Full-Scale Performance Comparison of an Induced Bed Reactor and a Control Reactor

Abstract

The induced bed reactor (IBR) anaerobic digester was developed to apply high-rate anaerobic digestion techniques to substrates with high suspended solids content (6% to 12% total solids) such as food waste and dairy manures. The purpose of this study was to examine IBR performance (waste stabilization and biogas production) at plant scale and compare the IBR to similar digesters with the IBR technology removed (control). In 2008, an IBR system at Sunderland Dairy Farm in Chester, Utah, was modified, including reconfiguring two of four 120 m3 IBR anaerobic digesters by effectively eliminating the solids-retaining capabilities of the reactors, providing a unique opportunity for controlled comparisons at full scale. This is the first time research has compared IBR to other digester technologies at this scale. Biogas production was recorded for two temperature conditions and hydraulic retention times (HRTs): winter (30C and ~8 d HRT) and summer (39C and ~11 d HRT). The IBR technology significantly outperformed the control in terms of substrate reduction and gas production during the winter, with IBR biogas production 74% higher than the control. Solids sampling over the same period demonstrated 31% reduction in influent volatile solids for the IBR and 22% reduction in volatile solids for the control. During the summer, however, the differences in biogas production and volatile solids reduction were significantly less, at 6% and 9%, respectively. The IBR demonstrated clear performance advantages for certain conditions, apparently due to its ability to maintain a separation of HRT and solids retention time. These results suggest that different optimal conditions exist for each reactor technology. Application of the Chen and Hashimoto model to the IBR and control reactors showed that the predicted and measured performance of the control correlated well with the predictions of the model, while the same model significantly underpredicted the performance of the IBR. However, if the model is modified by assuming that the solids retention time of the digester is large, then the model more closely predicts the observed IBR performance. There was a significant correlation for the Chen and Hashimoto model to the observed data that may be useful in the future with additional research into how to account for solids retention time.