Chemical(photo-activated) coupled biological homogeneous degradation of p-nitro-o-toluene-sulfonic acid in a flow reactor

This study presents the combined photochemical (Fenton) and biological flow reactor degradation of p-nitrotoluene-ortho-sulfonic acid (p-NTS). B-NTS is a compound whose degradation is not possible by waste water bacteria. From this point of view it is considered as a non-biodegradable intermediate found in the manufacture of dyes, surfactants and brighteners. By way of HPLC technique it is shown that the photochemical pretreatment of p-NTS induces dearomatization due to OH radical attack. A concomitant 20-25% decrease in the initial carbon content during the photochemical pretreatment was observed along the abatement of the aromaticity. This study shows that the intermediates produced in the pretreatment stage are biodegradable. After pretreatment a minimum residual H2O2 ( < 0.2 mg l(-1)) was attained. This level of oxidant did not interfere with the subsequent biological degradation. The influence of the reaction parameters such as: input concentration of p-NTS, rate of H2O2 addition, reactor flow rate, TOC reduction rate and BOD5/COD as a function of the time of photochemical pretreatment are reported. At a flow rate of 0.18 l h(-1) (5.5 h residence time) a photochemical degradation efficiency of 75%, a biological degradation efficiency of 52% and an overall degradation efficiency for the coupled process of 88% was observed. The disappearance of p-NTS in the photochemical reactor, the growth and degradation of the benzoquinone like aromatic intermediate followed by the appearance short chain aliphatic compounds are reported as a function of pretreatment time. The increase in BOD/TOC as function of pretreatment time has been correlated to the p-NTS and aliphatic recalcitrants existing in the solution. The biological degradation was observed to be strongly dependent on the flow used and on the pollutant loading of the solution. These were the two main parameters affecting the degradation in the bioreactor. (C) 1997 Elsevier Science S.A.