**4. Conclusions**

The study evaluated an optimised enzymatic cocktail that had been formulated with recombinant cellulases produced by *S. cerevisiae* Y294. The performance of the Opt CelMix was comparable to commercial preparations for paper sludge saccharification. At a protein loading of 7.5 mg/g biomass, over 80% glucose recovery was obtained using the formulated cellulase enzyme cocktail. When the enzyme cocktail was dosed at 15 mg/g biomass, it also showed consistent yields with a glucose recovery of 80% over a substrate loading range of 1 to 10% (*w*/*v*).

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

**Funding:** This research was funded by the Department of Science and Technology (DST), the National Research Foundation of South Africa (Grant Number 86423-Senior SARChI Chair: Biofuels and other Clean Alternative Fuels), Rhodes University and Stellenbosch University for financial support. Any opinion, findings and conclusions or recommendations expressed in this material are those of the author(s) and therefore the NRF does not accept any liability in regard thereto.

**Acknowledgments:** The authors would like to thank Adnan Cavka (Sekab E-Technology AB, Örnsköldsvik, Sweden) for providing the paper sludge sample from Domsjö Fabriker AB refinery, Örnsköldsvik, Sweden.

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