SEPARATE DIGESTION OF LIQUID AND SOLID FRACTIONS OF THERMALLY PRETREATED SECONDARY SLUDGE. ASSESSMENT AND GLOBAL EVALUATION

Abstract -The fractioning into separate liquid and solid fractions obtained by centrifugation of thickened fresh and thermally pretreated (170 ºC, 50 minutes) secondary sludge showed that 30% of the particulate organic matter was released during the pretreatment, correspondingly increasing the methane production of the particulate matter by 30% (from 259 to 329 mL CH 4 /g VS fed ). The responsible of this enhancement was the liquid fraction, as the biodegradability of the solid fraction remained constant after the pretreatment. Mass balances showed that 34% of the VS were released to the liquid fraction, generating nearly 50% of the total methane produced, with much faster kinetics compared to the solid fraction. These results support the hypothesis of a separate liquid-solid digestion of thermally pretreated sludge, which would result in decreasing the digestion volume to half while duplicating the methane productivity per kilogram of sludge fed to digestion

A new device to select microcarriers for biomass immobilization : application to an anaerobic consortium

A new device was designed to compare the biomass retention capacity of different microcarriers. Microcarriers were placed in as many as 28 independent, parallel minibioreactors under selected and identical flow conditions. Sepiolite pozzolana, clay, and foam glass (Poraver™) were examined for biomass retention capacity, characterized in terms of attached volatile solids and specific methanogenic activity, and examined with scanning electron microscopy. Sepiolite had the greatest biomass retention capacity and better internal porous volume for biomass immobilization. The specific methanogenic activity of the immobilized biomass in different materials was found to be inversely correlated to the amount of attached biomass. A maximum difference of 19% overall activity of the colonized material was observed between foam glass and pozzolana. Compared with the suspended biomass, a clear enhancement of syntrophic activity (up to 110%) and reduction of acetoclastic activity (up to 73%) was observed in the biofilm. This system of examination provides information useful for preselecting microcarriers for biomass colonization