Hi:
In a Bill and Melinda Gates Foundation Grand Challenges Exploration Grant we are developing a deployable, 9-m windmill driven system with no electrical power to achieve deep pathogen removal using autothermal thermophilic aerobic digestion on a small scale. I would be interested in any and all comments/ contributions this group might want to make. Regards all, Jim Blackburn

Thanks for posting here and congratulations on winning this grant from Bill and Melinda Gates Foundation! Can you tell us more? What are the applications exactly, what is the raw material, is it faecal sludge or just faeces?
What do you mean by "deployable"? Where and how will you trial it?

(and can you tell us a few more words about yourself and where you work?)

Regards,
Elisabeth

Hi, Thanks for your question. First I'm James Blackburn of the Department of Mecahnical Engineering and energy process at Southern Illinois University in Carbondale, IL, USA. My email is This e-mail address is being protected from spambots. You need JavaScript enabled to view it . I'm a Professor, but am trained and worked my career as an environmental/bichemical engineer.

I'm forwarding a "vision" of what this system might eventually look like. We are now working on a 100 gal prototype to be installed at the Carbondale NW WWTP Primary Sludge Effluent for operation as long as possible. The current seed money grant will allow us to run about 6+ months. The purpose is to test a small ATAD (100 wet gallons)on human waste (I have a lot of experience with swine waste and it's kinetics in ATAD systems) in real weather conditions. Carbondale's wind conditions are marginal so there will be times when the system goes anaerobic/anoxic, however the thermal mass may allow maintenance of sufficient temperatures to bridge many of the calm times. The system is designed for whole excreta. With this information we should be eventually able to identify characteristics of an actual (developing world) site which should be met for application. It will not be capable of solving the whole global problem, but may offer and alternative where wind conditions are good. We're hoping that that may be as high as 50% of the global problem. Our design objectives are wind power only (no electricity or fuel), small, agricultural-type windmill with an air blower-not water pump or generator), US Biosolids A product (10 days, 51-65 C) and minimal maintenance. The wet product should be safe for any agricultural use or even to seed solid compost systems with thermophile-enriched biosolids. We're targeting the people whom today only have pit latrine or open defecation options. I'll be glad to elaborate as requested.

My best regards, Jim

Dear Jim,
Nice to see you on this forum, I feel honoured that a professor from the US has posted here (how did you find out about this forum?).

Is your prototype going to take primary sludge from a primary settling tank at a WWTP?
This will be much more dilute than if you take faecal sludge from pit latrines though. Will the results really be comparable?

I vaguely remember the ATAD process from my dim distant past when I was a process engineer designing wastewater treatment plants back in the nineties... But can you remind me again how the aerobic part is done, i.e. what is done to aerate the sludge? You take the windmill to provide the power to get air bubbling through the sludge (how?)?

Are you confident that the ATAD process will destroy even the most persistent of pathogens, i.e. the helminth eggs? Will you spike with eggs, since most likely there won't be that many in the primary sludge (healthy Americans).

Which country do you have in mind to test it with real world conditions?

Regards,
Elisabeth

Dear Elisabeth (and all),
Thank you for your reply and interest. You asked very probing, but central questions about the technology and our work. I will try to answer them. Pardon the outline format, but this helps me address all of your questions.

1) We started the grant in May of this year (although I have about 8 years of experience in this particular technology with raw animal waste). I found out about your forum because I attended Africasans 3 this summer and apparently was put on a mailing list. I am excited to talk, interact, and learn with other global experts about the human sanitation problems of the developing world. This is why I joined the forum.

2) We are taking the primary sludge from our city WWTP for two reasons, real excreta is hard to come by in the US (at least anywhere near our University), and primary sludge at our plant has the highest solids and COD concentration of anywhere in the treatment plant. It is about 33 g/L Total COD. While I have been unable to actually locate literature on COD characteristics on excreta from the very poor in developing countries, I have cobbled together an estimate from several global health internet sources suggesting it may be around 50 g/L total COD. There is no question that while the physical/ chemical/ biological characteristics will be much different (eg viscosity/ particle or "lump" size distribution, etc.) our proposed and current focus is to demonstrate in a system exposed to the wind and weather with human waste, that we can maintain a 55-65 C temperature for 10 days residence time for 6+ months. By the way, if anybody can help lead me to physical/chemical/biological data on excrement from our target group of people, I would be delighted.

This is the focus of our "seed money" grant and we are aware that engineering problems remain to be addressed if we are fortunate enough to gain a BMGF second phase grant. Also, the trial in a developing country is planned for the second phase and will be the prime focus of a second phase grant... the country to be determined by ourselves, the BMGF and other interested parties in the world.

