Determination of the calorific value of wastewater and sludgefrom a municipal wastewater treatment plant

Key words: 
• wastewater /
• sludge /
• heat value /
• bomb calorimeter /
• element analysis

Abstract: It’s a primary step to establish thermodynamic indices for thermodynamic analysis of biological wastewater treatment processes, unfortunately standardized measurement method for chemical energy within wastewater and sludge has not been developed. An automatic calorimetric method was adopted to determine calorific values of influent, effluent, primary sedimentary sludge, surplus sludge, mixed sludge and dehydrated sludge samples from several municipal wastewater treatment plants. The samples were dried at 103～105℃ during preparing course and the quality control scheme of determination was set up. Referring to calorific value measurement of coal, gross calorific values of samples were acquired. The result indicates that the calorific value of effluent dry basis is 0.5 kJ/g, and that of the influent is above 4 kJ/g; moreover, the calorific values of the sludge samples are as high as above 12 kJ/g which is close to the Youjiang lignite’s level. The standard deviations (SD) of the test results are all less than±0.452% and the relative standard deviations (RSD) are no more than 0.136%. Based on the element analysis of the same set of samples, the calorific values were also calculated with the Dulong formula. The results of the two methods are pretty close.