## 1 Introduction  
The population of Japan is declining, and the population gap between rural and urban areas has become a social problem. The population is concentrated in big cities such as Tokyo, Nagoya, and Osaka, and the rural population is declining [1]. Therefore, tax revenues are expected to decrease in small cities, and reducing maintenance costs of social infrastructure is necessary. Therefore, environmental and economic reviews are underway at energy-intensive waste incineration plants and sewage treatment plants, which are representative of social infrastructure. In March 2019, the Ministry of the Environment's \"Wider area of waste treatment and integration of waste treatment facility to ensure sustainable proper treatment\", presented six methods for widening and integrating waste treatment facilities [2]. This notification established a waste treatment union, stating the necessity to carry out waste treatment in a wide area and promote the integration of waste treatment functions in cooperation with other infrastructures. The environmental and economic efficiency of a collaboration between waste incineration plants, sewage treatment plants, and industrial facilities is under evaluation [3, 4, 5, 6, 7]. A study that evaluated the environmental friendliness and business profitability of a waste incineration plant and a sewage treatment plant, located adjacent to each other and cooperating, showed that incinerating dry sludge at the waste incineration plant and reusing the heat from the process to heat the water supply for the fire extinguishing tank resulted in a 51% Greenhouse Gas (GHG) emission reduction compared to the normal method [5]. Furthermore, a study that evaluated the feasibility of supplying steam from a sewage treatment plant to an industry in Aichi Prefecture, Japan, showed that the strategy was cost-effective within a 1 km distance, but profitability decreased with increasing distance [6]. These assessments were based on the concept of the life cycle assessment (LCA). LCA is a method for quantitatively evaluating the environmental load of a product or service over its entire life cycle or at a specific stage [8]. This method was also used in the waste fields [9; 10; 11; 12; 13; 14; 15]. Food waste is incinerated in waste incineration plants as combustible waste in Japan. Its high water content causes a decrease in calorific value. To solve this problem, some studies have shown that carbon dioxide (CO\({}_{2}\)) emissions can be suppressed by separating food waste, performing intensive methane fermentation treatment, and using it as an energy source [16]. In sewage sludge treatment, thermochemical decomposition has been studied to reduce the risk to the environment by converting the sludge into products with added value [17]. Pyrolysis oils obtained with low heating rates, 5 \({}^{\circ}\)C/min and 10 \({}^{\circ}\)C/min, presented higher heating value compared with the oils obtained at 50 \({}^{\circ}\)C/min, which were rich in water and had energy values comparable to those of natural gas, biogas, and gases obtained from plastic pyrolysis [17]. In their study, [PERSON] et al. estimated the GHG reduction effect of using sludge fuel for industrial and waste incineration plants [4]. It was estimated that about 85% of the total amount of unused sludge could be utilized as energy, and 679,000 t-CO\({}_{2}\) of GHG can be reduced by using sludge fuel at paper, cement, and coal-fired thermal power plants within a 150 km radius and co-firing sludge at sewage treatment and waste incineration plants in the same municipality [4]. Recently, Japan has been focusing on mechanical biological treatment (MBT). MBT has become a popular method of treating municipal solid waste (MSW) worldwide [18]. MBT is commonly used across Europe currently [19]. The installation of 50 new MBT plants has increased the waste treatment capacity by 5,000,000 tons, especially in Spain [20].