3) You are correct that in this day of anaerobic digestion, ATADs are relatively obscure. In the latest edition of "Metcalf and Eddy, Fourth Ed., 2003" out of over 1800 pages, there are 5-6 pages dedicated to ATADs. However, in the sections devoted to pathogen removal, including helmith eggs, The US uses a Classification for Biosolids A which, if met, allows unrestricted agricultural use of the remaining treated solids, at least from a pathogen standpoint. In Table 14-11 (pg 1464) from the above reference, thermophilic aerobic digestion is listed as one of the accepted process to further reduce pathogens (PFRP). All literature I have seen indicates that if these conditions are met, helmith eggs will be removed to the detction limit. Of course, we don't know the effects of the physical properties of excreta.

We are planning to work with Profs. Michel and Galas from the "Servicio Enterobacterias”, the National Reference Laboratory for Enterobacteriaceae,“Instituto Nacional de Enfermedades Infecciosas - ANLIS Carlos G. Malbrán” in Argentina to explore the effects of survival of Cholera and Shigella in excreta at these conditions. When I applied for the BMGF grant Acute Diarrheal Diseases were the Foundation's focus. Profs. Michel's and Galas' work may result in a clue as to the matrix effects on pathogen survival.

3) A very good and recent review of the ATAD field is available in Juteau, P, 2006, Livestock Science 102: 187-196. Briefly, it is well known (confirmed over and over again by famous investigators in Environmental Engineering and other fields and traceable back to chemical theromodynamics at least 100 years ago) that about 14 Mj/(kg of oxygen removed) of heat is made regardless of organic waste, organism or conditions (within reason). ATADS simply add oxygen, mostly using air and manages the heat of biooxidation to maintain thermophilic temperatures. This requires a COD source (only a fraction is used by microorganisms), sufficient oxygen transfer to maximize heat production, good insulation and concern for the two big heat losses (hot mixed liquor removed and water saturated air (offgas) leaving the system. This hot air at reactor temperatures carries away significant amounts of evaporated water at 0.62 Mj/kg air at 65 C. All applications of which I am aware (including our past work) have carefully metered and controlled the air input (current US patent activity focuses on this), because it both controls the heat production and heat loss rates. These systems use electricity (lots of it) and expensive blowers.

We are exploring if the air provided in a windmill fitted with a rugged blower (not a pump or generator) can be used with the variable wind outside in the weather to hold the temperatures and residence times necessary for deep pathogen kill. Specifically this is a commercial windmill about 9-m high used for fish pond aeration and can be found on the internet worldwide. We are using a fine bubble diffuser air stone. We have done our own engineering tests and have established the performance data up to 4 feet of water head. This application will not require much deeper systems than that.

4) In Carbondale, we are addressing (spending our seed money) on the engineering issues and only measuring fecal coliform/E. coli by an EPA Certified laboratory. While our University has the knowhow for broader pathogen analysis and has famous investigators in these areas, we just don't have the funds. We are relying on the mass of literature sugggesting helmith eggs won't survive the reactor conditions and trying to establish that the reactor conditions can be held even with variable and even no wind (at least for limited durations).

I think I've addressed your questions and am anxious for comments and responses.

By the way, I'm attaching an unpublished steady-state modeled result showing that with current knowledge, we expect that the system will maintain the temperatures here in Carbondale in January.

Best Regards, Jim

Aha, I was also at AfricaSan 3 so you might have seen me present in one of the SuSanA sessions (and true: we added the e-mail addresses of those who attended and who gave their e--mail address to the SuSanA news mailing list - I hope that was not too cheeky and that you didn't mind).

Thanks for the detailed explanations, very useful! I think you will need to decide sooner or later if your ultimate application will be faecal sludge or pure excreta. Two very different things. Faecal sludge could be vaguely similar to your primary sludge (although with a lower water content). But faeces from dry systmes is a totally different story. For the later, it no longer makes sense to try and measure COD - COD is for concentrations in liquids, but here you have "solid" matter.

Based on what you describe with the fine bubble diffuser airstones, you will always need a waste which is rather liquidy. So I guess it will be faecal sludge. There are many good publications from Sandec on faecal sludge characteristics, you find some of them in the SuSanA library by putting into the search field "faecal sludge" here: www.susana.org/library

A recent publication from South Africa which seems to be very good and comprehensive is this one:
www.susana.org/lang-en/library?view=ccbk...p;type=2&id=1243

WIN-SA (2011). What happens when the pit is full? - Developments in on-site faecal sludge management (FSM). Water Information Network South Africa. Proceedings from FSM Seminar, 14-15 March 2011 in Durban, South Africa.

Hope this helps a little bit.

Regards,
Elisabeth

Thanks again for your interest and suggestions. You are right, we are dealing with the whole human waste, urine plus fecal material. I believe you call this faecal sludge, we've been using the term excreta. It is not dry, but beacuse it is wet, it is well known that thermal disinfection processes are very effective. Thanks for the reference lead, too. Regards, Jim

Dear Jim,
Ah, terminologies... Just a small correction: faecal sludge consists of faeces + urine + water. You get it from septic tanks and from pit latrines. Even though the pit latrines are "dry" toilets (unless they are pour flush pit latrines) usually when emptying them, water needs to be added to get the stuff out of the pit (especially if you want to use a pump or any mechanised equipment).

