DEMONSTRATION OF PHASE LENGTH CONTROL OF BIODENIPHO® PROCESS USING ON-LINE AMMONIA AND NITRATE ANALYZERS AT THREE FULL-SCALE WASTEWATER TREATMENT PLANTS

BioDenipho® process, a Phased Isolation Ditch (PID) technology, accomplishes nitrification and denitrification in a semi-batch manner by periodically changing the flow path through two parallel aeration tanks. The two aeration tanks are periodically aerated according to a fixed (or controlled) phase cycle. Varying phase lengths provides operating flexibility to achieve different treatment objectives. Typically, three control strategies of increasing sophistication are used for phase length control: 1) phase lengths are fixed, 2) phase lengths are controlled by constant setpoints, and 3) phase lengths are controlled by variable setpoints determined by criteria functions.Part of this paper presents results from a four-month testing, which was conducted to study the fixed phase length control strategy at the Louisburg, NC WRF. Three combinations of phase lengths were tested. The study indicates that on-line ammonia and nitrate measurements provided the information for the phase length optimization. The optimized combination of phase lengths resulted in a significant reduction in the effluent total nitrogen (TN) level and suggested a significant aeration energy savings.This paper also summarizes Danish experiences with the phase length control by the criteria functions in two full-scale BioDenipho plants. The experiences from these two plants indicate that the phase length control together with the ammonia dependent DO setpoint control is capable of 1) achieving a 30% reduction in aeration energy, 2) reducing the effluent TN level by at least additional 1.0 mg/L although the plants studied had already achieved excellent effluent quality, and 3) minimizing the occurrences of exceeding effluent limits.