Anaerobic waste‐activated sludge digestion–a bioconversion mechanism and kinetic model

Abstract

The anaerobic bioconversion of raw and mechanically lysed waste-activated sludge was kinetically investigated. The hydrolysis of the biopolymers, such as protein, which leaked out from the biological sludge with ultrasonic lysis, was a first-order reaction in anaerobic digestion and the rate constant was much higher that the decay rate constant of the raw waste activated sludge. An anaerobic digestion model that is capable of evaluating the effect of the mechanical sludge lysis on digestive performance was developed. The present model includes four major biological processes-the release of intracellular matter with sludge lysis; hydrolysis of biopolymers to volatile acids; the degradation of various volatile acids to acetate; and the conversion of acetate and hydrogen to methane. Each process was assumed to follow first order kinetics. The model suggested that when the lysed waste-activated sludge was fed, the overall digestive performance remarkably increased in the two-phase system consisting of an acid forming process and a methanogenic process, which ensured the symbiotic growth of acetogenic and methanogenic bacteria.

A mathematical model of a high sulphate wastewater anaerobic treatment system

“…Typically a first order function is used to model anaerobic sludge hydrolysis (East man and Ferguson, 1981;Lilley et al, 1990;Eliosov and Argaman, 1995;Shimizu et al, 1993), although other expression such as the Contois model have been used to describe hydrolysis in aerobic systems (Dold et al, 1980). The first order approach has been shown to fit experimental data extremely well and it is doubtful if a more complicated expression is necessary.…”

Separate Digestion of Liquid and Solid Fractions of Thermally Pretreated Secondary Sludge. Assessment and Global Evaluation

“…Hydrolysis being the rate limiting step for the biological degradation of WAS (Li and Noike, 1992;Shimizu et al, 1993), the introduction of a thermal hydrolysis pretreatment has proven to be a very interesting option (Kepp et al, 1999;Bougrier et al, 2008;Carrère et al, 2010), currently implemented full-scale (mainly Cambi® and Biothelys®).…”

Effect of Ultrasound Pretreatment on Sludge Digestion and Dewatering Characteristics: Application of Particle Size Analysis

“…However, waste activated sludge (WAS) is known to be more difficult to digest than primary sludge (PS) [2]. It has been reported that hydrolysis is the rate-limiting step in anaerobic digestion [3,4]. Extracellular polymeric substances (EPS) and microbial cells are recalcitrant to direct hydrolysis, and therefore, the pretreatment of sludge is required to rupture the cell walls, to facilitate the release of intracellular material into the aqueous phase and accelerate the low rate of biodegradation, and to enhance anaerobic digestion [5].…”