| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1996: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1995: ¥1,100,000 (Direct Cost: ¥1,100,000)
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| Research Abstract |
Due to the strict drinking water standards for hologenated natural organic compounds and synthetic organic compounds, granular activated carbon (GAC) filters are being employed as a barrier to abate such pollution. Removal of pesticides as well as other synthetic organic chemicals (SOCs) is one of the important treatment objectives of GAC adsorbers. In practice, however, the design and operation of GAC remain complicated because of the coexistence of background organic matter (BOM) and SOCs. The objective of this study is to predict GAC performance and to determine remaining life of GAC filter. The research report consists of 6 chapters.
The chapter 1 deals with a rapid experimental method for evaluating breakthrough pattern from fixed bed adsorbers by way of a high pressure micro-column technique. The design of micro-column was made on a similarity rule based upon nondimentional number derived from formula of adsorption kinetics and equilibrium. An almost identical breakthrough profile
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is obtainable in the experiments between the micro-column and lager column on the similarity rule. A little discrepancy observed was attributed to a difference of adsorption capacity or biodegradation.
The objective of chapter 2 is to determine how adsorbed humic substances affect the adsorption behavior of typical synthetic organic chemicals. From micro column tests, the adsorption effeciency of synthetic organic substances are markedly reduced when humic substances are presented. However the adsorption efficiency of humic substances are not influenced by the presence of synthetic organic chemicals. Batch and column isotherm studies show that preloading carbon with natural humic substances decreases its capacity for a synthetic organic chemicals with increasing the concentration of humic substances. The reduction in carbon capacity for simazine and diazinon is remarkable than tetrachloroethelen and tetrachloride. Preloading activated carbon also reduces adsorption rate.
In chapter 3, adsorption capacities of various types of six organic pesticides on GAC adsorber were studied by micro column technique. Pesticides of lower water solubility has higher adsorption capacity. This tendency is pronounced when humic substances are present as background.
In chapter 4, the removal efficiency of intermittently applied pesticides by a granular activated carbon bed preloaded with BOM was examined using the micro column test. Preloading with BOM decreased the removal efficiency of the pesticides. The more GAC adsoebs humics, removal efficiency of pesticide decreases. The removal efficiency was a function of the amount of BOM adsorbed, but was unrelated to the influent concentration of the pesticide. A modeling approach employing the Ideal Adsorbed Solution Theory (IAST) and a linear-driving force expression for intraparticle surface diffusion adequately simulated these phenomena.
In chapter 5, pilot plant and micro column test studies for 4 commercial GACs were conducted using ultrafiltration treated water of Kiso river and Lake Biwa. Almost identical breakthrough performances for natural organics removal were observed when their particle size and SV were the same. Intermittently spiked simazine during 20 months operation were well removed but hydrophilic pesticide, asulam, showed breakthrough. For micro column test, almost identical breakthrough patterns to pilot plant filter were obtained for natural organics but not for pesticides. Pesticide removal under the coexistence of natural organics for various GAC particle size and SV can be normalized to an standard particle size and SV.
In chapter 6, a procedure to predict the adsorption behavior of the total backgeound organics from a view point of multicomponent composition was presented. The total organics were categorized into a few hypothetical components. The plug flow homogeneous surface diffusion model was used to calculate the breakthrough curve for each component. The competitive effect was accounted for through the adsorption isotherms described by a simplified IAST (Ideal Adsorbed Solution Theory) -Freundlich expression. This procedure was validated for a peat water and biological process effluents of a night soil treatment plant before and after coagulation treatment. Less
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