No one knows everything there is to know about every subject.  But there are a handful of questions that members of city councils and town boards can ask to help clarify reported numbers, level the playing field, and present a more accurate picture of construction and operational realities.

Who paid for the research?

Perhaps the most significant influence on any research project is the entity that foots the bill.  Even university research is funded by someone … and it may not be the university.  The simple truth is no researcher is going to bite the hand that feeds him or her.  Non-profits may fund research, but they rely on the support of donors.  Government agencies can be funders, but governments are run by politicians.  When the private sector funds studies, the results may never see the light of day if unfavorable to the funding entity.  Student work may not be funded, but it’s still student work.

Was the research scientifically sound?

Some “research” may not be new research at all, but assumptions or conclusions based on a literature review that includes outdated or invalid findings.  Investigations may have been conducted in a manner that does not reflect “good science,” including a lack of statistically-representative sampling.  Some findings are more opinion poll than science.  But when sifting through millions of scientific papers for data, researchers won’t always pick up on these types of flaws.

Also know statistics can be presented in a manner that makes differences look more (or less) important than they really are.  (See an example in this SlideShare title:  Apples and oranges: comparing waste management technologies)

How old is the research data?

Unfortunately, it’s all too common to discover a case built on multiple levels of citations that eventually trickle down to data or conclusions that may not reflect present day realities.  Knowing the date and technological sophistication of the original study will help decision-makers evaluate the value/validity of the conclusions and recommendations included in the consultant’s report.

Don’t accept a current date on a citation at face value.  Follow the citation trail to the date and circumstances of the original research.

Is data based on full-scale operations using current technologies?

Was the data based on bench scale, pilot scale, field scale, or full scale?  Conclusions reached during early stages of product or system development can fail to “scale up” successfully.   Investigations based on dinosaur technologies of 20 or 30 years ago exclude advancements and enhancements made in recent years, distorting findings.

For composting specifically, ensure that systems and technologies are apples-to-apples comparisons using the most current data available.  If evaluating high-rate systems, include successful private-sector facilities, too, not just municipal.   Net expense and revenue values per ton processed can vary widely between different types of operations.

Using old data and processing systems for dollar comparisons could greatly skew conclusions when comparing composting to other waste management technologies.

Sometimes, imperfect is the only data available for composting cost comparisons

When conducting research in a field like composting, where meaningful research is scant, at best, the imperfect may be all there is.  Knowing and accepting this reality, proactively seeking out the most accurate information, and evaluating results based on a variety of studies and viewpoints can only help decision-makers make better choices for their respective communities.

Read the article:  Valuing composting as an infrastructure investment

questions before choosing a composting system

3 questions to ask before choosing a composting system

When evaluating choices for organics diversion, system cost tends to be a major influence in whittling down the available options.  But is capital investment a good indicator of true costs over the decades of composting facility operation?

There are many questions decision-makers need to ask before choosing a composting system.  But judging by the number of lackluster operations in existence, here are 3 biggies that don’t get asked nearly enough:

Co-mingled vs. source-separation — do you want to sell this compost?

At first glance, co-mingling organics with either the total municipal solid waste stream or with other recyclables for central separation (either pre- or post-composting) looks like a no-brainer.  No extra collections or special trucks.  No expensive outreach and education programs.

But co-mingling doesn’t work if the ultimate goal is the production of a salable compost product.  Contamination can be so high, it’s almost impossible to sell the stuff.  Sometimes, farmers won’t even take it for free.

Co-mingled may be acceptable if the objective is to dry organics prior to incineration/WTE, but destroying organic matter does nothing to increase rain infiltration across the region, store carbon, reduce reliance on synthetic chemicals or cut erosion.

But to derive the most benefit from compost use, compost manufacture must result in a high-quality product.  That means source-separation supported by a good education and enforcement program.

Does the management plan include a professional sales effort to maximize the dollar value of the compost?

An inferior compost brings in little to no revenue to offset production costs.  But a quality product, supported by a professional sales effort, can net top dollar.

The first step to getting top dollar value from product sales is to manufacture compost that falls into the premium class – dark, nutrient-rich, even-textured and odor-free.  Every manufacturing dollar spent improving an agricultural-grade product can return additional dollars in compost sales to high-value markets like landscaping, turfgrass management and stormwater management.

Before choosing a composting system, make sure that technology is capable of producing quality compost.

But that manufacturing effort will be wasted if the operation lacks a professional sales program designed and run by experienced marketers and sales pros.  Mounting an effective sales effort requires both premium product and premium people.

Hiring experienced sales pros pays off.  If faced with the choice between someone who knows compost but lacks sales experience and a sales pro with a good track record but no composting background, choose the sales pro to lead the team and put him/her in charge of the compost guru.

Why?  The right pro will be able to learn what s/he needs to structure a program and move product.  The compost person may or may not have what it takes to be successful in sales.   But working for and learning from a seasoned pro will make that compost expert the best salesperson s/he can be, generating maximum revenue for the operation.

Does the analyst’s cost:benefit considerations include the advantages of regional compost use?

Irresponsible soil management practices carry a cost.  Options for highest and best use for compost regionwide should be factors in the cost:benefit evaluation.

Analysists need to ask questions like:

  • If raising soil organic matter eliminates runoff and sedimentation from a typical rain event (1 inch or less), what impact would the use of a quality compost have on the region?
  • How could compost use influence current municipal costs to manage stormwater or treat contaminated drinking water sources?
  • What would be the savings to local farmers if they could cut their fertilizer bills in half?
  • Since compost reduces chemical use and the severity of impact injuries on playing fields, how would this influence things like maintenance budgets, player downtime and medical bills for athletic and recreation venues?

Use of compost in a region can have significant positive impact on costs for stormwater management, synthetic fertilizer and pesticide reduction, water treatment costs and much more.   Costs, cost savings and avoided costs should be discussed and considered when weighing pros and cons for a proposed project.

Decision-makers who look only at trees instead of the forest may be doing their communities a great disservice.  When reviewing analyses and recommendations prepared by staff or consultants, be sure those reports take in the big picture, not just impacts to waste management.

keys to successful composting

keys to successful composting

Composting “done right” can be easy or difficult.  Easy if facility operators understand and manage according to a handful of scientific principles.  Difficult if they do not.

The specific method in use or design of the physical plant may determine the level of difficulty and costs required to get it right, but both are secondary to what really matters – process management.

From the basic outdoor windrow to accelerated in-vessel processing, successful facilities are managed to meet goals linked to specific process influences. Without attention to these details common to every composting operation, even the most advanced, tricked-out facility can get composting wrong.

