Kindly, can anyone explain to me, What is the reason for pH reduction in case of adding wheat straw to sewage sludge in comparison with sewage sludge solo? I mean in the zero time without going into the conversion process.
Wheat straw contains mainly cellulose which is easily hydrolysed and acidified by facultative bacteria in the sewage sludge resulting in lower pH.
However the pH will rise again during anaerobic digestion (AD) of this sludge - straw mixture due to the production of biogas containing methane CH4 and acid carbon dioxide CO2.
Thank you so much Prof. Bruno Peeters, I totally agree with you, kindly do you have any reference that supported this reason because I urgently need it.
I am not a Prof. but a M.Sc. (Dipl. Ing.) with over 45 years worldwide expertise in advanced AD originally developed in cooperation with my Alma Mater University of Ghent (Belgium). My answer is based on my/our long experience, not on academic papers. Perhaps one of your students could do some literature research on this topic.
Is it possible that the wheat straw fermented a little before drying it? Or if it was not pre-dried, it is perhaps likely that it did go anoxic. Have you tested just adding some straw to distilled water and checking the pH?