Consistent potential pathogen kill during composting – how do we achieve this?

Composting regulations in most countries include minimum temperatures required to be achieved for a certain time period. The reason for this is that we know from extensive research that most potentially pathogenic microbes are not able to withstand temperatures of greater than 55 C for very long. The goal of the regulations are that all of the material being composted reaches these temperatures.

“By mixing the composting material, turned windrow systems insure that all portions of the pile are exposed to interior conditions sufficient to kill pathogens.  In-vessel and static pile systems are often insulated to insure that exterior temperatures are sufficiently elevated.” (CIWMB 2000)

“Unless the entire composting mass is subject to the pathogen reduction temperatures, organisms may survive and repopulate the mass once the piles or windrows are cooled. Therefore it is crucial that temperatures be attained throughout the entire pile. For aerated static piles or invessel systems using static procedures such as tunnels or silos, temperature monitoring should represent points throughout the pile, including areas which typically are the coolest.” (EPA 2003)

“Aerated static pile – Aerated static piles should be covered with an insulation layer of sufficient thickness to ensure that temperatures throughout the pile, including the pile surface, reach 55° C. It is recommended that the insulation layer be at least 1 foot thick.” (EPA 2003)

German Composting Regulation for windrow composting requires: 14 days at 55 °C; 7 days at 65 ° C – 3 representative zones: edge, core and base, and for aerated static pile and in-vessel: 7 days at 60 ° C – diagrams demonstrating process requirements include insulated layer (Gilbert, undated)

There has been some excellent research on temperatures throughout the composting material by the University of Alberta Civil and Environmental Engineering Department on covered aerated composting windrows in 2014 (Isobaev 2014)

  1. “During composting in CASP [covered aerated static pile] with single turning, the likelihood of every particle’s compliance to TTC [time temperature criteria] typically achieves 76 to 93% compliance.
  2. Pile turning is a significant step towards assuring the particle’s compliance with TTC.
  3. The CASP surface, if not insulated, remains in the mesophilic temperature range (≤45°C) up to 50 cm depth and provides a good environment for microbial proliferation. After a single turning with the front-end loader, 40% of the particles in the cool zones still remain mesophilic. It is recommended that: 1) the insulating layer up to 50 cm in thickness be used to cover the pile and ensure that the traditionally cool zones reach thermophilic temperatures; and 2) the cool zones be adequately handled during the mixing step to ensure that what was in the cool zone gets into the pile core after mixing.”

The recommendations for composting practitioners and regulatory authorities in this thesis included:

“several pile turnings don’t ensure 100% compliance with TTC. Each additional turning increases the chances of every particle to meet the required TTC. However, after 6th turn the probability of compliance increases to 98%; thereafter the impact of turning becomes negligible and practically unattractive. Furthermore, the effect of turning is significantly profound during active composting stage. Since, on average, the CASP requires more than three days for its temperature to reach 55°C we recommend not to turn the pile until seven days have passed from its construction, and every three days thereafter.”

We can conclude from evidence and research that piles must be insulated, or turned in order for all the particles to reach the composting temperatures of 55 C or higher. As we investigate further, we learn that the microbiology during composting and curing is complex. How the material is managed during the curing process has a significant impact in ensuring that the final composted product contains no potential pathogenic organisms.


California Integrated Waste Management Board (CIWMB) 2000. Composting Reduces Growers’ Concerns About Pathogens. Publication #442-00-014.

Gilbert, undated. Monitoring sanitisation in practice at composting sites. The Composting Association.

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.

US EPA. 1992. Environmental Regulations and Technology Control of Pathogens and Vector Attraction in Sewage Sludge (Including Domestic Septage) Under 40 CFR Part 503  EPA/625/R-92/013 Revised 2003.



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Indicator Organisms for Potential Pathogens: Fecal coliform or E. coli?

