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Impact of dynamic distribution of floc particles on flocculation effect

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Journal of environmental Sciences 2009年第8期21卷 1059-1065页

作者： nan jun, he weipeng, SONG Xinin, li guibai state key laboratory of urban water resource and environment, school of municipal and environmental engineering, harbin institute of technology, harbin 150090, china. state key laboratory of urban water resource and environment School of Municipal and Environmental Engineering Harbin Institute of Technology Harbin 150090 China

Polyaluminum chloride （PAC） was used as coagulant and suspended particles in kaolin water. Online instruments including turbidimeter and particle counter were used to monitor the flocculation process. An evaluation model for demonstrating the impact on the flocculation effect was established based on the multiple linear regression analysis method. The parameter of the index weight of channels quantitatively described how the variation of floc particle population in different size ranges cause the decrement of turbidity. The study showed that the floc particles in different size ranges contributed differently to the decrease of turbidity and that the index weight of channel could excellently indicate the impact degree of floc particles dynamic distribution on flocculation effect. Therefore, the parameter may significantly benefit the development of coagulation and sedimentation techniques as well as the optimal coagulant selection.

关键词： particle size distribution particle counter index weight flocculation process

Unlocking the potential of thin-film composite reverse osmosis membrane performance:Insights from mass transfer modeling

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Chinese Chemical Letters 2024年第5期35卷 66-76页

作者： Kexin Yuan Yulei liu Haoran Feng Yi liu jun Cheng Beiyang Luo Qinglian Wu Xinyu zhang Ying Wang Xian Bao Wanqian Guo jun Ma state key laboratory of urban water resource and environment School of EnvironmentHarbin Institute of TechnologyHarbin 150090China College of Architecture and environment Sichuan UniversityChengdu 610065China school of municipal and environmental engineering Shandong Jianzhu UniversityJi’nan 250101China College of water Conservancy and Hydropower engineering Sichuan Agricultural UniversityYaan 625014China

Thin-film composite(TFC)reverse osmosis(RO)membranes have attracted considerable attention in water treatment and desalination processes due to their specific separation ***,the trade-off effect between water flux and salt rejection poses huge challenges to further improvement in TFC RO membrane *** research works have been dedicated to optimizing membrane fabrication and modification for addressing this *** the meantime,several reviews summarized these ***,the existing reviews seldom analyzed these methods from a theoretical perspective and thus failed to offer effective optimization directions for the RO process from the root *** this review,we first propose a mass transfer model to facilitate a better understanding of the entire process of how water and solute permeate through RO membranes in detail,namely the migration process outside the membrane,the dissolution process on the membrane surface,and the diffusion process within the ***,the water and salt mass transfer behaviors obtained from model deduction are comprehensively analyzed to provide potential guidelines for alleviating the trade-off effect between water flux and salt rejection in the RO ***,inspired by the theoretical analysis and the accurate identification of existing bottlenecks,several promising strategies for both regulating RO membranes and optimizing operational conditions are proposed to further exploit the potential of RO membrane *** review is expected to guide the development of high-performance RO membranes from a mass transfer theory standpoint.

关键词： Reverse osmosis Mass transfer model Trade-off effect Membrane performance Optimization strategies

Analysis of floc morphology in a continuous-flow flocculation and sedimentation reactor

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Journal of environmental Sciences 2017年第2期29卷 268-275页

作者： Pengfei Ren jun nan Xinran zhang Kai Zheng school of municipal and environmental engineering Harbin Institute of TechnologyHarbin 150090China state key laboratory of urban water resource and environment Harbin Institute of TechnologyHarbin 150090China

The floc morphology was investigated in a continuous-flow reactor, in order to understand the evolution of flocs in practical flocculation and sedimentation processes in water utilities. Kaolin-humic acid suspension was used as the test water, and polyaluminum chloride was chosen as the coagulant. An in-situ recognition system was applied to analyze the floc size, boundary fractal dimension, and eccentricity ratios. Particle numbers and turbidity were also determined in the sedimentation stage. At a coagulant dose of 1 mg/L as Al, the average floc size increased from 62 to 78 μm and the boundary fractal dimension was around 1.14, suggesting that flocs were compact and continuously grew during the entire flocculation process. However, with the dose increased to 5 mg/L, the average floc size decreased and stabilized at around 65 μm, with the fractal dimension of 1.20. It can be concluded that the excess coagulant doses resulted in the formation of chain-shaped, lower density, and more branched structure flocs, thereby restricting flocs’ further growth in the subsequent flocculation. Floc morphology analysis suggested that charge neutralization dominated in the initial flocculation stage, then the bridge and sweep mechanisms were dominant in the subsequent flocculation. In addition, compared with the traditional inclined plate settler, a novel V-shaped plate settler introduced in this study had an advantage in small size floc（less than 5 μm） removal. The V-shaped region could promote aggregate restructuring and re-flocculation; therefore, the V-shaped plate settler provides an alternative method for sedimentation.

关键词： Flocculation Sedimentation Continuous-flow reactor In-situ recognition system V-shaped plate settler tank