Using water activity measurements to evaluate rheological consistency and structure strength of sludge

Abstract

In this study, an original method of characterization of water/solid matter interactions in sewage sludge has been developed, based on both rheological characteristics and thermodynamic water activity determinations, in order to check whether a link could be made with water activity and its mechanical properties. The effect of solid matter content, flocculation and ageing time on water activity and rheological parameters has been investigated. Through this study, we showed that rheological parameters (G’ and G’’) of both raw and flocculated sewage sludge at optimal dose of polymer increase with solids concentration following a power-law, whereas in the same way water activity decreases following an exponential relationship (Arrhenius dependence). A slight increase of water activity values and those of G’ and G’’ moduli with added polymer was also highlighted. On the other hand, we have shown that during ageing, the rheological parameters G’ and G’’ decreased upon increasing the ageing time whereas in the same way, water activity increases. Rheological parameters clearly evidenced thermodynamic water activity dependence, regarding solid concentration and ageing time, with a decrease of G’ and G’’ upon increasing water activity. Thus, water/solid matter interactions were supposed to intervene importantly in the rheology of sewage sludge. From all these results, it appears clearly that water activity measurements can be regarded as an effective and easy tool for evaluating the state of structuration of sewage sludge and for predicting its structural, textural and mechanical properties during dewatering and ageing

A uniaxial cyclic compression method for characterizing the rheological and textural behaviors of mechanically dewatered sewage sludge

“…Even at TS=16%, the sludge was flowable under tangential stress. The same observation was reported by Agoda-Tandjawa et al (2013). For another sludge at TS around 21.5%, Charlou (2014) reported a fracturing phenomenon in a horizontal plane using a parallel plate rheometer in oscillation mode.…”

“…The flocculation of municipal sewage sludge particles is a decisive step in sludge processing. The high cationic polymer forms the sludge structure with a good mechanical strength (Agoda-Tandjawa et al, 2013;Wolny et al, 2008). This may be one of the essential reasons that explain the similarity of the rheological behavior of these materials.…”

“…The main factors dominating the sewage sludge properties are the temperature (Lotito and Lotito, 2014;Feng et al, 2014;Dai et al, 2014;Battistoni, 1997;Baroutian et al, 2013;Baudez et al, 2013;Farno et al, 2014;Mori et al, 2006), the composition and the microstructure (Ruiz and Wisniewski, 2008;Lin et al, 2013;Nielsen et al, 1996;Pevere et al, 2009;O'Kelly, 2008;Baudez and Coussot, 2001;Baudez, 2008;Agoda-Tandjawa et al, 2013;Mori et al, 2008;Ma et al 2014) as well as the solid concentration. Until 2013 (Seyssiecq et al, 2003;Eshtiaghi et al, 2013), most of the rheological characterization studies were focused on sludge in liquid to pasty states (1.5% < TS < 15%).…”

Codisposição de lodos de tratamento de esgotos em aterros sanitários brasileiros: aspectos técnicos e critérios mínimos de aplicação

“…Os aterros de resíduos têm sido projetados, em termos de segurança estrutural, segundo os princípios da mecânica dos solos, considerando-se cada tipo de resíduo como nova unidade geotécnica. Embora pesquisas venham sendo realizadas sobre o comportamento geotécnico do lodo de ETE (BRINGHENTI, 1998;FERREIRA, 2010;FERREIRA et al, 2011;AGODA-TANDJAWA et al, 2013; entre outros), o nível de conhecimento das características e das propriedades geotécnicas desse lodo, para diferentes tipos e níveis de secagem, ainda é limitado (O'KELLY, 2006).…”

Experimental rheological procedure adapted to pasty dewatered sludge up to 45 % dry matter

“…Until now the literature mostly focused on the characterization of the rheological behavior of sludges at low (TS<4%) and moderate (4 < TS<17%) solid concentration (Baroutian et al, 2013;Baudez et al, 2013;Dong et al, 2011;Eshtiaghi et al, 2013;Farno et al, 2014;Jiang et al, 2014;Keiding et al, 2001;Lolito et al, 1997;Ma et al, 2014;Manoliadis and Bishop, 1984;Moeller and Torres, 1997;Mori et al, 2006;Pevere et al, 2009;Ratkovich et al, 2013;Ruiz-Espinoza et al, 2012;S egalen et al, 2015;Wang et al, 2016Wang et al, , 2012. Limited attention was paid on pasty and highly concentrated sludge mainly because of the difficulties to carry out relevant measurements (Agoda-Tandjawa et al, 2013;Battistoni, 1997;Baudez et al, 2016;Baudez and Coussot, 2001;Chaari et al, 2003;Charlou, 2014;Jiang et al, 2014;Liang et al, 2017). Indeed, as the TS content increases, dominating interactions move from a lubricated regime (indirect contacts) to a frictional regime (direct contact), leading to dilatancy (Bagnold, 1966;Jaeger and Nagel, 1992;Phillips and Davies, 1991;Sosio et al, 2007;Van Damme et al, 2002) and fractures (Baudez and Coussot, 2001;Chaari et al, 2003;Coussot, 2014).…”