Development of a novel oxygen-releasing material and microtox toxicity evaluation for a gasoline-con
The objective of the project was to establish a framework for the integration remediation in a contaminated groundwater. First, the bioassay, Vibrio fischeri light inhibition test, was used to determine the toxicity of petroleum-contaminated groundwater. The highly toxic groundwater was treated with chemical oxidation method. In contrast, biological method was applied for groundwater of moderate-to-low toxicity. The oxygen-releasing type for a biological method and activated persulfate oxidation were selected to remediate a BTEX-contaminated groundwater. For the biological method, novel immobilized beads for oxygen releasing were manufactured by incorporating calcium peroxide (CaO2), with BTEX-degrading bacteria using a biodegradable material composed of polyvinyl alcohol (PVA) and alginate. For the chemical method, two types of adsorbents (blast-furnace slag (BF slag), blast oxygen furance slag (BOF slag)) were used to activate sodium persulfate. Moreover, batch or column tests were conducted to investigate the amounts of beads and concentrations of sodium persulfate and adsorbents on BTEX decomposition for biological and chemical methods, respectively. Both BF and BOF slags show the capability in activating sodium persulfate leading to the biodegradation of BTEX and MTBE. The activation capability was increased with the increase of the amount of slags. To reduce the remediation cost and lessen the Fe (III) precipitation commonly occurred in the groundwater remediation site, BF and BOF slag were predominantly selected as activated agents in replacing Fe (II). Moreover, the MTBE degraded by-products (TBF and TBA) were also effectively degraded under activated conditions by BF and BOF slags. The higher oxygen released rate was observed using PVA/alginate-based hydrogel-encapsulated CaO2 freezing method. Oxygen was also consistently released with the addition of buffering material (citric acid). The oxygen-releasing rates were increased with the decrease of the volumetric ratio of binding material, which is attributed to due to the better oxygen transfer under less amount of binding material condition. DGGE analysis suggested that the microbial community in the PRB system acclimated by BTEX became simplified and approached to certain particular microorganisms. Microbial community structure changes were observed under transient shock organic loading conditions. However, microbial community gradually recovered to its simplified structure when system operated in normal conditions. The SEM photographs show that PVA/alginate beads were suitable for the immobilization of microbial cells. The photograph also indicated that microorganisms could be successfully entrapped inside the pores with homogenous distribution in the PVA/alginate beads. High sensitivity of Vibrio fischeri light inhibition test as a biotoxicity indicator for BTEX detection was observed. The relationship between BTEX concentrations and light inhibition rates was significantly positive. The application of 1% of persufate with 1 and 5 g/L BOF effectively reduced the toxicity of groundwater samples. However, the application of high dose of persulfate (5%) induced the high toxicity. Both immobilized beads-BTEX degrader column and PRB system were proved to effectively degrade the groundwater pollutants, thereby decreasing their biotoxicity.
Oxygen-releasing material, biotoxicity, cell-immobilized beads, activated persulfate oxidation