Managing Potential Pathogenic Bacteria in Our Composts

Managing potential human, plant and animal pathogens during composting is important to reduce the risk of spreading disease. It is now even more important with the increasing concern regarding antibiotic resistant microorganisms (WHO 2016) and the role of the microbes in our environment (Fletcher 2015). The World Health Organization published a list of bacteria for which new antibiotics are urgently needed (WHO 2017). Many of these bacteria may be present in the organic material that we are composting,  which means we must be diligent in managing potential pathogens, but also potential pathogens that may be antibiotic resistant.

A recent report linked the use of antibiotic resistance in animals with antibiotics in humans, and confirms that we need to be diligent with our waste management as well (ECDC/EFSA/EMA 2017):

“Vytenis Andriukaitis, European Commissioner for Health and Food Safety says: “To contain antibiotic resistance we need to fight on three fronts at the same time: human, animal and the environment. This is exactly what we are trying to achieve in the EU and globally with our recently launched EU Action Plan on antimicrobial resistance. This new report confirms the link between antibiotic consumption and antibiotic resistance in both humans and food-producing animals.” (

Many of us understand that there is a time temperature relationship for potential pathogen kill, where maintaining temperatures greater than 55-60 C in our composting material for a number of days will kill potential pathogenic organisms. Most fecal coliforms or potentially pathogenic organisms in our compost may not actually be pathogenic, however, we are not always able to easily distinguish them. Some of us are surprised and bewildered when, in spite of our best efforts at maintaining temperatures required for potential pathogen kill, the fecal coliform bacteria in our curing or finished compost are still high!

We are not alone. There have been some excellent research reviews on the survival of potentially pathogenic organisms in our compost. Jones and Martin (2003) observed that bacteria such as E. coli and Salmonella “may grow in the final compost if the process has been inefficient and the organic matter remains poorly stabilized.” Wichuk and McCartney (2007) reviewed the literature on time – temperature relationships for pathogen kill during composting and concluded that regrowth does occur. Brinton et al. (2009) found that 33% of 94 marketed composts in the US contained E. coli. 41. Isobaev (2014) provided an excellent literature review and research on potential pathogen survival during composting.

In our compost facility operator training courses, we have stressed that inactivation of potential pathogens during composting is a two step process. The first step is to ensure that all of the material being composted reaches temperatures required for potential pathogen kill. The second step is to allow the composting process to degrade the readily available carbon compounds on which the potential pathogenic feed. When we consider the science and what actually happens at compost facilities, it may not even be as simple as this!

In the next few blogs, we will review the following topics as they relate to managing potential pathogenic bacteria, including:

  1. Fecal coliform and E. coli as indicator organisms
  2. ensuring that all of the composting material reaches temperatures required for potential pathogen kill
  3. potential regrowth and the role of viable but not culturable microorganisms
  4. MPN and CFU, are they the same thing?
  5. Conditions during curing which may feed E.coli and other potentially pathogenic microorganisms.

Our goal is to be as diligent as we can in reducing the potential spread of potentially pathogenic microorganisms, particularly of antibiotic resistant microbes.


Brinton, W.F. Jr., P. Storms and T.C. Blewett. 2009. Occurrence and Levels of Fecal Indicators and Pathogenic Bacteria in Market-Ready Recycled Organic Matter Composts. Journal of Food Protection 72: 332–339.

ECDC (European Centre for Disease Prevention and Control), EFSA (European Food Safety Authority), and EMA (European Medicines Agency). 2017. ECDC/EFSA/EMA second joint report on the integrated analysis of the consumption of antimicrobial agents and occurrence of antimicrobial resistance in bacteria from humans and food-producing animals – Joint Interagency Antimicrobial Consumption and Resistance Analysis (JIACRA) Report. EFSA Journal 2017: 15 (7) 4872. 135 pp. doi: 10.2903/j.efsa.2017.4872

Fletcher, S. 2015. Understanding the contribution of environmental factors in the spread of antimicrobial resistance. Environ Health Prev Med 20:243–252 DOI 10.1007/s12199-015-0468-0.

