고유가와 기후변화 협약에 대처하기 위해 우리나라는 2008년, ``저탄소 녹색성장``을 대한민국의 새로운 국가비전으로 선포하고 "녹색성장 국가전략"을 수립하여 3대 전략 10대 정책방향을 추진 중에 있다. 더불어 장기적으로는 하수처리시설의 에너지 절감사업의 시설투자비 확보가 매우 중요한 만큼 ix) 하수처리시설의 경제적 가치 창출을 통한 지자체의 재정확보 방안이 수립되어야 한다.

In the 60th anniversary of founding the Republic of Korea in 2008, ``Low Carbon, Green Growth`` was declared as the new national vision to cope with high oil prices and climate change. The national strategy for "Green Growth" was established with three main strategies and ten policy directions, and the "Framework Act on Low carbon, Green Growth" was enacted in April 2010. Municipal wastewater treatment facilities are considered energy-intensive environmental infrastructures, and they are regulated under the GHG Target management which sets and implements targets for emission reduction, energy conservation, and energy efficiency to respond against energy depletion and climate change. As a result, the importance of energy conservation and recovery in wastewater treatment plants (WWTPs) are being emphasized. In this study, the energy consumption characteristics of WWTP and energy management-related systems were investigated. Also, energy efficiency comparisons among WWTPs were carried out. Finally, measures to improve energy efficiency and energy management at WWTPs are presented. In the last decade, the electricity cost at WWTPs with the capacity of 500 m3/day or more increased by 10.6% per year, and compared to year 2002, the cost increased to 101.9% in year 2009. These increases can be attributed to increases in wastewater that must be treated and advanced treatment technologies equipped to comply with increasingly stringent discharge requirements, among other reasons. In response, the Ministry of Environment has developed the "basic plan for energy independence at wastewater utility" in 2010, which placed a goal to achieve energy self-sufficiency rate of 50% by 2030. The energy efficiency opportunities suggested in the basic plan can be grouped into three broad categories as follows; Replacement of aging equipments with more efficient equipments, and operational improvements Energy recovery, such as biogas, through anaerobic sludge digestion or small hydro power using a discharge of treated wastewater Alternative energy production from photovoltaic power generation, wind power, and others However, most pilot projects implemented with the government`s financial support are focused on energy recovery or alternative energy production rather than energy savings through energy efficiency and maintenance of WWTPs. In 1992, the US EPA introduced ENERGY STAR as a voluntary labeling program designed to identify and promote energy efficient products to reduce greenhouse gas emissions. The EPA expanded the label to wastewater utilities in 2005, and its goal is to have more than 50% of the nation`s WWTPs earn the ENERGY STAR label by 2012. In addition, the EPA has highly recommended wastewater treatment operators to adopt PDCA (Plan-Do-Check-Act) approach to enhance their energy efficient management systems. In other words, the EPA has encouraged and assisted wastewater utilities in implementing energy saving practices through their operational improvements, as well as renewable energy productions. In the EU, automatic control systems have been widely applied to minimize the costs associated with energy and energy efficiency over time, and provide improved control and operation over the unit treatment processes. Moreover, EU has relied on renewable energy productions to improve the energy efficiency of wastewater utilities. In Japan, emphasis on energy efficiency to overcome environmental issues, such as global warming response, are enforced throughout all industries, and the country has consistently introduced new technologies to improve its energy efficiency and production of energy. In many wastewater facilities, Japan has developed and used various alternative energy production technologies, such as biogas production, sewage heat recovery, small hydropower, and windmill power, to improve the efficiency of its facilities. In this study, the energy usage and energy efficiency of wastewater utilities were evaluated to explore ways to save energy via operational measures. Using the standards from the end of 2009, it was found that the amount of energy used by WWTPs (treating 500m3/d or more wastewater) increased with increasing wastewater treatment capacity. The unit energy usage of each treatment process was analyzed in terms of inflow, organic removal, and nutrient removal. Wastewater treatment processes employing the media consumed relatively lower power compared to other advanced treatment processes. Among the secondary treatment processes, the lowest consumption of power was found in the activated sludge process. As such, energy usages in the wastewater utilities are affected by various parameters, such as inflow, process, and influent concentration of pollutants. Moreover, the correlation of each characteristic parameter to energy was assessed to find a set of parameters that explained most of the variations in energy use among utilities. Based on these results, a multi-parameter lineal regression model that captured the impacts of key characteristics on energy use was developed to assess the energy efficiency of wastewater utilities. The results show that increases in inflow, influent COD concentration, and ratio of advanced treatment generally increased the energy use. On the other hand, increases in load factor (influent average flow/design flow) reduced the energy use. In the regression analysis, the energy efficiency was highest in the A2O advanced process, followed by activated sludge, other advanced treatment processes, media advanced process, RBC, oxidation ditch, membrane advanced process, and contacted aeration process. These results show that the membrane process (among the advanced processes) and the contacted aeration process (among the secondary processes) require more efforts in saving energy. Overall however, energy efficiency varied within the same process and similar-sized treatment plants. Thus, each WWTP needs to establish its own measure systematically to optimize their energy efficiency operation. To promote operation-based energy saving and energy efficiency measures which are individually suited for each waste treatment plant, the followings should be established: i) energy use DB for all wastewater utilities, ii) energy use monitoring system for the wastewater unit process, iii) organizational energy management team, iv) energy management system (EMS), and v) collaborative network of energy saving through exchanges of technical information. Moreover, vi) improvements in energy efficiency rating and incentive programs for wastewater utility are required since the commitments of plant staff members are critical in enhancing energy effectiveness. To ensure practitioners` expertise in efficient sustainable energy operation of WWTP, vii) allow for a longer unit rotation for technicians instead of frequent unit rotations. Also, viii) the R&D support for the field of integrated control system is needed to develop key technologies and improve the localization rate. Lastly, ix) the financing plan of the municipality must ensure the economic value of WWTPs to secure investors` investments in facilities and equipments for sustainable energy savings.