Assessment of Heavy Metal Speciation and Mobility in By-Products from Wastewater Treatment Plant in Ouagadougou

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Résumé

The wastewater treatment plant (WWTP) generates by-products such as treated wastewater (TWW) and dried sewage sludge (DSS). This study assesses the speciation and mobility of metals in dry sewage sludge collected in 2022 and 2024 using a three-step sequential extraction based on the BCR method. The highest total metal concentration was Mg, followed by Zn > Cu > Mn > Cr > Ni for both years, indicating a relatively stable distribution over time. It suggests that the sampling year does not significantly affect the chemical stability or binding forms of metals in sewage sludge. Mg and Mn were predominantly associated with the exchangeable and acid-soluble fraction (F1) in both years. Cu and Cr were mainly concentrated in the oxidizable fraction (F3). Ni showed a relatively uniform distribution across fractions and years, with a consistent proportion in the oxidizable fraction. The undetectable Cd, Co, Hg, and Pb in raw and treated wastewater indicate a low industrial contribution of wastewater to the waste treatment plant. The sewage sludge analysis showed high levels of total organic matter, phosphorus, and nitrogen, suggesting its potential use as an agricultural soil amendment. The results provide important insights into metal behavior, informing safe sludge management and its potential use in agriculture.

Mots-clés

Heavy Metals, Mobility, Sequential Extraction, Sewage Sludge, Wastewater