Effects of particulate size in anaerobic acidogenesis using cellulose as a sole carbon source

Abstract

ABSTRACT: Pure cellulose with average diameters of 20 and 50 µm were treated in laboratory‐scale CSTRs to study the effect of pH, reactor hydraulic retention time (HRT), and substrate concentration on the rate of anaerobic acidogenesis for those two cellulose particle sizes. The pH effect was studied using a particle size of 20 µm at an HRT of 48 hours while controlling the pH at levels of 5.2, 5.6, 6.0, 6.4, and 6.8. After determining that a pH of 5.6 was optimum, the effect of HRT was evaluated by operating the reactors at HRTs of 24, 36, 48, 60, and 72 hours for both the 20 and 50 µm cellulose sizes. After finding that an HRT of 48 hours was sufficient for acidogenesis, the effect of organic loading rate (OLR) was studied by varying the OLR between 2 and 8 g/L/day. The results of the research indicate that the conversion of particulate cellulose to soluble chemical oxygen demand (SCOD) ranged from 31% (pH 6.8) to 44% (pH 5.6). The HRT studies illustrated that a substrate with a smaller particle size (20 µm) and operation at a longer HRT resulted in a higher conversion to SCOD compared with a larger particle size (50 µm) and operation at a shorter HRT. It was also observed that the effluent SCOD increased proportionally with increases in the influent particulate COD.