Pii: S0043-1354(98)00452-7

ÐA protocol was developed to rapidly assess the eciency of chemical washing for the removal of excess biomass from biotrickling ®lters for waste air treatment. Although the experiment was performed on a small scale, conditions were chosen to simulate application in full-scale biotrickling ®lters. From 18 treatments with di€erent combinations and concentrations of chemicals, only washing with 0.4% (w/v) NaOH, 0.26 and 1.31% (w/v) NaClO and 11.3% (w/v) H2O2 resulted in a biomass removal signi®cantly higher than treatment with pure water with wet biomass removal eciencies of 50.2, 49.2, 77.0 and 69.0%, respectively. Biomass removal by H2O2 and NaClO was accompanied by complete loss of activity of unremoved biomass, whereas after treatment with NaOH low residual biological activity was observed. However, treatment with NaOH resulted in generation of relatively large amounts of suspended solids (22.3% of dry biomass removed) and dissolved carbon (65.3% of C-biomass removed). NaClO was found to be the most promising reagent for biomass control in biotrickling ®lters because of its ability to remove large amounts of biomass and its low cost. # 1999 Elsevier Science Ltd. All rights reserved Key wordsÐbiotrickling ®lters, waste air treatment, biomass control, chemical removal