Arnold, CA…One of the questions we repeatedly get asked about usage of our Composting Outhouse is how long until the compost is safe. The answer? It depends, with compost bins in summer sun it can be as short as just a few days.
What do we recommend? Since the compost bins (32 Gallon Trash Cans) are inexpensive and ubiquitous. We recommend two years. Why two years? Since most guidelines and research suggest a year is safe we say double it for peace of mind and making the process brain dead simple. Swap a bin, set used bin aside and forget it. If you swap once a quarter that is only 8 bins for an entire two year cycle. Once cycle ends dump or use with confidence.
Key Points
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Research suggests human waste compost is safe as fertilizer after at least one year of proper composting, though some sources recommend a minimum of six months with high-temperature management.
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The evidence leans toward longer composting times for home use to ensure pathogen reduction, with controversy around the exact duration due to varying methods and local regulations.
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It seems likely that using the compost on non-edible plants reduces risk, and proper management, like maintaining high temperatures, can shorten the time needed.
Composting Duration
Human waste compost typically requires at least one year of proper composting to be considered safe for use as fertilizer, especially for home composting where temperature control may be inconsistent. This duration helps ensure that pathogens, such as E. coli and Salmonella, are reduced to safe levels. However, with industrial or well-managed hot composting, where temperatures reach 131°F for at least three days, some sources suggest it could be safe in as little as six months.
Safety Considerations
The safety of the compost depends on the composting method. For home use, it’s often recommended to wait a full year and use the compost on non-edible plants or bury it to minimize health risks. This is because human waste can contain viruses, bacteria, and other pathogens that may not be fully eliminated by standard home composting processes.
Unexpected Detail: Temperature’s Role
An unexpected detail is that maintaining high temperatures (around 131°F) during composting can significantly reduce the time needed, aligning with EPA guidelines for biosolids, but achieving this at home can be challenging without specialized equipment.
Survey Note: Detailed Analysis of Human Waste Composting Safety
This note provides a comprehensive overview of the time required for human waste compost to be safe for use as fertilizer, drawing from various sources to ensure a thorough understanding. The process involves balancing pathogen reduction with practical home composting methods, and the findings highlight both scientific recommendations and practical considerations.
Background and Importance
Human waste, rich in nutrients like nitrogen and phosphorus, can be a valuable fertilizer if properly composted. However, it poses significant health risks due to potential pathogens such as E. coli, Salmonella, and viruses, necessitating careful management. Composting leverages microbial activity to break down waste, with heat playing a critical role in killing pathogens. The duration required for safety varies based on composting methods, temperature control, and local regulations, making this a complex topic with ongoing debate.
Composting Process and Time Frames
The composting process typically includes an active phase, where temperatures rise due to microbial activity, followed by a curing phase for stabilization. For human waste, ensuring pathogen reduction is paramount, and the time required depends on how well the compost is managed.
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Standard Recommendations: Research from sources like Joseph Jenkins’ “The Humanure Handbook” and the Rich Earth Institute suggests that human waste should be composted for at least one year to ensure safety, particularly for home composting where temperature monitoring may be inconsistent. This aligns with findings from the University of Idaho Extension Service, which also recommends a one-year aging period.
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Shorter Durations with High Temperatures: Some sources, such as the Washington State Department of Health’s “Composting Toilets: A Guide for Users and Inspectors” (Composting Toilets Guide), indicate that with proper management, including maintaining temperatures above 130°F for at least three days, the compost could be safe in six months. This is supported by EPA guidelines for biosolids, which require 131°F for three days for Class A compost, considered pathogen-free.
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Practical Experiences: Anecdotal evidence, such as from Composting Toilets USA (Composting Human Waste Safely), suggests that with hot composting methods, compost can be ready in eight weeks in summer, but this relies on specialized bins like the Aerobin, which may not be typical for all home users.
