Estimating organic waste volumes for composting 

Imagine you’re the facilities manager for a large commercial building or institution, staring at a row of overflowing carts or roll-off boxes sidled up to the wall in the alley or back parking lot. 

They’re filled with crumpled paper, reams of old reports, food leftovers, used coffee pods, an avalanche of plastic bottles and aluminum cans, and pizza boxes with paper napkins stuck to the remnants of a variety of cheese toppings.    

You know all of those discards can be recycled and/or used as compost feedstocks.  Since most of that waste is compostable, diverting the organics from the landfill to composting could save money.   

The problem is, few composting operations will accept mixed waste loads.  The resulting compost is just too contaminated to use and winds up in the landfill anyway.  And if you want to develop an on-site composting project, knowing the volume/weight of compostables influences everything from sizing to siting to process selection. 

Source-separation – removing recyclables and compostables from the disposal stream at your location – is not as difficult as it sounds.  A good education program supported by a healthy dollop of (re)enforcement usually does the trick.   But before investing time, money, and brainpower in the project, you know the decision-makers will want to talk dollars and sense.  They’ll want assurances that the economics work.   

The first step is to determine how many pounds or tons of compostables are being generated each year.  Then, you can begin the planning process and start to gather cost estimates. 

Routes available for developing estimates all come with advantages and disadvantages, mostly related to things like people-power, total generation volumes and required degree of accuracy.  A web search will offer lots of ideas.  Here, we look at 3 broad categories: 

Route 1 – Develop estimates based on published norms and averages 

The easiest, fastest, and cheapest method to estimate compostable volumes is to glean “typicals” and “averages” from the web.   

The U.S. EPA says about 61% of the total MSW stream is made up of food, paper and cardboard, wood, and yard trimmings.  If your commercial or institutional stream is similar, this method could work for you.  Couple this percentage with known weight capacities of the specific receptacle in use, and the result is a baseline number you can use to calculate weekly or annual tonnage.   

Simply convert those gallons or cubic yards to pounds (based on container weight limits), divide by 2,000 to get tons, then multiply that number by .61 or 61%.  This is the estimated weight of all compostables. 

There are also sources that will provide weights based on generation rate per defined unit.  Example: 41 pounds MSW per week per household or 200 pounds per week for each fast food restaurant employee.  Again, convert pounds to tons and multiply that number by .61 for a rough estimate of compostable tonnage. 

Want to count bins or carts?  Contact your waste hauler for specific container sizes/weights or use a more generic number like 180 pounds for a 96gallon cart (from one online resource). 

Just focusing on food waste?  A cubic yard of food waste weighs about .5 tons. 

This method of estimating volumes for composting is probably best for low volume generators, because the total volume and weight of any “error” will be relatively small.  For everyone else, use this type of generic data for rough estimates only. 

You can find charts to help with weight estimates in our SlideShare title:  Estimating volumes of food waste and other organics for composting. 

Route 2  the DIY waste audit 

This method relies on statistically representative random sampling to develop a picture of the total waste stream.  There are several sample size calculators available online to help you get it right, and they come in handy for evaluating validity of other types of surveys, too. 

The following examples were calculated using the SurveyMonkey tool: 

Let’s say you counted a total of 40 trash cans in your office building.  Using a confidence level of 95% and a 5% margin of error, the calculator suggests a sample size of 37 trash cans. 

If you have a larger building with 400 trash cans, using the same confidence level and margin of error, the sample size is 197. 

Trying to pin down the generation volume of a city of 40,000?  The sample size is 381. 

Once you know how many units you need, identify a representative subset for sampling.  A human can do this, but to be totally unbiased in the choice of trash cans, let a computer randomize the list.  Using the 40-can building as an examplecreate a list of all trash can locations in a spreadsheet.  Then randomize the list Randomizing is easy … this site is just one of many with step-by-step instructions.   

