16
Figure A : Air input rate required to obtain a targeted backwash interval for the HPPG series can be
estimated from this graph. Flowrates are given at operating pressure as would be shown on an attached
rotameter.
The optimum frequency of backwash intervals varies with feed loading. Figure B below presents
recommended backwash regimes and associated air flowrates for targeted feed rates. These
recommended intervals should be considered starting points as true “optimums” are defined by
temperature, feed compositions, and recirculation rates. Under light loading conditions (<0.5 lbs
feed/ft
3
beads-day) you will find the HPPG provide excellent water quality across a broad spectrum of
backwash frequencies. Under heavily loadings (>1.5 lbs feed/ft
3
beads-day) the rate of biofilm abrasion
must be balanced with rate of biofilm growth more precisely. Small changes in the backwash interval
can results in dramatic drops in TAN or nitrite.