Nitrogen transformation in shallow tertiary lagoons: identification of ammonia volatization from liquid surface

• Grant number: 13/24213-3
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: December 01, 2013
• End date: August 31, 2014
• Field of knowledge: Engineering - Sanitary Engineering - Environmental Sanitation
• Agreement: SABESP
• Principal Investigator: Adolpho José Melfi
• Grantee: Karen Cristina Souza de Mello
• Host Institution: Escola Superior de Agricultura Luiz de Queiroz (ESALQ). Universidade de São Paulo (USP). Piracicaba , SP, Brazil
• Company: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALQ)

Abstract

The presence of ammoniac nitrogen in watercourses with high pH may lead to fish mortality due to its toxicity, even in small concentrations for the majority of species. Anthropogenic activities increase the level of nitrogen and other elements in water resources. The discharge of raw sewage or partially treated sewage can be considered one of the main agents to cause pollution and eutrophication of watercourses. Most of the stabilization ponds' effluents show ammonia concentration levels of over 20 mg/L, requiring a complementary treatment system to achieve effluents with lower values than this. To some authors, stabilization ponds are not considered an adequate alternative technique to remove nitrogen. However, recent studies intended to assess the impact of depth in tertiary ponds have shown that nitrogen can be reduced to concentration levels below 5 mg/L by using 50-cm deep tertiary ponds and 10-day hydraulic detention periods. There are disagreements regarding which processes are the most effective to remove this nitrogen form; nitrification, volatilization or nitrogen incorporation by the biomass. It is claimed that, due to the low concentration of nitrite and nitrate found in the ponds' effluents, the nitrification in this kind of system has an insignificant contribution to the reduction of ammonia concentration levels. Therefore, volatilization is recommended as a more significant method. However, in studies found in the literature, the nitrogen sedimentation associated to the biomass, nitrification and denitrification seem to be the main mechanisms to remove nitrogen from photosynthetic ponds. Thus, quantifying the volatilized part and its relevance within the process can ensure the development of more consistent pond dimensioning models for removing ammoniac nitrogen. (AU)