Dear Dr. Cansu Birgen

I wish to discuss about fed batch system. In production of pharmaceutical product use of substrate as feed is economically important. The problem exist with batch process is the organisms may be inhibited due to lack of sufficient nutrients and carbon source. In order to remove such inhibition, fresh feed is supplied in fed batch fermentation. If you provide hydrolyzate sugar from lignocellulosic material concentration of sugar for the fermentation is important for product formation and rate substrate utilization. Normally increasing concentration of sugar means removal of water from the solution. If acid hydrolysis is used, you have to remove acid or neutralize it withe base; that would cause dilute solution. Heating or evaporation in presence of acid cause deformation of sugar and synthesis of toxic material such as furfural and hydroymethy furfural (HMF) appeared in the sugar sulution. Low temperature vacuum pressure is required for partial evaporation, in order to prevent formation HMF and furfural. If you need additional info can look for my textbook entitle: Biochemical Engineering and Biotechnology 2nd Edition Elsevier, 2015.

Regards

Hi Cansu

Good to be a little sceptic before starting a project....

The fact that people do not really prove, how they work could be a hind of a problematic step in these processes.

The way of how to prepare the ligno-cellulytic feed is off course a key step in these processes, mostly driven by the costs.

You can do very effective liquidifiaction with Cellulases and Hemi-Cellulases, but if you use agricultural residues, green trash, compost or anything like this, you would enrich Lignin in your Fedbatch too,

In a regular batch process of f.E. developing a method to get rid of your green trash and use it f.E as Bio-Ethanol , you would do an enzymatic hydrolysis, transform the sugars to alcohol, strip this in vacuo from the mix and receive a mix of suspended lignin, undissolved in your mix.

You could separate this, press pellets and use them to generate thermal energy too.

But this process seems to be difficult if we talk about a fed-batch concept.

How would you f.E separate insoluble lignin from your cells?

The only possibilty that I see is, to use cellulosis in more purer form, like bleached pulp, where you already have removed the lignin.

I think it is not realistic that people propose using agricultural residues for fed-batch applications, when they do not show, how this could be done.

The reason might be, to gain more interest, because everybody wants to minimize the process costs, but it does not seem to be serious.

On the other hand: if you use a cellulosic instead of a lignocellulosic feed for a fed-batch process, the costs do not really increase dramatically.

Bleached pulp is a 30% cellulosis concentrate, the lignin is already removed and the costs are not unrealistic high..and you avoid any problems of Murphy's "Shit in - Shit out" theory...

good luck

Dear Cansu,

The answer to this question may not be known in the public domain (yet), and better be cautious in case you find it (multiple verification is advised!). Truth: we don't even know which type of biomass is the most used so far at industrial scale (2018), and thus other technicalities are a bit far from being "publicly" known.

The scenario is more complex due to proprietary issues (legal ©™), around these samples, that may not help you to work out your answer. However, it is worth trying. Stay motivated! You may be the first sharing that! All the very best.

Dear all,

more out of curiosity: Is it really necessary to concentrate the hydrolysate for a fed batch process? How high is the monosaccharide concentration after enzymatic hydrolysis?

I would have expected that you already have a rather high concentration that could be applied directly for a fed batch process.

Thank you all for Your valuable inputs. I tried to address them below:

- Lignocellulosic biomass is the feedstock in my Project, so it is fixed at the moment. Its Conversion to fermentable sugars is done by Our partners in Jadavpur University.

What we see from their inputs and literature is that the lignocellulosic hydrolysate contains a mixture of sugars (mostly glucose and xylose) and other Components in small amounts (acids, phenols etc.) With a total sugar concentration of 10-20 g/l.

- If we run a batch fermentation With 10-20 g/l sugar (essential nutrients added), final Product titer is rather small. If we run a continuous fermentation with the same feed, the product titer is even lower and process generates large amounts of Waste water.

- Therefore, we would like to increase the Product titer/Productivity by running the fermentation in the fed-batch mode. Using the same feed (10-20 g/l) causes the fermentation broth to be diluted thus decreasing the Productivity and the Product titer.

- To prevent the dilution, the common practice is to use a concentrated sugar/feed solution. However, where/how do we get that highly concentrated solution and at which cost? That is the question which is not addressed, not my knowledge.

- As Ghasem Najafpour explained nicely, vacuum evaporation is used for this purpose. I will dig more into the economics of this process.

Can you provide some information on your conversion process to get fermentable sugars from lignocellulosic biomass?

If you have a look at the bioethanol application notes for saccharification with enzymes from big enzyme producers, they claim to convert a solids load of 18 % (after chemical preteatment) - that should lead to much higher sugar concentration than just 10-20 g/L.

Our partners work on different pre-treatment methods and convert the pre-treated biomass via enzymatic hydrolysis. Sugar concentration seems lower since they are in the process of optimization. However, from what I read in the literature, total sugar is around 35 - 45 g/l.