Tujuan penelitian ini adalah untuk mereduksi kandungan cod, bod5, dan menormalkan ph pada air limbah rumah sakit, menggunakan sistem pengolahan air limbah mengunakan sistem biofilter aerob-anaerob. hasil penelitian yaitu unit pengolahan air limbah yang di desain dengan menggunakan sistem biofilter aerob – anaerob. biofilter aerob – anaerob yaitu proses pengolahan air limbah dengan cara menggabungkan proses biofilter aerob dan proses biofilter anaerob. dari hasil analisa menunjukkan tingkat penurunan konsentrasi cod yaitu 66,04 %, bod5 yaitu 14,08% dan ph yaitu -6,122%. berdasarkan hasil analisa menunjukan tingkat efektivitas unit pengolahan air limbah dengan sistem biofilter aerob-anaerob yang ditempatkan di rumah sakit angkatan laut ilyas kelurahan pamusian kota tarakan kurang efektif. kata kunci: unit pengolahan air limbah, biofilter aerob-anaerob, efektivitas

The objective of this study is to reduce the content of cod, bod5 and normalize ph levels on hospital waste water, using aerobic-anaerobic wastewater treatment. the result of the research which is the units of wastewater processing designed by using aerobic-anaerobic biofilter system. aerobic-anaerobic biofilter is a process of processing the wastewater by combining the aerobic biofilter system and the anaerobic biofilter system. from the analysis result, it shows that the decreasing level of the cod concentration is 35,86%, bod5 is 14,08% and ph is -6,12%. the criteria of the effectiveness level of the wastewater processing installation according to standard quality decree of the minister of the environment no. 58 of 1995 of cod and bod5 is less effective and the ph is very effective. according the analysis result indicates that the effectiveness level of the units of the wastewater processing by using aerobic-anaerobic biofilter system which is placed in navy ilyas hospital of tarakan city is less effective. keywords: units of wastewater processing, aerobic-anaerobic biofilter, effectiveness