<![CDATA[Variations in filtration media and hydraulic retention time are important factors in optimizing wastewater quality improvement. The objective of this study is to recommend the optimal height level of gravel and silica sand (SiO2) combination and contact time in physical treatment methods for improving the quality of coffee processing wastewater. Three height-level variations of the gravel–silica sand filtration media combination were tested, namely 10:5 cm (T1), 7.5:7.5 cm (T2), and 5:10 cm (T3), along with two flow rate variations of 5.5 mL/second and 9.5 mL/second. All treatments were conducted in three replications to determine the standard error of the experimental data. The best-performing treatment was a combination of 5 cm gravel and 10 cm silica sand (T3) at a flow rate of 5.5 mL/second, which reduced turbidity, Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD), ammonia (NH3), and phosphate (PO4) by 61.65±1.43%, 49.00±6.66%, 50.66±4.35%, 53.75±4.35%, and 76.99±4.54%, respectively, at a hydraulic retention time of 4 hours. The height level of the gravel and silica sand (SiO2) media, along with the optimum hydraulic retention time, had a positive effect on reducing pollutant content in coffee processing wastewater.]]>
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