Articoli di riviste: "Floc properties"

1

Mehta, Ashish J., William H. McAnally, Farzin Samsami e Andrew J. Manning. "REVISITING THE ROLE OF AGGREGATION IN THE SETTLING OF COHESIVE FLOCS IN THE MARINE ENVIRONMENT". Coastal Engineering Proceedings, n. 36 (30 dicembre 2018): 17. http://dx.doi.org/10.9753/icce.v36.sediment.17.

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The settling velocity is the single-most important property governing the transport of cohesive flocs in the marine environment. In that regard, the instantaneously changing diameter, density and shear strength of flocs are the defining properties which distinguish floc transport from that of cohesionless particles. Thus, consideration of aggregation, which includes the dynamics of floc growth and breakup due to floc-floc collisions as well as flow-induced shearing of flocs, is a critical component of floc transport modeling.

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Ding, Yanmei, Jianhai Zhao, Lei Wei, Wenpu Li e Yongzhi Chi. "Effects of Mixing Conditions on Floc Properties in Magnesium Hydroxide Continuous Coagulation Process". Applied Sciences 9, n. 5 (7 marzo 2019): 973. http://dx.doi.org/10.3390/app9050973.

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Magnesium hydroxide continuous coagulation process was used for treating simulated reactive orange wastewater in this study. Effects of mixing conditions and retention time on the coagulation performance and floc properties of magnesium hydroxide were based on the floc size distribution (FSD), zeta potential, and floc morphology analysis. Floc formation and growth in different reactors were also discussed. The results showed that increasing rapid mixing speed led to a decrease in the final floc size. The floc formation process was mainly carried out in a rapid mixer; a rapid mixing speed of 300 rpm was chosen according to zeta potential and removal efficiency. Reducing retention time caused a relatively small floc size in all reactors. When influent flow was 30 L/h (retention time of 2 min in rapid mixer), the average floc size reached 8.06 μm in a rapid mixer; through breakage and re-growth, the floc size remained stable in the flocculation basin. After growth, the final floc size reached 11.21 μm in a sedimentation tank. The removal efficiency of reactive orange is 89% in the magnesium hydroxide coagulation process.

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Nielsen, P. H., T. R. Thomsen e J. L. Nielsen. "Bacterial composition of activated sludge - importance for floc and sludge properties". Water Science and Technology 49, n. 10 (1 maggio 2004): 51–58. http://dx.doi.org/10.2166/wst.2004.0606.

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Activated sludge flocs consist of numerous constituents which, together with other factors, are responsible for floc structure and floc properties. These properties largely determine the sludge properties such as flocculation, settling and dewaterability. In this paper we briefly review the present knowledge about the role of bacteria in relation to floc and sludge properties, and we present a new approach to investigate the identity and function of the bacteria in the activated sludge flocs. The approach includes identification of the important bacteria and a characterization of their physiological and functional properties. It is carried out by use of culture-independent molecular biological methods linked with other methods to study the physiology and function, maintaining a single cell resolution. Using this approach it was found that floc-forming properties differed among the various bacterial groups, e.g. that different microcolony-forming bacteria had very different sensitivities to shear and that some of them deflocculated under anaerobic conditions. In our opinion, the approach to combine identity with functional analysis of the dominant bacteria in activated sludge by in situ methods is a very promising way to investigate correlations between presence of specific bacteria, and floc and sludge properties that are of interest.

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Yukselen, M. A., e J. Gregory. "Properties of flocs formed using different coagulants". Water Supply 2, n. 5-6 (1 dicembre 2002): 95–101. http://dx.doi.org/10.2166/ws.2002.0156.

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The effects of shear on the formation and break-up of flocs generated using aluminium sulphate (“alum”), polyaluminium chloride and a cationic polyelectrolyte have been investigated using conventional jar test procedure and by continuous optical monitoring. Using the experimentally determined optimum dosage, the breakage of flocs was followed at a high stirring speed, corresponding to average shear rate (G) of about 330-520 s-1. Most of the breakage occurred within a few seconds of increasing the shear rate. After each breakage the stirring rate was reduced to the original value to allow the flocs to re-grow. For alum and polyaluminium chloride, it was found that only limited re-growth of flocs occurred indicating a significant irreversibility of the floc break-up process. Residual turbidity increased after floc breakage and re-growth, indicating a reduction in sedimentation rate of the re-grown flocs, consistent with the continuous monitoring results. For the cationic polyelectrolyte, the re-growth of flocs occurred to a much greater extent and floc breakage was almost fully reversible.

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Ehlers, G. A. C., D. Wagachchi e S. J. Turner. "Nutrient conditions and reactor configuration influence floc size distribution and settling properties". Water Science and Technology 65, n. 1 (1 gennaio 2012): 156–63. http://dx.doi.org/10.2166/wst.2011.849.

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Floc formation and settleability is critical for effective solid–liquid separation in many wastewater treatment processes. This study aimed to investigate the relationship between particle size distribution and nutrient conditions in different bioreactor configurations. Size distribution profiles of flocs that formed in continuous (B1), continuous with clarifier and return sludge (B2) and SBR (B3) reactors were investigated in parallel under identical nutrient conditions. An eight-fold dilution of the influent COD of a synthetic dairy processing wastewater resulted in a ‘feast and famine’ regime that triggered significant effects on the biomass and flocculation characteristics. Floc size analysis of reactor MLSS revealed a shift in floc sizes when reactors were fed with the minimum (famine) COD wastewater feed (0.61 g L−1). Increasing floc size distributions were detected for all reactors during the minimum COD feed although different size patterns were observed for different reactor configurations. These increases corresponded with variations in aggregation and EPS quantities. The SBR yielded comparatively larger flocs when operated under both COD feeds as indicated by d(0.9) values (90% of particles ≤ d in size). Overall the results indicated that floc formation and floc size are mediated by nutrient concentrations and represents an important step towards improved solid–liquid separation.

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Zhao, Jianhai, Anmin Wang, Lei Wei, Wenqi Ge, Yongzhi Chi e Yanping Lai. "Effect of kaolin on floc properties for reactive orange removal in continuous coagulation process". Water Science and Technology 78, n. 3 (24 luglio 2018): 571–77. http://dx.doi.org/10.2166/wst.2018.327.

