Could this work??

af_thefragile

I thought of this idea.
Cows and sheep eat loads of grass everyday and they're able to get energy from the grass cuz they've got anaerobic bacteria in their bodies that can break down cellulose into sugars (and methane i think, which is why i believe cows fart methane).
Termites also have bacteria in their gut that breaks down cellulose into sugars so they can eat wood and live on it.

Now every time i mow my lawn, there's at least 5 kilos of chopped grass that i throw away.

Which brings me to an idea. That if i could use this waste grass and put it in a closed container along with some sugary stuff like waste food (to promote the bacteria growth), would it work that the bacteria could grow to break down this grass into sugars and methane. Then i could ferment the sugar to create methanol?

Macha

Isn't that anaerobic digestion?

http://en.wikipedia.org/wiki/Anaerobic_digestion

If so, it definitely works, if not, please explain further, as could be interesting!

dahak

af_thefragile wrote: »

...
Now every time i mow my lawn, there's at least 5 kilos of chopped grass that i throw away.

Which brings me to an idea. That if i could use this waste grass and put it in a closed container along with some sugary stuff like waste food (to promote the bacteria growth), would it work that the bacteria could grow to break down this grass into sugars and methane. Then i could ferment the sugar to create methanol?

Short answer no.
Reasons:

1. O2
2. Temperature
3. Starter culture
4. C:N ratio

Long answer, well that's a little more complicated and really depends on what you want your end product to be.

taconnol is correct in that part of what you are describing resembles anaerobic digestion. Read the Wikepedia article that taconnol linked for more info on anaerobic digestion.

Anaerobic digestion occurs in the absence of O2, the problem with grass is that it is very fluffy when chopped up and will hold lot of O2 between the broken fibres. All anaerobic digesters, to the best of my knowlage (that produce usable methane) occur in a liquid slurry. This removes O2 and helps control temperature and prevent hot spots.

Anaerobic digestion is also usually fairly difficult to get started. Getting the correct bacteria populations in place to produce usable levels of methane can take a lot of nursing. It would be extremely unlikely that you'd get the right populations in place to break down the grass clippings.

The carbon:nitrogen ratio of the material will also effect the gas composition and how far the anaerobic process will progress. Too much nitrogen can poison the process.

The sugars are an intermediary product in the production of methane so you won't any significant amounts in a final liquor.

To be honest I'd say that if you put grass clippings into a sealed container as best you'd get silage but most probably it'd just rot slowly.


If you are interested in producing methanol from organic matter pyorolas would probably be a better method. One of the older names for methanol is wood alcohol.

I presume the methanol would be for something like biodiesel production as it seems to be an unusual end product for anything else. If so getting the methanol 'dry' enough could be a problem along with maybe undesirable by-products of pyorolas.

I hope that helps, sorry if it comes across a wee bit negative.

Ball_of_Sex

A company in Limerick manufactures CHP units that run off organic waste like spent mushroom compost. Its a simple fluidised bed combustion chamber with an exhaust heat exchanger that rises steam for the turbine.

If it burns you can extract energy.

af_thefragile

Cheers for the reply.

I'm just trying to work some very basic and cheap (nothing to lose) set ups trying to utilise worthless trash to harness some/any energy.
Its more like an experiment to see if it'll work or if there could be a way i could make this work.

Regardless of the fuel consumed, i have to mow my lawn every few weeks anyway. So the chopped grass is complete waste to me.
Also there is a lot of organic food wastes produced which i could add to the system to see if it'ld make it any better or worse.

Basically the idea is to get a largeish container and put all the grass in it along with other organic food wastes from the kitchen, add some water and seal the container with one opening to let any gases (hopefully methane) come out from which i could like bubble under water to collect in a bottle or something.

I'ld probably just leave it to rot for a few days/weeks and see if any biochemical process starts to take place in there. As the container is sealed tight, it should help any anaerobic bacteria thrive in the rotting stuff which could hopefully producing the elusive methane.

If that doesn't work atleast i'll know it doesn't work!
So maybe the next step would be to try a different combination of organic matter. Maybe add some cow poo to it which would contain the anaerobic bacteria allowing it to grow and work away in the set up. I could also try finding and adding some termites (or its poo if i can find it) to see if termite bacteria could do a better job.

What i'm trying to achieve is the conditions within a cow's gut where anaerobic bacteria by the production of the certain enzymes breaks down grass and other plant stuff to produce the sugars and methane which could be processed into fuel.

If that doesn't work, then maybe i could just move to try drying and burning the grass directly to produce energy in the form of heat which could run a sterling engine or a boiler or something.



