ABSTRAKPenelitan ini bertujuan untuk mengevaluasi perbedaan lima konsentrasi total amonia nitrogen (TAN) dan amonia terhadap produksi methan dan kinerja digester biogas pada kondisi thermophilic (50°C). Penelitian menggunakan lima digester identik dengan pengisian subtrat secara kontinyu. Data diperoleh selama empat kali ulangan masa tinggal substrat di dalam digester. Data dianalisis dengan menggunakan fasilitas pengolahan data yang tersedia pada program Microsoft Excel. Lima konsentrasi TAN diperoleh dengan menambahkan urea sampai diperoleh konsentrasi TAN dan amonia yang diinginkan untuk selanjutnya konsentrasi tersebut dijaga dengan pemberian urea pada digester biogas disetiap harinya. Hasil penelitian menunjukkan adanya hubungan negatif yang sangat kuat antara konsentrasi TAN dan amonia terhadap produksi methan. Produksi methan berkurang sebesar 24, 30, 52 dan 66% pada digester yang mempunyai konsentrasi TAN 2.9, 3.6, 4.4 and 5.1 g/L setara dengan 0.7, 1.1,1.5 and 1.8 g/L AB. Konsentrasi total asam lemak mudah menguap, isovalerat dan isobutirat berada pada konsentrasi yang tinggi selama terjadinya penghambatan kinerja mikroorganisme oleh ammonia. Konsentrasi TAN pada digester biogas sebesar dan atau lebih dari 3 g/L mengindikasikan bahwa seringkali produksi methan di bawah kondisi produksi optimumnya, oleh karena itu untuk mengkompensasinya masa tinggal substrate pada digester biogas harus diperpanjang atau digester biogas dioperasikan pada temperatur yang lebih rendah. Kata kunci: inhibisi, total amonia nitrogen, amonia, produksi methan, asam lemak mudah menguap ABSTRACTThis study investigated the effect of five different concentrations of total ammonia nitrogen (TAN) and free ammonia (FA) on the methane yield and digester performance under thermophilic conditions (50°C). Five identical continuously fed digesters were used. The experiment was run for four times hydraulic retention time (HRT). Data were statitically analysed using the data Analysis Tool Pack available with the Microsoft Excel program. Different ammonia levels were obtained by pulsing urea to obtain the target level of TAN and FA, and to subsequently maintaining the concentration of ammonia levels by daily urea additions. The result showed a strong negative correlation between both TAN and FA concentrations and methane yield. The methane yield was reduced by 24, 30, 52 and 66% in digesters that had TAN levels of 2.9, 3.6, 4.4 and 5.1 g/L, respectively, corresponding to 0.7, 1.1,1.5 and 1.8 g/L FA. Total volatile fatty acid and especially isovaleric and isobutyric acid concentrations were elevated during ammonia inhibition. Concentration of TAN in the biogas digester exceeding 3 g/L indicating that very often the full biogas potential is not achieved due to ammonia inhibition and that longer HRT should be used to compensate or a lower process temperature should be chosen.

The biodegradation process of organic waste in anaerobic digestion can be in a single or two-phase bio-reactor. This study examined the effect of different biogas digester configurations (single and two-phase) on methane production of dairy cattle manure (DCM) at tropical ambient temperature. Three identical reactors were used in this study (R1, R2, and R3). The two-phase digesters consisted of reactors R1 and R2. R1 had a 2.1 L working volume and 3 d hydraulic retention time (HRT), while R2 had 5.25 L working volume and 22 d HRT (R1 and R2 had a 25 d HRT). The digested slurry of R1 was used to feed R2. R3 served as the single-phase digester and had 5.25 L working volume and 25 d HRT. Methane production were 14.31, 132.82, and 146 L/kg VS for R1, R2, and R3, respectively. The results showed that there was no positive effect of the application of a two-phase digester configuration on the specific methane yield of DCM per kg volatile solids added than that in the single-reactor. Methane production was detected in the first reactor of the two-phase digester configuration and the total methane production of the two-phase digester was found to be 29.98% higher (p<0.05) than that of the single reactor in terms of digester volume (0.41 VS 0.31 L/L/d). Both digester configurations performed well, indicated by a stable methane production and low volatile fatty acids and total ammonia concentrations. The two-phase bio-digester configuration can significantly increase methane production in terms of digester volume.

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