Isobaev. P. 2014. Developing and Testing a Framework to Measure the Sanitation Efficacy on a Random Particle Level in the Composting Industry. PhD Thesis. Department of Civil and Environmental Engineering, University of Alberta.

Jones, P. and M. Martin. 2003. A review of the literature on the occurrence and survival of pathogens of animals and humans in green compost.  Waste and Resources Action Programme.

WHO 2016. Antibiotic resistance. Factsheet October 2016. World Health Organization

WHO 2017. WHO publishes list of bacteria for which new antibiotics are urgently needed. February 27, 2017. World Health Organization.

Wickuk, K.M and D.M. McCartney. 2007. A review of the effectiveness of current time-temperature regulations on pathogen inactivation during composting. J. Environ. Eng. Sci. 6: 573-586

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Reflections on 2016

“If we can’t recycle our organic waste in a socially acceptable manner, we should keep putting it into the landfill” was a line that we used in 2006 when we started a food waste separation and composting pilot program for our Fraser Valley Regional District. Odor was one of the largest concerns then, just as it was even more so in British Columbia in 2016. Water quality was also a concern in 2006, but is more of a concern now with the World Health Organization and the FAO communicating clearly how our environmental management impacts increasing concerns regarding antibiotic resistance.

I used the same line this year, during our Compost Facility Operator training.  Recycling our organic waste in a socially acceptable manner is bigger than odour and water quality. Its bigger than simple diversion from landfill. The organic matter and nutrients have to be recycled back into agriculture. The health of our soil and our world depends on this. Phosphorus is one element that receives increased attention, because it is a limited resource, and we need to optimize our phosphorus use, including recycling of food waste and biosolids.

Biosolids also need to be managed in a socially acceptable manner, as we have seen from the increased attention in the last two years in British Columbia. There is excellent world wide research on the concerns with pharmaceuticals and personal care products, and an increasing conclusion that composting is an important step in reducing many of these compounds present in biosolids.  Conclusions from a 2016 conference on pharmaceuticals in sewage sludge in Europe included the importance of recycling biosolids into agriculture, and that public exposure to contaminants must remain in context of exposure from other routes including direct exposure, dust, water etc. We need to keep asking the questions.

In 2016, Transform enjoyed developing best management practices for composting animal mortalities. We realized once again how amazing the compost process is, and how well it can decompose animals in a sustainable manner. We heard stories of how grizzly bears can dig 10 ft down into the soil to recover a buried animal, yet will not touch one that is being properly composted above ground! We learned how an insulated bin can be adapted for composting for smaller communities as well as for mortality composting.

We look forward to what 2017 brings, and we hope that we can continue to be a meaningful contributor to the flourishing of our communities, through recycling our organic wastes to increase the health of our soils.

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Corrosion in compost facilities resulting from high pH

Is corrosion in compost facilities due to high or low pH? Its an important question if we are considering appropriate coatings for metals.

Corrosion at compost facilities can rapidly affect the integrity of roof structures if the metal is not adequately protected.

Corrosion at compost facilities can rapidly affect the integrity of roof structures if the metal is not adequately protected.

Corrosion in compost facilities is common, and has been addressed in a number of excellent publications more than 10 years ago (for example:,

Volatile compounds produced at compost facilities can also be highly corrosive, such as reduced sulphur compounds and ammonia. Research has not been entirely clear on what specifically causes the corrosion, whether its high or low pH. A 2009 study in Alberta indicated that low pH composting environments were more corrosive than high pH environments (,%20U%20Alberta,%20Quantifying%20Metal%20Contaminants.pdf)

We were recently put to the test. Was the corrosion in the metal near the ceiling already after one year of operation due to high or low pH? In composting environments where ammonia is emitted, theory suggests that it may be a high pH environment associated with high moisture and ammonia that may cause the corrosion. Physics and chemistry tell us the following:

  1. Ammonia is lighter than air and moves upward
  2. Warm, moist air moves upward
  3. Most reduced sulphur compounds are heavier than air and will tend to move downward
  4. Ammonia concentrations of 50 ppm in air will result in a condensate pH of just over 10.

