Assessment and application of kinetic reaction rates in pilot‐scale semi‐continuous aerobic sludge digestion

Abstract

The aerobic digestion of two different waste activated sludges was examined using a semicontinuous flow scheme and variable raw sludge loading rates. Due to daily perturbations of the system, resulting from sludge withdrawal/addition, the analysis of kinetic decay rates required a modification of the classic methodology, which could account for these external sources of variability in process performance analysis. The resultant kinetic decay coefficients reflected this operational variability, due both to observable and unobservable sources; at the same time, these values were able to describe the dynamic biological processes of the aerobic digester, and reflect the trends seen in volatile mass reduction. It was proposed that these values could subsequently be used in a valid analysis of temperature sensitivity within the digester, such that temperature ranges to be targeted for economical digester performance enhancement could be easily selected.Keywords: aerobic sludge digestion, semi-continuous operation, process variability, kinetic decay rates, Arrhenius temperature sensitivity, mixed liquor pH control INTRODUCTION their approach, and it is generally believed that endogenous metabolism is responsible for the In the field of biological wastewater majority of the mass reduction taking place, treatment, a great deal of research effort has beenIn the aerobic digester, it is assumed that expended in the modelling of aerobic microbial exogenous organic substrates have been depleted, activity, as related to sludge mass accumulation and in order to maintain life functions under in the activated sludge process and the loss of starvation conditions, the sludge mass sludge mass in the aerobic digester. As yet, no organisms must rely on endogenous substrates, real consensus exists pertaining to the "correct" This can be expressed mathematically as: model for these reactions; this is not surprising, given the fact that the reduction of biological dM yi /•) material in the aerobic digester is a function of dt several separate and concurrent physical and biochemical reactions, such as endogenous or, upon integration: metabolism, predation/grazing by the larger zooplankton species, and cryptic growth. The ^_ ^t ^ ^M^ _ ^..ĉ omplexity of the interrelationships between M o these various processes in the aerobic digester, in essence, forces the modellers to simplify where M = quantity of active mass in the system,

Pilot scale evaluation of anaerobic codigestion of primary and pretreated waste activated sludge

“…Overall solids removal: This was based on the influent solids concentration (WAS + primary sludge) being equal to the solids concentration before solubilization of WAS, that is, overall removal accounted for solids removal dur- This procedure has been successfully used in previous work, and a detailed explanation of this mass balance method can be found elsewhere (Anderson and Mavinic, 1992;Anderson and Mavinic, 1993a;Wareham el al., 1993).…”