The importance of nitrogen and phosphorus in stimulating eutrophic conditions in receiving waters has been well documented. As a result, over the last decade an increased emphasis has been placed on limiting these elements in wastewater effluents. In the future, new discharge permits will include limits on both of these elements. In 1985 a research program was initiated to conduct a pilot plant study of an anoxic/anaerobic/aerobic treatment train using primary effluent. The facility was operated at varying flow and Qr/Q ratios, and at effective mixed liquor suspended solids (MLSS) concentrations of 3100 mg/L. The results of the first 13 month operational phase indicated that the effluent concentrations of total BOD[SUB5], TSS and nitrate nitrogen were less than 5mg/L. Ammonia nitrogen was less than 0.2 mg/L. The solids settleability was excellent, and foaming due to Norcadia, was effectively controlled. The average overall phosphorus removal was 48%. Influent BOD[SUB5] concentrations of less than 100 mg/L significantly reduced the system's ability to remove phosphorus. A strong relationship between the amount of carbon source in the influent, phosphorus release in the anoxic and anaerobic tanks and phosphorus uptake in the aeration basin was established. [ABSTRACT FROM AUTHOR]