PENGHILANGAN ASAM SULFIDA DALAM BIOGAS MENGGUNAKAN BIOFILTER DENGAN BAHAN PENYANGGA BIJI SALAK

RETNO AMBARWATI SIGIT LESTARI, Prof. Ir. Wahyudi Budi Sediawan SU., PhD

2017 | Disertasi | S3 ILMU TEKNIK KIMIA

Sumber energi alternatif pengganti minyak bumi telah banyak dikembangkan, dan salah satunya adalah biogas. Namun adanya kandungan H2S dalam biogas perlu dihilangkan karena dapat menyebabkan korosi pada peralatan yang digunakan dalam pemanfaatan biogas. Penghilangan H2S dari biogas dapat dilakukan dengan beberapa cara, yaitu secara fisika, kimia maupun biologi. Proses secara biologi dipandang lebih efisien, murah dan lebih ramah lingkungan. Penelitian ini mempelajari eliminasi H2S secara biologi yang dilakukan dengan teknik biofiltrasi. Eliminasi H2S secara biofiltrasi dilakukan dengan menggunakan biofilter yang berupa kolom yang di dalamnya terdapat bakteri pendegradasi H2S yang diimobilisasi pada bahan isian. Bakteri diambil dari lingkungan sekitar, sedangkan untuk bahan isian dipakai biji salak, yang memiliki kandungan karbon cukup besar, berpori, dan memiliki daya serap air tinggi. Bakteri pembentuk biofilm diisolasi dari sludge yang diambil dari tempat pengolahan limbah cair tahu menjadi biogas di desa Srandakan, Bantul, Yogyakarta. Kolom biofilter dibuat dari bahan akrilic dengan dimensi diameter dalam 8 cm dan tinggi kolom 100 cm serta tinggi bahan isian 80 cm. Untuk mengetahui kemampuan biji salak sebagai penyangga biofilm dilakukan uji imobilisasi bakteri yang diambil dari sludge ke permukaan biji salak, dan termyata setelah waktu 2 hari permukaan biji salak sudah ditumbuhi bakteri. Dari hasil imobilisasi bakteri yang diambil dari sludge diperoleh 15 isolat. Uji terhadap 15 isolat untuk mendegradasi sulfida menunjukkan semua isolat mampu mendegradasi sulfida tetapi kemampuannya berbeda. Kemudian dipilih 3 isolat unggul yang dapat mendegradasi sulfida, yaitu isolat 7, isolat 11, dan isolat 12, untuk kembali diuji dalam pembentukan biofilm di permukaan biji salak, dan ternyata diperoleh hasil isolat 12 paling unggul. Dari analisa tersebut isolat 12 teridentifikasi sebagai bakteri Bacillus cereus dengan dengan nilai similaritas 98%. Uji eliminasi H2S yang terkandung dalam biogas menggunakan biofilter yang berisi bakteri Bacillus cereus yang diimobilisasi pada permukaan biji salak pada berbagai kecepatan alir biogas. Diamati kadar H2S pada berbagai posisi aksial kolom dan berbagai waktu operasi. Kolom biofilter juga dicoba untuk penghilangan H2S dalam air, yang ternyata bekerja cukup baik. Untuk mendapatkan diskripsi kuantitatif proses eliminasi H2S dalam biofilter berupa kolom, yang diharapkan dapat dimanfaatkan untuk perancangan biofilter skala besar, diajukan 4 model kinetika. Model 1 mengambil asumsi intra-film gradient tidak ada dan fasa gas quasi-steady-state. Model 2 mengasumsikan intra-film gradient ada dan fasa gas quasi-steady-state. Selanjutnya model 3 disusun berdasar asumsi intra-film gradient tidak ada dan fasa gas unsteady-state. Sedangkan model 4 berasumsi intra-film gradient ada dan fasa gas unsteady-state. Berdasar uji kesesuaian model dengan data percobaan disarankan penggunaan model 2. Namun untuk perhitungan yang tidak perlu teliti, bisa dipakai model 1 yang lebih sederhana. Dapat pula disimpulkan bahwa intra-film gradient cukup berpengaruh, sedangkan fasa gas dapat diasumsi quasi-steady-state. Kata kunci: biogas, biofilm, biofilter, biji salak, eliminasi, hidrogen sulfida

ABSTRACT Alternative energy sources to substitute fossil fuel has been developed, and one of them is biogas. However the content of hydrogen sulfide (H2S) in biogas needs to be removed, because it promotes corrosion in the equipment utilizing biogas. The elimination of H2S from biogas can be done using some methods, namely physical, chemical, and biological processes. Biological process has several advantages such as more efficient, cheaper and environmentally friendly. This research studies the biological elimination of H2S conducted in biofilters column. Elimination of H2S was performed by biofiltration, in which H2S degrading bacteria immobilized on the packing material inside a column. Bacteria was taken from the local area, while salak fruit seed was used as packing material because it has a quite large carbon content, porous and has a high water absorption capability. Biofilm-forming bacteria isolated from sludge was taken from liquid wastewater treatment that convert tofu industry waste into biogas in Srandakan village, Bantul, Yogyakarta. Biofilter column was made from acrylic material with dimensions as follows: 8 cm inside diameter and 100 cm height of a column which has 80 cm high of packing material. To determine the ability of salak fruit seeds as a packing material, it was performed biofilm bacteria immobilization test that taken from the sludge to surface of salak fruit seeds. After 2 days it was observed that salak fruit seed surface was covers with bacteria. From the results of immobilization of bacteria taken from the sludge 15 isolates were obtained. From the test to the 15 isolates in degrading sulfide, it was showed that all isolates have capability to degrading sulfide but with different abilities. Then 3 best isolates were selected, namely isolates 7, isolates 11 and isolates 12, to be re-tested their capability on forming biofilm on the surface of the salak fruit seeds. It was observed that isolates 12 is the best. Further identification showed that isolate 12 was Bacillus cereus with the similarity value of 98%. In the test of H2S elimination in the biogas using a biofilter containing the bacteria Bacillus cereus that immobilized on the surface of the salak fruit seeds at various biogas flow rate, H2S levels were observed at various axial positions of columns and various operating time. Biofilter column is also tested for the removal of H2S in water. It was also works quite well. To obtain a quantitative description of the process of elimination of H2S in the biofilter columns, which is usefull in the design of large-scale biofilters, four kinetics models were proposed. Model 1 assumes intra-film gradient does not exist and the gas phase is quasi-steady-state. Model 2 assumes intra-film gradient exists and the gas phase is quasi-steady-state. Meanwhile model 3 was set-up based on the assumption that intra-film gradient did not exist and the gas phase is unsteady-state. In the meantime model 4 assumes intra-film gradient exists and the gas phase is unsteady-state. Comparison of the calculation results using the four models to the eksperimental data suggested the use of model 2. However, for rough calculation, model 1 could be used for the reason that it is simpler than the other models. It can also be concluded that the model was influence by intra-film gradient, while the gas phase can be assumed to be quasi-steady-state. Keywords: biogas, biofilter, biofilm, elimination, hydrogen sulfide

Kata Kunci : biogas, biofilm, biofilter, biji salak, eliminasi, hidrogen sulfida