Here are 7 keys to successful composting, unlocking the full potential of any type of operation:

Feedstock selection

The choice of feedstocks, whether income generators or purchased amendment, can make or break a composting operation.  For most private-sector operators, feedstocks are tied to revenues and, as such, influence profitability based on positive or negative dollars at the gate.

But for all facilities – commercial, government and non-profit — feedstocks also impact the financial health based on ease of processing and how that material will add to or detract from the market value of the finished product.  Each ingredient is unique.  Each adds different variables to the blend.  Some feedstock influences can fluctuate from one load to the next.

It is the sum of these parts that must be considered when evaluating feedstocks and formulating processing blends.  Every aspect of successful processing relies on a good blend, and that blend is based on types and volumes of individual feedstocks.

C:N ratios

Carbon and Nitrogen ratios, a.k.a. C:N or C/N,  reflect the proportions of each in the feedstock blend.  The ratio, comparing the number of parts Carbon to 1 part Nitrogen, is sometimes expressed as a single digit, i.e, “20” as shorthand for 20:1 or “100,” meaning 100:1.

C:N ratios are critical considerations when blending.  Carbon (non-mineral) and Nitrogen (mineral) provide microbes with energy and food.  They also influence processing rate and odor generation potential.

High carbon materials include things like oak (200:1) and wheat straw (80:1), compared to nitrogenous materials like cattle manure (20:1) and alfalfa (13:1).

The ideal is 30:1 for blended feedstocks, but anything in the 25-35:1 range is considered good.  20-40:1 still works, but as numbers creep higher, the process slows.  As numbers drop, the need for more aggressive odor management increases.  (A strong ammonia smell can indicate a low C:N ratio.)

Feedstock testing and/or generic C:N ratio charts like this one, combined with manual calculations or computer modeling, can provide material types and volumes for determining the most efficient blends.

Moisture content

The microbes responsible for biodegradation – aerobes — require moisture, but not too much, since they can’t breathe under water.   Excess moisture blocks air passageways, resulting in oxygen starvation.  Too much water leads to anaerobic conditions, which cause odor and create toxic compounds.

Water is also used by microbes to move around the pile and is required for bio/chemical reactions.  If the pile is too dry, biodegradation pretty much grinds to a halt for both aerobic and anaerobic processes.

Like a lot of factors influencing the composting process, moisture has its Goldilocks Zone.  Shoot for a moisture content of 40-60 percent (by weight).

There are a number of testing methods for moisture (including one using the common microwave), plus lots of moisture meters on the market.  Meters start at around $10 for the backyard variety and move on up into the hundreds of dollars.  Compared to testing, which tends to be more precise, meters offer rapid feedback and the ability to quickly sample multiple pile locations to improve accuracy without having to wait for test results.

But the simple “Squeeze Test” can also be a good measuring tool.  Simply grab a handful of the mix and squeeze.    If water runs out, it’s way too wet.  Does it crumble?  Too dry.  But if the handful holds its shape and dribbles little to no water, it’s probably okay.

Regrettably, none of the methods used to determine moisture content are spot-on, even laboratory testing.  But the good news is that moisture level is a parameter with flexibility.

Just remember – the higher the volume of the composting mass, the higher the likelihood for error using crude estimations and monitoring techniques.  Multiple sampling locations and sampling depths will help improve accuracy.

Uniformity – A compost blend needs to be a homogeneous mix of all ingredients with no multi-colored swirls, clumps, or pockets of individual feedstocks. Visually, the blend should look like a single material with both texture and particle size consistent throughout the admixture.

Failure to achieve a uniform blend prevents microbes from degrading target compounds at an equal rate throughout the composting mass, which can lead to zones of unprocessed, smelly, and even toxic material in finished product.

Pore space — The free movement of air and water throughout a composting mass is essential to a successful process. Microbes need oxygen, and that oxygen is delivered as air moves through the spaces between individual particles, a.k.a., pores. This air flow also removes excess heat.  Microbes use those same pores (plus moisture) for migration.

Compaction is the enemy of pore space, and like the lack of uniformity, can retard or kill the process.  Keep loaders and people off piles.

Compost piles can slump as the material degrades.  Prior to curing, turning or screening will restore pore space.  When using a loader instead of a windrow turner, don’t just dump the bucket.  Use a shaking or sifting action to create, restore and/or preserve pore space, whether placing compost in a bay, building a new pile or turning.

Air flow – Composting is supposed to be an aerobic process. If air doesn’t flow, the process isn’t composting.  It’s anaerobic biodegradation.  Anaerobes create odors and toxins, so if a pile smells, lack of air flow is one of the chief suspects.

Keep the air flowing with an initial blend with good pore space and moisture level, augmented by turning or aeration — at the recommended volumes/velocities specific to the system in use.

However, too much air flowing through the pile can dry it out, so monitor moisture and add water, as needed.

Temperature – Heat buildup (not oxygen supply) is often the limiting factor in composting. When air delivery is sufficient to moderate temperature, microbes are being supplied with more than enough oxygen to maintain biochemical functions.

Therefore, keeping temperatures in the right zone for the specific phase of decomposition is composting’s equivalent of the Prime Directive.

There are precise time/temperature targets for pathogen kill.  While originally written for biosolids management, an EPA 503-approved process is now required by many states to kill pathogens inherent in everything from food waste to yard waste.

While reducing pathogens may be a regulatory mandate, those time/temperature requirements represent just one process influence demanding temperature management.  In fact, assuming the operator maintains control of temperatures from the beginning of the process to the end, pathogens cease to be a processing issue once the regulatory requirement has been met.

Far more important is the intentional management of temperature during both the mesophilic and thermophilic phases of composting.

Mesophilic microbes prefer moderate temperatures up to about 40 degrees C or 104 degrees F.  They are the initial decomposers, and their feeding activity generates a lot of heat.

Whenever temperatures within the composting mass rise unchecked, the process grinds to a halt (all microbes die), crashes (there’s no decomposition) and must restart (microbial populations must rebuild).  In nature, this happens repeatedly, which is one reason why Mother Nature’s system is so slow.

But a well-managed composting process stops this hot-cold cycling from happening.  If the blend is right, temperatures will start to climb within a few hours of process initiation.  As temperatures pass out of the mesophilic zone, microbial populations change to thermophiles – the heat-loving bacteria.

Thermophiles continue to work until temperatures reach about 65 degrees C or 149 degrees F – the ceiling of their comfort zone.  The objective of composting is to manage air flow to maintain the level of heat required to meet the time/temperature requirements for pathogen kill (over 55 degrees C or 131 degrees F) without killing the thermophiles.

