Manager wants me to look at using a Gas Plant spent caustic (ph=12.5; %caustic 5-7%) to control a WWTP DAF feed water pH in the range of 7.8-8.5.  I've asked our water Lab to analyze for pH, COD, BOD, Sulfides, O&G, TSS, Ammonia, phenols the feedwater mixed with spent caustic (jar tests of mixtures 70%v/30%; 50%v/50%v; 30%v/70%v). But, don't know if this is the correct path to follow.
Note: Rate =1200-1500gpm; parameters are for Clarifier effluent (permits). Spent caustic is disposed. Any thoughts? PRO's / CON's?

The DAF influent will look like: TOC=183-704 mg/l, COD=466-2002 mg/l, BOD = 270-1060mg/l, TSS=32-238 mg/l, O&G=57-302mg/l, TDS= 6542-1155 mg/l. ph=6.8-9.8 controlled by adding 50% caustic (which Manager wants to save $$ on by using the spent caustci).