**5. Conclusions**

In this study, NaOH pretreatment, AcoD technique, and their combination were used to test the performance and potential of the methane production of WW in anaerobic digestion. After pretreatment with NaOH was administered, the mean cumulative methane yield of the single digestion of WW increased from 175.81 mL CH4/g VS to 243.53 mL CH4/g VS, which was equivalent to a 38.5% increase compared with that of untreated WW. The mean methane yield of the co-digestion of WW and PM was 234.88 mL CH4/g VS, which was higher than that of the single digestion of WW (175.81 mL CH4/g VS) and was not significantly di fferent from that of the single digestion of PM (245.09 mL CH4/g VS). The mean cumulative methane yield of the co-digestion of WW pretreated with NaOH and PM was 309.06 mL CH4/g VS, which was increased by 75.8% compared with that of the untreated WW and was higher than those of the single-digestion of WW pretreated with NaOH and the co-digestion of WW and PM. The growth rates of the methane production of WW treated with NaOH and AcoD pretreated with NaOH were considerably higher than those of the RS under the same optimizing strategies. This work could provide useful insights into the development of WW as a new sustainable and e fficient alternative for biogas production.

**Author Contributions:** X.Z. (Xiaohui Zhang) and B.X. conceived and designed the experiments; R.L. and Q.S. performed the experiments; W.T. analyzed the data with suggestions by X.Z. (Xinyu Zhao) and Q.D.; W.T. and R.L. wrote the paper; B.X. and X.Z. (Xiaohui Zhang) proofed the paper.

**Funding:** This research was funded by the National Key Research and Development Program of China (No. 2018YFC1900102) and the National Natural Science Foundation of China (No. 51808519).

**Acknowledgments:** We thank Liang Zhao for assistance in the laboratory and with data analysis.

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