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Water Science & Technology—WST Vol 61 No 3 pp 555–561 © IWA Publishing 2010 doi:10.2166/wst.2010.856

Ammonia volatilisation in waste stabilisation ponds: a cascade of misinterpretations?

M. A. Camargo Valero and D. D. Mara

Sección de Saneamiento Ambiental, Departamento de Ingeniería Civil y Agrícola, Universidad Nacional de Colombia, Bogotá, Colombia E-mail: macamargov@unal.edu.co
School of Civil Engineering, University of Leeds, Leeds LS2 9JT, UK


ABSTRACT

Ammonia volatilisation has generally been reported as, or assumed to be, the main nitrogen removal mechanism in waste stabilisation ponds (WSP). Nitrogen removal via ammonia volatilisation is based on two observations: (a) in-pond pH values can reach high values (>9, even >10), so increasing the proportion of the total ammonia present as the un-ionized form or free ammonia (NH3); and (b) in-pond temperatures can also be high, so improving the mass transfer rate of free ammonia to the atmosphere. Consequently, one of the most widely accepted models for ammonia removal in WSP is that reported by Pano & Middlebrooks in 1982, which was developed to reflect the occurrence of these two observations. This work reports how simple mathematical models for ammonia volatilisation in WSP, in spite of the possibility of their giving good predictions, may not accurately describe the main pathways and mechanisms involved in ammonia removal in WSP.

Keywords: ammonia volatilisation; biological nitrogen uptake; maturation ponds; nitrogen removal


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