Purpose and Objective of the Project
2.1 The Project aims to collect, receive and treat source-separated organic waste (mostly food waste) from commercial, industrial, and institutional establishments so as to recover reusable materials and energy, such as compost and biogas from source-separated organic waste, thereby minimizing requirement for landfill disposal.
Need
for the Project
2.2
Biodegradable organic waste
constitutes the largest portion of municipal solid waste (MSW) disposed of in
2.3
Landfilling is currently the
major disposal method for organic waste in
2.4 In December 2005, EPD published “A Policy Framework for the Management of Municipal Solid Waste in Hong Kong (2005-2014)” (Policy Framework), setting out policy tools and initiatives to be implemented for the sustainable management of MSW in Hong Kong. The Policy Framework targeted to i) increase the overall recovery rate of MSW to 45% by 2009 and 50% by 2014; and ii) reduce the total amount of MSW to be disposed of in landfills to less than 25% by 2014. It was also suggested to implement biological treatment facilities to treat source-separated biodegradable organic waste from C&I establishments.
2.5 The Project is important, not only to mitigate landfill space depletion, but because resources are conserved, and valuable products such as composts and biogas (a renewable energy) can be generated. The compost could be used as organic fertilizer for farming and horticulture. The biogas, if employed to generate electricity, could meet the electricity demand of some 2,000 households, thereby contributing to reduction in use of fossil fuel and reduction in greenhouse gas emission. In addition, organic waste diversion from landfills reduces leachate and landfill gas generation. The Project would positively contribute to the Hong Kong SAR Government’s MSW Management Policy.
Consideration
of Different Site Options
2.6
A Site Search Study was
conducted under a separate study to identify suitable sites in
Stage
1: General Site Search
2.7 Stage I aimed to produce a long list of feasible sites generated from the site search carried out by the Planning Department (PlanD) and feasible sites proposed by the EPD after preliminary screening. Findings of the Stage I exercise are summarized in Appendix 2.1.
2.8 A total of 33 potential sites were proposed by EPD. After the preliminary screening process, only 5 potential sites were considered suitable for PlanD’s site search exercise evaluation. Based on PlanD’s recommendation, only 4 potential sites as listed below, were shortlisted for Stage 2 exercise:
·
Site
1 – Sha Ling Livestock Waste Composting Plant, Sheung Shui
·
Site
2 – EcoPark Phase II, Tuen Mun
·
Site
3 – Siu Ho Wan,
·
Site
4 – TKO Area 137, Tseung Kwan O
Stage
2: Specific Site Selection
Site Selection Criteria
2.9 Locations of the 4 shortlisted sites are shown in Figure 2.1. The proposed criteria used to select the most appropriate site for the OWTF are grouped into the following 5 main areas:
·
Environmental
impact (e.g. air, noise, visual and landscape, water quality and ecology,
etc.);
·
Engineering
feasibility (e.g. accessibility, site constraints, time availability, etc.);
·
Financial
viability (e.g. capital cost and operational cost);
·
Operability
(e.g. proximity to users/producers, waste disposal and wastewater treatment,
etc.); and
·
Social
issues (e.g. compatible with broad planning intention for the site and its
surrounding landuse, etc.).
Evaluation of Shortlisted
Sites
Site 1 – Sha Ling Livestock Waste Composting Plant,
Sheung Shui
2.10
The Sha Ling Livestock Waste
Composting Plant (SLCP) is currently being used as a livestock waste composting
plant and the whole site is expected to decommission in 2010. The site comprises a total area of
2.11 With only minimal and scattered residential development nearby, the development of SLCP site for OWTF is more likely to be accepted by the community and has less environmental implications. Since the site for SLCP is currently being used as a livestock waste composting plant, this would allow large-scale OWTFs to be developed with minimal modifications leading to lower capital and operation cost. In addition, the SLCP site falls within an area zone of “Government, Institution or Community (G/IC)” on the Outline Zoning Plan (OZP) and PlanD has in principal no objection to the development of OWTF at Sha Ling.
