Safe sludge – The disinfection of latrine faecal sludge with ammonia naturally present in excreta (University of California, Berkeley, USA)


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Safe sludge – The disinfection of latrine faecal sludge with ammonia naturally present in excreta (University of California, Berkeley, USA)

Safe Sludge
The disinfection of latrine faecal sludge with ammonia naturally present in excreta


Name of lead organisation: Regents of the University of California at Berkeley
Primary contact at lead organization: Kara Nelson, Temitope Ogunyoku
Grantee location: Berkeley, California, USA
Developing country where the research is being tested: Nairobi, Kenya

The Project Team:

Short description of the project:
Safe Sludge is a process for disinfecting faecal sludge in latrines by converting the ammonia naturally found in urine and faeces into a powerful disinfectant with an alkaline additive that will raise the pH level. By killing pathogens immediately and turning waste into “safe sludge,” all subsequent activities required for faecal sludge management can become safer. The project proved that urea from urine and urease from faeces produce ammonia after at least 2 hours of contact. Additionally, a toilet that applies the Safe Sludge process was designed, using a two-step system. In the first step urine and faeces mix and are stored for 2 hours to produce ammonia. In the second step, the waste is collected in a 10-gallon collection bin containing a lime solution, which raises the pH of the waste to 12, converting ammonia to a disinfectant. The safe sludge can then be converted to fertilizer or fuel
Ammonia (NH3) is a powerful chemical disinfectant that previous research shown to inactivate pathogens (i.e. viruses, bacteria, protozoan cysts, and helminths eggs). NH3 can be produced from mixing urine, which contains urea, and feces, which contains the enzyme urease. Urease is a catalyst that converts (via hydrolysis) urea into NH3.

It was determined that a 4-hour contact time between the feces and urine was needed to convert urea to ammonium using the urease enzyme present in feces. Importantly, the urease enzyme was not active above ~ pH 9. As a result, the Safe Sludge disinfection process required two stages, a 4-hour contact time for urine and feces (to hydrolyze urea) followed by the addition of an alkalinizing agent, calcium hydroxide (Ca(OH)2), to produce NH3 (Figure 1).

Figure 1: The Safe Sludge two stage disinfection process. Stage 1 is the hydrolysis period of urea. Stage 2 is the lime addition to covert ammonium to ammonia. It is estimated that it would take hours to weeks to disinfect pathogenic organisms in fecal sludge.

Goal(s): The goal of this project is to disinfect excreta in latrines by converting the ammonia naturally found in urine and faeces into a powerful disinfectant by adding an alkalinizing agent to raise the pH level.

Objectives (or activities or key research components):
Treat excreta at the point of collection by harnessing ammonia from human waste, compatible with downstream treatment and resource recovery.

Research questions:
1. What is the hydrolysis rate of urea in
a. Jack bean*
b. Faeces?
* Canavalia ensiformis, which is derived from jack bean is a high grade from of urease. The objective was to determine if the urease in feces was as effective as the high-grade urease from jack beans in the hydrolysis of urea in urine.
2. What is the best alkalinizing agent (lime, ash, biochar, quick lime, lime stone)?
3. What are inactivation rates of pathogen indicator organisms using Safe Sludge Process?
4. How can the Safe Sludge Process be incorporated into toilets? Under the requirements:
a. Two-stage process: i) Detention time for hydrolysis to occur; and ii) Followed by addition of alkalinizing agent
b. No water nor electricity

1.Hydrolysis rate of urea: 4-6 individual urine samples were collected and mixed with Ca(OH)2 to obtain pH 8-12. Urease sources were either pure urine OR jack bean OR feces. Duplicate samples were analyzed for total NH3 and pH at 8 time points.
2.Testing different alkalizing agents on their conversion power of ammonium into ammonia linked to the pH-value they give
3.Urine-faeces rates of 1.3:1 and 2.6:1 were
a. Spiked with MS2 coliphage and incubated for 24 hours[/li]
b. Slurries were split in half, one portion was amended with Ca(OH)2[/li]
c. Duplicate samples were analyzed for E. coli, total coliforms, MS2 coliphage, total NH3 and pH at 6 time point

  1. Natural urease in feces is the best source; confirmation that pH 12 is stable; urease has minimal activity at pH 12, therefore a two-stage process is necessary for the hydrolysis of urea
  2. Calcium hydroxide is the most powerful alkalizing agent
  3. Safe Sludge Disinfection process inactivated pathogens at a faster rate than controls; after one day the Safe Sludge process > 3 log removal of E. coli and MS2 was achieved
  4. The pHree Loo (Pathogen Free Toilet). The pHree Loo inactivates (i.e. disinfects) pathogens in fecal sludge; part of the disinfection process is to increase the pH; pHree "Free" is a play on words. Our toilet, which incorporates the Safe Sludge Disinfection process, will be pHree of Pathogens. It is designed for a family of 5. Stage 1 is the hydrolysis of urea. Mixing and detention time is about 2 hours. In Stage 2, the NH3 production and inactivation takes place. The slurry is transferred from Stage 1 into a collection bin containing Ca(OH)2 solution.