Does air quality testing confirm this? We tested this using a simple apparatus for capturing condensate using a bucket and two ice packs as per below:


Depending on the environment, it takes about 2 hours to collect the condensate. We measured ammonia concentration, relative humidity and temperature in the air. In our particular study,  where the ammonia concentration was up to 50 ppm and the relative humidity 100%, the pH of the condensate was 9.5 to 10.

High pH in condensate at the ceiling of compost facilities increases potential corrosion.

High pH in condensate at the ceiling of compost facilities increases potential corrosion.

We concluded that corrosion near the ceilings of compost facilities are most likely due to high pH resulting from high ammonia in the warm moist air that rises to the ceilings. This information cannot necessarily be extrapolated to metals within the composting environment where other compounds such as reduced sulphur compounds may also exhibit a strong corrosive effect. We have seen how a low pH environment in food waste compost facilities results in rapid corrosion of metal.

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Small Insulated Bin Composter as a Teaching/Learning Tool

If you are developing a composting program in your community, you may have the following questions:

How do I develop and prove a composting recipe that without a lot of cost or effort?

How do I take these principles that I see on a small scale and apply them to a larger facility?

How do I understand and evaluate various technology options?

If you teach composting, or are learning about composting, you may have the following question:

How can we teach/learn the principles of composting in a hands-on and meaningful way?

Seeing large scale systems in operation or hiring experts to design a process for us help develop our composting programs, however, we have a new simple tool available that demonstrates the principles of composting that we can apply to the specific material that we are composting!

A small insulated bin composter modified for aeration is a great teaching/learning tool.

A small insulated bin composter modified for aeration is a great teaching/learning tool.

The small insulated bin composter was originally developed to teach/demonstrate the principles of composting animal mortalities with the British Columbia Ministry of Agriculture. It was used as a teaching tool in a recent Compost Facility Operator Course. It is now used to develop recipes for composting unique organic materials in a cost effective manner.

The insulated box or container is adapted with aeration holes and a mesh floor to facilitate airflow through the composting material. The process is enclosed so that inputs and outputs can be easily measured.

Based on our recipe created at the last Compost Facility Operator Course, the temperature and oxygen profile of a blend of 35% food waste and 65% yard waste can easily be measured and evaluated.

temperature-and-oxygen-graphWe can demonstrate how warm and cold air affect the composting process, and how moisture moves. In the example with food waste and yardwaste, the moisture content at the bottom of the bin was 45% after one week with a composting recipe that was 64%. The overall moisture content decreased from 64% to 44% in a two week composting process with one mix after one week.

As a demonstration unit or for piloting a process with a new product or in a community, use of the small insulated bin can assist with answering question such as:

  1. Does my combination of materials (recipe) meet the parameter requirements for optimal composting?
  2. Can I make changes to this recipe to make it more efficient?
  3. What is the odour impact of my recipe?
  4. What happens to the moisture in my composting material?
  5. How often should I be turning the compost?
  6. What is the impact of natural or active aeration on the composting process?
  7. What is the impact of natural or active aeration on the pH of the composting material?
  8. How does lower pH in my compost affect odour?
  9. How long do I need to keep composting my material to reduce the risk of odour and achieve potential pathogen kil?
  10. Are there products that we can add to the composting recipe to make the process more efficient, or more environmentally sustainable.
  11. Does recycling some of the screenings speed up the composting process?

These questions can be easily answered using the small insulated composting bin in combination with a temperature and oxygen probe, a scale for measuring the compost inputs and outputs, a pH meter for measuring pH, an EC meter for measuring electrical conductivity of the compost, and a postal scale and toaster oven for measuring moisture content.

dsc04133As a teaching tool for compost facility operators, use of the small insulated bin can assist with teaching important concepts of the compost process including the following:

  1. The importance of moisture content, bulk density and air-filled porosity on the composting process.
  2. The importance of air supply and oxygen for the composting process
  3. How air and moisture moves through the composting material
  4. Demonstrating use of temperature and oxygen probes
  5. Importance of a consistent and thorough blend of materials

We would love to help you succeed in your composting program, or in your teaching of the composting process. The small insulated bin composter is another tool, along with others, such as the Compost Facility Operator Manual, which we first published in 2007.