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Abstract Magnesium hydroxide was used as a coagulant for treating reactive orange wastewater in a real continuous process. Effects of kaolin on coagulation performance and floc properties were investigated with controlled experiments through floc size distribution, zeta potential, scanning electron microscopy and Fourier transform infrared spectroscopy. Kaolin had significant influence on magnesium hydroxide-reactive orange floc formation and growth. The results showed that average floc size reached 16.31, 12.88 and 20.50 μm, respectively, in the rapid mixer, flocculation basin and sedimentation tank when kaolin concentration was 10 mg/L and reactive orange initial concentration was 0.25 g/L. The floc size tended to increase with the increase of kaolin suspension to 10 mg/L. All of the flocs under investigation showed that floc breakage led to decreased average floc size and remained stable in the flocculation basin. Reactive orange and kaolin could be removed effectively in the continuous coagulation process. Reactive orange was adsorbed in the surface of magnesium hydroxide through charge neutralization and adsorption.

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Chen, Bo, Daisuke Tatsumi e Takayoshi Matsumoto. "Floc Structure and Flow Properties of Pulp Fiber Suspensions." Nihon Reoroji Gakkaishi 30, n. 1 (2002): 19–25. http://dx.doi.org/10.1678/rheology.30.19.

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Moon, B. H., G. T. Seo, T. S. Lee, S. S. Kim e C. H. Yoon. "Effects of salt concentration on floc characteristics and pollutants removal efficiencies in treatment of seafood wastewater by SBR". Water Science and Technology 47, n. 1 (1 gennaio 2003): 65–70. http://dx.doi.org/10.2166/wst.2003.0017.

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Most seafood wastewater has been treated by the activated sludge process. Due to changes in salt concentration, pollutant loadings and raw materials, the process is not operated satisfactorily to meet effluent regulation. Most problems faced at present are solid liquid separation. In this study, effects of salt concentration on floc characteristics and pollutants removal efficiencies were investigated in treatment of seafood wastewater by SBR. For analyzing fractal dimension of flocs, the small angle laser light scattering (SALLS) method was applied using a Diffraction Particle Sizer (Malvern Instruments). Organic removal efficiencies (in terms of CODMn) decreased with increasing salt concentration, but eventually reached a steady state. Fractal dimension and floc size also showed similar trends with changing salt concentration. The main reasons to reduced pollutant removal efficiencies were deteriorated biological activity and settling properties. The biological activity was affected faster than the floc characteristics by increasing salt concentration. The deteriorated settling properties were explained by decreased size and fractal dimension of floc due to increasing salt concentration. The settling properties of floc such as sludge volume index (SVI) and zone settling velocity (ZSV) were related to size and fractal dimension of floc. The fractal dimension of floc was better related to the settling properties than the size of floc.

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9

Eriksson, Leif, Inga Steen e Marta Tendaj. "Evaluation of Sludge Properties at an Activated Sludge Plant". Water Science and Technology 25, n. 6 (1 marzo 1992): 251–65. http://dx.doi.org/10.2166/wst.1992.0127.

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Composition of pre-settled water, sludge properties in two different lines of an activated sludge plant, and suspended solids (SS) content in outgoing water were followed three times a week during one year. Sludge characteristics were: settling properties, residual turbidity, floc strength, filtration resistance, amount of extracellular polymers, microscope appearance and total length of filamentous organisms. The outgoing SS could be related to residual turbidity and sludge volume. These factors depended on the floc structure and the filament length. These were determined by sludge load or sludge age, water composition and the hydrodynamic history of the sludge. On basis of these and earlier findings a general model for properties of flocs built by floc-forming organisms in activated sludge is proposed.

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Gregory, J., e V. Dupont. "Properties of flocs produced by water treatment coagulants". Water Science and Technology 44, n. 10 (1 novembre 2001): 231–36. http://dx.doi.org/10.2166/wst.2001.0628.

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Hydrolyzing coagulants are extensively used in water and wastewater treatment, often under conditions where hydroxide precipitation is important, giving “sweep flocculation”. Pre-hydrolyzed coagulants, such as polyaluminium chloride (PACl) are also widely used and have several advantages over traditional additives, such as aluminium sulfate. Their action is usually discussed in terms of cationic species and charge neutralization. However, precipitation may also be important and this aspect has not been considered in detail. The present work has compared the action of alum and three commercial PACl products on model clay suspensions. The conventional jar test procedure has been used, along with measurements of settled floc volume and dynamic monitoring of floc formation and break-up by an optical technique. The latter method gives very useful information on the nature of the flocs produced and their response to different shear conditions. It is clear from the results that the PACl products form larger and stronger flocs than alum. With all coagulants floc breakage appears to be essentially irreversible. Sediment volumes are slightly lower for flocs produced by PACl than by alum, but the value is proportional to the dosage in all cases.

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11

Wilén, B. M., B. Jin e P. Lant. "Relationship between flocculation of activated sludge and composition of extracellular polymeric substances". Water Science and Technology 47, n. 12 (1 giugno 2003): 95–103. http://dx.doi.org/10.2166/wst.2003.0633.

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Activated sludge flocs are a flocculated mass of microorganisms, extracellular polymeric substances (EPS) and adsorbed organic and inorganic material. The structure of the flocs is very heterogeneous and flocs with very different properties and morphologies may occur, depending on the conditions in the activated sludge treatment plant and wastewater composition. Present thinking suggests that cations, such as calcium, create cationic bridges with EPS excreted by the bacteria and thereby hold the various floc constituents together. However, due to the complex and heterogeneous nature of activated sludge, the mechanisms have neither been thoroughly investigated nor successfully quantified. A better understanding and description of the biological flocculation process is necessary in order to establish more efficient operational strategies. The main aim of this study was to get a comprehensive and unique insight into the floc properties of activated sludge and to assess the relative impact of chemical and physical parameters. A variety of sludges from full scale treatment plants with different settling properties were characterised. The interrelationships between floc parameters such as composition of EPS, surface properties and floc structure, and their effect on the flocculation and separation properties were assessed. The results indicate that the EPS, both in terms of quantity and quality, are very important for the floc properties of the activated sludge. However, presence of filaments may alter the physical properties of the flocs considerably. The EPS showed positive correlations to sludge volume index (SVI) if only sludges with low or moderate numbers of filaments were included. The surface properties were more affected by the composition of the EPS than by the number of filaments. The EPS showed positive correlation to negative surface charge and a negative correlation to relative hydrophobicity and flocculation ability. The negative correlation between flocculation ability and amount of EPS was surprising. The shear sensitivity, measured as degree of erosion of flocs when subjected to shear, was more affected by floc size and number of filaments than amount of EPS.

