Sludge Disposal System

The sludge dewatering and disposal facilities in Huntington utilize continuous belt filter presses to convert the liquid sludges from the wastewater treatment processes into filter cake which contains approximately 24% solids and 76% water. The filter cake is then mixed with West Virginia coal and fed into a fluidized bed disposal system where it is burned at about 1600 degrees Fahrenheit.

The heart of the disposal system is a fluidized bed reactor which contains a bed of sand. Just before start-up, the stationary bed of hot sand inside the reactor is about 3 1/2 feet deep. When the fluidizing blower is turned on, the stationary bed of sand expands approximately 30-35%, to approximately 5 feet as the hot air forces its way upward through the bed. At this time, the bed is said to be fluidized which means that each individual grain of red hot sand is suspended in the rising stream of hot gases and a given grain of sand is free to wander throughout the bed in a random manner. Each grain is surrounded by a "cushion" of rising gas.

The bed of sand resembles a tank of boiling water in the sense that a definite bed level is maintained and there is considerable turbulence or "splashing" at the bed surface. There is another similarity between the fluidized bed and a tank of boiling water and that pertains to the density of the fluidized sand. Each cubic foot of fluidized sand has the same density as that of a cubic foot of water.

The fluidized bed is ideally suited for burning sewage sludge for the following reasons:

The fluid bed acts as a heat reservoirs able to supply enough heat to flash off the water the sludge carries so that combustion of the dry solids can proceed.

Individual pieces of sewage sludge "floating" within the bed are constantly worn down by the hot sand particles so that combustion continues evenly without clinker formation.

The rising flow of heated air supplies oxygen to burn the dehydrated solids. When the solids are burned, heat is released and in this way, the heat that was "borrowed" to flash off the water is returned to the hot sand.

Sewage sludge is a complex mixture of proteins, carbohydrates, greases and organic chemicals in varying stages of decomposition. Sewage Sludge contains the combustible elements carbon and hydrogen plus negligible traces of sulfur. When these elements combine with the oxygen in the air supplied by the fluidizing blower, combustion occurs and heat is released within the reactor.

The Huntington Wastewater Treatment Plant utilizes processes that are not only unique for West Virginia, but also the Nation.