**2. Review methodology**

For this bibliographic review, 92 articles have been selected from the 137 articles were carried out on the Scopus with the keywords "microalgae" and "anaerobic co-digestion" during the periods of 2011–2021 [8–100]. The bibliometric analysis was realized using the VOSviewer software using these 92-original articles.

Thanks to this software, it has been verified that there are few groups dedicated to the study of AcoD with microalgae. These investigations focus mainly on countries such as Spain (30 articles), the United States (17 articles), China (8 articles), Mexico (8 articles), and Brazil (5 articles). In addition, only eight authors have five or more articles to 321 authors (**Figure 1a**). In **Figure 1b**, as can see the connection between

*Anaerobic Co-Digestion of Microalgae and Industrial Wastes: A Critical and Bibliometric Review DOI: http://dx.doi.org/10.5772/intechopen.104378*

#### **Figure 1.**

*Bibliometric analysis with VOSviewer: (a) authors with five or more articles, (b) connexion between authors, (c) substrates and (d) microalgae.*

different authors and groups. The color and size indicate the group and the citations of these eight authors.
