Background: The use of strain-specific microbial fermentation in the production of organic acids for the removal of heavy metals from sludge has been extensively studied. However, there is scarce information on the use of microflora for fermentation.
Objectives: To assess the efficacy of cassava peel extracts for the removal of heavy metals from hospital sewage sludge in Nigeria.
Methods: A composite sewage sludge sample was collected from the University College Hospital sewage treatment plant in Ibadan, Nigeria and analyzed for heavy metals using standard methods. Aspergillus niger fermentation and crude fermentation extract were obtained from the cassava peels strain of Aspergillus niger and indigenous microflora, respectively. The experiment was carried out by adding 10 ml of the treatment to 3 g of each sludge sample (extracts and controls) at varied temperatures (room and elevated) and pH (3-5). The mixture was centrifuged after a contact time of 1-12 days at 1000 rpm for 1 hour. The filtrate was analyzed for heavy metals concentrations and compared with the standards. Data were analyzed using descriptive statistics and adsorption models.
Results: Mean heavy metal concentrations in the sludge were estimated for copper (2.22±0.2 mg/kg), zinc (52.3±0.1 mg/kg), chromium (1.46±0.1 mg/kg), nickel (5.6±0.01 mg/kg), and lead (1.9±0.1 mg/kg) and were below permissible limits. Optimum heavy metal removal for Aspergillus niger fermentation extract at room temperature was achieved on day 12 at pH 3.5 for zinc (74.5%), while optimum heavy metal removal at elevated temperature was achieved on day 9 at pH 3.0 for lead (79.3%). The optimum pH for crude fermentation extract lies between pH 3.0-4.5 for nickel (76.2%) at room temperature and chromium (76.6%) at elevated temperature.
Conclusions: Crude fermentation extract of cassava peel was found to be effective in removing heavy metals from sewage sludge. Therefore, its use could be adopted and promoted for removing heavy metals from sewage sludge to achieve safe disposal.
Competing interests: The authors declare no competing financial interests.
Keywords: Aspergillus niger fermentation extract; cassava peels; crude fermentation extract (CFE); heavy metals; sewage sludge.