Solar Cities IBC open source methane digester improvements?

Hello group,

 background:  My name is Mike Kendall.  Living in Philippines with my wife of almost 20 years and our 8 year old triplets (2 girls and 1 boy).  We have a bit over 1/2 hectare (around 6700 square meters).  We have a crazy amount of solar capability divided up into a non critical and a critical panel.  Non critical was designed to support a sewing production line with planned need of 11kw continuous.  After years of work, around 250 plus panels, super capacitor banks to add to battery bank and four series/parallel inverters to support the myriad of charge controllers our only real energy needs are in the evening when we depend on the grid.  Besides starting a hand woven denim (maong in local language) that obviously does not need solar panels and jeans fabrication biz that does we are also starting a working dog (EDD), protection dog business on the property.  We are teaming with locals that are already experts in the field to get things in proportion.  I'm good at electronics but zero experience with biogas.  There are lots of piggeries locally and most dump in the ditch.  Few responsible with resources will build methane digesters but they typically use concrete structures and do not scrub the gas.  They run it into surplus small car engines with crude valves and change the oil every 250 hours until the engine finally gasps it's last breath using the power to run fans mostly.  With the dog biz we are in the process of designing and building kennels.  These kennels will meet standards already outlined by other organizations but luckily I am not going to have to dig another septic system and instead may be able to opt for a methane digester.  Ran across plans from solar cities for the IBC container digester.  Looks great but from watching some vid's it seems that a mixer will give a higher yield?  Also, it appears that the uniseals are a really cool and simple idea but the opening at the top is so tiny that maintenance could be an issue if one really wants to get in quick and get to the bottom of things so to speak.  My first thought is to cut out a much larger opening and use some epoxy and fiberglass then cut off top of a large pool chlorine bucket and epoxy it in place.  Seal may be an issue?  I like the IBC because it is so much more durable than a poly bag and less space.  IBC's are available used out of Manila sub 100 dollars.  We do allot of stainless welding/fabricating here so a mixer should be easy enough to make if warranted and I'm asking for advice and help regarding how to make the item more reliable, easier to maintain, and more productive.  Lastly, I saw a vid out of Australia.  This gent in Australia used more than one container.  He had a large container with a floating smaller container.  When the smaller container started to fill up it then floated higher.  Purpose was to run the gas through water to scrub it.  The video had comments about it being the cleanest flame they'd seen with biogas but user updated a comment about the flame burping to the point of self extinguishing and the discovered cause was moisture in the gas.  Somehow he removed it and problem gone but left lots of questions for me.  I've read there will be a moisture content irregardless.  Nowhere I can find does anyone discuss if the water must be cycled and how much/often.  One online document discussed purity verse flow rate for the water scrubber so I'm assuming there is a connection.  Yet another document had 80 percent biogas mixed with 20 percent propane to get a reliable source of energy for a small 1 cylinder generator.  This could be a good solution for the water content and reliable/good fuel source for me as LPG containers are less than gasoline here and then I could provide evening electricity off the grid or supplement power during heavy rain when solar drops and not relying on a diesel generator.  The videos on the solar cities unit have bags that are suspended to store the gas which is cool because they could be moved to a different location to use the gas.  This would be my choice for the 3rd container with a big fat question mark on a 2nd/mid container for scrubbing and how much it'd really be needed.  Yet one more doc talked about taking shavings from a lathe at a machine shop then annealing and compacting to make a scrubber tube but again does not talk about how one could tell if it needs (if ever) to be changed out and why would one need to anneal metal scraps??  Annealing (done properly) is a long process in an oven with tightly controlled temperature curves.  It just seems they leave allot of black magic in this where they could instead expound and help one who is a beginner not have to re-invent the wheel and learn through mistakes all over again.  I would think open source could address these issues a bit better even if it meant links to more complicated descriptions instead of needing to just push the "i believe button" which I've never been all that good at.  Best regards, Mike and Glenn (and triplets) Kendall

OK,  Nobody replied but I see it has been read 32 times.  I looked at the Kindle e-book store and found one that is available both soft cover and e-book called "Biogas For Beginners" by George Eccleston.  It is answering many of my questions (if not all) such as the steel wool (or scrap metal shavings) being depleted over time as the rusted metal is consumed through the chemical reaction with the sulphur dioxide, the water scrubber converting the CO2, different types (including the solar cities IBC) etc.  It looks like I'll be able to do it on my own without anyone's help.

