Thermal hydrolysis for sewage treatment: A critical review

Exploring the impact of bulk and substrate physics on hydrolysis rates and biogas yields of anaerobic digesters pretreated with thermal hydrolysis

“…Therefore, of the two competing molecular structure changes imparted on BSA with temperature treatment, the formation of intermolecular bonds was the determining factor in the ease of colonization and hydrolysis performance. The formation of increased levels of recalcitrant organic nitrogen due to thermal treatment has been reported before by Higgins et al () and Barber () and correlated with the decreased biogas yield observed in our study.…”

“…As the k H values reported for polysaccharides (0.025–2.0/day; Vavilin et al, ) were significantly higher than for proteins (0.015–0.8/day; Vavilin et al, ) and thermal treatment increased the polysaccharide k H further (Table ), degradation of carbohydrates was likely not the rate‐limiting step in AD. This also has been confirmed by the increased difficulty in degrading waste activated sludge (WAS) in AD (Lin, Chang, & Chang, ) and the recommendation of Barber () to only thermally treat WAS rather than mixture of primary sludge and WAS. The increased protein and extracellular polymer substance content in WAS have resulted in a much clearer impact of THP on the biogas yields (Phothilangka et al, ; Panter et al, ) than reported for primary sludge (Wilson & Novak, ).…”

Recuperative thickening for sludge retention time and throughput management in anaerobic digestion with thermal hydrolysis pretreatment

“…In addition to the intensification potential of digesters by implementation of THP, enhanced biodegradability of activated sludge with 25%-62% increase in VSR (Barber, 2016) and improved digestate dewaterability resulting in increased cake solids from 20% to 35% (Barber, 2016;Higgins et al, 2017;Oosterhuis, Ringoot, Hendriks, & Roeleveld, 2014;Phothilangka, Schoen, & Wett, 2008) have been reported as drivers for such technology. Although increased digestibility has been observed in digesters with THP (Barber, 2016;Higgins et al, 2017;Li et al, 2017;Wang, Wang, Zhang, & Zhang, 2009), there is still an estimated potential for about 20%-30% higher biogas production when one compares the digester biogas production with the long-term biochemical methane potential (BMP) (Riffat & De Clippeleir, 2019). It is unclear if the limitation in reaching full digestion efficiency is limited by limitation in reaction time due to limited SRT or due to operation under unfavorable conditions in the digester.…”

“…Intensified AD systems can potentially suffer from limiting rates or digestion efficiency due to operation at increased inhibitory conditions. Due to the increased feed TS concentration in THP-AD systems, increased ammonium (2,400-3,500 mg N/L) and free ammonia (150-200 mg N/L) levels have been observed (Barber, 2016). These conditions could cause inhibition on hydrolysis (Fernandes, Keesman, Zeeman, & Lier, 2012;Griffin, 2012;Lü, He, Shao, & Lee, 2007) and methanogenesis given the reported inhibition levels for free ammonia of 150-620 mg N/L for methanogens (Chen, Ortiz, Steele, & Stuckey, 2014;McCarty & McKinney, 1961).…”

“…THP partially hydrolyzes solids and decreases viscosity. The latter allows for efficient pumping and mixing at increased digester TS concentration and increased volatile solid (VS) loading (Barber, ; Nielsen, Thygesen, Thomsen, & Schmidt, ). For example, AD systems with THP pretreatment have been successfully operated at high loading in the range of 2.5–8.8 kg COD/m 3 ‐day with feed at 9%–12% TS (Higgins et al, ; Norli, ; Pook, Mills, Heitmann, Panter, & Walley, ; Walley, ; Wilson, Tanneru, Banjade, Murthy, & Novak, ).…”