What is the Major Difference Between Coagulation and Flocculation in Water Treatment?

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Hi all,

What is one major difference between coagulation and flocculation in water treatment? What are the chemicals used for each process? I have noticed over the years that in water treatment processes, some professionals use coagulation and flocculation interchangeably or even cannot give a simple distinct explanation for both.

Regards,
Justin

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17 Answers

  1. Hell,Coagulation is -ve AND +ve particles attracts. Flocculation means we can large particle by small.The Polymers, aluminum coagulants include aluminum sulfate, aluminum chloride and sodium aluminate. The iron coagulants include ferric sulfate, ferrous sulfate, ferric chloride and ferric chloride sulfate. Other chemicals used as coagulants include hydrated lime and magnesium carbonate.Coagulation is rapid mix,flocculation is gentle mix.

  2. Hi Justin

    There is an amazing number of water industry references that confuse these terms.

    I support the answers below.

    Coagulation processes are those with a primary aim of charge neutralisation of a colloid.  A colloid being a particle whose size and surface charge result in such a viscous drag that it maintains the status of a suspended solid in water, not a settling solid.

    Flocculation is the process of accelerating the settling rate of suspended solids by physically flocculating multiple particles of any charge into a larger structure.  A flocculation process does not necessarily involve charge neutralisation but alot do.  Flocculation is usually achieved by a polymer molecule that has a length considerably longer then the size of the suspunded solids.

    Flocculation can also be used to aid sedimentation and dewatering processes.

  3. Hi Engr.Chinenye Justin Nwaogwugwu., coagulation and flocculation do go hand in hand but there is a significant difference between the two.

     

    Coagulation is ​a water ​treatment ​process in ​which chemicals ​(coagulants) ​are added to ​the water. ​

    It neutralises ​charges and ​forms a ​gelatinous mass ​to trap ​particles, ​forming a large ​mass that ​settles or is ​trapped in the ​filter. ​

    Dissolved and ​suspended ​particles can ​be found in ​most of natural ​waters. These ​suspended ​materials ​mostly come ​from land ​erosion, ​dissolution of ​minerals and ​decay of ​vegetation and ​domestic and ​industrial ​waste ​discharges. ​

    The water ​quality is ​deteriorated ​with their ​presence so ​they have to be ​removed. ​

    Coagulation ​and flocculation ​are relatively ​simple and cost-​effective, ​provided that ​chemicals are ​available and ​dosage is ​adapted to the ​water ​composition. ​

    In colloidal ​suspensions the ​particles would ​settle very ​slowly or not ​at all, since ​they carry ​surface charge. ​Same charges ​repel each ​other. ​Coagulants are ​added in order ​to agglomerate ​the particles.​  ​

    Coagulants can ​be classified ​into: ​

    · ​  ​  ​  ​  ​  inorganic coagulants  (e.g., ​aluminum and ​ferric salts) ​

    · ​  ​  ​  ​  ​  synthetic organic polymers  (e.g., ​polyacryl amide ​derivatives and ​polyethylene ​imine) ​

    · ​  ​  ​  ​  ​  natural coagulants  .

    All of them ​are very ​efficient at ​turbidity ​removal from ​water. ​

    Coagulation ​with Aluminium- ​and Ferric-​based ​coagulants, ​followed by ​disinfection by ​chlorinating is ​one of the most ​used methods of ​water treatment.​

    Water ​pretreatment by ​oxidation might ​be necessary ​when using them.​

    When the ​coagulants are ​added to water ​and stirred for ​a few minutes ​they dissolve.

     

    Coagulation  destabilises ​the charge of ​the particles. ​

    Coagulants ​with charges ​opposite to ​those of the ​suspended ​solids are ​added to the ​water to ​neutralise the ​charges on ​dispersed non-​settable solids ​such as clay ​and organic ​substances. ​

    Once the ​charge is ​neutralised, ​the small-​suspended ​particles stick ​together. ​

    The slightly ​larger ​particles ​formed through ​this process ​are called ​microflocs and ​are invisible ​to the naked ​eye.

    To achieve ​good coagulation ​and formation ​of the ​microflocs, a ​high-energy, ​rapid-mix to ​properly ​disperse the ​coagulant and ​promote ​particle ​collisions is ​needed. ​

    Over-mixing ​does not affect ​coagulation, ​but insufficient ​mixing will ​leave this step ​incomplete. ​Proper contact ​time in the ​rapid-mix ​chamber is ​typically 1 to ​3 minutes. ​

     

    Flocculation  is a process ​in which the ​colloids from a ​suspension form ​flocs of flakes.​

    During ​flocculation, ​the micro-​particles and ​charged ions ​are attracted ​and attached to ​flocs. The ​impurities are ​adsorbed onto ​the coagulated ​flocs. ​

    Flocs can ​further be ​removed by ​ sedimentation , ​but only ​partially and ​for complete ​removal ​filtration may ​be necessary. ​

    Gentle mixing ​stage, ​increases the ​size of ​submicroscopic ​microflocs to ​larger ​suspended ​particles. ​

    With slow ​mixing, the ​microflocs are ​come into ​contact with ​each other. ​Collisions of ​the microfloc ​particles cause ​them to bond to ​produce larger, ​visible flocs. ​The floc size ​continues to ​grow through ​collisions and ​macroflocs are ​formed.  ​

    Separation is ​done (​sedimentation, ​floatation or ​filtration) ​when the floc ​has reached its ​optimum size ​and strength. ​

    Contact time ​for flocculation ​ranges from 15 ​or 20 minutes ​to an hour or ​more. ​

     

    Hope this helps!

  4. Did not read all comments, but I think ALL of you are missing the point: Why engineers are not treating or segregating in speech or in practice both processes?. What are the consequences, the thought process involved and the correct protocols in design?

