Hydrolyzed urine for enhanced valorization and toxicant degradation of wet coffee processing wastes: Implications for soil contamination and health risk reductions

Coffee pulp (CP) and wastewater, from wet coffee processing plants, pollute water and soil ecosystems unless a greener management system is employed. The aim was to evaluate the effect of hydrolyzed human urine (HU) on the dynamics of total phenol, caffeine, and heavy metals during CP and coffee processing wastewater (CPWW) co-composting. The associated health risks reduction after application for cabbage production was also estimated. For the purpose, five treatments were prepared as C-0 (CP, control), C-1 (CP + CPWW), C-2 (CP + 1:1 CPWW:HU), C-3 (CP + 1:2 CPWW:HU) and C-4 (CP + 1:3 CPWW:HU). The optimum compost was applied for cabbage cultivation in comparison with mineral fertilizer and without fertilization in a greenhouse. The total phenol reduction was in the order of C1 (77.71%) < C0 (78.66%) < C-4 (79.89%) < C-3 (91.20%) < C2 (91.48%), and maximum significant reduction of caffeine was also observed in C3 (81.34%) and C2 (82.66%). Pb and Cd were significantly reduced in C2, and Cr in C-3 with a reduction of 4.38-15.13%, 12.50-33.00%, and 2.94-19.57%, respectively. The bio-concentration factor decreased in the order of Cd > Cr > Ni > Pb with concentrations, hazard quotient, hazard index (along with phenol) < 1, and cancer risk values below 1.00E-04, indicating very little risk. Thus, supplementing HU enhanced degradation of the anti-nutrient factors, and provide compost that enrich soil nutrients with little health risks of application.