Factors Affecting Safety
Several factors influence the time required and the safety of the compost:
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Temperature Management: High temperatures (131°F or higher) are crucial for killing pathogens quickly. Studies, such as one from the Journal of Environmental Quality on pathogen survival in compost, show that maintaining thermophilic conditions can reduce pathogen survival to weeks, but achieving uniform heat in home compost piles is challenging.
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Composting Method: Hot composting, which involves insulated bins and regular turning, can speed up the process compared to cold composting, where temperatures may not reach pathogen-killing levels, potentially requiring longer times like the three years mentioned in a Quora answer (Quora on Human Waste Fertilizer).
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Curing Phase: After the active composting phase, a curing period of several months allows remaining pathogens to die off and stabilizes the compost, with recommendations ranging from three to six months post-active phase, contributing to the total time of six months to a year.
Safety for Different Uses
The safety of the compost also depends on its intended use:
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Non-Edible Plants: Many sources, including Gardening Know How (Composting Human Waste Safety), recommend using human waste compost only on non-edible plants or burying it to minimize risk, due to the potential for pathogens to remain, especially in home composting.
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Edible Plants: Using compost on edible plants is controversial, with the WHO and other health organizations advising against it due to the risk of pathogen contamination, even after composting. This is echoed in practical guides like Composting Toilets USA, which stress the importance of testing for pathogens in large-scale facilities before use on crops.
Controversies and Variations
There is significant variation in recommended times, reflecting the complexity of the topic:
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Six Months vs. One Year: The discrepancy between six months (e.g., Washington State Department of Health) and one year (e.g., Joseph Jenkins, Rich Earth Institute) highlights a controversy. The shorter time is feasible with industrial or well-managed hot composting, while the longer time accounts for home conditions where temperature control is less precise.
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Regional Regulations: Local regulations, such as those from California’s Department of Resources Recycling and Recovery, may influence recommendations, with some areas accepting six months, while others may require longer periods or additional testing.
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Pathogen Survival Studies: Scientific studies, like one from the Journal of Applied Microbiology on pathogen survival in sewage sludge, suggest that some pathogens can survive for months, supporting longer composting times to ensure safety, especially for viruses with longer survival times.
Practical Considerations for Home Composters
For home users, achieving the ideal conditions for rapid composting can be difficult. The EPA’s general home composting guide (EPA Composting at Home) doesn’t specifically address human waste but notes composting can take two to twelve months, suggesting longer times for safety with human waste. Home composters are advised to:
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Use urine-diverting toilets to manage moisture, as seen in Mother Earth News (Composting Human Waste Article), which simplifies composting.
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Add carbon-rich materials like sawdust to balance the compost, as recommended in practical guides like Let’s Make It Clean (Safely Compost Human Waste).
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Regularly turn the pile to aerate and maintain heat, which can help reduce the time needed but still requires a curing period.
Table: Summary of Recommended Composting Times
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Source
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Recommended Minimum Time
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Conditions/Notes
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Joseph Jenkins, “The Humanure Handbook”
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1 year
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Home composting, includes curing phase, ensures safety
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Rich Earth Institute
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12 months
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General recommendation for human manure compost
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Washington State Department of Health
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6 months
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With proper temperature management (131°F for 3 days)
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Composting Toilets USA
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8 weeks (hot composting)
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Summer conditions, specialized bins, anecdotal
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University of Idaho Extension Service
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1 year
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Aging period to ensure pathogen reduction
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Quora Answer
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3 years
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Cold composting, may be overly cautious
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Conclusion
Given the variability, a conservative approach for home composting is to allow human waste to compost for at least one year, aligning with expert recommendations like Jenkins and the Rich Earth Institute. This ensures pathogen reduction, especially for non-edible plant use, and accounts for the challenges of maintaining high temperatures at home. For those with access to industrial facilities or advanced hot composting, six months may suffice, but testing for pathogens is recommended for safety, particularly for edible crops.
This detailed analysis underscores the importance of proper management and the need for further research to standardize guidelines, especially as sustainable practices like human waste composting gain traction.
Key Citations
How Long Until Compost is Safe? It Depends…3 Days to One Year! added by admin on
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