Role of Clays as Adsorbent and Microorganism Growth Supporting Media

抄録

The preliminary laboratory test to assess the ability of various clays sand and other mineral types (i.e. kaolinite bentonite 50% sand-50%bentonite river sand and CaCO3) as adsorbent of heavy oil was conducted. The result showed that bentonite alone was the best adsorbent of heavy oil than others. According to the findings we undertook the further laboratory assay to investigate their role on degradation rate of heavy oil. It was expected that these clays will be able to play a multiuse role not only as adsorbent but also as microorganism growth supporting media in accelerating degradation of heavy oil. In the present study we employed two types of clays that is smectite (bentonite) and kaolinite. In addition to the clays we also employed sand and organic-rich soil as comparison. The laboratory experiment was designed in batch culture. A pack of heavy oil sample collected from a heavy oil contaminated coastal area at Wajima Seashore (Ishikawa Prefecture) in! > Japan was used as the initial inoculum. Approximately 1% (v/v) of heavy oil was used to inoculate 250-ml flasks containing 200 ml of seawater medium supplied in the culture as the sole carbon and energy source. Cultures were inoculated with 300 mg/l of sand organic-rich soil mixture of bentonite and kaolinite (ratio 1:1) bentonite and kaolinite respectively and incubated at the room temperature for 60 days. Clay-uninoculated flask was also incubated as control. Thereafter microorganism growth was monitored by measuring the optical density at 600nm and deletion of heavy oil was detected using FTIR at wavenumber 2500-3500 cm-1. Organic compound removal was detected as COD (mg/l) and observation of microorganism morphology was conducted with using optical and epi-fluorescence microscope with DAPI staining and scanning electron microscope. Additionally measurement of pH dissolved-oxygen (DO) temperature electrode potential versus the standard hydrogen electrode (Eh) and electrical conductivity (EC) was undertaken to investigate the biodegradation process. The composition of minerals was estimated by using XRD analyzer. The results pointed out that the smectite type of clay was the best one to adsorb heavy oil than others and play an important role as microorganism growth supporting media in accelerating degradation of heavy oil. It can be concluded that degradation of heavy oil undergone was combination of two processes that is physical process by clay or other minerals and biological process by hydrocarbon-degrading microorganism.