최현미 Hyeon-mi Choi , 조용철 Yong-chul Cho , 이보미 Bomi Lee , 류인구 In-gu Ryu , 김상훈 Sang-hun Kim , 신동석 Dongseok Shin , 유순주 Soonju Yu

DOI:10.15681/KSWE.2021.37.2.75 Vol.37(No.2) 75-91, 2021

Ocean dumping manure was prohibited in Korea until the end of 2012. Undumped manure was treated by resourcification, purification, and public process in a facility. But poor storage of untreated manure and overproduced compost can pollute river water. In this study, linear regression, Mann-Kendall, Seasonal Mann-Kendall, LOWESS trend, and Spearman’s correlation analysis were conducted for investigating the changes in the water quality of Bukhan and Imjin river before and after the prohibition of ocean dumping. In 2017, the Imjin River basin had more than 5 .7 times livestock breeding heads than the Bukhan River basin and more than 3.5 times livestock manure. The areas of land, farmland, and nutrient balance were also higher in the Imjin River basin. Since the two basins have different environments, it is expected that the characteristics of changes in water quality due to the increase in livestock manure generation and treatment methods will be different when comparing the water quality trends before and after the ban. The result of the trend analysis revealed a decrease in EC before the ban but an increase afterward. T-N and BOD of Imjin river increased slightly before the ban but demonstrated great enhancement thereafter. Other sites and T-P exhibited no trend. The correlation analysis result showed that the increase in the number of livestock rearing was correlated with the increase in T-P of Bukhan River and BOD of Imjin River. The increase in livestock manure production was not correlated with the Imjin River basin, while a correlation was observed with the Bukhan River with an increase in T-N and EC and the decrease in T-P.

Bukhan river, Imjin river, Livestock manure, Ocean dumping ban, Trend analysis

김호섭 Ho-sub Kim , 오승영 Seung-young Oh

DOI:10.15681/KSWE.2021.37.2.92 Vol.37(No.2) 92-102, 2021

In this study, the distribution characteristics according to the type of BOD and the effect of nitrogenous oxygen demand (NOD) and algal oxygen demand on BOD in three streams (Bokhacheon, Byeongseongcheon, and Gulpocheon) were evaluated. Although the BOD and NOD concentrations demonstrated a difference in the three streams, the carbonaceous BOD(CBOD)/BOD ratio was 0.75 (p=0.053, one-way ANOVA), and there was no significant difference in the three streams (r²≥0.92, p<0.0001). The NOD concentration of the Bokhacheon with high NH₃-N was 1.7±1.3 ㎎/L, which was the highest among the three streams and showed a significant correlation with BOD. Seasonal variations in NOD in the three streams did not show a significant correlation with changes in NH3-N concentration (r²<0.28, p≥0.1789), and there was no significant difference in NOD even though NH₃-N concentration in Gulpocheon was about twice that of Byeongseongcheon (p=0.870, one way ANOVA). The particulate CBOD(PCBOD)/CBOD ratio of the three streams was 0.55~0.64, and about 60% of the biodegradable organic matter was present in the particulate form. When the Chl.a concentration in the stream was more than 7 ㎍/L, the PCBOD tended to increase with the Chl.a concentration (r²=0.61, p=0.003). In the three streams, particulate NOD accounted for 81% of NOD; however, despite the large variation in NH3-N concentration (0.075~3.182 ㎎/L), there was no significant difference in soluble NOD(SNOD) concentration that ranged from 0.1 to 0.3 ㎎/L. In this study, the low contribution rate of SNOD to NOD is considered as a result of the removal of nitrifying bacteria along with the particles during the filtration process.

