Special Issue

The Trends of the Studies on Hydrospheric Environmental Problems

Review

Characteristics of dyeing wastewater and decrease in total organic halide formation potential by ozonation

Abstract

This paper summarizes both the characteristics of dyeing-wastewater concerning toxicity and the decrease in organic halide formation potential of some typical dyestuffs and intermediates by ozonation. 

Triharomethanes (THMs) are suspected of being carcinogenic. A new law, which emphasizes as important the control of the discharge of precursors to THMs derived from industrial wastewater, was promulgated. Some dyestuffs are reported to have acute and gene toxicities. In addition, effluents from dye works containing dyestuffs, intermediates and auxiliaries, are also known to have high trihalomethane formation potential (THMFP).

Both the fourteen dyestuffs and six intermediates have organic halide formation potential, but the clear relationship between their molecular structures and the degree of total organic halide formation potential (TOXFP) and THMFP is not observed. The variation patterns of TOXFP and THMFP are roughly divided into two groups: (1) compounds showing a uniform decrease with the increase of ozone consumed and (2) other compounds showing a maximum in the initial stage. In spite of the different variation patterns and initial values, the values of TOXFP for most of the dyestuffs (intermediates) decrease to 50.0 (15.0~30.0) μg/mgTOC and that of THMFP to 20.0 (10.0) μg/mgTOC.

Key words: Dyeing wastewater, TOXFP, THMFP, Ozonation

(Language: Japanese)

Technical Review

Treatment and recovery of chlorinated ethylene solvent by activated carbon fixed bed and supercritical carbon dioxide

Abstract

A chlorinated ethylene solvent such as trichloroethylene (TCE) or tetrachloroethylene (PCE) was adsorbed from aqueous solution by activated carbon fixed bed, and the adsorbed chlorinated ethylene solvent was desorbed by use of supercritical carbon dioxide. The supercritical carbon dioxide with the desorbed chlorinated ethylene solvent was decompressed and cooled. Then the desorbed solvent was condensed and recovered.

TCE was confirmed to be well treated by activated carbon fixed bed for the concentration range of 1~100 mg/L, and the adsorbed TCE was desorbed well by supercritical carbon dioxide at 35°C and 100 kg/cm² . Optimal conditions for recovery of TCE were 10 kg/cm² pressure at -30°C. Regarding PCE, optimal conditions for desorption were same as those of TCE. The desorbed PCE could be recovered even above the temperature of -10°C at the pressure of 10kg/cm² . Slight dispersion was observed in condensation process, but carbon dioxide with little despersed chlorinated ethylene solvent could be compressed and reused for the recovery of the same kind of chlorinated ethylene solvent.

Infrared spectra of chlorinated ethylene solvents in supercritical carbon dioxide or recovered solvents were observed. Solvent recovered from activated carbon in aqueous solution contained water. On decompressing the supercritical fluid being passed through a zeolite layer immediately after extraction, solvent having the same infrared spectrum as original solvent spectrum was recovered. So, using the process of "activated carbon adsorption - supercritical carbon dioxide desorption", unlike steam desorption, the recovered solvent does not contain hydrolyzates or waters which lead to problems during recycling.

Key words: treatment and recovery, chlorinated ethylene solvent, activated carbon fixed bed, supercritical carbon dioxide, decompression and cooling

(Language:Japanese)

Review

Analytical Methods using Photochemical Reaction for Pollutants in Water (Review)

Abstract

Analytical methods using photochemical reaction do not need high temperature, high pressure, and hazardous chemical reagents. These advantages will contribute to the downsizing and automation of the analytical instruments. In the present paper, recent development of 1) ultraviolet radiation source, photochemical reactor and reaction mechanism, 2) removal of interference from organic matters by photooxidation in metal determination, 3) photochemical reaction in determination of carbon, nitrogen and phosphorus, 4) postcolumn, on-line photochemical reaction in liquid chromatography, and 5) photochemical reaction for elemental speciation, are critically reviewed. The future prospects of these techniques are also discussed.

Key words: Photochemical Reaction, metal determination, TOC, nitrogen, phosphorus, postcolumn reaction, elemental speciation.

(Language:Japanese)

Original Paper

Continuous Monitoring Technique Based on a Quartz Crystal Microbalance Sensor for Volatile Chloroorganic Compounds.

Abstract

Atmospheric and hydrospheric environments are widely polluted by volatile chloroorganic compounds such as trichloroethylene and tetrachloroethylene. The main emission sources of these compounds are ventilated air and wastewater from semiconductor factories and cleaning factories. However, since no methods are available to monitor the volatile chloroorganic compounds continuously, it is very difficult to estimate the amounts of emission and to take measures for reducing them.

The object of this investigation is to develop a continuous monitoring method based on a quartz crystal microbalance sensor.

The principle of the Quartz Crystal Microbalance (QCM) sensor is based on the frequency change of the quartz oscillator, which is proportional to the mass captured on the quartz crystal. Immobilization of thin film, which has a high affinity for volatile chloroorganic compounds, on the quartz oscillator, enables a sensitive and selective sensing. A series of lipid with various functional groups was examined, and three kinds of lipids of DC-7-12, IC-DC-1-12 and DN-1-12 gave good sensitivity and selectivity to trichloroethylene (TCE) and tetrachloroethylene (PCE). The adsorption and desorption of chloroorganic compounds were very rapid and reversible therefore rapid and continuous monitoring of these volatile chloroorganic compounds became possible. Among the three lipids, the DC-7-12 gave the highest sensitivity for TCE. The effects of covering quantity of DC-7-12 and operating temperature on the sensitivity were examined, and it was found that the best sensitivity was obtained with the covering quantity of 15000 ng and the operating temperature at 5°C, respectively. The QCM optimized as above gave the frequency change of more than 1 Hz per 1 ppm of TCE, and the calibration curve was linear up to 1000 ppm. The response time was less than 5 min. During the continuous operation, the sensitivity gradually decreased but the sensitivity after one month still showed more than 90% of the original sensitivity. Since each sensor coated with a different lipid had different affinity to these three volatile chloroorganic compounds, selective determination may also be possible by comparing the frequency changes of three sensors.

A preliminary experiment showed that the calibration curve for TCE from 25mg/L to 500mg/L was linear. The improvement of sensitivity is now under investigation by using a newly developed quartz oscillator, which operates more stably in water.

Key words: quartz crystal microbalance, lipid, volatile chloroorganic compound, monitoring

(Language:Japanese)