UASB Effluent Becomes High pH Upon Aeration

I have an industrial effluent containing high COD, BOD and VFA. Raw effluent with BOD 25,000 ppm, COD 50,000 ppm, VFA 400 - 500 ppm. After treatment by UASB, the total alkalinity is in the range of 4000 ppm as CaCO3 with pH 7.6 - 7.8 level, BOD = 2250 ppm, COD = 8000 ppm.  Biological aeration is used to further treat the effluent to reduce the BOD to less than 20 ppm (no control on COD for final discharge in this case). The problem that I am facing now is that the pH seems to increase too much upon biological aeration and will increase to pH 9.5 and this makes the aerobic process rather inefficient.  I would appreciate if anyone can share similar experience and advice on how to improve the situation.