Phosphorus and nitrogen removal at Cadillac, Michigan [Wastewater treatment]

• Published in: Journal - Water Pollution Control Federation Vol. 52; no. 11; pp. 2761 - 2770
• Main Author: Singhal, A.K
• Format: Journal Article
• Language: English
• Published: Water Pollution Control Federation 01-11-1980
• Subjects: Aeration; Ammonia; Biomass; Chlorides; Dyes; Nitrogen; Phosphorus; Plants; Wastewater; Wastewater treatment
• ISSN: 0043-1303; 2327-7467

The wastewater treatment plant in Cadillac removes phosphorus by adding ferric chloride in the aeration system, while ammonia nitrogen is removed by rotating biological surface followed by sand filtration. A full-scale plant study using ferric chloride and polymer was undertaken in January 1973. This study pointed out that the use of an aeration tank for phosphorus removal results in excessive shear on the floc particles formed in the process. At Cadillac 60 ${\rm second}^{-1}$ was found to provide good settling floc. Addition of polymer was not found to be very effective in improving the settleability of the floc particles. Ammonia nitrogen removal system was brought on line in March 1976. After the initial start-up, the plant was not achieving the desired levels of nitrogen removals. Tests were performed for evaluating the performance of the rotating biological surface units, which included microscopic examination and metals analyses of the biological growth attached to the units, and tracer studies for identification of short-circuiting in the rotating biological surface tanks. The test data indicated very significant amounts of short-circuiting, which was corrected, resulting in improvements of ammonia-nitrogen removal. Presently, the plant is achieving effluent ammonia nitrogen of less than 1 mg/l consistently, which is below the required effluent concentration of 2 mg/l.