Once the list is randomized, use locations 1-37 for your audit: 

  • Assemble supplies (gloves, aprons, scales, etc.) and identify helpers. 
  • Pull all 37 trash cans at the same time on the same day and move to your audit location. 
  • Provide training to any helpers who might not be able to distinguish compostable from non-compostable.
  • Separate can contents into those two piles.  If conducting a full waste stream audit, further subdivide the non-compostables into glass, metal, plastic, etc. 
  • Weigh the compostables pile and divide by 37 (sample size) to get an average weight per can.  Multiply that average by 40 cans (total building) for a daily average.  Multiply the daily average by the number of workdays per year to arrive at an annual weight and divide by 2,000 to convert pounds to tons. 
  • If you’re just doing compostables, you’re done.  Otherwise do the same calculations for each waste group you wish to audit. 

Advantages of this method are improved accuracy and the fact that audits can make good group projects.  But the audit is only as accurate as the volunteers, and auditor safety (masks, gloves, etc.) must be a top priority.  

Also consider, as an alternative to the internal DIY, the resources of a local university where a researcher, class or student may be looking for a project.  Some private companies and governmental entities also offer free audits.  Just make sure they understand the focus is compostables, not just the more traditional recyclables like plastic and glass. 

Route 3 – professional waste audits 

Sometimes, only a professional audit will do.  This will include sizeable and/or toxic waste streams where the expense of professional expertise is warranted.  Typically, these will be engineering firms and other specialists with experience in waste management. 

Professionals can charge by the hour or by the contract.  If taking this route, choose a reputable firm and make sure there is a clear set of deliverables, as well as a timeline, spelled out in the Scope of Work agreement. 

As might be expected, this option can require a healthy budget.  But on the plus side, using professionals can be more accurate than any other when estimating volumes for composting.  If composting costs less than landfilling in your region, the audit may well be a money-saver in the long-term. 

READ MORE: 

Global warming — Earth’s ‘carb’ overload 

Whether the basis for climate change is over-reliance on fossil fuels, loss of jungle canopy, too many chemical fertilizers, natural phenomenon, all of the above, or none of the above – the fact remains that global temperatures are showing an upward trend.  

Some claim the climb is caused by industrialization.   Others disagree and point to a Medieval Warm Period and other episodes of global warming through the ages.  But the crux of the matter is that, unlike our Middle Ages counterparts, the humans living in this era possess the skills, knowledge, and wherewithal to temper the impacts of rising global temperatures. 

We can pull less carbon out of those long-long-long-term storage deposits of coal and oil, plant a few more trees, and let cows eat grass instead of stuffing them with grain.  But we can also try to keep temperatures within our own Goldilocks Zone by sequestering more carbon in soils that won’t be disturbed for extended periods of time.   

Even if all new sources of carbon were reduced to zero, there’s still too much in the atmosphere now – and it has to go.  Scientists are working on numerous projects designed to remove excess carbon from the atmosphere, but soil sequestration remains among the simplest and least expensive solutions.   

First, it must be said that the much maligned “greenhouse effect” is actually a good thing.  It’s what makes this planet habitable for humans.   

In the atmosphere, radiation from the sun generates heat.  As it bounces around in the “greenhouse,” some of this heat is absorbed by the earth and some is released back to space.  But greenhouse gases like carbon dioxide and methane absorb and trap heat.  When there is an excess of this type of gas in the atmosphere, too much heat is trapped and radiated back to the earth, resulting in global warming.   

Other greenhouse gases include water vapor and nitrous oxide.  Industrial chlorofluorocarbons are highly-regulated, synthetic greenhouse gases. 

But carbon dioxide (CO2) has become a primary focus becausits increase is associated with human activity.  Atmospheric carbon dioxide levels have jumped from 280 parts per million to 400 parts per million since the mid-1800s, which coincide with the early days of the Industrial Revolution. 

To reduce carbon compounds in the atmosphere, science looks for ways to naturally or artificially sequester excess carbon for long-term storage. 

Putting the atmosphere on a low-carb(on) diet 

Limiting and reducing the amount of carbon in the atmosphere is the goal of carbon sequestration.     

Vegetation, oceans, and soils are examples of natural sequestration.  These carbon sinks naturally absorb atmospheric CO2.   

Carbon capture, ocean injection, and geological storage are examples of artificial sequestration.   Captured CO2 has a number of industrial uses, including the manufacture of fizzy beverages and plastic bottles.  Athe costs for these new technologies drop, their uses are expected to rise. 

