<![CDATA[PT.X bergerak di bidang produksi teh menghasilkan limbah dari proses pencucian mesin produksi. Air limbah hasil pencucian mengandung bahan organik dan oli yang menjadi faktor tingginya COD, mencapai 11.647 mg/L melebihi NAB (300 mg/L). Tujuan penelitian untuk mengetahui perbedaan waktu kontak aerasi 1 hari, 2 hari dan 3 hari terhadap penurunan kadar COD. Jenis penelitian studi eksperimen (desain pretest–posttest without control) secara grab sampling. Pengukuran 3 variasi dan 6 kali pengulangan setiap variasi. Volume reaktor 47,7 liter dan EM4 5%. Penurunan COD tertinggi adalah variasi waktu kontak 3 hari yaitu 8249 mg/L (80%) menjadi 2023 mg/L dari kadar awal COD 10.271 mg/L setelah pengendapan 1 hari. Persentase penurunan variasi 1 (64%), 2 hari (74%) dan 3 hari (80%). Uji One–Way Anova (p value?0,05). Persentase COD kurang maksimal diketahui karena kondisi oksigen yang tidak seimbang dengan jumlah bakteri. Saran yang dapat diberikan yaitu dengan pre treatment atau sedimentasi sebelum aerasi, serta menambahkan EM4 konsentrasi lebih tinggi agar menghasilkan penurunan COD sesuai baku mutu Abstract: PT.X is engaged in the production of tea producing waste from the washing process of production machines. The washed wastewater contains organic matter and oil which is a factor in the high COD, reaching 11,647 mg/L exceeding the NAV (300 mg/L). The purpose of the study was to determine the difference in aeration contact time of 1 day, 2 days and 3 days on the decrease in COD levels. The type of research is an experimental study (pretest–posttest without control) by grab sampling. Measurement of 3 variations and 6 repetitions of each variation. The reactor volume is 47.7 liters and EM4 is 5%. The highest decrease in COD was the variation in 3-day contact time of 8249 mg/L (80%) to 2023 mg/L from the initial COD level of 10,271 mg/L after 1 day precipitation. The percentage decrease in variation was 1 (64%), 2 days (74%) and 3 days (80%). One-Way Anova test (p value?0.05). The percentage of COD is not optimal because of oxygen conditions that are not balanced with the number of bacteria. Suggestions that can be given are pre-treatment sedimentation, and adding a higher concentration of EM4 to produce a decrease COD according to quality standards]]>
