Pretreatment optimization of membrane-concentrated leachate through enhanced coagulation

Abstract

Proper disposal of membrane-concentrated leachate (MCL) is problematic for municipal solid waste incineration (MSWI) plants. Many MSWI plants treat concentrated leachate using multistage processes, among which a pretreatment before advanced oxidation process (AOP) is the most common practice. In this study, four commonly used coagulants were applied to conduct enhanced coagulation pretreatment on a two-stage tight material MCL, which is collected from MSWI plants. Conditions of enhanced coagulation, including coagulant and its dosage (PSAF, 5 g L−1), coagulant aid dosage (PAM, 80 mg L−1), and initial pH (7), were determined through a single factor experiment. After pretreatment, the removal efficiency toward chemical oxygen demand (COD), UV absorption at 254 nm, total nitrogen, color, and turbidity were 80.6%, 89.0%, 97.8%, 17.0%, and 84.8%, respectively. Moreover, dissolved organic matter (DOM) characteristics before and after pretreatment were investigated via spectrum analyses in detail. UV-visible light and three-dimensional fluorescence analysis showed that the MCL was laden with refractory organic matter; concentration of DOM, especially that of humic-like acid, were deeply decreased after pretreatment. While flow field-flow fractionation measurements illustrated DOM molecular weight was just slightly reduced by the enhanced coagulation, and it was challenging for the enhanced coagulation to change the DOM molecular weight distribution. Finally, the results of gas chromatography-mass spectrometry analysis were illustrated that the main types of volatile organic compounds (VOCs) in MCL were chain organic compounds and some aromatic compounds with relatively low molecular weight, and they were easily removed or decomposed through enhanced coagulation. This study provides a theoretical basis for the enhanced coagulation for pretreatment of MCL.