• Location : a small lake situated about 10 kilometers downstream of a paper-mill

• Paper-mill handled the recycling of waste paper containing PCBs

• How serious? Approx. 400 kg of PCBs• Coverage : whole bottom of the lake• Thickness: 0.4 m to 2 m

• PCB is a fat-soluble, water-insoluble hydrocarbon containing chlorine

• Organic compounds originally widely used in industrial processes

• Extremely stable • Withstanding temperatures of up to 870°C• Fire-resistant

• Ecology : Damages to fishes’ internal organs, development and reproduction were expected

• PCBs are not readily biodegradable • Dermal contact with PCB-contaminated

sediment (or PCB-contaminated fish or other consumable aquatic organisms )is a potential concern to human health

• Phytoremediation

•Plants extract Cd from the soil and transport into shoots and leaves

where it can accumulate

Hydraulic dredgingHydraulic dredging •Mechanical dewatering and disposal of the sediments in a landfill

Activated carbonActivated carbon •Eliminate pungent odors and to reduce bioactivity of the PCB

Advantages: Advantages: • Generates little to no secondary wastes • In the form of In-situ treatment• Aesthetically pleasing• Reduce erosion of soil• Much cheaper than most other remediation techniques

Disadvantages: Disadvantages: •Time consuming•Volatilization can release contaminants into the air•Depth limitations •Possibility of contaminant entrance into the food chain

Advantages:Advantages:

Removes organics such as petroleum hydrocarbons & pesticides Removes taste and odour-causing agents such as hydrogen sulphide Removes chlorine and ozone Removes radon

Disadvantages: Disadvantages: Needs to be replaced frequently Hard to determine if the carbon is saturated with contaminantsDo not effectively remove bacteria, nitrates or metals Provides an excellent medium for bacterial growth

Advantages: Advantages: Permanently removes contaminated sedimentNo blockades for draining requiredEntire water surface area can be reached by the dredge, Sediment-water mixture is pumped & discharged safelyMinimal disturbance to surrounding land

Disadvantages: Disadvantages: Residual sediment Sediment re-suspension/ downstream migrationPresence of boulders/debrisCostly

Hydraulic DredgingHydraulic Dredging

Although costly but:Most efficient way of removing the contaminated settlement

Minimal disturbance to surrounding landEquipment and specialist readily available

•Horizontal auger or basket-type cutter heads removes contaminated settlement•Contaminants pumped to sludge de-watering equipment with aid of slurry and Geotextile screen•Uncontaminated sediments pumped to upland dredge disposal areas for natural de-watering and re-use of material.