Site 2 – EcoPark Phase II, Tuen Mun
2.12
EcoPark Phase II occupies a
total site area of about
2.13 However, according to PlanD’s comments, the development of large scale OWTF is not of the twelve approved categories of recycling process activities assessed under the EIA designated for the EcoPark (Phase II) site. While an enclosed composting process is covered by the EIA, impacts of the anaerobic digestion is not being catered for, it would much depend on the management organization on site to decide whether the proposed development would meet the criteria as set out by the Environmental Permit (EP) before commissioning. Considering these constraints, the likelihood of developing large-scale OWTF at EcoPark Phase II is low and could only be considered as a fall back option.
Site 3 – Siu Ho Wan,
2.14
Siu Ho Wan (SHW) is considered
to provide sufficient capacity for the development of large-scale OWTF. The SHW site comprises a total area of
about 2 ha with no nearby
residential development. The site can
be accessed via
2.15 Although part of the site at SHW is currently occupied by a private concrete batching plant, it is to be decommissioned and made available by 2011. In addition to the sitting advantages of established area and utilities provision, this site is considered to be highly suitable in terms of engineering feasibility. Infrastructural facilities such as sewerage and water treatment plants, refuse transfer station, etc are found in the vicinity of the SHW site. These infrastructural facilities are considered as potential users of the electricity production from biogas resulted from the organic waste treatment process.
2.16 In addition, the SHW site is zoned “G” and annotated “Possible Grease Trap Waste Treatment Facility” on the Siu Ho Wan Layout Plan, thus the proposed development of large-scale OWTF at SHW is in line with the planning intention for the site.
Site 4 – TKO Area 137, Tseung Kwan O
2.17
Tseung Kwan O (TKO) Area
2.18 During the site search study, it was noted that the site for TKO Area 137 was zoned “Other Specified Uses” annotated (Deep Waterfront Industry) on the TKO OZP and it was being used by the Fill Management Division of Civil Engineering and Development Department (CEDD) as temporary Construction and Demolition (C&D) material handling facilities. Planning permission from the Town Planning Board might be required for changing the landuse for developing large-scale OWTF subject to discussion with CEDD and Drainage Services Department (DSD). Due to the uncertainties of the site in terms of availability and neighbouring landuse, TKO Area 137 is considered as a fall back option for the development of large-scale OWTF.
2.19 Results of the evaluation are summarized in Table 2.1 below:
Table 2.1 Summary
of Assessment Results for Site Selection
|
Potential Site |
Environmental |
Engineering Feasibility |
Financial |
Operability |
Social Issues |
|
Sha Ling Livestock
Waste Composting Plant |
** |
** |
* |
** |
** |
|
EcoPark Phase II |
** |
* |
** |
* |
* |
|
Siu Ho Wan |
*** |
*** |
*** |
*** |
*** |
|
TKO Area 137 |
* |
* |
** |
* |
* |
** Preferable
*** Highly Preferable
Recommended
Site
2.21
Based on the findings of the
site search study, OWTF Phase I is proposed to be
located in the Siu Ho Wan,
2.22 Although part of the Project site is currently occupied by a private concrete batching plant, it is to be decommissioned and made available by 2011. Infrastructure facilities such as refuse transfer station, sewage treatment works, water treatment works and vehicle pound/vehicle examination and weigh station are located in the vicinity of the Project Site.
2.23 The Project is planned to be implemented through a Design, Build and Operate (DBO) contract. The Contractor will be selected through a competitive tendering exercise. Under the DBO contract, the Contractor will be responsible for the:
·
detailed
design of the facilities;
·
provision
and installation of the facilities;
·
testing
and commissioning of equipment;
·
operation
of the facilities; and
·
monitoring of operation.
Proposed
Treatment Technology for OWTF Phase I
2.24 A review of international organic waste treatment practices was carried out, the objectives and scale of the Project, and the future development of waste management facilities in Hong Kong were taken into consideration. Based on the review, anaerobic digestion (AD) and composting were shortlisted for further consideration because they were proven technologies and appear to be the most promising in terms of resource conservation.
