BOD increase of sewage treatment plant effluent after short time pumping due to contamination of nitrifying bacteria

Abstract

In a municipal sewage treatment plant in Tokyo, Japan, it has been observed that BOD value of a secondary effluent containing ammonium increased significantly after a short time pumping through a pipe of about 1 km long. An investigation was made for clarifying a cause of this BOD increase.
Both nitrifying activity and number of nitrifying bacteria increased markedly after pumping. This indicate that BOD increase was caused by the increase of O₂ uptake due to nitrification. Since almost no change of chemical quality was observed during pumping, increase of nitrifying bacteria must be the sole cause of the increase of the nitrifying activity.It was assumed that detachment of the population on the pipe surface was the cause of the increase of nitrifying bacteria after pumping.