As sinks go, compost use is among the best.  Amending soils with raw manures and biochar also sequester carbon, but neither offers such a wide range of other soil-enhancing benefits as does compost use.    

Almost everyone can contribute to carbon sequestration 

Regenerative agriculture can restore soil health and make a major impact on carbon sequestration.  In fact, the Rodale Institute says more than 100 percent of current global CO2 emissions could be sequestered if all pasture and cropland management was based on regenerative agriculture. 

But one needn’t be a farmer to create carbon sinks.  From backyard to utility easements to parkland, there is opportunity for every community to contribute to the reduction of the planet’s carbon overload.   

Know that things like soil type and local climate can influence carbon retention.  Tactics must reflect the region, because a good strategy for the arid west may not be the best choice for humid, subtropical Florida.   

Yet all sequestration approaches will have one thing in common – decades or centuries-long confinement of that carbon without disturbance: 

  • Establishing a lawn by incorporating compost?  Yes. 
  • Topdressing a garden plot that is tilled every year? Not so much. 
  • Using compost to amend a field that is plowed every season?  Not that great. 
  • Planting that same field with perennials or converting it to grassland?  Much better. 

Any patch of soil that can be amended, planted, and then left undisturbed for many years is a potential carbon sink.  This includes every community’s roadsides, athletic fields, and recreation areas. 

Bottom line:  Earth’s history is peppered with episodes of warming followed by ice ages.  Unless humans learn to manage carbon to moderate temperature extremes – no matter the cause — those who survive this era of global warming may learn the hard way that nature always seeks to return to a state of balance.    

FAQ: How do I sterilize soil?

When making your own potting soil from native soil or trucked in topsoil, it’s a good idea to sterilize that dirt to kill things like weed seeds and diseases before mixing with compost and other ingredients.  Large swaths of ground can be treated in-situ (in place) using plastic and the sun, but it takes time.  Fortunately,  small batches can also be treated using kitchen appliances.  Here’s a how-to article.  

Good compost starts with a good recipe 

Whether making a small batch or a big one, following basic instructions will get composting done right. 

While baking relies on an external heat source to trigger a myriad of chemical reactions, and composting generates heat as a result of biological activity, both processes have a great deal in common – including the end result. 

Whether baking cupcakes or making compost, a quality product starts with quality ingredients added in the right amount, at the right time, and in the right order.   

Mess up even one step of the process, and the end product may never be right. 

Ingredients 

Adding a pinch of sugar and 2 cups of salt to a cake recipe (instead of the other way around) could become an inedible disappointment.   

Composting is no different.   

For the process to work as it should, the carbon to nitrogen ratio must be right (25-30:1 by total C and N content, not “brown and green” feedstock volumes) and moisture levels must be in the zone (40-60% by weight). 

Blending 

In baking, improper or incomplete mixing of ingredients can result in gooey or dry pockets within the finished treat.  Batches must be thoroughly blended to distribute ingredients evenly throughout the mixture. 

Goof up a compost blend, and the same thing happens.  Wet or dry pocketsmarbling, and other mixing mishaps mean microbes will not have equal exposure to target compounds, air, or moisture.   

This can create zones of uncomposted materials in an otherwise completed batch, failed laboratory tests, smelly finished product, etc.   

When blending, focus on achieving uniformity in moisture distribution, texture, and porosity. 

Processing 

Convection ovens, equipped with fans that move heated air during the baking process, have become a favored appliance for bakers who once struggled to achieve even baking in older, conventional models. 

But the latest and greatest in kitchen gadgets are no help if temperature settings are wrong.  Heat levels must still be correct to bake a cake or casserole to the center without drying or burning the edges. 

For composting, that zone is 113-160 degrees for initial composting and 70-113 degrees for curing.  The time it takes to complete each processing stage depends on the level of control applied … which is where those fans come to the fore. 

It is possible to compost (and do it well) without an automated aeration system – it just takes more time and trouble.  But it’s not possible to compost without any aeration.  

