Application of bio-coagulants derived from banana peels, seashells, and eggshells for municipal wastewater treatment: A comparative study

Municipal wastewater treatment increasingly seeks sustainable alternatives to chemical coagulants due to their environmental impacts. This study evaluates bio-coagulants derived from calcined banana peels, seashells, and eggshells as potential substitutes for poly-aluminium chloride (PAC) in removing turbidity, colour, and chemical oxygen demand (COD). Banana peels were calcined at 600 ℃ , while eggshells and seashells were calcined at 800 ℃ . The resulting materials were characterised using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller and Fourier transform infrared spectroscopy to assess structural and functional properties relevant to coagulation. Experimental results showed that calcined bio-coagulants achieved over 80% removal across the tested parameters, with calcined banana peels (CBP) demonstrating the highest performance. Optimisation studies using the Box-Behnken Design identified ideal operating conditions of 87 rpm agitation speed, 11 min mixing time, 32 min settling time, and 4.22 g/L bio-coagulant dosage. Under these conditions, CBP achieved removals of 89.3% COD, 86.5% turbidity, and 80.1% colour. Although PAC achieved higher turbidity (98.6%) and colour (99.5%) removal, its COD reduction (54.6%) was significantly lower. CBP maintained consistently high efficiencies while reducing sludge toxicity. The findings of the study suggest that CBP, in particular, is a promising sustainable coagulant for municipal wastewater treatment, warranting further research into formulation enhancement and large-scale application.