Disentangling microbial coupled fillers mechanisms for the permeable layer optimization process in...

Area of Science:

• Environmental Science
• Water Treatment Engineering
• Microbiology

Background:

• Decentralized rural domestic wastewater treatment relies on Multi-Soil-Layering (MSL) systems.
• Suboptimal nitrogen removal in MSL systems necessitates understanding the role of permeable layers.
• Investigating diverse substrates and microbial communities is crucial for optimizing MSL performance.

Purpose of the Study:

• To investigate the mechanisms of rural domestic wastewater purification using different substrates and microbial systems within MSL.
• To elucidate the role of the permeable layer in enhancing nitrogen removal.
• To understand the microbial community structure and key metabolic pathways involved in wastewater treatment.

Main Methods:

• Experimental investigation of MSL systems with varied substrates (zeolite, green zeolite, biological ceramsite) and microbial inocula (activated bacterial powder, activated sludge).
• Performance evaluation based on removal efficiencies of Chemical Oxygen Demand (COD), Total Phosphorus (TP), and Ammonium Nitrogen (NH₄⁺-N).
• High-throughput 16S rRNA gene sequencing for microbial community analysis.

Main Results:

• Zeolite coupled with microorganisms achieved high removal efficiencies: 93.8% COD, 97.1% TP, and 98.8% NH₄⁺-N within 3 days.
• Activated sludge demonstrated superior nitrification and overall performance compared to specialized nitrifying bacteria powder.
• Zeolite exhibited significant NH₄⁺-N desorption (89.4%), with exchanged ammonium being a major component.
• Microbial analysis revealed dominance of aerobic and parthenogenetic anaerobic bacteria, with absence of obligate anaerobic bacteria.
• The heterotrophic nitrification-aerobic denitrification (HN-AD) process and denitrifying phosphorus-accumulating organisms (DPAOs) were key for simultaneous N and P removal.

Conclusions:

• The permeable layer is critical for MSL system performance, particularly for nitrogen removal.
• Zeolite and activated sludge are effective components for enhancing wastewater purification in MSL systems.
• Understanding the HN-AD mechanism and microbial ecology provides insights for optimizing MSL design and operation for rural wastewater treatment.