In nature, it doesn’t matter how long a pile of yard waste or a dead squirrel takes to decompose.  Sometimes, it can take years for nature to work its recycling magic. 

But most composting operations don’t have the luxury of unlimited time.  Speed and effectiveness of the process impacts everything from acreage requirements to the cost of operations.  Managing air flow through the composting mass must be a top priority for any municipal or commercial composting facility that needs to meet both throughput and budget targets. 

Here’s why: 

Remember that 70-160-degree temperature range?  Two types of composting microbes live and work within those zones.  Mesophiles are most active at the lower temps, while thermophiles dominate the higher levels where microbial activity and the resulting biodegradation is quite robust. 

Air flow is the primary mechanism for temperature control within the composting mass.  If temps are allowed to exceed 160 degrees F, thermophiles die off, the entire process crashes, and heat (generated by biological activity) must rebuild to productive levels. 

Every “crash” slows the process.  It’s like opening the oven door every five minutes to check the rise of a souffle — does more harm than good. 

But by using fans to move air through the composting mass, temperatures can be controlled.  More air cools the pile; less air allows warming.  By using sensors linked to microprocessors to automatically adjust those fans to meet specific time/temperature goals, a composting batch can meet regulatory requirements for pathogen kill in a matter of days instead of weeks or months.   

Of course, a manual probe will work, as well, if the budget allows for a person to walk around all day monitoring pile temperatures and making the necessary fan adjustments. 

Cooling/curing 

Food is rarely at its best when consumed straight from the oven.  Most dishes require a cooling/resting period prior to consumption, allowing sauces to thicken, juices to be absorbed and starch retrogradation to “happen.   

Compost, while it can be used fresh once PFRP/VAR requirements are met, is best when allowed to cooltoo. 

This is compost’s curing phase, when temperatures drop into the lower, slower zones preferred by the mesophilic organisms that will finish off the last of the food and bring the composting mass to a stabilized state. 

Farmers may prefer an immature compost because it can offer a slightly higher nutrient value than a more mature product.  But fair warning:  Use a compost before it’s fully cured only when destined for agriculture or other application away from sensitive noses.  Otherwise, wait until the pile offers only the sweet smell of rich, fertile soil before distribution.   

Depending on the initial feedstocks and technology used, the curing phase can last anywhere from a few weeks to several months.  Technologies used during curing can range from controlled aeration to occasional turning of a windrow to static pile. 

What is composting and how does it work? 

Composting is the managed degradation of plant and animal matter under aerobic (with air) conditions.  The process mimics natural decay in a controlled environment to speed up the breakdown of these organics. Composting results in a safe and easy-to-use soil amendment — compost.

Insects and bacteria are examples of the types of creatures that feed on discards like food waste and leaves during composting.  The larger animals tend to use mechanical methods, while the microscopic rely on chemicals to degrade these materials.

This feeding activity reduces complex compounds into simple molecules that are benign and odor free. Compost is used to build and replenish soils, closing the recycling loop for organic matter.  

The only byproducts of composting are CO2 and water;  the process produces no waste requiring disposal.  The CO2 is considered “carbon neutral” since its release during composting is the same as if decomposed by nature.

Most municipal, commercial, and non-profit composting facilities rely on microbes to do the bulk of the organic decomposition.  There are mancomposting methods in use, although outdoor windrows are among the most common.  Earthworms are the primary agents of decomposition in the controlled process known as vermicomposting. 

However, some other processes that have the word “composting” attached to their name in the vernacular may not be true composting processes.

Bokashi composting, for example, is an anaerobic (without air) fermentation process. Anaerobic composting is another misnomer.  Because neither is aerobic, neither is true composting.   Both can biodegrade organics, however.  Unfortunately, anaerobic decomposition may generate unpleasant odors since anaerobes produce mercaptan during biodegradation. (Mercaptan is added to odorless natural gas to give the gas its distinctive rotten egg smell.)   

Composting digestate, the by-product of energy extraction using anaerobic digestion, increases both the market value and uses for this waste material if managed for quality compost production.  

While neglected composting piles have been known to “go anaerobic,” too, a well-managed composting process — one that keeps the piles aerated — will not generate unpleasant odors.  Any odors present in the incoming feedstocks will be quickly neutralized, too.

