Transportation of Reclaimed Wastewater through a Long Pipe: Inhibition of Sulphide Production by Nitrite from the Secondary Treatment

Author： Delgado S. Álvarez M. Rodríguez-Gómez L. E. Elmaleh S.

Publisher： Taylor & Francis Ltd

ISSN： 0959-3330

Source： Environmental Technology, Vol.25, Iss.3, 2004-03, pp. : 365-371

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Abstract

The agricultural reuse of reclaimed wastewater has become a necessity in places with water shortages. Frequently, this involves the operation of long transportation pipelines, like in the South Tenerife reuse system, whose main element is a completely filled 61 km long gravity pipe in cast iron. Sulphide generation, which could contribute to pipe corrosion, is a usual process taking place during transportation if anaerobic conditions prevail. In the Wastewater Treatment Plant of Santa Cruz (Tenerife, Spain) a partial nitrification process was achieved by increasing the mean residence time through the aeration step at low dissolved oxygen concentration. Such conditions, combined with the right temperature and a free ammonia concentration above 1 mg l^-1, inhibited nitratation and favoured nitritation, which led to concentrations of NO₂-N above 8 mg l^-1 in the secondary effluent. During the transportation, nitrite inhibited the appearance of anaerobic conditions, and, consequently, no sulphide generation occurred. At the same time, a nitrite reduction process took place with a first order kinetics and a rate coefficient of 0.052 h^-1 at 25°C. A parallel behaviour between the nitrite depletion and the oxidationreduction potential evolution along the pipeline was also observed.