Algal oxygen demand, Carbonaceous BOD, Nitrifying bacteria, Nitrogenous oxygen demand, Particulate CBOD

강희만 Heeman Kang , 전지홍 Ji-hong Jeon

DOI:10.15681/KSWE.2021.37.2.103 Vol.37(No.2) 103-113, 2021

In this study, an Excel-based model (ROADMOD) was developed to estimate pollutant loading from the road and evaluate BMPs. ROADMOD employs the Chezy-Manning equation and empirical expression for estimating surface runoff, and power function for pollutant buildup, and exponential function for pollutant washoff in SWMM. The results of model calibration for buildup and washoff using observed data revealed a good match between the simulation results and the observed data. The long-term surface runoff and sediment simulated by ROADMOD demonstrated a good match with those by SWMM with 2 ~ 14% of relative error. The shorter sweeping interval (within 8 days) remarkably decreased sediment loads from the road. It was found that the effect of reducing sediment loads from the road was greatly affected not only by the sweeping interval but also by sweeping on the day before a rainfall event. The 48% of removal efficiency of sediment loads from the road was achieved with 26 times of road sweeping per year when sweeping was performed on the day before the rainfall event. A 4-day sweeping interval showed similar removal efficiency (48%) with 96 times of sweeping per year. It is considered that the road sweeping on the day before a rainfall event could maximize the effect of reducing the non-point source pollution from the road with minimization of the number of road sweeping. So, the road sweeping on the day before a rainfall event can be considered as one of the useful and best management practices (BMPs) on road.

Non-point source pollution, ROADMOD, Road sweeping, Sediment load

조용철 Yong-chul Cho , 최현미 Hyeon-mi Choi , 류인구 In-gu Ryu , 김상훈 Sang-hun Kim , 신동석 Dongseok Shin , 유순주 Soonju Yu

DOI:10.15681/KSWE.2021.37.2.114 Vol.37(No.2) 114-127, 2021

Water pollution in the lower reaches of the Namhan River is getting worse due to drought and a decrease in water quantity due to climatic changes and hence is affecting the water quality of Paldang Lake. Accordingly, we have used a water quality index (WQI) and statistical analysis in this study to identify the characteristics of the water quality in the lower reaches of the Namhan River, the main causes of water pollution, and tributaries that need priority management. Typically, 10 items (WT, pH, EC, DO, BOD, COD, SS, T-N, T-P, and TOC) were used as the water quality factors for the statistical analysis, and the matrix of data was set as 324 × 10·1. The correlation analysis demonstrated a strong correlation between Chemical Oxygen Demand (COD) and T-P with a high statistical significance (r=0.700, p<0.01). Furthermore, the result of principal component analysis (PCA) revealed that the main factors affecting the change in water quality were T-P and organic substances introduced into the water by rainfall. Based on the Mann-Kendall test, a statistically significant increase in pH was observed in SH-1, DL, SH-2, CM, and BH, along with an increase in WQI in SH-2 and SM. BH was identified as a tributary that needs priority management in the lower r eaches o f t he N amhan R iver, with a “ Somewhat p oor” ( IV) g rade i n T -P, “Fair” g rade i n WQI, and “Marginal” grade in summer.

Namhan River, RTWQI, Statistical analysis, WQI

박기학 Kihak Park , 이호식 Hosik Lee , 하준수 Junsu Ha , 김극태 Keugtae Kim , 임채승 Chaeseung Lim

DOI:10.15681/KSWE.2021.37.2.128 Vol.37(No.2) 128-136, 2021

It is generally known that a wastewater treatment plant (WWTP) consumes immense energy even if it can produce energy. With an aim to increase the energy independence rate of WWTP from 3.5% in 2010 to 50% in 2030, the Korean government has invested enormous research funds. In this study, cost-effective operating alternatives were investigated by analyzing the energy efficiency and economic feasibility for biogas and power generation using new and renewable energy. Based on the US EPA Energy Conservation Measures and Korea ESCO projects, energy production and independence rate were also analyzed. The main energy consumption equipment in WWTP is the blower for aeration, discharge pump for effluent, and pump for influent. Considering the processes of WWTP, the specific energy consumption rate of the process using media and MBR was the lowest (0.549 kWh/m³) and the highest (1.427 kWh/m³), respectively. Energy-saving by enhancing anaerobic digester efficiency was turned out to be efficient when in conjunction with stable wastewater treatment. The result of economic analysis (B/C ratio) was 2.5 for digestive gas power generation, 0.86 for small hydropower, 0.49 for solar energy, and 0.15 for wind energy, respectively. Furthermore, it was observed that the energy independence rate could be enhanced by installing energy production facilities such as solar and small hydropower and reducing energy consumption via the replacement of high-efficiency operating.

Benefit, Cost, Energy independence rate, Greenhouse gas, Sewage treatment