suspension and settled along with the sinking iron or aluminium. Once particles have stuck together they are called a floc, and the process of encouraging the formation of flocs is called flocculation. Once the particles in the water are destabilized through the mechanism of sweep flocculation, they are now able to collide with each other and stick together. 78 0 obj <>stream Yet, some aspects involved within floc formation and ... To maximize the sweep flocculation mechanism, as it is recommended for the removal of M. aeruginosa cells by sedimentation [17], Underdosing coagulants will cause problems with floc formation while overdosing coagulants can cause clogging during the filter process. %��}���� ����;�9�|9!���K1�Pw �Q�B��HL� X��dzT�xj} ޿'Ӳ(�t�-j��(|�����S�d .|J`f��s�9����2� ��+ by the charge neutralization and sweep floc formation was higher with PACB than with PAC. Material for this article was largely taken from reference1.Coagulation and flocculation are essential processes in various disciplines. Besides, flocs formed by ALCAT had better sizes than the flocs formed by PAX 18 and PAX XL19H. The sweep flocs can be described as large aggregates of Al(OH) 3 /Fe(OH) 3 that are formed when Al/Fe salt is added to water. Although both are used for similar purposes, they differ in their dosing method - in EC the coagulant is added by electrolytic oxidation of an appropriate anode material, while in CC dissolution of a chemical coagulant is used. %PDF-1.3 %���� The type of coagulation mechanism induced – be it surface adsorption or precipitate formation (“sweep “floc”) – when using metal salts (such as aluminum or iron) is governed by the solubility boundary of the coagulant and therefore is highly dependent on pH, and coagulant dose (Amirtharajah and O'Melia, 1990). Coagulation and flocculation processes are used to facilitate the elimination of suspended solids and colloids by gathering these together to form floc. dosages can provide for more sweep floc formation which can further reduce turbidity. Precipitation of amorphous metal hydroxide is necessary for sweep-floc coagulation. %PDF-1.5 %���� <1.0 NTU) may need to feed higher dosage of both coagulant and base The combined processes of coagulation and 9 flocculation aim to increase particle size for increased removal efficiency of very 10 small particles, colloids and micro-pollutants. Under the circumstances, direct filtration is the most logical option. At low concentrations and 0.5 s −1 shear rate, flow induced a formation of floc cylinders between the rotating cylinder and stationary cup surface. Frequently used inorganic coagulants include aluminum sulfate, aluminum chloride, and ferric sulfate. Influence of coagulation mechanisms and floc formation on filterability ... including floc growth speed and size, than the sweep flocculation mechanism. In civil engineering, and in the earth sciences, flocculation is a condition in which clays, polymers or other small charged particles become attached and form a fragile structure, a floc. 7. tm��� n�r����|���zl��:[����z�[-q�˵�X����\N�Y��A��'Z�� �ʊZi� The metal ions hinders the hydrolysis activity when a metal-based coagulant is added to a solution [24, 38, 40]. The higher the coagulant dosage was, the larger but the weaker the floc was. endstream endobj 58 0 obj <> endobj 59 0 obj <> endobj 60 0 obj <>stream FOCUS FLOC / POOL FAST POOL FLOC FOCUS FLOC / POOL FAST POOL FLOC 1. This is referred to as the “sweep-floc” mechanism. 64 0 obj <>/Filter/FlateDecode/ID[<35B4F09D71AD0B4391C840FF2335D05C>]/Index[57 22]/Info 56 0 R/Length 54/Prev 131923/Root 58 0 R/Size 79/Type/XRef/W[1 2 1]>>stream hޤ�_o�0���=n��؉4!Q6�JkW-h�T�R�f It is found that fractal dimension is lower for sweep-floc coagulation where larger and more irregular aggregates are produced. effective floc formation without subsequent floc breakup is critical to create stable flocculation units. Water B) where pH remains fairly constant and sweep floc is the main coagulation mechanism. 