최재훈 Jae-hoon Choi , 정성엽 Seong-yeob Jeong , 김지태 Ji-tae Kim

DOI: Vol.35(No.4) 299-307, 2019

The purpose of this study was to investigate the effect of low temperature thermal pre-treatment on biodegradation of waste activated sludge for anaerobic digestion as a countermeasure for increasing sludge generation. The experimental condition was accomplished in 2 %, 4 %, and 6 % TS concentration, and 70 ℃, 80 ℃, 90 ℃ of temperature for a maximum of 120 minutesretention time. Then, it was followed by analysis of physical/chemical properties, BMP test and composition of biogas. The biogas characteristic was evaluated by applying the modified Gomperz model. As a result, solubility of dissolved substrate, such as SCOD_Cr, soluble carbohydrate, and soluble protein, and biogas production increased as temperature increased.Solubilization efficiency at 90 ℃ was 18.4 %, 17.03 % and 16.88% in 2 %, 4 %, and 6 % TS concentration respectively. Also, solubilization rates of carbohydrate and protein similarly increased. BMP test results also showed that methane production in excess sludgeincreased to 0.194, 0.187 and 0.182 m³/kg VS. respectively, and lag phase decreased to 0.145, 0.220, 0.351 day due to acceleration of the hydrolysis step. Consequently, low-temperature thermal pre-treatment could increase biodegradability of sludge, positively affecting biogas production and sludge reduction.

BMP test, Solubilization, Thermal pre-treatment, Waste Activated Sludge

남수연 Sooyoun Nam , 최형태 Hyung Tae Choi , 임홍근 Honggeun Lim

DOI: Vol.35(No.4) 308-315, 2019

The objective of this study was to investigate mountain stream water and air temperatures, area, latitude, altitude, and forest coverage in headwater catchments located in Kangwon-do, Mid-eastern Korea from 2015 to 2017. Daily mean value of mountain stream water temperature was approximately 6 ℃ lower than the daily mean value of air temperature on the monitoring sites during the observation period. Monthly mean value of mountain stream water temperature increased with increasing monthly mean value of air temperature from May to August during the observation period. Seasonal variations of mountain stream water temperature were dependent on air temperature rising and falling periods. Correlation analysis was conducted on mountain stream water temperature to investigate its relationship with air temperature, area, latitude, altitude, and forest coverage of air temperature rising and falling periods. The correlation analysis showed that there exists a relationship (Correlation coefficient: -0.581 ∼ 0.825; p<0.05), particularly the air temperature showed highest correlation with mountain stream water temperature. Regression equations could be developed due to contribution of air temperature to affect mountain stream water temperature (Correlation coefficient: 0.742 and 0.825; p<0.01). Therefore, a method using various parameters based on air temperature rising and falling periods, could be recommended for predicting mountain stream water temperature.

Air temperature falling period, Air temperature rising period, Mountain stream water, Regression equation

이은주 Eunju Lee , 정세웅 Sewoong Chung , 박형석 Hyungseok Park , 김성진 Sungjin Kim , 박대연 Daeyeon Park

DOI: Vol.35(No.4) 316-331, 2019

Carbon dioxide(CO₂) emission from rivers to the atmosphere is a key component in the global carbon cycle. Most of the rivers are supersaturated with CO₂. At a global scale, the amount of CO₂ emission from rivers is reported to be five-fold greater than that from lakes and reservoirs, but relevant data are rare in Korea. The objectives of this study is to estimate the CO₂ net atmospheric flux(NAF) from the upstream of Gangjeong-Goryeong Weir(GGW), Dalseong Weir(DSW), Hapcheon-Changnyeong Weir(HCW), and Changnyeong-Haman Weir(CHW) located in Nakdong RiverSouth Korea) using field and laboratory experimentsand to apply data mining techniques to develop parsimonious prediction models that can be used to estimate CO₂ NAF with physical and water quality variables that can becollected easily. As a result, the study sites were all heterotrophic systems that often released CO₂ to the atmosphere, except when the algal photosynthesis was active.The median CO₂ NAF was minimum 391.5 mg-CO₂/m²day at GGW and maximum 1472.7 mg-CO₂/m²day at DSW. The CO₂ NAF showed a negative correlation with pH and Chl-a since the overgrowth of the algae consumed CO₂ in the water and increased the pH. As the parsimonious multiple regression model and random forest model developed, this study showed an excellent performance with the Adj.R² value higher than 0.77 in all weirs. Thus, these methods can be used to estimate CO₂ NAF in the river even if there is no pCO₂ measurement data.

