Acidithiobacillus sp. applied to sewage sludge bioleaching: perspectives for process optimization through the...

Using Acidithiobacillus sp. during bioleaching assays is a well-known biological approach to solubilizing metals within sewage sludge. However, sludge dewatering has also been reported as a secondary treatment benefit. Based on a literature review, the present work provides perspectives regarding the enhancement of bioleaching outcomes on a laboratory scale by establishing optimal operational parameters. Data from different studies suggest that greater bioleaching efficiency may be achieved using a 10% (v/v) mixed inoculum of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans in a ratio of 4:1, supplemented with ferrous sulfate (FeSO₄) and elemental sulfur (S⁰), and an initial system pH near 6.0. However, operational parameters must be established according to the type of sludge being treated due to differences in their compositions. Bioleaching duration is also an aspect that must be considered since treatments conducted for longer than 48 h increased the concentration of Extracellular Polymeric Substances (EPS), a characteristic associated with reducing dewaterability performance.