Sludge Treatment Facilities (STF)

Project Background

Potential Sludge Treatment Technologies

The sludge treatment technologies selected for STF should be proven and with comparable scale installations. As the key objective of the provision of STF is to further reduce the sludge volume before disposal at landfills in order to sustain the landfill life for Hong Kong, the following proven with comparable scale treatment technologies were therefore shortlisted for further evaluation:

Incineration
Heat Drying

Selection Criteria of Sludge Treatment Technology

The shortlisted sludge treatment technologies were then evaluated based on several criteria, including Environmental Acceptance, Engineering Feasibility and Financial Aspect, which could be further divided into several sub-criteria and the assessment results are shown in the following table:

Evaluation Criteria	Incineration	Heat Drying	Remarks
Environmental Acceptance
Waste Reduction	***	*	The end volume requiring landfilling after heat drying is about 2 times more than incineration
Potential for Reuse	***	*	Potential markets for salty dried pellets (which can be used as fertilizers) produced from heat drying is limited, while incineration can produce extra energy for reuse
Human Health Impacts	**	***	No adverse impact is expected from both incineration and heat drying based on the preliminary findings, however, as heat drying produces less air pollutants and is therefore has a higher score in both human health and air quality impacts
Air Quality Impacts	**	***
Water Quality Impacts	**	**
Noise Impacts	**	**
Ecological Impacts	**	**
Landscape and Visual Impacts	**	**
Engineering Feasibility
Process Performance	**	***	Process performance for both incineration and heat drying are acceptable. However, incineration has a higher potential down-time and is more complex requiring close operation control and significant maintenance expertise for proper operation
Operation and Maintenance	**	***
Operational Flexibility	*	**	Heat drying can adopt more readily to changes in calorific value than incineration
Operational Security	***	*	Heat drying has a potential dust explosion risk
Land Requirement	*	**	Incineration requires a larger footprint than heat drying
Financial Aspect
Life cycle cost	***	*	Heat drying has a higher life cycle cost due to its higher consumption of fuel and power

Note:

(1) * Less Preferable ** Preferable *** Highly Preferable

Recommended Sludge Treatment Technology

The incineration option was preferable based on environmental, engineering and financial considerations, compared to heat drying and hence was selected as the preferred sludge treatment technology for STF.