How do we know that our compost is free of potential pathogenic organisms? The test that we use in our British Columbia regulation (OMRR) is fecal coliform bacteria, as an indicator organism. This is in part based on the US EPA Biosolids Rule 503, which suggests that fecal coliform is a good indicator organism:

“Fecal coliforms are enteric bacteria that are used as indicators of the likelihood of the presence of bacterial pathogens. Although fecal coliforms themselves are usually not harmful to humans, their presence indicates the presence of fecal waste which may contain pathogens. These bacteria are commonly used as indicators of the potential presence of pathogens in sewage sludges. They are abundant in human feces and therefore are always present in untreated sewage sludges. They are easily and inexpensively measured, and their densities decline in about the same proportion as enteric bacterial pathogens when exposed to the adverse conditions of sludge processing.” (EPA 2003).

More recent Compost Regulations use E.coli as the indicator organism rather than fecal coliform, because of concerns with bacteria of non-fecal origin are included in the fecal coliform test.

“The microbiology literature is replete with reports of studies that correlate results of fecal coliform levels with the presence of E. coli including several recent examples that advocate the fecal coliform test as an acceptable indicator in manure composts and foods. However, the value of the fecal coliform assay as an indicator of fecal contamination is negated when bacteria of nonfecal origin are the principal microbes detected by the assay.” (Doyle and Erickson 2006).

Brinton et al. (2009) observed an excellent correlation between E.coli and fecal coliform in a composts produced in Oregon and California. More recent regulations (Ontario Ministry of the Environment 2012) and the UK PAS 100:2011 (BSI 2011) use E.coli as the indicator organism for fecal contamination. Gilbert (undated) reported that measuring E.coli “is useful to demonstrate a stable product without feacal bacteria” and measuring feacal coliforms “may be problematic due to variable species composition”.

In Scandinavia, recommendations for testing included both fecal coliform and E. coli:

“Most of the experts suggested that thermotolerant coliform bacteria [fecal coliform] or E. coli should be included in both direct process evaluation and the end-product analysis. These organisms were proposed because they have a heat resistance very similar to Salmonella and because of the increasing interest for E. coli as a pathogen in the environment.” (Nordic Council of Ministers 2000).

The discussion with indicator organisms has been occurring with water for a longer time. The World Health Organization (2001) has an excellent review of the indicators of water quality, and suggested that E.coli is a more specific indicator organism:

“Many members of the total coliform group and some so-called faecal coliforms (e.g. species of Klebsiella and Enterobactero) are not specific to faeces, and even E.coli has been shown to grow in some natural environments. Hence, the primary targets representing faecal contamination in temperate waters are now considered to be E. coli and enterococci.”

The BC Approved Water Quality Guidelines also discusses the limitations of measuring only fecal coliform:

“Fecal coliforms have historically been the indicator of choice, but their presence does not always correlate well with the incidence of disease. Coliforms are therefore now being supplanted by more specific indicators. These include Escherichia coli and enterococci which are good indicators of gastrointestinal disease, and Pseudomonas aeruginosa which correlates well with ear and skin infections. Criteria are set in this report for these three other indicators as well as for fecal coliforms. Although the fecal coliform criteria are the only ones that apply now, they will be phased out in the future as the change to other organisms occurs.”

We suggest that in BC, we measure fecal coliform as required by the current regulation, but also measure E.coli as a more specific indicator of potential pathogenic organisms.


BC Ministry of Environment. 2001. Approved Water Quality Guidelines Microbiological Indicators 2001 (

BC Ministry of Environment. 2002. Organic Matter Recycling Regulation.

Brinton JR., W.F., 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.

BSI. 2011. PAS 100:2011. Specification for Composted Materials.

Doyle, M.P. and M.C. Erickson. 2006. The fecal coliform assay, the results of which have led to numerous misinterpretations over the years, and may have outlived its usefulness. Microbe April 2006 (

Gilbert, undated. Monitoring sanitisation in practice at composting sites. The Composting Association.

Nordic Council of Ministers. 2000. Sanitary Aspects of Composting Biodegradable Waste. Towards a Nordic Evaluation Model. Copenhagen 2000

Ontario Ministry of Environment. 2012. Compost Quality Standards.

US EPA. Control of Pathogens and Vector Attraction Reduction in Sewage Sludge. Environmental Regulations and Technology. EPA/625/R-92/013 . Revised July 2003. (

WHO. 2001. Indicators of Water Quality. Chapter 13. In L. Fewtrell and J. Bartram, eds. Water Quality: Guidelines, Standards and Health. IWA Publishing, London, UK.

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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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