Effective sewage sanitation with low CO2 footprint (Duke University in Durham, North Carolina, USA)
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TOPIC: Effective sewage sanitation with low CO2 footprint (Duke University in Durham, North Carolina, USA)

Effective sewage sanitation with low CO2 footprint (Duke University in Durham, North Carolina, USA) 25 Jul 2012 12:12 #2952

  • JoanColon
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Title of grant: Effective Sewage Sanitation with Low CO2 Footprint

Researchers: Marc Deshusses, Joan Colon and Aaron Forbis-Stokes

Name of lead organisation: Duke University
Grantee location: Durham, North Carolina, USA
Primary contact at lead organisation: Aaron Forbis-Stokes
Developing country where the research is being tested: Kenya (Eldoret)


Goal: Provide proof of concept of anaerobic digestion coupled with heat sterilization for a self-sanitizing system for developing communities

Short description:
The overall objective of our project is to develop and demonstrate the proof of concept a novel self-contained and energy neutral sanitation technology that relies on anaerobic digestion of the wastes to generate biogas and utilization of the biogas thus produced to heat-sterilize the treated effluent. The system utilizes simple and reliable equipment so that it does not require a skilled operator or any special maintenance regime.

Flowsheet and concept of the novel sanitation technology (not to scale):
graph_system.jpg


The advantages of the proposed technology are:
  • Simple low-cost process/equipment, suited for deployment in developing countries
  • Effective sanitation of wastes in one single stage without sludge formation
  • Self-contained, energy neutral system
  • Eliminates methane emissions, a potent greenhouse gas while providing sanitation
  • No electricity or additional energy is required
  • No water is required during daily operation

Activities and objectives
The project has been divided in two main parts:
a) The anaerobic reactor (lab scale): design and performance
b) The heat sterilization system (full-scale or near full-scale): design, construction and proof of concept to heat-sterilize the treated sewage effluent

The main goal of the lab anaerobic reactor is to prove the suitability of a mixture of feces and urine to serve as a substrate for the anaerobic process focused mainly in the yield and rate of biogas production. The concern is mainly to achieve usual biogas yields and obtain suitable rates of biogas production.

Regarding the heat sterilization system, the challenge is to design a simple and low-cost system with virtually no moving parts, that can effectively deployed, e.g., as a replacement of pit latrines.

Start and end date: 1 Nov 2011 to 30 April 2013
Grant type: Grand Challenges Explorations Round 7
Funding for this research currently ongoing: yes
Research or implementation partners: Chepkoilel University, Eldoret, Kenya

Video of presentation by Marc Deshusses at the Fecal Sludge Management Conference in Durban 2012:



Further readings from the Fecal Sludge Management Conference in Durban 2012:
Presentation: www.susana.org/images/documents/07-cap-d...e-university-usa.pdf
Paper: www.susana.org/docs_ccbk/susana_download/2-1624-deshusses.pdf

***



Information from July 2012

The purpose of this report is to show the concept and the design of the prototypes of the anaerobic reactor and the heat sterilization system together with some preliminary results.
The picture below shows our prototype anaerobic digester and heat sterilization and recovery systems:
Untitled1.png


A semi-continuous floating dome digester with a working volume of 17 liters is used for the anaerobic digestion of simulant feces and urine (see our earlier report on the recipe and suitability of feces and urine simulants). The bioreactor is currently working with an organic loading rate of 1.8 gCOD/(lreactor day) with a maximum biogas production of 14 l/d and a total removal efficiency close to 85 % of the inlet COD. The biogas produced contains a methane concentration of about 65 %. For indication, the system is roughly 1:30 scale, and thus a full-scale digester for an extended family of 10 would have roughly a volume of 0,55 m3, and would produce about 400-450 l of biogas per day. Our experiments are currently determining how much of that biogas is required for the sterilization of the effluent.

