Reduction of nitrous oxide emissions in wastewater treatment: an analysis of operational parameters

Author(s)

Fernanda de Marco de Souza

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola de Artes, Ciências e Humanidades (EACH)
• Defense date: 2024-01-18

Examining board members

Marcelo Antunes Nolasco; João Paulo Bassin; Luciano Matos Queiroz

• Advisor: Marcelo Antunes Nolasco

Abstract

Nitrous oxide (N2O) is a greenhouse gas that is part of the nitrogen cycle and is primarily produced in aerated tanks of Wastewater Treatment Plants (WWTPs). Activated sludge processes are types of treatment widely employed in areas with high population density, such as the Metropolitan Region of São Paulo (MRSP). During the removal of organic and nitrogenous matter, factors such as pH, temperature, dissolved oxygen, and concentrations of ammonia and nitrite influence N2O formation. Thus, operational strategies can be adopted to mitigate emissions. This study aimed to conduct a consolidated analysis of operational conditions aimed at reducing nitrous oxide emissions in sewage treatment plants through conventional activated sludge processes in the MRSP. To achieve this, a four-year operational database (2019 to 2022) was structured, and descriptive and inferential statistical analyses were applied. Additionally, an integrative literature review covering topics related to nitrous oxide formation, emission, and mitigation was conducted to supplement the obtained characterization. A synthesis framework for potential emission classification based on criteria was developed. The ammonia load in aeration tanks ranges from 1.84 to 47.76 tons of N.NH4 per day, providing opportunities to explore recovery strategies. The summer months, and from August to November, are the most prone to emissions. Elevated levels of ammoniacal nitrogen, higher concentrations of nitrite, fluctuations in dissolved oxygen, low pH, and high temperatures are critical factors contributing to increased N2O formation and emission. Finally, a synthesis of operational suggestions for emission reduction was proposed. The aim of this research is to encourage WWTPs to explore new practices and approaches aimed at reducing emissions and optimizing the environmental and social benefits already provided by wastewater treatment. (AU)

• FAPESP's process: 21/02901-1 - Optimization of the operational processes of wastewater treatment plants to reduce nitrous oxide emissions
• Grantee: Fernanda de Marco de Souza
• Support Opportunities: Scholarships in Brazil - Master