Hiroyasu Ichikawa

Removal of chlorophenols from wastewater by immobilized horseradish peroxidase

Immobilization of horseradish peroxidase on magnetite and removal of chlorophenols using immobilized enzyme were investigated. Immobilization by physical adsorption on magnetite was much more effective than that by the crosslinking method, and the enzyme was found to be immobilized at 100% of retained activity. In addition, it was discovered that horseradish peroxidase was selectively adsorbed on magnetite, and the immobilization resulted in a 20-fold purification rate for crude enzyme. When immobilized peroxidase was used to treat a solution containing various chlorophenols, p-chlorophenol, 2,4-dichlorophenol, 2,4,5-trichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, and pentachlorophenol, each chlorophenol was almost 100% removed, and also the removal of total organic carbon (TOC) and adsorbable organic halogen (AOX) reached more than 90%, respectively. However, in the case of soluble peroxidase, complete removal of each chlorophenol could not be attained, and in particular, the removal of 2,4,5-trichlorophenol was the lowest, with a removal rate of only 36%. (c) 1996 John Wiley & Sons, Inc.

Treatment of PAHs in contaminated soil by extraction with aqueous DNA followed by biodegradation with a pure culture of Sphingomonas sp

The biodegradation of polycyclic aromatic hydrocarbons (PAHs) in aqueous deoxyribonucleic acid (DNA) solution from contaminated soil washing was investigated. Initial data with a model effluent consisting of anthracene, phenanthrene, pyrene and benzo[a]pyrene that were individually dissolved in 1% aqueous DNA solution confirmed their positive degradation by Sphingomonas sp. at around 10(8)CFU mL(-1) initial cell loading. For anthracene and phenanthrene, complete removal was achieved within 1h treatment. Degradation of pyrene and benzo[a]pyrene took a relatively longer time of a few days and weeks, respectively. DNA-dissolved PAHs were also degraded relatively faster than PAH crystals in aqueous medium to suggest that the binding of the PAHs in the polymer does not pose serious constraint to bacterial uptake. The DNA was stable against the PAH-degrading bacteria. Parallel experiments with actual DNA solutions obtained during pyrene extraction from an artificially spiked soil also showed similar results. Close to 100% pyrene degradation was achieved after 1d treatment. With its chemical stability, the cell-treated DNA was re-used up to four cycles without a considerable decline in extraction performance.

Flavin-sensitized photooxidation of substituted phenols in natural water

Abstract Photooxidation of substituted phenols in the presence of flavins as sensitizers was investigated under aerobic conditions to determine the fate of synthetic chemicals in the environment. Riboflavin was easily decomposed: lumichrome formed after several minutes of illumination with simulated sunlight. In contrast, lumichrome was extremely stable toward sunlight, and was found to be a major flavin component in natural water. From the result of the lumichrome-sensitized photodecomposition of substituted phenols, the order of photolysis rate is p- methoxyphenol > p- chlorophenol > phenol > p- nitrophenol . A decrease in total organic carbon (TOC) from the reaction solutions of all phenols except for p- nitrophenol was observed, and the carbon released was found to mainly originate from phenols. The compound p- chlorophenol has been shown to degrade readily by lumichrome-sensitized photooxidation, but the transformation occurs only by dechlorination. Polychlorophenols were completely dechlorinated in ∼ 1 hr after lumichrome-sensitized photolysis, and the rate increased with chlorine content on the aromatic ring.

Ferrite formation from photo-Fenton treated wastewater.

Photo-Fenton oxidation followed by ferrite formation was applied for the degradation of a representative organic compound, phenol, and the subsequent removal of the Fe ions. At a phenol:Fe(II):H(2)O(2) molar ratio of 1:0.5:15, TOC analysis showed almost complete mineralization of 10.6mM phenol after 2h at a controlled pH of 3. Recalcitrant low molecular weight organic acid by-products particularly oxalic acid were destroyed. A ferrous-rich solution was generated so that alkalinization at pH 10.5 generated a pitch black sludge of lower volume and moisture content than a ferric hydroxide control of the same Fe concentration. The flocs exhibited a strong affinity for a magnet and its X-ray diffraction pattern showed a close similarity to a standard spinel magnetite. With proper monitoring of Fe(II) and dissolved oxygen, the reaction was successfully controlled to generate flocs with more than 30% magnetite content. When photo-Fenton was employed as a pre-treatment step so that residual oxalic acid remained, ferrite formation was not inhibited. The presence of oxalates even allowed ferrites to form in a solution containing Ca(2+) ions, which is well-known to be deterrent to the process.

