TRA BI YOUAN CHARLES, AKO OLGA YOLANDE AKÉ, TOURE MAMADOU, ABOLY JEAN-BAPTISTE EHOUMAN NICAISE, KOUADIO MARC CYRIL, NIKIEMA MAHAMADI4 AND AKA BOKO
Abstract
The management of pig slurry in Côte dâIvoire poses environmental challenges due to inorganic mineral elements, particularly heavy metals, which can contaminate soils and water during the application of digestates as fertilizers. This study investigates the evolution of these inorganic mineral elements during anaerobic digestion within a circular economy approach and assesses the environmental risks associated with the use of digestates as biofertilizers. The analyses focused on pH, moisture content, volatile organic matter (VOM), volatile fatty acids (VFAs), chemical oxygen demand (COD), and inorganic mineral elements (lead, cadmium, zinc, copper). The pH remained stable: 6.24±0.19 in raw slurry (RS), 6.60±0.1 in mid-digestion slurry (MDS), and 6.37±0.18 in post-digestion slurry (PDS). Moisture content decreased from 56.93±1.4% (RS) to 1.77±0.23% (PDS), indicating progressive slurry concentration. VOM decreased from 87.93±2.37% (RS) to 8.26±0.88% (PDS), while COD dropped from 1543.23±1.98 mg O/L (RS) to 300.35±4.14 mg O/L (PDS), reflecting significant degradation of organic matter. Regarding inorganic mineral elements, sulfur and strontium levels remained stable at 0.008±0.0 mg/kg (RS) and 0.001±0.0 mg/kg (RS, MDS, PDS), respectively. However, elements like argon decreased from 0.166±0.0 mg/kg (RS) to 0.005±0.0 mg/kg (MDS and PDS), and chlorine levels fell from 0.042±0.0 mg/kg (RS) to 0.005±0.0 mg/kg (MDS and PDS). Tellurium and ruthenium were eliminated after digestion. These results demonstrate the effectiveness of anaerobic digestion in reducing certain inorganic mineral elements, thereby improving the quality of digestates for safe use as biofertilizers. Nevertheless, regular monitoring is essential to ensure the environmental safety of digestate utilization.