    2 Comments

    1. Hello. I am still learning using this tool (chat on Water). Several answers here have clarified me, so I thank you for the answers. Watt, Mark, Justin, Ademar,  and Thomas answers have brought me better understanding (I am not water expert, I am starting studying the nexus water-food-energy). I did not undestand Lisas' explanation. Sorry. I really would like to understand more about the protocol issue rised by Watt. Regards.

    2. No, they are answering the question asked. The point you bring up is a valid follow on to the observation made in the query.  Essentially, the interchangeable use of terms simply exposes the "ignorance" of those that do so.  However, as can be seen from the answers there is very little chance of consequences due to poor thought processes or improper design protocols.  Those that actually perform the design know the difference and go through the jar testing and perform the pilot study.

  5. Colloids are generally highly negatively charged. This is surrounded by a Stern layer of positively charged ions. Surrounding the Stern layer is a diffuse layer of positively charged counter ions and negatively charged co-ions. 

    Coagulation is the process whereby the nett negative charge of the colloidal particle is neutralized by a cationic species, whether it be an inorganic cation, such as alum or ferric chloride, or a cationic polyDADMAC or similar. 

    Flocculation is the process whereby neutralised particles are agglomorated, either naturally or by the addition of of a flocculation aid. This is done to increase the mass of the resultant floc to enable settling. 

    Answered on by

  6. Hi Justin:

    Coagulation is the addition and rapid mixing of a coagulant, the resulting destabilization of colloidal and fine suspended solids and initial aggregation of the destabilized particles.

    But, Flocculation is the next process after the Coagulation and is the slow stirring or gentle agitation to aggregate the destabilized particles and form a rapid settling flocs. 

    The second point is that the Coagulation is chemical conditioning of colloids, but Flucculation is physical conditioning of colloids and complete the Coagulation process.

     

  7. Hello,

    I agree with Ademar & Andre. 

    Further information. When the water/wastewater contains slowly settleable particles (e.g. like clay whose settling time could be close to 2hrs or tiny particles like colloids -whose diameter is smaller than 1 micron) or non settleable particles, coagulation & flocculation processes are used by adding chemicals.  

    So during coagulation, the objective is to destabilise ("detach") the particles from the water/wastewater while the flocculation process denotes the process of “floc” formation (i.e. consisting of bridging particles/creating an enmeshment of coagulated particles into "flocs") that will settle better/faster given their size & weight in the sedimentation process.

    Common coagulant chemicals are aluminum sulfate (Alum), ferric chloride, ferric sulfate, ferrous sulfate (copperas), sodium aluminate, polyaluminum chloride (PACI) and polymers. Selection of the most suitable coagulant depends on many things. Jar test would be right way along with into discussion/interaction with chemical providers.

    About flocculant chemicals, there are essentially polymer.

    Regards,

  8. Coagulation is essentially Charge Neutralization (with the help of coagulants/chemicals) and Flocculation is agglomeration of suspensions ( micro solids) in to settelable "FLOC".  by offering opportunity to re-contact. Coagulation preceeds flocculation.    

  9. Hello 

    As long as I know, coagulation relates to a chemical process in which aluminium sulfate is employed in order to remove impurities of the water. Floculation is a subsequent process, it is a mechanical rather than chemical process. Regards.

  11. Ademars is the best explanation. Most contaminants in natural waters are negatively charged - bacteria viruses and sediment. Coagulation occurs when an appropriate amount of a positively charged chemical or material such as aluminium ions (often in the form of alum) or cationic polyelectrolyte or ferric salts are added to neutralise the negatively charged contaminants, this reaction occurs rapidly. Flocculation follows and as said below is the agglomeration of the now neutralised particles. Flocculation may be enhanced by gentle mixing and sometimes the addition of a polyelectrolyte. The objective is to increase the particle size so that it can be filtered directly or be able to settle quickly.

  13. Being in broad agreement with most explanations, in plain English ... Coagulation is the a process that unites unsetteable submicro-particles (ie ions into salts )  ... flocculation is the process that unites submicro-particles to make easier settleable size particles...  Could you have coagulation without flocculation?: Yes... and the opposite?: also yes

  14. This is a GREAT question!

    Flocculation happens when a chemical component, such as a cationic polymer, binds to an anionic ionized (dissolved phase) contaminant such as sediment.

    So, when our cationic biopolymer is dosed into turbid water with soil or sediment suspended in it from stormwater runoff or equal, the cationic biopolymer binds to the negatively charged sediment particle, flocculating it or moving it from dissolved phase to particulate or solid phase.

    Coagulation happens when the flocculated particles agglomerate or "come together" and form even large "clumps" of solid particles.

     

    We have some video footage but are unable to get it uploaded so send us your email please.

    lisa@cleanwatertechnology.us

     

     

  15. Sometimes is it about physics after chemical reaction. The floculant float and you can extra it or dissolve it and the coagulant swimm ti the bottom

    Regards

  16. I totally agree with Ademar. In practice it is difficult to identify the end of coagulation and the start of flocculation and there will probably be some overlap depending in the distribution of mixing energy. Coagulation happens  in the first few seconds after dosing the coagulant (with high mixing intensity with short duration) while some time (order of 10 minutes +- 5 min) is required for the subsequent flocculation step, largely depending on the intensity of flocculation/mixing energy which will be much less than the coagulation mixing intensity. Energy input and duration will depend largely on subsequent treatment step.

  17. Coagulation is a destabilization of particles and it is one of first steps in water treatment. When it happens small particles are formed. Flocculation is the agglomeration of these particles which can be improved by using polymers These are quite simple answers. In theory each process is much more complex. Be sure that each process is different although they are considered the same. Regards.