Excess Sludge Reduction in Waste Water Treatment Plants

Abstract

Household waste water is taken under WWT (Waste Water Treatment) process and treated water is removed to the nature. Biological analysis method using activated sludge is well known and used method for the treatment of waste water as the running cost is cheap. But, a large amount of excess sludge is produced in the Waste Water Treatment Plants (WWTPs) which is a great burden in both economical and environmental aspects. Fig.1 is an example of annual industrial waste of Japan (Ministry of the Environment, Government of Japan, 2010). Sludge related garbage occupied 44.2% of the total industrial waste. In which about 86,860,000 ton of sludge related to WWTPs was produced in 2007. The excess sludge contains a lot of moisture and which is not easy to treat. There are several works done by many scientists to treat the excess sludge (Ide, 1990; Eckenfelder & Grau, 1998; Miyoshi, 2006; Sawada et al., 2005; Wei et al., 2003). These byproducts of WWTPs are dewatered, dried and finally burnt into ashes. Some are used in farm lands as compost fertilizer. The less dump places for ashes and the high cost to treat the excess sludge are huge burdens to our society. In Japan, an average of Yen 20,000/t is needed to treat of excess sludge. Again, burning of excess sludge evacuates the CO2 in air, which is a cause of global warming. So, the reduction of excess sludge is a growing demand to the modern society. It is not only a headache of Japan, but also to the rest of the world.