calculation of alum dosage for pace to flow at waste water plant.

[stewie38]

i currently work at a waste water pollution control facility.we do approximately dose anywhere from 1300-3300 m3 of raw waste water per day. currently we use from 300-350 liters of liquid alum per day depending on volume of raw. I am wondering what formula would i use to calculate dosage mg/l. we have no way on doing draw downs. We are investigating on getting pace to flow.specific gravity is 1.33. can anybody help?

 

[bimr]

Alum or hydrated aluminum sulphate is widely used precipitating phosphates and aluminum phosphates (AlPO4). The basic reaction is:

Al3+ + HnPO43-n ↔ AlPO4 + nH+

This reaction is deceptively simple and must be considered in light of the many competing reactions and their associated equilibrium constants and the effects of alkalinity, pH, trace elements found in wastewater. The dosage rate required is a function of the phosphorous removal required. The efficiency of coagulation falls as the concentration of phosphorous decreases. In practice, an 80-90% removal rate is achieved at coagulant dosage rates between 50 and 200 mg/l. Dosages are generally established on the basis of bench-scale tests and occasionally by full-scale tests, especially if polymers are used. Aluminium coagulants can adversely affect the microbial population in activated sludge, especially protozoa and rotifers, at dosage rates higher than 150 mg/l. Municipal wastewaters may contain from 5 to 20 mg/l of total phosphorous.

Read more:

http://www.lenntech.com/phosphorous-removal.htm#ixzz2Mo0Woh8l

http://www.ceep-phosphates.org/Files/Document/70/p006-010.pdf

http://www.pca.state.mn.us/index.php/view-document.html?gid=7095

 

[stewie38]

thank you very much for the info. i will do more research on this. Our plant is over 30 years old and are finally upgrading into the 20th century. I appreciate any help on this matter. thanks again.

 

[QualityTime]

I will give you the formula to figure out the dosing in mg/L. The formula is in metric:


WASTEWATER FLOW (MEGALITER/DAY) X DESIRED ALUM DOSE (MG/L)
LITER/DAY ALUM USED (L) = __________________________________________________________

SPECIFY GRAVITY OF ALUM (KG/L) X ALUM CONCENTRATION (%)


1. Liquid alum concentration is a 48.86% solution (check with your supplier)

2. Liquid Alum Specific Gravity @ 60oF 1.33 (check with your supplier)

 

[QualityTime]

Unfortunately the space button gets all mangled up when I posted my last reply and as such the formula I gave to you is all screwed up. I have appended an attachment that will clearly show the formula you are looking for. If you can it is best to prepare a spreadsheet and insert your maximum and minimum flows in a day and your maximum and miminum dosage and you will find out the envelope that your metering pump needs to work to

 

[stewie38]

Thank you for all your help. I figured out the formula on the weekend and is very close to what it should be. I'm glad I found this site and I appreciate all the help I have recieved. Hopefully I can sometime return the favour.