Laboratory-scale centrally heated biogas reactor design, construction and operation: the effect of mechanical stirring times on biogas production efficiency

This thesis study consists of three stages. In the 1st stage, the design and construction of a 10 L prototype Continuous Stirred Tank Reactor (CSTR) was performed, in the 2nd stage, the design and construction of 8 10 L volume laboratory scale centrally heated CSTR reactor systems were made, and in the 3rd stage, the effects different mechanical mixers 'operating times on cattle manure fermentation were carried out. Temperature control of CSTR reactor system was provided by temperature feedback control of the central automatic water heating system. In addition, the operation of the electric motors used for mixing in the biogas system, the water circulation in the outer jacket system of the reactors and the measurement of temperatures were made via PLC. Mechanical mixer operating regimes were determined as 5/30, 10/30, 15/30, 20/30 (minute run/stop). At the beginning of the trials, the main material properties (solids and volatile solids content and pH) were determined. The effective working volume was determined as 8 L, the hydraulic retention time was 20 days and the daily loading rate was 400 mL. Solids content was set at 8-9%. During the trials, biogas flow rate, methane concentration, daily loaded material amount, solids and volatile solids content, and pH values were measured. The trial results showed that the specific methane production rate increased slightly as the mechanical mixer operating times increased, and in terms of cumulative methane production, the 10/30, 15/30 and 20/30 (minutes run/stop) operating regimes were respectively higher than the 5/30 operating regime. An increase of 1.97%, 1.75% and 2.90% on biogas-methane production compared to 5/30 operating regime was determined when mechanical mixer operating time (10/30, 15/30 and 20/30) increased, respectively.