I know its possible to produce sufficiently large quantities of methane from poo. A lot of people do it, its fairly easy.
But I wanna see how easy it'ld be to produce fuel (any methane or ethanol or any combustible substance) out of the other worthless organic waste found around homes like food wastes and plant/grass waste with the input of minimum amounts of energy.

dahak

If you interested producing some methane as hobby or just to see if you can do it then that's great. To be honest though from the amount of organic material that you have to work with and it's type you're not going to get useful amounts of energy out of the system.

Just a quick primer first.
Ruminants (cattle and sheep are in this group) have four 'stomachs'. There isn't a single type of bacteria that operates in their 'stomachs' rather it's a number of different types where the by-products of one become the food source for the next in the chain. In this way cellulose is broken down and bacterial biomass and methane by product is produced. It's the bacterial biomass that is digested by the ruminant. The bacteria synthesise amino and fatty acids that the animal can not get from grazing. Thus by having a very highly regulated natural biodigester, the ruminant has ideal conditions for bacterial growth and symbiotic relationship is in place.
The thing is there is absolutely nothing simple and straight forward about a cows digestive system and doing this in a human controlled system is not straight forward either.
Oh and most of the methane produced by ruminates is burped as all the bacterial action happens in the 'stomachs'.

I'm not sure how terminates interact with their bacteria, all my knowledge comes from the ruminant side. However I'm not aware of any digesters that can take in lignin feedstock directly (I could be wrong on this though). I'd imagine it's a very specialised relationship though and it's very unlikely that by putting terminates in the container will do anything but kill the terminates (they still need O2


Assuming that you will get 0.4 m3 of methane per kg of organic material and that you have 5kg of grass clippings every two weeks, that would give you 2 m3 of biogas (this will be 50-80% methane) This sounds like a good lot but it's really not that much energy (if you have natural gas have a look at your last bill to see how much you use a month).

With just just grass clippings and household organic waste you. Green material on it's own doesn't digest well. Cows do a lot of mechanical action on the grass (chewing their cud, stomach muscles moving the material around and are producing enzymes to aid in the break down). Human organic food waste also tends to have very high levels of fats which will do very bad things to the anaerobic digestion process.

With regards to drying and burning grass, fresh grass has between 15-25% DM (dry matter) this means for every kg of fresh grass 750-850 grams is water. Firewood would have roughly between 10-20% moisture content (80-90% DM). To dry the grass clippings you'd have to lay them in a thin layer for a number of days. You would be basically be making hay on a very small scale, with all the inherent difficulties like the material getting wet etc. Even worse if the clippings are outside they are most likely going to be blown around the place as they dry (has is usually two to three foot long when it's mowed and that can still happen with strong winds)

It probably sounds like I'm being very negative about your project, I'm just trying to make it clear that there's a lot more going on than you might have originally thought.

If you're still interested in doing anaerobic digestion there's some very good internet resources available.
Here is a good introduction to anaerobic digestion (aimed at farmers) and there has been a lot of work done on small scale anaerobic digestion for third world countries. There is widespread use of small scale (though still on a very much bigger basis than what you're talking about) anaerobic digestion as a way to produce cooking gas. This is being pushed especially in areas where shortage of firewood (and deforestation) are becoming problems. It's one of those life changing technologies for the people involved that you hear very little about, I guess that producing gas from faecal matter is just not sexy!

Here is some info on small scale biogas production. Just google diy anaerobic digestion or small scale anaerobic digestion and you'll get lots of hits.

For my money though, composting is the best and most straight forward way of dealing with green waste. Still takes some looking after though, but if done right (and with a bit of luck) you can use it to feed your lawn and cycle the nutrients back from whence they came.

af_thefragile

Cheers mate, thats some really good information there! I'll be checking out all those links now...

What i'm planning to do is first set up a small experimental set up to just see if it works at all and how i could make it work.
If i start getting some good results, i can scale it up so i can have some workable fuel to work with.

I'm also thinking of getting a cheap diesel vehicle to experiment with producing biodiesel and running the car on it. But thats something for the future.

For now just see what I can do with the waste in my house.
I believe if everyone can just harvest their (or if someone can harvest everone's) waste recycling its nutrients or harnessing fuel/energy from it, then it could solve a lot of this world's energy problems and also greatly reduce the environmental impact as we wouldn't be releasing carbon trapped in the ground into the air but instead recycling the carbon already in the air in a closed cycle.

mikep

Hi there

Here is another process that might interest you...

The link is to a company that produces cellulosic ethanol.

http://www.iogen.ca/index.html

zod

https://www.youtube.com/watch?v=Nd3sDFfGH5E