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A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong
Waste Management xxx (2015) xxx–xxx
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A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong Kok Sin Woon, Irene M.C. Lo ⇑ Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Biogas fuel Collection Food waste Optic bag Separation Waste valorization
a b s t r a c t Hong Kong is experiencing a pressing need for food waste management. Currently, approximately 3600 tonnes of food waste are disposed of at landfills in Hong Kong daily. The landfills in Hong Kong are expected to be exhausted by 2020. In the long run, unavoidable food waste should be sorted out from the other municipal solid waste (MSW) and then valorized into valuable resources. A simple sorting process involving less behavioural change of residents is, therefore, of paramount importance in order to encourage residents to sort the food waste from other MSW. In this paper, a sustainable framework of food waste collection and recycling for renewable biogas fuel production is proposed. For an efficient separation and collection system, an optic bag (i.e. green bag) can be used to pack the food waste, while the residual MSW can be packed in a common plastic bag. All the wastes are then sent to the refuse transfer stations in the conventional way (i.e. refuse collection vehicles). At the refuse transfer stations, the food waste is separated from the residual MSW using optic sensors which recognize the colours of the bags. The food waste in the optic bags is then delivered to the proposed Organic Waste Treatment Facilities, in which biogas is generated following the anaerobic digestion technology. The biogas can be further upgraded via gas upgrading units to a quality suitable for use as a vehicle biogas fuel. The use of biogas fuel from food waste has been widely practiced by some countries such as Sweden, France, and Norway. Hopefully, the proposed framework can provide the epitome of the waste-to-wealth concept for the sustainable collection and recycling of food waste in Hong Kong. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction The disposal of mounting municipal solid waste (MSW) is an imminent problem for Hong Kong society. Currently, Hong Kong relies mainly on landfills for MSW disposal. In 2012, approximately 9000 tonnes of MSW were disposed of in the landfills every day. It is anticipated that the current three strategic landfills in Hong Kong, namely South East New Territories, North East New Territories, and West New Territories, will reach their maximum capacities by 2020 (HKEPD, 2013a). Of the 9000 tonnes of MSW disposed of at landfills, about 3600 tonnes is food waste, representing the largest waste component of MSW in Hong Kong. Food waste in Hong Kong generally refers to the organic waste generated during food production and processing, wholesale and retail preparation, after meal leftovers, and expired foods. The food waste per capita in Hong Kong is comparatively higher than those of other Asian cities of similar economic status. For example, the food waste per capita in Hong Kong is about 2 times higher than ⇑ Corresponding author. Tel.: +852 23587157; fax: +852 23581534. E-mail address: [email protected] (I.M.C. Lo).
those in Singapore and South Korea. In addition, the food waste recycling rate is low in Hong Kong (0.6%), which is far below compared to other urban cities in Asia such as South Korea (95%), Taiwan (31%) and Japan (25%) (MOE, 2012; LegCo, 2013; EPA, 2014a,b). The current practice of disposing food waste at landfills is not a sustainable approach in Hong Kong, as it incurs fast depletion of landfill space, generates odour nuisance, and produces greenhouse gases and leachates, thus causing severe adverse environmental problems. A landfill ban on organic waste has been practiced by a few countries. In South Korea and Sweden, a banning disposal of food waste at landfills has been imposed since 2005. In Germany, zero disposal of biodegradable municipal waste at landfills has been reported since 2006. Similarly in Norway, a landfill ban on biodegradable waste was enforced in 2009. Meanwhile, the accelerating human population growth and growing global energy demand in the society have stimulated rigorous research efforts to valorize waste to resource in order to meet such global targets. The security of supply energy may likely become an increasingly important aspect of decision making for developing a sustainable city. Due to these circumstances, unavoidable food
http://dx.doi.org/10.1016/j.wasman.2015.03.022 0956-053X/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Woon, K.S., Lo, I.M.C. A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.03.022
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K.S. Woon, I.M.C. Lo / Waste Management xxx (2015) xxx–xxx
waste should be collected systematically and valorized to a valueadded product for advancing environmental sustainability and economic development.