Hi Mike, two possible reasons for no responses yet.  First, it's only been a day and sometimes it takes a few days for people to see topics that are less mainstream like digester plans.  Second, your long paragraph was kind of hard to read so I didn't get through it myself.  Maybe I'm just lazy...  If you could reply with what your actual questions and/or thoughts are it could make it easier for people to answer you.  Perhaps split apart in separate paragraphs or bullet points.

If you do build a digester, we'd love to see how it goes.  Updates and pictures are lovely.

Hi,  Thanks for the reply.  First I was looking for improvements in the IBC/Solar Cities design and mostly if I should add a mixer or not (or maybe even pre mix and methods for doing it) and also just as important should I modify the top for a large easy access lid or if that is needed for maintenance.  I've read about maintenance on these digesters and if I need a large access hole at the top is a big question for me that is not included in the IBC design.  Example we have surplus of solar here and I could buy a cheap blender (yes that must sound really gross to have a cheap dedicated blender...making sure the top does not fly off) or if I should even just use a paddle and a mixing bucket.  Reading about it the design appears to be for developing countries and people with little to no tools (example the video shows how to heat a pipe to punch a hole if no drill and hole saw is available).  I ran into same purchasing plans for the "Flying-8" countermarche hand loom out of Germany in that it was designed mostly for people in Ethiopia it seems (before the Chinese built 20 industrial parks there taking advantage of 25 USD/month labor and the fact that the government there will do anything for a dollar with the Chinese out of desperation) and someone with little to very little hand tools.  What I found out is that the design was lacking in not only functionality/size (not deep enough) but also in many other ways.  My immediate assumption is that the IBC container design in it's exact form will give less methane output than improved designs that are slightly more complicated.  Second I was frustrated in the lack of information in regards to methods for scrubbing not only in the IBC design but others I found freely documented on the internet.  For example nobody gave a simple description of how often water needs to be changed when co2 scrubbing or metal shavings when sulphur dioxide scrubbing (apparently I now have read that it gets 'eaten" by the chemical process and when there is less one knows to add more metal shavings or steel wool simple as that).  

  Lastly, the long description was to describe our temperate zone (Philippines) and that there is going to be primarily dog poo as the food source for the wee little beasties working away in the digester but also that I have excess electricity available via PV's in the day if that assists and that my primary desire is to run a generator for evening electricity.  We use cheap induction coils in the day and are also working on a solar collector cooker that is large so no daytime need for the methane and likely little to no evening.  This is why I talked about the potential of mixing low cost and easily available LPG at lets say 20 percent with the methane digester product if it is necessary or not into the genset.  I have since found another article that talked about pure dog poo called "P" compared to "P" mixed with grass shavings "PG" and "P" mixed with cow dung "PC" and yield studies.  Apparently both "PG" and "PC" (best yield) are an improvement.  We can easily mix grass shavings for example.  

 To summarize it I have zero biogas experience, it appears not to be rocket science and mostly a case of just working for the product and overcoming any mental/nose blocks in doing that, and much simpler than the concrete dome (China style) that folks are using here.  They also use the plastic bags but those are going to be prone to real nightmares when there is a hole in them.....kind of like finding a hole in one's water bed mattress but much smellier.

Best regards,
Mike

Hopefully someone with real biogas experience will chime in here.  I've watched some videos on youtube to see what the fuss is all about.  But I don't actually know anything about the process yet.  

What maintenance would there need to be in an IBC tote?  I'm assuming every few years the sludge might need to be removed but I'd think it could be drained out through the bottom valve as more water is added.  Or pressure washed from the small top port.

I'm also curious about the plastic bags and how to properly store the gas.  And then delivering it cleanly to an appliance.

