HRP/LiP Catalyzed Removal Of Nonylphenol From Water

In environment, Nonylpheonl (NP) mainly comes from the degradation of non-ionic surfactants called nonylphenol ethoxylates (NPnEO) which are widely used in industrial, institutional, commercial, and household applications. Due to its physical-chemical characteristics, such as low solubility and high hydrophobicity, strong bioaccumulation and extremely low concentrations (ng/L～μg/L) in aquatic environment, NP has become a unique challenge from the perspective of conventional sewage treatment technologies. In addition, NP has confirmed to be a kind of endocrine disrupting chemicals (EDCs). It may interfere with endocrine and reproductive systems of aquatic organisms, mammals and even humans, consequently declining the reproductive capacity, impacting immune system and inducing cancer. Therefore, the problem of NP has caused widespread concern. Currently, a class of heme peroxidase, such as horseradish peroxides (HRP) and lignin peroxides (LiP) have been widely used in pollution control. HRP and LiP have strong oxidizing ability and are capable of catalyzing a wide range of oxidative reactions of persistent organic pollutants, especially those exhibiting strong reduction potentials, such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and aromatic dyes. The paper described below focuses mainly on a systematic investigation of peroxides catalyzed removal of nonylphenol from water.We firstly conducted batch of experiments to study the removal of NP mediated by HRP or LiP and systematically assessed the reaction efficiencies at varying conditions. Then the kinetic parameters of polyethylene glycol (PEG) to HRP and the veratryl alcohol (VA) to LiP were calculated particularly in the reaction systems to compare the reaction behaviors since both of them played a role in mediating enzyme activity respectively. Finally, experiments obtained the change spectrums of the enzymatic removal of NP affected by natural organic matter (NOM) with the three-dimensional fluorescence spectra.The main results obtained in the studies are as follows:(1)The optimal value of pH was investigated in enzymatic removal of NP. NP was removed efficiently by LiP at pH4.6and at pH7.0for HRP. Both a too high and a too low pH value would decrease catalytic efficiency.(2)The data of NP (10μM) removal in reactions at varying H2O2concentrations were displayed. When the reaction stoichometry was among1:1to1:5([NP]:[H2O2]), this range can be saturated for LiP to remove NP efficiently. Moreover, the optimum ratio was1:1, that is, H2O2concentration was10μM. Similarly, the proper reaction stoichometry was among1:3to1:15([NP]:[H2O2]) in HRP reaction system, and the optimum value was1:7.5, that is, H2O2concentration was75μM. The behavior of enzymatic degradation trend was that:the removal efficiency improved with the increasing H2O2concentration during the insufficient H2O2conditions while during excessive H2O2conditions, the rate of removing efficiency was reduced, which was mainly due to that excess H2O2led to enzymatic inactivation.(3) Enzymatic activity regulation experiments showed that:adding1.0mM VA or100mg/L PEG to the enzymatic reaction system could both significantly enhance the removal of NP. At the same time, it could also prolong the survival of enzyme. In our study, the LiP reaction activity increased by65%at the presence of VA, the reaction time extended to90min or so, the enzymatic kinetic parameter ln(kCAT) increased from8.89s-1to9.79s-1; the HRP reaction activity increased by10%at the presence of PEG, extended time was about60min, the parameter ln(kcAT) increased from8.89s-1to9.79s-1.(4) It is well-known that NOM and its main components humic acid (HA) and fulvic acid (FA)(about5mg TOC/L) play an important role in the enzymatic removal of contamination in the environment. Our study found that the efficiency of HRP or LiP catalytic removal NP decreased when the concentration of NOM, FA and HA increased. Moreover, among them, HA had the strongest inhibitory effect while FA had the weakest effect. Further experiments also confirmed that the removal efficiency was also improved after adding100mg/L PEG or1mM VA to the reaction system containing NOM separately.(5)The three-dimensional fluorescence (3D-FLD) scanning picture revealed the result of absorption intensity as follows:FA> NOM> HA. We speculated that the organic structure may contain a large number of carbo nyl and carboxyl, and these functional groups acting as the free radicals may impact HRP/LiP catalyzed removal of NP from water. Another scan results showed that the spectrum of NOM changed during the HRP/LiP enzymatic reaction, which also suggested that the reaction caused some structure changes of NOM.