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12

Liu, Xinliang, Hailiang Yin, Jian Zhao, Ziqi Guo, Zhen Liu e Yizhou Sang. "Understanding the coagulation mechanism and floc properties induced by Fe(VI) and FeCl3: population balance modeling". Water Science and Technology 83, n. 10 (19 aprile 2021): 2377–88. http://dx.doi.org/10.2166/wst.2021.150.

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Abstract Coagulation kinetics and floc properties are of great fundamental and practical importance in the field of water treatment. To investigate the performance of Fe(VI) and Fe(III) salt on particle coagulation, Malvern Mastersizer 2000 was employed to continuously and simultaneously monitor the kaolin floc size and structure change, and population balance modeling was used to investigate the coagulation mechanism. The results show dosage increase had positive effect on collision efficiency and floc strength and negative effect on restructure rate. Low shear rate resulted in higher collision efficiency and stronger floc. Low water temperature had a pronounced detrimental effect on coagulation kinetics. Temperature increase showed the most significant positive effect on collision efficiency, floc strength and restructure rate. The optimum pH zone for the coagulation was found to be between 6 and 8. Further pH increase lowered the collision efficiency and floc strength and increased the restructure rate. FeCl3 resulted in a larger ratio of the mass to volume of kaolin flocs (compactness) than those induced by ferrate.

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de Ridder, D. J., e D. van Halem. "Influence of particle properties on iron flocculation". Water Supply 18, n. 5 (16 novembre 2017): 1617–24. http://dx.doi.org/10.2166/ws.2017.216.

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Abstract In this study, the importance of charge interactions during flocculation of Fe3+ in the presence of particles and anions/cations at various pH values was investigated. SiO2, (s) and ZnO(s) were dosed as particles to promote charge interactions and/or serve as a nucleus to accelerate floc formation. In the pH range 6–9, SiO2, (s) is negatively charged, while ZnO(s) carries a positive charge. Ca2+ and HPO42− were selected to investigate charge interactions in the water phase. A significant delay in floc growth due to charge repulsion between negatively charged iron species was observed at pHini 9. For positively charged species at pHini 6, a delay in floc growth was observed as well, but to a lesser degree. These effects could be neutralized by either dosing (positively charged) ZnO(s) or Ca2+ at pHini 9, or (negatively charged) SiO2, (s) at pHini 6. The addition of phosphate did not hinder floc growth at pHini 6. While phosphate completely inhibited floc growth at pHini 7–9 in the presence of negatively charged SiO2, (s), the presence of positively charged ZnO(s) partly neutralized the detrimental influence of phosphate on floc growth. Similarly, dosing Ca2+ partly neutralized the effect of phosphate.

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Kjellerup, B. V., K. Keiding e P. H. Nielsen. "Monitoring and troubleshooting of non-filamentous settling and dewatering problems in an industrial activated sludge treatment plant". Water Science and Technology 44, n. 2-3 (1 luglio 2001): 155–62. http://dx.doi.org/10.2166/wst.2001.0765.

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A large industrial activated sludge wastewater treatment plant had temporary problems with settling and dewatering of the sludge. Microscopical investigations revealed that the poor settling properties were not due to presence of filamentous bacteria, but poor floc properties. In order to characterise the changes in floc properties that led to settling and dewatering problems and to find reasons for this taking place, a comprehensive monitoring program was conducted during more than one year. The monitoring program included various measurements of floc settleability, floc strength and sludge dewaterability. The monitoring program revealed that a deterioration of the floc strength and the settling properties in the process tanks was closely connected to downstream dewatering problems and poor effluent quality. Particularly severe problems were observed a few weeks after the production at the factory had started after summer closedown. Possible reasons for the changes in floc properties in the process tanks were found by a) analysing change in wastewater composition by evaluating the different production lines in the industrial plant, b) evaluating the operation of the plant, and c) performing short-term laboratory experiments testing factors that could potentially affect floc properties (absence of oxygen, presence of sulphide, detergents, etc). Among several measured parameters, the use of floc strength measurements in particular proved useful to monitor the activated sludge floc properties at this industrial plant. The described strategy can be useful in general to find and solve many solid/liquid separation problems in activated sludge wastewater treatment plants.

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Lintern, G., e G. Sills. "Techniques for Automated Measurement of Floc Properties". Journal of Sedimentary Research 76, n. 10 (1 ottobre 2006): 1183–95. http://dx.doi.org/10.2110/jsr.2006.085.

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Larsen, P., P. S. Eriksen, M. A. Lou, T. R. Thomsen, Y. H. Kong, J. L. Nielsen e P. H. Nielsen. "Floc-forming properties of polyphosphate accumulating organisms in activated sludge". Water Science and Technology 54, n. 1 (1 luglio 2006): 257–65. http://dx.doi.org/10.2166/wst.2006.394.

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The physico-chemical characteristics of polyphosphate-accumulating organisms (PAO) involved in enhanced biological phosphorus removal (EBPR) was investigated in order to find a novel method for phosphorus recovery. If the physico-chemical characteristics of PAO are different from those of other main floc components, it may be possible to enrich PAO in bulk water or in the floc material for improved recovery of phosphorus. A combination of shear tests, chemical manipulation, and quantification of PAO by fluorescence in situ hybridization was applied. The microcolony strength of both Rhodocyclus-related PAO and Actinobacteria-related PAO was generally high as no treatment could break up more than 20% of all PAO in microcolonies. In contrast, it was possible to remove 20–40% of the organic matter and other bacterial cells by applying a high pH value or adding EDTA. With that a selective enrichment of PAO in the remaining floc material was possible. The feasibility of applying this selective PAO enrichment in flocs remains to be evaluated in full-scale plants for P-recovery.

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Govoreanu, R., D. Seghers, I. Nopens, B. De Clercq, H. Saveyn, C. Capalozza, P. Van der Meeren, W. Verstraete, E. Top e P. A. Vanrolleghem. "Linking floc structure and settling properties to activated sludge population dynamics in an SBR". Water Science and Technology 47, n. 12 (1 giugno 2003): 9–18. http://dx.doi.org/10.2166/wst.2003.0622.

