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 ).

BACKGROUND:The microbial biomass present in activated sludge contains lipidic compounds that can be used as biodiesel feedstock. In this study, the production of biodiesel from activated sludge from Tuscaloosa, AL was optimized based on the yield of fatty acid methyl esters (FAMEs). In situ transesterification was used with sulfuric acid as catalyst. A general factorial design of 4 × 6 × 5 for temperature, methanol to sludge ratio and catalyst concentration, respectively, was considered for optimization.

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BACKGROUND: The production of biodiesel from activated sludge obtained from Tuscaloosa, AL was optimized based on the yield of fatty acid methyl esters (FAMEs) using an in situ transesterification process. An orthogonal central composite response surface design was considered to investigate the main and interaction effects of temperature, methanol to sludge ratio, and catalyst concentration.

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