Inhibition of low molecular organic acids on the activity of acidithiobacillus species and its effect on the removal of heavy metals from contaminated soil

Application of organic fertilizer can reduce the solubility and bioavailability of heavy metals in contaminated soil, but in the flooded anaerobic environment, organic fertilizer will be decomposed to produce a large number of low molecular organic acids, which can inhibit the biological activity of Acidithiobacillus species. Batch cultures studies showed that the monocarboxylic organic acids including formic acid, acetic acid, propionic acid, and butyric acid exhibited a marked toxicity to Acidithiobacillus species, as indicated by that 90% of inhibitory rate for Fe2+ and S0 oxidation in 72 h were achieved at extremely low concentrations of 41.2 mg·L-1, 78.3 mg·L-1, 43.2 mg·L-1, 123.4 mg·L-1 and 81.9 mg·L-1, 230.4 mg·L-1, 170.1 mg·L-1, 123.4 mg·L-1, respectively. Of these organic acids, formic acid was the most toxic one as indicated by that Fe2+ and S0 oxidation was almost entirely inhibited at a low concentration. In addition, it was found that Acidithiobacillus ferrooxidans was more sensitive to low molecular organic acids than Acidithiobacillus thiooxidans. What's more, there was little effect on biological acidification process of heavy metal contaminated soil when organic acids were added at initial stage (0h), but it was completely inhibited when these acids were added after 12 h of conventional biological acidification, thus decreasing the efficiency of heavy metals dissolution from soil. © 2016, Science Press. All right reserved.