Abstract: [Objectives]　Co-incineration of solid wastes such as sludge and digestate in waste incinerators has become one of the main disposal methods. To achieve more efficient and economical co-incineration, an economic analysis of multi-source solid waste co-incineration involving municipal sludge and food waste digestate in waste incinerators is conducted using thermal calculations.[Methods]　The univariate analysis and L₁₆(4³) orthogonal analysis are employed to examine the impacts of the dry-basis sludge co-incineration ratio, dry-basis digestate co-incineration ratio, and the moisture content of sludge/digestate fed into the furnace on the net present value of economic benefits. Investment suggestions on whether to introduce multi-source solid waste co-incineration are provided, taking into account variations in income from sludge and digestate treatment fees.[Results]　The economically optimal co-incineration conditions are a dry-basis sludge ratio of 7%, a dry-basis digestate ratio of 3%, and a moisture content of sludge/digestate fed into the furnace of 40%. On the basis of co-incinerating one type of solid waste, the conditions of introducing another to achieve multi-source co-incineration are determined as follows. When the income from digestate treatment fee is higher than 33 yuan/t after deducting the transportation cost, co-incineration of digestate could be adopted. When the subsidy for sludge is higher than 15 yuan/t after deducting the transportation cost, co-incineration of sludge could be introduced.[Conclusions]　When single-source solid waste is co-incinerated, the co-incineration ratio can be increased as much as possible within the allowable range of combustion condition deterioration. When multi-source solid waste is co-incinerated, the interaction between the two should be considered to explore the optimal co-incineration ratio.

Key words: economic analysis, orthogonal analysis, co-incineration, thermal calculations, waste incinerator, sludge, food waste digestate, net present value