Polymer addition system- dewatering

[chemEIT]

We are currently involved in a feasibility study
for a hog manure treatment plant utilizing primary and secondary anaerobic digesters along with a dewatering option. The sludge from secondary digester is
82,000 kg/day @ 15% solids. we are planning to use a cationic polymer, 10lb/ ton DS for dewatering. I am trying to figure out the amount of dilution water I will need for diluting the polymer. Could anyone give me the calculations for dilution water???

 

[bimr]

Uou will know what is the dilution of polymer.

For example if the polymer solution after dilution is 0.5% the math is:

82,000 kg/day @ 15% solids = 12,300 kg DS/day = 13.56 US Tons per day

13.56 tons per day X 10 lbs = 135.6 lbs /day polymer.


135.6 lbs/day polymer / 0.005 solution strength = 27,120 lbs/day solution

27,120 lbs/day solution / 8.34 lbs/ gal = 3,251 gal/day polymer

 

[chemEIT]

We have 82,000 kg/day @ 15% solids sludge to be dewatered. According to recommended range of 15 lb/ton, we will need 91 kg/day of active polymer or 365 kg/day of concentrated polymer (assuming 25% active). At 0.5% dilution, we will need around 73,000 kg/day or 73 m3/day of water. This number is near to the amount of incoming sludge !!! It seems crazy to add that much water to a system that you are using to remove water from sludge. Let me know if I am misintrepreting anything. Any help you could provide regarding this is most appreciated

 

[bimr]

Don't know the details of what you are trying to accomplish. You just inquired as to how to calculate the polymer dilution.

In regards to the polymer, the type of polymer mixing equipment required will vary, depending on the selected polymer, viscosity, and solids characteristics. Before injection, polymers are mixed into a dilute solution typically between 0.25 and 0.50 percent by weight. In addition, a metered, potable water supply connected to the mix tank discharge is recommended to further dilute the polymer solution and thoroughly disperse the polymer into the solids.

The reason that polymers are diluted is that they are difficult to mix into the sludge and the polymers are expensive. You get more bang for the buck by diluting the polymers.

Not knowing the details of your operation, the 15% dry solids concentration from your digester appears to be a little on the high side. But, it may be correct. One would expect that a 15-20% dry solids concentration would be what is called a “cake” consistency in the industry.

So you are starting with something that is close to cake consistency in the first place. The question is, how do you plan to mix polymer into it? Most applications of polymers involve adding polymer to a liquid sludge, typically around 4% dry solid solution.

The 10-15 Lbs/ton polymer dosage appears to be on the high side as well.

 

[chemEIT]

we are trying to increase the solids content of sludge from 15% to around 30/40% using a polymer system along with a dewatering equipment. we might use a inline mixer (

http://www.wateronline.com/content/...p?docid=6eb4b766-a1a5-11d3-9a73-00a0c9c83afb)

or a seperate mixing tank for mixing sludge and polymer solution. what is the recommended optimum polymer dosage rate?? i know its difficult to say without the benefit of jar tests, but could you provide a ballpark figure..

 

[bimr]

My guess would be 4-10 Lbs/ton polymer dosage.

 

[chemEIT]

thanks bimr,
I did some calculation using 4 lbs/ton polymer dosage, I got around 24 kg/day active polymer or 97 kg/day concentrated polymer (assuming 25% active content) and 20,000 kg/day or 20 m3/day of dilution water @ 0.5% dilution. I feel that the amount of dilution water is still too high, which we anyways have to remove in the dewatering equipment. This dilution water will also reduce the solids content of sludge considerably which is contradictary to what we desire. Could you please give some inputs on this.

 

[bimr]

Not really sure what you are trying to accomplish.

As previously noted, the 15% ds that you have proposed, sounds like it is high end of what can be expected. Most digesters operate at lower ds concentrations.

manure.unl.edu/adobe/v7n10_01.pdf

You have not said what type of dewatering device that you plan to utilize. One would assume that you are talking about a screw press.

http://www.makingenergy.com/Dairy Waste Handbook.pdf

Polymers are added to dilute waste streams, especially to those containing very small size suspended solids. The polymer will flocculate the solids, agglomerating them to the point where they can be pressed. Not sure if polymer will be beneficial for your application with the high dry solids concentrations that you are proposing.

Talk to Fan separator, they may be able to help you:

http://www.fan-separator.de/