No abstract

Municipal wastewater treatment plants in the USA produce over 6.2 · 10 6 t of dried sewage sludge every year. This microorganism-rich sludge is often landfilled or used as fertilizer. Recent restrictions on the use of sewage sludge, however, have resulted in increased disposal problems. Extraction of lipids from sludge yields an untapped source of cheap feedstock for biodiesel production. Solvents used for extraction in this study include n-hexane, methanol, acetone, and supercritical CO 2 . The gravimetric yield of oil was low for nonpolar solvents, but use of polar solvents gave a considerably increased yield; however, the percentage of saponifiable material was less. Extraction of lipids with a mixture of n-hexane, methanol, and acetone gave the largest conversion to biodiesel compared with other solvent systems, 4.41% based on total dry weight of sludge. In situ transesterification of dried sludge resulted in a yield of 6.23%. If a 10% dry weight yield of fatty acid methyl esters is assumed, the amount of biodiesel available for production in the USA is 1.4 · 10 6 m 3 /year. Outfitting 50% of municipal wastewater plants for lipid extraction and transesterification could result in enough biodiesel production to replace 0.5% of the national petroleum diesel demand (0.7 · 10 6 m 3 ).

An innovative approach to increase biofuel feedstock lipid yields from municipal sewage sludge via manipulation of carbon-to-nitrogen (C:N) ratio and glucose loading in activated sludge bioreactors was investigated. Sludge lipid and fatty acid methyl ester (biodiesel) yields (% cell dry weight, CDW) were enhanced via cultivation in activated sludge bioreactors operated at high initial C:N ratio (!40:1) and glucose loading (!40 g L À1 ). Under C:N 70, 60 g L À1 glucose loading, a maximum of 17.5 AE 3.9 and 10.2 AE 2.0% CDW lipid and biodiesel yields, respectively, were achieved after 7 d of cultivation. The cultured sludge lipids contained mostly C 16 AC 18 fatty acids, with oleic acid consistently accounting for 40-50% of the total fatty acids. Microbial composition in activated sludge exposed to C:N 70 shifted toward specific gammaproteobacteria, suggesting their relevance in lipid production in wastewater microbiota and potential value in biofuel synthesis applications.

No abstract

The solubility of nonanoic acid (also known as pelargonic acid) in supercritical carbon dioxide has been determined at (313.15 and 333.15) K over a pressure range of (10 to 30) MPa. The experimental apparatus was of a flow-type, dynamic design, and the solubility was obtained gravimetrically. The solubility ranged from a pelargonic acid concentration of (0.14 ( 0.07) kg • m -3 (333.15 K, 10.0 MPa) to (25.39 ( 0.61) kg • m -3 (313.15 K, 30.0 MPa). The results showed that the solubility of pelargonic acid at 313.15 K was always greater than at 333.15 K at each pressure considered, a common behavior in liquid + SCF phase equilibria. No supercritical fluid solubility data for pelargonic acid were found in the literature. To ensure the validity of the experimental technique, solubility data for oleic acid were measured and compared to literature values. Oleic acid solubilities agreed with literature data within estimated uncertainties. A modified Adachi-Lu model, in terms of dimensionless variables, was used to correlate the solubility of pelargonic acid. Excellent agreement between experimental data and the correlation was found.