[Nitrification and denitrification in the integrated vertical flow constructed wetlands]

Area of Science:

• Environmental microbiology
• Wastewater treatment technologies
• Biogeochemical cycles

Context:

• Integrated Vertical Flow Constructed Wetlands (IVCW) are engineered ecosystems designed for wastewater treatment.
• Understanding microbial processes, specifically nitrification and denitrification, is crucial for optimizing IVCW performance.
• The distribution and activity of nitrifying and denitrifying bacteria within different strata of IVCW systems are not fully elucidated.

Purpose:

• To investigate the nitrification and denitrification rates in various layers of IVCW systems.
• To quantify the abundance and distribution of nitrifying and denitrifying bacteria across IVCW strata using the most probable number (MPN) method.
• To determine the correlation between microbial populations and their respective biogeochemical processes, and the relationship between nitrification and denitrification.

Summary:

• Nitrification and denitrification rates were quantified in IVCW strata, with rates ranging from 0.01-6.35 µg/(g×d) and 3.37-4.19 µg/(g×d), respectively.
• Bacterial populations were assessed, revealing 7.5 x 10^3 - 1.1 x 10^5 MPN/g for nitrifiers and 7.5 x 10^6 - 1.1 x 10 MPN/g for denitrifiers.
• A significant negative correlation (r = -0.9776, p < 0.001) was observed between nitrification and denitrification rates, alongside positive correlations between bacterial numbers and their activities (r = 0.9661, p < 0.001; r = 0.7722, p < 0.025).

Impact:

• The study reveals a spatial gradient in microbial activity within IVCW, with decreasing nitrification and increasing denitrification downstream.
• Findings provide critical data for the design and operation of IVCW systems to enhance nutrient removal efficiency.
• Establishes a quantitative link between microbial communities and nitrogen cycling processes in constructed wetlands, informing future research and application.