Biogas (or a mimic of methane and CO2 in some experiments) is then used to maintain the effluent heater above 70 °C. In order to increase the total efficiency of the heat sterilization system a simple countercurrent heat exchanger is incorporated for heat recovery. It is well known that a short exposure to temperatures ranging from 55-75 °C provides several log reductions of bacteria, virus, and helminth ova. The next step of the project is to carry out different pathogen inactivation analysis to demonstrate and quantify the efficiency of the heat sterilization system.
Last Edit: 26 Jun 2013 14:04 by muench.

Re: Effective Sewage Sanitation with Low CO2 Footprint (Duke University in Durham, North Carolina, USA) 25 Mar 2013 18:40 #3993

  • aforbisstokes
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Dear all
My name is Aaron Forbis-Stokes, and I am working with the team of the "Effective Sewage Sanitation with Low CO2 Footprint" grant at the Duke University.
It is now almost one year since our last update on our project (find a presentation of the project above)
Before this project moves to a field demonstration phase, I would like to give you a short overview on the current status.

Results of part I (anaerobic digester):

  • Overall, the data demonstrate that efficient anaerobic digestion can be obtained using undiluted human excreta as a feedstock. A well-adapted bacterial inoculum can effectively convert wastes to biogas (about 350-400 liters of biogas per day in a full-scale digester for an extended family of 10 persons) even in the presence of high ammonia and volatile fatty acids concentrations.
  • A COD balance can be used to estimate the amount of biomass formed. The results indicate an average total COD (chemical oxygen demand) removal in the range of 80 to 85%. More research, in particular with actual faeces and urine, is needed to refine this number and understand the true rate of biomass accumulation under actual field conditions.

Results of part II (heat sterilization system):
  • A low-cost system that uses the biogas produced during the anaerobic process to heat-sterilize the treated sewage effluent with an efficient heat recovery was designed and tested. The heat-sterilization system comprises a heater and a countercurrent heat exchanger for a heat recovery. Both are constructed using common and cheap materials (paint/food can, steel sheet, simple tubing).
  • The countercurrent heat exchanger is capable to recover energy from the stream leaving the heater and heat the digester effluent reaching energy savings close to 800 kJ/d, reducing the biogas consumption by 15-20 %.
  • A biogas flow rate of 230 – 280 L/d is enough to maintain the heat-sterilization system between 65 and 75 °C with a normal loading. This is an estimated 60-70 % of the total biogas produced in the anaerobic reactor, thus leaving surplus gas (~150 L/d) for other uses.
  • To demonstrate the efficiency of the heat-sterilization system to inactivate pathogens, two tests were conducted using Escherichia coli as an indicator organism. The results show a complete elimination of E. coli at both temperatures (65 and 75 °C) in the effluent of the heater.

Ongoing research:
Research is underway to optimize biogas production, and improve the design and thermal efficiency of the heat sterilization system. Further, pathogen disinfection experiments with virus and helminth ova are being considered. Demonstration of the efficacy of the system as a replacement for pit latrines in the field is warranted.

Main challenges / frustration:
Field test under actual conditions needs to be done yet.
Aaron Forbis-Stokes
Duke University - Graduate Student
Environmental Engineering
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Last Edit: 10 Apr 2013 15:19 by aforbisstokes.

Reply: Effective Sewage Sanitation with Low CO2 Footprint (Duke University in Durham, North Carolina, USA) 27 Mar 2013 05:04 #4005

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Dear Sir First thanks for good news.I'm professor of Mongolian University of Science and technology, working and focusing development low cost sanitation in rural Mongolia, I would like share your experience and knowledge in Mongolian case.

rgs,

Prof.Basandorj

Re: Effective Sewage Sanitation with Low CO2 Footprint (Duke University in Durham, North Carolina, USA) 09 Apr 2013 15:37 #4091

  • dorothee.spuhler
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Dear Aaron

Many thanks for the update on your project and the additional picture.

I have one burning question: You’re idea seems obvious – use the biogas from the sludge to sanitize it. Did nobody so far test it in the past?

And if yes? Isn't it difficult to control the optimal urine/feces composition you need to have enough biogas in the field? What is the critical level of needed biogas to feed the heater (faeces/persons per day)?
Aren't there any other ways to proceed the slurry from the digester?

I understand that your prototype is in the very early stage, but when and where is field testing planned? And what happens at the end to the effluent? What would be the niche for such a toilet?