This thermophilic zone – 131 degrees F to 149 degrees F – is where rapid decomposition takes place.   The longer the composting system holds temperatures within this zone, the faster the process will be.  Systems that do this well are referred to as accelerated or high-rate processes.

Eventually, the thermophiles run out of food.  As they die off, temperatures drop back into the mesophilic zone, where mesophiles slowly finish off remaining food supplies.  This natural decline in temperature signals the beginning of the curing phase of composting.


bioremediation-microbe smorgasbord

How does bioremediation work?

Organic waste offers up a smorgasbord to hungry microbes

Unseen by the human eye, microbes are the soil’s equivalent of worker bees.  They are responsible for a slew of soil functions.  Without them, soils don’t work as they should.

“Soil organisms decompose organic compounds, including manure, plant residue, and pesticides, preventing them from entering water and becoming pollutants. They sequester nitrogen and other nutrients that might otherwise enter groundwater, and they fix nitrogen from the atmosphere, making it available to plants. Many organisms enhance soil aggregation and porosity, thus increasing infiltration and reducing runoff. Soil organisms prey on crop pests and are food for above-ground animals.”   — NRCS/USDA

Algae, bacteria, fungi, nematodes, protozoa — aerobic microbes and other soil fauna need oxygen, water, and food.  Other survival influences include environmental factors like temperature and pH.

In a managed setting like composting, microbial feeding activity quickly turns organic waste — including some toxic compounds — into a safe, carbon-rich soil amendment product known as compost.

The organics can be food waste, yard debris, biosolids, petroleum derivatives, or anything else that was once alive.  As long as the waste stream is free of agents that would kill bacteria and the like, the material should compost.

Of course, the time required to break things down depends on the specific type of waste, particle size, the composting process in use, etc.  But for the most part, a few days of controlled, high-rate composting followed by a curing period of several weeks is enough to turn common organics into dark, aromatic compost.

How does bioremediation work?

All matter – including organic waste — is made up of individual atoms.  Atoms join with other atoms to become molecules.  Molecules hook up to become compounds, and they’re all held together by chemical bonds.  For organic material, that bond is commonly of the “covalent” variety.  This means the atoms share, rather than gain or lose, electrons.  This makes for a more stable molecule.

During composting, hungry microbes dine on the waste stream’s inherent sugars and proteins, releasing enzymes as they digest their food.

These critters are mostly after the carbon, but their feeding also releases the nitrogen, potassium and phosphorus that plants use as food.  (There are also some microbes that can pull nitrogen from the air and convert it to plant-available form.)

Their enzymes break chemical bonds, eventually reducing compounds to molecules and molecules to atoms.  Toxic compounds disintegrate.  Along the way, elements and simple compounds realign, creating more benign substances like carbon dioxide and water.

Controlling the composting environment ensures ideal conditions for these microbes, setting the stage for rapid biodegradation.  Where decomposition and stabilization could take months (or years) in a natural setting, composting achieves the same outcome in a matter of weeks.

The tighter the control, the faster the bioremediation process.

How does bioremediation work?  Very well.

perennial food crops and carbon storage

Can compost and perennial food crops save the planet?

A match made in food science heaven has the potential to forever change agriculture’s environmental impact.

Long ago, humans abandoned the hunter-gatherer lifestyle in favor of agriculture. They tweaked deep-rooted perennial grasses, turning them into shallow-rooted annual grain crops with higher yields.

But farming came at a price.  Domestication of wild edibles set off a destructive cycle of soil depletion.

Seasonal tilling loosened soil particles. Wind and rain carried topsoil away. With it went the earth’s ability to store water and sequester carbon.

In the last 200 years alone, the top 2 meters of the earth’s soil have lost 133 billion tons of carbon.

Soil loss has turned into a big problem for today’s humanoids. Topsoil is at a fraction of historic levels.  Storage capacity is dwindling.  Greenhouse gases are building, and global temperatures are rising.

No-till agriculture was once thought a solution to soil loss. By planting in the rubble of the previous crop, farmers didn’t need to plow the soil.  But many no-till farmers rely on heavy doses of chemicals to control weeds. This, we now know, generated its own set of problems.

But no-till put agriculture on the right track.

Perennial crops like orchard fruit, tree nuts, berries, and asparagus produce food.  Because the soil remains undisturbed season to season, these crops are also no-till.

Through photosynthesis, they sequester carbon in the soil for many years.  By adding carbon-rich compost before planting and throughout the crop’s lifecycle, carbon storage becomes even more significant.

But from maize to melons, most of today’s plant-based foods are annuals. These dead-within-a-year plants constitute 85 percent of human calorie intake.  Yet they offer no long-term carbon sequestration and require tillage year after year.

Compost application may boost soil productivity on annual cropland. But much of its carbon is released with the next tilling, too.

So scientists began to ask:

Is it possible to revert more crops, especially grains, to perennial form? Could agriculture meet this goal without sacrificing yields?

Back to the future with Kernza®

The answer appears to be a resounding … could be. Probably … yes. A cautious … quite likely.

Researchers have gone back through time to marry the characteristics of two crops. One is an ancient perennial wheat-like grass. The other is a modern, annual wheat.

Together, they have produced a perennial wheat with the trademarked name, Kernza. This year, General Mills’ Cascadian Farms plans to produce 6,000 boxes of a breakfast cereal featuring the grain as a research fund-raiser. Though total acreage is still small, other commercial applications for Kernza include bread and beer.

In photographs, Kernza kernels look more like a wild rice (a grass) than a wheat berry. But it is considered flavorful and can be harvested using conventional farming equipment.

Deep-rooted (10-20 ft.), this intermediate wheatgrass grows from a rhizome.  It is planted in the fall (in Minnesota).  Most growers plant in rows, but solid seeding is also used.  Weeds are not a big issue, because as the rhizomes spread, they choke out weeds.

The problem is that the kernel is small, like the yield per acre.  Conventional milling equipment doesn’t work.  And, currently, Kernza growers reap a meager 500 pounds per acre. Their conventional wheat-growing counterparts get an average of 2,856 pounds in the U.S.

After a few years, those thick, horizontal stems can run out of expansion space, too. Yields decrease.  As a result, some growers replant every 3-5 years. At least one farmer is experimenting with chisel plow strips to extend productivity to lengthen the time between replanting.  (More cultivation information:  Farmers voice their experience growing intermediate wheatgrass for grain)

The importance of deep root systems and perennial food crops

Worldwide, several annual food crops, including rice, have become the focus of similar research.  Perennials for biofuel production are being studied, too.

Minimizing soil disturbance is one reason. The benefits that come with deep-rooted crops is another.