2.25 The typical strengths and weaknesses of the AD and composting for organic waste treatment were compared and summarized in the Table 2.2.
Table 2.2
Strengths and Weaknesses of Anaerobic Digestion and Composting
|
Technology |
Strengths/Opportunities |
Weaknesses/
Constraints |
|
Anaerobic Digestion |
· Highly
applicable for organic waste including food waste · High
volume reduction of organic waste · Production
of considerable amounts of energy from waste · Reducing
greenhouse gas emission, positive effect on climate change · High
acceptance by public · Moderately
land demanding · Good
odour control · Usually
fully automated and requires minimal manpower operation, hence minimum risk
for personal exposure |
· Presence
of combustible gas, application of explosive proof instrumentation |
|
Composting |
· Well-proven
technology · Capable
to treat a large range of organic waste types · Low
manpower requirement · Reduction
of greenhouse gas and waste to be landfilled · Robust
process |
· Microbiological
and chemical exposure risk · Land
demanding · Considerably
high energy consumption and cost · Limited
flexibility for large variation in capacity · Good
odour control possible but some emission will remain · Moderate
waste volume reduction |
2.26 Considering the flexibility of the treatment system, appropriateness for the situation in Hong Kong, suitability for the treatment of organic waste with variations in quantity and composition, limitations with respect to the available space, prevention of unfavourable emission and possibly the production of energy from the organic waste, it was concluded that AD would be the most preferred option to be adopted for OWTF Phase I.
Design
Flows
2.27 A reference design of OWTF has been prepared. There are different AD processes commercially available in the market, for example, wet AD-system or dry AD-system. While the wet AD-system is suited to treat low solid content waste (solid content of 15% total solids (TS) or less), the dry AD-system are designed to treat higher solid content waste (solid content of 25% TS or more). Compared with the dry AD-system, the wet-AD system has relatively higher land requirement, environment and health implications. The wet AD-system requires more intensive pre-treatment process and greater reactors volume, and generates more biogas and wastewater from the biological treatment process. In this connection, the application of wet-AD system was therefore adopted in the reference design of OWTF, as the worst case scenario for environmental assessment.
2.28 The preliminary layout plan of the proposed buildings and facilities of OWTF is illustrated in Figure 2.2 and the process flow diagram is presented in Figure 2.3. In general, the key elements of OWTF are listed below:
·
Pre-treatment
facilities;
·
Anaerobic
digestion process;
·
Post-treatment
of digestate;
·
Energy
recovery system; and
·
Air
and wastewater treatment facilities.
2.29 OWTF Phase I will be operated on a 24-hour basis daily, while the reception of organic waste would be 14 hours per day. The collected source-separated organic waste should be transported to the Project Site by enclosed waste vehicles. In the reference design, the incoming waste would be delivered to the enclosed waste reception area and pre-treated through a trammel screen, overhead magnets and shredder, etc.
2.30
The pre-treated material would
then be fed into the buffer tanks to start the anaerobic digestion
process. From the buffer tanks, the
material would be pumped to the individual digester where a major portion of
the organic material is converted into biogas. In the reference design, five numbers of
vertical cylindrical digesters were provided, each with a design capacity of
approximately
2.31 Since the biogas generated from the digesters would be saturated with moisture and contain a small amount of particulate matters and hydrogen sulphide, these biogas would be treated by a biological desulphurisation process to remove the condensate and reduce the concentration of hydrogen sulphide to at least 250mg/m3. The treated biogas would be compressed to approximately 100mbar and stored in the form of double membrane gas buffer. The design of energy recovery system aims to convert the energy contained in the biogas to electricity and heat by the application of cogeneration units (Cogen Units). A stand-by flare was also provided for burning the surplus biogas in emergency or under abnormal circumstances.