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Over a period of 227 days properties of activated sludge grown in an aequencing batch reactor (SBR) operated under stable conditions were analyzed. Settling properties (sludge volume index (SVI)) of the activated sludge were compared with on-line measurements of floc size and size distribution obtained by using a laser light scattering technique (Malvern Mastersizer/S, Malvern, UK), and with measurements of microbial community dynamics analyzed by denaturing gradient gel electrophoresis (DGGE) patterns of 16S rRNA genes. In addition, microscopical observations were used to confirm the results. Three distinct stages in the SBR evolution were observed. In the first stage the structural floc properties showed predominant presence of floc-forming bacteria in the activated sludge. A good correlation between floc size, settling properties and microbial community evolution was observed. The second stage showed a good balance between floc-forming and filamentous bacteria, with good settling properties and a highly dynamic community in the SBR. In the third stage, an increase in the filamentous bacteria, which became predominant in the system was observed. Again, a good correlation between settling properties and floc size distribution was obtained and a new dominant species was observed in the DGGE patterns, which can be assumed to be a filamentous organism.

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Wang, Zhenbei, Jun Nan, Meng Yao, Pengfei Ren e Yueming Yang. "Evaluation of kaolin floc characteristics during coagulation process: a case study with a continuous flow device". RSC Advances 6, n. 54 (2016): 48745–52. http://dx.doi.org/10.1039/c6ra06046c.

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Oliveira, Pedro, Marion Alliet, Carole Coufort-Saudejaud e Christine Frances. "New insights in morphological analysis for managing activated sludge systems". Water Science and Technology 77, n. 10 (26 aprile 2018): 2415–25. http://dx.doi.org/10.2166/wst.2018.189.

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Abstract In activated sludge (AS) process, the impact of the operational parameters on process efficiency is assumed to be correlated with the sludge properties. This study provides a better insight into these interactions by subjecting a laboratory-scale AS system to a sequence of operating condition modifications enabling typical situations of a wastewater treatment plant to be represented. Process performance was assessed and AS floc morphology (size, circularity, convexity, solidity and aspect ratio) was quantified by measuring 100,000 flocs per sample with an automated image analysis technique. Introducing 3D distributions, which combine morphological properties, allowed the identification of a filamentous bulking characterized by a floc population shift towards larger sizes and lower solidity and circularity values. Moreover, a washout phenomenon was characterized by smaller AS flocs and an increase in their solidity. Recycle ratio increase and COD:N ratio decrease both promoted a slight reduction of floc sizes and a constant evolution of circularity and convexity values. The analysis of the volume-based 3D distributions turned out to be a smart tool to combine size and shape data, allowing a deeper understanding of the dynamics of floc structure under process disturbances.

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Andreadakis, Andreas D. "Physical and chemical properties of activated sludge floc". Water Research 27, n. 12 (dicembre 1993): 1707–14. http://dx.doi.org/10.1016/0043-1354(93)90107-s.

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Lin, Qintie, Huanlong Peng, Qinlu Lin e Guangcai Yin. "Formation, breakage and re-formation of flocs formed by cationic starch". Water Science and Technology 68, n. 6 (1 settembre 2013): 1352–58. http://dx.doi.org/10.2166/wst.2013.377.

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The efficiency of flocculation can be significantly improved through floc breakage and re-formation under appropriate conditions. To obtain a better understanding of the mechanisms involved and to relate floc properties to separation efficiency, the effects of mixing conditions on the formation, breakage and re-formation of flocs formed by kaolin and cationic starch were investigated through conventional jar test procedure and continuous optical monitoring. It has been found that the breakage of flocs was fully reversible and the polymer flocculant could resist strong shear; even having been sheared for four times, the flocculation index (FI) value would be higher than that of the original flocs. The results indicated flocs formed at neutral and alkaline conditions had better shear resistance than those at acidification conditions, and the mode of floc rupture was large-scale fragmentation.

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Wilén, B. M., M. Onuki, M. Hermansson, D. Lumley e T. Mino. "Influence of flocculation and settling properties of activated sludge in relation to secondary settler performance". Water Science and Technology 54, n. 1 (1 luglio 2006): 147–55. http://dx.doi.org/10.2166/wst.2006.382.

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Floc characteristics were studied at a full scale activated sludge treatment plant with a unique process solution incorporating pre-denitrification with post-nitrification in nitrifying trickling filters. Since greater nitrogen removal is achieved when more secondary settled wastewater is recirculated to the trickling filters, the secondary settlers are always operated close to their maximal capacity. The flocculation and settling properties are therefore crucial and have an effect on the overall plant performance. Since the plant is operated at a short sludge age, these properties change quickly, resulting in variable maximal secondary settler capacity. The dynamics in floc structure and microbial community composition were studied and correlated to the secondary settler performance. Fluorescence in situ hybridisation was used to investigate the microbial community structure and their spatial distribution. The floc structure could to some extent be related to the flocculation and settling properties of the sludge. Even small differences had an influence suggesting that colloidal properties also play a significant role in determining the floc properties. No correlation between microbial community composition and settling properties could be established with the group-specific probes investigated.

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Liu, Jian, Junguo He, Yixing Yuan e Jie Zhang. "Effects of different coagulants on flocculation performance and floc properties in northwest China raw water treatment". Water Supply 15, n. 3 (27 gennaio 2015): 599–605. http://dx.doi.org/10.2166/ws.2015.012.

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The water of northwest China, characterized by low turbidity, low temperature, and micro-pollution, has posed difficult problems for water treatment plants. This study deployed a pilot-scale grid flocculation system to treat melt water from the Qinghai-Tibet Plateau in northwest China. A range of traditional coagulants were used on the low temperature, low turbidity, and micro-polluted melt water, to investigate the effect of coagulant types on flocculation performance and floc properties. Flocculation performance varied, depending upon the coagulant used. Turbidity and organic matter were removed with the greatest efficiency by polyaluminum chloride (PAC), followed by polyaluminum ferric chloride, followed by aluminum sulfate (alum). At a PAC dosage of 25 mg/L, the settled water's residual turbidity was lower than 1 NTU, meeting the Chinese national water-quality standard. Floc fractal dimensions of the three coagulants initially decreased, and then increased as the flocculation process yielded larger particles. This suggested that low turbidity could significantly affect the floc fractal dimension. Studying floc size distribution indicated that floc size in the grid flocculation tank was relatively uniform; the floc size distribution of PAC was the narrowest. The results could be used to inform operations of the Xining water treatment plant.

