Enhanced Anaerobic Digestion: A Sanitation and Energy Recovery Technology (San Diego State University, USA)


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Re: Enhanced Anaerobic Digestion: A Sanitation and Energy Recovery Technology (San Diego State University, USA)

Dear Temesgen Garoma,

First, thank you for sharing the details of your research.

As Elsabeth has summarized, the three more potential advantages your system has, compared to that of the conventional anaerobic bio-digester, include: higher biogas production (this may positively affect the feasibility of practical application of the system for domestic wastewater treatment), mitigating eutrophication and the significant improvement on the buffering capacity (which may significantly reduces the burden on the operation of anaerobic systems specially in developing countries where there is limited capacity).

Although I like the idea of adding the algae in the anaerobic digester, I am very much concerned if harvesting algae from rivers and lakes is practically viable option. Instead of mitigating eutrophication by removing algae from rivers and lakes why not trying to mitigate eutrophication from the source? I mean we know that wastewater contains N and P which has significant contribution to eutruphication if discharged in water bodies. In addition; we also know that the N and P content of the wastewater are preserved in the anaerobic digester. In other words the anaerobic process treats organic matter but not N and P. My question is: Why do not use the effluent wastewater, which has high nutrient content, from the anaerobic digester to grow the algae and add this algae back to the anaerobic digester to increase the biogas production? Did you thinkabout this option? If so, what are the limitations? From the youtube link provided by Elisabeth (Thank you, Elisabeth for that and the summary of the discussions), from your discussion part, I heard you saying that you doing a research on growing algae for biodiesel production. This makes it simple for you to integrate the two processes

Hope to hear from you.

Regards, Henock
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Re: Enhanced Anaerobic Digestion: A Sanitation and Energy Recovery Technology (San Diego State University, USA)

Dear Garoma,

Maybe the mentioned information are helpful to your further developments on AD.

See at SUSANA-Forum
- presentation of Prof. Born from University of Applied Science Flensburg, Germany on "container scale"-ABR:


- a more recent (Jan 2013) research paper from Petronas University Malaysia on a 75 Litre "lab scale"-ABR: scialert.net/fulltext/?doi=jas.2012.2586.2591 and at forum.susana.org/media/kunena/attachments/1550/2586-2591.pdf

To my very limited knowledge, this is the first study which shows nicely, that each stage of anaerobic digestion processes can be more or less related/connected to a compartment of this digester technology.

Both institutions used independent by choice simple ABR-technology as the biogas-digester it self.

As fare I understand the ABR technology been used for decentralised sanitation purpose to treat the effluent (COD reduction) of biogas-digester "only", rather the ABR is being used as the biogas-digester by it self. Maybe some one can correct me on this?

Beside it's simplicity, the advantages of this at least 4 compartments AD-technology are, each of 4-stages of anaerobic digestion process can be adjusted more directed them in one tank-digester where those AD processes "run" simultaneously (mixed).

Good Luck
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Re: Enhanced Anaerobic Digestion: A Sanitation and Energy Recovery Technology (San Diego State University, USA)


Thank you for the follow-up questions.

The guideline I was referring to was originally developed by the US EPA ( water.epa.gov/scitech/wastetech/biosolid...ds_503pe_503pe_5.pdf ). I think the same guideline has been adapted by WHO (I am not sure which publication) and used by other agencies around the world.

For the 1000 liters (1 cubic meter) biogas requirement per household of 5 to 6 people, please refer to the following GTZ publication: www.susana.org/docs_ccbk/susana_download...-sanitation-july.pdf

At the moment it would be very difficult to quantify the level of effort involved in collecting algal biomass from lakes and rivers. However, it may require the same level of effort as fetching firewood for cooking and lighting purpose.

Thank you,
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Re: Enhanced Anaerobic Digestion: A Sanitation and Energy Recovery Technology (San Diego State University, USA)

Dear all,

For those of you wanting to learn a bit more about Garoma's * research with the algae and biogas production, you are welcome to watch the online discussion that we recorded with him and a few others on 1 July. His explanations about his research project (with some powerpoint slides; attached below) starts at 29:36 into the recording; it is followed by questions and answers that start at around 38:58 and last until 51:37. It was a very interesting discussion.