Water Solubility Enhancement Effects of Some Polychlorinated Organic Pollutants by Dissolved Organic Carbon from a Soil with a Higher Organic Carbon Content

To elucidate the role of a soil humic acid (HA) in the transport of polychlorinated organic pollutants (PCOPs), such as polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and coplanar-polychlorinated biphenyls, their partition coefficients (K doc) into an HA were compared with their adsorption coefficients (K OC) for a soil with a higher organic carbon (OC) content. The soil sample (ando soil) used in the present study was collected in the same location as the HA. The log K doc values were positively correlated with logarithm of octanol-water partition coefficients (log K OW) of the PCOPs, indicating that the partitioning of PCOPs into the HA was mainly due to hydrophobic interactions. However, the correlation between log K doc and log K OC was negative. This can be attributed to the enhanced water solubility of the PCOPs as the result of the dissolved organic matter from the soil. That is, when the more hydrophobic PCOPs with higher log K OW values are partitioned into the HA, then the larger quantities of PCOPs that are partitioned into the HA are able to dissolve in the aqueous phase. These results suggest that, in a soil with a higher OC content, the HA can serve as more effective carrier of PCOPs from the soil to an aquatic environment.

Enhancing the release and plant uptake of PAHs with a water-soluble purine alkaloid.

The effect of a common plant alkaloid, caffeine, on the release and plant uptake of some polycyclic aromatic hydrocarbons (PAHs) in soils was investigated. Cucurbita pepo (ssp. pepo cv. Gold Rush) was grown in PAH-spiked media in the presence and absence of caffeine. Solubility tests initially confirmed the ability of caffeine to dissolve PAHs mixtures of anthracene, phenanthrene, pyrene, benzo[a]pyrene and benzo[ghi]perylene. Extraction experiments also highlighted its potential as a PAH-releasing agent from an aged soil. Phytoextraction from a low organic sand medium (f(OC)=0.056+/-0.03%) indicated a significant enhancement of pyrene uptake with three weeks daily watering with 500mgL(-1) caffeine solution. The average pyrene content of roots was 35.3 and 16.0microgg(-1), in caffeine and non-caffeine set-ups, respectively. In the shoots, the corresponding values were 3.60 and 1.67microgg(-1). Both showed more than twofold increase with caffeine. Caffeine also accumulated mainly in the leaves of the treated samples at 2800mgkg(-1) dry weight. Further tests with a 1-year aged soil (f(OC)=5.2+/-1%) containing a mixture of phenanthrene and pyrene yielded parallel results. However, lower PAH content in these samples were observed due to the stronger PAHs partitioning in aged-soil matrix. After four weeks of caffeine, phenanthrene in shoots and roots increased by one and a half and four times, respectively. The corresponding enhancements for pyrene were two and a half and three and a half times.

Nature of bioavailability of DNA-intercalated polycyclic aromatic hydrocarbons to Sphingomonas sp.

The nature of bioavailability of DNA-intercalated PAHs in aqueous solution was investigated. The degradability of different PAHs including anthracene, phenanthrene and pyrene by Sphingomonas sp. was not inhibited even at a high DNA concentration of 2%. The DNA was stable against the PAH-degrader as indicated by the unchanged electrophoresis gel chromatograms after treatment. This shows that a structural change in the polymer is not necessary for the release of PAHs. Partitioning experiments using phenanthrene as a model PAH illustrated the presence of an initial passive uptake by autoclaved cells. Subsequent intracellular degradation became apparent from parallel data with live cells. Phenanthrene transfer from the DNA was diffusion-controlled and the exit of this molecule from their intercalation sites is favored in lieu of the presence of stronger hydrophobic binding sites in the cell membrane.

Ozonation of Dyestuff Solutions Using a Fine Bubble Generator System

The ozonation of four water-soluble dyestuff solutions using a contactor with three conventional diffusers (CD) and that with a fine bubble generator (CFB) was conducted to investigate the improvement of both reaction extent and cost-effectiveness. The use of CFB increased the amount of ozone consumed by 1.1–1.7 times at 1 h and by 1.1–1.3 times at 2 h, compared to the use of CD. The difference in the decrease in both color and dissolved organic carbon (DOC) with ozonation time between CD and CFB was obvious at the initial stage of ozonation. However, regarding the relationship between the amount of ozone consumed and the decrease in both color and DOC, the superiority of CFB to CD was hardly observed, indicating that the effective amount of free radicals that would cause the decreases in color and DOC was not generated by the decrease in bubble size. The promotion of reaction extent brought about by CFB was lower than the increase in the amount of electric power consumed.