This study investigates the use of pozzolan, a volcanic slag, as a packing material in a fixed culture system for biological wastewater treatment. Experimental work was conducted to evaluate the performance of pozzolan in terms of removalofBOD (Biochemical Oxygen Demand), COD (Chemical Oxygen Demand) and NH4+ under different substrate concentrations and bed heights. The results reveal that pozzolan achieved BOD removal efficiencies of up to80% at a concentration of 1g/L with a 20 cm bed height, while COD degradation rates demonstrated a kinetic constant K of 0.080 min-1under the same conditions. At higher concentrations (1.5 g/L) and a 40 cm bed height, the performance was slightly reduced, with COD degradation exhibiting K=0.040min−1K = 0.040 min-1, likely due to substrate saturation effects. Comparatively, scoria showed lower efficiency, with kinetic constants ranging from 0.018 to0.065 min-1, highlighting the superior performance of pozzolan as a packing medium, NH4+