For the ATAD to work, I assume you need to have a sludge or slurry where the total solids content is not too high (or put in other words: you need a minimum water content). Which dry solids content do you envisage to be still workable? Primary sludge has a dry solids content of about 3-5% if I remember right (= 30,000 to 50,000 mg/L of solids). Faecal sludge will usually be higher. Could aeration still work if you have something like a "cake" from a belt press which is 12% d.s.? I can't imagine that it would (?).

Regards,
Elisabeth

Elisabeth,
Thank goodness we have this communication for us new-comers to come to an understanding of terms-in-use. We will use fresh-hot (as high as 37 C)human excreta--mixed urine + feces and if we have to, some toilet paper. This is the material eliminated periodically from the bottom end of humans. It is possible in the second BMGF to consider recycle of some of the treated liquid for pour-flush or maybe even a new type of mechanical system to flush the recycled excreta into the treatment section with no new net water usage. Even after pouring over your important reference, it still seems that "excreta-urine plus feces" held for around 10 days will still be in the 50g/l COD range, not the 157,000 mg/l value quoted in your reference. The latter is clearly inorganic and/or/ organic solids or biosolids, (and trash)compacted for months or years in Latrines. The solids in the fresh excreta will hold 60-80+% water and we do have signifcant solids removal including significant cellulase activity), releasing some of the fecal-boundwater in the aqueous phase, maybe lowering viscosity by it's own dilution as well as by high treatment temperatures

We expect our fluids to be flow-able during the 10 days residence time at temperature, even though we expect them to be more viscous (and rheologically difficult)than our US treatment plant trial. We are exploring building systems above ground to use gravity flow when possible and to make the predictable eventual "clean-out" easier.

It is clear that nearly all physical/mechanical/rheological issues addressed in your suggested reading for current latrines, will be very different than those we are expecting to face at Global-Scale Demonstration, if we are fortunate to win a BMGF Phase 2 award. A good deal of work will be needed to prepare for and address that phase.
As you are discovering, there are some difficult engineering problems to be addressed at that time.

In our swine waste work (3-m3 reactor) we have worked up to about 4% Total solids with no noticeable effects, the Carbondale work is a little under 3% TS. I expect we will have to face 7-10% TS with a Phase 2 International Demonstration on "urine and feces--excreta." We don't have all the answers yet, but we are only 5 months into this project.

A belt filter press cake at 12% TS at the moment seems out of our reach, at least with no electricity and wind-power only--The small windmills can only generate a few psi pressure drops. As you know, belt-presses are 1) expensive, 2) complicated mechanisms, 3)require infrastructure and maintenance, 4)I would not think them to be easily deployable. On the other hand, a material with low enough water can be combusted at small scale with it's own heat, (I teach air pollution) even if the control of the off gasses may be frightening to comprehend.

Elisabeth, lets keep talking, I'm learning a lot. Regards, Jim

Dear Elisabeth and Jim,

Jim thank you. It is a very interesting subject you are working on and it gives room for a lot of research.

And Elisabeth thanks for the link, I didn´t see before the mentioned publication about fecal sludge management it covers really interesting points.

I knew the ATAD as a sludge treatment process which never got really to a break through as it is VERY energy consuming (and therefore I never thought about it for developing countries). On the other hand it is a method which is well proven for fecal sludge to work out quite fine (at least I remember from the 90th that there have been some ATAD approaches for fecal sludge treatment in Germany…I could try to make you a contact if needed). I remember there were complete technical solutions. The main point is the energy aspect, so the wind mill approach is an interesting one. I remember as well that they had some odor problems due to the combination of high temperature and NH3. So that might be an important aspect for a decentralized solution as well.
I imagine that you work on the energy balances (how many days could I live with without wind, maintaining the temperature sufficiently high). I could imagine that the crucial point is the right size and the costs per unit.

Thanks again for this discussion.

