Simultaneous nitrification and p-cresol oxidation in a nitrifying sequencing batch reactor.

Area of Science:

• Environmental Microbiology
• Biotechnology
• Wastewater Treatment

Background:

• p-Cresol is a common industrial pollutant that can inhibit nitrification processes.
• Nitrifying sludge requires evaluation for its tolerance and kinetic behavior when exposed to organic contaminants.
• Sequencing batch reactors (SBRs) are versatile systems for biological wastewater treatment.

Purpose of the Study:

• To assess the tolerance, kinetic behavior, and oxidizing capacity of nitrifying sludge exposed to varying p-cresol concentrations.
• To evaluate the simultaneous removal of ammonium and p-cresol in a nitrifying SBR.
• To understand the long-term effects of p-cresol exposure on nitrification and sludge characteristics.

Main Methods:

• Operation of a sequencing batch reactor (SBR) with nitrifying sludge.
• Exposure of sludge to initial p-cresol concentrations ranging from 25-150 mg/L.
• Feeding the SBR with 200 mg NH(4)(+)-N/L and monitoring ammonium oxidation and p-cresol consumption.
• Analysis of specific rates for ammonium oxidation, nitrate formation, and organic carbon consumption.
• Assessment of microbial growth rate and sludge settleability (Sludge Volume Index).

Main Results:

• The nitrifying SBR successfully operated up to 300 mg/L of p-cresol, achieving complete ammonium oxidation and total p-cresol consumption.
• p-Cresol significantly inhibited ammonium consumption rates, indicating pathway inhibition.
• After 7 months, specific rates were 0.6g NH(4)(+)-N/g protein-N/h, 0.3g NO(3)(-)-N/g protein-N/h, and 0.24g TOC/g protein-N/h.
• Microbial growth rate remained low (max 12.2 mg protein-N/L/d) with good sludge settleability (SVI < 21 ml/g).
• p-Cresol oxidation accelerated over cycles, and nitrification inhibition decreased with continued operation.

Conclusions:

• Nitrifying sludge demonstrates significant tolerance and oxidizing ability towards p-cresol, enabling simultaneous pollutant removal and nitrification.
• Long-term operation in an SBR improves the efficiency of p-cresol degradation and reduces nitrification inhibition.
• The study highlights the potential of nitrifying SBRs for treating wastewater contaminated with p-cresol and ammonium.