{"title":"Unraveling the mechanisms underlying AOM-induced deterioration of the settling performance of algal floc","authors":"Ziqian Cheng, Zhe Lin, Xin Chen, Xuezhi Zhang, Haiyang Zhang","doi":"10.1016/j.watres.2025.123115","DOIUrl":null,"url":null,"abstract":"The influence of algal organic matter (AOM) on the settling performance of algal flocs remains poorly understood. To address this, we employed fractionation techniques based on molecular weight to isolate different AOM fractions and analyzed their effects on floc structure and settling performance. This involved comparing the concentrations, compositions, potentials, and functional groups of organic matter before and after coagulation-sedimentation. The results demonstrated that AOM significantly impacts floc characteristics, including size and compactness, ultimately hindering floc settling performance. Specifically, AOM fractions smaller than 100 kDa, such as humic substances, preferentially consumed coagulants without directly participating in floc formation, leading to smaller and slower-settling algal flocs. This was particularly evident for fractions with a molecular weight below 5 kDa, where only 25% of the material participated in floc formation. In contrast, over 90% of the AOM with a molecular weight exceeding 100 kDa, such as proteins, exhibited negatively charged functional groups (e.g., carboxyl groups) that interacted with coagulants via electrostatic forces to form larger complexes. These complexes enhance the coagulant's ability to capture and bridge algal cells, directly binding to the flocs, resulting in an increase of 20.3% in the size and a 37.5% faster settling velocity of the flocs formed by >100kDa AOM compared to <5 kDa. This study elucidates the mechanisms by which AOM influences algal floc settling performance from the perspectives of AOM composition and its interactions with coagulants and algal cells. The findings provide a theoretical basis for a deeper understanding of algal flocculation mechanisms and for accelerating algal flocculation and sedimentation.","PeriodicalId":443,"journal":{"name":"Water Research","volume":"7 1","pages":""},"PeriodicalIF":11.4000,"publicationDate":"2025-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Water Research","FirstCategoryId":"93","ListUrlMain":"https://doi.org/10.1016/j.watres.2025.123115","RegionNum":1,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ENGINEERING, ENVIRONMENTAL","Score":null,"Total":0}
引用次数: 0
Abstract
The influence of algal organic matter (AOM) on the settling performance of algal flocs remains poorly understood. To address this, we employed fractionation techniques based on molecular weight to isolate different AOM fractions and analyzed their effects on floc structure and settling performance. This involved comparing the concentrations, compositions, potentials, and functional groups of organic matter before and after coagulation-sedimentation. The results demonstrated that AOM significantly impacts floc characteristics, including size and compactness, ultimately hindering floc settling performance. Specifically, AOM fractions smaller than 100 kDa, such as humic substances, preferentially consumed coagulants without directly participating in floc formation, leading to smaller and slower-settling algal flocs. This was particularly evident for fractions with a molecular weight below 5 kDa, where only 25% of the material participated in floc formation. In contrast, over 90% of the AOM with a molecular weight exceeding 100 kDa, such as proteins, exhibited negatively charged functional groups (e.g., carboxyl groups) that interacted with coagulants via electrostatic forces to form larger complexes. These complexes enhance the coagulant's ability to capture and bridge algal cells, directly binding to the flocs, resulting in an increase of 20.3% in the size and a 37.5% faster settling velocity of the flocs formed by >100kDa AOM compared to <5 kDa. This study elucidates the mechanisms by which AOM influences algal floc settling performance from the perspectives of AOM composition and its interactions with coagulants and algal cells. The findings provide a theoretical basis for a deeper understanding of algal flocculation mechanisms and for accelerating algal flocculation and sedimentation.
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.