Phosphorus dissolution from dewatered anaerobic sludge: Effect of pHs, microorganisms, and sequential extraction

Area of Science:

• Environmental Science
• Environmental Chemistry
• Microbiology

Background:

• Wastewater treatment plants (WWTPs) play a crucial role in nutrient management.
• Phosphorus (P) removal and accumulation in wastewater sludge, particularly Dewatered Anaerobic Sludge (DWAS), require further investigation for resource recovery and disposal.
• Understanding P behavior in sludge under varying conditions is vital for optimizing treatment processes.

Purpose of the Study:

• To investigate the key parameters influencing phosphorus dissolution from DWAS under low pH conditions.
• To evaluate the impact of specific bacterial additions on P dissolution and sludge characteristics.
• To assess the implications of P extraction on the methane production potential of residual sludge.

Main Methods:

• Mass balance analysis of Phosphorus (P) and iron in Limassol WWTP.
• Experimental examination of P dissolution from DWAS under varying pH, anaerobic conditions, and sequential extraction protocols.
• Assessment of the effects of chemolithotrophic acidophilic bacteria and acidophilic Heterotrophic Iron Reducing (HIR) bacteria on P dissolution.
• P fractionation analysis of residual sludge.
• Methane production assays on treated and untreated DWAS.

Main Results:

• Exposure to pH 2.5, anaerobic conditions, and sequential extraction significantly enhanced P dissolution from DWAS.
• Chemolithotrophic acidophilic bacteria inhibited P dissolution, while HIR bacteria slightly increased it and helped maintain lower pH.
• Organically bound P demonstrated low solubility even after acid treatment.
• Residual DWAS after acid treatment exhibited a 45% reduction in methane generation compared to initial DWAS.

Conclusions:

• Low pH (specifically pH 2.5) and anaerobic conditions are critical factors for effective P extraction from DWAS.
• Acidophilic HIR bacteria show potential for aiding P dissolution, but their impact on subsequent anaerobic digestion (methane production) must be considered.
• The recalcitrance of organically bound P limits complete recovery, and acid treatment significantly reduces the biogas potential of the sludge.