Optimizing iron removal from sewage sludge ash for enhanced phosphate fertilizer bioavailability

Area of Science:

• Environmental Science
• Materials Science
• Chemical Engineering

Background:

• Sewage sludge derived fertilizer offers a sustainable source for phosphorus (P) recovery from biowaste.
• The presence of iron in sewage sludge ash (SSA) negatively impacts the P availability in fused calcium magnesium phosphate fertilizer (FCMP).

Purpose of the Study:

• To investigate the efficacy of carbothermal reduction for iron removal from SSA.
• To evaluate the impact of carbon addition on P availability and fertilizer properties.
• To develop a process for co-producing FCMP and ferrophosphate.

Main Methods:

• Carbothermal reduction was employed for iron removal from SSA.
• Systematic evaluation of carbon addition performance was conducted.
• Analysis of P availability, chemical composition, and melting point was performed.

Main Results:

• A carbon addition of 4.50% significantly increased P availability from 9.50% to 11.00%.
• Iron removal reduced the required amounts of calcium/magnesium and allowed ferrophosphate production (20.20% P).
• Carbon addition effectively lowered the system's melting point, indicating reduced energy consumption.

Conclusions:

• Carbothermal reduction with carbon addition is a viable method for iron removal from SSA.
• This approach enhances P bioavailability in FCMP and enables co-production of valuable ferrophosphate.
• The study provides a process design for sustainable fertilizer and valuable by-product generation with reduced energy input.