Prediction of Methane Potential Production from High Volatile Fatty Acids in Modified Anaerobic System of Palm Oil Mill Effluent

Abstract

The treatment of palm oil mill effluent (POME) remains a major challenge due to its highly complex characteristics, comprising elevated concentrations of organic pollutants, suspended solids, oils and greases, and recalcitrant lignocellulosic compounds. Conventional anaerobic systems frequently experience operational instability resulting from the accumulation of volatile fatty acids (VFAs), imbalances between the fermentation and methanogenesis phases, and a substantial fraction of refractory COD that cannot be effectively degraded. Therefore, this study was conducted to evaluate an integrated treatment system combining an oil palm empty fruit bunch (OPEFB) fiber filtration unit as a pretreatment step and a modified anaerobic rotating biological contactor (AnMRBC) as the biological treatment unit to enhance POME processing efficiency. The research utilized stalk and spikelet fibers from OPEFB as physical adsorptive filtration media to reduce particulate and organic loads before the biological reactor. The AnMRBC unit was operated under continuous flow with hydraulic retention times (HRTs) of 4, 3, and 2 days. The results showed that the OPEFB filtration unit successfully reduced TSS, OG, TN, and BOD by an average of 55.62%, 44.39%, 35.45%, and 20.17%, respectively, thereby decreasing the organic loading entering the biological unit. Variations in HRT in the AnMRBC (4, 3, and 2 days) produced TCOD removal efficiencies of 71.40–83.50%, SCOD 42.60–84.46%, BOD 28.57–77.78%, OG 29.09–96.57%, and TN 49.58–79.70%, with the best performance observed at an HRT of 4 days. Based on the empirical formula of POME (C7H11O2N), the stoichiometric methane yield was calculated to be 0.385 L CH4/gCOD with a theoretical methane composition of 69.77%, while the estimated daily stoichiometric methane production ranged from 9.83 to 39.45 L CH4/L·day. Kinetic modeling produced parameter values of µm (3.255 day?¹), Ks (0.246 g/L), B0 (0.335 L CH4/gCOD), and a refractory coefficient (0.485), indicating a high proportion of non-degradable COD. The kinetic evaluation revealed that hydrolysis in the AnMRBC reactor was not inhibited, yet suboptimal methanogen growth limited methane generation. Overall, the integrated system demonstrated effectiveness as a pretreatment and primary treatment approach, but the effluent still failed to meet regulatory discharge standards, indicating the need for additional polishing units.

Pengolahan limbah cair kelapa sawit (LCKS) masih menjadi tantangan besar sebab karakteristiknya yang sangat kompleks, mengandung polutan organik yang tinggi, padatan tersuspensi, minyak dan lemak, serta komponen lignoselulosa yang sulit terdegradasi. Pengolahan dengan sistem anaerobik konvensional cenderung mengalami ketidakstabilan akibat akumulasi asam lemak volatil (VFA), ketidakseimbangan fase fermentasi-metanogenesis, serta tingginya fraksi COD resisten yang tidak dapat didegradasi secara efektif. Oleh sebab itu, penelitian ini dilakukan untuk mengevaluasi sistem terintegrasi antara unit filtrasi serat tandan kosong kelapa sawit (TKKS) sebagai pra-perlakuan dan anaerobic modifikasi rotating biological contactor (AnMRBC) sebagai unit pengolahan biologis untuk meningkatkan efisiensi pengolahan LCKS. Penelitian dilakukan dengan menggunakan stalk dan spikelet fiber dari TKKS sebagai media filtrasi fisik-adsorptif untuk menurunkan beban organik dan partikulat sebelum memasuki reaktor biologis. Unit AnMRBC dioperasikan dengan variasi hyraulic retention time (HRT) 4, 3, dan 2 hari dalam sistem aliran kontinyu. Hasil penelitian menunjukkan bahwa unit filtrasi OPEFB mampu menurunkan TSS, OG, TN, dan BOD dengan rata-rata 55.62%, 44.39%, 35.45%, dan 20.17%, sehingga menurunkan beban organik menuju unit biologis. Variasi HRT pada AnMRBC (4, 3, dan 2 hari) menghasilkan efisiensi penghilangan TCOD 71.40-83.50%, SCOD 42.60-84.46%, BOD 28.57-77.78%, OG 29.09-96.57%, dan TN 49.58-79.70%, dengan performa terbaik pada HRT 4 hari. Berdasarkan formula empiris POME (C7H11O2N), nilai stoichiometric methane yield diperoleh sebesar 0.385 L CH4/g COD dengan komposisi gas teoritis 69.77% CH4, sedangkan stoichiometric methane production harian berada pada kisaran 9.83-39.45 L CH4/L·hari. Analisis kinetic model menghasilkan parameter µm (3.255 hari?¹), Ks (0.246 g/L), B0 (0.335 L CH4/gCOD), dan refractory coefficient (0.485), menandakan tingginya fraksi COD yang tidak terurai. Hasil evaluasi kinetika menunjukkan bahwa hidrolidid di dalam reaktor AnRBC tidak terhambat, namun pertumbuhan methanogen yang belum optimal menyebabkan metana belum terproduksi. Secara keseluruhan, sistem efektif sebagai pengolahan awal dan primer, namun efluen belum memenuhi baku mutu sehingga diperlukan unit polishing tambahan.