Best regards

Dorothee
Dorothee Spuhler
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Re: Effective Sewage Sanitation with Low CO2 Footprint (Duke University in Durham, North Carolina, USA) 10 Apr 2013 15:55 #4110

  • aforbisstokes
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Thank you for the response Dorothee. As for your questions:

1. I have not seen a similar project. For one, household biogas digesters have been used for a while, especially in rural areas of China and India, but were mainly used for livestock wastes and sometimes with human wastes added. Using only undiluted human waste was mainly thought to not be a sufficient feedstock for effective biogas digestion due to the high nitrogen content within urine. Biogas digesters have been used often for providing biogas as a energy source for many things, but I have not seen it for sterilizing the human waste itself. Additionally the heat-exchanger is a novel addition that helps make the sterilization possible.

2. In our prototype, we are using typical amounts of urine and feces per person per day to daily feed the reactor to simulate field conditions. Issues could arise if the urine input greatly increases over feces input in the field. This is why our system is being geared towards households instead of public facilities where the feces input would be more regular and large influx of urine only less likely.

3. We have not modeled for the critical level of feces input (though would be good to do), but our feeding of typical urine and feces per day is based on a 10-person household. With this feeding, our system would produce about 400 L biogas per day, and maintaining our heater (with the first version heat exchanger) at 75C would use about 230-280 L per biogas per day. We have a second version heat exchanger that is tube-in-shell instead of counter-current that from initial tests will reduce biogas requirements due to increased efficiency.

4. I am not sure if I understand this question. We are looking into other ways that could be used in conjunction with our heater to sterilize digester effluent such as passive solar so that biogas production could be diverted into other uses.

5.a. We have run our lab-scale prototype for one year now. Full-scale systems will be installed this June in Eldoret, Kenya, and sometime within the year in Iquitos, Peru.

5.b. The final effluent is pathogen-free but high levels of nutrients (nitrogen) remain. The sterilized effluent can be used as a fertilizer or can be allowed to percolate through the ground.

5.c. I see the niche location as peri-urban and urban areas where municipal sewage is not available, and land space for pit latrines or other systems is limited. Additionally, areas that have need for fertilizer could also find this system attractive.

Thank you,
Aaron Forbis-Stokes
Aaron Forbis-Stokes
Duke University - Graduate Student
Environmental Engineering
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Re: Effective Sewage Sanitation with Low CO2 Footprint (Duke University in Durham, North Carolina, USA) 15 May 2013 08:53 #4397

  • AquaVerde
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McCarty's Anaerobic Baffled Reactor (ABR) and CHP's (CON2 or prefab ABR's) for "Effective Sewage Sanitation with Low CO2 Footprint"?

Dear Joan,

It seams to me your US-group and the EU funded biogas-group "speetkits" for security related research (2012-2016), working more or less on the same issues involved, but very separated!

In my opinion the existing German containerised ABR + CHP "CON2" (insulated and heated) for mesophilic temperature range in Germany is doing already the "job" your separated groups are looking for. You can use the excess heat of the CHP for the needed thermal treatment to sanitise/kill pathogens in effluent/sludge and might dry the sludge or use the gas straight in a heater. Furthermore heat pumps could be used too.

As Prof. McCarty's (USA, 1981) original ABR-Design is an "Open-Source" and do not has a user restricting Patent attached, you might do your own ABR + biogas heater + heat pump or CHP.

2007 Colloquium on Water - Prof. Perry L. McCarty: (1 h 12 min)

Instate of simple purchasing a German CON2 (45-75kWel. (costs 5,000EUR/kWel.)) you might better do your "own" simple ABR, by stacking two fibreglass body's of ready made prefab ABRs from BORDA e.V., Bremen (Made in Asia or Africa), in an used and insulated container. An additional heating and insulation between the two fibreglass body's could keep the fermenter easier in the mesophilic temperature range in cold climates. Maybe add on top of your self-made ABR an insulated airtight fabrics for simple gas storage above the ABR it self, or store gas in a separate used sea-container (with airtight fabrics) nearby.

