Dear Ramlan in my experience ...

Dear Ramlan in my experience Boron is not so simple to treat.

Before of all is interesting to identify the complete quality of the  wastewater, and so considering the different available treatment (preciptation, RO, resins, evapoconcentration..) identify the best process scheme of treatment.

If your waste water  is characterized by, TSS, DCO, Metals, and others.. I think

- first step must Be preciptation

normally best condition for B preciptation are around pH 10-11 using Ca(OH)2 and MgCl2 (I found and test that Mg improve a lot the B removal, seems thorugt something like and adsorption on the precipitated - floc)

in this case working on the dosing, contact time and chemical condition (depending on your wastewater composition and B compounds) you can remove about 60 -90% of the initial B.

in the same time you remove a lot of others pollutant that normally are wrong for the next purification step

- after precipitation and clarification I suggest a Sand filtration, and depending on your waste water any other pretreatment to prepare to RO (so AC filtration, UF, or others) any backwash or other downstream msut be sent back to the precipitation stage

- RO  could be  final step (if your focus is to reach 5 ppm could  treated only a stream of it and after blend ).. normally by my experience with RO (there are dedicated membrane) you can reach value lower  than 5 ppm .. and regarding the salt rejection.. it must be recycled  to the precipitation stage ..

if your B limit is lower than 0.5 - 1 ppm I think you need to add a final stage of resins.. also in this case resins regeneration liquid must be sent to precipitation stage or concentrated by evapoconcentration  or sent to external treatment plant 

hope to be helpfull

best regards

ciao