Making waves: Reevaluating iron dosing for carbon recovery in mainstream wastewater treatment system

Area of Science:

• Environmental Engineering
• Water Treatment Technologies
• Sustainable Wastewater Management

Background:

• Wastewater treatment plants (WWTPs) aim for energy efficiency and carbon neutrality.
• Iron-enhanced primary treatment (Fe-CEPT) is a strategy for carbon capture and energy recovery.
• The impact of Fe-CEPT on downstream processes, particularly anaerobic digestion, requires further investigation.

Purpose of the Study:

• To comprehensively evaluate iron dosing for carbon recovery in mainstream wastewater treatment.
• To assess the effectiveness of Fe-CEPT in capturing organic carbon and phosphorus.
• To investigate the influence of iron-rich sludge on methane production during anaerobic digestion.

Main Methods:

• Review of existing literature on Fe-CEPT and its effects on wastewater sludge.
• Analysis of iron content in sludge and its correlation with organic carbon bioavailability.
• Evaluation of methane production inhibition in anaerobic digestion due to high iron concentrations.

Main Results:

• Fe-CEPT effectively captures particulate organics and phosphorus but is less effective for soluble organic carbon.
• Sludge from Fe-CEPT contains high iron levels (100-200 mg Fe/g SS), significantly inhibiting methane production.
• Elevated iron binds approximately 20% of sludge carbon, reducing its bioavailability for anaerobic digestion.

Conclusions:

• Coupling Fe-CEPT with anaerobic digestion may not be optimal for carbon recovery due to methane inhibition.
• A modified approach using high-rate activated sludge (HRAS) with limited iron dosing (<10 mg Fe/L) is proposed.
• This revised strategy could enhance carbon recovery, improve phosphorus management, and reduce the environmental footprint of WWTPs.