2. Proposed framework of food waste collection and recycling for renewable biogas fuel in Hong Kong Among the 3600 tonnes of food waste generated daily, domestic households give rise to about 2500 tonnes, while around 1100 tonnes come from food associated with commercial and industrial (C&I) sources (HKEB, 2014). Assuming that the food waste collection rates of domestic household and C&I sectors are 50% in the future, the total food waste collection rate in Hong Kong is about 1800 tonnes per day (tpd). This amount renders a massive challenge to society if the collected food waste is not recycled and valorized to a value-added product, as far as possible. A systematic food waste separation and collection system, together with environmentally friendly food waste valorization technologies is, therefore, imperative in order to form a sustainable food waste management framework in Hong Kong. In light of this need, a sustainable framework of food waste collection and recycling for valorizing the food waste to renewable biogas fuel is proposed in this study. The proposed framework is established in consideration of the food waste collection and recycling systems in certain cities such as Oslo in Norway, Linköping in Sweden, and Lille in France, as well as with reference to the food waste management environment and community needs in Hong Kong. The proposed framework of the food waste collection and recycling for the food waste valorization in Hong Kong is shown in Fig. 1, and consists of three parts: (i) food waste separation at source and collection; (ii) food waste valorization to value-added products; and (iii) other MSW treatment. It is hoped that the proposed framework can also act as a reference for other urban cities that face a food waste disposal dilemma similar to Hong Kong’s environmental conditions.
3. Proposed optic bag system for food waste separation and collection at source in Hong Kong Source separation is a critical step in dealing with the increasing problem of food waste in society prior to transporting the food waste to various recycling facilities. In Hong Kong, most of the food waste, particularly the food waste from domestic households, is not sorted out from other types of MSW prior to discarding in the three strategic landfills. Residents, nevertheless, are responsible for separating the food waste from the other MSW produced in their home. If the residents fail to sort the food waste at source, the food waste will be contaminated and cannot then be recycled. A complicated sorting process in households, however, can discourage the residents from sorting their waste. A less behavioural change of the public is needed for the collection and separation of food waste. This is important to reduce any changes that might affect the lifestyle of the public and minimise potential impacts on the livelihoods of the public. In addition, the food waste collection system should be reasonably practicable built based upon the existing waste management system. By doing so, the public will not be required to travel to a new place or change their daily routine substantially for the sorting of food waste, and thus be more willing to take part in separating food waste at source. As such, a simple sorting process needing less behavioural change by residents is a key part in order to motivate the residents to sort the food waste from the other MSW. In order to achieve this objective, food waste and other types of MSW can be efficiently separated via an optic bag system.
By introducing the optic bag system, food waste will be packed in an optic bag (e.g. a bag in green colour), while the residual MSW will be packed in a common plastic bag or a pre-paid designated bag if MSW charging scheme is implemented by the Hong Kong Special Administration Region (HKSAR) Government. The optic bag comes in two sizes, which are 10 l size with 270 mm width 130 mm depth 480 mm height and 30 l size with 300 mm width 220 mm depth 640 mm height (Mepex, 2014). All the packed wastes will still be disposed of at the existing collection bins or rubbish chutes. By doing so, it will avoid the need for the households and C&I sectors to reconfigure the waste storage space in their properties. All the wastes will then be collected by the refuse collection vehicles and transported to the respective refuse transfer stations in Hong Kong. As such, no changes to collection routines are required. It is observed that the optic bag is comparatively thicker than the common plastic bag used in Hong Kong. In Oslo, Norway, the optic bag remains intact in the optical sorting plant after it is transported via refuse transfer vehicles. The refuse transfer vehicles used in Oslo are of similar configuration (i.e. with rear compactor) to those in Hong Kong. Hence, it is believed that the optic bag will not be damaged when it arrives at the refuse transfer stations in Hong Kong. Upon arrival at the refuse transfer stations, all the waste bags will be unloaded into a receiving pit. At this point, the optic bags have yet to be separated from the other bags. All the bags will then be sent to a main conveyor belt, in which an optic sensor technology will be used to sort the bags. The green colour of the optic bag allows the optical camera in the sorting plant to identify and sort the optic bag from the other plastic bags automatically. When an optic bag of green colour (i.e. food waste) is detected, a signal will be sent to push the green bag off the main conveyor belt to a second belt. An Enviflex system (i.e. an automatic bag-opener and breaker of food waste) can be employed to separate the collected food waste from the optic bag. In the system, a hydraulically driven roller will be used to open the optic bag. The optic bag will be pulled in a long strip and the food waste will be broken into pieces of approximately 35–50 mm. The food waste and the optic bag will then be screened for separation. Finally, the food waste will be compacted and containerized in purposely built containers and then transported to various food waste recycling facilities for further treatment. Meanwhile, the other residual MSWs such as plastics and papers, which are packed in common plastic bags, will be sent to a proposed advanced incineration facility. After combustion, the heat generated will be used in a steam turbine for generating electricity. The HKSAR Government is going to launch the MSW charging scheme based on a quantity-based system. According to this system, the waste charge could be introduced through the mandatory use of pre-paid designated garbage bags. The optic bag can be assigned as one of the pre-paid designated garbage bags for packaging food waste (the cost of an optic bag is about 0.1 Swedish Krona (SEK) or 0.1 Hong Kong Dollar (HKD) based on Swedish case), while the other pre-paid designated garbage bags can be used for the disposal of other types of MSW. To promote the implementation of optic bag system in Hong Kong, the HKSAR Government should work hand-in-hand with local industry, consumers and communities. It can be done through education by fostering positive behaviour change along with legislation, such as mandatory use of optic bag for packaging food waste or food waste disposal ban in strategic landfills. 3.1. Applications of optic bag system in other countries The optic bag system has been applied in several countries especially in European countries such as Sweden and Norway. An optical sorting plant can be constructed in many different forms
Please cite this article in press as: Woon, K.S., Lo, I.M.C. A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.03.022
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(i) Food waste separation at source and collection
Food waste
Other MSW
Packed in an optic bag (i.e., green bag)
Packed in a common plastic bag or designated bag if MSW charging is launched
Discard at existing collection bins or rubbish chutes Deliver to refuse transfer stations via refuse collection vehicles Unload all waste bags into a receiving pit. The waste bags are sent to a main conveyor belt
Separate the food waste and other MSW using optic sensor installed in the refuse transfer station
Food waste
Other MSW
To assorted food waste recycling facilities
To proposed advanced incineration facility
Compost, swine feed, fish feed
Renewable biogas
Electricity, city gas
Recovered energy
Biogas fuel for vehicle use
(ii) Food waste valorization to value-added products
Electricity
(iii) Other MSW treatment
Fig. 1. Proposed framework of food waste collection and recycling for food waste valorization in Hong Kong.
and configurations in order to meet the specific requirements. Typically, the capital cost of an optical sorting plant with an annual treatment capacity of around 30,000 tonnes for the sorting of two fractions (i.e. optic bag and other residual waste bags) is about 30 million SEK or 29 million HKD, based on a plant in Sweden in 2011 (OptiBag, 2014). In Linköping, Sweden, the optic bag system has also been operated by a waste collection company called Tekniska verken. About 80% of the domestic households in this city have adopted the optic bag system (Book, 2014). Fig. 2 illustrates a simplified flow diagram for separating the optic bag from other bags in an optical sorting plant operated by the Tekniska verken company. Based on the performance of the optical sorting plant, the food waste fraction can be collected with a high level of purity, with an
optimum separation efficiency of 98% (Tekniska verken, 2012). Optic bags that are not detected accurately or any loose materials that pass through the optical sorting system are treated as residual fractions. In Oslo, Norway, the Haraldrud sorting plant has adopted optic bag sensor technology since 2009. The plant handles approximately 150,000 tonnes/year of food waste and is currently the world’s largest optical sorting facility for separating food waste from other household wastes (Envac, 2014). Experience from this city suggests that the residents quickly accept this type of waste sorting system. Other examples of optical sorting plants with two fractions (i.e. food waste and other residual wastes) can be found in cities such as Södertälje and Borås in Sweden, Øras and Mo i Rana in Norway, and Jakobstad in Finland.
Please cite this article in press as: Woon, K.S., Lo, I.M.C. A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.03.022
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Optic bag (i.e., green bag)
All bags are dumped into a receiving pit
All bags are sent to a conveyor belt
Optic bags and common plastic bags are separated using an optic sensor
Optic bags with food waste are collected in a container Fig. 2. Simplified process flow diagram of an optical sorting plant in Linköping city, Sweden.
