Wastewater treatment using bentonite, the combinations of bentonite-zeolite, bentonite-alum, and bentonite-limestone as adsorbent and coagulant

Health problems caused by aluminium salts have been recently reported. Various reports have mentioned the direct and indirect toxic effects of metals in the form of tumours, cancers, and allergies. In order to replace aluminium salts as adsorbents and coagulants, the capability of bentonite and combination of bentonite used as coagulants in wastewater treatment via adsorption, ion exchange, and coagulation-flocculation processes were investigated. The optimum conditions (pH and coagulants dosage) were identified for bentonite, the combinations of bentonite-zeolite, bentonite-alum, and bentonite-limestone. The investigation conducted found that bentonite can be a good coagulant which can absorb Chemical Oxygen Demand (COD) for 90.5% of removal. Based on the optimum dosage of the combinations of bentonite, bentonite-zeolite mixture gave high efficiency removal of iron (98%) and turbidity (95%) from others. Meanwhile, the bentonite-limestone mixture produced less sludge volume index and showed lowest zeta potential values. The zeta potential of treated bentonite and bentonite mixed were -26.7 mV for bentonite-alum, -20.7 mV for raw bentonite, -19.9 mV for bentonite-zeolite, and -17.6 mV for bentonite-limestone which demonstrated the coagulation and adsorption process occurred. On the other hand, the effects of contact time indicated that the adsorption capacity of combination bentonite was higher than raw bentonite.