Christoph Platzer

Elisabeth and Christoph

Even though I have been working with ATAD for 10 years and sometimes I think I've heard it all, I'm very interested in comments from this forum. I'm aware of 1st and 2nd generation approaches (at least most of them.) It is important to note that we are developing technology to directly deposit warm urine and feces plus a little toilet paper from the human body into the ATAD using an appropriate toilet mechanism. We can recycle treated liquid to increase dilution if necessary, but no additional water will be needed. By the way, our windmill blows air, it does not pump water or generate electricity. No electricity is planned. This is the source of the savings over past electrical blower systems used in Large-scale ATADs--the largest operating cost of the systems. Our idea is to build a small system, to prove out our kinetics (gained from 17 fresh,--whole pig waste feed demonstrations, 3m3 wet volume systems) and to determine how long the system can stay between 55 and 65 C when the wind stops blowing. This would help determine where in the world the system might be applied. We are using a 100 gal (wet) system with a 100 gal head space and replacing 10 gal per day in a "fill and draw" design. Our target is only for small decentralized systems. The system throughput is dependent on its volumetric COD, natural wind (the more the better), the windmill efficiency, fine bubble diffuser efficiency and a few tricks some of which we have patented. For decentralized systems, the Capital Cost may be high, but may be able to qualify for subsidies. Operating costs will be in the $0.05/person/day as dictated by the Bill and Melinda Gates Foundation. The ease of operation virtually eliminating the blower capital costs and electricity to drive them (they are only 60% efficient, you know) and the benefit of virtually pathogen free liquids and solids for any agriculture application (at least in the US) is too good to pass up. By the way while it is easy to find excretion data for Developed Countries literature, by surveying a number of internet reports and SuSana Reports. I arriveed at a "shakey" COD loading rate of 0.07 Kg COD person-1 day-1. I'm still looking for a more reliable value. This is lower than the developed countries. You may also be interested in the number of people serviced if all of our design data proves out in our trial system. I attach our graph. Notice that the capacity depends hugely on the wind flow rate. Also we are also only looking at the 10 day residence time to meet US EPA standards for Biosolids A quality. This allows any agricultural use without restriction.

Oh, you mentioned, rightly so, ammonia. It is true that the nitrifiers stop working at this temperature. However, how much ammonia emitted depends on the pH and buffers, and whether use of control devices such as biofilters or fertilizer recovery devices such as acid scrubbing are used (this last option would require routine handling of a acid, harsh chemicals prohibited under the BMGF GCE6 rule.) It may even be possible to operate a nitrification-denitrification system, but that would require care and maintenance beyond the BMGF scope. I think the developing world may be different than the developed world, since with urine diverting toilets, nobody seems to mention the urine smell??
By the way in our livestock work 90% of the fresh swine odor was removed in 6 days and the 10% of odor left was ammonia.

Any flush toilets would be operated by recycling our treated recycle water with no net increase in water produced.

Finally, the liquid. it can be safely used for any agricultural use under current US BIOSOLIDS A standards. In the developing world I would think that it could be used safely for food production and maybe some other uses, yet to be proven.

Thanks for your comments, keep them coming. Regards, Jim

Dear Jim,
I tried to understand your graphic. I admit do not understand it completely. I understand that the reactor size depends on the wind…energy, I imagine that the cao 20 – 50 situations are estimations of lack of wind. A relevant residence time would be above 6 days or not? So about a 420 l will serve 10-45 people. From your post I understand that the windmill will aerate directy the reactor and that you are interested in the fresh material. As BMGF does not allow a sewer there would be the necessity of one 9 m windmill for each of these installations? I do have a problem to imagine that, especially together with the typical electricity “spaghetti” situation.
Concerning the ammonia, it might be an option to use urine diverting toilets to avoid the ammonia problem.
As for the COD I would go more for a 100 g of COD /d,pe, 70 does seem a very low figure to me, where did you find that?
A question about “Any flush toilets would be operated by recycling our treated recycle water with no net increase in water produced.” Do you do a phase separation? How do you assure a clarified water for recycling? Up to now I understood that you are doing ATAD, but additionally treating the water for reuse?
Lots of questions

Yours Christoph

Christof, First let me describe the graph I sent, I apologize for not doing so before since it is of importance to colleagues such as you. I'll try to do better next time.

For one set of steady state solutions of the model varying over windspeed, temp, feed COD--this the meaning of Cao the concentration of COD FED in g/L, a common abbreviation in chemical engineering. Wind speeds may be found to stimulate the oxidation heat generation without excessive heat loss at a variety of places using a 100 gal liquid Fill-and Draw insulated reactor. An old way to converge the system is to make changes until the overall reactor heat balance is zero. For what ever the reactor temperature chosen and for all the other assumptions, this represents a stable state point of the system. I showed you some of these data a few discussions ago.

The slide you asked about was a derivative slide essentially made just for our specific circumstance and with blower v wind data we collected our selves and is based on our 100 gal fill and draw reactor to be operated for months to confirm kinetics and assumptions in our model. It is modeled data yet to be confirmed.

Having said all that, the issue that came up last time was the number of people using a facility. For a particular site in the world (wind and Temp, for a particular amount of people with some known average strength of COD, and our interest to run at 10 days RHRT there could be such a curve generated showing how much wind on average was needed to maintain the reactor temperature here 65 C, (Carbonadle, January, 33.3 g/L COD and 8 mph on average.) This would be a function of the number of people(excreta rate) x Cao ^COD

Most important it only applies to 100 gal of wet reactor liquid( only our current and chanageable wet reactor volume)

A heuristic that might make sense to you is that for a group of 30 people using the 100 gal system, with a Coa (average C_COD of50 g/L, fresh and warm,at 10 days, they would need an average of about 9 mph wind to sufficiently drive the biooxidation blower. 50 g/L seems to be popping several places up for COD average concentration of human warm urine, feces and a little toilet paper. I still don't have an authoritative number for this but several oblique sources seen to point to 50.