4. Valorization of food waste to value-added products in Hong Kong In order to promote the waste-to-wealth concept, collected food waste should be valorized to a value-added product after the separation and collection processes. After separating and collecting the food waste efficiently, the sorted food waste can be sent to various food waste recycling facilities and recycled as a source of valuable material or as a source of renewable energy in the case of Hong Kong. As a source of valuable material, the food waste can be valorized as compost or animal feed such as swine feed and fish feed. As a source of renewable energy, the food waste can be converted into electricity, city gas (i.e. heating fuel for cooking purpose), and biogas fuel for vehicle use.
4.1. Valorization of food waste to compost, swine feed and fish feed There are a few companies currently practicing the aforementioned conversion of food waste into different valuable materials in Hong Kong, such as Kowloon Bay Pilot Composting Plant (turning food waste to compost), Green Environmental Kitchen Residue Recycle Limited and Hong Kong Organic Waste Recycling Centre (turning food waste into swine feed), and Kowloon Biotechnology
Limited (turning food waste to fish feed). In addition, a food waste processing plant in the Hong Kong Ecopark with a treatment capacity of 200 tpd is expected to be commissioned in 2015 in order to produce high protein fish feed. In Asian countries such as South Korea, Taiwan and Japan, more than 40% of the food waste is processed into compost, swine feed, and fish feed to partly substitute for chemical fertilizers and conventional feed ingredients. There are, however, some challenges in valorizing food waste to compost, swine feed, and fish feed in Hong Kong. The recycling of food waste into compost, swine feed, and fish feed in Hong Kong is low mainly due to the diminishing agricultural and fisheries industries. Hence, the current food waste recycling rate in Hong Kong is relatively lower compared to these Asian countries. It is projected that the demands for compost, swine feed and fish feed in Hong Kong are only about 340 tpd, 170 tpd, 10 tpd of food waste, respectively. For the valorization of food waste to swine feed, it is not encouraged by the Agriculture, Fisheries and Conservation Department of the HKSAR Government. This is because recycling of food waste into animal feed requires caution due to the fact that food waste can be a medium for spreading contagious diseases. Some notifiable diseases, namely foot and mouth disease, swine fever, highly pathogenic avian influenza, and transmissible spongiform encephalopathies (TSEs), have been identified in the conversion of food waste to
Please cite this article in press as: Woon, K.S., Lo, I.M.C. A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.03.022
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animal feed processes (DARD, 2013). To avoid disease transmission, the European Commission has prohibited this practice since 2002, as stated in Regulation (EC) No. 1774/2002. Meanwhile, the export of feed products to the other countries or regions, such as mainland China can be difficult, mainly due to license and regulatory hurdles. For example, a feed factory license from the HKSAR Government is necessary in order to apply for a feed import license from the Ministry of Agriculture of the Chinese Central Government (AQSIQ, 2014). Due to these challenges, it is not feasible to valorize all collected food waste to compost, swine feed, and fish feed in Hong Kong. 4.2. Renewable biogas generation from proposed Organic Waste Treatment Facilities As abovementioned, the local market for compost, swine feed, and fish feed can only account for about 520 tpd of food waste. Based on the assumed food waste collection rate of 1800 tpd and the market demand of compost, fish feed, and swine feed in Hong Kong, there is still about 1280 tpd of collected food waste that remains to be recycled. In this context, the feasibility of valorizing the food waste into sources of renewable energy should be explored. The HKSAR Government has recently published a government report entitled ‘‘A Food Waste and Yard Waste Plan for Hong Kong 2014–2022’’. In the report, the HKSAR Government envisages that Hong Kong needs to build a network of Organic Waste Treatment Facilities (OWTF) in different locations between 2014 and 2024 in order to recycle food waste. In the OWTF, the food waste will undergo an anaerobic digestion process, producing biogas that can be recovered for energy generation. Two phases of the OWTFs have been proposed by the HKSAR Government. Phase 1 and phase 2 of the OWTFs are planned to be located at Siu Ho Wan in North Lantau Island and Shaling at North District of New Territories, respectively. For OWTF phase 1, it is expected that 200 tpd of food waste will be treated, while 300 tpd of food waste will be treated by OWTF phase 2. The design and construction of OWTF phase 1 began in 2014 and it is expected to be commissioned in 2016. Meanwhile, the