Browsing by Author "Njau, Oscar"

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Assessing the Performance of Constructed Wetland for Acid Mine Drainage Treatment Using Sugarcane Molasses as a Carbon Source
(Scientific Research Publishing, 2025-04-22) Buddy, Zainabu; Njau, Oscar; Rugaika, Anita; Njau, Karoli
Acid mine drainage (AMD) is a widespread environmental issue at mining sites globally. AMD is caused by pyrite oxidation which produces an acidic discharge > 2500 mg/L of sulfate, dissolved heavy metals at high amounts and low pH (2 - 4.5). AMD has serious health impact on living organisms. The present study aimed to assess the performance of locally available, high-organic matter containing by-products, specifically sugarcane molasses (SCM), as a carbon source for AMD treatment. In batch experiments containing SCM and control, 99% sulfate and nitrate reductions were reached. Heavy metal removal efficiencies > 94% were achieved for Cu, Fe, Mn, and Zn, in the SCM inoculated columns, while efficiencies > 42% were recorded in the control columns. The column experiments removed 99% of the initial Al concentrations but were not very effective in COD reduction to acceptable limits. The findings reported by this study verify that high carbon containing substrates can be used to remediate metal and sulfate contaminated water in mining areas.
Fluoride and pathogens removal from water using combined electrocoagulation-inline-electrolytic disinfection process
(NM-AIST, 2024-08) Njau, Oscar
The consecutive removal of fluoride (defluoridation) and pathogens (disinfection) in drinking water through combined electrocoagulation-inline-electrolytic disinfection (EC–ECl2) process with aluminum and dimension-stable mixed oxide electrodes was reported in this study. Laboratory trials have been conducted on the effects of flow rate, initial pH, current density, and supporting electrolytes for defluoridation and disinfection processes. The results have shown that with a flow rate of 10 L/h, initial pH of 6, the current density of 9.4 mA/cm2 (EC cell) and 3.1 mA/cm2 (ECl2 cell), supporting electrolyte concentration of 165 mg/L, and electrolysis time of 50 min, a defluoridation rate of 88% (initial concentration of 12.3 mg/L) and complete disinfection (initial fecal coliforms of 19,700 colony-forming units per 100 mL (CFU/100 mL)) can be reached. The final concentration of fluoride and pathogens in treated water was 1.44 mg/L and 0 CFU/100 mL, which are within the acceptable limit of the World Health Organization and the Tanzania Bureau of Standards of 1.5 mg/L and 0 CFU/100 mL, respectively. The EC–ECl2 system is a promising approach for consecutive defluoridation and disinfection of water to save millions from fluorosis and waterborne diseases. However, optimization potential with regard to energy efficiency and system complexity were identified.
Removal of fluoride and pathogens from water using the combined electrocoagulation-inline-electrolytic disinfection process
(IWA Publishing, 2023-07-01) Njau, Oscar; Otter, Philipp; Machunda, Revocatus; Rugaika, Anita; Wydra, Kerstin; Njau, Karoli
The consecutive removal of fluoride (defluoridation) and pathogens (disinfection) in drinking water through combined electrocoagulation-inline-electrolytic disinfection (EC–ECl2) process with aluminum and dimension-stable mixed oxide electrodes was reported in this study. Laboratory trials were conducted on the effects of flow rate, initial pH, current density, and supporting electrolytes for defluoridation and disinfection processes. The results have shown that with a flow rate of 10 L/h, initial pH of 6, the current density of 9.4 mA/cm2 (EC cell) and 3.1 mA/cm2 (ECl2 cell), supporting electrolyte concentration of 165 mg/L, and electrolysis time of 50 min, a defluoridation rate of 88% (initial concentration of 12.3 mg/L) and complete disinfection (initial fecal coliforms of 19,700 colony-forming units per 100 mL (CFU/100 mL)) can be reached. The final concentration of fluoride and pathogens in treated water was 1.44 mg/L and 0 CFU/100 mL, which are within the acceptable limit of the World Health Organization and the Tanzania Bureau of Standards of 1.5 mg/L and 0 CFU/100 mL, respectively. The EC–ECl2 system is a promising approach for consecutive defluoridation and disinfection of water to save millions from fluorosis and waterborne diseases. However, optimization potential with regard to energetic efficiency and system complexity was identified.