As usual I have too many slides for the time allotted. So I will try to talk slow. If I start talking too fast maybe someone can give me a sign (like Occupy Wall street)
One of the reasons California has the most developed composting sector in the US is a law passed in 1989. In California plants grow profusely and in some places yards are big—at least by European standards, so homes generate a lot of yard waste and local officials figured out pretty quick that recycling yard waste was a smart way to get to that 50% mandate. In 2011, there were some amendments to the law. That included a goal of 75% statewide diversion by 2020. CalRecycle is tasked with achieving this goal. The new law said that businesses and apartments must also recycle. In many places in CA, businesses and apartment dwellers DO recycle, but not everywhere, so this law will ensure that the contributions of the commercial and multi-family sectors to the recycling rate will be going up.
This is a satellite view of a typical California compost facility. Most composting in CA is still relatively low-tech, in giant elongated piles, called windrows. This is definitely a low cost and efficient way to do things, by simply amplifying the natural processes nature has been using for millenia. Each one of these are probably 2 meters tall, 3 or 4 meters wide, and maybe 50 meters long Up at the top here you see what looks to be the processing area and I’m sure if we could zoom in closer we’d see the grinders and screens and other equipment. The reason open windrow composting is the dominant type of facility in California is cost. Land is still very cheap in the Western US. So is landfilling. In some places, you can landfill a ton of material for as little as 15 Euro. There is no requirement that organic wastes be stabilized before landfilling. So these facilities must compete with landfills for feedstocks. If they raise their tipping fees too much they may lose their raw to somebody else who will accept them for less.
Most of the compost is purchased by agriculture. California produces 20 percent of the US dairy (talk more about that later), and more than half of the country&apos;s fruits, nuts and vegetables. California produces around 90% of the grapes in the US, and the wine industry has very much embraced compost use. So, composting is important to agriculture, but farmers don’t want to pay very much for compost, the average price for finished compost is probably around 10 euro per ton. So in the US composting is a high-volume business that depends on low-cost production. The problem is that air and water quality compliance is not low cost. It turns out that paving a 20-hectare pad is really expensive, actually. Aeration systems and biofilters are expensive to build and expensive to operate. So our infrastructure will have to be modernized but right now the economics don’t support that. And now we are raising the bar in terms of our recycling goals, but it is becoming very challenging to open new organics facilities.
Everybody know what ASP means? Point out the brown arrows. This is a modern facility handling biosolids mixed with ground green and wood waste. The operators of this facility say they capture somewhere around 85% of all VOCs and 99% of all ammonia. They have two biofilters which occupy somewhere around 1 hectare of land. The facility uses about same amount of electricity per month as running 9,000 refrigerators, and these aren’t small, efficient European refrigerators, they are giant American refrigerators. So, they use a lot of power but they use less diesel than the open windrow facility, since they do not turn windrows.
This facility uses even more electricity and has a bigger biofilter because they change the air inside the building 8-12 times per hour when it is operating and there are workers inside. The biosolids economics in California are a little better than greenwaste, so that is why we see these facilities for this feedstock. You just can’t dispose of biosolids as easy or as cheaply as you can greenwaste.
This is a relatively new type of system that has a good combination of emissions control and costs. Already a few have been built in California, both for greenwaste/foodwaste and also for biosolids composting. There are several vendors of these systems, these photos are from some facilities designed and built by a company called Engineered Compost Systems, or ECS. One of the things ECS does that is a little different is that they have these inflatable sausages that they use to create an air space under the pile when it is formed. After the pile is built, the sausages are deflated and removed, leaving an air channel which is used to aerate the pile. It can then be turned with a windrow turner just like an ordinary pile. These types of systems have an added benefit of keeping rainwater off of the pile during the rainy season, they also help keep the piles from drying out too much during our long, hot summers, so they are good on air quality and also on water. Another vendor, Gore, use a totally different system, with air blowing into the pile and the micro-organisms living on the underside of the tarp consuming the organic compounds. This type of system does not need a biofilter.
