Biodegradability of wastewater and activated sludge organics in anaerobic digestion

Abstract

The investigation provides experimental evidence that the unbiodegradable particulate organics fractions of primary sludge and waste activated sludge calculated from activated sludge models remain essentially unbiodegradable in anaerobic digestion. This was tested by feeding the waste activated sludge (WAS) from three different laboratory activated sludge (AS) systems to three separate anaerobic digesters (AD). Two of the AS systems were Modified Ludzack - Ettinger (MLE) nitrification-denitrification (ND) systems and the third was a membrane University of Cape Town (UCT) ND and enhanced biological P removal system. One of the MLE systems and the UCT system were fed the same real settled wastewater. The other MLE system was fed raw wastewater which was made by adding a measured constant flux (gCOD/d) of macerated primary sludge (PS) to the real settled wastewater. This PS was also fed to a fourth AD and a blend of PS and WAS from settled wastewater MLE system was fed to a fifth AD. The five ADs were each operated at five different sludge ages (10-60d). From the measured performance results of the AS systems, the unbiodegradable particulate organic (UPO) COD fractions of the raw and settled wastewaters, the PS and the WAS from the three AS systems were calculated with AS models. These AS model based UPO fractions of the PS and WAS were compared with the UPO fractions calculated from the performance results of the ADs fed these sludges. For the PS, the UPO fraction calculated from the AS and AD models matched closely, i.e. 0.30 and 0.31. Provided the UPO of heterotrophic (OHO, fE_OHO) and phosphorus accumulating (PAO, fE_PAO) biomass were accepted to be those associated with the death regeneration model of organism "decay", the UPO of the WAS calculated from the AS and AD models also matched well - if the steady state AS model fE_OHO = 0.20 and fE_PAO = 0.25 values were used, then the UPO fraction of the WAS calculated from the AS models deviated significantly from those calculated with the AD models. Therefore in plant wide wastewater treatment models the characterization of PS and WAS as defined by the AS models can be applied without modification in AD models. The observed rate limiting hydrolysis/acidogenesis rates of the sludges are listed.

Characterization of Hydrolysis Kinetics in Staged Anaerobic Digestion of Wastewater Treatment Sludge

“…The biodegradable fraction of the sludge was estimated 3 times over the duration of the study as per eq 1 and found to range from 0.59 to 0.62 mg COD mg TCOD -1 . The average biodegradable fraction (0.61) was found to be lower than that reported for primary sludge (Ikumi et al, 2014;Parkin and Owen, 1986), while it was higher than the typical values reported for waste activated sludge (Parker, 2005). This was attributed to the use of a mixed primary sludge and WAS in the experiments.…”

Influence of phase separator design on the performance of UASB reactors treating municipal wastewater

“…However, there is evidence (Wentzel et al, 2006, Ikumi et al, 2014 that f up in an anaerobic environment is not very different from f up in an aerobic environment, where it is about f up = 0.08 (Marais and Ekama, 1976) for raw sewage. In that case an estimated value for the apparent yield factor can be calculated: Y ap = 0.05 mgSVS/mgCOD.…”

Transformation and utilization of slowly biodegradable organic matters in biological sewage treatment of anaerobic anoxic oxic systems

“…However, differences in sewage composition cannot be described by COD. Currently, the Activated Sludge Models (ASMs) as suggested by the International Water Association are the most widely recognized methods for characterizing COD components (Ikumi et al, 2014;Wichern et al, 2006;Wu et al, 2016). The quantitative characterization of these components is required for the application of ASMs.…”