Living plants remove carbon dioxide (CO2) from the air. They keep some of the carbon (C) and release the rest, along with the oxygen (O2), back to the atmosphere. The retained carbon resides in stems, leaves, and roots. Plants use water and light to turn that carbon into sugars to fuel growth. When plants die and decompose, the carbon becomes a constituent of soil organic matter (SOM).

Deep roots extend the rhizosphere, the zone where roots, soil, and microbes interact. Microbes aid in the transfer of carbon from plants to soil.  Researchers say increasing this area could raise soil carbon storage.

Deep-rooted crops are a tool of what has become known as “carbon farming.”  The goal is carbon sequestration — removing excess from the atmosphere and storing it in the soil, instead.

Moisture and temperature increases could speed up carbon release at lesser depths.   But research suggests deeper soils buffer that carbon from climatic change.

If true, consider the carbon impact of a 20-ft. Kernza root compared to the typical agricultural plant (~3 ft. root depth).  To better understand the potential, this article includes an image comparing perennial Kernza and annual wheat root systems.

Assessing carbon storage potential of perennial food crops

Estimates of the carbon storage potential of “perennialized” annuals are sketchy, at best. None of the new grains have yet to hit their commercial stride.

Research on deep-soil carbon storage is a bit thin, too. It’s difficult to find sequestration estimates that consider all possible impacts like:

  • Reductions in fossil fuel extraction and use
  • Conversion of annuals to perennial crops+
  • Capture of all organics for composting and reuse

But as food for thought, here are some numbers from recent articles and research papers:

  • The soil carbon storage from improved root growth in agricultural crops could offset human-caused environmental emissions for the next 40 years.
  • Reuters: The U.S. emits around 5 billion tonnes of carbon dioxide per year. Better soil management could boost carbon stored in the top layer of the soil by up to 1.85 gigatonnes each year. This is about the same as the carbon emissions of transport globally.
  • Peak Prosperity: A 1 percent increase in SOM stores approximately 10 tons of carbon per acre. Doing the math: There are about 130 million U.S. acres in major annual grain crops. If converted to perennial varieties, carbon storage potential equals 1.3 billion tons.  That’s roughly 1/5 of the U.S. carbon pollution.
  • Bulletin of Atomic Scientists: Devote 5 percent of the world’s cropland to plants bred for carbon storage. Capture ~50 percent of current global CO2 emissions.  (That’s an area about the size of Egypt.)
  • USEPA: In 2015, about 38 million tons of food waste were burned or buried. Only 2 million tons went to composting. Doing the math: Composting all 40 million tons would produce ~20 million tons of soil amendment. This would cover roughly 600,000 acres in 1/2 inch of compost. Its ~11 million tons of carbon (20 million tons of compost @ 54 percent carbon) could go to deep-soil storage under perennials.
  • Life Cycle Assessment (LCA) of landfilling organic waste vs. composting and recycling estimated a net greenhouse gas mitigation benefit of 23tCO2eq/ha over a 3-year period when organics were composted. That’s 23 tonnes (1 tonne = 1,000 kilograms) of carbon dioxide equivalent per hectare — about 25 tons spread over 57 acres.  As little as a 1.3 cm (about a half inch) topdressing of compost resulted in “substantial” increases in carbon storage on rangeland, too, attributed to better water retention and improved grass productivity.

 Economic benefits add up, too

Looks like there’s yet one more reason to bank on perennials — economics.

Agricultural investors say annualized income for perennials rose ~13 percent over 10 years. Income from annual cropland stagnated at about 4 percent during the same period.

And in a few spots, Kernza is generating more profit than the more traditional corn and soybeans. In addition, Kernza leaves and stems remain green at ripening, making its hay more valuable than wheat straw.

Commercialization of annual-to-perennial food crops is a tantalizing possibility.  The day may come when “perennial food” labels sway consumer purchases, just like organic, gluten-free, and other profitable food-niche certifications.

But most enticing is this factoid — at $0-$100 per ton, soil carbon sequestration is the cheapest carbon mitigation tool currently available.

It should be noted that soils can eventually reach a point where no additional C can be absorbed.  Sequestration is not a miracle cure.  People still need to work on reducing CO2 generation.

But in the interim, agriculture offers one opportunity to reduce the human carbon footprint.  And compost under foot makes this challenge easier.

deep-soil carbon storage

Can compost use impact deep-soil carbon storage?

Atmospheric carbon dioxide (CO2) levels have reached a 3-million-year high.  The overload has been building up since the Industrial Revolution hit its stride about 200 years ago.  One culprit is conventional farming, which releases stored soil carbon, (C) relies on synthetic input, and degrades soils.  The use of fossil fuels — which adds even more carbon to the air — is another major contributor to the increase. 

Impacts include reduction in carbon storage capacity due to topsoil loss, pollution, and climactic changes linked to global warming.

While some say CO2 levels are a non-issue, others believe the opposite and are working to reduce atmospheric carbon by cutting greenhouse gas emissions and sequestering more carbon.

Proposed solutions include ideas like basalt rock injection and ocean storage.   But one of the simplest and most cost-effective options already in play is to simply return carbon to soils.

But there is a catch.  Since soil disturbance releases carbon, farmland dedicated to annual crops offers little to no upper layer storage potential.  Unless the farm — organic or conventional — has adopted no-till practices, the soil is disrupted every year during planting.  Therefore, acres that will remain undisturbed for long periods of time are the best candidates for long-term carbon storage, a.k.a. carbon farming.

This translates into a need for conversion of annual grains and other crops to perennials to maximize soil carbon storage potential.  But developing high-yielding perennial grains is a process that will take time.

Applying compost to both annual and perennial acres is something that can be done now.

Long-term soil carbon storage has two primary pathways — plant-based via deep-rooted perennials (like some trees and grasses) and soil amendment.  Compost leads the pack as the amendment of choice, offering a plethora of soil- and crop-enhancing benefits in addition to carbon storage.

The carbon sequestration benefit of compost use is two-fold.  It adds compost’s inherent carbon content to the soil.  But it also improves soil productivity, increasing above- and below-ground biomass, which stores more carbon.  This positive impact can persist for many years from just one compost application.

Microorganisms and insects like earthworms and ants also influence carbon storage.

Current research emphasis seems to focus on C storage potential in agriculture.  That’s because worldwide, farmers crop 4.62 billion acres — a treasure-trove of carbon storage potential.

But it should be noted there are many more non-ag acres that can offer long-term, deep-soil carbon storage, too.  No need to wait for researchers to develop new perennial grains or convince farmers to make the switch from annuals to perennials.

