Hello Pavel,

The answers to your questions depend largely on the kind of substrate(s) that you want to hydrolyse. If this would be FOG (fat, oil, grease) then thermo-chemical hydrolysis at pH 10 and 55 °C seems to be very effective.(Chenxi Li et al, WS&T 6902 pp. 443-450, 2014). For other substrates biochemical (enzymatic) hydrolysis at neutral or slightly acid pH at 50 - 55 °C would be more cost-effective.

Thank you Bruno. Unfortunately, I can't find the paper you recommended. The feedstock can be various but mostly agricultural wastes and solid organic wastes. Have you got any experiences with gas quality control within Hydrolysis tank?

OK Pavel. In that case enzymatic hydrolysis would be recommended after adequate pre-treatment. Enzymatic hydrolysis does not generate gas. Hence I don't understand your question about gas quality from hydrolysis. If you are referring to the next bioconversion steps, then this would be another topic. Please clarify.

Optimal conditions for enzymatic hydrolysis depend on the specific enzymes or enzyme mixtures, each will have certain temperatures or pH ranges of optimal activity.

For microbial hydrolysis, 65 C seems to give very good results, but again this is substrate specific.

There is a good review paper of pre-treatment technologies by Carrere et al. Journal of Hazardous Materials. 11/2010; 183(1-3):1-15.  

Good Luck.

Bruno, thank you for your answer and help. By the gas quality, I meant the amount of oxygen and CO2 in the gas. I suggest to aerate hydrolysis with a separate gas cycle to support aerobs that are main producers of enzymes. The idea was to keep oxygen level at lower level, but don't know what is the ideal proportion to help hydrolysis process and don't loose too much organics.

Paul, thank you too. I got your point. It will be very depending on feedstock and therefore enzymes composition.

Hi Pavel, in my previous work I developed an approach to look for existing natural microbial ecosystems that are efficient in biodegradation. For instance, for cellulosic waste I looked at the the microbial ecosystem in the rumen of cattle. The rumen is a very efficient bioreactor for the degradation of cellulosic waste (to an extend that it is 20 to 50 times faster than man made bioreactors). Factually the rumen is a microbial hydrolosis system, as it converts biopolymers to simple organic acids like acetic, propionic and butyric acids (which constitutes the main food for the cattle). Besides anaerobic bacteria, highly specific protozoans only found in ruminants play an important role in hydrolysing cellulose and other biopolymers. The conditions of the rumen are: pH neutral, oxygen - very low, T 38 C. I managed to simulate the microbial acidification process in a reactor, but due to the efficiency and rapid production of the mentioned organic acids, a second (methanogenic) reactor needed to be coupled to this in stage 2 to convert the acids in methane. otherwise the reactor 1 would acidify and the process would stop. The effluent of reactor 2, after removal of acids, would then go back to reactor 1, so a closed cycle could be generated. This 2-stage system is referred to as RUDAD (Rumen Derived Anearobic Digestion), and you can find further information and papers on this in my publication list. I then also looked at other natural systems, such as the hindgut of cockroaches! this revealed other anaerobic microbial systems that are highly effieint in the digestion of biopolymers. My advise, look at natural systems, as these have millions of years of experience!