Highly efficient solid-liquid separation of anaerobically digested liquor of food waste: Conditioning approach screening and mechanistic analysis

Hao Wang; Yifeng Yang; Boran Wu; Xiaoli Chai; Xiaohu Dai

doi:10.1016/j.scitotenv.2021.152416

Highly efficient solid-liquid separation of anaerobically digested liquor of food waste: Conditioning approach screening and mechanistic analysis

Sci Total Environ. 2022 Mar 10:811:152416. doi: 10.1016/j.scitotenv.2021.152416. Epub 2021 Dec 16.

Authors

Hao Wang¹, Yifeng Yang², Boran Wu³, Xiaoli Chai⁴, Xiaohu Dai⁴

Affiliations

¹ State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China.
² Shanghai Municipal Engineering Design Institute (Group) Co., Ltd, 901 Zhongshan North 2nd Road, Shanghai 200092, China.
³ State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China. Electronic address: boranwu@tongji.edu.cn.
⁴ State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China.

PMID: 34923015
DOI: 10.1016/j.scitotenv.2021.152416

Abstract

Anaerobic digestion is known for its effectiveness and environmental friendliness in treating food waste. However, it produces anaerobically digested liquor (ADL). ADL usually has a high solid content and high concentrations of nitrogen (N), phosphorus (P), and chemical oxygen demand (COD) carried by suspended solids (SS). Thus, when ADL with amounts of SS reaches the subsequent biochemical treatment units, they negatively impact the microbial stability of corresponding processes, causing unstable effluent qualities. For this reason, the solid-liquid separation of ADL acts as a crucial step for the wide application of anaerobic digestion. In this work, the typical sludge conditioning approaches, including flocculation/coagulation, coagulation, oxidation and advanced oxidation processes (AOPs), were systematically screened for their feasibility in enhancing the solid-liquid separation of ADL. The modified Fenton treatment combined with centrifugation was found to be the most effective approach, which realized the removal of 91.36% SS with FeSO₄•7 H₂O (5.96 g/L) and H₂O₂ (2.79 g/L) but without pH adjustment of ADL. The mechanism analysis showed that the modified Fenton promoted ADL colloidal aggregates to form looser medium-sized flocs with pores, increased the zeta potential to -17.6 mV, and highly reduced the total interfacial free energy. Also, extracellular polymeric substances (EPS) were released into liquid phase, which further eliminated the water-retaining properties of solid compositions. The analysis of surface chemical composition suggested that the modified Fenton decreased the hydrophilic component from 53.37% to 43.81% and the relative content of protein-N from 45.43% to 23.57%, while increased carbon chain and hydrocarbyl species. Furthermore, principal component analysis (PCA) suggested that SS, zeta potential, Lewis acid-base interfacial free energy, two-dimensional fractal index (2-D_f) and C-(N, O) relative content were more sensitive to variations in conditioning approaches than protein-N relative content, and hydroxyl free radical (•OH) played the key role for the modified Fenton to improve SS removal from ADL.

Keywords: Anaerobically digested liquor; Fenton; Food waste; Solid-liquid separation.

MeSH terms

Food
Hydrogen Peroxide
Refuse Disposal*
Sewage
Waste Disposal, Fluid*

Substances

Sewage
Hydrogen Peroxide