In the U.S. alone, millions of acres could take and store compost-applied carbon today:

  • 40 million acres of lawns
  • 50 million acres of managed turf including 700,000 athletic fields and 17,000 golf courses
  • 7 million acres of public lands under the jurisdiction of the Bureau of Land Management (FY 2017)
  • Umpteen million acres in government-controlled roadside easements, utility rights-of-way, local and state parklands, and other managed greenspace, both public and private.

Just a 1% increase in soil organic matter (about 20 tons of compost per acre or a 1/4-inch application depth) can store 10 tons of carbon per acre

While it may not be practical or possible to add compost to all those acres, the potential for long-term, compost-based carbon storage in the U.S. alone is … well … pretty big.  And the deeper the storage, the longer the retention time.  Even annually tilled acres can offer C sequestration if that carbon can find a pathway to deeper soils below the plow layer.

But how does compost-applied carbon migrate from upper soil levels to deep-soil storage?

Below the plow layer — deep-soil carbon storage

A “plow layer” is the layer of soil disturbed when a plow (plough) is dragged through a field.  Depending on the type of plow used and its settings, the layer depth can range from a typical 8 inches to 20 inches or more.

The trick is to facilitate the movement of carbon from the plow layer to deeper soils where it can lie locked up and undisturbed for centuries.

Typically, the root systems of trees and perennial grasses grow deeper than annuals.  As the root systems of plants bury themselves in soil, they do more than just carry carbon in their tissues.

Downward growth also creates passageways for water and a transportation route for microbes.

Critter burrows create pathways for water and microbes, too.  Well below the plow line, termite colonies can be found as deep as 6 meters.  Some types of ants live at depths of 3-4 meters.  (1 yard = .91 meters)

Nightcrawlers will work their way down several meters into the soil, bringing organic matter with them.  Their castings (excreta) have a carbon-to-nitrogen ratio of 12-15:1 and include beneficial microbes.  A healthy soil layer above ensures plenty of available carbon for below-the-plow-layer earthworm storage.

C storage depends on many factors

It is important to remember neither the C cycle nor microbial metabolic processes operate in isolation. These functions are influenced by many factors like:

  • Nutrients
  • Temperature
  • Moisture
  • pH

Climate plays a role, too.  Globally, cool-wet regions tend to have the highest concentrations of soil carbon and deserts the lowest.  One of the more disturbing aspects of a warming planet is that more soil-bound carbon may be released to atmosphere as temperatures rise.

Effective solutions will require wholistic approaches, but compost use continues to rank among the top options due to its affordability, universal applicability, ease of use, and immediate availability.

Bottom line:  The potential for deep-soil carbon storage exists, even on annually tilled cropland, through management programs designed to improve soil health and encourage symbiotic facilitators like nightcrawlers.


reclaiming the desert

Can organic waste help green the Sahara for carbon storage?

It has been suggested devoting 5 percent of the earth’s land mass to plants bred for carbon storage could capture about half of global CO2 emissions.

That’s an area about the size of Egypt, a country that has already embarked on a program to reclaim some of the Sahara.  Project drivers are linked to food production, not climate change.  But the Land of the Pharaohs has not had an easy time of it, and some question the plan’s chances for long-term success.

Yet, as agricultural acreage declines worldwide and so many global minds focus on ways to feed a growing earth population, the Egyptian effort does beg the question:

Can reclaimed deserts store carbon and grow food?  More to the point, could composted organic waste help green up deserts like the Sahara or the Kalahari or the Sonoran?

Search the web for successful desert reclamation projects.  The use of compost is integral to all and has been referred to as “fertility priming.”

Capturing and composting organics would be the easy part. Unfortunately, there are major hurdles between barren sand and arable acres:

  • Tilling releases carbon. Unless the crops planted are perennial, some of that applied carbon will be lost.  In Egypt’s case, the goal is more annual grains like wheat and corn, perennials.  However, it should be noted, soil sampling at two of Egypt’s desert farms suggest carbon supplied from organic soil amendments will accumulate, even in oft-tilled fields.
  • While compost holds water, that water has to come from somewhere — if not rain, then rivers and aquifers or, as a last resort, desalination. But river water can be diverted by projects upstream.  Fossil aquifers, like those under northern Africa, are not replenished and will, eventually, dry up.  Desalination is still considered an expensive solution.  This means water availability will continue as the most critical factor to project success.
  • Desert soils tend to be salty, too, which creates unfavorable growing conditions. Fortunately, one permaculture specialist has reported a de-salting effect from building a living soil in the desert.

There seems to be a wealth of anecdotal material out there on desert reclamation, but not much peer-reviewed, scientific research.  Some “research” is based on calculations, not long-term field testing/studies.

In addition, the reclamation farms tend to be smaller “niche” operations — organic, biodynamic, permaculture, etc. — and not large, conventionally managed acreage.

That said, by simply looking at photos and videos, it’s obvious that desert reclamation is possible.  Whether or not it can also be profitable on a large scale remains to be seen.

But if these issues could be resolved, resulting in a clear path for resurrecting vast expanses of sandy soil, how much compost would it take to green a desert?

Most desert soils contain less than 1 percent organic matter.  To make the calculation easy, assume that number to be zero and add enough compost to boost organic matter content (OM) to the recommended 5 percent.

Based on this example,  a 1 inch application requires 135 cubic yards or 54 tons of compost per acre.  This assumes a 60 percent organic matter content, a bulk density of 800 lbs./cubic yard, and 30 percent moisture.

The author of this article about raising soil organic matter (SOM) levels says bumping SOM 1 percent “requires an additional 20,000 lbs. (10 tons) of soil organic matter or 11,600 lbs. (5.8 tons) of carbon, as soil organic matter is roughly 58 percent of carbon.”

The article further calculates stover and root mass from a no-till wheat cover crop system can only be expected to add about 0.1 percent of organic matter to soil.  Obviously, though that percentage might fluctuate a bit depending on the crop and cropping system, one of the fastest ways to build soil organic matter content is not through plants, but through compost use.

At 3.6 million square miles or about 2.3 billion acres, the Sahara is roughly the size of the United States.  It would take billions of tons to make those acres productive.

But balancing out CO2 emissions only requires a couple of plots the size of Egypt.  That’s about 500 million acres.  It sounds like a daunting task until considering there are nearly twice that many farm acres — more than 900 million as of the 2017 agricultural census — in the U.S. alone.

This is doable.  And the best news?  Nary an ounce of waste or compost needs to be hauled to Egypt.  Those 500 million acres can be divvied up and spread across the globe.  From tenders of 10,000-acre ranches to diggers of 100 sq. ft. gardens, anyone can contribute to carbon sequestration.