Yes, we can build a composting facility for you

Do you want to build a composting facility?  Are you —

  • A private waste management company hauling 35,000 tons or more of biodegradable waste annually and paying more than the U.S. average tipping fee to dispose of that waste at a landfill,  WTE facility, or incinerator?
  • An AD system operator wanting to maximize the market potential of a low-value digestate?
  • A landfill owner hoping to extend the life of the landfill or trying to devise a strategy to meet the growing demand for food waste composting?
  • The utility director of a municipality currently hauling compostable waste to a commercial landfill or incinerator with service contracts expiring within the next few years?
  • A food processor with food waste and other biodegradables like DAF sludge and packaging waste (broken pallets, dirty cardboard, etc.) at multiple plants within 100 miles of a central location?

If the answer to any of these questions is yes, building your own composting facility may offer cost and efficiency savings, as well as long-term pricing stability for the biodegradable fraction of any waste stream,  all while offering a real revenue opportunity from the sale of high-grade compost to plump up the bottom line.

We’re not talking about throwing some clay down in a cow pasture and calling it a composting operation. We’re discussing modern, advanced technology, high-rate facilities that can handle everything from yard waste to biosolids to food waste and biodegradable plastics with aplomb.

And if you’re currently paying high tipping fees or driving long miles to dispose of this material, owning your own composting plant may be just the ticket to price-hike independence and lower costs.

These indoor, industrial operations are weather independent, providing reliable, predictable throughput.  When coupled with a modern process and professional management, they will produce a high-grade compost product with real market value for high-end customers in the golf course, turfgrass, parks and rec, retail lawn and garden, and like industries.

One of the best things about modern, environmentally-secure composting operations is that they take up very little space compared to outdoor windrows.  Ten high-rate facilities can be built within the boundaries of one outdoor windrow operation with the same throughput.   

Because of their biofiltration systems, they can also be sited much closer to population centers than the old-fashioned variety.  Contained, encapsulated processing and aerated processing systems all but eliminate headaches like leachate, off-site odors, and failed tests as management issues. This high level of control also results in a very rapid degradation process, with primary processing completed in a matter of days.

When choosing a composting system vendor, look for a firm with deep experience and a string of financially and technically successful composting operations under its belt.  Companies like McGill (which both operates its own industrial facilities and designs facilities for others) offer a definite advantage over those without these credentials.

Decades of hands-on experience processing some of the most challenging organic waste from municipal, industrial, and agricultural streams will trump a design-only firm with no operating expertise.  

McGill’s design-build options also include operations management and product marketing.   Learn more about McGill’s DBO services here.

How to make topsoil

When you order topsoil, do you really know what you’re getting?  

In some developed areas,  most of the topsoil has been scraped away or eroded.  What passes as topsoil is really subsoil – nearly dead dirt.  It will not function like good soil.

The good news?  You can make your own, be assured of its quality, and likely pay less than having topsoil trucked in.  Here’s how:

FOR EXCAVATED SOIL:  Mix the native soil with compost at a ratio of about 1 bucket or shovelful of compost to every 2 of soil.  A 30 percent compost content is recommended for raised beds and containers.  

FOR IN-SITU SOIL:  Work 2-3 inches of compost into the top 6-8 inches of native soil.

Compost is a very “forgiving” material.  It’s hard to use too much  (though you shouldn’t use it instead of topsoil),  and as little as 1/8 inch can be enough to give your soil a boost.

Whatever the amount, be sure to blend well so the compost is evenly distributed.

How can you tell if a soil is good or bad?  

The ideal soil for growing things will be a mix of sand, clay, and organic matter.   If having your soil tested, be sure the report will include these parameters.

Forging ahead without the soil test? The first part of this article describes various soil types and provides simple methods of identification.  

If you need to add sand or clay in addition to compost, ask your landscape supply yard for a custom blend.

According to this article,  most soil scientists agree that 50% pore space, 45% mineral matter (sand, silt, clay), and 5% organic matter make up an ideal ratio.  A typical compost is 50%-60% organic matter (dry weight). 

How much compost for my garden?

