강경모 Kyung-mo Kang , 형원길 Won-gil Hyung

DOI:10.9786/kswm.2020.37.3.151

Abstract

In this study, certain portions of non-sintered cement mortar were replaced with industrial subsidiary high-calcium fly ash (HCFA) and fly ash (FA) to reduce CO₂ emissions. After fixing the ratio of FA to 30%, 20%, 30%, 40% of HCFA was added to produce mixed cement. We conducted a through-flow test, strength experiment, absorption test, neutralization test, XRD analysis, and SEM scanning to identify the physical characteristics of HCFA and determine its applicability as cement. Our results showed that a higher proportion of HCFA in non-sintered cement mortar resulted in higher W/B and absorption rates and lower strength and neutralization resistance. Our findings confirm that non-sintered cement mortar is applicable in secondary PC product areas where rebars are not used and where long-term stability or high strength is not required (particularly at the beginning of construction).

Key Words

Fly ash, Non-sintered cement, High calcium fly ash, Mortar, CO₂

오정례 Jung-rye Oh , 배재근 Chae-gun Phae

DOI:10.9786/kswm.2020.37.3.158

Abstract

This study evaluated Vietnam’s waste management system compared to Korea. Vietnam is the largest recipient country of Korea’s ODA (Official Development Assistant). First, we found that relevant regulations have been implemented for end-of-pipe pollution control, but systems for pollution prevention are inadequate. Moreover, waste management responsibilities dispersed among different government agencies limit effective management, calling for institutional as well as organizational improvements. Second, waste generation continues to rise with the highest contribution from food waste. Therefore, it is imperative to minimize waste generation while promoting waste recycling. Third, the current waste sorting and collecting system require improvement, as it insufficiently considers the different attributes and harmfulness by waste type. Fourth, supplementary measures are needed to improve landfill facilities, where installation criteria are established under weak management. In particular, measures are required to improve incineration facilities, where air pollutant emissions limits are set in the absence of installation and management criteria. We conclude that the waste management system in Vietnam requires an overhaul based on waste management priorities.

Key Words

Developing countries, ODA, Vietnam, Integrated waste management, Eco-friendly energy town

박동규 Dong Kyoo Park , 김동주 Dongju Kim , 구재회 Jae-hoi Gu , 김동철 Dong-cheol Kim

DOI:10.9786/kswm.2020.37.3.170

Abstract

The increasing demand and the environmental impacts of fossil fuel consumption calls for increasing efforts to reduce greenhouse gas emissions, improve energy efficiency, and manage energy demand. Recently, the focus has been placed on technologies that effectively use unutilized energy in the industrial setor. Thermal Energy Storage (TES) is a key technology in the development of storage and distribution of waste heat, and a heat delivery technology using a mobile- TES system has been proposed. In this study, we constructed a 2 GJ-scale TES module based on latent heat storage using a Phase Change Material (PCM) and investigated its heat charging and discharging characteristics. Docosanol-organic fatty alcohol-was selected as a heat storage medium, and steam and water were used as heat transfer fluids. The test results showed that approximately 2 GJ of heat could be stored at a charging rate of 190 kW. After the heat charging process, hot water can be produced at 43oC with a flow rate of 0.6 m3/hr, and the discharging heat is equivalent to 1.9 GJ with a thermal efficiency of 92%.

Key Words

Waste heat, Phase change material, Thermal energy storage, Heat charging, Heat discharging

박동규 Dong Kyoo Park , 김동주 Dongju Kim , 구재회 Jae-hoi Gu , 김동철 Dong-cheol Kim

DOI:10.9786/kswm.2020.37.3.179

Abstract

The domestic industrial sector accounts for more than 60% of the nation’s total energy consumption. However, approximately 10% of the energy used in the industrial sector is wasted as unused heat. The utilization of the waste heat can not only improve the energy efficiency in both target and linked processes but also reduce greenhouse gas emissions. In this regard, herein the focus has been placed on thermal energy storage (TES) technologies to store the waste heat and a heat delivery system incorporating mobile-TES. In particular, a 500 MJ-scale TES module based on the latent heat storage of phase change material (PCM) was developed for the application of a heat delivery system. The TES module consisted of 48 PCM units with an internal and external finned tube. Docosanol-a type of organic fatty alcohol-was used as the thermal storage material, and steam and air were used as heat transfer fluids. The results showed that a heat of >700 MJ can be charged at a rate of 160 kW, and a hot air equivalent of approximately 550 MJ could be produced at an 85% thermal efficiency. Each unit could store the heat of 30 MJ and release the heat of 23 MJ.

