Comparative Study of Iron-Oxidizing and Sulfur-Oxidizing Bioleaching Processes for Heavy Metal Removal and Nutrient Leaching from Pig Manure

The potential of using iron-oxidizing and sulfur-oxidizing bioleaching process for removal of heavy metals (HMs) was investigated at initial unadjusted pH of pig manure (PM). The indigenous iron-oxidizing and sulfur-oxidizing microorganisms enriched from PM were primarily Alicyclobacillus and Acidithiobacillus thiooxidans, respectively. After 12 days of bioleaching, 95% of Cu, 96.5% of Zn, 93.6% of Mn, and 92.7% of Cd were removed from the PM in sulfur-oxidizing bioleaching process. Besides, 92.9% of Cu, 94.1% of Zn, 91.9% of Mn, and 90.5% of Cd were removed in iron-oxidizing bioleaching process. Furthermore, 18.1% of TN, 63.3% of TP, 65.4% of TK, and 45.6% of TOC were leached from the PM in the sulfur-oxidizing bioleaching process, whereas only 21.6% of TN, 32.8% of TP, 4% of TK, and 49% of TOC were solubilized in the iron-oxidizing bioleaching process. The X-ray diffraction analysis results demonstrated that there was a large amount of sulfur remained in bioleached manure from the sulfur-oxidizing process which poses a potential risk of soil re-acidification. The Standards, Measurements and Testing Program extraction protocol study on fraction of P in PM showed that the amount of bioavailable P in the sulfur-oxidizing bioleaching process was dramatically declined, whereas it was elevated by 25.9% in the iron-oxidizing bioleaching process. The results obtained in this study indicated that both the sulfur- and iron-oxidizing bioleaching process were able to efficiently remove HMs from PM at initial unadjusted pH, whereas the iron-oxidizing process was proved better method in reserving the fertilizing property and more friendly to the environment.