101 questions about Coagulation.

[rocketballz]

I understand that "alum" liquid 8% implies aluminium sulphate content 8% w/w. If this is correct and a small batch sewage treatment system utilizes 400 mL of alum to a 500 L source of sewage wastewater for initiation of flock, then what is the best way to quantify or describe this in discussion with colleagues. If I want to assess treatment of another source of waste water, say from an electroplating plant or other industrial source using a multi-chemical process of coagulation and flocculation, and choose to use "alum 8%" as an initial coagulant choice, how does one predict the likely dose range requirement for jar testing. Do you just set up an organized trial and go into it blindly, how would you win that $20 bet with a colleague as to the likely requirement. With experience, is there analytic parameters that top end engineers can look at like TSS, or TDS or the like. I do understand that there is a role for looking at streaming conductivity but this is quite expensive.

 

[bimr]

There is an experience factor that is gained from working with various types of water.

 

[QualityTime]

Dosing is expressed as mg/L of alum.

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#ix...

http://www.ceep-phosphates.org/Files/Document/70/p...

http://www.pca.state.mn.us/index.php/view-document...