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Langer, Stefan J., Rudolf Klute e Hermann H. Hahn. "Mechanisms of floc formation in sludge conditioning with polymers". Water Science and Technology 30, n. 8 (1 ottobre 1994): 129–38. http://dx.doi.org/10.2166/wst.1994.0396.

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In flocculation of dilute suspensions a period of slow mixing is necessary to increase the probability of particle collisions that are necessary for flocculation to occur. When flocculating sludges, the collision frequency is so high that flocs are formed immediately after rapid mixing. However, controlled mixing of the flocculated sludge for some time period does improve dewaterability. The mechanisms that are involved have been studied in detail and the subject of this paper. The results show that after rapid mixing and initial floc formation there might still be polymer in solution, depending on polymer dose. Prolonged mixing results in breakage of large aggregates and in particle/floc surfaces that are not yet covered with polymers. Subsequently the excess polymer adsorbs onto these surfaces. From changes in sludge rheology one can see that within a period of about one half to one minute the bulk properties change dramatically. After the initial floc formation the suspension is in a state characterized by a three-dimensional network structure with strongly interacting, voluminous flocs. After the mixing period there are more discrete and less interacting flocs. Especially the properties of the filter cake from pressure filtration are then more favorable.

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Jiwani, Ashifa, Nigel J. D. Graham e Martin C. Day. "Activated sludge process control via particle monitoring". Water Science and Technology 36, n. 4 (1 agosto 1997): 269–77. http://dx.doi.org/10.2166/wst.1997.0135.

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The interrelationships between activated sludge plant operation and floc characteristics were examined in order to determine process control mechanisms for the effective treatment of domestic wastewaters and surplus activated sludge. A quantitative indicator of the physiological floc characteristics was developed and termed the morphological index. This may be evaluated by plant operators using a simple assessment form and matching photographic guide of various floc structures. The morphological index and floc size distribution were found to be useful tools for activated sludge process control and monitoring the dewaterability of surplus activated sludge. It was found that floc size, morphology and in turn the dewaterability of surplus activated sludge varied with different operating conditions. Hydraulic retention times (HRTs) of < 10 hours and sludge ages of ≤8 days, resulted in the presence of small diffuse floc structures in the mixed liquor. The effluent quality was poor and the activated sludge had unfavourable filtering and dewatering properties. Switching plant operation to sludge ages in the region of ≥8 days and HRTs of ≥10 hours, was found to improve effluent quality and the dewaterability of surplus activated sludge. Here the flocs were large compact structures with short filaments protruding from the floc body.

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Adachi, Yasuhisa, Azusa Kobayashi e Motoyoshi Kobayashi. "Structure of Colloidal Flocs in relation to the Dynamic Properties of Unstable Suspension". International Journal of Polymer Science 2012 (2012): 1–14. http://dx.doi.org/10.1155/2012/574878.

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Dynamic behaviors of unstable colloidal dispersions are reviewed in terms of floc formation. Geometrical structure of flocs in terms of chemical conditions and formation mechanics is a key to predict macroscopic transportation properties. The rate of sedimentation and rheological properties can be described with the help of fractal dimension (D) that is the function of the number of contacts between clusters (Nc). It is also well known that the application of water soluble polymers and polyelectrolytes, which are usually used as a conditioner or flocculants in colloidal dispersions, critically affects the process of flocculation. The resulted floc structure is also influenced by the application of polymer. In order to reveal the roles of the polymers, the elementary rate process of polymer reaching to colloidal interface and subsequent reconformation process into more stable adsorption state are needed to be analyzed. The properties of permeable flocs and adsorbed polymer (polyelectrolyte) layers formed on the colloidal surfaces remain to be worked out in relation to inhomogeneous porous structure and electrokinetics in the future.

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27

Barbusinski, K., e H. Koscielniak. "Activated sludge floc structure during aerobic digestion". Water Science and Technology 36, n. 11 (1 dicembre 1997): 107–14. http://dx.doi.org/10.2166/wst.1997.0400.

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Additional observations of the physical characteristics have been introduced to current monitoring of aerobic digestion of sludges coming from two wastewater treatment plants. New parameters have included determination of floc size and sludge specific surface. The internal floc structure was also examined with the use of microtome technique for slicing flocs into very thin sections. During aeration, considerable changes in floc dispersion occurred. Analysis of floc size distribution enables observation of regroupment of different sludge fractions and successive increase in frequency occurrence of the finest fractions, which usually hinder dewatering process. The decrease of average floc size has been accompanied by the increase in sludge specific surface. The time needed for “biological stabilization” has not occurred simultaneously with the time when physical parameters have been shaped in the best possible manner for further sludge treatment. The joint analysis of biochemical and physical properties including above mentioned parameters has enabled the assignment of aerobic digestion time more precisely. It has special meaning in pre-designing research as well as during the start-up of the aerobic digestion systems.

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28

Seo, Dongil, Wan Hee Im, Hye Jung Youn e Hak Lae Lee. "The effects of process variables for GCC pre-flocculation on floc and handsheet properties". Nordic Pulp & Paper Research Journal 27, n. 2 (1 maggio 2012): 382–87. http://dx.doi.org/10.3183/npprj-2012-27-02-p382-387.

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Abstract Pre-flocculation is a technique that aggregates filler particles by means of polyelectrolytes. The size of the filler flocs is a critical factor affecting the properties of the paper. Process variables including the concentration of the flocculants, the stirring speed, and the dilution of the suspension change the size of the flocculated fillers. Ground calcium carbonate and cationic polyacrylamide were used to investigate the influence of these variables on flocculation. The median particle size and size distribution were examined and the tensile and optical properties influenced by the floc size and ash levels were evaluated. The addition of high concentration C-PAM increased the median particle size. Stirring speeds in the range of 1000 ~ 3000 rpm were used to simulate various turbulent environments, and it was shown that high stirring speeds drastically decreased the floc size. Diluting and low speed stirring the flocculated GCC suspension was effective in keeping the particle size intact without disruption before sheet forming. Larger GCC flocs in the handsheets resulted in better mechanical properties.

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29

Curran, K. J., P. S. Hill e T. G. Milligan. "Time variation of floc properties in a settling column". Journal of Sea Research 49, n. 1 (febbraio 2003): 1–9. http://dx.doi.org/10.1016/s1385-1101(02)00195-8.

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30

Moudgil, B. M., e T. V. Vasudevan. "Evaluation of floc properties for dewatering fine particle suspensions". Mining, Metallurgy & Exploration 6, n. 3 (agosto 1989): 142–45. http://dx.doi.org/10.1007/bf03402705.