Hi Mike,  I am diligently reading the book now and will be finished soon.  These IBC containers can be had for a reasonable amount of money so I like them from the get go.  Online here they are sub 100 USD and I read same in USA approximately.  I like the metal cage around them and the ability to move with a pallet jack or fork lift.  You have a good point that experience can only tell if they are suitable for maintenance.  The Mrs. and I were joking around.  She asked me please if I get a blender not to blend the poo in the house!  Of course not.  Then she said if someone sees me doing it on an extension cord outside they may gossip I am crazy.  The cheap blenders are exactly that....low cost and a good blend of the poo and grass along with food scraps sounds like the right recipe just make sure the top does not come off or accidentally turned on while top is off.  I have burnt out high end blenders making peanut butter so know my limits there.  This book is really worth the $9.99 and feel that I chose right to buy one that is also available in soft cover.  Not complicated but good at explaining all the details to newbies and I'm able to read it off the cloud reader no prob's.  I'm on travel for a while as of tomorrow to the Middle East for 2 days but will work on it upon return.  Typically I have 3 to 7 workers around here (it is insane how low labor is and over paying them is still insanely low).  I would have thought (but then again I have zero experience in permaculture also) that the digesters would have been an integral part of the permies cycle but then again maybe in just some cases?  The other option of digging another septic tank was completely out of the question.  I'm excited to run a genset off it.  A little bit of digressing here but there is an online mag called "low tech magazine" that has a real cool article on gas bag vehicles I read some time back.  They had gas bag busses in one city in China until the 90's and used to use them in Europe during the war.  Link below.  We have an e-trike that uses li-ion batteries mfg. here in the Philippines from domestic and overseas parts.  I sure would like to extend the range on it.  Mazda this upcoming year is coming out with a redesigned wankel engine that pretty much reverses the theory of a peanut shape inside of a housing to the housing becoming the peanut shape.  DARPA has funded a US company that is making micro engines similar in robots and UAV's and Mazda is now jumping on board with a similar suit case sized "range extender" that will actually meet emissions.  I've considered putting a small 1kw generator  on a hitch type mount on the back and if I can figure out how to use a gas bag may just try it and let others wonder/ask lots of questions and gossip about the Cano (local dielect for Americano).  This e-trike is a philippine equivalent to a Ferarri as they use allot of trikes here and an electric one that is fully enclosed is like a sports car to many.  https://www.lowtechmagazine.com/2011/11/gas-bag-vehicles.html  Best regards,
Mike
edited comment:  my typical range on the e-trike is not excessive but when I go into the city it can become a 30km round trip.  All said what I really want is evening electric production most.

Hello Mike,

Sorry I missed your post.  I am in the RP.  We have had an Solar Cities style IBC digester for about a year now.  When I first ran into the topic of A.D. I was extremely excited.  Now after a year of operation not so much.  Don't get me wrong.  Its a wonderful improvement to an old technology.  But its limitations are not stressed enough.  And that can cause disappointment.

Let me say that we are retired in the bario-tek Luzon provinces so decent materials are scarce,  but here is the straight skinny as I see it.

1.)  Under ideal conditions, (temp / feed-stock) the IBC digester will produce about 1 cbm of bio-gas in a 24 hour period.  That equates to 2.5 hours of MEDIUM FLAME - MEDIUM BURNER SIZE in a 24 hour period.  For us cooking Rice / Tilapia / Pork / Gulay for a family of 6 it is ALMOST enough to cook lunch.

An important issue to consider is E.R.O.E.I.  Energy returned on energy invested.   In order to get cooking gas you have to process feedstock.  That takes time / labor / energy.  There is always reluctance to handle "nasty stuff".   At the 1 cbm scale for gaseous fuel it is a toss up as to usefulness / economy.


2.)  We feed 20 liters of 1:1 ground scraps / water mixture.  About 10 -> 15 kgs of solids depending on what your scraps are.  We have a 1hp Insinkerator plumbed in direct to the feed pipe so we feed a wider range of kitchen scraps that those without a grinder could.  

I am very pleased with the Insinkerator.  We managed to get a few units cheaply off of Ebay.  And shipped them here in a B.B.  Bear in mind the Insinkerator is only available in 120vac configuration.  We have a largish active tracking off grid solar array.  So it is not so much of an issue for us.  But for smaller installs the motor inrush current will trip your inverter offline.

When we do not have enough kitchen scraps we make up the difference with Baka / Kambing / Coneho / Patu manure.  Not sure how much mileage you could get from Tae ng Aso.  My guess is that it would not be much.  Getting quality feedstock is not really much of a problem here.  The local wet market is happy to provide all the waste we want.  But you have to sort the plastic out of it before you can grind or feed.

We have tried to utilize grasses and other cellulose / lignin heavy items as feed stock.  They produce a lot of gas but the plant structure does not digest easily.  Eventually it fills up the digester and you have to do a manual clean out.

I am currently using a method of extracting the digester useful portion of nutrients from finely shredded grass.  An Indian professor named P. Sankar Ganesh did his doctoral thesis on extracting volatile fatty acids from water hyacinth.  I bastardized his methods to fit our flora and so far it seems to be working out.  Search for his name and  you will find his paper on line.

3.)  The current design issues with the Solar Cities style IBC digester are thus.

a.  The feed / gas / effluent plumbing is through the top of the IBC.  This makes it pretty easy to seal the digester ........ but ..... now the digester is "pressed up" with digestate.  And the floating scum causes lots of plugging up issues.

