Hydrocarbons removal and microbial community succession in petroleum-contaminated soil under hydrogen peroxide treatment.

Chemical oxidation as a pretreatment step coupled with bioremediation for petroleum-contaminated soil may pose serious impacts on indigenous microorganisms and the available nutrients. Petroleum-contaminated soil were treated by hydrogen peroxide (H2O2) at initial concentrations of 105 mM (HH), 21 mM (HL), and 105 mM in three equal amounts (HT) without adding any external catalyst. The contents of total petroleum hydrocarbons (TPH) and dissolved nutrients (total organic compounds, nitrogen, and phosphate), and the indigenous bacteria community succession (analyzed by high-throughput sequencing of 16S rDNA) were investigated over 50 days. Compared to the control treatment without H2O2 addition, H2O2 treatments for the petroleum-contaminated soil significantly promoted the TPH removal especially in the first 4 days and impacted the contents of dissolved nutrients. Both of chemical oxidation and nutrients contributed to microbial community structure changes in alpha diversity. Although the soil microbial community structure had undergone significant changes after different chemical oxidation pretreatments, Firmicutes, Proteobacteria, Gemmatimonadetes, and Actinobacteria were the main bacterial phyla. Compared with adding H2O2 at one time, H2O2 added in stepwise was beneficial to indigenous bacterial diversity recovery and TPH removal. H2O2 oxidation treatments showed a great influence on the microbial community structures in the start-up stage, while recovery time rather than the oxidation treatments presented greater effects on the composition of the microbial community structure with the incubation time extended. Therefore, adding H2O2 as pretreatment for petroleum-contaminated soil showed little effect on the structure of soil indigenous microbial community from a long-term scale, and was conducive to the continuous removal of TPH by indigenous microorganisms.

Dye mineralization under UV/H2O2 promoted by chloride ion at high concentration and the generation of chlorinated byproducts.

Chloride ion (Cl-) may promote or inhibit the oxidation of specific organic compounds treated by hydroxyl radical based advanced oxidation processes (HR-AOPs) depending on the reactivity of chlorine radicals towards the organics. However, the effects of high contents of Cl- on the removal of total organic compounds (TOC) in high salinity organic wastewater treated by HR-AOPs were unclear. The removal and mineralization of azo dye Orange II (OrgII) by UV/H2O2 process with Cl- at high contents under various pH conditions were investigated. As the pH conditions increased higher than pH 5, TOC removal rates increased slightly possibly related to the increase of O2- production and the reduce of futile decomposition of H2O2 into O2. Cl- at relative high concentration (1000 and 2000 mM) significantly promoted the mineralization of dyes with TOC removal increasing by 10 %-40 % under both acid and alkaline conditions. The proposed mechanism is that the reaction of Cl- with OH would decline the decomposition of H2O2 into O2 by inhibiting the reaction between OH and H2O2, and the generated chlorine species (Cl and Cl2-) could further promote the oxidation of dye molecules into intermediates and be helpful for the subsequent mineralization process. In addition, H2O2 and Cl- can slowly react to give HClO and ClO-, which may partly contribute to the decolorization and mineralization of OrgII. Meanwhile, an appropriate relative proportion between Cl2- and OH depending on Cl- contents and pH conditions is important to enhance the TOC removal. However, the formation of various chlorinated byproducts especially under alkaline condition may increase the risk of environmental pollution accidents. The results demonstrate the promotion of TOC removal by UV/H2O2 under certain high contents of Cl- and provide new insight into the application of HR-AOPs to the pretreatment of high salinity organic wastewater.

[Induction of chilling tolerance and heat shock protein synthesis in rice seedlings by heat shock].

Heat shock applied to germinated rice seeds increased the chilling tolerance of seedlings. Comparison with the control, brief heat shock applied before chilling at 4 degrees C for 2 days and recovery at 25 degrees C for another 2 days decreased the permeability of cellular membranes and increased the content of proline in rice seedlings. Heat shock applied before chilling also increased the activities of superoxide dismutase, catalase, and peroxidase and the content of ascorbate in rice seedlings. In contrast, the lipoxygenase activity and the malondialdehyde content in the heat-shocked rice seedlings were lower than those in the control. Germinated rice embryos synthesized heat shock proteins of Mr 78, 70, 64, 46, 38, 24, 17 and 16 kD during heat shock. The results of Western blot suggested that the binding protein (Bip) of HSP70 play an important role in protecting the rice seedling against chilling damage.