Abstrak. Penelitian tentang penggunaan membran selullosa asetat menggunakan sistem aliran cross-flow untuk mengolah limbah cair emulsi minyak yang berasal dari industri automotif pada bagian pemotongan logam telah dilakukan. Tujuan dari penelitian adalah untuk mengolah limbah cair emulsi minyak dan untuk melihat pengaruh proses pretreatment terhadap kinerja membran. Mekanisme pemisahan proses ultrafiltrasi adalah filtrasi yaitu molekul yang lebih kecil dari ukuran pori membran akan lolos melewati membran sedangkan yang lebih besar akan tertahan oleh membran. Kinerja proses ultrafiltrasi ditentukan oleh fluks permeat dan rejeksi. Jenis membran yang digunakan adalah jenis membran hidrofilik selulosa asetat. Operasi membran ultrafiltrasi dua tahap ini melibatkan membran selulosa asetat komposisi 12 % (CA-12) untuk operasi tahap I dan membran selulosa asetat komposisi 15 % (CA-15) untuk operasi tahap II dengan waktu operasi masing-masing 90 menit. Tekanan yang digunakan adalah 3,5 Bar. Dua jenis variasi umpan yang akan diolah membran, yaitu umpan limbah tanpa pretreatment dan umpan limbah dengan pretreatment. Fluks untuk operasi membran tahap I, pada limbah tanpa pretreatment 17,03 L/m 2 .jam sedangkan pada limbah dengan pretreatment 59,05 L/m 2 .jam. Pada operasi membran tahap II, fluks pada ke dua umpan hampir sama yaitu 22,08 L/m 2 .jam untuk limbah tanpa pretreatment dan 24,86 L/m 2 .jam untuk limbah dengan pretreatment. Rejeksi COD dan rejeksi surfaktan secara keseluruhan pada kedua operasi membran untuk umpan limbah tanpa pretreatment rejeksi COD mencapai 96,57 % dan rejeksi surfaktan 96,35%, sedangkan untuk umpan limbah dengan pretreatment rejeksi COD mencapai 98,56 % dan rejeksi surfaktan 97,44 %. Dengan adanya proses pretreatment memberikan keuntungan dalam peningkatan fluks dan kualitas permeat yang lebih baik.

Kata kunci : Cutting oil; ultra filtrasi; cross-flow, pretreatment; fluks, konstanta pembentukan cake, analisa SEM, deformasi Effect of pretreatment to the formation of cake layer and membrane structure in the application of ultra filtration cross-flow Membrane for the treatment of oil-water emulsion waste Abstract. A study on the effect of pretreatment on the use of cellulose acetate (CA) membrane using cross-flow system to treat oil-water emulsion waste came from metal cutting process of an automotive industry has been done. The objectives of this research are to see the impact of pretreatment process to flux and cake forming, indicated by cake forming constant (k'), and to study membrane structure. The ultra filtration process performance was determined by obtaining the values of permeate flux and rejection. The material of membrane used in this process was cellulose acetate membrane with 12 % of cellulose acetate composition for first stage operation and 15 % for second stage operation. The duration of the process was 90 minutes operation time, by applying operation pressure at 3, 5 Bar. There were two types of feeding mode applied, the first was feeding without pretreatment and the second was feeding with pretreatment. After some operation periods, the permeate flux decreases due to fouling. On the first stage of membrane operation, for waste without pretreatment, we obtained the value of k'= 0,0004 m 2 /L and for waste with pretreatment k'= 0,0001 m 2 /L. On the second stage membrane operation, for waste without pretreatment the value of k'= 0,0009 m 2 /L and for waste with pretreatment k'= 0,0002 m 2 /L. The results mean that pretreatment reduce significantly formation of the cake. It was also obtained that the structure of the membrane is asymmetric. It was shown that deposition of contaminant also occurs within the spinger of the membrane (inner structure of the membrane). Deformation of the membrane spinger was also observed. It is concluded that pretreatment applied to feeding solution increase the running time of the membrane. The benefit of membrane operation used feed with pretreatment, beside increases permeate fluks also decreases the cake forming constant which will longer operation time of membrane.