My solution to this was to fabricate a manual scum breaking armature that mounts to the IBC lid.  You can find my build plans in the Solar Cities "Methanogens" FB group.  Or I can send it to you direct given your contact info.

A better solution is to plumb the effluent out into the side of the IBC at the appropriate height so that the IBC never fills completely.  This will lower your digestate capacity by a few percent.  But believe me the loss is far better than the hassle of dealing with scum obstructions.

b.  The 2" plumbing is fine for the feed inlet.  Not large enough for the effluent out.  The hot weather causes the digestate in the out tube to dry a little and that forms a plug that backs up the system.  A 3" output is better.

c.  IBC's are fabricated out of HDPE plastic.  Nothing bonds to it.  Not glue / epoxy /  Vulca-seal.  Don't waste your money.  The only good seals I have are mechanical compression or plastic welded.  I have searched high and low and have never found a source for Uni-seals here.  If you find one please let me know.  Without Uni-seals you will have to fabricate your own bulkhead fittings of the appropriate diameter.   I tried a lot of different things with a lot of failures until I finally settled on plastic welding my own custom fittings using a jig-saw and soldering iron.

d.  We had a very hard time getting gas storage bags.  The stuff that is readily available is VERY poor quality.  Shipping stuff in is too expensive.  In the end I ended up welding my own gas bags out of the clear PVC plastic that is commonly used for Tricycle windows.  Use a little PVC glue / low heat clothes iron / parchment baking paper.


Now having trashed small scale anaerobic digestion I will talk about its good parts.

1.)  Effluent.  Magnificent fertilizer.  We use it in various dilutions for various tasks.  I have built several air-lift pump aero-ponic grow towers and produced a lot of pechay / bok - pak choi / leaf cabbage / lettuce on effluent, water, and air alone.  The main problem with above ground grow towers here is the heat.  I've boiled a lot of seedlings.

As an applied to soil fertilizer it is even better.   So much so that I no longer view the digester as an gaseous energy producer.  It is a fertilizer factory.  We add powdered minerals at feeding time and get what appears to be a more balanced product.   Viewed in this light it is a very good solution for Aso waste.

2.)  The "empty" shredded grass byproduct of the above VFA method is an excellent grow medium.  Especially for mushrooms.  We use it all over our place, with effluent as a fertilizer, with VERY good results.


So there is my data dump.  Good luck.

Mike, I am not an engineer so I can't help with the technical questions unfortunately. What I can help you is from ten years' experience running a small (6 cubic metre) fibreglass ready made model (Agama Biogas Pro) as well as some professional experience researching the human/technology interface of biogas here in South Africa. Your concept is absolutely spot on and actually the one I am recommending to our local City Council. Solar during the day and biogas during evening peak is an excellent solution in theory, although as you can see the nuts and bolts can be complex.

1. Brown and green waste mixed will produce approximately three times as much gas as brown alone.  You do not necessarily require a mixer as long as you remember to add both, in the heat of the Phillippines you will get quite satisfactory production even if you don't finely shred your greens. I guess you would have to work out how much energy you earn by mixing. With plentiful solar power during the day this may not be an issue but don't forget the human energy it will take to run a mixer.

2. Keeping the Ph level correct is the key to good production. Add a cupful of lime or a bucket of potashes now and then to keep digestion up to speed, and this will prove to be more beneficial than mixing. Both together of course will give you optimal production, but in practice where there is plentiful brown and greens you will find that you do not need to worry too much about decomposition rates.

3. With dog poo I have not seen any studies showing whether the pathogens are killed by the anaerobic process but studies definitely show that human germs are. To be on the safe side do not use your effluent for things like annual vegetables but rather trees where the effluent never touches the fruit. Or harvestable crops like vetiver or bamboo.

4. You should absolutely aim to find a use for the effluent. I too find that the value of the fertilizer exceeds the value of the gas at least by a factor of three. If nothing else you can use the effluent to grow an energy crop nearby, like comfrey or alfalfa. The latter you shall have to shred because the stems take long to decompose. Water hyacinth is great if you can make a pond, and with an overflow pond you get to use your fertilizer twice.

5. Be sure to add Bacillus Thurungensis, neem oil or bokashi to your overflow catchment, mosquitoes like to breed in it and this forms one of the biggest objections to biogas uptake in many countries. Easily solved but a factor one needs to be aware of.

