Heavy metal wastewater which is released from research, educational and medical facilities of universities often contains organic acids. The aluminum coagulation-sedimentation process is one of the usual methods to remove heavy metals from inorganic wastewater, however it is interfered by the coexistent organic acids.
In order to improve the heavy metal removal efficiency, this paper proposes a method using the precipitation with aluminum hydroxide after a pH-shift from 10 to 7. In this study, zinc wastewater was examined as an example. Zinc ions are soluble at pH 7, but zinc forms an unsoluble hydroxide at pH 10. When the pH shifts from 10 to 7, the zinc hydroxide will be removed by the aluminum hydroxide before it reaches a dissolution equilibrium. When the treatments were applied to wastewater containing oxalic acid, malonic acid, succinic acid or glutaric acid, the oxalic acid interfered the zinc removal to a great extend in the case of conventional method. However, using the pH-shift method, wastewater containing oxalic acid could be effectively treated.

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For the purpose of clarifying the properties of fulvic acid, considered to contribute much to trihalomethane production, the method of determining molecular weight by using gel chromatography or ultra-filtration, for the case of samples coexisting with salts, was studied. And, the molecular weights of the fulvic acids separated from 4 humic acid reagents and Tone River water were compared.
The gel chromatograms of desalted fulvic acid samples showed a broad peak. Second peak appeared when NaCl was added into the samples. The Kd value of the second peak rose and reached the value of 1.0, with increasing NaCl concentration in the samples. The reason of this rise of Kd value was considered to be the “promotion of adsorption or dispersion”, instead of the “negation of ion exclusion effect” by NaCl. The solute separation by ultrafiltration was found to be smaller for the samples with higher NaCl concentration, and larger for the samples with higher pH.
So, for the determination of the molecular weight of fulvic acid by using gel chromatography or ultrafiltration, it is necessary to measure by desalting the samples, or extrapolating the salt concentration to zero.

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The mechanism of phosphate release from lake sediments in aerobic condition was investigated from the view point of solubilization of Fe (III) through formation of complex with dissolved organic matter. If the formation of Fe (III) -hydroxide which adsorbs phosphate was prevented by complexation of Fe (III), the release of phosphate into water will be possible even in aerobic condition.
In this study the complexing capacity of natural waters was measured by the copper (II) solubilization method. The method gave high recovery for strongly complexing ligand such as EDTA and NTA and low recovery for weakly complexing ligand such as glycollic acid and aspartic acid.
The measured complexing capacities of water ranged from 0.54 to 3.15 μM in Lake Teganuma and from 0.58 to 14.16 μM in the inflowing rivers. The seasonal change of the complexing capacity was exactly similar to those of s-Fe and PO₄-P.
The measured concentrations of s-Fe in water were much higher than estimated from the solubility of Fe (III) -hydroxide and almost equal to the levels of complexing capacity of water. It suggests that s-Fe is dissolved through complex formation with organic ligands.

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[in Japanese]

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