Biological excess phosphorus removal under high rate operating conditions in a suspended growth treatment process

The primary objective of this research was to determine if efficient biological phosphorus removal could be established under low sludge retention time of 2 days and a nominal hydraulic retention time of 4 to 6 hours. The two-stage Phoredox process was selected because of the practical application of retrofitting high rate treatment plants to achieve bio-P removal without the additional tankage required for an anoxic section and the additional expense of a recycle system. It has been shown that nitrate recycled into the anaerobic reactor impacts on bio-P removal and the two-stage Phoredox process provides no control over nitrates entering the anaerobic reactor. Therefore a secondary objective of this research was to determine if a low sludge retention time mode of operation could be used as an effective way to prevent nitrification in the activated sludge treatment process. Another objective was to observe mixed liquor settling characteristics of the two-stage Phoredox process operated under high rate conditions. A pilot scale two-stage Phoredox activated sludge treatment process operating under high rate conditions was used to meet these objectives. The desired bio-P removal biomass was not observed under SRT operating conditions of 2, 3 and 5 days. Partway into the research a sludge bulking condition developed which was identified as filamentous growth. On two occasions this severe filamentous growth resulted in the process failing and the system being restarted. On one occasion after the system was restarted using a seed sludge from a three-stage Phoredox pilot plant, a bio-P removal biomass was present. This condition only lasted for a short period and ended as filamentous growth began to become dominant. The process failed because of this phenomenon. The system was restarted using a seed sludge and again filamentous growth dominated. Chlorine addition was found to be the only method to control this phenomenon and was continued to the end of the research. The desired bio-P removal biomass was not observed even during the last period of the research when the SRT was increased to 8 days. During this research a stable bio-P removal biomass was not established. For a short period a bio-P removal biomass was present but failed to persist. Nitrification never became established at any time. Sludge settleability was poor due to filamentous growth which developed partway into the research and was present throughout the remainder of the study. Chlorine addition was the only method found that remedied this settling problem.Applied Science, Faculty ofCivil Engineering, Department ofGraduat