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