An efficient oxic-anoxic process for treating low COD/N tropical wastewater: Startup, optimization and nitrifying...

Area of Science:

• Environmental Engineering
• Microbiology
• Wastewater Treatment Technologies

Background:

• Developing tropical countries face challenges with wastewater treatment, particularly for low chemical oxygen demand-to-nitrogen ratio (COD/N) wastewater.
• Conventional treatment systems can be costly and complex, hindering sustainability in resource-limited regions.

Purpose of the Study:

• To assess and optimize a low-dissolved-oxygen oxic-anoxic (low-DO OA) process for cost-effective and sustainable wastewater treatment.
• To determine optimal operating conditions, including hydraulic retention time (HRT) and sludge retention time (SRT), for the low-DO OA process.
• To investigate the microbial community dynamics, specifically nitrite-oxidizing bacteria (NOB) and comammox, under optimized conditions.

Main Methods:

• Optimization of a low-dissolved-oxygen oxic-anoxic (low-DO OA) process.
• Analysis of effluent quality for ammonia and nitrate nitrogen (NO3-N).
• 16S rRNA gene sequencing to characterize the microbial community, focusing on NOB and comammox.

Main Results:

• The optimized low-DO OA process achieved complete ammonia removal.
• Effluent nitrate nitrogen (NO3-N) levels were below 0.3 mg/L.
• A sludge retention time (SRT) of 20 days enriched nitrite-oxidizing bacteria (NOB) and comammox, affiliated with "Candidatus Nitrospira defluvii", leading to efficient nitrification.

Conclusions:

• The low-DO OA process is an efficient and simpler alternative to conventional wastewater treatment methods.
• The recommended operating conditions (16h HRT, 20 days SRT) support robust nitrification performance.
• This process presents a sustainable solution for wastewater treatment in developing countries with low COD/N wastewater.