To simplify your design you might not use insulation and heating of fermenter, only in cold climates you will need insulated and additional heating of fermenter, in the tropics they "run" easier within the mesophilic temperature range, see many examples of BORDA's very simple ABR's in Asia and Africa.

I hope my hands-on view as an biogas-outsider is heplfull to you and your project/research outcome.

Good Luck & Best Regards,

Detlef SCHWAGER

See:
forum.susana.org/forum/categories/61-wg-...isposal-faecal-sludg
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Sanitation-Solutions without external energy
Low-Tech Solutions with High-Tech Effects
"Inspired by Circular Economy"
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Last Edit: 15 May 2013 08:54 by AquaVerde.

Re: Effective Sewage Sanitation with Low CO2 Footprint (Duke University in Durham, North Carolina, USA) 19 May 2013 12:19 #4425

  • F H Mughal
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Dear Mr. Joan,

Quite often, the anaerobic digesters are fixed with mixing device to hasten and enhance gas production; mixing the contents; and prevent the formation of scum.

Regards,

F H Mughal
F H Mughal (Mr.)
Karachi, Pakistan

Re: Effective Sewage Sanitation with Low CO2 Footprint (Duke University in Durham, North Carolina, USA) 21 May 2013 06:01 #4445

  • Marijn Zandee
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Dear Aaron,

Thank you for the posts and the updates.

I also have a few questions.

1.) a family size of 10 seems large to me (based on my Asian experience, maybe for SSA this is more realistic). This brings me to the question of how well the process would cope with under-feeding. For instance if some of the children of the household get send to boarding school, leave to work abroad or get married. What would be the minimum amount of people daily using this toilet for there to be sufficient gas to sterilize the effluent?

2.) Why did you select a floating dome approach. My intuition is that it could be cheaper and more reliable to work with a fixed dome concept, but then again I have never thought about such small units, so I may be overlooking something.

3.) For how much flushing water are you designing this? It seems it would have to be fairly low flush in order to not dilute the waste too much.

4.) Similar, if designed for wipers, is the retention time high enough to break down toilet paper. And if designed for washers, is the extra water ok for the mass balance?

regards

Marijn
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Re: Effective Sewage Sanitation with Low CO2 Footprint (Duke University in Durham, North Carolina, USA) 26 May 2013 12:52 #4502

  • aforbisstokes
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Detlef,

Thank you very much for the comments. Our current target locations are in Kenya and Peru, so we are not looking into the the need for heating at the moment, but the information is helpful for future considerations. The ABR design is something that we are considering based on available materials. I will look more into the resources you've provided.

I am unfamiliar with the abbreviation "CHP." What does that stand for?

Thank you again for your comments,
Aaron
Aaron Forbis-Stokes
Duke University - Graduate Student
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Re: Effective Sewage Sanitation with Low CO2 Footprint (Duke University in Durham, North Carolina, USA) 26 May 2013 12:59 #4503

  • aforbisstokes
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Mr. Mughal,

Thank you for the comment.

We prefer the floating dome design because of the constant gas pressure as well as slurry level because we operate the heating system continuously.

Mixing is still under consideration. We have not done any mixing in the lab system and have not found any issues so far. Some mixing is provided by waste loading as well as rising biogas bubbles. We will be implementing field systems soon, and these also do not have mixing devices. Fibrous materials will not be added, so scum formation related to that is not a concern at the moment, but future considerations and monitoring will be needed to address the mixing question.

Thank you,
Aaron
Aaron Forbis-Stokes
Duke University - Graduate Student
Environmental Engineering
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Re: Effective Sewage Sanitation with Low CO2 Footprint (Duke University in Durham, North Carolina, USA) 26 May 2013 13:19 #4504

  • aforbisstokes
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Marijn,

Thank you for the questions.

1) The family size was an estimation for lab studies and organic loading. We are currently beginning implementation in Kenya for a multi-family system that will serve about 20 people. The system design will be altered for the amount of people regularly using the system. Considerations for residents not always being there will be made.

2) We like the floating dome because of the constant gas pressure and slurry level that it offers. Yes, it is more complicated and expensive, but we think this design would be more reliable for us.

