Identification of Inhibitory Substances Affecting Bioleaching of Heavy Metals from Anaerobically Digested Sewage Sludge

Abstract

Significant inhibitory effects of the filtrate medium of anaerobically digested sewage sludge on iron oxidation by Acidithiobacillus ferrooxidans ANYL-1 were observed in our preliminary experiments, indicating the presence of inhibitory substances in anaerobically digested sewage sludge. The objectives of the present study were to identify the possible inhibitory substances and to evaluate their impacts on metal solubilization during bioleaching of sewage sludge. The results showed that the concentrations of total reducing sugars, all tested metal ions, and anions were too low to suppress iron oxidation, and only organic acids, especially acetic and propionic acids, were found at concentrations higher than their inhibitory levels. The presence of 10.8 mM acetic acid and 9.88 mM propionic acid in sewage sludge (sludge N) led to long lag periods of 6 and 7 days for solubilization of Cu and Cr, respectively, as compared to a lag period of only 1 day in the control and another sludge (sludge S) with a low level of organic acids. Meanwhile the leaching time for maximum solubilization of Zn also extended to 6 days in the presence of organic acids as compared to 3 days in the control. Acetic and propionic acids posed an unfavorable bioleaching condition for anaerobically digested sewage sludge; therefore, further studies are required to explore the means to remove the inhibitory effects to improve the heavy metal bioleaching efficiency.

Effect of Sludge Dissolved Organic Matter on Oxidation of Ferrous Iron and Sulfur by Acidithiobacillus Ferrooxidans and Acidithiobacillus Thiooxidans

“…Generally, sewage sludge is a complex mixture consisting mainly of organic compounds, while organic compounds are potentially inhibitory to chemolithoautotrophic bioleaching bacteria, thus probably decreasing the efficiency of metal dissolution from sludge. In fact, Gu and Wong (2004) have found that the presence of 10.8 mM acetic acid and 9.88 mM propionic acid in anaerobically digested sewage sludge led to long lag periods of 6 and 7 days for solubilization of sludge-born Cu and Cr, respectively.…”

The Effects of Bacterial Leaching on Metal Partitioning in Sewage Sludge

“…Chan et al (2003) have compared iron-and sulphur-oxidizing bacteria on the bioleaching of heavy metals from sewage sludge and obtained a similar pH decreasing trend but at different rates. Considering the organic-rich composition of sewage sludge and the effectiveness of Acidithiobacillus ferrooxidans on metal bioleaching, Gu & Wong (2004) have identified the organic acetic and propionic acids as substances inhibitory to metal bioleaching and solubilization in sewage sludge. From the literature, we observe that in the 80s and 90s, most related texts investigated the fundamental aspects of the process, whereas more recently, research has been focused on specific aspects of optimizing the process.…”

Bioleaching of copper from metal concentrates of waste printed circuit boards by a newly isolated Acidithiobacillus ferrooxidans strain Z1

“…It is an efficient and ecologically benign process because of its low energy consumption and investment, without generating offensive gases, and with relatively low maintenance cost. Therefore, bioleaching has been widely used to recover metals from low-grade minerals, and to remove heavy metals from sludge [2,3], fly ashes [4], heavy metals' contaminated soils [5,6], and sediments [7,8]. It has even been used to leach metals from e-wastes, such as spent batteries [9][10][11][12] and waste printed circuit boards (PCBs) [13][14][15][16].…”