To quantitatively evaluate a sludge recycling effect at the time of sludge treatment by applying solubilization treatment to sludge (excess sludge) extracted out of a biological treatment system to incorporate the treated sludge into a wastewater treatment apparatus for reducing the volume of sludge by recycling based on organic acid fermentation or gas fermentation.

The sludge recycling evaluation system is equipped with a means 10 for estimating the estimated amount of excess sludge in a case that a sludge treatment system 2 is not present on the basis of the qualities and flow rates of the raw water and treated water of a wastewater treatment system 1, a means 11 for weighing the actual amount of excess sludge not treated in the wastewater treatment system 2, means 12 and 32 for determining the organic acid and gas formed in the sludge treatment system 2, means 13 and 33 for measuring the power and consumables consumed in the sludge treatment system 2, a means 31 for calculating a converted money amount required in the disposal of sludge with respect to the difference between the estimated amount of excess sludge and the actual amount of excess sludge, a converted money amount obtained with respect to the determined value of the formed organic acid and the gas and a converted money amount required for the power and the consumables consumed in the sludge treatment system 2, and a means 31 for calculating the recycling effect from the converted money amounts.