AWWA WQTC62528

The impact of nutrients on growth of nitrifying bacteria is investigated under extreme circumstances encountered in premise plumbing. Growth of nitrifying bacteria used in this study could not be maintained long-term on glass pipes during days of stagnation between introduction of freshwater. However, if pieces of concrete were present, growth was greatly stimulated. With continuous inoculation, nitrifying bacteria could not oxidize ammonia in stainless steel and pure lead pipes for a month of exposure, but could do so thereafter. Similar effects were observed after three months for galvanized iron but not in copper pipe after five months. Studies of nitrification in glass pipe revealed that zinc levels above 150 ppb and copper levels above 500 ppb inhibited nitrification. Phosphorus levels below 1 ppm, calcium below 0.27 ppm and potassium below 3.89 ppm were associated with lower levels of nitrification. Other elements including magnesium, molybdenum, cobalt, manganese, chelated iron, iron, nickel, chromium, tin, lead, aluminum did not have a strong effect on nitrification at levels encountered in drinking water. Control of nutrients including phosphate could be an important strategy to prevention of nitrification. Includes 22 references, tables, figures.