I reread your question and since I took so much time already, forgive me if I just touch on 2 I missed. There will be a windmill at each location, but only a fraction of
possible locations will be suitable for this siting.
AAQPS Air ammonia regulation in rural areas in the US only seems to be a driver as a "nuisance" at least in Illinois . In essence the nuisance is "odors" and in Illinois, proving odors and odor thresholds is really hard to do. Recent emphasis on the fact that since ammonia reacts with nitric and sulfuric acids, it has become a precurser of fine particular matter, a criteria pollutant. There has also been talk about ammonia regulation around large (very large relative to a developing country, I suppose) animal feeding lots (100-1000s of animals)? And its very minor(not methane) potential role as a CO2 equivalent in Global Climate Change is surely not a dominant factor?

Here it comes-- your question... Why do you expect ammonia to be an issue for developing countries while I imagine much worse odor problems are part of their daily lives?

Alway intrested

Again Regards, Jim


I know the countries deal with pollution widely different--
Christof, call anytime, ask any question --beware-- When I find out your specially, I may be the asking. Until later friend.

blackburn wrote:


Hmm... with fresh manure/faecal sludge you would obviously result in a high amount of ammonia de-gassing at these temperatures. Is it really necessary to use acid scrubbing though? I could imagine a fresh-water spraying of the exhaust could yield a relatively highly concentrated and more or less sterile ammonia fertilizer solution. Or am I missing a crucial point which requires the adding of acids?

On a related note, since I am researching that currently, wouldn't it be feasible to used the air exhaust of a vacuum sewer system to aerate such a ATAD system? What would be an approximate air volume requirement per qm of typical liquid sludge?

Greetings, You must tell us more about your work with ATADs.
In reply to your comments on ammonia, I must also tell you that the feed material was fresh swine waste. The quantities of ammonia emitted were significant and if used on a US pork farm (whom at the time was fighting the attorney general to stop odors), a minimal solution to the problem was not in the cards. So we went to an acid scrubber and solved the problem and made a liquid fertilizer as a by product. We eventually recommended against acid scrubbers because of the safety aspect and the fact that huge amounts of acid (truckloads a month) would have to be delivered to a production-sized farm. We just didn't believe that farmers could become part-time chemical workers on the long haul.



In principle I agree with you that there are many ways to solve the problem beginning with the compositional diets of pigs and people. One may have an abundance of nitrogen, the other a relatively small amount. In the latter case (if it were people) your ideas may fit very well, with the caveat that there is a physical designed water scrubber included to assure even water/gas contact. That, of course in agriculture means large volumes of air.

I see no particular reason that a vacuum sewer gas line could not be used except It would have little or no methane and other flammable/toxic components in it. It should be a highly oxidizing system and a small amount of a reducing agent should not have a negative effect. As to a depletion of oxygen in the sewer, we have run with our recycle system as low as 17-18% O2 in the reactor feed gas with no negative effects.

To digress, once I had a pharmaceutical client in a dense residential neighborhood who had been wasting process liquids to its sewer for years, they decided to become green and put rebuilt systems and placed tight-fitting lids on all the sewer openings. It was a very short time before the neighborhood kids (I guess) found out that the could drop a match in the sewer outside the plant and see all the sewer lids in the plant pop up about 100 feet.

I'm afraid I don't understand the last question.

Let's keep in contact
Jim

Thank you for the fast reply!

I am currently in an early research/brainstorm phase to use vacuum sewers for (among other uses) emergency camp sewerage systems, and after reading your post I thought an ATAD treatment of the sludge would be probably a good solution for making sure the effluent is low in pathogens, hence the question about reusing the air flow from the vacuum pumps/compressors.

My last question was related to the needed amount of air for aeration.
A typical vacuum system will pump about 6 litres/person/minute of air (albeit usually not continuously but in batches and this rule of thumb was established for a population producing about 150 l/p/d waste-water, which would be obviously less in a water saving system). My guess is that this is more than sufficient to aerate an ATAD reactor, but I don't know what amounts of air are typically pumped into such a system.

Greetings,

It is true that a well designed ATAD achieves very low amounts of pathogens of all types. Along with the literature in the area, one can note that the US EPA regards ATADS as a PSRP or a Process to Significantly Reduce Pathogens. There are requirements for residence time and operating temperatures, but if you meet these, the treated water and solids can be used for agricultural uses without further regard. I don't know but would doubt that trace amounts of vacuum pump oil in the ATADS air input would hurt the system performance.

As to your second question, air is the key to using the system. Air controls biological processes which generate heat and as the temperatures get high (in the ranges specified by the EPA PSRP) a great deal of water evaporates requiring over 2.3 kj/kg water and together with hot liquid flowing out these are the main heat losses. A good deal of patent activity addresses various strategies to minimize air, often by increasing the oxygen transfer efficiency.

As to ratios, I am working on small decentralized systems and fresh excreta (not diluted or stored). 38 L/day liquid/solid treatment in our pilot system requires about 63 standard m3/d. Using the best data I can find, this would serve in the neighborhood of 30 people. In our patent we recycle about 60% of the offgas and gain higher oxygen transfer efficiencies and several other benefits. Thus the fresh air fed to our system and actual offgas would be about 25 standard m3/d.

