ashtree
Bioengineer
- Nov 28, 2015
- 703
I am undertaking pilot trials on an iron removal process as pre-treatment for an RO plant treating brackwish water from a very deep well.
The water comes out of the ground at about 55C.
One of the options i have been trialling is oxidising the iron with sodium hypochlorite and then dosing with a coagulant to settle the floc prior to cooling the water.
I have had some success and works well at a labscale but i have also had a lot of problems with the carry over of coagulant.
I have trialled both alum and an ACH with mixed results. Typically i have tried dose rates between 10 and 30mg/l.
The water has a pH about 6.7 alkalinity above 1000mg/l and is reasonably clean (1-2ntu) except for turbidity associated with the iron.There is up to 5mg/l of iron.
I had gone in with the assumption that within reason the temperature should not matter that much except that mixing energy would be lower and settling rates higher because of the lower viscosity. Likewise the higher temperature should speed up the general rate of reaction.
It seemed this assumption was not correct as i find even over 2 hours of settling time and a very low rise rate in the clarifier that i still carry over some floc. There is also carry of coagulant which at face value still appears to be in solution but fouls the next process stage(media filter).
Are my assumptions correct?
It has been suggesstted that Ferric Chloride would be more suitable for this application. Is there any opinions on that?
Is it a matter of trialling a couple of different coagulants or is operating at this temperature just difficult?
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
The water comes out of the ground at about 55C.
One of the options i have been trialling is oxidising the iron with sodium hypochlorite and then dosing with a coagulant to settle the floc prior to cooling the water.
I have had some success and works well at a labscale but i have also had a lot of problems with the carry over of coagulant.
I have trialled both alum and an ACH with mixed results. Typically i have tried dose rates between 10 and 30mg/l.
The water has a pH about 6.7 alkalinity above 1000mg/l and is reasonably clean (1-2ntu) except for turbidity associated with the iron.There is up to 5mg/l of iron.
I had gone in with the assumption that within reason the temperature should not matter that much except that mixing energy would be lower and settling rates higher because of the lower viscosity. Likewise the higher temperature should speed up the general rate of reaction.
It seemed this assumption was not correct as i find even over 2 hours of settling time and a very low rise rate in the clarifier that i still carry over some floc. There is also carry of coagulant which at face value still appears to be in solution but fouls the next process stage(media filter).
Are my assumptions correct?
It has been suggesstted that Ferric Chloride would be more suitable for this application. Is there any opinions on that?
Is it a matter of trialling a couple of different coagulants or is operating at this temperature just difficult?
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"