Efficient conversion of municipal sludge to practical carbon source via N/MxOy in catalytic wet air oxidation

IF 11.4 1区环境科学与生态学 Q1 ENGINEERING, ENVIRONMENTAL

Water Research Pub Date : 2025-05-18 DOI:10.1016/j.watres.2025.123859

Kaiyu Fang , Yang Tong , Yuting Zhu , Guodong Yao , Xu Zeng , Yecheng Xue , Yangyuan Zhou , Jianfu Zhao , Siqing Xia

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Abstract

The residual liquid phase after wet air oxidation of sludge has long been recognized as a potential carbon source due to its richness in volatile fatty acids (VFAs). However, nitrogen inevitably accumulates in the form of ammonia during the process, undermining the goal of adding a carbon source to aid bioreactors in nitrogen removal. To address this issue, different N/M_xO_y catalysts were synthesized with noble metal (N=Ru, Pt, Pd) and metal oxide supports (M_xO_y=Al₂O₃, TiO₂, CeO₂, ZrO₂). The entire process comprised the liquefaction of sludge and the subsequent refining of oxidation liquid. The performance of these catalysts was compared using various parameters, including total nitrogen (TN) removal, practical carbon source (PCS) production, and volatile fatty acids (VFAs) production, to ensure both the quantity and quality of the carbon source. Ru/TiO₂ was found to be the best catalyst, achieving a TN removal rate of 94.6 % and a PCS concentration of 2760 mg/L under optimized reaction conditions of 260 °C, 1.5 MPa O₂, 4.0 h, an initial pH of 7.1, and the addition of 3.0 g/L vacuum-dried catalyst. In general, 110.1 g COD carbon source could be produced per kg dry sludge. The reusability of the catalyst was examined, and PCS only decreased 4.7 % after four cycles of usage. The change in other dissolved organic matter was also investigated, with CHON and CHO molecules, as well as lignins and condensed hydrocarbons, being considered the dominant components. This study offers a viable approach for the resource utilization of municipal sludge.

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湿式空气催化氧化中N/MxOy有效转化城市污泥为实用碳源的研究

污泥湿式空气氧化后的残余液相富含挥发性脂肪酸（VFAs），长期以来被认为是一种潜在的碳源。然而，在这个过程中，氮不可避免地以氨的形式积累，破坏了添加碳源以帮助生物反应器去除氮的目标。为了解决这一问题，用贵金属（N=Ru, Pt, Pd）和金属氧化物载体（MxOy=Al2O3, TiO2, CeO2, ZrO2）合成了不同的N/MxOy催化剂。整个过程包括污泥液化和随后的氧化液精炼。以总氮（TN）去除率、实用碳源（PCS）生成量和挥发性脂肪酸（VFAs）生成量为指标，对催化剂的性能进行了比较，以保证碳源的数量和质量。结果表明，在260℃、1.5 MPa O2、4.0 h、初始pH为7.1、添加3.0 g/L真空干燥催化剂的条件下，Ru/TiO2的TN去除率为94.6%，PCS浓度为2760 mg/L。一般情况下，每千克干污泥可产生110.1 g COD碳源。考察了催化剂的可重复使用性，4次循环使用后，PCS仅下降4.7%。其他溶解有机物的变化也被研究，与CHON和CHO分子，以及木质素和缩合碳氢化合物，被认为是主要成分。本研究为城市污泥资源化利用提供了一条可行的途径。

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来源期刊

Water Research 环境科学-工程：环境

CiteScore

20.80

自引率

9.40%

发文量

1307

审稿时长

38 days

期刊介绍： Water Research, along with its open access companion journal Water Research X, serves as a platform for publishing original research papers covering various aspects of the science and technology related to the anthropogenic water cycle, water quality, and its management worldwide. The audience targeted by the journal comprises biologists, chemical engineers, chemists, civil engineers, environmental engineers, limnologists, and microbiologists. The scope of the journal include: •Treatment processes for water and wastewaters (municipal, agricultural, industrial, and on-site treatment), including resource recovery and residuals management; •Urban hydrology including sewer systems, stormwater management, and green infrastructure; •Drinking water treatment and distribution; •Potable and non-potable water reuse; •Sanitation, public health, and risk assessment; •Anaerobic digestion, solid and hazardous waste management, including source characterization and the effects and control of leachates and gaseous emissions; •Contaminants (chemical, microbial, anthropogenic particles such as nanoparticles or microplastics) and related water quality sensing, monitoring, fate, and assessment; •Anthropogenic impacts on inland, tidal, coastal and urban waters, focusing on surface and ground waters, and point and non-point sources of pollution; •Environmental restoration, linked to surface water, groundwater and groundwater remediation; •Analysis of the interfaces between sediments and water, and between water and atmosphere, focusing specifically on anthropogenic impacts; •Mathematical modelling, systems analysis, machine learning, and beneficial use of big data related to the anthropogenic water cycle; •Socio-economic, policy, and regulations studies.