Activated Sludge

I designed an activated sludge aeration basin. Qmax=3Qavg. if i don't want to use an equalization tank so the basin volume (V) should be design according Qmax. and for calculating HRT, we have HRT=V/Qavg. HRT &SRT calculated from this method is much more from standards (also SRT may negative). I Think SRT must be under 30  for activated sludge. Can anyone help?Qavg= 5000 m3/dayQmax= 14400 m3/dayF/M=0.3 1/day MLSS=3000 ppm BODin=240 BODout=20 ppm -Calculate V: F/M=(Qmax.BODin)/(V.MLVSS)  v= 5485 m3 -Calculate HRT= V/Qavg=1.09 day Calculate SRT using Y=0.4 and kd=0.04 1/day: MLSS=SRT×Y×(BODin-BODout)/(HRT×(1+kd×SRT))SRT=-75 day !!!!!