Performance of UASB and DAEB reactors in the anaerobic digestion of synthetic wastewater containing sodium oleate and sodium stereate

This study aimed at evaluating the performance of five laboratory-scale reactors, three UASB and two downflow anaerobic expanded bed (DAEB), fed with saccharose and long chain fatty acids (LCFA) for 410 days. Reactors operated at a temperature of 35 °C. The organic load rates were changed between 3.45 and 6.38 kg COD.m³.d⁻¹.During period I the substrate was saccharose and in periods II, III and IV it was saccharose plus sodium oleate, stereate and a mixture of sodium oleate and stereate. The UASB and DAEB reactors showed a similar performance. In UASB reactors specific methanogenic activity decreased in the periods II, III and IV. COD removal, biogas production and CH₄ concentration in biogas decreased in all reactors at the end of the study. A washout occurred in UASB 2 and 3 when sodium stereate exceeded 500 mg.L⁻¹. In DAEB reactors the main problem was adsorption of LCFA particles onto the solid support.