A new approach to quantify the degradation kinetics of linuron with UV, ozonation and UV/O3 processes.

The degradation of linuron, one of phenylurea herbicides, was investigated for its reaction kinetics by different treatment processes including ultraviolet irradiation (UV), ozonation (O3), and UV/O3. The decay rate of linuron by UV/O3 process was found to be around 3.5 times and 2.5 times faster than sole-UV and ozone-alone, respectively. Experimental results also indicate overall rate constants increased exponentially with pH above 9.0 while the increase of rate constants with pH below 9 is insignificant in O3 system. All dominant parameters involved in the three processes were determined in the assistant of proposed linear models in this study. The approach was found useful in predicting the process performances through the quantification of quantum yield (Phi(LNR)) (rate constant for the formation of free radical HOO(.-) from ozone decomposition at high pH), rate constant of linuron with ozone ((k(O3,LNR)), rate constant of linuron with hydroxyl radical (k(OH,LNR)), and alpha (the ratio of the production rate of OH() and the decay rate of ozone in UV/O3 system).