Future work:
Field testing of Safe Sludge Approach, started in November 2nd, 2012. Partner is Sanergy in Nairobi, Kenya. The goals were 1) to determine the minimum amount of urine needed to be mixed with faeces to create the NH3 concentrations needed for disinfection and 2) to retrofit an existing Sanergy toilet (Shared urine diverting toilets) to divert a portion of the urine into the feces receptacle to see if we get comparable results.
General future goals are to apply Safe Sludge Approach that was developed during Phase 1 to:
1. Further develop the household pHfree Loo
2. Adapt pHfree Loo to shared toilets
3. Develop chemical additives to disinfect waste in existing pit latrines

Start and end date: May 1, 2011 through May 15, 2013

Grant type: Grand Challenges Explorations, Round 6 (GCE R6)

Funding for this research currently ongoing: Work on the project is continuing through student team projects in design classes at UC Berkeley. Funding has been obtained through campus to support field work in Nairobi in summer 2013, in collaboration with Sanergy.

Research or implementation partners: Sanergy in Nairobi, Kenya

Current state of affairs:
Field Testing occurred Nov - Dec 2012. The main objective of the field investigation was to determine if the Safe Sludge Disinfection process could be applied to treat waste from Sanergy's urine diverting shared toilets. One of Nelson's graduate students plans to return to the field this summer to do follow up experiments.
A team of UC Berkeley graduate students designed the second prototype of the pHree Loo this past spring semester that should simplify the disinfection process, minimize odours and make the design easy to understand and use. Currently, no further plans have been made for the prototype. Hopefully this prototype can be tested in the field in fall 2013.

Biggest successes so far:
Using a Sanergy urine diverting toilet in Kenya, the safe sludge process worked effectively in the field: inactivation rates of pathogens were even higher than under laboratory conditions

Main challenges / frustration:
The main challenge/frustration was the collection of human excreta. It took about four months to for the UC Berkeley Committee for Protection of Human Subjects to approve our sampling protocol. It was difficult to recruit volunteers to donate individual feces samples. We got more volunteers to donate urine than feces. It was assumed that volunteers were more willing to donate urine than feces because there was less of an ick factor. We offered gift certificates to participants, but it was not enough motivation for people to donate their excreta. Collection sometimes took up to 3 days to collect 300 g of feces. All experiments had to be run on a small scale because we did not get enough material. Long collection periods delayed the start of experiments.
We looked into collecting excreta from other sources (i.e. wastewater treatment plants, portable toilets, composting toilets, RV and sail boat toilets, hospital waste). The reason why we did not collect from these other sources was because the excreta was comprised in these systems (i.e. semi-treated, microbial community of feces degraded). We wanted to use the freshest source of human excreta for our experiments.

Links, further readings, etc:

Documents in the SuSanA library:

Innovations magazine article:


Kara L. Nelson
Civil and Environmental Engineering
University of California
Berkeley, CA 94720-1710, USA

Director of Graduate Education
ReNUWIt, NSF ERC on Reinventing our Nation's Urban Water Infrastructure

663 Davis Hall

faculty web page:
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  • gitum
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Re: Safe sludge – The disinfection of latrine faecal sludge with ammonia naturally present in excreta (University of California, Berkeley, USA)

Dear Kara,

Thank you for sharing your interesting project with us. I would like to ask couple of questions regarding to the pHree Loo. How does emptying applied to your system? Is there a time frame for your users to empty the bin (for stage 2) and refresh the CaOH2 solution? Also, how easy for your users to reach this solution in Nairobi?

Moreover, as a first impression I feel that pHree Loo might be used more than 4 times in 2 hours in a shared toilet. This means the excreta stays in stage 1 less than 2 hours. How does this affect the disinfection rate?


M.Sc. Gökce Iyicil
Research Assistant
Technical University of Munich
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  • Temitope
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Re: Safe sludge – The disinfection of latrine faecal sludge with ammonia naturally present in excreta (University of California, Berkeley, USA)

Hello Gokce,
My name is Temitope Ogunyoku. I am the former postdoc that worked on this project. The pHree Loo is conceptual; it is not in full operation in Nairobi. The plan was to incorporate the pHree Loo with an existing sanitation service collection model. The service collection model is already being deployed by Sanergy in Nairobi and Uniloo in Kumasi. A clean team would collect the waste every 2 to 3 days. The clean team would replace the bin (in stage 2) with a new bin containing lime solution. Users would not be responsible for collection or transportation of the waste. The pHree Loo has not been tested in the field. We tested the Safe Sludge Disinfection method with waste that was collected from Sanergy's shared latrines.