74 0 obj << /Linearized 1 /O 76 /H [ 774 364 ] /L 515634 /E 311455 /N 7 /T 514036 >> endobj xref 74 17 0000000016 00000 n 0000000687 00000 n 0000001138 00000 n 0000001292 00000 n 0000001469 00000 n 0000002259 00000 n 0000002298 00000 n 0000002753 00000 n 0000004470 00000 n 0000005259 00000 n 0000005743 00000 n 0000011706 00000 n 0000017669 00000 n 0000311028 00000 n 0000311167 00000 n 0000000774 00000 n 0000001117 00000 n trailer << /Size 91 /Info 73 0 R /Root 75 0 R /Prev 514026 /ID[<670b2e1a7bfbcb5918ddc0c60bd1f0bf><670b2e1a7bfbcb5918ddc0c60bd1f0bf>] >> startxref 0 %%EOF 75 0 obj << /Type /Catalog /Pages 62 0 R /JT 72 0 R /PageLabels 61 0 R >> endobj 89 0 obj << /S 186 /L 281 /Filter /FlateDecode /Length 90 0 R >> stream Sedimentation, flotation and/or filtration systems are then used to separate the floc (see the section sedimentation, filtration, as well as flocculators – settlin… 0 It is intuitive that the sweep flocs are weak and prone to breakage. This sweep-floc precipitate readily adsorbs organic materials such as oil and grease. "sweep floc" theory. erned by the sweep floc mechanism. Floc formation and breakage 7 Floc strength is directly related to floc structure and is therefore highly dependent 8 upon the floc formation process. In potable water treatment, clarification of water using coagulating agents has been practiced from ancient times. Zone 4 coagulation, also known as sweep floc, was used for these experiments. … 4 ... formation, development, and settlement of floc can be watched just as it would be in the full-scale treatment plant. Accordingly, when Al2O3 concentra-tion was similar in the coagulant, PACB showed higher removal efficiencies of turbidity, CODMn, TP, and PO4-P comparing with PAC, especially in the lower range of coagulant dose. Although slightly less alum than ferric chloride was needed to reach an . 2. This allows the organic molecules to contribute to floc formation and is often The alignment of polyelectrolyte in solution is significantly affected by the ionic strength which causes the floc formation. Clogged filters lead to head loss problems in the filters and increased filter washing. Coagulation and flocculation are an essential part of wastewater treatment in a variety of industries. This article provides an overview of the processes and looks at the latest thinking. Dissolved organic can be removed by adsorption on aluminum precipitation (Benschoten, 1990). Further, sweep flocs are positively charged and the colloids of clay minerals abundantly found in the water are negatively charged. Case A. Flocculation will be useless in this case due to the low number of particles present, unless sweep floc formation is desired (which is not the case). 3��z���&+��d�*P�6j��؞U1�*�6eE~�6��W�:���Ͳ��7+�#�L6u�dz����CV�Su�"[�_}�Z �I��5����L(>��}�P�r�f�'�bCWQ�ZQ$|��zi'���&9w#�4F��A��y Consequently, secondary sedimentation will also be redundant. The coagulant dosage governed the floc size and strength in the sweep floc region. Compared to … �l`�&~������@B���]�4#w��1�Ϩ ` ;�� While effective, this process adds to the overall sludge volume that needs to be removed from the water. Carefully vacuum or sweep up spill and place in suitable containers for reuse or disposal. h�bbd``b`j�@�� H�H ��$�02� )a`$����� � m�� Rapid mixing effects were different, de-pending on raw water characteristics. The solubility of Al(OH) 3 (s) and Fe(OH) 3 (s) is minimal at a particular pH and increases as the pH increases or decreases from that value. The evolution of aggregate size distributions resulting from sweep flocculation has been investigated using laser light scattering technique. Previous studies have mostly focused on … Colloids can be destabilized by sweep flocculation (Enmeshment in a precipitate) If metal salts, e.g., Al 2 (SO 4) 3 , FeCl 3 are added in sufficient quantities to exceed the solubility products of the metal hydroxide, oxide or, sometimes carbonates a “sweep floc” … *If an excess coagulant is added so that the dosed water pH is less than 5.0, then the metal ions will directly neutralize the negatively charged organic compounds and colloids in the raw water. Coagulation and flocculation are an essential part of drinking water treatment as well as wastewater treatment. 