Insight into removals of PARAFAC components from dissolved and particulate organic matter in wastewater treatment process by two-dimensional correlation and structure equation modeling

Benxin Yu,Yingxue Sun,Jian Wang,Dongping Liu

doi:10.1186/s12302-021-00558-z

Abstract

BackgroundMost particulate organic matter (POM) cannot be directly degraded in the conventional wastewater treatment, which should be transformed into dissolved organic matter (DOM) through a hydrolysis process. However, non-hydrolyzed POM in the biological treatment can limit treated efficiencies for the wastewater treatment plants (WWTPs) facilities. Hence an operational tool is indispensable for insight into removals of DOM and POM factions in the WWTP. In this study, excitation-emission matrix fluorescence spectroscopy (EEM) combined parallel factor analysis (PARAFAC), two-dimensional correlation (2D-COS) and structural equation modeling (SEM) was employed to evaluate removals of DOM and POM in a wastewater treatment plant.ResultsFour fluorescence components were identified in DOM and POM substances from the WWTP by EEM combined with PARAFAC, i.e., tyrosine-like (TYLF), tryptophan-like (TRLF), microbial byproduct-like (MBLF), and fulvic acid-like (FALF). In A2/O process, the TYLF and TRLF of DOM were removed to a larger extent than those of MBLF and FALF in anaerobic tank, while TYLF and MBLF of POM were removed to a great extent than those of TRLF and FALF in primary sedimentation and aerobic tanks. By the 2D-COS, a decreasing variation order of DOM fractions in the wastewater treatment process was UV-FALF → MBLF2 → Vis-FALF → TRLF → TYLF, while the decreasing order of POM fractions was Vis-FALF → UV-FALF → MBLF2 → TYLF → MBLF1 → TRLF. SEM revealed that TRLF and TYLF of DOM were degraded by anaerobic microorganism, and TRLF could be transformed partially into FALF. However, TRFL and TYLF of POM were discomposed by aerobic microorganism.ConclusionsThe 2D-COS and SEM can be practicable tools as EEM-PARAFAC for monitoring DOM and POM in the WWTP. The study could present a theoretical support to improving the retrofit of WWTP and formulating emission standards for organic pollutants.

Highlights

Most particulate organic matter (POM) cannot be directly degraded in the conventional wastewater treatment, which should be transformed into dissolved organic matter (DOM) through a hydrolysis process
The POM with relatively low surface area is well known as a restrained factor of biodegradation process, and most of POM cannot be directly degraded in the conventional wastewater treatment, which should be transformed into DOM through a hydrolysis process
Extraction of parallel factor analysis (PARAFAC) components A strong peak and four weak shoulders were represented in the excitation-emission matrix fluorescence spectroscopy (EEM) spectroscopy of DOM from the wastewater sample at the preliminary grit chamber (Fig. 1a)

Summary

Introduction

Most particulate organic matter (POM) cannot be directly degraded in the conventional wastewater treatment, which should be transformed into dissolved organic matter (DOM) through a hydrolysis process. Organic matter exhibited in wastewater is derived largely from anthropological activities and microbial metabolites, which mainly contains roughly 50% protein and amino acids, 40% carbohydrates, 10% aliphatic compounds, and trace amounts of emerging pollutants, priority contaminants, and surface-active substances [1,2,3]. The POM with relatively low surface area is well known as a restrained factor of biodegradation process, and most of POM cannot be directly degraded in the conventional wastewater treatment, which should be transformed into DOM through a hydrolysis process. The DOM with a relatively higher surface area exhibits an important role in improving microbial activities and pollutant degradation, but can induce membrane fouling and disinfection by-products [7, 8]

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