(253e) In-Situ Hydrogen Sulfide Removal and Biogas Upgrading Via a One-Reactor System Integrating Solid-State Anaerobic Digestion of Food Waste and Bioelectrochemical Treatment

Authors: 
Ding, L., University of Minnesota
Chen, Y., University of Minnesota
Hu, B., University of Minnesota
Food waste (FW) is estimated to account for 40% of the food produced in the United States, making it a critical and urgent environmental concern with a magnitude of 280-300 kg per year per capita. Among the approaches to valorize FW for biochemical/bioenergy production and to reduce its environmental footprint, solid-state anaerobic digestion (SSAD, total solids content ≥ 15 wt%) offers the superiorities such as smaller reactors required, lower energy input for heating and stirring, easier disposal of digestate with lower moisture as biofertilizer or soil amendment, etc. However, with the higher organic contents accompany some shortcomings, typically including easy digester acidification and even failure caused by accumulation of excessive volatile fatty acids (VFAs), buildup of hydrogen sulfide (H2S) in the biogas that is toxic to personnel and corrosive to facilities, etc. Conventional countermeasures such as extra addition of water or some bulk agents (e.g., yard wastes) reduce the capacity of FW treatment.

To fill in this knowledge gap, an innovative one-reactor system incorporating SSAD of FW and bioelectrochemical (BEC) treatment of leachate was studied. In the upper layer of this reactor, FW was hydrolyzed and VFAs were produced and washed down into the leachate. In the lower layer of reactor inserts the BEC unit. A pair of electrodes made of low carbon steel were submersed into the leachate and applied a voltage of 0.7 V, which secured the removal of most H2S with relatively less material consumption of electrodes and increased the buffering capacity of leachate. A cyclic flow of leachate was created so that the BEC-treated leachate with a stronger buffering capacity was pumped back to upper layer for a more thorough mass transfer of SSAD. Moreover, the biogas profile was upgraded since the BEC treatment contributed to the reduction of some CO2 to CH4. Consequently, in-situ H2S removal, biogas upgrading, and process stabilization were simultaneously achieved through this one-reactor design integrating SSAD of FW and BEC treatment of leachate.