Chitosan-Type Bioadditive-Modified Electronic Industry Waste Sludge for Heavy Metal Stabilization with Assistance of Microwave Heating

Abstract

Cement solidification is used as the common method for stabilizing industrial wastewater sludge in Taiwan. However, this method has the disadvantage of increasing the volume of waste. In contrast, chitosan-type biopolymer is used by several researchers for biosorption applications and dye discoloration in aqueous solutions. Therefore, in this study, commercially available low-cost chitosan-type material was used as an alternative bioadditive to stabilize the leaching of heavy metal ions in industrial sludge. The effects of additive dosage amount, power of microwave irradiation, and reaction time were studied. The heavy metal leaching capacity was determined using a standard TCLP test, and the elemental content in the leachate was analyzed by ICP. It was found that chitosan effectively stabilizes copper ions with higher selectivity in the presence of microwave irradiation and other toxic heavy metal ions. The optimized additive mixing in industrial sludge for the control of the leaching of copper and other heavy metal ions was found to be <5 mg L−1 after a microwave heating process in nitrogen atmosphere rather than air. Complete stabilization was achieved for chromium and cadmium (not detected after a TCLP test) compared to other heavy metal ions. The heavy-metal-ion-stabilized sludge was further tested for dye discoloration efficiency. Chitosan-modified sludge exhibited complete discoloration for the dye compounds methlylene blue and acid red 114.