• 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

To reduce the environmental damage caused by coal waste landfills, it is necessary to look for rational methods for their management. One method for their development is the creation of soil-like substrates. This study aimed to assess the properties of soil-like substrates from coal mining waste, combined with a varied sample of sewage sludge and waste mineral wool. The properties of the substrates were evaluated in a pot experiment. The properties of the substrates and their yield potential were determined. Coal mining waste as a substrate, compared to anthropogenic soil, was characterized by a significantly higher sorption capacity; the content of alkaline cations and pH; significantly higher contents of organic carbon, nitrogen, and available forms of K and Mg; and a lower content of available P. The substrates enriched with sewage sludge showed a significant increase in content of organic carbon, nitrogen, and assimilable forms of P and Mg, as well as the optimization of sorption properties. Extending the composition of substrates with mineral wool resulted in further improvement of their properties. The yields of plants grown on coal mining waste were significantly lower than those of those grown on anthropogenic soil. Substrates with sewage sludge and mineral wool had a significantly higher yield potential.

Biodiesel expansion is currently limited due to high raw material costs for its production. The potential of using sludge from municipal wastewater treatment plants as an alternative lipid feedstock for biodiesel production was investigated. Experiments were conducted to evaluate the suitability of four different types of wastewater sludges for biodiesel production. Lipids were extracted from primary, secondary, blended and stabilized sludge in a Soxhlet extractor, using hexane as a solvent. Finally, the lipids were converted by acid catalysis transesterification into their corresponding fatty acid methyl esters (FAMEs) - biodiesel. Results indicated that among four sludge tested, primary sludge achieved the greatest lipids and biodiesel yields. The amount of extracted lipids for primary sludge was 25.3% compared to 21.9%, 10.1% and 9.1% (dry wt) for blended, stabilized and secondary sludge, respectively. The FAMEs yields obtained in this study were 13.9%, 10.9%, 2.9% and 1% (dry wt) for primary, blended, secondary and stabilized sludge, respectively. The estimation of annual biodiesel production based on the sludge generated in WWTP of Reus was evaluated, showing that primary sludge consists of 87% of the total biodiesel among the wastewater sludges. Gas chromatography analysis of the FAMEs revealed a similar fatty acids composition for all sludge tested with a predominance of palmitic acid, stearic acid, oleic acid and linoleic acid. Comparison of sludge fatty acid profile with common biodiesel feedstocks showed their suitability for the production of biodiesel. http://dx.doi.org/10.1016/j.proeng.2012.07.456

Abstract This study proposes a novel method to extract lipids from wet primary sludge for biodiesel production using ionic liquids. Tetrakis(hydroxymethyl)phosphonium chloride and widely used 1-butyl-3-methylimidazolium methyl sulfate were evaluated to extract lipids from raw and dried sludge (96% and 2%, wt. water content, respectively) and compared to the conventional Soxhlet method using organic solvents. Both these ionic liquids showed suitability for lipid extraction from raw sludge, giving even better results than expected from dried sludge. The [C 4 mim][MeSO 4 ] ionic liquid reached 18.5% and 26.9% of lipids, 14.1% and 18.4% of biodiesel from dried and raw sludge, respectively. The [P(CH 2 OH) 4 ]Cl ionic liquid gained 23.4% and 27.6% of lipids, 17.0% and 19.8% of biodiesel from dried and raw sludge respectively, reaching comparable results to the conventional Soxhlet method (27.2% of lipids, 19.4% of biodiesel). Therefore, the proposed ionic liquid process is efficient in lipid extraction directly from wet primary sludge, eliminating the expensive step of sludge drying and the use of volatile organic solvents. Under the optimised extraction conditions using [P(CH 2 OH) 4 ]Cl ionic liquid and raw sludge (1:5 sludge (g/TS):IL (cm 3 ) ratio, 100 °C and 3 h), the obtained yield of lipids and biodiesel amounted to 25.7% and 21.1%, respectively. Additionally, lipid extraction using [P(CH 2 OH) 4 ]Cl ionic liquid also precipitates cellulosic material, which allows for direct and easy cellulose-based co-product recovery, giving high additional value to the process. Consequently, the economic and environmental aspects of biodiesel production from sewage sludge could be improved.

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