*Future Research Perspectives in Faecal Sludge Management*

Studies on characterization and potential applications of biochar for several uses have been performed and research gaps have been indicated. Potential research lines that can be summarized as: (i) focus on potential secondary ecological risks in the process of biochar production by screening and pre-treating raw material to remove pollutants derived from biomass [100]; (ii) long-term stability and effect of biochar on agricultural soil characteristics; (iii) assessment of multifunctional biochar materials on multi-heavy metals contaminated soils and as engineering application; (iv) cost-benefit analysis to enhance economic availability to improve production efficiency and reduce economic constraints [63,100]; (v) soil toxicity to organisms and plants induced by biochar [63]. These research gaps are also applicable for biochar use in faecal sludge management. The integration of biochar on faecal sludge management has the potential to be adopted by smallholder farmers who have limited access to fertilizers due to financial limitations. The success for this integration requires additional detailed studies considering that the smallholder farmers have more possibilities to produce charcoal than biochar:


**Author Contributions:** Conceptualization, M.M., J.J.v.T. and M.P.A.; methodology, M.M., J.J.v.T., M.P.A., A.B.J.C.N., L.M.C. and A.C.; validation, J.J.v.T., M.P.A., A.B.J.C.N., L.M.C., A.C., H.C., J.C.M. and R.B.A.R.; investigation, M.M., J.J.v.T., M.P.A., A.B.J.C.N., L.M.C., A.C., H.C., J.C.M. and R.B.A.R.; resources, J.J.v.T., L.M.C. and A.C.; data curation, M.M.; writing—original draft preparation, M.M.; writing—review and editing, M.M., J.J.v.T., M.P.A., A.B.J.C.N., L.M.C., A.C., H.C., J.C.M. and R.B.A.R.; supervision, J.J.v.T. and M.P.A.; project administration, J.J.v.T., L.M.C. and A.C.; funding acquisition, J.J.v.T., L.M.C. and A.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Research Fund (NRF) and South Africa– Mozambique–Zambia NRF Trilateral Joint Research (ZAM180911357528-118479).

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the General/Human Research Ethics Committee (GHREC)- N.o-UFSHSD2019/1012. Environmental and Biosafety Research Ethics Committee (EBREC)-N.o-UFS-ESD2019/0066, University of the Free State, SA.

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study. Written informed consent has been obtained from the patient(s) to publish this paper.

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

## **References**