Key Words

Waste heat, Thermal energy storage, Heat delivery, Phase change material, Module

송연민 Yun Min Song

DOI:10.9786/kswm.2020.37.3.188

Abstract

This study investigated the effect of sodium hypochlorite (NaOCl)-an oxidizing agent-on COD removal rates in wastewater containing SO2, NaHSO3, and Na2SO3 that are biologically non-degradable and strong reducing substances. The COD removal efficiency was measured as functions of pH and other factors affecting the oxidation reaction rate. NaOCl had little impact on the removal of COD from the wastewater, and the pH variation did not affect the NaOCl concentration. The COD removal rate by atmospheric oxygen was 23%, and approximately 61.5% of total COD was removed by the oxidation of the iron catalyst. The COD removal rates were 90.3% and 87.2% at ferric sulfate catalyst concentrations of 5,000 mg/L and 2,500 mg/L, respectively. This meant that the COD removal rates are unaffected by the catalyst concentration within the concentrations tested in this study. The form of ferric sulfate was changed and recirculated from Fe²⁺→ Fe³⁺→ Fe²⁺ during the reaction, and all forms of iron could be reused as a catalyst in the Fenton oxidation process.

Key Words

Reducing substance, Fenton oxidation, Iron catalyst

이호경 Ho-kyung Lee , 백승민 Seung-min Baek , 김우석 Woo-suk Kim , 곽윤근 Yoon-keun Kwak

DOI:10.9786/kswm.2020.37.3.194

Abstract

In this study, a prediction model based on the size effect of reinforced concrete members was established to investigate the shear strength of recycled aggregate reinforced concrete beams. The main variables of the prediction model are the tensile reinforcement ratio, the effective depth of the beam, the beam width, the concrete compressive strength, and the shear span-to-depth ratio. Measurements of 408 normal coarse aggregate concrete beam specimens and 10 recycled coarse aggregate concrete beam specimens were investigated. The means between experimental values and prediction model values of all the test data for α = 100 (normal beam: a/d > 2.5) and α = 103 (deep beam: a/d 2.5) were 1.07 and 1.0, respectively. In addition, the mean for recycled aggregate reinforced concrete beams was 1.06 with the standard deviation of 0.18. This result was used to predict a more accurate value by applying the correction coefficient for the recycled aggregate to the normal concrete shear proposal equation and reflecting the change in shear strength according to the effective depth of the beam. The results of this study indicate that the prediction model was well matched to the experimental data.

Key Words

Shear strength, Size effect, Prediction model, Recycled aggregate

이혜성 Hyesung Lee , 김용진 Yongjin Kim

DOI:10.9786/kswm.2020.37.3.204

Abstract

Tread wear particles generated from tires enter the water system either from the road surface (non-point pollution source) or through a combined/separated sewer (point pollution source). In particular, inflow through separated (rainwater) sewers is discharged into the water system without being treated by a sewage treatment facility. Accordingly, this study investigated the microplastics in the rainwater inlet connecting the road and sewer. Especially, we assessed the abundance and type of dominant microplastics on the road and inferred possible inflow sources to the water system. Our results showed that tread wear particles contributed ≥60% of the total microplastic abundance, regardless of sampling location and time. Yellow and white dye particles as well red, blue, and green microplastics of various types were also identified.

Key Words

Tire, Tread, Wear, Microplastic, Rainwater inlet

조영석 Young-seok Jo , 장연수 Yeon-soo Jang

DOI:10.9786/kswm.2020.37.3.211

Abstract

In this study, as a study on bioreactor landfills, the effect of Food Waste Leachate (FWL) injection on the acceleration of waste biocompression was examined by performing settlement experimentation using lysimeters. In the experiment, liquid was injected into the waste through three conditions, i.e. injection of distilled water, leachate recirculation, and recirculation of leachate mixed with FWL. Compared with two other liquid supplying conditions, analyses of the chemical oxygen demand (COD) and pH value of leachate showed that the recirculation method of mixing leachate and FWL which supplies additional nutrients, i.e. the organic matter in FWL, increases microbiological activities that decompose the waste and allows an optimal pH value for waste biodegradation. Analysis of waste settlement curves and the characteristics of waste settlement showed that the recirculation of leachate mixing FWL could accelerate the waste settlement as much as 2.9 times and 2 times more than those of the distilled water injection and the leachate recirculation, respectively. Based on the results of this study, the recirculation of leachate mixing FWL would help to stabilize the landfill early by accelerating the waste settlement and to gain additional spaces in the landfill.

Key Words

Bioreactor landfills, Food Waste Leachate (FWL), Biocompression, Waste settlement, Leachate recirculation