• Geomechanics and Engineering
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• v.19 no.1
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• pp.37-47
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• 2019

The main objective of this study is to evaluate and compare the efficiency of ordinary Portland cement (OPC) in enhancing the unconfined compressive strength of soft soil alone and soft soil mixed with recycled tiles. The recycled tiles have been used to treat soft soil in a previous research by Al-Bared et al. (2019) and the results showed significant improvement, but the improved strength value was for samples treated with low cement content (2%). Hence, OPC is added alone in this research in various proportions and together with the optimum value of recycled tiles in order to investigate the improvement in the strength. The results of the compaction tests of the soft soil treated with recycled tiles and 2, 4, and 6% OPC revealed an increment in the maximum dry density and a decrement in the optimum moisture content. The optimum value of OPC was found to be 6%, at which the strength was the highest for both samples treated with OPC alone and samples treated with OPC and 20% recycled tiles. Under similar curing time, the strength of samples treated with recycled tiles and OPC was higher than the treated soil with the same percentage of OPC alone. The stress-strain curves showed ductile plastic behaviour for the untreated soft clay and brittle behaviour for almost all treated samples with OPC alone and OPC with recycled tiles. The microstructural tests indicated the formation of new cementitious products that were responsible for the improvement of the strength, such as calcium aluminium silicate hydrate. This research promotes recycled tiles as a green stabiliser for soil stabilisation capable of reducing the amount of OPC required for ground improvement. The replacement of OPC with recycled tiles resulted in higher strength compared to the control mix and this achievement may results in reducing both OPC in soil stabilisation and the disposal of recycled tiles into landfills.

• Journal of Korean Society of Water and Wastewater
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• v.36 no.2
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• pp.59-79
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• 2022

Conventional wastewater treatment plants (WWTPs) do not fully remove micropollutants. Enhanced treatment of sewage effluents is being considered or implemented in some countries to minimize the discharge of problematic micropollutants from WWTPs. Representative enhanced sewage treatment technologies for micropollutant removal were reviewed, including their current status of research and development. Advanced oxidation processes (AOPs) such as ozonation and UV/H₂O₂ and adsorption processes using powdered (PAC) and granular activated carbon (GAC) were mainly discussed with focusing on process principles for the micropollutant removal, effect of process operation and water matrix factors, and technical and economic feasibility. Pilot- and full-scale studies have shown that ozonation, PAC, and GAC can achieve significant elimination of various micropollutants at economically feasible costs(0.16-0.29 €/m³). Considering the current status of domestic WWTPs, ozonation and PAC were found to be the most feasible options for the enhanced sewage effluent treatment. Although ozonation and PAC are all mature technologies, a range of technical aspects should be considered for their successful application, such as energy consumption, CO₂ emission, byproduct or waste generation, and ease of system construction/operation/maintenance. More feasibility studies considering domestic wastewater characteristics and WWTP conditions are required to apply ozonation or PAC/GAC adsorption process to enhance sewage effluent treatment in Korea.

• Journal of Environmental Health Sciences
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• v.28 no.1
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• pp.51-65
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• 2002

This study was carried out to apply some basic physical and chemical treatment options including Fenton's oxidation, and to evaluate the performances and the characteristics of organic and nitrogen removal using lab-scale biological treatment system such as complete-mixing activated sludge and sequencing batch reactor(SBR) processes for the treatment of leachate from a municipal waste landfill in Gyeongnam province. The results were as follows: Chemical coagulation experiments using aluminium sulfate, ferrous sulfate and ferric chloride resulted in leachate CO $D_{Cr}$ removal of 32%, 23% and 21 % with optimum reaction dose ranges of 10,000～15,000 mg/$\ell$, 1,000 mg/$\ell$ and 500～2,000 mg/$\ell$, respectively. Fenton's oxidation required the optimum conditions including pH 3.5, 6 hours of reaction time, and hydrogen peroxide and ferrous sulfate concentrations of 2,000 ～ 3,000 mg/$\ell$ each with 1:1 weight ratio to remove more than 50% of COD in the leachate containing CO $D_{Cr}$ between 2,000 ～ 3,000 mg/$\ell$. Air-stripping achieved to remove more than 97% of N $H_3$-N in the leachate in spite of requiring high cost of chemicals and extensive stripping time, and, however, zeolite treatment removing 94% of N $H_3$-N showed high selectivity to N $H^{+}$ ion and much faster removal rate than air-stripping. The result from lab-scale experiment using a complete-mixing activated sludge process showed that biological treatability tended to increase more or less as HRT increased or F/M ratio decreased, and, however, COD removal efficiency was very poor by showing only 36% at HRT of 29 days. While COD removal was achieved more during Fenton's oxidation as compared to alum treatment for the landfill leachate, the ratio of BOD/COD after Fenton's oxidation considerably increased, and the consecutive activated sludge process significantly reduced organic strength to remove 50% of CO $D_{Cr}$ and 95% of BO $D_{5}$ . The SBR process was generally more capable of removing organics and nitrogen in the leachate than complete-mixing activated sludge process to achieve 74% removal of influent CO $D_{Cr}$ , 98% of BO $D_{5}$ and especially 99% of N $H_3$-N. However, organic removal rates of the SBR processes pre-treated with air-stripping and with zeolite were not much different with those without pre-treatment, and the SBR process treated with powdered activated carbon showed a little higher rate of CO $D_{Cr}$ removal than the process without any treatment. In conclusion, the biological treatment process using SBR proved to be the most applicable for the treatment of organic contents and nitrogen simultaneously and effectively in the landfill leachate.e.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.3
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• pp.179-185
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• 2009

