A backwash cycle is initiated when the nitrogen release cycle no longer reestablishes sufficient headloss, filter effluent rate is minimized, or the filter run maximum time is reached. Backwash frequency for the DDBF™ is comparable to that of a conventional filter.
After backwash, reduced denitrification performance may initially occur for several minutes due to biomass loss. Thus, more DDBF™ cells are typically designed than for a conventional filter arrangement in order to produce the required blended effluent nitrogen concentration.
Orthos’ compound loop algorithm of feed-forward and feedback with effluent concentration control delivers required effluent quality with no carbon increase through the DDBF™.
Ortho-Wash™ filter controls may be either split-flow/ constant-level or variable-level. Constant-level operation prevents influent cascade, minimizing DO and its related carbon addition expense, whereas variable-level typically provides longer run times.