**9. Conclusions**

Although domestic wastewater cannot completely satisfy the industrialized society's energy demands, it is a valuable resource that should be widely exploited and used in the future. Wastewater these days is no longer wastewater, however, most of agencies look at it as a resource rich in organic content and minerals. These all components could be utilized for the production of renewable energy products or to grow plants and algae that later on can be converted to various types of biofuels as per the requirement. The complex nature of effluent and wastewater make it difficult for the existing technology to remove all the pollutants effectively. So, there is an urgen<sup>t</sup> need to develop a combined strategy using biological, chemical, and physical processes to treat the wastewater as well as to recover valuable products from this untapped resource. Using some of the advanced technologies like membrane bioreactors can be useful, but these have higher operation and maintenance costs compared with conventional processes. Moreover continuous efforts should be there on the development of suitable consortia that not only work on variable conditions, but also help to recover the valuable products from the wastewater. Despite all these facts, on one hand, there is a need for strict discharging standards to be implemented, and on the other hand, researchers and the scientific community need to develop the cutting-edge technologies to recover all the desired products in a sustainable manner.

**Author Contributions:** Conceptualization, R.K.B.; formal analysis, D.S. and S.M.; data curation, D.S. and S.M.; writing—original draft preparation, R.K.B.; writing—review and editing, A.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** There is no any funding source for this study.

**Acknowledgments:** The authors would like to acknowledge all the facilities provided by the Department of Biotechnology Himachal Pradesh University, Summer Hill Shimla; Department of Microbiology, College of Basic Sciences, CSKHPKV Palampur, are duly acknowledged.

**Conflicts of Interest:** The authors declare that there is no conflict of interests regarding the publication of this paper.
