We proposed an energy network in waste treatment facilities and sewage treatment facilities. This network can reduce the energy consumption and the environment loads from their treatment facilities, in case collected energy (waste heat and sludge-digestion gas) are utilized each other in their treatment facilities. A means to collect the energy is as follows: Case-1 is that all energy are collected as electricity, Case-2 is that methanol is produced from sludge-digestion gas and Case-3 is that sludge-digestion gas is collected as fuel. As the result, Case-2 is better than the another cases in this evaluate at reduction of the energy consumption and the environment loads from the system. Furthermore, it is possible to reduce about 40% of the energy consumption and the environment loads in the system of 100, 000 persons and about 100% of them in the system of over 400, 000 persons.