Oil palm empty fruit bunches (EFB) and palm oil decanter cake (DC) were used to investigate biogas production by using solid-state anaerobic co-digestion (SS-AcoD) with 15% total solid (TS) content. Solid state anaerobic digestion (SS-AD) using substrate to inoculum (S:I) ratio of 3:1, methane yields of 353.0 mL-CH4/g-VS and 101.5 mL-CH4/g-VS were respectively achieved from mono-digestion of EFB without oil palm ash (OPA) addition and of DC with 10% OPA addition under mesophilic conditions 35 °C. By adding 5% OPA to SS-AD using 3:1 S:I ratio under thermophilic conditions (55 °C), mono-digestion of EFB and DC provided methane yields of 365.0 and 160.3 mL-CH4/g-VS, respectively. Furthermore, SS-AcoD of EFB:DC at 1:1 mixing ratio (volatile solid, VS basis), corresponding to carbon to nitrogen (C:N) ratio of 32, gathering with S:I ratio of 3:1 and 5% ash addition, synergistic effect is observed together with similar methane yields of 414.4 and 399.3 mL-CH4/g-VS, achieved under 35 °C and 55 °C, respectively. According to first order kinetic analysis under synergistic condition, methane production rate from thermophilic operation is 5 times higher than that from mesophilic operation. Therefore, SS-AcoD could be potentially beneficial to generate biogas from EFB and DC.

This paper reports on the optimum conditions for simultaneous hydrogen and butyric acid production from microalgae (Chlorella sp.) using enriched anaerobic mixed cultures as inoculum. The fermentation was objectively carried out under acidogenic conditions to achieve butyric acid for further ABE fermentation in solventogenesis stage. The main effects of initial pH (5 and 7), temperature (35 °C and 55 °C), and substrate concentration (40, 60, 80, and 100 g-VS/L) for hydrogen and butyric acid production were evaluated by using batch fermentation experiment. The major effects on hydrogen and butyric acid production are pH and temperature. The highest production of hydrogen and butyric acid was observed at pH 7 and temperature 35 °C. Using initial Chlorella sp. concentration of 80 g-VS/L or 100 g-VS/L at pH 7 and temperature 35 °C could produce hydrogen with an average yield of 22 mL-H2/g-VS along with high butyric acid production yield of 0.05 g/g-VS, suggesting that microalgae (Chlorella sp.) has potential to be converted directly to butyric acid by using acidogenesis under above optimum conditions.

The economical bio‐butanol‐based fermentation process is mainly limited by the high price of first‐generation biomass, which is an intensive cost for the pretreatment of second‐generation biomass. As third‐generation biomass, marine macroalgae could be potentially advantageous for conversion to clean and renewable bio‐butanol through acetone‐butanol‐ethanol (ABE) fermentation. In this study, butanol production from three macroalgae species (Gracilaria tenuistipitata, Ulva intestinalis, and Rhizoclonium sp.) by Clostridium beijerinckii ATCC 10132 was assessed comparatively. The enriched C beijerinckii ATCC 10132 inoculum produced a high butanol concentration of 14.07 g L−1 using 60 g L−1 of glucose. Among the three marine seaweed species, G. tenuistipitata exhibited the highest potential for butanol production (1.38 g L−1). Under the 16 conditions designed using the Taguchi method for low‐temperature hydrothermal pretreatment (HTP) of G. tenuistipitata, the maximum reducing sugar yield rate of 57.6% and ABE yield of 19.87% were achieved at a solid to liquid (S/L) ratio of 120, temperature of 110°C, and holding time of 10 min (Severity factor, R0 1.29). In addition, pretreated G. tenuistipitata could be converted to 3.1 g L−1 of butanol using low‐HTP at an S/L ratio of 50 g L−1, temperature of 80°C (R0 0.11), and holding time of 5 min.

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