There are various approaches to consider, each with its own ratios. I hope this helps.

Regards, Jim

Thanks again Jim!

Sounds like it might be worthwhile to investigate further for our project.
If it actually gets approved I might get back to you to discuss further details.

Hi Christof, haven't heard from you lately. While running the system currently in the "fed and "batch mode we are finding that our feed may not have the kinetics of those years of swine waste. There is one thing different, our current feed is a mixture of office tape manufacturer waste, dairy wastes and Chese Whey and a litle bit of human excreta.. We can still develop understanding about the heat transfer portion, but may not be able to forecast animal wastes (except swine waste.)

Have a good day, Jim

Hi Jim,
yes I´m here and available. I just did not write anymore for due to the lack of time and themes I thought I should/could contribute.
I would be glad to hear some more of your experimentes.
Yours
Christoph

I'm Jim Blackburn and I'm interested in a windpowered ATAD. We have one, but in the six months we ran, only an industrial waste was available. I'm trying to find a material of significant TS %6-8? and a BOD/COD ratio of the feed at or above .5 (10 gal day). the volume needs drive us to sources from waste water treatment. Any suggestions. Thanks Jim


(note by moderator: I have moved this posting to the earlier existing thread on this topic. EvM)

Hi.
We have completed the first 6 month run of the system and are just now analyzing data.
I will probably have a report to BMGF soon and will submit a paper thereafter. Regards, Jim

A centrally located Autothermal Thermophilic Aerobic Digestion (ATAD) system is very useful and probably essential to receive the content of any toilet system including UDDTs in an urban environment, provided the UDDTs can be emptied regularly. Link with the discussions on UDDT would be fruitfull.

To my understanding, the ATAD digester e.g. www.dayton-knight.com uses water and air to process the content at high temperatures and sanitizes the content.
However, the capture and burning off of the methane gas is very important. This however, is hardy possible in an aerated system. The effect is that methane gas escapes into the atmosphere, being 21 time more insulating than the CO2.

The windmill ATAD needs some essential technologies to consider.
1. More wind energy is obtained at higher level above the ground. For detailed information on windmills see website of: www.RETscreen.net
2. Other wing or propellor designs will generate more electricity for heating with the same amount of wind. Heating will be required in low temperature environments. The low-speed rotor in the picture is suitable for mechanical transmission such as a water and air pump, but less energy efficient for electric power.
3. Because of the moving parts in the windmill, such design requires high maintenance; this however is a serious problem in many (developing) countries.
4. Thermal insulation of the (underground) tank or reservoir is important in the colder areas to obtain thermophillic processing. This becomes more important in countries with a cooler season and essential in countries with a winter such as South Africa, and higher altitude zones world wide. The process time should be short, otherwise the retention time needs to be substantially increased.
5. Stirring of the content of the ATAD reactor is important not only to mix the air, because people throw all types of waste into the toilet such as non-digestable paper, condoms, sanitary napkins and even used seringes. These plastics and solids need to be removed occasionally.

The question raised is if the production of methane gas is avoided in an ATAD, or how it can be avoided?

Dear Sjoerd,
it seems you got something wrong. It is not Automatic Thermophilic Anearobic Digestion it is autothermal thermophilic AEROBIC digestion.
As well as UDDT are AEROBIC not anaerobic systems. That is a very crucial point. I really don´t understand your posts (some in the Forum) which are pointing to anaerobic UDDT..if a UDDT is anaerobic soemthing has gone very wrong.

Christoph

@Christoph, Thanks, I have clarified the text.
The content of the UDDT you can dump in a biogas reactor for sanitization and gas production. The UDT, being a wet system (even anal wash is possible), can be directly over a biogas reactor. Since the ATAD is also a wet processing system, it is likely that methane gas with bad odour is generated. This is actually the case. Given the importance and the danger of global warming, one need to ask how methane gas is avoided, and if the ATAD is a suitable system in this context.

Hi.

We've just finished our 6 month Windmill-ATAD system and can add to the discussion of methane. Surely no one wants to make methane as an integral part of a decentralized system. It is just too dangerous.

Our continuous ORP data shows over a span of wind speeds and an underpowered windmill, reactor liquid never enters the methanogenisis range and except for a brief time span where we "wired" the system to be in the high aerobic range, It was steady in the denitrification range. We had no observable odors. Regards, Jim

Here is the photo of our system, capable of handling 15-20 people. No power, no water needs, no chemicals, low maintenance, cheap (BMGF Grant Requirements) Regards, JWB

All sanitation systems have advantages and disadvantages, wheres we try to reduce these disadvantages. Sanitation systems however, produce methane somewhere along the line, where dry or wet systems.
In relation to sanitation you can possibly define three levels; Private, Public and Global.

Private is appealing to the individual user and includes personal and family health, personal expenses, comfort, recurrent cost, etc.