6. When you build, build BIG. Not enough gas is one of the most common complaints amongst biogas users.  One big one is better than three small ones because it digests better and does not fill up as quickly. When I build again I will at least triple the size, and if I can get above 25 cubic metres I will be happy.

7. The most popular model is the Nepalese GC20, you can find plans online and on Youtube. Like I said I can't be very helpful on the technical details but to me popularity means something about how user-friendly a design is. The great virtue of building it yourself is that you will know how to maintain it, and again maintenance is an issue which often makes people cease using the technology. Also this is a very durable model which will last for decades.

I think maybe the reason people are slow to respond is because your post appears in the growies forum.  If it could be moved to the energy forum there are plenty capable people there who could maybe assist.

Best wishes and I look forward to hearing how it goes.

I don't know about scrubbing but here is my understanding.  Methane from the generator is made up of methane, carbon dioxide, ammonia, various sulfur compounds including hydrogen sulfide and sulfur dioxide, a bit of free hydrogen, a bit of air short on oxygen.  By bubbling the mix thru clean water the carbon dioxide chemically combines with water to form carbonic acid,  the ammonia dissolves in the water, the hydrogen also bonds with the water making things slightly acidic.  There again some of the sulfur compounds will end up in the water as sulfuric acid.  Notice a theme here?  With the exception of the ammonia which will tend to make the solution basic all the others will tend to make the scrubber water acidic.  So my guess is you can track water replacement need based on pH.  Simply pick a fairly a slightly acid pH point like 5 or 6 and use the scrubber water on acid loving plants while replacing it to maintain the pH.

As for removing the moisture from the methane before the easiest would be to simply raise the pressure seriously in a storage tank and drain the water off the bottom.  Otherwise some sort of condensation system before burning would be the ideal.  The problem is in a warm environment condensations systems are difficult to achieve without refrigeration and pressure systems are complex, expensive and require outside energy.  And the whole goal of a tote type system is its simplicity.

Mark Cunningham wrote:

We have tried to utilize grasses and other cellulose / lignin heavy items as feed stock.  They produce a lot of gas but the plant structure does not digest easily.  Eventually it fills up the digester and you have to do a manual clean out.

I am currently using a method of extracting the digester useful portion of nutrients from finely shredded grass.  An Indian professor named P. Sankar Ganesh did his doctoral thesis on extracting volatile fatty acids from water hyacinth.  I bastardized his methods to fit our flora and so far it seems to be working out.  Search for his name and  you will find his paper on line.

The pdf at Biochemical Engineering Journal says that the Volatile Fatty Acids (VFA) are extracted in 24 hours from finely chopped weeds kept in a dilute acid (cow dung slurry) "so maintained that the system does not become anaerobic." The liquid is then fed to the digester and the left over fibrous content is composted separately. This process proved to boost gas production by 22% compared to "cow-dung slurry alone".

Hi Mike,

TH Culhane shared a link to the SolarCities Facebook group ( https://www.facebook.com/groups/methanogens/?ref=group_header ) .  I was unaware of this thread, but have had a lot going on, both personally and with the goat farm I live on, in the intervening time, since your initial post.

I am currently in the process of working out a timeline to construct 3 of the Puxin 10 Cubic Meter ADs with a site manager.  Those 3 will be in series for a combination of reasons:
1) Increased total Hydraulic Retention Time (HRT)
2) Increased total quantity of biogas
3) To explore the potential to naturally upgrade Biogas to Renewable Natural Gas standards (pipeline injectable grade).

So, to simplify that, Input 'A' gives Biogas 'B' from #1, about 1/2 'B' from #2, about 1/4 'B' from #3.  So, 1.75 x 'B' biogas available, due to triple the HRT from 1 'A' input.

Biogas has roughly 50% of the heat value that pipeline grade Natural Gas has.
1.75 x 2 = 3.50  is the total expected heat value, as RNG, compared to a single unit of feedstock 'A', by only FEEDING 'A', by providing a longer (3x)HRT AND some additional MECHANICAL steps.

The final effluent will have a much lower BOD/COD (Biological/Chemical Oxygen Demand), so, it is more environmentally friendly.

Even if the RNG system fails to fully achieve the expected upgrade, the simple increase in quantity of biogas can be worth the increased system complexity and the RNG upgrading can be readily eliminated.

In addition, my methodology eliminates compressors, by utilizing much simpler pumps for liquid circulation.

Jeffrey L. Frusha
Head of R&D
LoneStar BioGas
1411 Gravel Pit Road
Seguin, Texas 78155

lonestarbiogas.org