I have added the Youtube link below to start at exactly the right time for Garoma's presentation:

In the question session (which starts at 38:58), the following was discussed:

Gabrielle asked about the degree of treatment and which indicator he uses to measure the degree of treatment and what the intended reuse of the digestate was:

Temesgen Garoma replied that WHO specifies that residual biosolids should have less than 2 million coliform forming units (CFU) per gram of solids before applying it on land (my follow-up question to Garoma: which WHO guidelines exactly are you referring to, or are these standards from the US?). He said it takes 30-60 days to achieve this at the optimum temperature of 35°C. In the lab, they ran the reactor for 1 year at 10°C to achieve this pathogen kill. At 20°C it was 6 months.

I pointed out the guidelines for digestate reuse in China which Heinz-Peter Mang had shared with us here on the forum:
Might be useful to compare these.

I also asked: what is the main difference between your system and conventional anaerobic digestion? It is just the fact that algae is added?

Garoma replied: Yes, that’s the main difference. The idea is to generate a sustained production of biogas (and to give the community a good incentive to look after their wastewater treatment process because it gives them biogas!). On cannot only rely on human waste because that does not give enough biogas (from excreta about 90 g COD per day per person; this translates to about 50 L per day of biogas, if the digester runs at 35°C). An average household requires about 1000 L of biogas for cooking and lighting (he mentioned a GTZ publication as the source for this figure (Garoma: which one?)). If a household is 5 people then we need 250 L of biogas per person per day.

When the algae is added it has 3 benefits:
  • It increases the biogas production
  • It would remove algae from lakes and rivers that are suffering from eutrophication due to agricultural run-off and wastewater discharge (lakes and rivers are blanketed with algae) (follow-on question from me: how easy or difficult would it be for the villagers to get the algae from the lake and river surfaces? I imagine this would be quite labour intensive to harvest/remove the algae)
  • Adding algae adds alkalinity (buffering) to the process because algae contains proteins – when broken down, there is ammonification which adds alkalinity. This helps to keep the pH stable and can prevent a digester from going “sour” if it is overloaded with organic matter.
Kim asked how much algae would have to be added?

Garoma replied that they tested this in the lab. For organic matter they used thickened waste activated sludge (TWAS). They tested with 10% algae + 90% TWAS, also with 20% algae, up to 100% algae. The result was always the same, which indicates that algae is a good substitute for biomass in terms of biogas production. Therefore, add as much algae as you have available. If you add more than 20% you already get this beneficial buffering effect from the extra alkalinity (pH value then remains stable around 6.5-7.5). The alkalinity helps if you have accumulation of acids in the digester.

Toni asked if salt could be a problem when digesting the algae.

Garoma answered that he had not observed any problems with salt; but he was only working with algae grown in the lab. Also the intention is to use algae from rivers and lakes, not from the ocean. Therefore he said that salt should not be a problem.

I hope I have done this transcription of the discussion correctly.
If he gets more funding, then he has plans to do field tests in Kenya and Ethiopia.


* I get confused whether Temesgen Garoma would like to be addressed with Temesgen or with Garoma. In the video, it was Temesgen; but I think I will stick to Garoma. The first name, last name convention is different in different countries...
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Re: Enhanced Anaerobic Digestion: A Sanitation and Energy Recovery Technology (San Diego State University, USA)

Dear Mr. Mughal,

Thank you for your continued interest in the technology. We will keep you and members of this forum informed about the progress of the project. The next few months will be critical for us as we seek addition funding to field test the technology.

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Re: Enhanced Anaerobic Digestion: A Sanitation and Energy Recovery Technology (San Diego State University, USA)

Dear Dr. Garoma,

Thank you for your interesting and informative feedback. I appreciate. It is a useful system and, I'll be looking forward to your research findings, and particularly your strategy in addressing the concerns, I pointed out. Please keep this forum posted with your further research.

Good luck and best regards,

F H Mughal
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Re: Enhanced Anaerobic Digestion: A Sanitation and Energy Recovery Technology (San Diego State University, USA)

Dear Mr. Mughal,

Thank you for your questions and detailed discussion on the anaerobic digestion (AD) process. As you pointed out, the process is sensitive to fluctuations in organic load and change in operational parameters, making the conventional AD system impractical in developing countries. Moreover, the low recoverable energy content of human excreta will not provide enough incentive for a community in developing country to adopt and self-sustain the system. So, the main goal of our research is to evaluate the potential of using an enhanced AD process as a sanitation and energy recovery technology for communities that lack access to basic sanitation. For the enhanced AD system to generate a reliable supply of biogas, so that it can be adopted and self-sustained by the community, the use of algal biomass as a supplementary feedstock to the system is evaluated. In addition, the effects of operational parameters on waste mineralization and biogas production is investigated.

