Biological phosphate removal was investigated in pilot and plant scale at Mansfield, Ohio, to determine waste and sludge amenability and the suitability of the activated sludge plant for a full-scale research or demonstration project. Pilot studies on the effect of MLSS, BOD, phosphate, and hardness concentrations showed only BOD exerted a significant change in phosphate removal. The addition of iron or aluminum salts effectively precipitated the phosphate. Amenability was established following sludge acclimatization when high levels of phosphate were removed from the primary effluent supplemented with a BOD material. Plant studies prior to and following manipulation of the operating conditions did not reveal phosphate removal. The plant is not suitable for full-scale research or demonstration studies without design modifications. (Author)