Transformation of dissolved organic matters produced from alkaline-ultrasonic sludge pretreatment in anaerobic digestion: From macro to micro

Dan Lu, Keke Xiao, Yun Chen, Yan Ni Annie Soh, Yan Zhou*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

97 Scopus citations

Abstract

Soluble organic compounds released by alkaline (ALK), ultrasonic (ULS) and combined alkaline-ultrasonic (ALK-ULS) pretreatment as well as their transformation in the anaerobic digestion systems were investigated. The maximum methane production of 197.1 ± 3.0 mL CH4/g tCODfeed was observed with ALK-ULS pretreated sludge (pH 12 and specific energy input of 24 kJ/g TS). The combined treatment likely enhanced the sludge solubilization and produced more low molecular weight (LMW) substances, which were beneficial to improve the biogas generation rate. However, such pretreatment released not only easily biodegradable substances but also more recalcitrants, such as humic substances (HS) and complex high molecular weight (HMW) proteins. Thus, more residual dissolved organic matters (DOMs) were detected after digestion, which may pose adverse effects on the downstream water treatment. Refractory HS and hydrophobic dissolved organic carbon (HO DOC) were the main components of the residual DOMs, which accounted up to 35.0% and 22.3% respectively. At the molecular level, a large amount of residual polycyclic steroid-like matters, alkanes and aromatics were identified. Specific higher MW residual compounds, e.g. polar metabolites (like dipeptide, benzene and substituted derivatives), and non-polar lipids (like diacylglycerols, long chain fatty acids, alkenes, flavonoids, sphingolipids, glycerolipids, glycerophospholipids and their derivatives) were also identified. The results indicate that further polishing steps should be considered to remove the remaining soluble recalcitrant compounds. This study helps to understand the insight of sludge treatment from macro to micro level.

Original languageEnglish
Pages (from-to)138-146
Number of pages9
JournalWater Research
Volume142
DOIs
StatePublished - 1 Oct 2018
Externally publishedYes

Keywords

  • Alkaline
  • Anaerobic digestion
  • Dissolved organic matters
  • Pretreatment
  • Recalcitrant compounds
  • Ultrasonic

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