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Composting and Soil Management in a Regenerative Economy

Recycling organic waste to improve our soils is an integral part of a circular economy, and can even be described as contributing to a regenerative and restorative economy (Webster 2015). In 2015, we celebrated the International Year of Soils. We made commitments to our environment at the Paris Climate Change conference.  Now in 2016, the economy appears dismal. Who really cares about the soil or the environment if our economy is poor?

A Circular Economy can both improve our environment as well as grow our economy. Europe has been encouraging a Circular Economy, to “boost global competitiveness, foster sustainable economic growth and generate new jobs” (EU 2015). In Europe, moving to a Circular Economy would save costs, create jobs and innovate, as well as improve our environment (Ellen MacArther Foundation 2015). They predicted that by 2030, CO2 emissions could be reduced by 48%, pesticides and agricultural water use, fuels and non-renewable electricity by 32%. They further suggest that if Europe chose to take a circular economy approach to food systems, synthetic fertilizer use could decrease by up to 80%.

“The circular economy, by moving much more biological material through the anaerobic digestion or composting process and back into the soil, will reduce the need for replenishment with additional nutrients.” (Ellen MacArthur Foundation 2015).

This is how recycling organic material through composting is important.  We have to move from our linear thinking of food being produced in agricultural areas, moving to urban areas, and the resulting waste piling up – whether it is landfilled or “recycled”. We are encouraged to begin with the end in mind – how do we restore and improve the soils that produce our food, so that we can benefit the economy of our rural communities as well as the amount and quality of our food?

In a recent Bio-Nutrient Circular Economy Conference,  Thornton (2015) discussed the resource consumption and food security benefits, the synergies with environmental sustainability, innovation and distributed employment benefits from moving to a bionutrient Circular Economy.  Siebert (2015) of the European Compost Network, discussed the importance of recycling carbon, nitrogen and phosphorus from our organic waste, and the importance of our soil organic matter. Webster (2015) stated:

“cattle grazing lush ranch land gives some clue to what a restorative biological cycle means: in this case better water retention as carbon levels are built up in vegetation and soil systems, leading to more resilience during drought periods; better output in terms of cattle per hectare; less erosion and greater biodiversity. Better flood control is a by-product for land downstream. All these benefits really need to be accounted for, but most are not.”

In the year ahead, I am excited to see how we can implement Circular Economy principles in our organic waste management to benefit our economy and our environment. The News reminds us that we need to do this in ways that protects our air and our water. Many of us are already doing some of this good work, work that contributes to healthy and sustainable communities.

One example of how composting fits into a circular economy can be found at: Its a video called “Soil Organic Matter Offering Hope for Climate Change”


Ellen MacArthur Foundation 2015. Towards a Circular Economy: Business Rational for an Accelerated Transition.

EU 2015. European Union – Environment.

Siebert, S. 2015. Policies and tools for the bio-nutrient circular economy: Carbon, Nutrients and Soils. European Sustainable Phosphorous Platform Conference Dec 2015.

Thornton, C. 2015. Policies and tools for the bio-nutrient circular economy. European Sustainable Phosphorous Platform Conference Dec 2015.

Webster, K. 2015. Exclusive preview from “The Circular Economy: A Wealth of Flows”

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Can We Compost Invasive Weeds?

Should we bring our invasive (or noxious) weeds to our local compost facility? What does the science and current regulations tell us about whether noxious weeds can be composted? Many have asked this question in the last few years as there is more concern regarding the spread of noxious weeds. Evidence suggests that most invasive weed species,  including seeds, rhizomes and other plant parts can be successfully composted at temperatures at or above 55 C. We recommend that our regulations, particularly for yard waste composting, should reflect this so that we can potentially control invasive weeds via composting.

In British Columbia, composting facilities processing yard waste only, do not require high enough temperatures to reduce potential weeds or plant pathogens. The emphasis of the Organic Matter Recycling Regulation appeared to address primarily potential human pathogens, rather than plant pathogens and weeds.