Compost makes a great addition to any garden plan.  But how much compost do you need?

A new plot in sand may require wheelbarrows of the stuff.  But if you are digging up a patch of lawn that has seen repeated compost applications over the years, the soil beneath the sod should be in pretty good shape.  A sprinkle might be all that’s needed.

How can you tell if the soil is good?  

The best method is soil testing.  (Contact your county Cooperative Extension Service for more information).  But you can use visual clues, too.  

Weeds like purslane, crabgrass, and dandelion are signs of a troubled soil.  

Stick a spade in the ground and turn over a shovelful of soil.  If it’s sticky and looks like modeling clay or dry and resembles beach sand, you’ve got big problems.  Fortunately, your soil is probably somewhere between these two extremes. 

Is it dark brown and loose?  Are there earthworms?  That’s what you want to see.  

How much compost do you need for a garden?

If building raised beds or container gardening, the soil blend should be about 30 percent compost.  When breaking new ground, incorporate 2 to 3 inches into the top 6 to 8 inches of soil.  

If your soil is very hard,  and you are planning deep rooted vegetables like tomatoes,  consider digging a little deeper.  Maintain the compost-to-soil ratio at about one part compost to two parts soil.

For an established garden with decent soil, just rake an inch or two into the surface before planting.   A 1/8 to 1/4 inch layer of compost sprinkled on the surface as needed throughout the growing season can revitalize flagging rows or containers.  The compost will feed your plants when you water. 

Three to 4 inches of compost can also be used as mulch during the growing season or as blankets when putting beds to sleep for the winter.  However, don’t pile compost up against tree trunks and stems of woody ornamentals.   

Our compost calculator can help you determine how much to buy.       

How much does compost weigh?

Depending on moisture level, figure 2 to 2.5 cubic yards of compost per ton.  A one cubic foot bag of compost will weigh about 40 pounds (1 cubic yard = 27 cubic feet).

A product shipped at 30 percent moisture will weigh less than one at 60 percent when it crosses the weigh scale, resulting in more cubic yards per ton than the wetter material when delivered.  

This may be good for keeping transportation costs low. But it also means the microbes responsible for aerobic degradation of the composting mass might die of thirst.  Weights that are too high could be indicative of low oxygen levels resulting from compaction and/or too much moisture — again, not good for the beneficial microbial populations.

An ideal compost will be 40-50 percent moisture.

Are compost and fertilizer the same?

Compost and fertilizer are not the same. But compost does have fertilizer value.

Wikipedia describes fertilizer as any material of natural or synthetic origin that is applied to soil or to plant tissues to supply one or more plant nutrients essential to the growth of plants.”

Compost’s nitrogen, phosphorus, and/or potassium (a.k.a. NPK) values are low compared to a synthetic fertilizer.  Some may add ingredients like urea to hike these macronutrient numbers.

That said, compost’s NPK value does have dollar value. The nutrients delivered by a compost product should be a factor in any input decisions involving synthetic fertilizer purchases.  Compost also adds a slew of micronutrients not typically found in common synthetics and improves nutrient uptake.

Compost feeds the soil. In turn, the soil takes care of the plants, offering a smorgasbord of nutrients, pest and disease resistance, and more.   But those nutrients are slow-release, feeding plants over time.  The benefits of a single compost application can stretch over multiple seasons.

Fertilizer’s sole purpose is feeding plants.  The primary function of most synthetic fertilizers is adding N, P, and/or K.  Application gives an immediate burst of nutrition.

Do you need fertilizer if you use compost?

For the home gardener, probably not, especially if that gardener is a long time compost user.

But for a commercial grower?  Maybe.  If the crop likes a punch of nitrogen (for example) at a certain point in the growth cycle, the addition of a synthetic fertilizer may be warranted.

However, the smart grower will carefully weigh the cost of any input against the expected return on investment. Sometimes, a lower yield will still net higher profits if input costs for synthetic fertilizers and pest control products are reduced or eliminated as a crop management expense.

Also, keep in mind that compost-amended soil reduces rainwater and irrigation runoff, which means more nutrients are retained in the soil.   This will impact synthetic fertilizer input requirement, as well.