**4. Conclusions**

In this work, three mMFCs (each with a working volume of 1.7 L) were run and compared in the batch mode and continuous flow mode. The system could be applied for both secondary and tertiary treatment as depicted by the results. The secondary treatment was performed as the organics were removed, and the tertiary treatment was performed as nutrient removal was achieved using algae. The COD removal was greater in MFC-B, but MFC-C had a greater CE. OCV was similar in both systems. However, in a closed circuit, MFC-C had a greater voltage output. The combined voltage was enough to power the MEC and the results showed that the supplied voltage overcame its potential barrier, and thus, the hydrogen was produced along with the treatment of wastewater.

**Author Contributions:** Conceptualization, B.M., S.A., U.R. and Z.S.; methodology, B.M. and Z.U.; software, B.M., Z.U. and S.A.; validation, B.M., S.A., U.R., Z.U. and Z.S.; formal analysis, B.M. and Z.U.; investigation, B.M., S.A., U.R. and Z.U.; resources, S.A. and Z.S.; data curation, B.M., S.A., Z.U. and Z.S.; writing—original draft preparation, B.M.; writing—review and editing, B.M., Z.S. and Z.U.; visualization, B.M., S.A., Z.S. and Z.U.; supervision, Z.U. and Z.S.; project administration, Z.U. and Z.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data is contained within the article.

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