Assessing nitrogen transformation processes in a trickling filter under hydraulic loading rate constraints using...

Area of Science:

• Environmental Engineering
• Microbiology
• Water Treatment

Background:

• Micro-polluted source water requires effective treatment to ensure water quality.
• Trickling filters (TFs) are a common technology for wastewater treatment.
• Understanding nitrogen transformation processes is crucial for optimizing TF performance.

Purpose of the Study:

• To investigate the treatment performance of a trickling filter (TF) under variable hydraulic loading rates (HLRs).
• To elucidate the dominant nitrogen transformation pathways and their molecular drivers within the TF.
• To assess the coupling of nitrogen removal processes at the molecular level.

Main Methods:

• Operation of a trickling filter treating micro-polluted source water at HLRs from 1.0 to 3.0 m(3)/m(2) d.
• Monitoring of chemical oxygen demand (COD) and ammonium-nitrogen (NH4(+)-N) removal efficiencies.
• Analysis of functional gene groups (e.g., amoA, anammox, narG, napA, nxrA, nirK, nirS) using path analysis to determine their role in nitrogen transformation.

Main Results:

• The TF demonstrated high and stable removal efficiencies for COD (97.7-99.3%) and NH4(+)-N (67.3-92.7%).
• Nitrification and anaerobic ammonium oxidation were identified as the primary nitrogen removal processes.
• Path analysis confirmed specific functional gene groups (e.g., amoA/anammox, amoA/(narG+napA), anammox/amoA, nxrA/(nirK+nirS)) as key drivers for different nitrogen species transformations.

Conclusions:

• Trickling filters are effective for treating micro-polluted water, achieving significant COD and NH4(+)-N removal.
• Nitrogen transformation processes within the TF are complex and driven by specific microbial functional gene groups.
• Nitrogen removal processes are molecularly coupled, contributing synergistically to overall treatment efficiency.