| Summary: | 碩士 === 國立中山大學 === 環境工程研究所 === 90 === Abstract
The purpose of this study was to evaluate the efficiency of biosparging for in situ remediation of groundwater at a site contaminated by petrochemicals. To this end, laboratory-scale (lab-scale for short) and pilot-scale tests were carried out. In the lab-scale study, three possible ways (i.e., by injecting air, by adding hydrogen peroxide, and by adding magnesium peroxide) of increasing the dissolved oxygen content in the groundwater were evaluated in terms of the resulting total bacterial count. Under the conditions used in this work, air injection was found to the most effective one. By injecting compressed air into the mixture of petrochemicals-contaminated soil and groundwater at a flow rate of 175mL/min for five minutes, the total bacterial count of the aerobic bacteria was increased greatly from 102CFU/mL to 107CFU/mL. The concentrations of benzene, toluene, ethyl benzene, and xylenes (BTEX) also were reduced to lower than 0.5μg/L.
Based on the findings obtained from the lab-scale study, air injection was adopted for the enhancement of pilot-scale in situ bioremediation of petrochemicals-contaminated groundwater at a selected site in a petrochemical plant. To evaluate the treatment efficiency of biosparging for the removal of BTEX and naphthalene, in addition to an upstream groundwater well, six one-meter-apart monitoring wells were installed in at the test site the flow direction of groundwater. In the center of the test site, one air injection well and ten soil gas monitoring points also were installed to determining the radius of influence of the air injection well. It was found that an air injection rate of 40L/min was capable of providing sufficient air to all of the monitoring wells of groundwater and increasing the total bacterial count of aerobic bacteria from the order of 102CFU/mL to 106CFU/mL. For a test period of 99 days, the concentrations of all target contaminants in each groundwater monitoring well were decreased markedly. More specifically, the total organic carbon was reduced from 12.7-43.4 mg/L to 3.5-14.9 mg/L; biochemical oxygen demand, from 124-526 mg/L to 43-153 mg/L; benzene; toluene, from 29.88-62.34 mg/L to 11.72-12.82 mg/L ; ethyl benzene, from 0.92-5.30 mg/L to 0.86 mg/L-< 0.5μg/L; xylenes, from 9.31-47.58 mg/L to 4.07 mg/L -< 0.5μg/L; and naphthalene, from15.31-0.92 mg/L to < 0.5 μg/L. Additionally, pH, temperature, and concentrations of various cations determined for the groundwater as well.
During the 99-day test period, the following were found: pH varied in the range of 6.75-7.45; temperature, 30-32℃; Ca2+, 45-65 mg/L; Mg 2+, 16-24 mg/L; Na+, 35-60 mg/L; K+, 8-14 mg/L; and total iron, 2.0-4.0 mg/L.
Thus, under the conditions used in this work, the biosparging technology employed was found to have an overall treatment efficiency of over 60% for BTEX and 100% for naphthalene. To increase the overall treatment efficiency, a prolonged air injection is needed at this test site.
Keywords: biosparging, groundwater, contaminated site, petrochemicals
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