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31

Bura, R., M. Cheung, B. Liao, J. Finlayson, B. C. Lee, I. G. Droppo, G. G. Leppard e S. N. Liss. "Composition of extracellular polymeric substances in the activated sludge floc matrix". Water Science and Technology 37, n. 4-5 (1 febbraio 1998): 325–33. http://dx.doi.org/10.2166/wst.1998.0657.

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The precise role of extracellular polymeric substances (EPS) in relation to the formation and physicochemical properties of microbial floc in wastewater treatment systems is not well known. Studies were undertaken to provide more comprehensive descriptions of EPS and properties of microbial floc. Acidic polysaccharides and DNA were relatively labile components of the EPS when biomass was stored at 4°C or at −20°C, and significant losses of these components were observed within 24 hours. The composition and properties of activated sludge were found to vary between different full-scale treatment systems reflecting the importance of wastewater composition and operation conditions on microbial communities and the response to environmental conditions. The COD:N:P ratio was found to influence hydrophobicity, surface charge and the EPS composition of microbial flocs in well-controlled bench-scale sequencing batch reactors. Phosphorus depleted and P-limited conditions resulted in a decrease in surface charge but increases in acidic polysaccharides which corresponded to a strong carboxyl stretch at 1740 cm−1 when the biomass was analysed by FTIR-spectroscopy. Electron dense particles, identified by energy-dispersive spectroscopy as containing iron, phosphorus and sulfur, were observed in the fibrils of the floc matrix by transmission electron microscopy.

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32

Tsai, CH, e SC Hwang. "Flocculation of sediment from the Tanshui River estuary". Marine and Freshwater Research 46, n. 1 (1995): 383. http://dx.doi.org/10.1071/mf9950383.

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Experiments on the flocculation of fine-grained sediments from the Tanshui River estuary, Taiwan, were carried out. The effects of fluid shear, sediment concentration and salinity on floc growth were investigated. The ranges of these parameters were 12.5 to 400 s-1 for the shear, 50 to 600 mg L-1 for the sediments concentration and 0% to 100% sea water for the salinity. The results showed the following. (1) The time required to reach a steady state ranges from 2 to 44 h and median floc sizes range from 100 to 520 μm. (2) The steady-state median floc size decreases with the increase in sediment concentration. (3) The floc size increases as the shear increases. (4) Increasing the proportion of sea water from 0% to 50% decreases the floc size to one-fourth of that of freshwater flocs, and a further increase in salinity does not decrease floc size significantly. (5) The time required to reach a steady state decreases with the decrease in shear, the increase in sediment concentration and the increase in salinity. (6) The larger the steady-state flocs, the longer they take to form. Comparison of these results with those obtained in similar studies of Lake Erie sediments shows that the flocculation properties of Tanshui sediments are substantially different from those of Lake Erie sediments. Tanshui sediments are much more difficult to aggregate, but once flocs are formed they are larger. The reasons why different types of sediment behave differently should be studied further.

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33

Liu, Meile, Jingfang Lu, Lei Wei, Kang Wang e Jianhai Zhao. "Magnesium hydroxide coagulation performance and floc properties in treating high pH reactive orange wastewater". Water Science and Technology 71, n. 9 (21 febbraio 2015): 1310–16. http://dx.doi.org/10.2166/wst.2015.083.

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Application of magnesium hydroxide as a coagulant for treating high pH reactive orange wastewater was studied. The coagulation performance and magnesium hydroxide-reactive orange floc properties were investigated under different dosages, feeding modes and pH values. Flocculation index (FI) was then discussed with controlled experiments using an intelligent particle dispersion analyzer and optimum coagulant dose of 150 mg/L (magnesium ion) was obtained for pH value 12. The results showed that the optimum magnesium ion dose tended to decrease with the increase of initial pH value. One time addition feeding mode led to relatively large FI value and higher removal efficiency compared with other addition modes. All of the flocs under investigation showed a limited capacity for re-growth when they had been previously broken. Based on the changes of zeta potential and floc properties, charge neutralization and precipitate enmeshment were proposed to be the main coagulation mechanisms.

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34

Liu, J. R., e S. N. Liss. "The impact of reduced phosphorus levels on microbial floc properties during biological treatment of pulp and paper wastewaters". Water Science and Technology 55, n. 6 (1 marzo 2007): 73–79. http://dx.doi.org/10.2166/wst.2007.214.

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The effect of limiting P in activated sludge was investigated in laboratory scale sequencing batch reactors (SBRs) fed effluent from a container board mill. Floc characterization included measurement of hydrophobicity, surface charge, and analysis of extracellular polymeric substances (EPS). Reactor performance was assessed by monitoring COD and inorganic P removal, MLSS, and sludge settleability (SVI and batch settling flux) over a period of eight months. Control reactors (BOD:N:P of 100:5:1) were compared to reactors run under P-limited conditions (100:5:0.3; 100:5:0.1). Reactor performance at lower temperatures (14 °C; control = 26 °C) was also studied to assess the impact of P-limitation. Changes in floc structure and the composition of EPS occurred within 1 to 3 days following a reduction in P levels. There was an insignificant increase in SVI; however, gravitational settling velocity and batch settling flux values for low P floc were consistently higher than for floc generated under control conditions. Lower temperatures (14 °C) resulted in a deterioration in floc settling properties at a BOD:N:P of 100:5:1. This impact on settling was significantly reduced at a BOD:P of 100:0.1. Reducing P concentrations in the wastewater treatment system has the potential to improve sludge settleability and reduce final P discharges.

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35

Jenkins, David. "Towards a Comprehensive Model of Activated Sludge Bulking and Foaming". Water Science and Technology 25, n. 6 (1 marzo 1992): 215–30. http://dx.doi.org/10.2166/wst.1992.0124.

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The physiological properties of filamentous and floc-forming microorganisms found in activated sludge are reviewed. From this review four model microorganisms - two floc formers and two filamentous organisms - are proposed for use in an activated sludge model that predicts activated sludge “quality”.

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36

Shi, Mingming, Yunjie Ruan, Binxin Wu, Zhangying Ye e Songming Zhu. "Performance evaluation of Hydrodynamic Vortex Separator at different hydraulic retention times applied in Recirculating Biofloc Technology system". Transactions of the ASABE 60, n. 5 (2017): 1737–47. http://dx.doi.org/10.13031/trans.12415.

