Making a trickling filter/solids contact process work for cold weather nitrification and phosphorus removal

Abstract

It is anticipated that the West Windsor Pollution Control Plant (WWPCP) (Windsor, Ontario, Canada) will be required to be upgraded from its current chemical primary treatment to full secondary treatment, with phosphorus removal maintained. A steering committee established effluent design objectives for effluent suspended solids and total 5-day biochemical oxygen demand of 15 mg/L, total phosphorus of 0.5 mg/L, and ammonia-nitrogen of 3 mg/L. Four processes were tested; among these, the trickling filter/solids contact (TF/SC) process had not been tested previously for consistent nitrification in colder climates where average monthly wastewater temperatures fall to 9 to 10°C. A novel TF/SC treatment scheme was identified that took advantage of the low biochemical oxygen demand of the WWPCP's chemical primary effluent and used higher density cross-flow media than had previously been used in the TF/SC process to achieve nitrification. In initial testing, the TF/SC process nitrified successfully but failed to meet the other objectives. A detailed diagnosis showed that the best process configuration had not been tested and that the pilot design was flawed in several respects. The inclusion of a sludge reaeration tank, the substitution of a flocculator-clarifier for a conventional scraper clarifier, and the elimination of head losses causing excessive floc breakup corrected the problem. In testing over a year-long period, the TF/SC process consistently met the target objectives, moving it up from fourth place to a tie with the other first-ranked process, the biological aerated filter (BAF). Capital costs were found to be lower than for the activated-sludge process and the BAF processes.