Water Treatment Plant 1

[hdes82]

I am designing the water treatment plant for our project. My question is, the quality of water is hard. The Ca value is 118 mg/l means CaCO3 value is 295 mg/l, which comes under hard water. The flow is about 80 m3/hr. Now, due to hardness of water is it necessary or advisable to use water softening unit before Reverse Osmosis.
Thanks in advance for your help.

 

[shahyar]

Download RO softwares (free) like ROSA or PUREDESIGN and check if your water is precipitating or not. If your water has low precipitating index, possibly you can fix the problem just by injecting acid upstream of RO, otherwise you need to soften your water.

Hope this help.

 

[hdes82]

Thanks for your reply. I did try ROSA, but still i am not able to figure out about the requirment of softening unit.

 

[cub3bead]

The answer is it depends on the other ionic species, recovery and the cost of scale inhibitors at your site.

Both CaCO3 and CaSO4 scaling are easily inhibited by the scale inhibitors currenty available.

If you intend to operate at 85+% recovery then you had better look at an IX softener.

The easyway is to set up your model in ROSA (i.e. chemistry, flow recovery, etc.) and then check under the third tab, Scaling. If brine is projected to be saturated or supersaturated then you have to decide reduce (usually) the feedwater pH, change the recovery, add the softener or bring in the chemical guys.

Don't forget to look at CaF2, Ca3(PO4)2 and Ba2SO4 scaling.

If you have a clarifier and the operator insists on using a cationinc polymer then the IX softener is a really good idea. It will help trap the polymer slip that will do major harm to the RO membranes.