**4. Conclusions**

An MEC was combined with AD in a single chamber to increase organic matter removal and energy production. The AD-MEC treatment produced 137.9% more CH4 + H2 in the produced biogas compared to the AD-only treatment. Furthermore, COD conversion e fficiency was 14.5% higher in AD-MEC compared to AD-only. The e fficiency of electrical energy recovery for MECs reached a maximum of 324%, with an average of 170% over the 11-day period. Incorporating AD with MEC could increase overall energy production from dairy manure digestion, even if added as a polishing step after 20 days of digestion.

**Author Contributions:** Conceptualization: A.H., F.W., S.L., L.Q., and Y.L.; Methodology: A.H. and F.W.; Software: A.H.; Validation: A.H. and F.W.; Formal analysis: A.H., F.W. and Y.L.; Investigation: A.H.; Resources: A.H., S.L., and L.Q.; Data curation: A.H., F.W.; Writing—original draft preparation: A.H.; Writing—review and editing, A.H., F.W., S.L., L.Q., and Y.L.; Visualization: A.H., F.W., L.Q., and Y.L.; Supervision: L.Q.; Project Administration: A.H., S.L., and L.Q.; Funding acquisition: A.H. and L.Q. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the China Scholarship Council (CSC) PhD program.

**Acknowledgments:** The first author acknowledges support from CSC.

**Conflicts of Interest:** The authors declare no conflict of interest.
