Influent Solids Retained High Biomass Reactor Treating Dairy Manure Wastewater and Kinetics Study

In large-scale dairies, flushing system is employed as a major means of manure collection for the sake of its efficiency and less labor requirements. The large amount of wastewater needs to be treated for reuse. Anaerobic digestion converts the organic carbon in dairy manure to biogas that can be used as renewable energy to reduce greenhouse and odor gas emission. Flushed dairy manure poses challenges to conventional anaerobic digestion technology. To address this issue, fixed-film digesters with submerged high specific surface area media were introduced to retain active biomass through bacterial attachment. Nevertheless, fixed-film was classified as an inappropriate process for dairy manure anaerobic digestion due to its vulnerability to media clogging. Apparently, a process with no need of exotic media addition would be preferred for anaerobic digestion of flushed dairy manure.

In this study, a strategy using fiber in the dairy manure as biomass carriers for anaerobic digestion of solid wastes was investigated by using anaerobic sequential batch reactor (ASBR) in lab scale, floor scale and pilot scale.  Operating parameters, such as settling time, hydraulic retention time (HRT), and organic loading rate (OLR) were evaluated for process optimization. In lab scale experiments, it was revealed that settling time play a key role in biomass retention in form of biofilm. Short settling time favors biofilm formation due to high selection pressure. Bench scale results showed optimum HRT for volumetric methane production rate and methane productivity were 4d and 8 d, respectively. Pilot study confirmed these results and showed 6d HRT should be optimum for ASBR treating flushed dairy manure. A kinetic study was carried out for process control and design. Four basic models, i.e. first-order, Grau, Monod and Chen & Hashimoto were compared with the aim to choose appropriate models. Chen & Hashimoto model based model gave the best simulation with R² of 0.99. However, Monod based model showed a poor performance since influent concentration was not include in steady state effluent concentration. At optimized condition (6 d HRT), the volumetric methane production rate of 0.18L/L/d and VS removal of 40% were achieved.  It was proved that ASBR using manure fiber as support media not only improved methane production but also reduced the necessary HRT to achieve a similar treating efficiency compared with other study.