Article

# Kinetics of thermophilic batch anaerobic digestion of thermal hydrolysed waste activated sludge

INRA, UR50, Laboratoire de Biotechnologie de l’Environnement, Avenue des Etangs, Narbonne, F-11100, France
(Impact Factor: 2.47). 10/2009; 46(2):169-175. DOI: 10.1016/j.bej.2009.05.003

ABSTRACT Enhancing waste activated sludge (WAS) anaerobic digestion by thermal pretreatment has become of high interest. However, thermal treatment has been mainly combined to mesophilic anaerobic digestion. This paper presents the combination of sludge thermal pretreatment (110, 165 and 220 °C) and batch thermophilic anaerobic digestion (55 °C). Optimal conditions of thermal pretreatment were shown to be 165 °C, involving a chemical oxygen demand (COD) and volatile solids (VS) solubilisation of 18 and 15% and a biodegradability increase from 47 to 61%. Treatments at 165 °C were carried out in electric and steam modes and no significant difference on the impact of heating mode on sludge anaerobic biodegradability was observed. Moreover, it may be recommended not to carry out successive batch experiments to assess thermophilic BMP of sludge as accumulation of volatile fatty acids (VFA), particularly propionate, and a decrease of VFA uptake rates may occur. However, thermal pretreatment at 165 °C allowed the decrease of propionate accumulation and an higher methane production.

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Available from: Hélène Carrere, Sep 27, 2015
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• "It has been hypothesized that thermal pre-treatment can enhance the biological activities of some thermophilic bacterial populations; for this reason, it can be considered a valid pre-treatment step before thermophilic digestion [16] [17]. However, very few studies have addressed the combination of thermal pre-treatment and the thermophilic anaerobic digestion of sludge [1] [4] [16] [18]. "
##### Article: The impact of sludge pre-treatments on mesophilic and thermophilic anaerobic digestion efficiency: Role of the organic load
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ABSTRACT: Anaerobic digestion has been recognized as the most appropriate stabilization technology for approaching sludge reuse task, in part because of the methane production involved. The mesophilic anaerobic processing train can be upgraded by adding a pre-treatment step or by increasing the digestion temperature to thermophilic conditions. In this study, semi-continuous mesophilic (MAD) and thermophilic (TAD) anaerobic digesters were operated for 180 days at low (0.7–1.0 kg VS/m3 d), medium (1.4–1.8 kg VS/m3 d) and high (2.8–3.7 kg VS/m3 d) organic loading rates (OLRs). The impact of ultrasound and thermal hydrolysis pre-treatments on the mesophilic and thermophilic digestion efficiency, respectively, was assessed by performing parallel digestion tests. The increase of soluble COD (Chemical Oxygen Demand) and colloidal surface charge after the sludge pre-treatments suggested biopolymers solubilization and changes in surface floc properties. Thermal hydrolysis enhanced the release of lipids and long chain fatty acids, while ultrasounds application resulted in proteins being the main component of the released matter. Operating the digesters at OLRs between 0.7 and 1.4 kg VS/m3 d the methane conversion rate was not significantly affected by the temperature increase up to thermophilic conditions, whereas the integration of the pre-treatments accelerated the organic conversions, resulting in a noticeable methane gain (up to +51%). Conversely, at higher organic loads, the TAD yields were significantly higher with respect to the MAD ones, assuring the sustainable economic benefit of operating smaller anaerobic digesters to obtain higher methane productions. Nevertheless, the colloidal charge increase during thermophilic digestion impaired the sludge filterability much more rapidly than in mesophilic conditions.
Chemical Engineering Journal 06/2015; 270:362-371. DOI:10.1016/j.cej.2015.02.037 · 4.32 Impact Factor
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• "Because the thermal hydrolysis process holds the combined benefits of decreasing biosolids quantity and increasing biosolids acceptability, it is of great interest to the wastewater industry (Wilson and Novak, 2009). Nevertheless, few authors have investigated the effect of thermal hydrolysis on thermophilic digestion of waste activated sludge alone, and these studies are mostly carried out in batch systems (Bougrier et al., 2008; Liu et al., 2012; Mottet et al., 2009). There is however an upper limit of temperature (around 180– 200 °C) beyond which the effectiveness of THP not only starts to drop but rather results in the production of hardly degradable compounds. "
##### Article: Reduced temperature hydrolysis at 134°C before thermophilic anaerobic digestion of waste activated sludge at increasing organic load
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ABSTRACT: The performance of thermophilic digestion of waste activated sludge, either untreated or thermal pretreated, was evaluated through semi-continuous tests carried out at organic loading rates in the range of 1-3.7kgVS/m(3)d. Although the thermal pretreatment at T=134°C proved to be effective in solubilizing organic matter, no significant gain in organics degradation was observed. However, the digestion of pretreated sludge showed significant soluble COD removal (more than 55%) whereas no removal occurred in control reactors. The lower the initial sludge biodegradability, the higher the efficiency of thermal pretreated digestion was observed, in particular as regards higher biogas and methane production rates with respect to the parallel untreated sludge digestion. Heat balance of the combined thermal hydrolysis/thermophilic digestion process, applied on full-scale scenarios, showed positive values for direct combustion of methane. In case of combined heat and power generation, attractive electric energy recoveries were obtained, with a positive heat balance at high load.
Bioresource Technology 06/2013; 143C:96-103. DOI:10.1016/j.biortech.2013.05.069 · 4.49 Impact Factor
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• "This gave the K values, and the regression equation with its corresponding R square values. The kinetic reaction was assumed as a first order reaction, as it has been commonly selected as an appropriate model to illustrate the anaerobic digestion of complex substrates (Borja et al., 2003; Fernadez et al., 2010; Mottet et al., 2009). The basic equation is described by: "
##### Article: The impact of intermediate thermal hydrolysis on the degradation kinetics of carbohydrates in sewage sludge
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ABSTRACT: The purpose of this paper is to report the results, from laboratory-scale investigations, on the impact of Intermediate Thermal Hydrolysis Process (ITHP) on already digested sludge in general, and sludge carbohydrate content degradation process efficiency in particular. The ITHP performance data were compared with the performance of established conventional thermal hydrolysis process (THP). The degradation of sludge carbohydrates as a result of thermal pre-treatment and anaerobic digestion followed the first order kinetics. The overall sludge organic matter degradation kinetics rate constants indicated that the use of THP as an intermediate digestion step can enhance the already digested sludge organic matter degradation; further reducing the sludge mass and increasing its conversion to biogas.
Bioresource Technology 06/2013; 137:239-244. DOI:10.1016/j.biortech.2013.03.121 · 4.49 Impact Factor