It is depend of the selection of microbial strain which produce the duel enzyme mechnisms. and compare to the starch the using of lignocellulosic wastes such as rice straw and sawdust etv is very chief and cost effectve for bioethanol production.

Hi Samani, and welcome to my world! First, the operating cost (opex) to produce ethanol from starch can be lower than from whole raw material, but the cost of refining the starch (minus the value of any co-products) is usually higher than the small additional cost of handling the non-fermentables and the slightly higher enzyme requirement. Starch separation plants can easily cost 50% more (capex) than those that use raw feedstocks.

Next, the enzymes used in first generation ethanol production have been developed and optimized for many years to reduce cost in use, and/or enable reduced water and energy usage. So, I'm puzzled that you say they are so expensive! Some substrates (maize, for example) contain compounds which destabilize some enzymes, but tropical starch sources such as cassava and rice do not, so enzyme dosages will be quite low. In fact, I would expect that both enzymes, if used in a commercial-scale process producing 12-15 volume% ethanol, should only cost $0.01-0.02 USD per liter of anyhydrous ethanol. There is a range which depends on shipping costs, size of order, and your process conditions (the old capex vs. opex trade-off), but I'd be happy to discuss this with you. Let me know the size of plant you are evaluating, the feedstocks, location, and whether you have any current process design biases (I certainly do!) .

On an average if one examines the starting material to be starch, then it is affordable ( I would have reservation on saying it is cheap). However, Starch is not cheap every where on the surface of this earth. It all depends what starch is available in excess in any place. Maize starch though, is affordable in certain place but is very scanty in other places. Potato or tapioca starch is not uniformly available every where in a price which would make the ethanol affordable.. Therefore, it is essential to survey the local region and then decide on the process.

If you are referring to sugar cane juice/ molasses as raw material, the cost of producing ethanol from such materials would definitely be lower than producing ethanol from starch. However, if lignocellulosic biomass, such as plant/ crop residues is used as raw material for ethanol production, the production cost would be much higher than the ethanol production cost from starch.

Using the rice straw and bagasse as lignocellulosic substrate for ethanol production is cheapest source than producing ethanol from strach.

Excellent answers from all the collegues in this intresting post. If though Samani , you could give a bit more details on your raw materials that would be great. If you are using ignocellulosic biomass, such as plant/ crop residues, you would have to consider the mass transfer step and potential pre tretaments to make the material more accesible to enzymes. There are also studies suggesting better ethanol production from less complex carbohydrates it all depends on the culture strains you are gonna use. Plese support the post with more info to get a better answer. The cost though of such a process is clustered into many parts you have first to consider the cost of each process separately, (culture strain, inoculum development, raw materrail treatment, process operation cost , labour) and then calculate the total cost of your process. Often in Chemical Engineering what seems as the obvious easy choise is much more costly.

I agree with the comments above. Bioethanol production is a many-faceted problem and there is a rich literature on the issues and possible solutions. The choice and pretreatment of complex feedstocks into substrate for the final ethanol fermentation is one step and the decisions at that step have important impacts on the fermentation. I wish to add only that residual salts and other characteristics from the feedstock pretreatment can have dramatic effects on the speed and efficiency of the fermentation as can the strategy for ethanol extraction (e.g. continuous or batch). So, while each step needs to be considered in detail, the impact of one on another in the complete process must also be considered in your plans. Good luck!

Hi Thank you very much for all this, sorry for the late reply i just got back into office its just 9am here in the pacific (Samoa). I am a biodiesel person but have been given the role to look into bioethanol.

the reason why i used starch is because its very cheap to make here.. the one i am currently using is starch from cassava.. the starch making is traditional (Samoan Style) just a piece of white clean cloth material and raw cassava freshly taken from the field and about 1 liter of water. chopped it into fine pieces with a knife etc then put those inside the white cloth and then pressed with the liter of water. After take off the the fibers etc and leave the milky liquid to settle over night. in the morning just pour out the water can be reused again if needed then take the white wet starch and leave it in the sun for couple of hours its very good starch. from this process i used 200g/L of this starch with 0.5% v/w (weight of starch) of alpha amylase and then amyloglucosidase it gives me a 90% conversion from starch to glucose but that's after 30 hrs. but was a good initial experiment.

but the thing is when i did the fermentation using a s.cerevisiae strain i used for glycerol cultivation studies, the yeast strain didnt effectively consume the glucose. so i am hoping to either experiment with a brewing yeast, buy another yeast strain or retrain the yeast i used for glycerol cultivation studies to re adapt to glucose???

Hi Larry, yes your going to be very helpful in this hehe... now i am working on lab scale experiments but the big bosses are talking about a small pilot plant between 100L to 500L do you think we can work on such initial levels.

