Phosphorus Recovery from Sewage Sludge Using Acidithiobacilli

Abstract

Sewage sludge contains a significant amount of phosphorus (P), which could be recycled to address the global demand for this non-renewable, important plant nutrient. The P in sludge can be solubilized and recovered so that it can be recycled when needed. This study investigated the P solubilization from sewage sludge using Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans. The experiment was conducted by mixing 10 mL of sewage sludge with 90 mL of different water/liquid medium/inoculum and incubated at 30 °C. The experiment was conducted in three semi-continuous phases by replacing 10% of the mixed incubated medium with fresh sewage sludge. In addition, 10 g/L elemental sulfur (S) was supplemented into the medium in the third phase. The pH of the A. thiooxidans and A. ferrooxidans treated sludge solutions was between 2.2 and 6.3 until day 42. In phase 3, after supplementing with S, the pH of A. thiooxidans treated sludge was reduced to 0.9, which solubilized and extracted 92% of P. We found that acidithiobacilli supplemented with S can be used to treat sludge, i.e., achieve hygienization, removal of heavy metals, and solubilization and recovery of P.

Keywords: Acidithiobacillus ferrooxidans; Acidithiobacillus thiooxidans; bioleaching; phosphorus solubilization; recovery; sewage sludge.

Figure 1

The pH of the incubated solution with different treatments in phases 1, 2, and 3. In phase 3 or 42 days of incubation, 10 mL of sample was replaced with 10 mL of new sludge +1 g of S to 100 mL. The symbols describing the treatments are presented in Table 3.

Figure 2

The total P in sludge at the beginning of each phase and the soluble PO₄-P in supernatants (after filtration) at the end of the different phases of the study. The solution symbol in this figure resembles the total P in the incubated solution at the beginning of each phase.