The British Compost Specifications, PAS100-2011 (BSI 2011) addresses the potential adverse effects on plant health due to plant pests, pathogens or toxins, as well as the introduction of or increase in weeds seeds or propagules  resulting from the use of compost. To reduce the risk of plant pathogens, weed seeds or propagules, the entire mass of composting material must be composted for a minimum of 7 days at a temperature of 65 C or higher. There are specific testing requirements for the finished compost where the tolerance for weed seeds or propagules is zero.

The PAS 100-2011 compost specifications was in part based on the results of bench and commercial scale testing of 60 plant pathogens or nematodes (Noble et al. 2004). It appears that the PAS 100-2011 allows composting of all noxious weeds except the Japanese Knotweed. The Organics Recycling Group (2013) reports that the UK PAS 100-2011 compost specifications does not allow Japanese Knotweed to be composted.

The Soil Association (2003) stated that destruction of most weed propagules occurs when composting temperatures reach 55-75C. They also reported that under controlled composting conditions,  Japanese Knotweed rhizome (crown and runners) did not regenerate if exposed to temperatures of 55 C or greater for one week or more (see also Xian et al., undated).  Day et al. (2009) reported that composting for more than 3 days at temperatures greater than 55 C effectively killed growth of roots and crowns of Japanese knotweed.

In order to kill weed seeds, Wiese et al. (1998) reported that all of the six common weed species that they studied were killed in a 3 day composting process at temperatures of 72 C, whereas field bindweed required 12 days. During windrow composting of beef cattle feedlot manure, Larney and Blackshaw (2003) reported that more than 70 days of composting was required to kill seeds of the five weeds tested, and that temperature variation in the windrow may have been a significant factor in longer composting times required.

Washington State suggests that some city composting facilities may be hot enough to effectively kill noxious weeds, but that home composting is ineffective (Noxious Weed Control Board 2011).

In summary, it appears that an adequate composting process (all of the material being composted at temperatures greater than 55 C for a minimum of 7 days) will be suitable to control invasive or noxious weeds. It is also a more sustainable management strategy than burning or burying.  For composting facilities in British Columbia that are meeting the OMRR requirements for yard waste only (lower temperature requirements), the temperatures may not be high enough to kill potentially invasive weeds.

We recommend that the Organic Matter Recycling Regulation be updated to require all organic material be composted at temperatures greater than 55 C to ensure destruction of noxious weeds, weed seeds and plant pathogens. Another option is that local governments can require more stringent and controlled composting requirement for yard waste to ensure that the composting process meets the higher temperatures consistently for all the material being composted. A germination test of the finished compost will also assist in ensuring adequate weed destruction such as required in the UK PAS 100 specifications.


BSI 2011. PAS100:2011 Specification for Composted Materials. British Standards Institute, January 2011.

Composting Association. 2003. Information Sheet 15. Composting Noxious Weeds.

Day, L., J. Rall, S. McIntyre and C. Terrance. 2009. Japanese knotweed composting feasibility study, Delaware County, NY.

Larney, F.J. and R. E. Blackshaw. 2003. Weed seed viability in composted beef cattle feedlot manure. Journal of Environmental Quality 32: 1105-1113.

Noble, R., P.W. Jones, E. Coventry, S.R. Roberts, M. Martin and C. Alabouvette. 2004. Investigation of the Effect of the Composting Process on Particular Plant, Animal and Human Pathogens known to be of Concern for High Quality End-Uses. Warwick HRI (Wellesbourne), BBSRC Institute for Animal Health (Compton) and UMR INRA-Université de Bourgogne (France). Published by the Waste & Resources Action Programme, Banbury, December 2004, ISBN 1-84405-141-2.

Noxious Weed Control Board. 2011. Noxious weed disposal – what to do with noxious weeds. Washington State Noxious Weed Control Board pamphlet.

Organics Recycling Group. 2013. Composting Noxious Weeds Information Sheet. Issued February 20, 2013 Issue 1, Revision 1.

Wiese, A.F., J.M. Sweeten, B.W. Bean, C.D. Salisbury and E.W. Chenault. 1998. High temperature composting of cattle feedlot manure kills weed seed. Applied Engineering in Agriculture, 14: 377-380.

Xian, C., P. Bardos, S. Robinson. undated. Can composting kill Japanese Knotweed.

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