No abstract

Abstract:In this study, batch biohydrogen production by co-digestion of raw rice straw and activated sewage sludge was investigated with different inoculum heat treatment, pH, S/X ratio (based on VS) and substrate sizes under mesophilic condition. In order to achieve a high bio-hydrogen yield and methanogens activity inhibition, heat treatment of inoculum was optimized at different exposure times (30, 45 & 60 min) and temperature ranges (80, 90 and 100 °C) prior to dark fermentation process. Collected data was analysed using response surface methodology (RSM).The heat treatment of inoculum at 100 °C for 60 minutes produced the highest bio-hydrogen yield of 14.22 NmL H2/g VS at concentration of 70.97 % and Production of 0.073 NmLCH4/gVS at 0.17% concentration in total produced biogas. The raw rice straw was also co-digested with heat-treated inoculum at different ratios of volatile solids (2:1, 4:1 and 6:1) and initial pH (4, 4.75 and 5.5) as numerical variables and 4 categories of substrate size ( (250-500 µm], (500 µm-2mm], (2-20mm), [20-30mm]) . The highest bio-hydrogen yield of 14.70 NmL/g VS was recognized at the optimum initial pH of 5.01 and S/X ratio of 4.54:1 using 2-20 mm rice straw.

The yield and composition of the biocrude obtained by hydrothermal liquefaction (HTL) of Nannocloropsis gaditana using heterogeneous catalysts were evaluated. The catalysts were based on metal oxides (CaO, CeO 2 , La 2 O 3 , MnO 2 , and Al 2 O 3 ). The reactions were performed in a batch autoclave reactor at 320 • C for 10 min with a 1:10 (wt/wt) microalga:water ratio. These catalysts increased the yield of the liquefaction phase (from 94.14 ± 0.30 wt% for La 2 O 3 to 99.49 ± 0.11 wt% for MnO 2 ) as compared with the thermal reaction (92.60 ± 1.20 wt%). Consequently, the biocrude yields also raised in the metal oxides catalysed HTL, showing values remarkably higher for the CaO (49.73 ± 0.9 wt%) in comparison to the HTL without catalyst (42.60 ± 0.70 wt%). The N and O content of the biocrude obtained from non-catalytic HTL were 6.11 ± 0.02 wt% and 10.50 ± 0.50 wt%, respectively. In this sense, the use of the metal oxides decreased the N content of the biocrude (4.62 ± 0.15-5.45 ± 0.11 wt%), although, they kept constant or increased its O content (11.39 ± 2.06-21.68 ± 0.03 wt%). This study shows that CaO, CeO 2 and Al 2 O 3 can be promising catalysts based on the remarkable amount of biocrude, the highest values of C, H, heating value, energy recovery, and the lowest content of N, O and S.

Relationships between lipid and carotenoid synthesis by Rhodosporidium diobovatum were investigated for cell cultures in nitrogen-limited medium (GMY) containing equimolar amounts of carbon of glucose or glycerol. The cultures were also supplemented with additional substrate at 120 h postinoculation (pi) and during a fed-batch experiment. Growth of R. diobovatum on glucose resulted in higher yields of triacyglycerides (TAGs) and carotenoid than when grown on glycerol, even though the cultures contained equimolar amounts of carbon. After the addition of fresh substrate at 120 h pi, total carotenoid concentrations were significantly different from the concentrations measured at 120 h pi in both glucose and glycerol cultures, with no concomitant increase in lipid concentrations, suggesting that carotenoid synthesis is linked to exponential-phase growth, while lipid synthesis is linked to stationary phase. We also compared the calculated properties of biodiesel that could be made with TAGs derived from R. diobovatum with properties of biodiesel made from TAGs of other oleaginous yeasts, microalgae, vegetable oils, and animal fats. This study shows that R. diobovatum can be an effective strain for production of neutral lipids containing high percentages of oleic acid, palmitic acid, and linoleic acid, as well as carotenoids.

No abstract