Ozone high up in the stratosphere is a good thing, it protects us from harmful radiation. But ozone at ground level is bad for humans, bad for plants, bad for crops. In the US, the Clean Air Act directs local air quality management agencies to do everything possible to reduce ozone levels, and by extension, ozone precursors like VOCs. This year, two California air quality districts enacted regulations to reduce emissions from compost piles. These are the first two such regulations in the US. Any new composting facilities in these areas will be built to much higher standards, and will cost a lot more to construct, more than the economics of composting can support in the US. The people who are already composting will have to change the way they operate their business, we’ll see how in a minute.
Point out California. So where are the places in the US that have persistent ozone problems? Most of the big cities in the US have ozone issues. So, it would seem that ozone is directly linked to population and human activity. People drive, they clean and paint their houses, they cook food every day. All of the cumulative activities of a big city appear to result in ozone formation, with cars and trucks probably being the biggest factor. Ironically, the SJV– RIGHT HERE -- has a relatively low population. But it has a lot of agriculture, and two big highways running up and down its length that are loaded with trucks. And it is backed up by the Sierra Nevada, mountains going up to 4000 meters. The 8-hour standard means 0.08 parts per million (ppm) averaged over eight hours.
The first people to test compost piles for emissions in CA was the air district in the Los Angeles area, known as the AQMD. They have traditionally had the worst air in America and have been leaders many air pollution control techniques. The air in Los Angeles now is much, much better than it was 20 or 40 years ago. These numbers were converted from lbs per ton, meaning for every ton of feedstock, we could expect X pounds of pollutant. (basically x 500) So for every kilogram of feedstock, the the AQMD folks expected this many milligrams of pollutants to be emitted. CalRecycle and the AQMD did some testing at this time, trying to see if lasers and traditional measurement techniques using flux chambers, (point to it) this little device here which is barely a half meter across. There was not good correlation between these methods. We did some work on process controls and found, to no ones’ surprise, that a windrow with a lot of woody material gave off less emissions than one with a lot of grassy material. We also found that a turned windrow gave off more emissions than a static pile, but that it also matured faster.
RESULTS CalRecycle’s second study was probably the most ambitious attempt in the US to quantify the non-methane VOC emissions from open windrow composting, and to test some potential mitigation measures. More than 100 emissions samples were analyzed for this study, probably 5 times more than any of the studies before or since. We came up with a number for straight green waste of about 450 mg per kg, or about one pound of VOC emissions per ton of material. This number does not include grinding emissions, or piles of freshly tipped waste waiting for processing. We also found that a pseudo-biofilter compost cap, which I explain next, was very effective in reducing emissions. Since this study has been done, there have been other studies done privately, and private facilities, that have found much higher rates of emissions, maybe 20 or 30 times higher. So I think, the truth is, composting emissions are highly variable. Where you set down the little flux chamber really matters, because it is small and the pile is big. The emissions vary hour by hour, and a spot five feet away on the same pile could be really different.
The pseudo-biofilter compost cap is basically a layer of fully composted material on top of a new row of material. This management technique reduces emissions, and takes advantage of materials on site, such as finished product and oversized materials screened out of finished product. You are going to hear about it three more times in this presentation because it is effective in reducing emissions. How it works is that the natural convection of the pile draw air upward from the fresh materials. The microbes living in the cap consume the VOCs for food, converting those complex emissions to CO2.
In 2009 the San Joaquin Valley Air Pollution Control District contracted for its own study of mitigation measures for open windrow composting. Several methods were tried, and two were deemed to be effective The first was that irrigating piles within three hours before turning, so that the top of the pile was wet, reduced emissions by 24%. Based on this study, the district created a regulation which requires composters to measure the moisture in the top of the compost pile before turning, and to add water if it is too dry. The irrigation system does not have to look like this, but this certainly is an inexpensive way to do it. This second method proven effective, and for the second time, was the pseudo-biofilter compost cap. These caps were made of unscreened finished compost, they were re-applied every time the pile was turned for the first 3 weeks. So the APCD wrote a regulation that said really big compost facilities had to cover each new windrow with a compost cap, and keep it covered for 3 weeks.
