A sand-media upflow filter was installed at an existing trickling filter sewage treatment plant which receives combined domestic and industrial waste, to test its effectiveness in a tertiary treatment function. Preliminary testing was performed at three different flow rates and with different chemicals as flocculants and coagulant aids to determine optimum conditions for final, full-scale testing. In the final, full-scale test phase, a flow rate equivalent to 0.5 MGD was used, and alum was injected as required to produce satisfactory turbidity levels in filter effluent. The operation was monitored constantly for flow rate, inlet pressure, water temperature and alum input; influent and effluent values for turbidity, suspended solids, BOD, COD, total phosphate, orthophosphate and pH were determined. Filter performance was inconsistent and generally unpredictable. Alum as a coagulant was effective as an aid in contaminant reduction. Polyelectrolytes used as coagulant aids to the alum proved ineffective in developing floc strength and extending the cycle duration.