Effects of pre-ozonation in refractory leachate treatment by the biological activated carbon fluidized bed process

The removal efficiency of refractory landfill leachate organics by the biological activated carbon fluidized bed (BACFB) process was compared with and without pre-ozonation. Furthermore, the effects of ozonation upon the characteristics of the refractory leachate such as UV absorbance, dissolved organic carbon (DOC), BOD5, adsorbability, molecular size distribution and the content of humic substances were evaluated. The effectiveness of pre-ozonation in treating a refractory landfill leachate through the BACFB process was confirmed. The steady-state DOC removal was enhanced from 42% to 57% at a hydraulic retention time of 24 h. This improvement was due mainly to the preozonation-enhanced biodegradability of the high-molecular-weight organics that could not be removed by the BACFB process alone. Ozonation of the leachate resulted in an exponential decrease in UV absorbance and a linear decrease in DOC with increasing the contact time. High-molecular-weight leachate organics degraded through ozonation to organic compounds having intermediate and low molecular weights. Humic substances accounted for 37% of the leachate DOC, and 60% of the humic substances were removed within 30 min of the contact time. Ozonation caused a significant decrease in adsorbability on activated carbon of the leachate and produced a substantial amount of non-adsorbable organics. The BACFB treatment of the pre-ozonated leachate enhanced its adsorbability and removed the non-adsorbable fraction.