Samani, Boiling and/or acid treatments can also free the sugars from the starch. Both of these have advantages and disadvantages. Unless the boiling is carefully regulated (for temp and time) and the starch is very well mixed, you'll end up with either unreacted starch clumps and/or 'over-cooked' sugars that have carmelized, meaning the yeast won't digest them. Acid treatments (usually hydrochloric acid) work well but the solution will need to be neutralized before fermentations begins and the resulting 'salty' solution can inhibit ethanol production.

Another possibility is to look into genetically modified organisms that already produce the desired enzymes so you don't have to purchase them. Just like everything else, GMOs have their own special considerations.

Good Luck!

Hi Andrea yes, the alpha amylase enzyme (from sigma) its a heat stable enzyme and the temperature i used for this is 80-85C for 2 hours while amyloglucosidase i leaved it for about 30 h. i am working on the kinetics of this and after then will see what the data looks like and then modified it to improve the process retention time etc... and yes it would been nice to trial it with organisms like zymomonas mobilis... my Former research supervisor is an expert on the bioethanol and zymomonas...

Hi Samani,

There are many full-scale plants running on cassava. Why go to the high expense of building a pilot plant? There's not much that isn't known about cassava ethanol production. Your method of extracting the starch sounds fine for a lab, but not for commercial scale. Those who extract cassava starch to produce clear food and brewing syrups leave a lot of untouched starch in the fiber. Typically, Onggok contains 50 wt% starch. Why do that??? Fresh roots or dry chips (my preference) are easy to handle, and enable you to access all of the starch and reduce your waste headache. Under proper conditions, I would expect you to use 0.04 wt% alpha amylase (0.4 kg/dry ton) of cassava. So unless you made a typo, you are over by a factor of 10! Also, your yield is OK. I would typically target 93% yield, because some of the glucose is used to produce cell mass (about 0.5%), some for glycerol (about 6%), some for residual starch/sugars (1-2%), and a few miscellaneous organic acids that are produced by the yeast (not infection). If your fermentation didn't finish, I'd check pH (4.0-5.0 is OK. Higher is better for yeast but more difficult to control infection.) Temperature (even with thermotolerant yeasts, keep it below 35C, and I prefer 32-33.) Free amino nitrogen (FAN). For starters, try adding urea. It's cheap and easy. Add about 400 PPM, which will give you 184 PPM FAN. You can also use acid protease. Yeast can't bud and create babies without protein, and budding yeast produces EtOH about 33 times faster than live stationary yeast. So it's worth focusing on yeast health and well-being. It will pay you back. At your ethanol levels, a good quality baking yeast will be fine. 20 wt% starch will produce about 10.5 wt% (13 vol%) ethanol. (in case you care, the equation is simple: % yeast x 1.11 (wt gain due to starch hydrolysis) x 0.511 (stoichiometry of glucose to EtOH) x 0.93 (my efficiency factor) x 1.23 (if you want to convert wt% to vol%). No magic here.

The only other "watch out" is if you ran a saccharification prior to fermentation. I do NOT recommend that. It will osmoticlly shock the yeast, maybe killing it, meanwhile, the bacteria LOVES it. So, if your fermentation smells like lactic acid and isn't boiling with CO2, that's your problem. I suggest SSF for real world plants.

Hi Larry Yes, i agree with you on the scale of production. just one thing the initial process i used for my fermentation was saccharification prior to fermentation, thank you very much for the recommendation. this time im going for the Simultaneous saccarification and fermentation (SSF).it seems that after the gelatinization then will cool down the slury before adding both the amyloglucosidase and a yeast inoculum with a nutrient solution.... this is what research and networking is for.. thanks for this..you've suggested 0.04%wt of alpha amylase wouldn't this be too low or would it take alot longer to geltinized the starch??

90-120 min at 80-82C is good. In this range, there is a direct trade-off of enzyme to residence time. If you want to do it in 10 minutes, plan to use ten times as much enzyme! Longer times will increase enzyme denaturation and Maillard reaction.

thanks to Larry. u have briefed the entire process in a paragraph.

that sounds good.

also, i have one suggestion. if u start from starch, the purchase cost will be more than using direct raw material.

in a more greener and economical way, instead of using acids or bases, u may go for direct microbial usage in the saccharification(enzymatic) stage and filtration should be carried out to prevent cross microbial contamination.

else, we can use a co-culture of yeast and a symbiotic microbe to the production medium.

Cost is very important factor in process design. If it is only a question of cost, then compare process cost to get starch from raw material and cost of ready available starch in the market. If your process cost is more than ready starch available in the market it is better to choose option of buying starch. Again choice depends upon other factors like raw material availability, know how, investment required to get starch out from the raw material. Once you have starch, further process to produce ethanol remains same and so cost remain same. In my opinion getting ready starch from market will be a cheaper option if existing starch suppliers available locally. Local supplier is very important aspect.

Use half of the enzyme at 100C for 15 minutes and reduce the temperature to 85C and add the second amylase part for 1hr, and then change the pH to 5.5 and temperature to 60C and add the glucoamylase for 2-3hrs.