• Energy Research

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.

Biodiesel production is currently limited due to high raw material costs. The potential of using sludge from municipal wastewater treatment plants as an alternative lipid feedstock was investigated. Four different types of sludge (primary, secondary, blended and stabilised) were tested in lipid extraction by Soxhlet using hexane, and biodiesel production by acid catalysis. To improve the extraction efficiency, the influence of pre-treatment methods (ultrasonic and mechanical disintegration) and duration of these treatments were investigated. Finally, the effect of sludge acidification with concentrated HCl was also evaluated. The pre-treatment methods did not increase significantly the amount of extracted lipid as well as biodiesel yield. Previous sludge acidification showed lower yield of lipids from primary, secondary and blended sludge. However, the amount of saponifiable lipids was higher, giving the overall biodiesel yield almost unchanged. Among the four sludges tested, primary sludge achieved the greatest lipid and biodiesel yields, 27% and 19% respectively, on the basis of dry sludge. The highest biodiesel yields obtained from blended, secondary and stabilised sludge amounted to 15%, 4% and 2% respectively, on the basis of dry sludge. No significant influence of the pre-treatments and acidification on the fatty acid composition was found. At least 8 fatty acids were determined, with a predominance of palmitic (C16:0), stearic (C18:0) and oleic acid (C18:1). The comparison of sludge fatty acids profile with common biodiesel feedstocks showed suitability of WWTP sludge for production of biodiesel. Peer Reviewed