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.
Highlights
Phosphorus (P) is an important plant nutrient and an increasingly valuable natural resource due to its limited supply
This study showed that A. ferrooxidans and A. thiooxidans pure and mixed cultures survived very well in the sewage sludge for 63 days at 30 ◦ C (Table 4)
In phase 2, the exchange of 10 mL of sludge increased the pH of the solution (Figure 1) and the higher pH might have reduced the solubility of sulfate, which in turn might have inhibited the growth of A. thiooxidans
Summary
Phosphorus (P) is an important plant nutrient and an increasingly valuable natural resource due to its limited supply. A large amount of sewage sludge is generated worldwide every day and the amounts of sludge are expected to increase as a consequence of population growth. There are, several constraints to the reuse of sewage sludge in agriculture: (1) sludge contains a large number of pathogens, (2) it may contain high concentrations of heavy metals, and (3) it is bulky and expensive to transport. Despite these constraints, a significant amount of sludge is recycled in agriculture, which in turn, means that this is one of the main sources of P contamination in water bodies [1]. The sewage sludge has to be treated properly before reuse
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