CO₂ emission, Data mining, Nakdong river, Net atmospheric flux, River pCO₂

황광현 Kwanghyun Hwang , 김동익 Dongik Kim

DOI: Vol.35(No.4) 332-339, 2019

A comparative study on the anaerobic digestion efficiency according to the temperature change was conducted considering the characteristics of domestic food wastes with high water content of about 80 % or more. The substrate was tested for anaerobic digestion efficiency in two substrates, a liquid component separated naturally from food waste and food waste itself. In the anaerobic digestion experiments, the digestion efficiency was the highest at 55℃ (thermophilic temperature). However, the digestion efficiency at 45 ℃(middle high temperature) was lower than that at 35 ℃(mesophilic temperature). The comparison of general food wastes anaerobic digestion requiring 30 days of hydraulic retention time to the liquid component indicated a stable digestion efficiency even after 15 days of hydraulic retention time.In the experiments conducted on food waste, the digestion efficiency at 55 ℃ was higher than that at 35 ℃. When the food waste, especially the liquid component originating from food waste, is treated by anaerobic digestion method, the mesophilic temperature and thermophilic temperature conditions are more favorable in the digestion efficiency than the middle high temperature (45 ℃). However, when applying thermophilic or mesophilic temperature anaerobic digestion process operation in the field, the amount of energy input should be considered.

Anaerobic digestion, Biogas, Food wastes, Mesophilic, Thermophilic

공동수 Dongsoo Kong , 김범철 Bomchul Kim

DOI: Vol.35(No.4) 340-351, 2019

In this study, the relationship between trophic state indices was analyzed based on the monthly or weekly water quality data of 81 lakes (mostly man-made) in Korea between 2013-2017. Carlson’s TSIC and Aizaki’s TSI_m were calculated using the summer (Jun.-Sep.) average data at the upper water layer. The previous Korean trophic state index (TSI_KO) and the newly suggested index (TSI_KON) was calculated using the annual average data at the whole layer and at the upper layer, respectively. While previous trophic state index (TSI) such as Carlson’s TSI included logarithmic function, we devised newly Monod-type TSI_KON(Chl) that is 50 when half-saturation concentration of chlorophyll α (Chl.α) measured by UNESCO-method is 10 μg L^-1. MMF-type TSI_KON(TP) was derived based on the relationship between TP and Chl.α. A comprehensive TSI_KON was decided as the larger one of the two TSI_KON values. The range of previous TSI was usually 40-50 for the mesotrophic state, which seemed narrow to discriminate trophic characteristics of the class. The upper limits of TSI_KON for oligotrophic, mesotrophic, and eutrophic state were set to 23, 50 and 75, respectively. Classification by TSIC and TSI_m showed higher frequency of eutrophic class compared to TSI_KO and TSI_KON. This means that the estimation by TSIs developed in foreign natural lakes can lead to distorted results in the classification of the trophic state of Korean lakes. This is due to the decrease of transparency by non-algal material and the reduction in phosphorus availability to algal growth, particularly in Monsoon period.

