CONSTRUCTION WASTE HONG KONG STYLE
RECYCLING HONG KONG’S CONSTRUCTION WASTE
With its dense population and tightly packed skyscrapers, construction in Hong Kong presents many challenges, not least managing waste. Having implemented a new construction waste management policy in 2006, waste generated by the sector has fallen significantly. What can others learn from Hong Kong’s experience?
Solid waste arising from construction activities is a grave concern in Hong Kong. The latest figures show that in 2011 some 13,458 tonnes of municipal solid waste was landfilled every day, and that construction and demolition (C&D) waste accounted for around a quarter of that. In addition to the environmental impacts, construction waste places tremendous pressure on valuable landfill space in the compact city.
CHANGING BEHAVIOUR
To tackle the issue, a series of construction waste management (CWM) policies have been introduced by the Hong Kong Government. Based on the ‘polluter pays’ principle, the Hong Kong government implemented a Construction Waste Disposal Charging Scheme (CWDCS) in 2006. In line with the CWDCS, a levy of HK$125 ($16) is imposed for every tonne of construction waste a contractor disposes of in landfill.
However, the levy will be HK$100 ($13) per tonne if the waste has first been processed at off-site sorting facilities. Further, waste will be charged at just HK$27 ($3.5) per tonne if it consists of inert materials which are accepted by Public Fill Reception Facilities. It is envisaged that this will alter contractors’ behaviour.
C&D WASTE COMPOSITION
Construction waste is often a mixture of inert and non-inert construction materials. In Hong Kong, for example, the inert material, which comprise predominantly sand, bricks, and concrete, is deposited at Public Fill Reception Facilities for use in land reclamation. The non-inert portion which consists of materials such as bamboo, plastics, glass, wood, paper, vegetation and other organic materials, is buried in landfills as solid waste. It is important therefore, that the two should be properly sorted. To this end both on-site and off-site Construction Waste Sorting (CWS) are the two favoured options. However, it is all well-known that construction sites are very compact in Hong Kong and construction works are very demanding. Without enough space and time, contractors were mostly reluctant to conduct on-site sorting, and simply sent waste directly to landfills or public fill reception facilities for disposal.
To counter this, an off-site CWS program was introduced and two off-site waste sorting facilities were set up. Between from commencing operations in 2006 to February 2012, the two off-site CWS facilities have handled a total of 5.11 million tonnes of C&D waste.
SORTING PRACTICES
Owing to the price difference, there has been a significant shift in the behaviour of construction contractors, who now usually send all waste to off-site CWS facilities, or preferably to Public Fill Reception Facilities.
The first challenge was to make sure that the mixed waste received at the off-site CWS facilities is acceptable for sorting. To determine this there are a number of criteria which are applied. Furthermore, the off-site sorting facilities only accept construction waste containing more than 50% by weight of inert materials.
The qualified construction waste will then enter the first process of sorting (known as Process 1), which is performed by using a Vibratory Grizzly Feeder (VGF). In this process waste which has a radius greater than 250 mm is segregated. Further to this, mobile plant and/ or handpicking is also used at this stage.
Following this, in Process 2 magnetic separators remove metals for recycling.
In the third process the waste is passed through a heavy duty scalping screen, which is filled with holes with the radius of 150 mm. With this screening process, waste with radii ranging from 150 mm to 250 mm can be separated. This is further separated by handpicking and the use of air blowers to remove non-inert materials.
Waste with radii less than 150 mm will enter ‘Process 4’, in which it is filtered by a rotary trommel screen. Similar to the scalping screen this piece of equipment is bestrewn with hollows of radii from 50 mm to 150 mm. The separated waste is further be processed by a density separator, handpicking and air blowers to sort non-inert materials.
Finally the residual construction waste from Process 4 will pass through a conveyor belt so that non-inert materials can be sorted by handpicking. It should be noted that having gone through all four sorting processes, the mixed construction waste is eventually sorted into two piles – inert materials and non-inert. Inert materials will be sent to the public fill reception facilities and the non-inert to landfill.
The two major public fill reception facilities for receiving inert fill materials for reuse currently operate in Tseung Kwan O and Tuen Mun. They are managed by Hong Kong’s Civil Engineering and Development Department (CEDD) and have been deliberately located next to landfills.
However, in the future the adverse effects resulting from CWS processes should be investigated and corresponding mitigation measures ought to be taken.
ILLEGAL DUMPING
To prevent illegal dumping, which had been envisaged to increase following the enactment of the CWDCS, in 1999 a Trip Ticket System (TTS) was introduced. The system consists of a form which is completed by contractors and details the load of waste for disposal. This in turn generates a receipt from the sorting facility to ensure contractors comply with policy. The system ensures construction waste is properly disposed of through tracking its destination.
The system, which was enhanced in 2004, keeps track of not only the destination of the waste generated by a particular construction project, but also of the route it travelled to reach its destination.
South East New Territories Landfill in Hong Kong currently recieves around 4800 tonnes of waste per day, including construction wastes
In addition to the TTS system, policies such as the Country Parks and Special Areas Regulation and the Dumping at Sea Ordinance are in place to prevent that construction waste is illegally dumped in undesignated places.
RESULTS & RECOMMENDATIONS
On the face of it the changes to the management of C&D wastes in Hong Kong would seem to be a major success. In 1999 the city sent on average 7890 tonnes of C&D waste to landfill every day – accounting for 21% of total arisings, with the remainder being sent to public filling areas. In 2011 it sent just 6% of its C&D waste to landfill, or 3331 tonnes per day.
There has also been a significant drop in the total amount of waste generated from 40 to 70 tonnes of non-inert waste per million HK$ of construction work between 2000 and 2005, to around 20 tonnes between 2008 and 2011. The ratio of inert to non-inert waste also fell significantly.
However, while the inert materials can be used for land reclamation, over recent years there have been fewer land reclamation projects in Hong Kong. Hence, the materials received at the public filling facilities have been transported to the cities such as Huizhou or Taishan.
Promoting environment awareness amongst the whole of society as a long-term strategy has also contributed to the implementation of the off-site CWS program. Society’s awareness toward construction waste management has been significantly promoted and enhanced over recent years.
This forms a favourable institutional environment for improving the management of construction. For example, the CWDCS as well as the off-site CWS program were not introduced overnight, or without resistance. Rather, there has been a relatively long period before these regulations were accepted by stakeholders.
The elimination of loopholes is one contributor, while the increasingly improved societal environment, in particular the environment awareness, is another factor that cannot be ignored.
The CWDCS has been effective at stimulating both on-site and off-site CWS. However, with C&D waste accounting for around a quarter of total MSW generation, it still presents a significant challenge in Hong Kong. In the future, efforts should be made to increase C&D waste recycling to maximise its value and provide incentives to CWS contractors.
Dr Wilson W.S. Lu is assistant professor of real estate and construction at The University of Hong Kong, Hong Kong. e-mail: wilsonlu@hku.hk
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