Acidification and recovery of phosphorus from digested and non-digested sludge

Area of Science:

• Environmental Chemistry
• Wastewater Treatment Engineering
• Resource Recovery

Background:

• Wastewater sludge contains significant phosphorus, a valuable resource.
• Current phosphorus recovery methods face challenges with efficiency and sludge type variability.

Purpose of the Study:

• To investigate the efficacy of acid dissolution for phosphorus recovery from digested and non-digested wastewater sludge.
• To determine optimal conditions for phosphorus release and assess associated heavy metal mobilization.

Main Methods:

• Acidification of digested and non-digested sludge from five wastewater treatment plants using sulfuric acid.
• Varying pH levels to determine optimal phosphorus dissolution.
• Analysis of phosphorus release and heavy metal concentrations in the treated sludge.

Main Results:

• Acidification dissolved up to 80% of phosphorus from digested sludge, compared to ~25% from non-digested sludge.
• Optimal phosphorus release occurred at pH 2.
• Iron and calcium compounds were primary drivers of phosphorus release at low pH.
• Heavy metal release (Zn, Cd, Ni) was generally low (<30%), with higher mobilization observed in non-digested sludge.

Conclusions:

• Acidification is a viable method for enhancing phosphorus recovery from wastewater sludge, especially digested sludge.
• Controlling pH is critical for maximizing phosphorus release while minimizing heavy metal mobilization.
• Understanding sludge composition, particularly buffer systems, is key to optimizing acid consumption for phosphorus recovery.