Influence of sulfur concentration on bioleaching of heavy metals from industrial waste sludge.

The bioleaching process, including acidification and solubilization of heavy metals, is a promising method for removing heavy metals from industrial waste sludge. Solubilization of heavy metals in industrial waste sludge is governed by adding elemental sulfur. A sulfur concentration exceeding 0.5% (w/v) inhibits sulfate production and the activity of acidophilic bacteria. Sulfate production was described well by a substrate inhibition expression in Haldane's kinetics. After 15 days of bioleaching, 79 to 81% copper, 50 to 69% lead, and 49 to 69% nickel were solubilized from sludge with a sulfur concentration of 0.5 to 1.0% (w/v). Experimental results indicated that the optimal sulfur concentration for the maximum solubilization rate of copper and nickel was 0.5% (w/v) and 1.0% (w/v) for lead. The profiles of denaturing gradient gel electrophoresis confirmed that indigenous acidophilic Acidithiobacilli (A. thiooxidans and A. ferrooxidans) existed and were the dominant species in the bioleaching process.

Denitrifying characteristics of the multiple stages enhanced biological nutrient removal process with external carbon sources.

This research investigated denitrifying activity of activated sludge with three external carbon sources (sodium acetate, methanol and glucose) via a series of batch experiments. Activated sludge used was cultivated in a multiple stages enhanced biological nutrient removal (EBNR) process that exhibited high removal efficiency of effective carbon, nitrogen, and phosphorus. Results showed type of external carbon source had a significant influence on specific nitrate utilization rate, nitrite accumulation, adaptive time of microorganisms, and nitrate removal efficiency. Sodium acetate addition resulted in high phosphate concentration in effluent; meanwhile methanol caused increasing turbidity and carbon breakthrough problem. When glucose was fed to be the external carbon source, accumulative nitrite concentration was higher than that with sodium acetate or methanol addition. When sodium acetate, methanol and glucose were used to be the electron donor, average dosages for nitrate elimination were 6.97, 5.85, and 5.65 mg-COD/mg-N, respectively. Because the final polyhydroxyalkanoates (PHAs) concentrations contained within the biomass were more than the original level and no phosphate re-release was observed, glycogen-accumulating organisms (GAOs) might exist in the multiple stages EBNR process and increased carbon dosage for further nitrate removal.