Of course, playing with numbers is just that — play.   A tremendous amount of effort, plus a megadose of dollars, would be required to convert all world organics to compost.  But rough numbers and real-world economics suggest sequestering carbon through compost use is possible.  (View the SlideShare title: Compost to the Rescue)

And as the World Bank expects the global waste stream to grow by 70 percent by 2050, it sounds like there will be plenty of organics available to get the job done.

Bottom line:  We have the know-how.  We have the technology.  We have the organics.  Costs to produce compost are competitive with landfilling and WTE/incineration.  And whether existing farmland, greenspace, or desert, whether Africa, Asia, or the Americas, we have the acreage needed to clear the air.  The only thing missing? The will to do so.

High-rate composting

High-rate industrial composting – what is it?

View the SlideShare title:  Modern composting.  No art.  Just science.

High-rate industrial composting — the scientific management and enhancement of the natural biodegradation process — is a method of accelerating the decomposition of organic wastes.

Whether processing food waste, sludge, vegetation or any other organic-based material, the use of an accelerated composting system can convert biodegradable waste to a high-value product much faster than more traditional, low-tech composting technologies.

Why is acceleration significant?

Rapid breakdown of target compounds results in a smaller facility footprint able to recycle about 10 times the volume of a windrow operation in the same space.  But also significant is the fact that high-rate composting can produce 10 times the volume of a high-grade, salable product.   Can any responsible facility owner — public or private sector — afford to disregard revenue potential multiplied by a factor of 10?

For a commercial operation, the ability to generate 10 times the revenue can mean the difference between profitability and business failure.  For a public-sector project, designing and managing a composting facility to generate meaningful revenue can offset operating costs and represent a real savings to those who foot the bill — the taxpayers.

For urban settings, the facility design and high level of control inherent to high-rate systems also protects sensitive receptors from environmental breaches that lead to nuisance complaints.  Preemptive design, process selection, and siting can all but eliminate things like leachate, odors, and flies when combined with “good neighbor” management practices.

What makes high-rate industrial composting scientific?

Unlike more primitive composting methods, scientific processes establish and maintain an environment conducive to the proliferation of the specific microbial populations responsible for natural biodegradation.

Scientific composting does not put engineering first.  Instead, engineering plays second fiddle to biology, specifically, controlling the biochemical processes that take place during biodegradation.

Here’s how science plays a significant role:

Aerobic microbes — those responsible for biodegradation — prefer temperature, oxygen, and moisture levels within a certain range.   When these conditions are met in the presence of an ample food supply, microbes eat and reproduce at a rapid rate.

Microbes release enzymes as they feed on the sugars and proteins that make up the organic waste.  The enzymatic action breaks down compounds at the molecular level.  This feeding activity results in the release of water, heat and CO2.  The steam rising from a compost pile is a sign of this activity.

With windrow composting, every ingredient, batch or windrow is treated the same.  Wastes are blended and windrowed.  At minimum, the piles are turned as often as government regulations require.  Periodic temperature readings (usually, with a manual probe) may be used to monitor internal temperatures, with a windrow subjected to additional turns if it gets too hot or too cold for the aerobes.

But this hot/cold cycling, even for short periods, lengthens the time required to break down the material.  In addition, if history is any indication, most windrow processes are not sufficiently robust to breakdown more complex compounds like biodegradable resins/plastics.

Instead of just turning a pile and letting it sit until a regulation or periodic manual temperature reading says it’s time to turn it, scientific composting recognizes the individuality of every blended batch and creates the perfect environment, regardless of ingredients or ambient temperature.

The science in feedstock selection and blending

Process control starts with the choice of feedstocks for every processing batch.  The blending goal is to achieve optimum moisture levels and carbon-to-nitrogen (C:N) ratios, as well as ensure adequate porosity and homogeneity for each batch.

Moisture — provided there’s not too much of it — is used by microbes for transportation, making consistent moisture levels throughout the batch a critical blending and processing goal.  If there are dry pockets within the blend, microbes will not be able to move in to do their work.  If too wet, the wrong kind of microbes — anaerobes, the ones responsible for odor generation — will take over.

Pore space serves as the conduit for water migration and air flow.  Air flow is necessary to deliver oxygen to the microbes and prevent heat build-up during processing.

Homogeneity means the batch is well-blended with no marbling of wastes or other indicators of an improper mix.  Lumps and clumps in the blend can leave pockets of non-degraded waste within a “finished” processing batch.  A homogeneous mix equalizes opportunities for microbial contact with target compounds throughout the blend and speeds up the degradation process.

Sometimes, getting the blend just right may require the sourcing or purchase of specific amendment materials or even turning away waste products that either offer no benefit or prove detrimental to the process and/or quality of the finished compost.

In some cases, these undesirable wastes can be pretreated at the generation source to make them more amenable to composting.  Dewatering might be considered an example of a composting pretreatment for residuals and by-products that are mostly water.

The science in processing

Typically, high-rate industrial composting technologies will rely on some sort of process containment to achieve the level of control required for a quick and efficient composting.

The objective is to control as many process influences as possible — especially weather — which can wreak havoc on an outdoor composting facility.  While a well-constructed compost pile will continue to generate heat during cold months, it will do much better in containment.   The same may be said for a pile exposed to rainfall.  Excess moisture can kill an aerobic process, requiring extra turning or even re-blending to get the composting restarted.   Time issues aside, extra materials handling means higher equipment and labor costs per ton processed.

There are many containment options available, ranging from covering outdoor piles to banked, indoor composting to fully encapsulated processing bays.  Full containment, of course, offers the most control over the process.

Advantages (compared to open air processing) include:

  • Elimination of weather as a biodegradation influence.  While tarps and covers offer some protection from rain, they do little to negate the impacts of ambient temperature changes or exposure of the blended admixture during placement, turning or removal.  Temperature fluctuations will impact degradation rate.  Tarps and other covers also have a limited life and must, periodically, be replaced.
  • All-indoor operations allow for air extraction/biofiltration from both the processing bays and work zones.  This not only improves visibility and worker health, but also allows the operation to fit more comfortably into the host community.  Covers and tarps are little help in mitigating odors generated during off-loading and blending in open-air environments.
  • Automated monitoring and process control keep temperature levels constantly within the “zone” for aerobic microbes, regardless of blend constituents.  The more control exerted over the process, the faster the biodegradation rate.  When it comes to high-rate industrial composting, control equals speed.  This is the reason a high-rate composting system can have a throughput rate 10 times that of a windrow operation within the same footprint.

abstract of microbes for industrial composting

Industrial, high-rate composting:  exploiting the power of microbes

Thirty years ago, beyond the entry sign announcing the location of a composting operation, it wasn’t unusual to see a former cow pasture crowded with long rows of rotting yard waste.