The reason for using algal biomass as a supplementary feedstock is to enhance the biogas production, not to make to make it different from conventional AD.

We do understand the challenge with handling methane gas and will address it during the field test and full-scale implementation of the technology. With the current research, we are primary tasked to prove the concept in a lab setting.

With regards,

Temesgen Garoma
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Re: Enhanced Anaerobic Digestion: A Sanitation and Energy Recovery Technology (San Diego State University, USA)

Dear Dr. Garoma,

It was interesting to go through your research on enhanced anaerobic digestion. As I understand (please correct me, if I’m wrong), you add algae in the system, to make it different from conventional anaerobic digestion, where, in lab work, we add nutrients (N&P), instead.

The main advantage of anaerobic digestion is the low production of sludge. As you already know, biological reactions double for every rise in temperature (up to a limit). You can get relatively more methane gas production in mesophilic and theremophilic ranges. Higher SRT (solids retention times) and higher SRT to HRT (hydraulic retention times) ratios are helpful for increased treatment efficiency. In South Asia, we have relatively higher ambient temperatures.

As you can see from the detailed discussion on anaerobic digestion, which I have given at the end of this write-up, the process is highly sensitive, biologically. If the formation of volatile fatty acids is more than their utilization by the methane formers, the process will “struck up,” biologically.

Methane is an explosive gas and, if the gas production is uncontrolled, explosion takes place. Literature review would show documentation of such cases, where anaerobic digesters have exploded. In Karachi, Pakistan, way back in 1966, trickling filters wastewater treatment plants were designed and constructed. Design was done by the famous Dutch company. The primary and secondary sludge was designed to be treated in anaerobic digesters. The local staff lacked expertise, and as a result, all the anaerobic digesters got struck, biologically, with a year of their operation.

In the rural areas of Sindh province (Pakistan), the village women store cow dung in an improvised contained environment (digester), on a small scale, from where they get the biogas for cooking.

The effluents from anaerobic process are devoid of oxygen. If they are discharged in a receiving stream, they will create oxygen sag. On the other hand, the solubility of oxygen in water at higher ambient temperatures (> 25 degrees C) is low. This further compounds the oxygenation problems in the receiving stream.

How are you going to address those problems? How would you compare the costs per unit of methane (biogas) production from your system and, from the improvised digesters in rural areas, which the village women use for cooking? I would love to travel down to Kenya, Ethiopia and San Diego to see your research, if the grants from the Grand Challenge Explorations Program of the Bill and Melinda Gate Foundation have provisions for such visits.

Your research is interesting and useful and, is going to be very educative for the researchers, doing research in anaerobic digestion. The review, as promised, follows:

Anaerobic digestion is a three-stage process. In the first stage, the complex insoluble organics are hydrolyzed to simple soluble organics by the extra cellular enzymes. During this stage, the cellulose and starch are hydrolyzed to simple sugars, while proteins bifurcate into amino acids. In the second stage, called the acid phase, the acid formers (various species of Pseudomonos, Alcaligens, Flavobacterium, Escherichia and Aerobacter) convert simple organics to organic fatty acids (acetic acid). This results in higher acid concentration and low pH. In the third stage, called methane phase, methane formers utilize the organic acids and metabolized them to methane and carbon dioxide. Amino acids give rise to ammonia, which in turn, neutralize the remaining acids.

Methane formers (species of Methanobacterium, Methanococcus and Methanosarcina) are highly frail in nature. They are strict anaerobes, grow over a wide range of temperature, difficult to cultivate and, they remain inalienable. They are highly sensitive to low pH conditions.

These concomitant reactions in actual digestion occur simultaneously. Flawless performance of the digester will take place only when there is a balanced bacterial population of acid formers and methane formers, or, in other words, the volatile acids production equals volatile acids breakdown. If the volatile acids formation is greater than its breakdown (which usually is the case, in actual digesters), the pH lowers, inhibition or wash-out of methane formers occurs and, the process fails, biologically.

