Revealing degradation and enhancement mechanisms affecting copper (Cu) immobilization using microbial-induced carbonate precipitation (MICP)

Abstract

Inappropriate handling of copper-rich water bodies could cause serious threats to surrounding environments and human health. Remedying Cu2+ using the environmental-friendly MICP technology starts drawing great attention from scientists and practitioners, but a rather low Cu immobilization efficiency has been reported in a significant body of research. The present work investigated how the degree of urea hydrolysis and pH surrounding conditions varied with the effect of culture medium, bacterial suspension dosage, and CaCl2 addition using the test tube experiments. The speciation of carbonate precipitation was further analysed by the numerical simulations to reveal the underlying mechanisms affecting the Cu immobilization efficiency. The results indicated that a low Cu immobilization efficiency is attained either using lower or higher degrees of urea hydrolysis. Although higher bacterial suspension dosages cause an improvement in the resistance of the ureolytic bacteria against the effect of Cu toxicity, pH surrounding is lifted up, promoting the formation of copper-ammonia complex and imposing risks of Cu2+ migration. A combination of yeast extract and CaCl2 addition can not only improve the degree of urea hydrolysis by competing for adsorption with Cu2+ but also accelerate the consumption of OH-, thereby securing the Cu immobilization efficiency. The findings shed light on the potential of applying the MICP technology to copper-rich water bodies immobilization.