Biodegradation kinetics of ozonated NOM and aldehydes

The batch recycle attached growth reactor (BRAGR) was found to be a conveni ent technique to determine simultaneously the biodegradable dissolved organ ic carbon (BDOC) concentrations and the biokinetic rate constants for BDOC and aldehyde removal. The rate of biodegradation was first-order with respe ct to the BDOC remaining. A second-order, intrinsic rate constant was obtai ned by dividing the first-order rate constant by the attached biomass conce ntration in the biofilter. The intrinsic rate constant did not increase wit h an increasing ozone-to-DOC ratio and averaged 8.5 x 10(-5) mg/L cells(-1) min(-1). The biokinetic rate constants for aldehydes were first-order with respect to remaining substrate concentration. The second-order, intrinsic rate constants (mg/L cells(-1) min(-1)) for the aldehydes were much larger than those for BDOC, with the order being: methyl glyoxal (5.93 x 10(-4)) > glyoxal (4.42 > x 10(-4)) > formaldehyde (2.23 x 10(-4)) >> BDOC (8.5 x 10 (-5)). Removal of aldehydes in a laboratory-scale, continuous-flow biofilte r packed with anthracite and exhausted granular activated carbon (GAC) was predicted fairly well with rate constants derived from the BRAGR. BDOC remo val was significantly underpredicted on GAC biofilters, possibly because of residual adsorption capacity. An empty bed contact time that achieves good natural organic matter (NOM) removal will also yield very high removal of aldehydes because aldehydes are degraded much faster than NOM, regardless o f the ozonation level. Biokinetic modeling could possibly be improved by ac counting for differences in the biodegradability of NOM fractions and by be tter techniques to measure the concentration and activity of attached bioma ss in calculation of the intrinsic rate constant.