The studies that I did with my colleague, Dr. Peter Green at the University of California, Davis, are fundamentally different than previous studies of composting process VOC emissions. In the past, everyone tried to answer the question, “How much VOCs?” As I’ve said, it varies… a lot. Dr. Green and I wanted to answer a different question; what kind of VOCs, and even more importantly, do they make ozone? Because the point of all these air quality regulations is not to protect us from VOCs, though some may be dangerous, but to reduce the build up of ground-level ozone in our air. The assumption has been, if you have VOCs, you make ozone. That’s the assumption in the Clean Air Act, too. Unfortunately, it’s not really true. Not all VOCs are created equal. A pound of isoprene makes 10 times more ozone than a pound of ethanol. A pound of acetaldehyde makes 10x more ozone than a pound of methanol. Where do compost emissions fit in?
To perform this type of study we use a portable ozone formation chamber, which we tow behind a pickup truck to different types of sites. The 1000-liter bag inside the chamber allows us to make real-time ozone measurements using a photo-acoustic gas analyzer. This provides a critical double check for our modeled ozone formation estimates, which are based on measurements of the gases captured in stainless steel canisters and in sorbent tubes. We run the samples captured in the canisters and tubes through a chromatograph to find out what kinds of gases are in the mix, then we run that information through a computer model, which predicts how much ozone will be formed. Then we compare the two. If the two numbers are in agreement, we know we have characterized all of the important compounds in the emissions mixture.
After we fill up the canisters and tubes, we fill up the 1000 liter bag, seen on the left. Then we turn on the lights, which don’t look terribly bright but do reproduce the ultraviolet portion of the light spectrum, which is the portion of sunlight which forms ozone in the atmosphere. Into the bag goes the emissions from the compost pile, and we add to that a surrogate gas specially created to mimic the existing air quality of the area on a summer day. The idea is to see not whether the compost gases will form ozone in a pristine environment, because we don’t have that. What we want to know is whether these emissions, when added to the ambient air will increase the amount of ozone formed. Each experiment takes about 3 hours.
Bottom line, not much ozone formed in the chamber, not much predicted by the model. Compounds like ethanol will form ozone, but in a diverse atmosphere, there are other compounds which are more attractive (reactive). It’s like a high school dance. These compounds are the nerds. Every once in a while they get lucky, but most of the time the NOx is going to dance with somebody else.
One of the things we see here is that the 2-3 week old pile actually has a slightly higher percentage of medium and high reactivity emissions. That’s important, but one has to also remember that the fluxes on the 2-3 week old piles are still much lower, so there’s a lot less gas even though it’s a tiny bit more potent. Introducing the term MIR here. Stands for Maximum Incremental Reactivity. European scientists use a concept called POCP, which stands for Photochemical Ozone Creation Potential. Basically it’s the same thing, though the scale is different.
In this phase of the work we focused on overs, EXPLAIN what they are. Our efforts showed that a cap of oversized, previously composted materials, first of all, was not a source of VOCs on its own, and second of all, reduced both the observed ozone formation in the chamber and the ozone predicted by the model. Using chamber observations alone, the effectiveness of the cap was 27% for the young windrow and 36% for the three week old windrow. Alcohols still dominated the total emissions, even more so this time. The fourth most prevalent VOC was acetone, which is so benign it is exempt from the Clean Air Act. In 2010 the association of folks who operate sewage treatment plants saw what we were doing, and hired the same research team to investigate the ozone formation potential of emissions from the co-composting of biosolids and woody waste. (do I need to explain biosolids??). They got very similar results.
