Effect of digester surface area on biogas yield

Abstract

Poultry manure, cow dung and swine manure were digested in cube-shaped anaerobic digesters of equal volume but different surface areas (SAs) (5.38, 10.0 and 11.6 dm²) in a two-factor experiment. The digesters were agitated once a day during the experiment. The results showed that neither the manure type nor SA affected (p > 0.05) substrate temperature and pH, but both had (p ≤ 0.05) on biogas yield (BY. Poultry manure had the highest BY followed by swine manure and cow dung (1.00, 0.59 and 0.11 dm³ kg^-1 VS fed day^-1, respectively). Within the SAs investigated, BY increased as digester SA increased (0.27, 0.68 and 0.74 dm³ kg^-1 VS fed day^-1 for 5.38, 10.0 and 11.6 dm², respectively). The results of the regression analysis showed that digester diameter to substrate height ratio and BY had a polynomial relationship with a dome-shaped curve, indicating that BY would not keep increasing exponentially with increase in digester SA at the expense of substrate height.