Optimization of Biogas Production in Dry Anaerobic Digestion of Swine Manure by the Use of Alkalinity Index to Monitor a Prototype Cylindrical Digester

Abstract

Anaerobic digestion (AD) is one of the best alternative sustainable technologies for energy production and recovery from organic solid wastes. Up to now dry AD has been commercialized in the treatment of municipal solid wastes. Little information could be found on the practical application of dry AD to manure wastes or waste activated sludge. This study aimed at testing the feasibility of using alkalinity to manage dry AD system for swine manure treatment and clarify its effect on the stability and efficiency of the newly-developed prototype cylindrical digester system. A prototype cylindrical digester with a diameter of 40 mm and a volume of 1.3 liters was designed and fabricated. It was operated under mesophilic conditions (38°C). The alkalinity of manure was increased by 3000 g/L (R 1 ) and 6000 g/L (R 2 ) by adding sodium bicarbonate with the raw swine manure as the control (R 0 ). Results showed that R 1 and R 2 maintained a relatively higher level of alkalinity during the whole operation compared to the control (R 0 ). Only one peak appeared in biogas production for the control reactor (R 0 ) which almost ceased on day 12, whereas R 1 and R 2 exhibited two biogas peaks. The 30 days' biogas yield for R 2 was 276.6 ml/g-VS added while R 1 was 204.8 ml/g-VS added which corresponds to an increase by 2.7-and 1.7-fold respectively as compared to the control (R 0 ). 2.2-and 4.1-fold increase in methane production was achieved in R 1 and R 2 respectively as compared to R 0 . This difference is most probably attributable to the high alkalinity in R 1 and R 2 that stabilized the digestion process and minimized the influence of pH variations on methanogenesis.