In California we have this thing called MIR, maximum incremental reactivity. Here in Europe, you have POCP, which stands for Photochemical Ozone Creation Potential. It is basically a measure of relative reactivity; how much more likely is one compound to form ozone versus another. In this slide, we look at how composting compares to other emissions sources, including baselines such as cars and pickup trucks, not heavy duty trucks. We also have the average urban VOC mix here, and two different isomers of pinene, which is a moderately reactive VOC, about 4.5 on a scale that can go up to about 15. As you can see, the reactivity of composting emissions is quite low, and very close to cow manure. Compost and cow patties are about 1/3 as potent as the typical mix of VOCs found in urban areas. The one agricultural source which is actually fairly potent is silage, the fermented grain and vegetative matter fed to dairy cows. The team from UC Davis tested a lot of different agricultural sources in the San Joaquin Valley, and this was probably the most important revelation. The dairy farmers were not pleased to hear this, but the fact is that the emissions from dairy silage may contribute as much to air pollution in the San Joaquin Valley as automobiles, because there are something on the order of 3 million cows in the Valley, and last I heard, they like to eat every day. The good news is that this should be a win-win situation, because the same management practices which reduce emissions will preserve the value of the food.
The conference organizers asked me to include a discussion of odors. That’s a little different than VOCs, but there is some overlap. Odors are very subjective, many types of perfumes are VOCs, people say that smells good. There is a famous product in America called Pine-sol, a cleaning product, smells like pine. Do you have that here. Anyhow, millions of bottles have been sold. California manages odors at compost facilities through the use of a document called and odor impact management plan. This document outlines how you will prevent odors, and how you will respond to complaints about odors. So the process is complaint driven, and when there are continuing complaints there is no way to end the process. The inspector will say, well, you have to do more, and the facility operator will say, well, I’ve done everything listed in my plan, I have spent $X, and I can’t do any more. And so the process may not resolve itself in a way that is satisfactory to anyone involved. This year one facility operator went to the Legislature to try change the law, but that didn’t happen. So, we will see what we can do with our existing authority to make a better process. That will happen over the next year.
Aldehydes are a very potent ozone forming compound, but we didn’t find very many of them in compost emissions, and yet, a sort of sweet, pungent odor is very common around composting. Whether or not that odor bothers you is another matter. Things that smell like rotting fish or dead animals, on the other hand, will bother most people. A 2011 study which included two researchers from the autonomous university of Catalonia here in Barcelona found that Trimethylamine correlated most strongly with odors when municipal solid waste was composted. Trimethylamine smells like rotting fish. A 2001 study out of England found that hydrogen sulfide and dimethyl sulfide were most closely correlated with odors from the composting of horse and poultry manure. This study found that ammonia levels did not impact odor, but that VFAs and trimethylamine were factors. So, out of the five categories on this list, amines, sulfur compounds and VFAs are the ones that studies have shown to really be associated with bad smells.
The CCORP report grew out of an environment where composting facilities were increasingly being encroached by neighbors in fast-growing communities, and were having trouble with their new neighbors. It was an attempt to bring some science to the issue, and to find out which odor mitigation strategies might work. The best performing mitigation, again, was the compost cap. This report runs more than 100 pages and is available for free from the CalRecycle web site.
Based on the literature search performed for the CCORP study, these are some of the potential impacts of variations in the composting parameters and how they might impact emissions, but this is all situational. Some of it is intuitive; too much nitrogen or not enough carbon in the feedstock and some of it goes up into the air as ammonia or amines. And what the report points out is you need to measure AVAILABLE carbon when calculating a C:N ratio. If you are only measuring total carbon you are overestimating the amount of carbon in your pile, which will likely result in too much nitrogen, and resulting in amine odors Similarly, the relationship with temperature is not always straightforward. Certainly, high temperatures indicate healthy microbes and fast decomposition, which is good. Temperature increase up to a certain point does not correlate with more odors, because odorous intermediate products are being broken down. But at very high temperatures, say above 75 C, dimethyl disulfide or DMDS can form rapidly but cannot be degraded biologically. So, my advice if you have odor problems is to download this report for free from our website, and I will have the address in a few seconds.