Start-up for these primitive facilities was (and still is) relatively cheap.  A windrow operation is viewed as simple and attracts owners whose primary goal is to get a facility up and running without investing much in capital.

However, in all but the most arid climates, the Great Outdoors is not that great for the microbes responsible for composting’s biodegradation.  Aerobic microbes — the stars of every bona fide composting operation — will only reach peak performance levels if they are protected from the elements, provided with an ample food supply and a bit of water, and live in an environment equivalent to a microbial Goldilocks Zone.

Bring all of these conditions together in one place, and composting doesn’t just happen.  It goes gangbusters.

Today’s industrial composting plants and advanced biodegradation systems are designed to do just that, because the realities of high-volume organics recycling often demand more than the typical windrow can provide.

Science-based recycling systems — exploiting the power of microbes

When serving metropolitan areas, composting operations can be expected to recycle everything from fecal-laden yard waste to industrial by-products — in high volumes. These facilities intake and process hundreds of tons each day.  The larger operations may be processing 100,000 tons or more per year.

Odors emanating from some of these feedstocks can be unpleasant.  The materials can be very wet.  A few will carry chemical residues that require an advanced degradation technology to render them safe for reuse as ingredients in soil amendments.

That’s why more modern plants, those tasked with managing multiple types of organics from large geographic regions, are indoor operations.  Some may still turn under that roof, but others have kicked it up a notch by employing more advanced systems (i.e., aerated static pile or ASP) instead of turning.

While a windrow tends to plod along, controlled aeration accelerates composting, turning stodgy microbes into sleek degradation athletes.  With high stamina and a voracious appetite for all things organic, these Olympians of the microscopic world bring speed, reliability and high performance to an otherwise lackadaisical process.

The industry’s transition from windrow to ASP turbocharged composting, exploiting the power of microbes and giving it the efficiency and predictability required to successfully compete with landfills and incinerators.  But this metamorphosis did not result from genetic manipulation, chemical additives or fairy dust — it was simple biology.

That’s it.  Not engineering.  Not artistry.  Just biology, specifically, exploiting the power of microbes.

Prior to some notable research by scientists beginning in the 1950s, folks may have known how to keep a compost pile chugging, but not why their management efforts worked.  But once researchers figured out the why, they were able to control the process by giving aerobic microbes exactly what they needed to survive and thrive (air, water, food, temperature) in the right amounts and within ideal ranges.

They discovered composting’s Goldilocks Zone.

By the 1990s, this academic exercise had captured the eye of the commercial sector.  With some tweaking to improve efficiency and profitability at scale, a robust, predictable process emerged, one with the ability to cost-effectively recycle high volumes of organics.

But back to those microbes…

After many trials and several errors, industrial composting moved into the waste management mainstream.   But to make biology work as the power behind the progress, both designers and facility operators had to grasp, embrace and deploy a few scientific principles.

At the core was a rudimentary understanding of the two broad categories of biodegradation processes – aerobic and anaerobic.  Each identifier reflects the environment in which the microbes live.

Aerobic organisms require air and water, but like people, they cannot breathe under water.  Conversely, anaerobic microbes are like fish – they’ll die when exposed to air.

Anaerobes live and thrive in much wetter conditions than can be tolerated by aerobes. Both prefer a moderate temperature zone.  Anaerobes will die off at around 150 degrees Fahrenheit (F) or 65.6 degrees Celsius (C).  While aerobes can tolerate more extreme temperatures, the most active phase of aerobic composting takes place between 55 and 155 degrees F (12.8 to 68 C), with a preferred range of about 122-140 degrees F (50 to 60 C).

Anaerobic fermentation generates methane, which can be a good thing if captured and used for heating, cooking and generating electricity.  If not, then it’s a bad thing, a potent greenhouse gas.  When anaerobes are at work, certain compounds are created during intermediate degradation stages that result in unpleasant odors.  That is why some wet, decaying materials carry an offensive stench — the rotting organic matter has “gone anaerobic.”

But an aerobic process neutralizes odors by creating drier conditions, killing odor-causing anaerobes.  Methane is not generated during a well-managed aerobic composting process, and the resulting carbon dioxide emissions are considered carbon-neutral since the gas generation volume is the same as if the materials degraded naturally.

Beneficial bacteria and fungi are among the aerobic microbes that make compost “happen.”  About 2,000 species of bacteria and 50 species of fungi are ably aided in their degradation efforts by a zoo of macro-organisms like beetles and worms.  However, aerobes are the worker bees of the compost pile.  They break down organic matter at the chemical level as opposed to the physical rending of the macros.

Feeding on organic waste, aerobes power the engine that drives moisture from the composting mass, degrades pollutants, and eliminates odors.  The enzymatic action associated with aerobic digestion breaks molecular bonds, releasing by-products (heat, water, carbon dioxide) in the form of steam.  Once these microbes have consumed all available food, they die fat and happy, their microscopic bodies becoming part of the residual mass.

In a controlled composting process, a temperature drop signals a decline in food supplies and a correlating reduction in microbial populations.  Degradation slows, but still continues at the lower temperatures associated with compost curing.

If left to time and nature, organic matter will continue its disintegration until nothing remains.  But long before that happens, biodegradation enters a phase where the residual is relatively stable, while still microbiologically active and chock-full of both macro and micronutrients.  With its soil-like aroma and appearance, the material is pleasant and easy to use – a critical requirement for any product intended for widespread general use — and really, really good for rebuilding depleted topsoil.

This stuff, of course, is compost.

Microbes just keep going and going and…

When talking microbes, conversion of waste to valuable product is only half the job.  Once that compost has been added to soil, the little critters take on even more tasks:

  • DEGRADATION OF POLLUTANTS – microbes break down synthetic compounds to neutralize the impact of things like petroleum products and fertilizers/chemicals that can negatively impact both soil and runoff quality.
  • IMPROVE NUTRIENT UPTAKE – microbes convert nutrients to plant-available form, making more food available to plants and reducing the need for synthetics.
  • IMPROVE DISEASE RESISTANCE — microbial activity is responsible for the plant disease suppression associated with compost use.

The influence of science on facility design

The biggest problem with outdoor operations is not weather, per se, but the fact that weather cannot be controlled.

If a composting mass needs moisture, rainfall can be a welcome addition.  While it’s common for the sides of a compost pile to “crust,” discouraging rain infiltration, piles can be flattened and then concaved on top to capture rainfall for slow infiltration over time.  In this regard, rainfall can be a compost manufacturer’s friend.

But excess rainwater rolling down the crusted sides of a pile will settle into pools of “black liquor” (a.k.a. leachate) at the base.  Leachate and associated runoff contaminate ground and surface waters, attract flies and harbor unpleasant odors.  If the pile gets too wet too soon, pathogens rebloom.  When composting outdoors, a heavy rainfall can set the stage for nuisance complaints and regulatory intervention.