Eutrophication, Trophic state classification, Trophic state index, Water quality

이현미 Hyeon-mi Lee , 신라영 Ra-young Shin , 이정호 Jung-ho Lee , 박종근 Jong-geun Park

DOI: Vol.35(No.4) 352-361, 2019

The purpose of this study is to analyze the characteristics and correlations of the Yeongcheon Lake in order to reduce the occurrence of harmful cyanobacteria. In this study, we investigated the water quality and phytoplankton of the lake from May to November in 2017. Correlation and data mining analyseswere performed to analyze the relationship between the two factors. The water temperature was lowest at the point where the Yeongcheon Lake inflow occurs at Imha Lake. It was highest at the point where the outflow occurs to Angye Lake. The pH was also highest at the outflow point, but in the case of DO, it was highest at the midpoint between the inflow and outflow. The main cyanobacteria that emerged during the study period were Oscillatorialimosa, Microcysti saeruginosa and Aphanizomenon flos-aquae. As a result of correlation analysis, the water temperature, inflow, COD loading, TOC loading at the inflow point of the Yeongcheon Lake were the items that were related to the harmful cyanobacteria. The data mining analysis indicated that the TP loading and harmful cyanobacteria in the inflow point of the Yeongcheon Lake were influential on the detrimental cyanobacteria in the Yeongcheon Lake outflow point. When the TP loading was less than 39.0 kg/day at the inflow site, it wasexpected that the amount of harmful cyanobacteria could be maintained below 10,000 cells/mL.

Cyanobacteria, Data mining, HABs(Harmful Algal Blooms), Yeongcheon Lake

최재훈 Jae-hoon Choi , 정성엽 Seong-yeob Jeong , 김지태 Ji-tae Kim

DOI: Vol.35(No.4) 362-369, 2019

In this study, biodegradation efficiency improvement of mixed sludge for the anaerobic digestion process in wastewater treatment plant was investigated. In order to release the organic material contained in the sludge cell and promote the hydrolysis step, mixed sludge of 7% TS (Total Solids) was physically shear-treated at a shear strength of 1,000 ~ 4,000 rpm and a maximum of 120 mins. As a result of the comparison between mixed sludge before and after the treatment, the concentration of SCOD_Cr(Soluble Chemical Oxygen Demand-chromium method) was increased through the conversion of granular organic matter into dissolved organic matter as shear strength and treatment time increases. The solubilization efficiencyincreased rapidly after 30 min of solubilization application time, and they were 11.23 %, 20.10 %, 22.52 % and 25.43% at 120 min for each shear strength conditions, respectively. Additionally, the BMP(Biochemical Methane Potential) test was conducted with the optimized samples to determine the increase of methane production by the shear pre-treatment. Consequently, methane production of each samples were 0.275, 0.310, 0.323 and 0.335 m³/kg VS_add, which indicates that methane production was increased to a maximum of 21.28 % compared to the control without the solubilization process (0.262 m³/kg VS_add). As a result, the physical shear-treatment is a promising process for sewage sludge pre-treatment to reduce the organic waste and increase the energy production.

BMP test, Mixed Sludge, Shear Pre-treatment, Solubilization

김태우 Taewoo Kim , 이호식 Hosik Lee

DOI: Vol.35(No.4) 370-378, 2019

In the recent years, various studies have presented stable and economic methods for increased regulations and compliance in sewage treatment plants. In some sewage treatment plants, the effluent concentration exceeded the regulations, or the effluent concentration was manipulated. This indicates that the process is currently inefficient to operate and control sewage treatment plants. The operation and control method of sewage treatment plant is mathematically dealing with a physical and chemical mechanism for the anticipated situation during operation. In addition, there are some limitations, such as situations that are different from the actual sewage treatment plant. Therefore, it is necessary to find a more stable and economical way to enhance the operational and control method. AI (Artificial Intelligence) technology is selected among various methods. There are very few cases of applying and utilizing AI technology in domestic sewage treatment plants. In addition, it failed to define specific definitions of applying AI technologies. The purpose of this study is to present the application of AI technology to domestic sewage treatment plants by comparing and analyzing various cases. This study presented the AI technology algorithm system, verification method, data collection, energy and operating costs as methods of applying AI technology.

Algorithm, Artificial Intelligence, Data collection, Reduce energy & operating costs, Wastewater treatment plant