Tertiary treatment on effluent from the EPA-DC Pilot Plant's step aeration activated sludge system included two-stage or single-stage lime clarification, air stripping of ammonia, dual-media filtration, neutralization, and activated carbon adsorption. With a good secondary effluent to the lime clarification units and the dual-media filtration system, the two-stage process produced residual BOD and phosphorus (as P) concentrations of 1.4 mg/l and 0.09 mg/l, respectively. With fresh carbon, the TOC was less than 3 mg/l after treatment by carbon adsorption. Single-stage operation with sodium carbonate addition and with a good quality secondary effluent as feed produced an average phosphorus residual of 0.53 mg/l as P after clarification. Following dual-media filtration, the phosphorus residual as P was reduced to 0.10 mg/l. With a poor quality secondary effluent (filamentous growth), the slurry pool in the first-stage solid contactor unit was unstable and produced lower quality effluents. At warm air temperatures (greater than 75F), 80 percent of the ammonia was air stripped from the effluent of the two-stage lime system. Recalcined lime was recycled to the clarification system without a reduction in the efficiency of the tertiary system.

Contract no. 14-12-818. Project officer: Dolloff F. Bishop. "EPA-600/2-76-251." "November 1976."