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Abstract. Recirculating biofloc technology (RBFT) has been gradually acknowledged for its positive effect on the control of biofloc concentration using a hydrodynamic vortex separator (HDVS). To operate an RBFT system at maximum performance, the removal efficiency of an HDVS at different hydraulic retention times (HRTs) must be fully predictable. Hence, a numerical study of the fluid flow and particle dynamics was performed to characterize the performance of an HDVS at varying HRTs. First, flow simulation was conducted to determine an economical mesh size at an HRT of 248 s. Then, with respect to the total suspended solids (TSS) in the RBFT system and the physical properties of the flocs, two-way coupling of the dense discrete phase model (DDPM) and discrete element model (DEM) methods was used to predict floc tracking in an HDVS. Additionally, the Reynolds averaged Navier-Stokes (RANS) equations with the Reynolds stress turbulence model (RSM) were solved using the finite volume method based on the semi-implicit method pressure-linked equations (SIMPLE) pressure correction algorithm in the computational domain. Finally, pilot-scale studies were conducted to verify the simulation models. Based on the simulation results, floc management in an RBFT system is briefly discussed. Due to limited research on the numerical simulation and operating conditions of an HDVS in an RBFT system, this article describes an original investigation of the modeling approach. Keywords: Computational fluid dynamics, Dense discrete phase model, Discrete element model, Floc management, Flow field, Removal efficiency, Total suspend solids.

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37

Jenné, R., E. N. Banadda, I. Y. Smets e J. F. Van Impe. "Monitoring activated sludge settling properties using image analysis". Water Science and Technology 50, n. 7 (1 ottobre 2004): 281–85. http://dx.doi.org/10.2166/wst.2004.0471.

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The goal of this study is to develop a monitoring system for activated sludge properties, as this is an essential tool in the battle against filamentous bulking. A fully automatic image analysis procedure for recognising and characterising flocs and filaments in activated sludge images has been optimised and subsequently used to monitor activated sludge properties in a lab-scale installation. The results of two experiments indicate that the image information correlates well with the Sludge Volume Index. It is shown that, at the onset of filamentous bulking, there is an increase in total filament length on the one hand, and a change in floc shape on the other hand.

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38

Droppo, I. G., G. G. Leppard, D. T. Flannigan e S. N. Liss. "The freshwater floc: A functional relationship of water and organic and inorganic floc constituents affecting suspended sediment properties". Water, Air, & Soil Pollution 99, n. 1-4 (ottobre 1997): 43–53. http://dx.doi.org/10.1007/bf02406843.

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39

Murthy, Sudhir N., e John T. Novak. "Factors Affecting Floc Properties During Aerobic Digestion: Implications for Dewatering". Water Environment Research 71, n. 2 (marzo 1999): 197–202. http://dx.doi.org/10.2175/106143098x121879.

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40

Clémençon, Isabelle, e Alessandra Gerli. "The effect of flocculant/microparticles retention programs on floc properties". Nordic Pulp & Paper Research Journal 14, n. 1 (1 gennaio 1999): 23–29. http://dx.doi.org/10.3183/npprj-1999-14-01-p023-029.

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41

Negro, C., E. Fuente, A. Blanco e J. Tijero. "Flocculation mechanism induced by phenolic resin/PEO and floc properties". AIChE Journal 51, n. 3 (2005): 1022–31. http://dx.doi.org/10.1002/aic.10352.

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42

Clauss, F., D. Helaine, C. Balavoine e A. Bidault. "Improving activated sludge floc structure and aggregation for enhanced settling and thickening performances". Water Science and Technology 38, n. 8-9 (1 ottobre 1998): 35–44. http://dx.doi.org/10.2166/wst.1998.0788.

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The effluent quality of a sewage plant using the activated sludge process depends upon the flocculation efficiency. Intensive research work has been devoted to understanding flocculation phenomena and to correct biological disorders. The addition of very fine but dense mineral particles to the aeration tank immediately improves floc formation and increases the weight of the new flocs created. The first consequence is an effective separation between the solid and the liquid phases in the secondary clarifier. In the longer term, the fine particles improve floc structuring and form stable and strong flocs. This has been demonstrated by sending a modified activated sludge through the high shear strength of pumps and hydrocyclones. The mineral of choice is a natural blend of talc and related minerals. These fine talc particles offer a solution to solve floc settleability problems which so frequently arise when biological disorders appear in waste water treatment plants. Despite the addition of insoluble particles the amount of sludge expelled does not increase. The thickening and dewatering properties are improved.

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43

Tauber, J., B. Flesch, V. Parravicini, K. Svardal e J. Krampe. "Influence of road salt thawing peaks on the inflow composition and activated sludge properties in municipal wastewater treatment". Water Science and Technology 84, n. 2 (4 febbraio 2021): 314–22. http://dx.doi.org/10.2166/wst.2021.045.

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Abstract Operational data over 2 years from three large Austrian wastewater treatment plants (WWTPs) with design capacities of 4 million, 950,000 and 110,000 population equivalent (PE) were examined. Salt peaks, due to thawing road salt were detected and quantified by electrical conductivity, temperature and chloride measurement in the inflow of the WWTPs. Daily NaCl inflow loads up to 1,147 t/d and PE-specific loads of 0.26–0.5 kg NaCl/(PE · y) were found. To mimic the plants' behaviour in a controlled environment, NaCl was dosed into the inflow of a laboratory-scale activated sludge plant. The influence of salt peaks on important activated sludge parameters such as sludge volume index, settling velocity and floc size were investigated. Influent and effluent were sampled extensively to calculate removal rates. Respiration measurements were performed to quantify activated sludge activity. Particle size distributions of the activated sludge floc sizes were measured using laser diffraction particle sizing and showed a decrease of the floc size by approximately two-thirds. The floc structure was examined and documented using light microscopy. At salt concentrations below 1 g/L, increased respiration was found for autotrophic biomass, and between 1 and 3 g NaCl/L respiration was inhibited by up to 30%.

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44

Papavasilopoulos, E. N., e D. H. Bache. "Parallel studies on dewatering and conditioning of an alum sludge and an aluminium hydroxide suspension". Water Science and Technology 44, n. 10 (1 novembre 2001): 293–99. http://dx.doi.org/10.2166/wst.2001.0644.

