Efficiency of various water treatment processes in the removal of biodegradable and refractory organic matter

A new drinking water treatment train has been developed in the water treatment plant at Sant Joan Despí (Barcelona). It takes the raw water from the Llobregat river, which supplies water to Barcelona city and surroundings. We studied the efficiency of the different steps in this plant for the removal of biodegradable dissolved organic carbon (BDOC). The processes, at the beginning of the monitoring, were break-point prechlorination, flocculation-sedimentation, filtration through granular active carbon (GAC) and postchlorination. A sand filtration step and an ozonation step, between sand filtration and GAC filtration, were then added. Results show that the combined effect of the processes between raw and sand filtered water caused a significant decrease in dissolved organic carbon (DOC), while it had no effect on BDOC. The ozonation process significantly increased BDOC. Finally, GAC filtration significantly decreased DOC and BDOC.