Water and Wastewater.com Help Forums - Coagulation vs. Flocculation

George YaBB Newbies Offline Posts: 11 Company or Organization: McGill University	Coagulation vs. Flocculation Jun 07^th, 2005, 1:31pm Can anyone tell me the difference between coagulation and flocculation? I would also like to know which chemicals (specific examples) are mostly used as coagulants and flocculants.
Back to top	IP Logged

Tom Keenan - nesa

God Member

Offline

Environmental
Consultant - contact
info@nesa.ie

Posts: 1221

Gender: male

Company or Organization: nesa

Re: Coagulation vs. Flocculation
Reply #1 - Jun 7^th, 2005, 4:31pm

Hi George,
Here are a number of published definitions that may help you:

Coagulation: a process that alters the surface charge on dispersed colloidal particles in a liquid so that they are able to agglomerate; the first stage in floc formation

Coagulation: The destablization and initial aggregation of finely divided suspended solids by the addition of a polyelectrolyte or a biological process.

Coagulation: Clumping of particles in wastewater to settle out impurities, often induced by chemicals such as lime, alum, and iron salts.

Flocculation: the agglomeration of coagulated particles to form a floc which can settle or float; may be assisted by biological, chemical or mechanical means

Flocculation: Gentle stirring or agitation to accelerate the agglomeration of particles to enhance sedimentation or flotation.

Flocculation: Process by which clumps of solids in water or sewage aggregate through biological or chemical action so they can be separated from water or sewage.

Back to top

tomkeenan@nesa.ie
Environmental Consultant
www.nesa.ie

IP Logged

The_Solution

Senior Member

Offline

Water and
Wastewater.com is
the best!

Posts: 325

Gender: male

Company or Organization: Andrew Stewart Ltd

Re: Coagulation vs. Flocculation
Reply #2 - Jun 8^th, 2005, 1:54am

The following is a definition that I previously posted in May.

Coagulation is the destabilisation of particles/solids/colloids in a liquid so that they can agglomerate together to produce a larger particle. Most coagulants that can be added are iron or aluminium salts that react with alkalinity to form metal hydroxides which initiates the coagulation process.

Flocculaton normally follows coagulation and essentially is the 'bridging' of coagulated particles to form larger flocs which can then settle (or float) quicker. There are two types of flocculation:
Orthokinetic - deliberate agitation by a slow speed mixer/impeller to prevent floc break up,

Perikinetic - natural movement of particles in a liquid caused by Brownian motion, therefore uncontrolled flocculation.

Trust this helps!

Back to top

IP Logged

wan YaBB Newbies Offline Water and Wastewater.com is the best! Posts: 12 Company or Organization: Polyplastics Asia Pacific	Re: Coagulation vs. Flocculation Reply #3 - Jun 8^th, 2005, 2:18am normally which one is required more? floculants or coagulants? If I see in my settling tank prior to discharge, there are lots of coagulated particles won't settle down, does this mean I dont add enough floculants?
Back to top	IP Logged

grrun

God Member

Offline

WaterandWastewa
ter.Com is the best!

Posts: 2003

Company or Organization: Freelance Environmental Engine

Re: Coagulation vs. Flocculation
Reply #4 - Jun 8^th, 2005, 2:44am

Wan,

You need to provide more information about the process before the clarifier. Is it a physical-chemical process or a biological treatment process? There are a variety of reasons for poor settling and reasons for poor coagulation or flocculation. In some cases, chemical additions will promote coagulation or flocculation. Quite often, pH and gentle mixing can affect either. Microscopic examination of activated sludge may also yield clues as to the reasons for poor settling.

Anyway, the more information that you provide about the process; the more likely you will receive good advice from the Help Forum members. I would suggest that you start a new topic with more information.

grrun ???

Back to top

IP Logged

sobisch

God Member

Offline

Posts: 1372

Gender: male

Company or Organization: L.U.M. GmbH

Re: Coagulation vs. Flocculation
Reply #5 - Jun 8^th, 2005, 5:10am

Dear George, Dear Wan

flocculation is mostly carried out with polymeric flocculants, in most cases with cationic polyelectrolytes, given that particle surfaces have a net negative surface charge.

Coagulation is a preferred method for water treatment, in wastewater treatment it is mostly used when finely dispersed colloids with lower mass concentration have to be removed. On the other end for sludge dewatering flocculation is preferred.

Poor settling, besides other operational parameters, might be caused by using the wrong flocculant, by under and overdosing as well.

Kind regards
T. Sobisch

Back to top

T. Sobisch
for@appliedcolloidssurfactants.info
http://AppliedColloidsSurfactants.blogspot.com
http://www.AppliedColloidsSurfactants.info
http://www.lum-gmbh.com

IP Logged