[ONeil]

Alcohol is a waste product of yeast based fermentation. Carbon dioxide is the other waste by-product of the yeast induced fermentation. Yeast eats sugar.

Alcohol is a pretty wicked waste product to produce. Important notice! Forget about drinking any of the experimental fermentations! If you want to drink the stuff go to a wine and beer store and pick up what you need. Some alcohol can blind and kill you, if you can't tell the difference don't mess around! Experiment feeding yeast sugar and food scraps.

Fermentation produces heat. This is good for a couple of reasons. First yeast metabolism increases with temperature. Second, a room of 50L bottles fermenting could help heat a well insulated home.

Alcohol can be burned. It can be used for cooking, heating, lighting and hot water. Just be realistic about how much alcohol you can get from this one fermentation process.

Carbon dioxide sounds bad as a waste product. I think of the carbon dioxide as a feedstock material for bio diesel projects. I have not heard of any successful algae to bio diesel implementations but there are other carbon recycling concepts that would also benefit from the yeast created carbon dioxide.

Alcohol can also be used for refrigeration through evaporation. If you had a large enclosed evaporation chamber coupled with an alcohol compressor you could make some serious cold and keep your alcohol for another winter blast, another day.

The state of the art for these concepts is really pretty bad. I would say pre hydro carbon man could do this stuff better that I can at this point in time, even with all my advanced technology.

[Devil]

I quote this from another thread on the grounds that this method provides economy of scale (ie higher efficiency):

A number of cities in Switzerland and Austria already have purpose-built incinerators for household garbage. The heat from these is used to produce steam for electricity generation. The effluent is scrubbed and electrostatically precipitated and has almost no environmental impact. In addition, in Lausanne, the waste heat is used to provide heating and hot water for the Cantonal (teaching) hospital and some nearby apartment blocks. Landfill waste is reduced to ~10-15% of the volume required for the waste without incineration. The electricity generated is sufficient to supply nearly 10% of the consumption of the catchment area. The last figure I heard for Switzerland alone was a total capacity of over 230 MW, which is not negligible. There is no intermediate gasification.

To take this in context, it should be said that all household rubbish is carefully sorted before collection and the "fuel" is mostly food waste and dirty packing, unsuitable for recycling. A description of this may be found at http://www.cypenv.org/Files/waste.htm (see 2nd photo and text under it).

[ONeil]

I reviewed the link. There was not much in the way of detail.

I'm not an expert here, but, I think the two processes could coexist. Ferment the kitchen waste first (converting the sugar to alcohol, distilling the alcohol) then sending the left overs for incineration. Their incineration scheme must have a process for drying out the combustible material before incineration.

The advantage of this fermentation process is the simplicity. None of the materials required are high tech. It could be implemented in the first world as easily as it could be in the third world. The process can be implemented on an individual basis or scaled up to a neighborhood with relative ease.

Incineration provides immediate heat. Fermentation provides an energy source that can be stored, sold and used for many purposes.

[Devil]

The chemical energy in a given tonne of kitchen waste is n joules, no matter how it is used. To allow it to ferment to produce alcohol(s) which are then extracted, will lower the available energy in the residues by the same amount of energy as is contained in the alcohol, provided that the fermentation/extraction process is 100% efficient.

Unfortunately, most yeasts will not proliferate in liquors containg more than about 14% alcohols. This means that for every kg of alcohol produced, you must have at least 86% water or ~7 kg. So how does one separate the alcohol from the water? Distillation will produce an alcohol/water azeotrope, which is OK as a fuel, by itself, but not mixed with hydrophobic hydrocarbon fuels. The crunch lies in the fact that distilling off the azeotrope requires a large amount of thermal energy, so the process becomes much less than 100% efficient. IOW, you will lose as much energy as you are ever likely to gain from the alcohol AND the residue combined.

Sorry, but the direct incineration is much more energy-efficient.

[ONeil]

Hey Devil,

ok, for now I will simply accept as fact your statements with regards to the efficiency. It looks like you know what you are talking about and to be honest, I'm a really wasteful person. In fact I am terribly wasteful and unapologetic about it as well.

Efficiency is not the primary goal here. The primary goal is useful energy created or transformed (whatever term is appropriate) with low technology and limited knowledge required.

A process like this can be implemented in a third world slum. Could the incineration process in the link you provided be implemented by slum dwellers?

A process like this can be implemented by someone on a homestead in the boonies. A high tech incineration scheme may be nice, but would the heat generated by the incineration always be useful? The alcohol on the other hand can be stored and used on demand. The left over sludge (following the distillation process) can be composed. The energy required to distill can be acquired by burning wood.

Again, who cares about efficiency, I care about quality of life. If that means I use far more energy than is required to accomplish a thing, so be it.

Now one other objective in this is to keep environmental damage to a minimum. There are no toxic substances released in this process (that I know of) and the waste from these processes can be recycled.

Cheers,

[Devil]

If you think that efficiency doesn't matter, so be it. I happen to believe that poor efficiency = waste of God-given resources. And not all "slums" (or homesteads) have a lot of wood available for distillation fuel. In crude systems such as you describe, you would, in any case, get more energy from burning the wood usefully than you would ever get from the alcohol produced, unless the "slum" had a very sophisticated still with a chilled condenser.

As for composting the residues, as much of the energy has been removed, the energy for soil conditioning is also sadly reduced, so the compost would be far less than if you composted the kitchen waste in the first place and captured the resultant methane.

I'm sorry, I'm not a believer in your idea.