Public includes the cost of delivering water, the entire sewerage system and the sewage cleaning activity or other communal services that are not individual. These expenses however, are somehow paid for by the individuals through specific tariffs or general taxes. General public health related to no sanitation or better sanitation also falls in this category. When we look at sanitation systems we see that more water results in more sewerage, through which the cleaning also becomes more costly.

Global is related to the impact of human sanitation on the environment. One of the most important aspects is the cleaning of the sewage so that it does not affect negatively all our surface water, irrigation, fish or algae development, etc. The emissions of CO2 and methane gas are part of the global and environmental issues. Human excreta produces methane gas when aerated or in biogas reactors. While the methane gas is captured in biogas reactors and can be burned off to CO2, with other sanitation systems this methane is emitted into the atmosphere. It is 21 time more insulating as a greenhouse gas than CO2. Human faeces composted or aerated including from septic tanks and ATAD is there fore a major contributor to global warming. Global warming in turn leads to permanent melting of more polar ice, larger and more frequent tornadoes, expansion of deserts and more droughts in some regions with resulting food shortages, and excess of rain worldwide causing floods, and not the least of all the rising of sea level with two storeys, requiring a billion people to move to higher land and loss of agricultural land. The book/film "An Inconvenient Truth" gives a short account of the issue.

It is my opinion therefore that all sanitation systems need to be assessed on CO2 and more import on methane emissions (NH4) into the atmosphere and rated. This can be an interesting task for SuSanA. Most likely the least damaging systems are the UDT models in combination with a biogas reactor, from which the biogas is used for cooking.

One more thing. On our next battery of runs, I will monitor lower explosion limits and try to analyze for CO2. This may be months from now. Regards, Jim

Dear Jim,

I was a little surprised when you wrote " Surely no one wants to make methane as an integral part of a decentralized system. It is just too dangerous".

I assume that you don't consider bio-gas technology as too dangerous to use? If so I would be interested in your reasoning.

@ Sjoerd, I agree it would be interesting to look at sustainable sanitation from a global warming perspective as well. As long as we don't tie it up to carbon credits or similar. (I know we disagree there) By the way, here in Nepal we have some bio-gas attached UD toilets, seems to work fine as-long as you have a couple of animals to create enough feed-stock (or connect a lot more toilets).

Kind regards

Marijn Zandee

@marijn. I think that an important priority is to reduce any methane emissions from sanitation systems through the integration of biogas reactors with sewage. At city level the UASB is being used but other city sewerage make the sludge dangerous. Therefore direct toilet based biogas reactor is preferred.

In Nepal the biogas project attaches the house pourflush toilets to their small farm based biogas reactor, but urban development for cluster houses is not yet done. The few cattle produce much more dung of good quality than the household members. When we did the first methane leakage measurements on these small rural biogas reactors (now over 250.000 constructed) it appeared that there was substantial leakage. See sketch. This leakage was not resolved but the project managed to get good carbon credits anyhow, co-financing the management costs.

In developing toilet systems you can forget the carbon credits because you need massive results to make it economic or recover the investments. But when you have large numbers it is a worthwhile financial contribution. If some countries continue to frustrate the Kyoto protocol that financing may not be sustainable.

@Jim. I figure that blowing air through toilet and animal faecs with methane gas produces an explosive mixture. It will be dangerous to burn this mixture off. When not done it contribute strongly to global heating. That is why it is important to quantify the methane production of all sanitation units and design systems that capture the biogas (without air).

We will see. I believe it depends on the oxidation reduction potential. Regards and thanks for pointing out a possible problem to solve. Regards, Jim

Your correct, my comments were only aimed at the windmill ATAD we are developing.
Surely there are 1000s of biogas systems operating safely around the world. Thanks for the correction. Jim

I've analyzed much of the large set of computer-logged data and now have a presentation. After I submit it to BMGF, I will try to submit it to SuSanNa. Probably a couple of weeks. Regards, Jim

Hi Jim,

It sounds like a really interesting project. I was wondering if you have been able to quantify the volume of air produced ie cubic meters per hour or day under varying wind conditions?

Thanks, I thought I saw somewhere and article or publication of how to stop methane production in an aerobic system. Does anyone else remember this? Jim

Hi Jim
Sorry I am confused . First I did not respond, as Sjoerd from my point of view mixes anaerobic treatment with ATADS and these are two different technologies. But now you are writing about methane as well. Maybe I´m of university since too long, but from my understanding Methane production is very sensible to aerobic conditions...simply does not happen in aerobic conditions. Could you indicate a paper that states Mathane production in an aerobic process?
Yours
Christoph

I am mainly interested in the amount of methane or other GreenHouse Gasses (GHG) coming from the various sanitation systems, but I do not find much information on the subject. When Jim can do an off-gas analysis, it may turn out that the ATAD actually reduces the methane emissions as compared to other sanitation systems.

