Treatment of cattle-slaughterhouse wastewater and the reuse of sludge for biodiesel production by microalgal heterotrophic bioreactors

Microalgal heterotrophic bioreactors are a potential technological development that can convert organic matter, nitrogen and phosphorus of wastewaters into a biomass suitable for energy production. The aim of this work was to evaluate the performance of microalgal heterotrophic bioreactors in the secondary treatment of cattle-slaughterhouse wastewater and the reuse of microalgal sludge for biodiesel production. The experiments were performed in a bubble column bioreactor using the microalgae Phormidium sp. Heterotrophic microalgal bioreactors removed 90 % of the chemical oxygen demand, 57 % of total nitrogen and 52 % of total phosphorus. Substantial microalgal sludge is produced in the process (substrate yield coefficient of 0.43 mg(sludge) mg(chemical) (-1)(oxygen demand)) resulting in a biomass with high potential for producing biodiesel (ester content of more than 99 %, cetane number of 55, iodine value of 73.5 g (lodine)100 g(-1), unsaturation degree of similar to 75 % and a cold filter plugging point of 5 degrees C).