Removal of humic acids by the ozonation-biofiltration process

A study on ozonation and biofiltration of model humic acid (HA) solutions was performed. The model solutions of commercial HA (concentration of approx. 8 mg l-1) both oznated and non-ozonated were filtrated through biologically activated carbons (BAC). In the ozonation process an ozone dose of 1.4 mg per mg of total organic carbon (TOC) and a 1-min contact time were applied. Biological activity of the GAC filters were obtained by circulation of river water through the filters over periods of 3 months (WG-12 and AG-5 carbons, designated as WG-3M and AG-3M, respectively) or 23 months (WG-12 carbon designated as WG-23M). Four empty bed contact times in range of 2.3- 23.1 min were applied in the biofiltration experiments. The amount of biomass was measured as an indicator of biological activity of the granular carbon. For this purpose, a phospholipid extraction method was used. During the experiment the WG-23M filter had the highest biomass (in a range of 28-81 nmol PO4 g-1) while biomass on the AG-3M was the lowest (ranging from 6 to 32 nmol PO4 g-1). The effectiveness of the HA solution purification was measured by the following parameters: TOC, UV254 absorbance, chemical oxygen demand and color. The results showed that ozonation improved the extent of the model solution purification. The most efficient in purification of both ozonated and non-ozonated HA solution was the BAC designated as AG-3M, whereas WG-23M was the least efficient in removing HA from water.