Production and Utilization of Volatile Fatty Acids in Various Types of Anaerobic Reactors

Abstract

Production and subsequent utilization of fatty acids (from C2 to C6) was followed in three types of anaerobic reactors:uplow sludge bed reactor (USBR),upflow fixed bed reactor (UFBR),downflow fixed bed reactor (DFBR). It was found that the concentrations of lower fatty acids increased exponentially with increasing volumetric loading of the reactor in the range up to 15 kg m−3d−1 (as COD). Up to a loading of about 4 kg m−3d−1, only acetic and propionic acids appeared. Butyric and valeric acids were found only at a loading higher than 4 kg m−3d−1, caproic acid at a loading higher than 8 kg m−3d−1. The highest removal rates along the reactor were observed for butyric acid, the lowest for propionic acid. The volumetric rate of biogas production (volume of gas per volume of reactor per time) increased with increasing loading rates up to 4.6 m3m−3d−1. The UFBR was in general less sensitive to inhibition by fatty acids and to lower temperatures and fluctuation of loads than the other two types of reactors.