In this research, the removal capacity of Cr(VI) by the reused powdered wastes (RPW) containing aluminium oxides was studied. As a pre-treatment process for the preparation of calcined wastes, calcination was conducted at $550^{\circ}C$ to remove organic fraction in the raw wastes. In order to study the adsorption trend of Cr(VI) ions from aqueous solutions, the pH-edge adsorption, adsorption kinetic and adsorption isotherm were investigated using a batch reactor in the presence of four different background electrolytes($NO_3\;^-,\;CO_3\;^{2-},\;SO_4\;^{2-},\;PO_4\;^{3-}$). Cr(VI) adsorption was greatly reduced in the presence of $SO_4\;^{2-}$ and $PO_4\;^{3-}$ over the entire pH range. Meanwhile the inhibition effect by $NO_3\;^-$ and $CO_3\;^{2-}$ was relatively lower than that by $SO_4\;^{2-}$ and $PO_4\;^{3-}$. Cr(VI) adsorption was maximum around pH 4.5 in the presence of $NO_3\;^-$ and $CO_3\;^{2-}$. As the concentration of background electrolytes increased, Cr(VI) adsorption decreased. This result mightly suggests that adsorption between the surface of RPW and Cr(VI) occurs through outer-sphere complex. Cr(VI) adsorption onto the RPW was well described by second-order kinetics. From the Langmuir isotherm at initial pH 3, the maximum adsorbed amount of Cr(VI) onto the RPW was 11.1, 10, 3.3, 5 mg/g in the presence of $NO_3\;^-,\;CO_3\;^{2-},\;SO_4\;^{2-}$, and $PO_4\;^{3-}$, respectively.

• Economic and Environmental Geology
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• v.53 no.3
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• pp.297-306
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• 2020

The red mud generated from bauxite during the Bayer alumina production process has been regarded as an industrial waste due to the high alkaline property and high content of Na. Despite of its environmental problem, various studies for recovery of the valuable resources from red mud has been also carried out because of high content (25.7 wt.% as Fe₂O₃ in this study) of iron in red mud. In order to recover the iron resource in the red mud, microwave heating experiments were performed with adding of activated carbon and elemental sulfur to the red mud. Through the microwave heating the powdered red mud mixtures converted to porous and vitrified solid aggregates. The vitrified aggregates produced by microwave heating are composed of goethite, zero valent iron (Fe⁰), pyrrhotite and pyrite. And then, the microwave heating samples were dissolved in the aqua regia solution, and Fe precipitates were obtained as a Fe-chlorides by adding of NaCl salt in the aqua regia solution. The Fe recovery rates in the Fe-chloride precipitates showed differences depending on the experimental mixture conditions, and Fe grades of the end products are 49.0 wt.%, 58.0 wt.% and 59.5 wt.% under mixture conditions of red mud, red mud + activated carbon, and red mud + activated carbon + elemental S, respectively. The Fe content of 56.0 wt.% is generally known as the grade value of Fe in a iron ore for iron production, and the Fe grades of microwave heating samples with adding activated carbon and elemental S in this study are higher than the grade value of 56.0 wt.%.

• Korean Journal of Soil Science and Fertilizer
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• v.42 no.6
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• pp.500-512
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• 2009

This study was carried out to evaluate the effect of temperature on soil microbial biomass, enzyme activities, and PLFA content in the volcanic(VAS) and the non-volcanic ash soil(NVAS). The soils were treated with organic materials such as organic fertilizer pelleted(OFPL), organic fertilizer powdered(OFPD), pig manure compost(PMC), and food waste compost(FWC). Two grams of organic materials were well mixed with 30g of dried volcanic and non-volcanic ash soil(< 2 mm) with 50% of soil moisture content. And the soils were incubated at 10, 20, $30^{\circ}C$ in incubator. Soils were analysed on the incubation times as followed; soil pH, total nitrogen, organic matter(at 75, 150, 270 days), microbial biomass C and PLFA (at 75, 270 days), microbial biomass N and soil enzyme(at 150, 270 days). pH values of soils treated with PMC and FWC had no changes on soil type, and incubation temperature. However, the pH was increased with temperature in the soils treated with OFPL. The changes in NVAS was higher than in VAS. Soil microbial biomass C content were high in the condition of high temperature and organic fertilizers treatment in VAS. But the contents were gradually decreased with incubation period in both NVAS and VAS. Soil microbial biomass N was high in NVAS treated with organic fertilizers and in VBS treated with PMC and FWC. PLFA content was higher in NVBS than in VBS at 75 days but showed high in VBS at 270 days. Urease activity of NVBS treated with OFPL showed $10^{\circ}C$ (75.0)> $20^{\circ}C$ (16.3)>$30^{\circ}C$ ($4.6ug\;NH{_4-}N\;g^{-1}\;2h^{-1}$) at 150 days. It were decreased gradually high temperature and time passes. And it showed high at $10^{\circ}C$ in VBS. Glucosidase activity was higher in NVBS than in VBS. Correlation coefficient of between soil microbial biomass C and microbial activity indicators showed that PLFA was high significantly at $r^2=0.91$ in NVBS and ${\beta}-glucosidase$ was $r^2=0.83$ in VBS. Soil microbial activities showed differences in the relative sensitivities of soil type and soil temperature.