Application of new bacterial regrowth potential method for water distribution system - A clear evidence of phosphorus limitation

Conventionally, biologically available organic carbon is assumed to be the sole limiting nutrient for bacterial regrowth in drinking water distributio n system. A new method,termed bacterial regrowth potential (BRP) method, wa s developed in The University of Tokyo to take into account of other possib ly limiting nutrients. The BRP method is a bioassay, produced results withi n 5 days, had the capability of identifying the limiting nutrient in the sa mple using the indigenous inoculum, and supported the attached bacterial gr owth due to incubation of test tubes in a. rotating plate. The BRP method w as applied for a survey of Tokyo metropolitan drinking water distribution s ystem. The system was distributing around 6 x 10(6) m(3)/d through 14,616 k m long pipes (pipes were interconnected between ten treatment plants) for a round 11 million people. Before distribution, the water had undergone diffe rent treatment trains but all had chlorination as the last step. Mostly the trains included conventional rapid sand filtration system. Exceptions were that one had advanced treatment such as ozonation and biological granular activated carbon in between coagulation/sedimentation and rapid sand filtra tion, two had slow sand filtration, and two others had ground water supply. The survey covered the whole area with a total of 28 samples collected fro m different points at two different limes over a three month period (April- June '95). The results of the survey had clearly illustrated that Inorganic nutrients were limiting in more than half of the samples analyzed. In the rest of the samples biologically available organic carbon was limiting. Wit h the use of phosphorus instead of inorganic nutrients, the limiting inorga nic nutrient was confirmed to be phosphorus. Hence, proper analysis of the water for its actual limiting nutrient and thus the proper control measure is proposed. (C) 1998 Elsevier Science Ltd. All rights reserved.