57 0 obj <> endobj Electrocoagulation (EC) and chemical coagulation (CC) are employed in water treatment for particle removal. Flocculation is the second stage of the combined process and … The sweep flocs can be described as large aggregates of Al(OH)3/Fe(OH)3 that are formed when Al/Fe salt is added to water. A low shear rate resulted in heterogeneous floc structure, which was also detected by an increase in the ratio of the viscous component to elastic component in the rheological measurement. By measuring the (volume) distributions of floc size, it is possible to distinguish clearly among floc formation, growth and breakage. December 5, 2011 SUBJECT:Finalization of Guidance on Incorporation of Water Treatment Effects on Pesticide Removal and Transformations in Drinking Water Exposure Assessments FROM:/s/ Donald Brady, Director, Environmental Fate and Effects Division (7507P), Office of Pesticide Programs TO:Environmental Fate and Effects Division (7507P), Office of Pesticide Programs Through this memorandum I am announcing a limited update and revision of the existing guidance entitled "The Inco… "\�Q��&baVg�:/���TyV�53��Z3������T�| �e�� The floc formation growth indicated that PACl coagulation occurred not only by charge neutralization but also by a form of sweep flocculation. Water treatment plants operating under an optimization program that emphasizes sedimentation turbidity and establishes exceedingly low limits (e.g. The process is basically a combination of destabilisation (charge neutralisation) and transport (physical entrainment) (Amirtharajah, 1990). From the numerous reviews of the fundamental theory and mechanisms of coagulation, various mechanisms for destabilizing contaminants using chemical coagulants have been identified. As early as 2000 BC the Egyptians used alm… This is known as ‘sweep-floc’ coagulation (Packham, 1965). I'�0���r2��U�)H���㱶��K�i ��f��*_=4�(�䃲K#��٪���3_\���#! For this sweep floc. referred to as sweep-floc coagulation. This theory simply postulates that the coagulant(s) added form a precipitate (a solubility product is exceeded) which settles by gravity in a reasonable time. %%EOF Conventional drinking water treatment processes: flocculation Flocculation or mixing Rapid mixing: for mixing the coagulant Detention time is approx. Key Words :Coagulation, Basicity, Phosphorus Sweep floc occurs when coagulant is added past the point of solubility, creating insoluble “flocs” that aggregate. Other particles in the water are swept up into the ... floc formation. The growth of the sweep floc is continuously increased in the slow mixing step up until the floc breakage dominates. The precipitate generally dewaters to low moisture concentration, making this choice of coagulant particularly well-suited to unit operations that generate hazardous sludge, such as DGF and IGF units in oil refineries. endstream endobj startxref Product Name Focus Floc / Pool Fast Pool Floc ... Avoid dust formation. In contrast, like-charges of a polymer chain tend to expand when there is a mutual repulsion. During the process of h�b```f``��,�@�� (����cÐV)��-�&}� ö�|M�q06�144 � ���P � It was found that flocs formed by preformed Al 13, where formation mainly depends on the neutralization mechanism, contributed to flocs with larger fractal dimension than those formed using AlCl 3 (Xu et al., 2011). H�b```"6V��� ce`a�`�d`�V� u�9J�a��#Ʈ�O��:@T�%qT�l4Y�q�P������V�0xV�̢Zܑ̑�(���ऻ�i���L�Ӵ# ���@�0|�� �]0��9��@ ��@���>���b��:��| L�� @_90.n/`����!f��6�#����jUk�4Np`. Experiments on floc development were carried out at the optimised pH values and under conditions in which the turbulence scaling parameter, ε, the rate of energy dissipation per unit mass was held constant at each of the reference temperatures. In dispersed clay slurries , flocculation occurs after mechanical agitation ceases and the dispersed clay platelets spontaneously form flocs because of attractions between negative face charges and positive edge charges. This result indicated that sweep flocs are produced at high formation rate in the rapid mixing step as also noted by Amirtharajah and Mills, 1982. Flocculation, in the field of chemistry, is a process wherein colloids come out ofsuspension in the form of floc or flake; either spontaneously or due to the addition of aclarifying agent. 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