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The paper shows a comparison between properties of an alum sludge gained from the coagulation of a coloured water with those of a suspension of aluminium hydroxide at a concentration equivalent to the coagulant fraction within the sludge. Background information is provided on composition and aspects of the source floc. The comparisons embraced floc size, polymer adsorption, and dewatering parameters including specific resistance to filtration, capillary suction time and the equilibrium moisture content under pressure. In all cases, there were strong similarities in the behaviour of the two suspensions. It is suggested that such features emanate from a common fractal structure within the source floc, whose fractal index (= 1) has been found to be insensitive to the composition of the floc.

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45

Tarpley, Harris, Friedrichs e Sherwood. "Tidal Variation in Cohesive Sediment Distribution and Sensitivity to Flocculation and Bed Consolidation in An Idealized, Partially Mixed Estuary". Journal of Marine Science and Engineering 7, n. 10 (25 settembre 2019): 334. http://dx.doi.org/10.3390/jmse7100334.

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Particle settling velocity and erodibility are key factors that govern the transport of sediment through coastal environments including estuaries. These are difficult to parameterize in models that represent mud, whose properties can change in response to many factors, including tidally varying suspended sediment concentration (SSC) and shear stress. Using the COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) model framework, we implemented bed consolidation, sediment-induced stratification, and flocculation formulations within an idealized two-dimensional domain that represented the longitudinal dimension of a micro-tidal, muddy, partially mixed estuary. Within the Estuarine Turbidity Maximum (ETM), SSC and median floc diameter varied by a factor of four over the tidal cycle. Downstream of the ETM, the median floc size and SSC were several times smaller and showed less tidal variation (~20% or less). The suspended floc distributions only reached an equilibrium size as a function of SSC and shear in the ETM at peak tidal flow. In general, flocculation increased particle size, which reduced SSC by half in the ETM through increased settling velocity. Consolidation also limited SSC by reduced resuspension, which then limited floc growth through reduced SSC by half outside of the ETM. Sediment-induced stratification had negligible effects in the parameter space examined. Efforts to lessen the computation cost of the flocculation routine by reducing the number of size classes proved difficult; floc size distribution and SSC were sensitive to specification of size classes by factors of 60% and 300%, respectively.

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46

Fuente, Elena, Angeles Blanco, Carlos Negro, María A. Pelach, Pere Mutje e Julio Tijero. "Study of Filler Flocculation Mechanisms and Floc Properties Induced by Polyethylenimine". Industrial & Engineering Chemistry Research 44, n. 15 (luglio 2005): 5616–21. http://dx.doi.org/10.1021/ie0503491.

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47

MacDonald, Iain T., e Julia C. Mullarney. "A Novel “FlocDrifter” Platform for Observing Flocculation and Turbulence Processes in a Lagrangian Frame of Reference". Journal of Atmospheric and Oceanic Technology 32, n. 3 (marzo 2015): 547–61. http://dx.doi.org/10.1175/jtech-d-14-00106.1.

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AbstractA novel drifter platform was used to measure the properties of aggregated particles called flocs—a key component of sediment transport in muddy environments. Also concurrently measured were turbulence, suspended sediment concentration (SSC), velocity, and salinity in both Lagrangian and Eulerian frames of reference. In Lagrangian mode the system performed well in a heavily sediment-laden river, providing measurements over a large spatial scale. The platform navigated itself through a complex geometry encompassing many bends and significant depth changes. Observed velocities relative to the drifter and salinities indicated that the drifter motion was almost Lagrangian with minimal slippage between the drifter and the water motion. The small amount of slippage that did occur was sufficient to ensure that the drifter oriented itself into the oncoming flow.High-quality in situ images of flocs were collected using a high-magnification floc camera (FlocCam). An automatic image analysis routine was developed to identify and characterize flocs within each FlocCam image, employing an artificial neural network (ANN) to ensure that only in-focus particles were included in the analyses. The results indicated that the FlocCam system had an upper working SSC limit of around 350–400 mg L−1.The SSC estimates show that the drifters encountered considerable variability as they were advected downstream; however, concentrations predominantly remained under the image processing threshold of 350–400 mg L−1. The system captured the evolution of floc characteristics over short spatial scales (hundreds of meters). The median floc size (d50) was found to be positively correlated with SSC (r2 = 0.5). A comparison between Eulerian and Lagrangian floc histories can then be used to evaluate the role of antecedent conditions within the flocculation process.

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48

Malkoske, Tyler A., Pierre R. Bérubé e Robert C. Andrews. "Coagulation/flocculation prior to low pressure membranes in drinking water treatment: a review". Environmental Science: Water Research & Technology 6, n. 11 (2020): 2993–3023. http://dx.doi.org/10.1039/d0ew00461h.

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49

Wang, Ziyang, Yan Wang, Cong Yu, Yanxia Zhao, Meixia Fan e Baoyu Gao. "The removal of silver nanoparticle by titanium tetrachloride and modified sodium alginate composite coagulants: floc properties, membrane fouling, and floc recycle". Environmental Science and Pollution Research 25, n. 21 (16 maggio 2018): 21058–69. http://dx.doi.org/10.1007/s11356-018-2240-7.

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50

Henderson, R., E. Sharp, P. Jarvis, S. Parsons e B. Jefferson. "Identifying the linkage between particle characteristics and understanding coagulation performance". Water Supply 6, n. 1 (1 gennaio 2006): 31–38. http://dx.doi.org/10.2166/ws.2006.005.

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Abstract (sommario):

The coagulation/flocculation process is important for particle separation in water treatment. However, difficulties arise when coagulation is not optimised for the dominant particle. This paper investigates the surface characteristics and floc properties of three common systems– natural organic matter (NOM), algae and clay – in order to aid understanding of the coagulation/flocculation process. It was demonstrated that charge density and specific surface area are important parameters with respect to coagulant demand for charge neutralisation for all systems. However, extracellular organic matter (EOM) affected the coagulant demand of algae to the extent that it appears that the presence of EOM could dominate the coagulation process. Controlling the zeta potential of the systems prompted improved particle aggregation and hence removal efficiency in all cases. Floc growth profiles revealed that algal flocs required five times the flocculation period to reach a steady-state floc size compared to NOM and clay and on exposure to increased shear were much weaker. Despite similarities between algae and NOM in terms of organic content and coagulant demand, the fact that algae is a dynamic, biological system as opposed to an inert system creates numerous problems for the coagulation/flocculation process.

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