title: Factors Affecting Process Temperature and Biogas Production in Small-scale Rural Biogas Digesters in Winter in Northern Vietnam.
abstract: This study investigated the main factors influencing digester temperature and methods to reduce heat losses during the cold season in the subtropics. Four composite digesters (two insulated and two uninsulated) were buried underground to measure their internal temperature (°C) at a depth of 140 cm and 180 cm, biogas production and methane (CH4) concentration in biogas from August to February. In parallel the temperature of the air (100 cm above ground), in the slurry mixing tank and in the soil (10, 100, 140, and 180 cm depth) was measured by thermocouple. The influent amount was measured daily and the influent chemical composition was measured monthly during the whole experimental period. Seasonal variations in air temperature significantly affected the temperature in the soil, mixing tank and digester. Consequently, biogas production, which is temperature dependent, was influenced by the season. The main factors determining the internal temperature in the digesters were insulation with Styrofoam, air temperature and temperature of slurry in the mixing tank. Biogas production is low due to the cold climate conditions in winter in Northern Vietnam, but the study proved that storing slurry in the mixing tank until its temperature peak at around 14:00 h will increase the temperature in the digester and thus increase potential biogas production. Algorithms are provided linking digester temperature to the temperature of slurry in the mixing tank.
authors: Institute of Chemical Engineering, Bio- and Environmental Engineering, Faculty of Engineering, University of Southern Denmark, DK5230 Odense, Denmark .
authors: C H
authors: CH
authors: Pham
authors: Institute of Chemical Engineering, Bio- and Environmental Engineering, Faculty of Engineering, University of Southern Denmark, DK5230 Odense, Denmark .
authors: C C
authors: CC
authors: Vu
authors: Institute of Chemical Engineering, Bio- and Environmental Engineering, Faculty of Engineering, University of Southern Denmark, DK5230 Odense, Denmark .
authors: S G
authors: SG
authors: Sommer
authors: Department of Plant and Environment, Faculty of Science, University of Copenhagen, DK1871 Frederiksberg, Denmark .
authors: S
authors: S
authors: Bruun
keywords: Air and Soil Temperature; Digester Temperature; Insulation; Season; Simple Biogas Digester