We immersed a coil-type heat exchanger with a heat exchange area of about 40［m2］ in a chlorine mixed pond from a sewage treatment plant in order to recover cold and hot heat from sewage. Then, a heat pump with a cooling capacity of 62［kW］ and a heating capacity of 65［kW］were used to produce cold and hot water. During the two years of this continuous sewage heat recovery experiment, 50-70［kWh］ of sewage heat was recovered stably. Also, the thermal conductivity was also stabilized during the experiment. Based on these results obtained in this experiment, we estimated the amount of heat recovered when multiple heat exchangers were immersed in a chlorine mixed pond with an average daily inflow of 23,000（m3）. The 100 to 400［GJ/day］ of sewage heat was able to be captured throughout the year on the assumption that the heat exchanger（total heat exchange area of 1,600［m2］）was 40 times as large as the one we are currently using was installed in a mixed chlorine pond. This basic unit of heat recovery in this case was 0.054［W/ton・m2］ for cold energy and 0.051［W/ton・m2］ for thermal energy, and the water temperature difference between the inlet and outlet of the chlorine mixing pond was predicted to be about 1.6［℃］ and 1.7［℃］ for cold energy and thermal energy, respectively.

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We evaluated the economics of a project to produce and sell hydrogen from sewage sludge at a 50 t-WS（wet sludge）/d chemical looping gasification（CLG） plant, which is maintained and managed by a private SPC （Special Purpose Company） for 20 years with a processing fee paid by the municipality and hydrogen sales revenue under a DBO（ Design Built Operation） project scheme. The economic feasibility of the project was evaluated by a private SPC（ Special Purpose Company）, which maintains and manages the project for 20 years with the processing consignment fee paid by the municipality and the revenue from hydrogen sales under a DBO （Design Built Operation） project scheme. The economic evaluation of the project was conducted by determining the treatment consignment fee that would result in a Net Present Value （NPV） of ≧ 0 for the municipality in relation to the sewage sludge disposal cost borne by the municipality, and by determining the operating profit if the SPC operated the maintenance and management project for 20 years with the treatment consignment fee and hydrogen sales revenue of 30 yen/Nm3. The initial economic evaluation was conducted to determine whether the project was feasible or not. As a result of the evaluation of three cases of sewage sludge disposal costs （16,000, 20,000, and 24,000 yen/t-WS）, if the municipality bears more than 20,000 yen/t-WS as sludge disposal costs in the early 2030s, SPC profitability can be fully expected and hydrogen production from sewage sludge by CLG and the hydrogen production and sales business from sewage sludge by CLG was evaluated to be a viable long-term profitable business at a hydrogen transaction price of 30 yen/Nm3.

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