The methane production from faeces is a matter of deduction. All humans have methane producing bacteria in their intestines (anearobic). Cattle have mch more because of a different digestive system. When we defecate these faeces continue for a while to produce methane. This is observed by smell and in septic tanks. When the ATAD is fitted with (pour) flush toilets it is logical that some methane is produced. Maybe, by forced aeration the methane producing bacteria are rapidly killed off. This can be an additional environmental benefit of the ATAD ascompared to other systems. In that case it is worthwhile to measure and document it.

In general I think it is important that each santation system has a rating on GHG emissions, which are not limited to methane or CO2. Such rating can be a recommendation for specific systems versus other systems.

Sir, you raise a good point. We have always been aware that if the excreta has a low enough ORP methanogenisis would occur and we would have to do something. Even more locally to the users sitting on top of the reactors, if we cross 25% of the Lower explosion limit (mostly methane) a user could flip a cigarette in the reactor and the result would be deadly for a user. It has always been on our list and we will address it in our next run (since we are out of BMGF funds our progress will be proportional to the new funds we hope to raise). Thanks for you advice Jim

Christof, Please don't quit being or "devil's Advocate. Most of your comments have bourn fruit! Our six months autothermal thermophilic AEROBIC digestion experiment to date shows mostly ORPs around -200 mv. This is an accepted proxy for estimating the electrochemicistry and particularly what might be the main terminal electron acceptor. For most of our run we were

at -200 to -250 mv, dangerously close to the ORP related to methane formation. The system is really a mixture of all types of organisms and the orp shows some kind of average. We need to rerun with a home designed windmill and a sludge being much closer to strong aerobic ranges, >0 orp. and measure the methane at that level. I attach a chart showing the relationship between reactor temperature and ORP. Note we know we did not achieve the required temperatures, another reason for a second run.

I'm happy to discuss the issue. Jim

Yes Christof, reuse of the water even to the potable point is technically possible, though too expensive for meeting Gates' target of less than $0.05/person-day. Right now the emphasis is on generating pathogen-free water. Regards, Jim

Hi.

We have 6 months operating data for our windmill-atad. I'm looking for suggestions as for where to publish. It is multi disciplinary 1) Environmental engineering, 2) chemical engineering, bioengineering, 3) sustainability, 4) energy production, 5)renewable energy production.

If you are not aware of the project, just search for ATAD

Thank you very much. Regards, Jim Blackburn

Dear Jim,

When you say a place for publication, do you mean a peer-reviewed journal? I could suggest the IWA journals: Water Research; Water, Science & Technology; Journal of Water, Sanitation and Hygiene for Development; or Water SA. What I like in particular about Water SA is that it has a good status (citation index) but it is nevertheless open access which I find important.

If you are not after a peer-reviewed journal, and just want to get it out, then the SuSanA library could also be an option.

By the way: I have moved your posting to become part of the thread that you started over a year ago so that it all belongs together. This new category will actually be populated in the next few months with information about all the ongoing research grants funded by the WSH team of the Bill & Melinda Gates Foundation (forum.susana.org/forum/categories/97-inn...ing-country-settings) - as part of the project to make the previously closed "Sanitation Network" run by the Foundation into a public-facing community here on this forum. You were I think the first BMGF grantee ever to make use of the SuSanA forum to discuss your research - so I call you an "early adopter".

Regards,
Elisabeth

:)Hi. Our windmill-driven ATAD has been run for about six months. See description by searching for "ATAD." We are preparing a journal submission and I'd like your feedback on the best jourbal to publish in. Our work is very broad and could be published by:
Chemical Engineers,
Sanitary and Environmental Engineers,
Public Health
Environmental science
and so on. The work will cover system description, comparitive kiketic data and analysis of results.

I'd very much like your opinions. Thanks Jim Blackburn

Hi.

We’ve just finished all the packing and will be picked up on Monday. Our team is looking at Wind-mill driven Autothermal Aerobic Digesters at a very small scale. We’ve run this system at scale for about 5 months, and we think it may work for people who live in places of moderate or higher wind. It’s thermal mass buffers changes in the environment. We’ll bring the system itself and show how it works as well as bringing a model that shows how the ATAD might fit into an enclosure. We are also very optimistic that water produced from the system will be so low in pathogens that it could, with a hand pump, allow the benefits of a flush toilet with treated water without the problems. The only problem (but a big one) was that we were unable to get the reactor above 34 degrees C when it requires 55-65 degrees C to do the disinfection. We believe that this is due to the inhibition and toxicity of the mostly-industrial waste sludge we had to work with.

We hope we can continue with an all biological WWTP return sludge which will simulate the final all excreta material and very high reductions in pathogens–the goal of the Foundation.

I am coming: to meet all of my colleagues, to learn from their experiences, to maybe gain some information of issues we’ll still have, after proving the disinfection potential, to introduce two of my co-workers and to have some fun.

Regards, Jim

++++++++
We have started a new thread, it was getting a bit long. The new thread starts here:
forum.susana.org/forum/categories/105-hi...l-report-and-results