It is not clear to me what ...

Published by

It is not clear to me what exactly you need. 

At first reading I understand that you are designing that water treatment unit with an RO and you are taking at reject water 80 ppm SiO2, high (?) pH and LSI=4,2.

After that you need to diminuish SiO2 concentration on Reject Water. Why? Will you have SiO2 scaling problems? What 's the SiO2 saturation value? 

I can help you if you send me the full designing results of your RO Unit. 

If you add acid into the feed water, you will have a lower pH at Reject Water and lower LSI, but higher SiO2 saturation. There is always risk in any action you make. 

If you need help send me pm (personal mail).