Molecular Composition And Chemical Diversity Of Dissolved Organic Matter In Sludge Based On High Resolution Mass Spectrometry

Municipal sludge is an inevitable by-product of sewage treatment system.Its increasing output year by year brings great challenge to the field of environmental engineering.In the current macro background of climate change,energy shortage,environmental crisis and so on,it is necessary to effectively recycle and utilize potential biomass resources in sludge to improve the sustainability and comprehensive benefits of sewage treatment plants.Therefore,it is very important to understand the molecular composition and possible molecular structure of dissolved organic matter（DOM）in waste sludge.This project focuses on the important technical problem of the influence of different extraction methods and ion modes on the molecular composition of DOM in sludge.Spectroscopy and organic matter recovery index were used to evaluate the recovery efficiency of organic matter in sludge derived DOM by different pretreatment methods（electrodialysis（ED）and solid phase extraction column（styrene divinylbenzene polymer（PPL）,octadecyl（C18）））.Molecular composition of DOM(DOM_WAS)of waste activated sludge and DOM(DOM_WAS)of anaerobic digestion sludge was analyzed by ESI（+）and ESI（-）models using high resolution mass spectrometry（ESI（+））.Identify and compare the molecular information of organisms with high abundance in DOMWAS and DOMADS.Specific research results are as follows:（1）The effects of different pretreatment methods（ED,PPL,C18）and ionization modes on DOM of sludge were discussed,aiming at the problems of low recovery rate and incomplete composition of organic matter caused by the enrichment and purification of DOM of sludge by traditional solid phase extraction method.The results showed that ED pretreatment had the highest recovery rate of DOM derived from sludge（70%～95%）,which was more than 2 times higher than that of solid phase extraction column.According to the results of organic matter recovery and spectroscopy characterization,ED pretreatment has strong specific selectivity for substances unlike solid phase extraction,which can maximize the retention of the original components and functional group containing substances in sludge DOM.From the perspective of molecular composition,the molecular characteristics of ED and PPL in the recovery of sludge DOM were highly similar（lipids,proteins/aliphatic groups and lignin/CRAMs were the main substances）,while C18 method was not effective in the extraction of carbohydrates and unsaturated hydrocarbons.Multivariate statistical analysis（PCA and HCA）on the molecular properties identified by different pretreatment methods showed that ED and PPL had a strong correlation（PC1+PC2>80%,R>0.99）,combined with organic matter recovery comprehensive analysis,ED is a better choice for sludge derived DOM pretreatment.In addition,compared with the single ESI（-）analysis mode,the number of molecules identified by ESI（+）mode increased by 200%,and the composition and species of identified elements were significantly higher than ESI（-）mode,indicating the superiority of the dual-ion mode for DOM analysis of sludge.Therefore,the electrodialysis pretreatment combined with dual-ion mode analysis method of DOM molecular composition of sludge was established to provide technical support for subsequent sludge treatment and disposal and resource utilization.（2）Regarding the unclear molecular composition and structure of DOM in sludge,the FT-ICR MS dual-ion mode was used to jointly analyze the molecular composition of DOM in sludge,and the Chemspider chemical database was used to screen its possible molecular structure,so as to identify the possible pollutant types.The results showed that for the identification of CHON compounds in DOM_WAS/ADS,pretreatment of PPL and C18was mostly N₁O（such as emerging containments ECs）,while pretreatment of ED could retain substances with higher molecular weight（such as N₃O compounds such as amide and valine）.CHO compounds were mainly concentrated in O₂-O₁₂,including soluble microbial metabolites（such as hydroxyl fatty acids）and ECs（such as dioctyl terephthalate（DOTP）and dibutyl phthalate（DBP））.The main proportion of S₁O compounds in CHOS is alkyl benzene sulfonic acid（anionic surfactants,such as shampoo and detergent）.GC-MS assisted verification showed that dissolved microbial metabolites（such as DKPs,hydroxyl fatty acids,etc.）and ECs（such as surfactants,plasticizers（DOP,DBP,etc.））were the main substances in DOM of sludge.ECs accounted for more than80%of the top ten substances with the highest abundance of DOM in sludge.This work enriches the understanding of the molecular characteristics of DOM in sludge,and provides reference value and important theoretical guidance for efficient and safe utilization of organic matter in sludge.