**Conflict of interest**

*New Advances on Fermentation Processes*

*FAN variation during the experimental period.*

*Redox potential variation during the experimental period.*

In **Figure 8**, a constant redox potential in the reactors CR1 and CR2 was obtained throughout the whole experimental procedure. After 50 days, the redox potential in MR1 and MR2 slowly starts to increase. The increase may be due to small oxygen leakages in, e.g., the tubing connections. Small air leakages in the commercial bioreactors can be better handled by the system because more biomass is available (the same concentration but larger volume) to consume the oxygen. In the small microbioreactors, a similarly sized leakage causes considerable more disturbances to the strictly anaerobic methanogenic archaea. The smaller amount of biomass is not able to metabolize all of the intruded oxygen, and the redox potential will increase.

Although there are several opportunities in the biogas sector, new challenges and barriers cannot be ignored and have to be overcome by using new process

**186**

**4. Conclusion**

**Figure 7.**

**Figure 8.**

The authors declare no conflict of interest.

## **Author details**

Spyridon Achinas and Gerrit Jan Willem Euverink\* Engineering and Technology institute Groningen, University of Groningen, Groningen, Netherlands

\*Address all correspondence to: g.j.w.euverink@rug.nl

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
