Pemanfaatan stillage menjadi biogas melalui proses co-digestion stilage dan kotoran sapi

DAMAYANTI, Sri Ismiyati, Wiratni, S.T.,M.T.,Ph.D

2010 | Tesis | S2 Teknik Kimia

Krisis energi adalah alasan kuat pencarian sumber energi lain, salah satunya adalah biogas. Stillage dengan kandungan senyawa organik yang tinggi dan ketersediaannya yang melimpah seiring meningkatnya produksi bio-etanol, berpotensi dijadikan biogas. pH stillage yang sangat rendah bukanlah kondisi hidup yang baik bagi metanogen. Salah satu hal untuk mengatasinya adalah dengan pengenceran. Namun, pengenceran membuat kandungan air dalam stillage menjadi relatif lebih tinggi. Untuk mendapatkan komposisi senyawa organik yang ideal bagi proses anaerobik, maka ke dalam stillage yang telah diencerkan ditambahkan biomassa lain yaitu kotoran sapi sehingga terbentuk sistem codigestion. Penelitian ini bertujuan mencari starter yang cocok bagi proses co-digestion stillage-kotoran sapi. Biogas dengan kadar metana tinggi diharapkan dihasilkan lebih cepat. Selain itu juga bertujuan mencari konsentrasi stillage yang tepat, dimana pada konsentrasi tersebut sudah tidak terjadi lagi efek penghambatan terhadap proses anaerobik. VFA yang merupakan senyawa intermediate pun, pada konsentrasi tertentu menjadi toksik bagi metanogen. Penelitian ini juga akan mencari strategi pengumpanan stillage yang tepat sehingga akumulasi VFA yang berlebihan pada sistem dapat dicegah. Seluruh pembandingan terhadap berbagai kombinasi komposisi ataupun kondisi proses dalam penelitian ini dilakukan secara kualitatif maupun kuantitatif. Analisis kuantitatif disusun berdasar model matematis yang juga merupakan unsur kebaruan tersendiri dalam penelitian ini. Penelitian dilakukan dalam tiga tahap seperti tampak pada diskripsi berikut. Tahap pertama penelitian bertujuan mengekslorasi starter. Lima digester dioperasikan batch pada suhu kamar. Tiap-tiap digester berisi 275 gram kotoran sapi, 500 mL basal medium dan starter. Dua starter dibandingkan yaitu effluen digester aktif dan cairan rumen. Pada tahap dua, penelitian bertujuan mencari konsentrasi stillage yang tepat. Empat digester dioperasikan secara batch pada suhu kamar. Tiap-tiap digester berisi 200 gram kotoran sapi, 100 gram effluen digester aktif, serta 100 gram stillage pada berbagai variasi konsentrasi. Tahap ketiga penelitian digunakan untuk menentukan strategi pengumpanan yang tepat. Lima digester beroperasi pada suhu kamar, dimana tiap-tiap digester berisi 200 gram kotoran sapi, 100 gram effluen digester aktif, dan 300 mL stillage 3%VS yang diumpankan dengan berbagai variasi pengumpanan. Hasil penelitian menunjukkan bahwa starter yang cocok bagi proses adalah effluen digester aktif. Biogas berkadar metana 50% atau lebih, diperoleh lebih cepat 1 minggu. Stillage berkonsentrasi di bawah 5%VS, dapat menjadi media hidup yang baik bagi metanogen. Pengumpanan yang lebih sering dilakukan adalah strategi pengumpanan yang tepat.

The energy crisis has driven the efforts to find alternative energy sources, one of which is biogas. Stillage with a high content of organic compounds and its abundant availability with the increasing production of bio-ethanol, is potential biomass to produce biogas. However, stillage has a very low pH and this does not provide good living conditions for methanogens. One of possible way to overcome this inhibitory effect is by dilution. On the other hand, the dilution makes the water content in the stillage become relatively higher. To get the composition of organic compounds as close to ideal as possible for anaerobic process, another biomass of cow dung can be added into the diluted stillage to create a codigestion system. This study aimed to find a suitable starter for co-digestion process beetwen stillage and cow-dung. Biogas with high methane content is expected to be produced at a faster rate with the suitable starter. It also aimed to determine the concentration of stillage which did not induce inhibitory effect to the anaerobic process. The stability of the process was observed by monitoring the level of volatile fatty acid (VFA). VFA is an intermediate compound in the anaerobic digestion process that can be toxic to methanogens at certain level of concentration. This research also looked for the stillage feeding strategy that could prevent excessive accumulation of VFA in the system. All comparisons among different combinations of compositions and process conditions/schemes were conducted both qualitatively and quantitatively. Quantitative analysis was performed by mean of mathematical model which was also originally derived in this study. The experiment was conducted in three phase as the following. In the first phase of the experiment for starter exploration, five batch digesters were operated at room temperature. Each digester contained 275 grams of cow dung, 500 mL basal medium, and the starter. Two starters were compared, i.e. active digester effluent and rumen fluid. The second phase of the digester was intended for stillage concentration variation, four batch digesters were operated at room temperature. Each digester contained 200 grams of cow dung, 100 grams of active digester effluent, and 100 grams of stillage at various concentrations. The last phase of the experiment to define the feeding strategy. Five digesters were operated at room temperature. Each digester contains 200 grams of cow dung, 100 grams of active digester effluent, and 300 mL of 3% VS stillage which was fed with a variety of feeding rate. The results indicated that active digester effluent was much better starter to be compared to rumen fluid. With active digester effluent as starter, biogas with methane concentration of 50% or even higher had been obtained in less than 1 week. With respect to stillage concentration, stillage with the concentration below 5% VS was found to be a good medium for methanogenic microorganism.

Kata Kunci : Starter,Kadar metana,Effluen digester aktif,Cairan rumen,Stillage,Co,digestion,Strategi pengumpamaan, starter, methane concentration, active digester effluent, fluid rumen, stillage, co-digestion, VFA, feeding strategy