• Energy Research

10.1016/j.renene.2014.10.019 Isochrysis galbana and Selenastrum capricornutum, marine and freshwater microalgae species respectively,were co-digested with sewage sludge under mesophilic and thermophilic conditions. The substrates and the temperatures significantly influenced biogas production. Under mesophilic conditions, the sewage sludge digestion produced 451 ± 12 mLBiogas/gSV. Furthermore, all digesters were fed with I. galbana, or mixed with sludge, resulting in an average of 440 ± 25 mLBiogas/gSV. On the contrary, S. capricornutum produced 271 ± 6 mLBiogas/gSV and in the mixtures containing sludge produced intermediate values between sludge and microalgae production. Under thermophilic conditions, the sewage sludge digestion achieved yet the highest biogas yield, 566 ± 5 mLBiogas/gSV. During co-digestion, biogas production decreased when the microalgae content increased, and for I. galbana and for S. capricornutum it reached minimum values, 261 ± 11 and 185 ± 7 mLBiogas/gSV, respectively. However, no evidence of inhibition was found and the low yields were attributed to microalgae species characteristics. The methane content in biogas showed similar values, independently from the digested substrate, although this increased by approximately 5% under thermophilic condition.

Although the hydrothermal liquefaction is considered a promising technology for converting microalgae into liquid biofuels, there are still some disadvantages. This paper demonstrated that the bio-oil yield can be significantly improved by adding alcohols as co-solvents and carrying out the conversion at mild conditions (<250°C), but at the expense of a reduced bio-oil quality. By adding ethanol, the bio-oil yields obtained (up to ∼60%) were comparable to the yield obtained at severe operating conditions using only water as solvent (54±2% on average), but the quality of the bio-oil was lower. However, the main advantages of the process here described lie in the utilisation of wet microalgae (∼75% moisture) and alcohol concentrations which avoid both drying the microalgae and decreasing the amount of microalgae loaded in the reactor.

Advance oxidation process was employed as a pretreatment of industrial wastewater. For this purpose, the use of heavy metals as a catalyst is necessary but also complicated because homogeneous catalysts are difficult to recover after reaction process. The heterogenization of Cu(II) ions was proposed by taking advantage of the adsorptive characteristics of polymeric matrices. Crosslinked poly(4‐vinylpyridine) of 2 and 25% and poly(D‐glucosamine) were tested as supports of copper. Adsorption was employed to heterogenize Cu(II) by considering the influences of pH and temperature on the process. The catalysts were evaluated by their metal content, catalytic behavior for the oxidation of phenol and leaching degree after reaction. Poly(4‐vinylpyridine) 2% was the best material for Cu(II) immobilization with an adsorption capacity of 90 mg g−1. Afterward, poly(4‐vinylpyridine) 2%, Cu(II) achieved 64% of phenol conversion, which represents a favorable result for the oxidation of phenol as the model of industrial wastewater pretreatments. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 269‐278, 2013

Production of biodiesel from sewage sludge lipids was catalysed by six different Brønsted acidic imida-zolium and long chain ammonium ionic liquids; both with an alkane sulfonic acid group and with differentanions. Among the ionic liquid tested, 4-(3-methylimidazolium) butanesulfonic acid trifluoromethane-sulfonate, [mimC4SO3H][SO3CF3], was selected as the best catalyst due to its high catalytic performanceand purer biodiesel obtained than the equivalent ammonium ionic liquid, 4-(trihexylammonium) butane-sulfonic acid trifluoromethanesulfonate, [N666(C4SO3H)][SO3CF3]. The influence of different reactionvariables on the biodiesel yield was studied using [mimC4SO3H][SO3CF3] as a catalyst. The yield of fattyacid methyl esters (biodiesel) reached 90% (based on saponifiable lipids) under the following optimisedconditions: 10:1 molar ratio of methanol to saponifiable lipids, 7 wt% ionic liquid catalyst (wt%, based onlipids), 100◦C and 5 h. In addition, the ionic liquid has a good reusability and can be easily separated fromthe biodiesel. These acidic ionic liquids were found to be efficient catalysts for the synthesis of biodieselfrom low-cost and non-edible feedstock like sewage sludge lipids. doi: 10.1016/j.apcatb.2015.08.039

Municipal sludge from wastewater treatment plants is a promising lipid feedstock for biodiesel production as it contains a significant amount of lipids. However, the energy necessary to remove its high water content is a major inconvenience for scaling up because of the high associated cost. In addition, the expensive conventional sludge drying methods are not effective enough for lipid recovery, thus reducing the potential biodiesel production. This study explores an alternative method, the direct sequential liquid-liquid extraction, which was performed in a batch mixer-settler reactor at room temperature, using hexane as a solvent, after previous sludge acidification showed significant increase in the lipid efficiency. The optimisation study demonstrated that, after three stages, 91% of lipid from primary sludge was recovered. The optimised extraction gave slightly higher lipid (27%, dry sludge) than the standard method (25%, dry sludge), supporting the suitability of the proposed process. Finally, this work demonstrates that the residual lipid-extracted sludge is still a good feedstock for energy production via anaerobic digestion. Anyway, the economic and environmental aspects of biodiesel production from sewage sludge could be improved. (C) 2014 Elsevier B.V. All rights reserved. Peer Reviewed

The freshwater microalgae species Chlorella kessleri and Chlorella vulgaris, and the marine microalgae species Nannochloropsis oculata were cultivated in urban wastewater. The freshwater species demonstrated the possibility of growing in urban wastewater reaching high biomass production and nutrient removal when cultured in batch mode using a flat-panel airlift photobioreactor. Both microalgae species reached high biomass dry weights, 2.70 ± 0.08 g/L and 2.91 ± 0.02 g/L respectively, accompanied by nitrogen concentration reduction around 96% and 95%, and a phosphorous concentration reduction around 99% and 98% respectively. N. oculata was able to uptake nutrients from wastewater to grow but with less efficiency, indicating the need of microalgae acclimation or process optimisation to achieve high nutrient removals. During C. kessleri and C. vulgaris cultivation, the nitrogen consumption led to a progressive N-starvation process which increased the microalgae potential for biofuels production; both species produced 346 ± 3 mL CH 4 /g VS and 415 ± 2 mL CH 4 /g VS during anaerobic digestion, and 7.4 ± 0.2 g Biodiesel /100 g VS and 11.3 ± 0.1 g Biodiesel /100 g VS respectively.