Conversely, maintaining acceptable processing conditions outdoors during dry spells requires sprinkler systems or a hose brigade if the microbes and the process are to be saved.

Add complications like high winds and ice storms to the mix, and the operation of an outdoor facility becomes more about battling Mother Nature than recycling organics.

Having to reprocess ruined piles and windrows adds cost and retards throughput. When hundreds of tons of waste arrive at the gate each day, a stuttering throughput rate can cause massive pile ups that compound and exacerbate the weaknesses of outdoor facilities.

Exploiting the power of microbes means protecting the creatures from the vagaries of weather is a top priority for modern facility designers.  Solutions can range from a shed roof to encapsulation to full facility enclosure.  Each rung on the containment ladder offers an elevated level of environmental control and protection, as well as fewer operational complications.

On that list are the elimination of materials handling woes related to weather delays and the ability to capture inside air and processing off-gases for biofiltration.  Indoor facilities can also make a composting operation more palatable to the locals by providing visual camouflage and sound buffering.

Making biology work for day-to-day operations

Putting a roof over a composting operation may remove many headaches from the manager’s plate, but design is only as effective as the people running the place.  Any composting facility — from the most basic to the most sophisticated — can still run into trouble if mismanaged.

Exploiting the power of microbes requires a multi-faceted strategy.

Feedstocks like food waste and biosolids can be wet and odor-laden when they arrive at a composting facility.  One of the top priorities for modern composting operations is to get these types of materials blended with dry amendment and aerated as soon as possible to kill off anaerobes and encourage the proliferation of aerobes.

But if the blend isn’t right, a batch can be doomed before the admixture ever hits the composting pad or aeration floor.  Wet or dry pockets impact microbial movement throughout the composting mass.  An irregular texture means patchy distribution of target compounds and uneven exposure to the microbes.  Pockets of untouched raw waste can survive an otherwise successful process, leading to regeneration of odors and reblooming of pathogens.

Particle size needs to be consistent to achieve an even degradation rate for all blend ingredients.  Material placed on the composting pad should not be compacted.  Aeration pipes must be free of debris.  Windrows may need more turnings than required by regulations to keep the process humming.

Many items on the list of best management practices (BMPs) are common to all composting operations, from backyard to industrial.  Many items on the DO list relate to the creation and maintenance of an ideal environment for the microbes responsible for biodegradation.  The DON’Ts focus on discouraging of the kind of microbes that cause and perpetuate odors.

But no matter the design or process, people are ultimately responsible for making the science work as it should, keeping those all-important “bugs” happy and ensuring a trouble-free operation.


Calculating C:N ratios

Calculating C:N  ratios – hitting the sweet spot when blending multiple feedstocks

Cooking may allow the chef to add a pinch of this and a daub of that to create an incredibly edible meal, but more exact measurements and methodologies are required for successful baking.  That’s because cooking is mostly about building and enhancing flavors.  Baking is about understanding and exploiting science.

Composting is about science, too.  Just as curdled custard and flat cookies are indicative of science gone awry, a sluggish composting process and offensive odors are signs someone failed to adhere to the science.

One of the common culprits of composting-science-gone-bad is getting it wrong when calculating C:N ratios.

C means Carbon.  N stands for Nitrogen.  Together, they influence microbial feeding activities.  C provides energy and microbial cell structure while N is linked to proteins, enzymes and other substances integral to cell growth and other biological functions.

The trick, of course, is to hit the composting “sweet spot” with a carbon-to-nitrogen ratio of about 30:1 for the initial feedstock blend.

Forget about “brown” and “green” for calculating C:N ratios

The ubiquitous brown:green rule of thumb for composting — brown materials are carbon, green are nitrogenous — is often promoted to help the backyard composter recognize differences in materials.  But one cannot categorize feedstocks based on color alone.

Coffee grounds may be brown, but they are rich in nitrogen and can actually serve as a substitute for manure (which is also a brown).  Therefore, coffee grounds are “green.”  Peanut shells, also brown, have a near-perfect C:N ratio for composting of 35:1 without combining with any other carbon or nitrogen.

Adding to the brown-green confusion is a mistaken belief that the ratio relates to volumes of brown material and volumes of green, as in 30 buckets of sawdust to one bucket of cut grass.

It does not.

C and N values are derived from the actual carbon and nitrogen content of the individual blend ingredients, not by feedstock volumes, and those numbers are derived from materials testing or generic charted values based on someone else’s tests.

At a micro-scale, the margin of error associated with color confusion may be small enough to make little difference in odor generation or degradation rate for a home compost pile.  But at industrial-scale, calculating C:N ratios needs to be more precise.

The best method of determining carbon and nitrogen content is feedstock testing.  Then, calculations can be made to determine the mix.  When testing isn’t possible or practical, assumptions can be made based on charts like this one.  Washington State University also makes a Compost Mixture Calculator available online that does the math.

C:N impacts on the composting process

C:N is an indicator of the nutrient content of any given material.  Sometimes, a C:N ratio may be expressed as a single number — i.e., 45, 30, 13, etc. This means 45:1 or 30:1 or 13:1.

A lower “C” number indicates higher nitrogen.  Higher Cs indicate more carbon.

For a composting blend, anywhere in the 25-35:1 range is considered good.

A higher carbon content will slow the biodegradation process.  But if carbon content is too low, odors and anaerobic conditions can become management issues.  Too much nitrogen can also raise pH, killing off desirable microorganisms.

Carbon content will naturally drop during composting as microbes use it for energy.  Carbon is also released as CO2.  Nitrogen, however, gets recycled, so the amount at the end of processing is the same as it was in the beginning.

C:N impacts on compost use

The 30:1 ratio is the Goldilocks Zone for composting, but a typical finished compost might have a ratio of 20-25.  (Soil microbes prefer a C:N ratio of around 24:1.)

When added to the soil, composts with higher numbers can encourage microbes to lock up any available nitrogen for their own use, leaving less for plants. Lower ratios reduce the likelihood for food (nitrogen) competition between plants and microbes, since the feeding microbes will still leave plenty of N for plant growth.  Even at a 10-20:1 ratio, there will still enough carbon and nitrogen to allow plants and microbes to successfully share.

However, when the C:N ratio drops below 10, degradation rate for organic matter becomes very high, negating some of the benefit of compost use.

Soil tests, product tests and a chat with the local agricultural or horticultural extension agent should tell growers what they need to know to maximize yields based on the C:N ratio of finished compost.

LEARN MORE:  Carbon to Nitrogen Ratios in Cropping Systems