Method for controlling filamentous organisms in wastewater treatment processes

A method of reducing the growth of filamentous organisms in an aerobic wastewater treatment process in which the wastewater is deficient in nitrogen comprising the step of:

• adding to wastewater deficient in nitrogen, a nitrogen source selected from the group of nitrogen sources consisting essentially of an oxidized nitrogen source and reduced nitrogen source being added alternately and to the substantial exclusion of each other, and said oxidized nitrogen source being added for periods not exceeding approximately two sludge ages, wherein said nitrogen source supplies substantially all the nitrogen requirements of said aerobic process, said oxidized nitrogen source is selected from the group of nitrogen compounds consisting of sodium nitrate, nitric acid, nitrous acid, sodium nitrite, and calcium nitrate, and said reduced nitrogen source is represented by the formula:
• X--NH.sub.Z
• wherein "X" is an organic or inorganic moiety capable of disassociation or being metabolized to release the NH.sub.Z moiety and "Z" is the integer 1, 2, 3, or 4.