Best regards,

F H Mughal
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Enhanced Anaerobic Digestion: A Sanitation and Energy Recovery Technology (San Diego State University, USA)

Dear all,

I am happy to join this community to also introduce to you my grant today.

Title of grant: Enhanced Anaerobic Digestion: A Sanitation and Energy Recovery Technology
Subtitle: The ModAD Process - Resource Recovery Oriented Sanitation Technology

Name of lead organization: San Diego State University Foundation
Primary contact at lead organization: Temesgen Garoma
Grantee location: San Diego, California, USA
Developing country where the research is being or will be tested: Future plans: Kenya and Ethiopia

Short description of the project:

Modified Anaerobic Digestion (ModAD) technology, developed at San Diego State University with a grant from the Grand Challenge Explorations Program of the Bill and Melinda Gate Foundation, has the potential to address the sanitation challenges in developing countries. Laboratory results showed that the technology can be developed into a reliable, affordable, and sustainable waste treatment system (Garoma and Williams, 2012). ModAD technology has produced residual biosolids that meet US Environmental Protection Agency (USEPA) requirements for pathogen and volatile solids reductions, thus these biosolids can be applied to soil as fertilizer (USEPA, 1999). In addition, the technology recovers biogas as a fuel for energy. The recovery of these resources, biosolids and biogas, provide additional incentives for a community to adopt and sustain this technology.

The ModAD technology is versatile and the design can be modified to fit for communities of all income levels. Furthermore, it can be scaled to treat waste at any size facility, from a group of households at rural communities to a high rise building in big cities.

Goal(s): The goal of this project is to modify and adapt an anaerobic digestion system that will treat waste and generate a reliable supply of biogas from the co-digestion of algal biomass and waste.
  • Start and end date: Nov. 2011 to 31 Oct 2012
  • Grant type: GCE R7
  • Funding for this research currently ongoing (yes/no): Yes
  • Research or implementation partners: Jimma University, Ethiopia and Jomo Kenyatta University of Agriculture and Technology, Kenya.

Current state of affairs:
We are still running some experiment which we hope to complete by the end of August. Afterwards, we plan to submit an application to the BMGF for phase II grant. In phase II, we will field test the technology in developing countries where the technology would be deployed. We have already assembled a highly qualified team of experts for field testing the technology in Ethiopia and Kenya.

Biggest successes so far:
We proved the concept, and we think that is a big success as far as the goal of the grant is concerned.

Main challenges / frustration:
We think that the biggest challenge is still ahead of us, i.e., securing the necessary funding to field test the technology and develop an implementation plan for full-scale adoption of the technology. Also, securing a high-level of commitment from the stakeholders is another challenge we could face going forward. To this end, the PI traveled to Ethiopia in November of 2012 and met with a number of stakeholders, including academic institutions, NGOs working on sanitation, real estate developers, the construction industry, municipalities, and etc. He had discussed the details of the field test and received commitments from some of the stakeholders. He had also several conversations with faculty in Kenya.

What is the role of the Kenyan and Ethiopian researchers so far?
All the research pertaining to phase I grant is conducted in the US, while we plan to conduct the field test, if we secure funding, in Ethiopia and Kenya. So, the Ethiopian and Kenyan researchers are for the next phase of the project, Phase II.

Where would people get the algae from and how much does it cost to transport algae from A to B?
The algal biomass can be harvested from aquatic environment. In developing countries, freshwater algae blooms resulting from excessive nutrients, particularly phosphorus and nitrogen originating from fertilizers that are applied to land, are common. Thus, the process of algal biogas gas production can also be used for mitigating the adverse effects of algae blooms. Where access to algal biomass is limited, household wastes can be added to serve as a supplementary feedstock. We plan to test the feasibility of that during the field test. As far as costs for securing and transporting the algal biomass are concerned, we have not done analysis, but that is something we plan to do during the field test.

Links, further readings – results to date:

The project has a website: modad.sdsu.edu/

Documents available in SuSanA library:

Video of me giving the presentation at the FSM2 Conference:

Further videos:

Do you have any questions or comments? What do you think?

Kind regards,

Temesgen Garoma, Ph.D., P.E.
Associate Professor and Graduate Adviser
Department Civil, Construction and Environmental Engineering
San Diego State University San Diego, CA 92182, USA
Website: garoma.sdsu.edu

Another impression of our experimental work so far:
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