Controlled sequential biocathodic denitrification for contaminated groundwater bioremediation.

Area of Science:

• Environmental Science
• Water Treatment Technologies
• Biotechnology

Background:

• Nitrate groundwater contamination is a significant global environmental and health concern.
• Existing denitrification methods face challenges in efficiency and scalability.
• Autotrophic denitrification offers a sustainable alternative for nitrogen removal.

Purpose of the Study:

• To evaluate the efficacy of a novel two-stage, sequential biocathodic denitrification system for synthetic groundwater.
• To determine the system's performance across various nitrate loading rates and hydraulic retention times (HRT).
• To assess nitrate and total nitrogen removal efficiencies and identify operational parameters for optimal performance.

Main Methods:

• A two-stage, sequential biocathodic denitrification system was employed.
• The system was operated with synthetic groundwater at constant nitrate concentration (40 mg NO3--N/L).
• Nitrate loading rates were varied from 66 to 301 g NO3--N/m3NCC/d, and HRT from 14 to 3 h.

Main Results:

• Achieved >95% nitrate and >92% total nitrogen removal at loading rates of 66-200 g NO3--N/m3NCC/d.
• The first stage met WHO drinking water guidelines for nitrate (<11.3 mg NO3--N/L) and nitrite (<0.9 mg NO2--N/L) up to 167 g NO3--N/m3NCC/d.
• N2O accumulation in the first stage was observed above 200 g NO3--N/m3NCC/d but effectively removed in the second stage; maximum removal rate was 259.83 g NO3--N/m3NCC/d at 3.19 h HRT.

Conclusions:

• The two-stage biocathodic system is highly effective for autotrophic denitrification of groundwater.
• The system demonstrates robust performance, achieving high nitrogen removal efficiencies.
• Optimized HRT and loading rates are crucial for maximizing efficiency and minimizing by-product formation.