The effect of nitrification on sampling sites

• Published in: Water engineering & management 1997-11, Vol.144 (11), p.22-27
• Main Authors: Tokuno, Shin-Ichi, Baker, Floyd
• Format: Article
• Language: English
• Subjects: Ammonia; Bacteria; Basins; Biofilms; Chemical reactions; Chlorination; Chlorine; Disinfection; Disinfection & disinfectants; Effluents; Laboratories; Measurement; Pathogens; Sampling; Studies; Surface water; Surface waters; Water distribution systems; Water quality; Water treatment; Water treatment plants
• ISSN: 0273-2238

Formation of nitrite by nitrifying bacteria in distribution systems could affect water parameters associated with disinfection procedures, including chloramine, ammonia, nitrite, nitrate, pH and heterotrophic bacteria. Where pipework was used to convey a sampling feed of plant water to the laboratory, filming by nitrifying bacteria could affect the analytical results. This was demonstrated at the O.N. Stevens plant in Corpus Christi where plant disinfection used chloramine to a concentration of 3.5-4.5 mg per litre in the finished water. Samples obtained from the primary and secondary basins by dipper showed significant differences from samples taken from the basin by the laboratory taps, particularly from the primary basin samples. The chloramine concentrations were significantly reduced in samples from the laboratory taps compared with dipper samples. Washing the pipework with high test hypochlorite solution restored the equivalence of dipper and tap tests and equivalence was also restored when the basin sampling pipework was not in use during a 14 d basin cleaning period, presumably because of the die-back of nitrifying bacteria. Additional plant and laboratory studies were carried out on the effects of nitrite, temperature and sampling vessel on the stability of chloramine. The information collection rule would require more sampling sites and precautionary measures were required to avoid the effects of nitrification on the accurate measurement of chloramine residual.