Transportation of reclaimed wastewater through a long pipe: inhibition of sulphide production by nitrite from the secondary treatment.
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 degrees C. A parallel behaviour between the nitrite depletion and the oxidation-reduction potential evolution along the pipeline was also observed.
Delgado
S
S
Dpt. Chemical Engineering, University of La Laguna, Av. Astrof. Fco. Sánchez, S/N. 38200 La Laguna. Spain.
Alvarez
M
M
Rodríguez-Gómez
L E
LE
Elmaleh
S
S
D000641:Ammonia / Q000032:analysis; D003247:Conservation of Natural Resources; D003343:Corrosion; D009566:Nitrates / Q000032:analysis; D009573:Nitrites / Q000032:analysis*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis; D012722:Sewage / Q000032:analysis*; D013440:Sulfides / Q000032:analysis*; D013997:Time Factors; D014186:Transportation / Q000379:methods; D018505:Waste Management / Q000379:methods*
D009566:Nitrates; D009573:Nitrites; D012722:Sewage; D013440:Sulfides; D000641:Ammonia; D010100:Oxygen