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Making ethanol from waste

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January 28, 2010, 04:44 PM
Making ethanol from waste
Hi guys,
I know that fruit/veg/plants are rich in carbohydrate and fibre and they are made of cellulose which is essentially a glucose polymer. I was looking for a way to unleach these glucose monomers to fuel the reaction to make ethanol.

My question is, what would be the cheapest method of hydrolysing these starches/carbs?

i could either do it enzymatically or i could use acid hydrolysis.
if i was to use the latter, which would be the cheapest acid to use? ie. hydrochloric, sulphuric, vinegar.

what sort of pH should i be hydrolysing at?

I also wanted to know if i could use waste paper and cardboard, would this be possible? i would assume so seing as they are made from trees (cellulose).

My idea was to shove my fruit/plants/paper into a food processor or blender and then soak the mush in an acid bath.

After the carbs have been hydrolysed what would be the cheapest alkaline substance to neutralise the acid so that the glucose can be converted into ethanol by yeast?

any ideas will be much appreciated
Thanks in advance,
January 28, 2010, 09:48 PM
Tim c cook
From my reading, and other folks testing, (search the forum and archive for "ethanol", there are several discussions) it appears that it is BARELY cost effective to make ethanol from even a source that is a direct sugar, if processing from a starch the extra cost of the enzyme and added heating steps only make it practical with some sort of cost substities. If using celulose as the feedstock it is basically a huge looser, there are millions of dollars being granted to universities trying to develop some enzyme procees but I have not read of any breakthroughs yet. Cellulose is at least a 5-6 primary step process - Convert the cellulose to a shorter chained starch, Use enzyme to turn the starch into even shorter chained sugar that IS NOT fermentable, then more enzyme to convert these into even shorter chained fermentable sugars, then ferment using yeast, then distill.

You can do the acid process but it only converts a few percent of the cellulose into starch that you then have to correct the PH of and reprocess using enzymes, then more enzymes to convert to the correct sugar, then more heat for the distillation. NOT Practical, even processing corn my calculations showed it would cost around $2.50 per gallon of ethanol to produce, this was with $2.50/bushel corn and did not take the cost of the fuel for heating into account. Good luck, let us know if you find anything interesting.

Do a general web search for "cellulosic ethanol" or some such terms, there is a ton of info.
January 29, 2010, 06:10 AM
Thanks for the comments Tim C Cook.

can i just first of all mention that i have no intention of using this ethnaol for biodiese purposes.

as far as the cost of making the ethanol is concerned:

My calculations have shown that using plain flour which has a 68% starch content,
(assuming that i am able to fully hydrolyse the starch into glucose) 1kg of plain flour would produce a theoretical yield of 425ml.

and the cost of 1kg plain flour at my local shop is £0.29

working out at £0.68 per litre of ethanol.
and this is without sourcing a cheaper source of flour.

This is assuming all of the starch is hydrolysed although i dont think this is a very difficult task.

I remember an experiment we did at college. dilute hydrochloric acid was able to almost fully hydrolyse starch within 15 minutes at 100 degrees celcius.

that was within 15 minutes whereas i am willing to leave my starchy feedstock in an acid bath for days! surely that should hydrolyse the starch? (admittedly this won't be at 100 degrees celcius but it will be heated with solar power in a black drum out in the sun)

This is all very theoretical of course, what do you think?

i am actually pretty dissapointed in yeast as an organism, can it not process starch? or simple disacharides? does it have to be glucose monomers? what about fuctose/maltose/ribose?

As for the acid, what would be the cheapest, strongest acid to use?

Thanks again,
January 29, 2010, 04:15 PM
Tim c cook
I don't have a clue about "hydrolyzing" a starch directly into sugar, I will have to read up on the process but I dought it is that simple or the indistrial ethanol guys would be using it rather than fermentation using yeasts. Yeast needs simple sugers, just which sugar depends on the strain of yeast but the more exotic the yeast strain the more expensive it is so the cheapest yeat to use is simple bakers yeast, these require sucrose in a somewhat week solution to get a reasonable conversion yield without killing the yeast due to alcohol poisening (Wikipedia about yeast).

The enzyme A-amalayse does the first conversion from starch to long sugars, B-amalayse does the second conversion from long to short fermentable sugar. I dought processed flour or day old bread would still contains adequate enzyme but these enzymes are available in grain so you can do a "mash" with the ground grain and get a lower than possible yield of sugar from the grain starch but it will take a day or two to process, using added enzymes will do both steps in a few minutes with a high conversion but you also need to heat the process and somewhat control the temperature. Bulk amalayse enzyme is available at a reasonable cost but still increases the cost. Web search - Mashing - beer brewing etc, tons of info. This links to a past discussion posted by "imakebiodiesel" who indicates that he is successfully processing 40 gallon batches of day-old bread and whey using amalayse.