I want to tell you about one more study which is underway and funded by CalRecycle. This project is part of California’s efforts to assess its greenhouse gas balances as directed under a landmark climate change bill passed in 2006. One of the early action measures was collaborative research on nitrous oxide, which is around 300x more potent than CO2. We are working with a team of researchers to determine what role composting plays in helping California manage its GHG emissions. This is part of a larger effort to establish GHG baselines for California soils under a number of agricultural production systems, a very big project and one which the agriculture industry is participating in with some trepidation. Unfortunately, I don’t have any data from this study for you today, and it’s going to be a couple of years until I do, so you’ll have to invite me back in 2014 and I will be happy to report on that!
In this study, we will not only be trying to determine the GHG emissions from composting piles of organic materials, we will also look at what happens when these materials are applied in farm fields, because one thing we know is that intensively farmed and fertilized lands are the largest man-made source of N2O in the US. So we want to know how much GHG comes from our big compost piles, but we also want to know what happens to GHG emissions when we apply compost to farm land, both alone and in combination with fertilizer applications and other techniques such as cover cropping.
This is a crop duster. I don’t know if you use them very much here. It is spraying something. The point I want to make here is that we all know that there are impacts from business as usual. We have to make tradeoffs. Compost piles do give off some odors and bad molecules. But it may be that composting can reduce other practices which contribute more to air pollution or global climate change. If using more compost results in one less farmer doing this, then it is probably worth it. Therefore, all of us need to continue working at the national and international levels to quantify and gain recognition for the benefits of compost, whether that be research into water savings through compost use, fertilizer savings, or healthier crops.
Every one of the CalRecycle studies I’ve mentioned today is available free on the internet. This is the true beauty of publicly-financed research. So please take advantage of that.
So, here is the money slide, the summary. If you can remember these points then it was worth it to you, for me to travel across the world. Because it’s going to be worth it for me no matter what! Thank you so much for listening.
That’s all, folks! If you have any questions… take them now or stop me any time during the conference. Happy to talk to anybody about this subject.
Los retos en la gestión de residuos urbanos en una economía
Els reptes en la gestió de residus urbans en una economia
Challenges in waste management in a globalized economy
ORGANIZADO POR: CON LA COLABORACIÓN DE:
VOC emissions from organics management:
Measurement, speciation and mitigation
California Dept. of Resources, Recycling & Recovery (CalRecycle)
1. Composting in California today
2. Do compost emissions lead to
harmful air pollution?
3. Composting emissions research
4. Odor issues and research
5. Climate change research
Cities and counties must divert >50% of their
solid waste away from landfills or CalRecycle
can issue fines
Composting IS recycling
NEW: CA recycling goal: 75% by 2020
NEW: Businesses with >3 cubic meters of
garbage per week must recycle
NEW: Apartment buildings with 5 or more
units must offer recycling to residents
20 hectare green waste facility near Modesto, CA
Composting in California
Most facilities compost source separated green
waste in open windrows
115 facilities / 4 million tonnes processed
Most compost sold to agriculture, but farmers do
not want to pay too much
New air- and water-quality regulations will
require facility upgrades better windrow
management and engineered systems to capture
volatile organic compounds and ammonia
Economics do not support engineered facilities
Biosolids and bulking agents
Indoor tipping and mixing areas
Negative aeration; biofilter
Synagro-Southern Kern County
85% VOC/ 99% NH3 Capture
95% VOC capture
99% NH3 capture
Biosolids and bulking agents
Converted IKEA warehouse
8-12 air changes per hour
Negative aeration; 1.2 ha biofilter
Inland Empire Utilities District - Rancho Cucamonga
Tarped, aerated systems
80%-plus VOC &
Scalable size and
or positive aeration
Do composting emissions lead
to harmful air pollution?
