Incineration can be used as means 1) to reduce the volume of the dry sludge and 2) to produce a sterile non-harmful residue that is free from volatile content. It provides a safe alternative solution when facing with problems dealing with land scarcity available for waste disposal and apart from that it also helps to recover back some of the energy used in the combustion process especially in large treatment plants whereby there is a huge quantity of sludge generation.
Normally incineration can help to further reduce and concentrate the solid content after the sludge thickening process and dewatering happened in the earlier processes have reduced the moisture level to below 30%. With lower volume this helps to decrease the needs and requirements later part on disposal at landfills. While operating cost and environmental impacts related to air pollution will continue to pose major barrier, the advantages in the long run is still very much worthwhile to be considered. Technologies used in sludge incineration mainly focused on the use of heath incinerators and fluidized bed incinerators. Let’s analyze each and every option provided here which has its own advantages and disadvantages for us to look into details.
The hearth incinerator is the most widely used technology in the world and the system usually consists of multiple hearths stacked together into the furnace. Incoming sludge is fed from the top and as it drops down below, the rotating arm extending from a vertical shaft placed in the middle will distribute the solids evenly throughout the system. As the sludge travels and move from one hearth to another, this will help to dispense the sludge and expose new surface area for gas combustion which is what makes it efficient compared to the other methods. Flue gas will exit at another channel located at the top of the furnace while the residue will collect at the bottom and then taken out from the system.
Fluidized Bed Incinerator
Use of pressurized gas to create fluidized floating sand bed is the key principle to this technology because doing this will allow maximum contact with large surface area available between the sludge and the gas for incineration. Usually the control of air inlet is very important because too much gas to sludge ratio will translate to wastage and the same goes for sludge entering into the system. Care must also be taken to prevent the sludge from floating to the top of the bed and overall, the system allows high utilization of energy and thus leads to cost saving. Another advantage regarding the use of the system is that start-up time can also be reduced because once the process stops the whole bed will act as a heat sink that traps the heat and prevent losses of energy.