3) The initial design was no flush. Field systems will be designed to be as little flush as possible. American Standard has developed a pan that can operate on only 1 L. Designs such as this will be explored to minimize flushing.

4) The additions of toilet paper, flush water, and other organics are still be evaluated in terms of biogas production as well as required biogas use to treat the effluent. Where we are currently implementing, users are wipers. The retention time raises a good question as I have not looked specifically for the retention time required for TP. The extra water is some ways is beneficial as it would reduce the nitrogen concentrations of the waste which can be inhibitory, but it does require considerations in system size designs.

Thank you again for the thoughtful questions,
Aaron
Aaron Forbis-Stokes
Duke University - Graduate Student
Environmental Engineering
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Re: Effective Sewage Sanitation with Low CO2 Footprint (Duke University in Durham, North Carolina, USA) 19 Sep 2013 11:41 #5691

  • NaomiRadke
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This is to make you aware of Aaron’s contribution to the second expert chat with a group of BMGF grantees on September 12.

Aaron was representing the research team of the Duke University that is lead by Marc Deshusses. He was presenting the current state of the project – currently the anaeorobic digestion-pasteurisation latrine is field tested in Kenya – and subsequently answered to questions posed during the expert chat.

Please find a link to the youtube video of the expert chat below, starting at the beginning of Aaron’s presentation. I have also attached a pdf of his presentation below.
youtu.be/mD1kXv_avVM?t=3m26s
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I have compiled below some points that struck me. You might find them interesting and as food for thought. Please do not hesitate to contact Aaron and his team members for questions/ideas/advice.

The set-up is quite simple: The toilet directly charges excreta into a the digestion tank of a aerobic digester with a floating dome so that both the slurry volume and gas pressure stay constant. The contents that enter the digester are urine, faeces and less than a litre of flush water per toilet visit. The heating tank is powered by the biogas produced in the digester and the system is thus self-containing. Extra biogas can be used at home for example for cooking or lighting.

Since March 2013 they had very steady conditions in their laboratory setting. Pleased with this process they started setting up their pilot study this May in Eldorte, Kenya, in collaboration with the University there.

3 systems had been built in the field, serving around 25 people each. The digester and heating system will continuously be monitored as has previously been done in their laboratory.

In the future they would like to learn about the strengths and weakness of the systems in the field setting they can improve on. Field of interests will also be 1) the feasibility for scale-up, 2) cost-benefit analysis for the extra biogas as burning fuels are very expensive and the treated waste is high in nitrogen and makes a great fertiliser, 3) health impacts of implementing the system.

Main take-aways from the results of their laboratory setting are:

- Digester: is expected to produce about 400 l of biogas per day for a system that was designed for the use by 10 persons
- Heater: for temperatures greater than 65 °C, 100% of the E. Coli was inactivated. To operate the heating tank at this level, 230-280 l of biogas per day are needed. Thus, access biogas is expected

The latrines need to be elevated so the system could work by gravity fall. Below the latrines are the digester and the heating tank. The treated waste that comes out of the heating system goes into the collection barrel where residents can come and collect the treated waste and use it as a fertiliser

Question 1: Regarding pathogen inactivation: have you tried micro-organisms apart from E. Coli?

Answer 1: No other pathogens have been tested in the laboratory yet. Yet, with the tested temperature and time in the tank they would expect to have an inactivation for other pathogens, too. This is something they would like to test in the future.

Question 2: Water content is important for biogas production. How do you manage to regulate that?

Answer 2: In the laboratory the setting was 1 litre of urine and 400 grams of faeces per person per day. That was the portions that were tested. In one phase a higher ratio of water as compared to urine and faeces was taken but they went back to the initial ratio after about 75 days.

Question 3 : How long is the digestion time?

Answer 3: In the laboratory a retention time of 40 days was chosen. The systems in the field are a little different: 45-50 days for a plot that is used by about 25 people. The digesters hold 2 cubic litres.
// Naomi Radke
MSc Sustainable Development
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Last Edit: 19 Sep 2013 12:02 by muench.
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