The Philadelphia Water Department is investigating the biological stability of drinking waters throughout its treatment processes and distribution systems by studying natural organic matter (NOM) dynamics. Biologically stable water will not support the growth of microorganismsduring transmission from the treatment plant to the user. The study is using the biodegradabledissolved organic carbon (BDOC) bioassay as a measure of biostability. The goal is to characterize the BDOC within the pool of NOM, beginning with the raw water or treatment plant influent. Biofilm reactors were used to measure BDOC concentrations, installing duplicate bioreactors in the filter galleries of Baxter Water Treatment Plant (WTP) and Belmont WTP. The bioreactors were colonized and continuously fed with filtered water from the Schuylkill River (Belmont) and the Delaware River (Baxter) providing the bacterial inoculum and the nutrient plus energy supplies. Weekly water samples were taken for the measurement of dissolved organic carbon (DOC) in the bioreactor influent and effluent to calculate the raw water BDOC by difference. The results demonstrate the feasibility and utility of operating bioreactors within full-scale treatment plants as a means of following the temporal dynamics of surface water supplies from large urban rivers. A colonization phase was observed within the bioreactors, followed by a stable or plateau phase at both WTPs, good precision between duplicate bioreactors, and consistent differences between the two river supplies. BDOC concentrations in the Delaware River were significantly lower than those measured in the Schuylkill River. The bioreactor BDOC method yielded more stable and faster results than BDOC measurements made with a month-long batch culture method. Includes 8 references, figures.