The 2 hour detention time is for the production of ammonia (i.e. via hydrolysis of urea). It was later discovered through experimentation, the ideal time for nearly complete hydrolysis of urea was 4 hours. A smaller quantity of ammonia is produced if the waste is not retained for 4 hours. Disinfection rates decrease with lower ammonia concentrations.

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Re: Safe sludge – The disinfection of latrine faecal sludge with ammonia naturally present in excreta (University of California, Berkeley, USA)

Dear Temitope:

You had any problem with odors with this unit? I think that a mix between humid feces and ammonia, can't have a good smell. We have thought about ammonia from urine for feces disinfection in the UDDTs we are developing, but the smell problem is a priority for us.
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Re: Safe sludge – The disinfection of latrine faecal sludge with ammonia naturally present in excreta (University of California, Berkeley, USA)

As mentioned in the last post, our research group did not get the opportunity to build and test a full prototype of the pHree Loo. We recognized that smell is a huge issue for this household toilet. If we had obtained additional funding, one of our objectives was to design and test sealing mechanisms so that odors would be trapped in certain compartments of the toilet. In addition, we wanted to partner up with other institutions, such as Firmenich and specifically work with Dr. Christian Starkenmann, to help research and develop a chemical additive that would mask the foul odors of the toilet.

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  • Patty
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Re: Safe sludge – The disinfection of latrine faecal sludge with ammonia naturally present in excreta (University of California, Berkeley, USA)

Dear Kara and Temitope,
It is nice to read about your interesting project; thank you very much for sharing your research. It is an interesting way to disinfect the fecal sludge that you have developed. After reading the summary of your project I have several questions and thoughts that I would like to share:
- What is the estimated cost of this design for a 5 member’s family? And the additional cost for operation and management, considering the addition of lime and the cleaning stuff? Will it be an affordable solution in the context of Nairobi or Kenya?
- As Temitope commented, the clean team collected the waste every 2 or 3 days during the pilot period. But you also point that finding volunteers was one of the main challenges of the project. Could it be possible to expand the collection interval time in order to reduce the disturbance of the daily life family? Or did you consider involving the family in the operation and maintenance, generating the feeling that they are cooperating and not only being volunteers. This could give feedback from the users of both positive and negative aspects of employing this technique.
- As you said in your last post Temitope, the smells issue have been a weakness during the test, do you have any more concrete ideas how you could control this issue?

Best Regards,
Patricia Villarrubia.
(SEI intern).
Patricia Villarrubia Gomez
Stockholm Environment Institute

Kräftriket 2B
10 691 Srockholm, Sweden
Skype: patty_villarrubia
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  • Elisabeth
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Re: Safe sludge – The disinfection of latrine faecal sludge with ammonia naturally present in excreta (University of California, Berkeley, USA)

I just saw that a journal article was recently published about this project. It is behind a pay wall (not open access).

Here are the details:

In-toilet disinfection of fresh fecal sludge with ammonia naturally present in excreta

Temitope A. Ogunyoku, Fikreselam Habebo, Kara L. Nelson
Published March 2016, 6 (1) 104-114; DOI: 10.2166/washdev.2015.233


A simple treatment method, Safe Sludge disinfection, was developed to disinfect pathogens in fresh fecal sludge using the ammonia naturally present in excreta. In the first step, urea is hydrolyzed to ammonia (NH3/NH4+). In the second step, Ca(OH)2 is added to raise the pH level such that NH3, a known disinfectant, is the dominant form of ammonia; subsequently, the waste is stored until sufficient disinfection is achieved. In a closed system at 23 °C, Safe Sludge disinfection achieved >9.3 log10 and >4.0 log10 decrease of indigenous Escherichia coli and seeded MS2 coliphage, respectively, within 10.6 hours, and 2.0 log10 inactivation of seeded Ascaris suum eggs within 2 weeks.

Disinfection of feces at high pH with no urine addition was tested for comparison, and similar inactivation levels were achieved for E. coli and MS2 bacteriophage. However, for Ascaris eggs only 0.38 log10 inactivation was achieved over 2 weeks. For control samples (feces plus urine only), no inactivation of bacteria or virus indicators was observed and inactivation of Ascaris eggs was also low (0.42 log10). To illustrate how the Safe Sludge concept could be incorporated into a waterless household toilet, a conceptual design and prototype was developed, called the pHree Loo.


P.S. I noticed that the question by Patty from 2 years ago haven't been answered yet. I will try to alert the people from the project to them, perhaps they could still answer them.
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