Biofiltration of ozonated humic water in expanded clay aggregate filters

Treatment of humic water was studied in a pilot-scale ozonation/biofiltrati on treatment plant. The raw water had TOC and CODMa, concentrations of 3.2- 5.0 and 4.1-6.6 mgO l(-1), respectively, and colour (410 nm) of 30-50 mgPt l(-1). The effect of biofilter loading rate on removal of organic matter an d ozonation by-products was investigated in two upflow biofilters containin g expanded clay aggregate (Filtralite) media. The empty bed contact times r anged from 11 to 54 min. The TOC removals varied from 18 to 37% and the COD Mn removals from 30 to 48% with ozone dosages from 1.0 to 1.7 mgO(3) mgTOC( -1). The ozone dosage seemed to have larger effect on removal efficiency th an the loading rate. Concentrations of aldehydes (sum of formaldehyde, acet aldehyde, glyoxal and methyl glyoxal) were 41-47 mu g l(-1) in ozonated wat er. Formaldehyde and glyoxal were the only aldehydes detected from the biof ilter effluents at concentrations higher than 1 mu g l(-1), but their mean concentrations were below 2.1 mu g l(-1). The ketoacid concentrations (sum of glyoxylic, pyruvic and ketomalonic acids) ranged from 272 to 441 mu g l( -1). Average biofilter effluent concentrations varied from 5.3 (glyoxylic a cid) up to 67 mu g l(-1) (ketomalonic acid) with steady-state reductions ge nerally over 80%. The aldehydes and ketoacids accounted on average For 16% of the biodegraded TOC. The results show that expanded clay aggregate media is a good alternative as biofiltermaterial. (C) 1999 Published by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved.