Characterization of organic matter in the thermal hydrolysis pretreated anaerobic digestion return liquor

Quantification of soluble recalcitrant compounds in commercial thermal hydrolysis digestates

“…Secondly, the THP solubilize the substrates, giving higher concentrations of soluble nutrients in the digester feed (Bougrier, Delgenes, & Carrere, 2007; Suarez‐Iglesias, Urrea, Oulego, Collado, & Diaz, 2017). Due to the high operating temperature of the THP, typically 165°C, the formation of recalcitrant compounds has been reported by several authors and been mainly linked to the Maillard reactions between sugars and proteins (Dwyer, Starrenbury, et al, 2008; Gupta, Novak, & Zhao, 2015; Higgins et al., 2017; Tampio et al., 2014). Thirdly, improved degradation of organic material will also further increase the concentration of ammonium in the digestate compared with conventional AD (Barber, 2016).…”

“…Melanoidins consist of a large range of different molecules that are formed via condensation during Maillard reactions (Maillard, 1912) at high temperatures (140–165°C), which is a typical temperature range in THP processes. Melanoidins related to THP treatment have been defined as recalcitrant compounds having a higher molecular weight than 10 kDa with strong color and high ultraviolet absorbance (UVA254) capacity (Dwyer, Starrenbury, et al, 2008; Gupta et al., 2015; Higgins et al., 2017; Tampio et al., 2014). Maillard reactions may cause the production of thousands of distinct chemical compounds from only a few initial precursors (Hemmler et al., 2018), and thus melanoidins are a tremendously complex pool of compounds.…”

“…The increase in THP temperature has also been linked to the increase in UV absorbing compounds (Dwyer, Starrenbury, et al, 2008; Higgins et al., 2017) which can have a negative impact on downstream processes such as UV disinfection as reported by Dwyer, Starrenbury, et al (2008). Compounds identified as the dissolved organic nitrogen (DON) after THP and AD have also been linked to melanoidin formation (Dwyer, Starrenbury, et al, 2008; Gupta et al., 2015; Higgins et al., 2017). The contribution of total nitrogen to eutrophication processes in sensitive water recipients has led to strict legislations concerning the concentration of nitrogen in the WRRFs effluent in some areas (Oleszkiewicz & Barnard, 2006).…”