Importância do pH no equilíbrio químico de biodigestores anaeróbios

Abstract

The anaerobic digestion process are very important, due to its growth as productor of renewable energy. The biodigestion process is extremely sensitive to environment conditions, including temperature, the nitrogen content, total solids and, mostly important, the hydrogen potential (pH), being, therefore, necessary to the adequate control of pH in the chemical balance of the biodigesters. The main aim of this research is utilizing solid waste to produce biogas, and to evaluate the pH in the chemical balance, the functions of alkalinity, buffering of the medium, balance between carbonate, bicarbonate and carbon dioxide. In the experiment, it was utilized a 4 liters batch reactor with semi-continuous rotation, in which a digestate and substrate ratio of approximately 2:1 were used, the first with the Ceará Water and Sewer Company (CAGECE) sludge and the second with cooked white rice from the Federal university of Ceara’s University Restaurant. Sodium bicarbonate was used to control de pH, looking to increase and maintain it in the ideal range (of 6,5 to 7,5) of methanogenic bacteria. The results obtained, from 10 to 20% of methane, showed that the biogas produced, even in small quantities, beyond the small time of the reactor functioning, as well as a production increase since the pH stabilization with the sodium bicarbonate use. The total volatile solids value was 37 g/L to the inoculum and 16 g/L for the substrate used in the reactor. The results also explained the interdependence between the anaerobic digestion phases and how the chemical balances involved, directly and indirectly, interfere in the production of biogas. The same goes for buffering the use of sodium bicarbonate and the balance between the carbonate, bicarbonate and carbon dioxide species, coinciding with the ideal methane production pH. The pH values found were between 5 and 7, approximately. The study proved to be important to explain the hydrogen potential importance in the biodigesters, as well as the biogas small production, related to the experiment time.