Sludge is the by-product of sewage treatment. Organic matters contained in the sewage partly come from human and animal waste. It is no wonder that sludge comprises organic matter.
Organic matters are considered ignitable. In sludge incineration, the combustion zone is around nine hundred degrees Celcius. The sludge volume can be ninety percent reduction after incineration. The left-over is the ash.
One of the concerned compounds in gas, H2S or Hydrogen sulfide, is colourless but flammable, toxic, and has an unpleasant rotted-egg smell. The release of H2S would pose environmental and operational health and safety hazards when operators are dealing with them in the incineration process.
The chemical deodorisation treatment to remove the gas compounds emitted from the sludge is the wet scrubber system. The system works in the spray tower, which is filled with odorous gas. The chemical liquid, commonly calcium carbonate, sprays into the gas. The odorous gas will be showered. It is estimated that about 98% of sulfur removed from the gas. The wet scrubber processes before sludge are put into incineration.
Incineration is the next core step to tackle the environmental problem we face each day. The incineration has earned its reputation of minimising the waste volume to ten percent left through combustion. The controversy about incineration is public health.
Dioxin can be formed when chlorine-containing organic substances (e.g., PVC) are burned. The eight-hundred-and-fifty-degree-Celcius combustion is the solution to destroy dioxin. The incinerator is the creator of air pollution; it can, in turn, be the solver for the own problem.
Another noticeable incineration product is the flue gas produced from combustion. The dry reactor injects the chemical powder – Sodium bicarbonate and activated carbon to get rid of the heavy metals, acidic gas, and organic compounds.
Bag filters work like a vacuum cleaner. They filter fine ashes and by-products in this last flue gas treatment stage. These residues are out of the final emission by sucking the gas from outside to inside of the bag filter. The residues from these stages will be sent away with the inert ash to the landfill for disposal.
The last resort of the incineration train is the continuous emission monitoring system (CEMS). The CEMS on key parameters is equipped at the stack to ensure combustion and air pollutant removal processes are functionally well. The automatic sludge feed cut-off system is installed at the incineration train. Sludge feed to the incineration train will be stopped automatically when the CEMS detects any likely sign of the control parameters’ exceedance.
By: ANewR Consulting Limited, a digital environmental consultant headquartered in Hong Kong since 2008. Our expertise has grown into the context of air and water qualities, noise, green building, waste management, and remediation. With extensive know-how in environmental planning and assessment, feasibility study and policy review, ecological design, monitoring, and audit (EM&A), ANewR has matured to be a leading management consultancy. Standing in the digital transformation reign, ANewR has participated in various environmental digital projects – interactive 3D visualisation, immersive automation virtual environment, Virtual reality, automation system, and monitoring platforms.
(Website: https://anewr.com, LinkedIn: ANewR Consulting Group, Twitter: ANewR – Everyday Newer, YouTube: https://www.youtube.com/channel/UCnpvmxnR9hbNxytSfBdfV8Q/videos)