Removal of Heavy Metals from Sewage Sludge Using Sugarcane Waste Extract

Introduction: The disposal of Sewage Sludge (SS) or its application on farmlands is of public health concern, owing to the potentials of Heavy Metals (HMs) in SS to deteriorate soil, ground water quality and bioaccumulate in food chains. Conventional inorganic chelating agents used for removing HMs are mostly expensive and have negative environmental impacts.
Aim: This study, therefore, determined the efficacy of fermentation extracts from Sugarcane Wastes (SWs) in removing HMs from sewage sludge.
Methodology: An experimental design was adopted. Crude Fermentation Extract (CFE) and Fungus-specific Fermentation Extract (FFE) were used to remove Copper, Zinc, Chromium, Nickel, Cadmium and Lead from SS, and Commercial-grade Citric Acid (CCA) used as control. The experiment was carried out by adding 20 ml of the treatment (extracts and control) at various pH (3 – 6) to 1g of SS each. The mixture was centrifuged after a contact time of 1-5 days at 1000 rpm for 1hour. The filtrate was analysed for Heavy Metals Concentrations(HMCs) and compared with National Environmental Standards and Regulations Enforcement Agency (NESREA) permissible limits. Data were analyzed using descriptive statistics and ANOVA at P=0.05.
Results: The HMCs (mg/Kg) in the SS were Cu (311.4±4.8), Zn (2081.0±30.0), Cr (10.8±1.3), Ni (31.5±1.4), Cd (2.5±0.1) and Pb (167.5±9.4). The concentrations were below the permissible limits (mg/Kg) set by NESREA for Cr (100.0), Ni (70.0) and Cd (3.0) but higher for Cu (100.0), Zn (421.0) and Pb (164.0). Optimum HMR was achieved on day 5 at pH 3 for Cu, Cr, Cd and Pb by CFE, FFE and CCA; and at varying pH (3-4) for Zn and Ni. The concentration of Cr, Ni and Pb removed by CFE was significantly higher than FFE, but showed no significant difference for Cu and Cd. Both extracts showed higher HMR compared with control, except for Cu and Pb; and reduced the concentrations of Zn and Pb to acceptable levels.
Conclusion: Crude fermentation extract of sugarcane wastes was most effective in removing the heavy metals except Copper from sewage sludge. Therefore, its use could be adopted and promoted for removing these heavy metals from sewage sludge to achieve safe disposal.