Use of sewage sludge in the production of yerba mate seedlings

Wastewater treatment plants (WWTPs) play an essential environmental and social role. However, the treatment process and water reuse generate solid residues (sewage sludge), which, if improperly disposed of, can be highly harmful to the environment. Yerba mate (Ilex paraguariensis St. Hil.) is widely cultivated in southern Brazil, with 80% of the cultivated area on small family farms. This study evaluated the feasibility of using sewage sludge to produce yerba mate seedlings. The treatments consisted of six different doses of sewage sludge (0, 10, 20, 40, 60, and 80% soil substitution in the cultivation substrate) mixed with soil used to prepare the cultivation substrate for the seedlings, combined with various mineral fertilization treatments. Applying 10% sewage sludge, combined with a controlled-release mineral fertilizer at an adequate dose, resulted in the best development of yerba mate seedlings, suggesting that sewage sludge use can be a viable alternative for repurposing organic solid waste generated by WWTPs.