Wastewater sludge as raw material for microbial oils production

Biodiesel is a promising alternative energy source as it is renewable, biodegradable, and environmental friendly. This study deals with oils production from wastewater sludge. Primary, secondary, and mixed municipal sludge and pulp and paper secondary sludge collected in Québec City, Canada has 5-11% oil content (based on weight) in initial sludge. The oil content is in the order of pulp and paper secondary sludge > municipal primary sludge > municipal mixed sludge > municipal secondary sludge. Different types of sludge were also used for lipid production by Pichia amethionina sp., Galactomyces sp., and Trichosporon oleaginosus. The results showed that maximum lipid content was obtained in municipal secondary sludge among all types. Further, the effect of initial sludge suspended solids concentration (10-30 g/L) on lipid accumulation was investigated. The maximum lipid content of 30.17% and 32.42% w/w dry weight, was reached by P.amethionina sp. and Galactomyces sp., respectively, at 25 g/L suspended solids concentration, and that of 37.69% w/w dry weight by T.oleaginosus at 30 g/L suspended solids concentration all with municipal secondary sludge. The results showed that carbon to nitrogen ratio had more obvious effect on lower suspended solids concentration (10 g/L) than on the higher one (30 g/L) in lipid accumulation of the three strains.