2.32 In the reference design, a centralized air pollution control unit was provided to treat the vented air extracting from a number of operation units, including the pre-treatment and post-treatment facilities. The centralized air pollution control unit would consist of a scrubber, a biofilter and a stack. In addition, a wastewater treatment was provided in the reference design to treat the filtrate generated from the dewatering process and a small amount of wastewater produced from waste reception area, biogas handling and scrubber and truck washing facility.
Consideration of Alternative Construction
Methods and Sequences of Works
Alternative
Construction Methods
2.33 To minimize the potential environmental impacts, alternative construction methods were considered. For the piling works, percussive piles and socketted H-piles were considered. Percussive piles would cause substantial noise and vibration impacts, whereas the noise and vibration impacts due to the construction of socketted H-piles would be significantly lower. Considering the environmental benefits and dis-benefits of the alternative piling methods, socketted H-piles is recommended for this project to minimize the potential noise impact during the construction.
Alternative Sequence of Works
2.34 Concurrent construction sequence involves various construction activities occurring at the same time. The environmental benefit of this construction sequence would be the reduction of the construction period and hence the duration of impact due to the construction. However, the magnitude of the overall environmental impact could be significant.
2.35 Phased construction sequence involves construction activities being carried out one followed by another. This construction sequence would help reducing the magnitude of the overall impacts, but the construction period would be longer.
2.36 As the two approaches have their environmental benefits and dis-benefits, a balancing approach which involves a combination of concurrent and phased construction sequences in different stages of the construction will be adopted to alleviate the potential environmental impact and to meet the target commission date. For instance, the phased construction sequence would be adopted to avoid construction activities which would induce considerable noise (e.g. pilling works) to be carried out at the same time.
2.37 The construction of OWTF Phase I will commence in 2011. The OWTF is tentatively scheduled for commissioning by early 2013. The tentative project programme is shown in Table 2.3.
Table 2.3 Construction
Program
|
Description |
Tentative
Date |
|
Site Handover to EPD |
May
2011 |
|
Award of Contract |
September
2011 |
|
Site Establishment and Temporary Works
Preparation |
September
2011– May 2012 |
|
Construction of OWTF Phase I and Ancillary
Facilities |
May
2012 – March 2013 |
|
Testing and Commissioning |
March –
May
2013 |
Interactions with Other Projects
2.38 Relevant concurrent projects in the vicinity of OWTF which may have cumulative environmental impacts during its construction period are shown in Table 2.4. Cumulative impacts from the concurrent projects, if any, have been assessed in the individual section of this EIA Report.
Table 2.4 Concurrent
Projects
|
Concurrent
Projects |
Project
Proponent |
Tentative
Construction Programme |
|
Lantau Logistics Park |
Civil Engineering and Development Department
(CEDD) |
No programme available |
|
Further Landscape Enhancement Works to
North Lantau Highway |
Highways Department |
May 2010 to November 2012 |
|
Extension of Siu Ho Wan Water Treatment
Works |
Water Services Department (WSD) |
Early 2013 to end 2016 (the project programme will be further reviewed
based on the latest water demand assessment) |
|
Integration of Siu Ho Wan and Silver Mine
Bay Water Treatment Works |
Water Services Department (WSD) |
Early 2013 to 2016 |
2.39 It is noted that there are other planned developments including Tuen Mun - Chek Lap Kok Link (TM-CLKL), Hong Kong - Zhuhai - Macao Bridge Hong Kong Boundary Crossing Facilities (HKBCF) and Hong Kong - Zhuhai - Macao Bridge Hong Kong Link Road (HKLR), would be constructed and operated concurrently with the OWTF Phase I development. Since the project sites for the HKBCF and HKLR would be located far way (more than 2km) from the proposed site for OWTF Phase I development, adverse cumulative environmental impacts due to HKBCF and HKLR are therefore not expected. For the TM-CLKL, the proposed construction works in North Lantau would be land-based and any potential air quality impact from this concurrent project would be insignificant as mentioned in the respective approved EIA report, no adverse cumulative environmental impacts from this concurrent project are expected.