Windmill-driven ATADS

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Re: Windmill-driven ATADS

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. :cheer:
Yours
Christoph
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Re: Windmill-driven ATADS

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
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Re: Windmill-driven ATADS

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.
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Re: Windmill-driven ATADS

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
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Re: Windmill-driven ATADS

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.
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Re: Windmill-driven ATADS

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
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Re: Windmill-driven ATADS

blackburn wrote: 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.)


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?
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Re: Windmill-driven ATADS

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 CCOD 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.
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Re: Windmill-driven ATADS

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? :woohoo:
Lots of questions

Yours Christoph
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Re: Windmill-driven ATADS

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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

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Re: Windmill-driven ATADS

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
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Re: Faecal sludge Windmill-driven ATADS

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
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