Compost piles emit Volatile Organic
When reactive VOCs mix with oxides of
nitrogen (NOx), in the presence of sunlight,
photochemical “smog” results
Smog includes ground-level ozone
Ozone is very harmful to human health, as
well as plants and agricultural crops
US Clean Air Act regulates ozone levels,
mandates action to cut precursors like VOCs
Ozone non-attainment areas
in the USA
8-hour ozone (1997 standard)
As of April, 2011
1996-2002 Emissions Studies
Southern California—AQMD & CalRecycle
First attempts in CA to quantify emissions
factors for composting facilities
CalRecycle helped with concurrent testing
using lasers, and studied process controls
Emissions factors in mg of pollutant per kg
VOC CH4 NH3
Biosolids 1205 8930 1525
Greenwaste 1880 435 410
AQMD data, average of two studies
2005-6 CalRecycle Study
Modesto - Northern California
70-80% of total VOCs emitted during 1st
70-85% of total VOC emissions vent through top of
“Pseudo-biofilter” compost cap reduced VOC
emissions up to 75% for first two weeks.
Additives reduced VOC emissions 42% for first
week; 14% for first two weeks
15% food waste roughly doubled VOC emissions
compared to “straight” green waste
Lifecycle VOC emissions from pure greenwaste
windrow @450 mg/kg of feedstock
Pseudo-biofilter compost cap
15 cm layer of unscreened finished
compost or overs on top of actively
Takes advantage of natural pile
Active compost pile
2009 San Joaquin APCD study
Study: Irrigation system used for 3 hours
before turning reduced emissions by 24% over
first 3 weeks
New Rule 4566: Facilities between 10,000-
200,000 tons/year must achieve 24% reduction
Study: Pseudo-biofilter compost cap reduced
emissions by 53% over first three weeks.
New Rule 4566: Facilities over 200,000 tpy
must achieve 53% emissions reduction
2009-2011 Compost Emissions
Not all VOCs are equal; focus on ozone
formation potential (OFP)
Compare modeled ozone formation to
ozone measured in portable chamber
Tested OFP of windrows, tip piles, overs
Tested impact on OFP of a pseudo-
biofilter cap made of composting overs
Proven method used at many agricultural
sites in San Joaquin Valley
Mobile Ozone Chamber
Holds 1000-liter teflon bag
Used at many ag sites
Inside the MOChA chamber:
UV light similar to summer day
More 2010-2011 results
Alcohols more than 90% of emissions
MIR of greenwaste composting
emissions mix:.9 - 1.5 - LOW
MIR of biosolids co-composting
emissions mix @1 - LOW
Overs cap effective in reducing
observed ozone formation by 27-36%
Reactivity scale (MIR)*
*Similar to POCP
VOCs and Odors
Not all VOCs are odorous and not all
composting odors are VOCs
A lot of research but still subjective when it
comes to what is offensive
Odors issues are the single biggest threat
to any composting operation
California currently looking at its
regulations to see whether there is a more
objective way to handle odor complaints
Comprehensive Compost Odor
Response Project, 2007
CalRecycle study, available on line
Literature review on odor impacts of
temperature, C:N, moisture, aeration
Laboratory test of mitigation strategies
Misting, odor neutralizers, oxygenators,
hydrogen peroxide, compost cap
Pseudo-biofilter compost cap out-
performed all commercial preparations
Too much woody
Too much grass or
Not enough oxygen?
More odors of all kinds
Composting GHG study
Funded by CalRecycle
Research conducted by Univ. Calif.
Focus on N20 and CH4
Field work 2010-2013
Final report May, 2014
Concurrent with and complementary
to other ongoing ag GHG studies
1. Measure CH4 and
N20 from composting
windrows of green
waste and food waste
2. Measure N20 and
CH4 emissions from
Increasing compost use…
…may decrease use of less sustainable methods.
Related Web Pages
My CalRecycle web page:
CalRecycle Greenwaste Compost Reactivity Study:
CASA Biosolids Co-compost Reactivity Study
CalRecycle/Modesto Compost Study
Composting: Feedstock control vs. Aeration study
Comprehensive Composting Odor Response Project
• Composting gives off VOCs
• Emissions rates are highly variable
• MIR / POCP for emissions is LOW
• Composting VOCs around 1/3 as potent as
average urban air for ozone formation
• Pseudo-biofilter compost cap effective in
reducing emissions and odors
• Greenhouse gas impacts of compost
production and use need further research