This links to one past discussion concerning ethanol.

This links to another one.
January 30, 2010, 09:21 AM
Hi Tim, long time no speak. I have to agree with you the production of ethanol on a small scale is barely economic. By my calculations if I was paid to collect the cheese whey and the waste bread and was able to sell the distillers grains I would just about be able to make ethanol at the price of buying it from a commercial supplier.
January 30, 2010, 10:11 AM
The traditional source for amylase enzyme is malted Barley. It has enough excess to convert additional starches to sugars, so it's added to corn mash and the like. Presumably it would work on bread, too.

My favorite book on small-scale homebrewing ethanol is David Blume's "Alcohol can be a gas". I built a packed-column still using 3-inch automotive tailpipe stock instead of more expensive copper. It worked surprisingly well. I'm using a modified version of my "bird waterer" to boil the mash.

January 30, 2010, 12:41 PM
Traditional malted barley contains both a and b amylase enzymes so it will convert starch into short chain sugars. It is a hassle to make and can be variable in quality so I opted for synthetic enzymes which are very fast and consistent but do add to the cost.
I did a series of experimental 20litre batches with different quantities of whey, bread, yeast types etc and the best I could manage was just under 2 litres of pure 100% ethanol using a reflux still and molecular sieve. I considered scaling up to a batch size of 500 litres which would have yeilded nearly 100 litres of fuel per week. The problem was that it would have involved 8 to 12 hours labour to process that much and if you do the maths that just does not make sense. I can buy 100 litres of gasoline with what I earn in 4 hours at my day job.
The only way that I could see to alter those figures was to charge for collection of the whey and waste bread and also sell the by product distillers grains. This could be done but I wasnt prepared to commit that much time and capitol into a project that would be only barely profitable.
I hate to sound so negative on this subject and would be only too pleased if someone would find a way of doing it better or for less cost. I would be glad to share my experiments with any one who wants to have a go.
I think it was Tim who suggested another way of producing ethanol at a lower cost. If bars could be persuaded to collect all of their unfinished drinks, slops, into drums which could be collected each week you would have a source of ethanol without all of the hassle of mashs enzymes and fermentation.
January 31, 2010, 05:16 PM
Hey guys,
thanks for the comments.

hydrolysing or hydrolysis basically means breaking dow starch or other sugar polymers into single glucose sugar units.

you can either hydrolyse using enzymes or by using acid.

I forfeited the idea of using enzymes as it would add to cost but i didn't know how much.
can anybody give me an indication as to how much it would cost to use industrial enzymes and where i can get them?
as for enzymes within barley, are these effective at all? how much barley would i have to add per kg of feedstock? how long would i be expected to wait for my starch to be hydrolysed into sugar? what is the optimum ph and temperature for these enzymes?

what do you think about my idea of leaving my feedstock in an acid bath of vingar out in the sun (for heat) for several days?
as i mentioned earlier with reference to my experimetns at college
almost full hydrolyses of starch had occured within 15 minutes at near boiling temperature with weak acid.

I was away for the weekend and left a small experiment running. i basically soaked a piece of paper (1cm x 1cm) in a container full of vinegar and would see how much the paper would shrink over the weekend. Shrinkage would indicate that hydrolyses has occured and the mono/di sugars would become dissolved in the vinegar.
Unfortunately my neice spilled everything and the piece of paper was lost!
i'm re-running the paper experiment alongside some plain flour in vinegar.
flour is FULL of starch and starch is insoluble. it has therefore made a very cludy solution. the rate of clearing up of the cloudy solution will represent the rate of hydrolysis as the starch is being broken down.

i'll let you guys know the result of the experiment.

at the same time of course i would appreciate some info on malted barley/commercial enzymes.

@imakebiodiesel - i would love to see the results from some of your experiments if you dont mind.

Thanks again for the help,
January 31, 2010, 05:33 PM
Tim c cook
This links to a 9 chapter Mother Earth News magazine manual about making alcahol fuel, it will answer a lot of your questions.

This links to a Mother Earth alcohol fuel "cookbook".

This links to brewing discussion about "mashing".

Enzyme info and sources - HERE, HERE, HERE, HERE , HERE, HERE, HERE, HERE, HERE, on-n-on. You can do these general web searches yourself and find more current info.
February 03, 2010, 04:58 PM
Mubs. I would reccommend you have a look at a forum called . You will find the answers you are looking for there.
I posted my experimental results there under ethanol fuel. Those guys have a wealth of experience with every kind of alcohol distillation.
February 06, 2010, 12:25 PM
Thanks for the advice and links guys.
I'll check all of the above out and let you know how i got on.