Microelectrode was used to investigate oxygen consumption mechanism in activated sludge. Oxygen fluxes and distributions of oxygen consumption activity were determined from the microprofiles. The spatial distributions of oxygen and nitrate consumption activity were heterogeneous. Under conditions in which oxygen concentration in the bulk liquid was less than 120μM, oxygen consumption activity was high in the outer zone and anoxic zone developed in the center part of the activated sludge. Oxygen consumption activity of the activated sludge was comparable to that of the domestic wastewater biofilm. Distribution of nitrate consumption activity showed that denitrification occurred in the anoxic zone of the activated sludge. Oxygen consumption activity increased as oxygen concentration in the bulk liquid increased, which resulted in increase in oxygen fluxes of the activated sludge. In contrast, when oxygen concentration in the bulk liquid was more than 120μM, oxygen fluxes were unchanged due to limitation of microbial density. Oxygen fluxes at more than 120μM of oxygen in the bulk liquid were lower than those at about 120μM of oxygen.

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To develop a practical environmental protection technology for purification of lakes, ponds and arm of the sea, an efficient magnetic separation system for phosphate and heavy metal ions removal was studied using ferrimagnetic fine particles (FMFP), which can be prepared from Fe²⁺ and Fe³⁺ ions in the alkali aqueous solution. With the Fe³⁺ ions of 15 mg·l^-1 (without addition of FMFP), the phosphate ion recovery decreased from 80% to 20% with decreasing the magnetic field from H=8T to 0.8T. By addition of the FMFP of 5 mg·l^-1 along with the Fe³⁺ ions of 15 mg·l^-1, above 95% recovery was achieved in a wide range of the magnitude of magnetic field (H=0.8-8T). In case of using cadmium ion instead of the phosphate ion, addition of the FMFP of 5 mg·l^-1 together with the Fe³⁺ ions of 20 mg·l^-1 enhanced recovery of the Cd²⁺ ion. We demonstrated that in the presence of the FMFP all of the heavy metal ions were recovered 80% yields or more. These would come from a high magnetic gradient characteristically generated on the surface of FMFP, which results in the enhancement of the magnetic coagulation of the complex with the phosphate or the heavy metal ions and the Fe³⁺ ions.

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Growth inhibition test using Chlamydomonas reinhardtii were performed to estimate a toxicity to alkylphenols under short-term cultural length. C1-10-Alkylphenols, 4-Butoxyphenol(ButoP), Bis-phenol-A(BPA), Di-2-ethylhexyl phthalate (DEHP) and 17β-Estradiol as a chemical substances were added and tested to determine ErC₅₀ for growth inhibition of Chlamydomonas reinhardtii in this study.
Through the result of growth inhibition test of Chlamydomonas reinhardtii, the difference between 0-24h ErC₅₀ and 0-72h ErC₅₀ were found in dose of 4-t-Octylphenol and 4-Nonylphenol, and sensitivity of short term test for 24 hours was rather higher than that of conventional 0-72h algal inhibition test. In addition, high negative correlationship between log 24h-ErC₅₀ of alkylphenols BPA to Chlamydomonas reinhardtii and their log Pow was recognized in short-term growth inhibition test under the various combination of eleven alkylphenols except for ButoP and DEHP.
It is indicated that toxicity of alkylphenols to growth of Chlamydomonas reinhardtii is sensitively estimated in short-term test within 24 hours.

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Though alkylphenol ethoxylates (APEOs) are hydrophilic, their biologicial degradation by-products, alkylphenols (APs), are hydrophobic and are known to affect the endocrine system. Therefore, it is necessary to decompose the aromatic ring of APs and APEOs before their load to the environment, as the biological decomposition of them is very difficult.
In this study, we focused on decomposition characteristics of nonylphenol ethxylates (NPEs) by ozonation (O₃) and ozone/hydrogen peroxide process (O₃/H₂O₂). Acetate, oxalate, and formate ions were detected as their oxidation by-products. The aromatic ring was easily broken down by O₃ alone, however the higher decomposition ratio of NPEs to acetic acid was achieved by using smaller doses of ozone with hydrogen peroxide. For example, at ozone gas concentration of 1.9mg·l^-1, the ozone dose required to degrade NPEs (10μM) to acetic acid of 154μM (i.e., 88% decomposition) was 70μM O₃ with H₂O₂ dose of 76μM, while 392μM O₃ without H₂O₂ (O₃ alone).
It was confirmed that O₃ and O₃/H₂O₂ processes could be used to increase the biodegradability of recalcitrant; smaller doses of ozone can be sufficient to change the structure of the recalcitrant, making it more amenable to bacteriological breakdown.

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In this study, a new method has been developed for the direct removal of algae from eutrophic water. A pair of electrodes consisted of copper (or aluminum) plate cathode and aluminum plate anode was set in an eutrophic water suspended algae, and then direct current was applied. The applied current and concentration of algae were varied in the range of 10-180 mA and 1.00X10⁸-9.96X10⁸cells·ml^-1, respectively.
As algae have negative charge in water, they migrated to the anode and then adhered on its surface. The adhered algae were easily detached from the anode and removed from the water at high efficiency. The accumulation rate of algae on the surface of anode was increased with increasing applied electric current and initial concentration of algae.

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The water quality of roof runoff was investigated. The runoff characteristics of mutagenicity and polycyclic aromatic hydrocarbons (PAHs) with two to five rings were elucidated. The following results were obtained: (1) The runoff of roof deposits depended on their state and rain conditions. (2) The changes in concentration of particulate PAHs corresponded with those of suspended solids, whereas the concentrations of the soluble PAHs decreased with time because of the decrease in the rainwater concentration and the amount of detentions. (3) When the molecular weight of PAH was higher, the ratio of soluble PAH to total PAH became smaller because of the lower water solubility. (4) The partition to particulate phase was observed to be ten- to a thousand-times larger than that in the equilibrium state. (5) The major components of the particulate PAHs were four- to five-ring PAHs, while those of soluble PAHs were two- to three-ring PAHs. (6) The PAHs concentrations and mutagenicities showed a tendency to change similarly in most cases. This suggested that one of the main causes for mutagenicities was a combined effect of PAHs and their derivatives.

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