design and construction of OWTF phase 2 will begin in 2015 and it is projected to be commissioned in 2017 (HKEPD, 2013b). However, it should be pointed out that the proposed OWTFs phase 1 and phase 2 are only able to accommodate 500 tpd food waste. Hence, it is expected that 3 or 4 more OWTFs, each with a proposed capacity of 200–300 tpd, need to be constructed in order to consume the remaining 780 tpd food waste (i.e. after the demand of compost, swine feed, fish feed, phase 1 and 2 of OWTFs). For OWTF phase 1, the biogas produced from the OWTF will be used as a renewable energy for electricity generation. It is estimated that about 14 million kW h/year of surplus electricity can be generated from the OWTF phase 1 and sent to the power grid, which is adequate for use by 3000 households (HKEPD, 2013b). The energy recovery system in the OWTF is beneficial to food waste recycling. This is attributed to the fact that it reduces the amount of fossil fuels in the fuel mix for electricity generation in Hong Kong, thus reducing the environmental pollution and greenhouse gas emissions. Nevertheless, the HKSAR Government is obligated to collaborate with the power companies in Hong Kong (i.e. China Light & Power and Hong Kong Electric) in employing the electricity generated from the OWTF. Negotiations with the power companies in transmitting the excess electricity to the grid are necessary and there is a possibility that the power companies might not want the electricity generated from the OWTF. In addition, a combined heat and power (CHP) will be used to generate the electricity in the OWTF. The efficiency of electricity generated by the CHP, nonetheless, is expected to be low and the heat produced
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will not be applied in Hong Kong. Besides converting the biogas into electricity, another alternative is to valorize the biogas to city gas and to use for cooking in domestic households. The conversion of biogas to city gas, however, faces the same challenge as turning biogas into electricity. The HKSAR Government also needs to negotiate with the Hong Kong and China Gas Company Limited (i.e. Towngas company) in using the biogas. Hence, there is also a possibility that the Towngas company might not want to be involved in the purchase of biogas produced from the OWTF.
5. Valorization of food waste to renewable biogas fuel for vehicle use in Hong Kong More alternatives should be explored in order to utilize the biogas generated from the OWTF. For OWTF phase 1, the biogas generated after the anaerobic digestion process has been proposed to be used as electricity (LegCo, 2014). Nevertheless, the use of biogas generated from the OWTF phase 2 is yet to be confirmed. In view of the caveats encountered when turning the food waste into electricity or city gas in Hong Kong, the biogas generated from the phase 2 or later phases of OWTF is recommended to be upgraded to a quality suitable for use as a vehicle biogas fuel. Using advanced biogas upgrading technologies, the methane (50–70% by volume in raw biogas) and carbon dioxide (25–45% by volume in raw biogas) can be separated effectively and efficiently, turning the biogas into biogas fuel for vehicle use. There are a lot of existing biogas upgrading technologies available in the market, such as pressure swing adsorption, water scrubbing, amine scrubbing, and membrane separation. Table 1 shows some of the key parameters (e.g. energy requirement, methane losses, technical availability per year, etc.) of various biogas upgrading technologies. Yliopisto (2013) reported that water scrubbing is the most suitable process for most large-scale systems (>100 N m3 biogas/h), while membrane separation system appears to be most suitable for smallscale systems (<100 N m3 biogas/h). Sweden is considered the most advanced country in terms of the application of biogas upgrading technologies. Currently, there are 32 biogas upgrading plants in Sweden located in cities such as Stockholm, Linköping, Falkenberg, and Göteborg (Patterson et al., 2011). By using biogas fuel from food waste, it reduces the use of imported fossil fuel supplies, as well as significantly providing lower emissions of greenhouse gases, nitrogen oxides and particles, compared to petrol and diesel fuel. Papacz (2011) reported that biogas-fuelled vehicles can reduce greenhouse gas emissions by between 75% and 200% compared with fossil fuels. Francis and Bell (2008) stated that each bus running on biogas fuel in Linköping, Sweden, contributes to reducing CO2 emissions by 90 tonnes/year and NOx emissions by 1.2 tonnes/year. Table 2 shows the consumption of different types of fuels for light good vehicles, heavy good vehicles, and buses. For a travel distance of 100 km, the consumption of biogas fuel is about 10.6% less compared to petrol. In view of economic perspective, Murphya et al. (2004) highlighted that the use of biogas fuel for vehicle use has the potential to save 0.39 EUR/N m3 (3.99 HKD/N m3) as a petrol substitute and 0.28 EUR/N m3 (2.87 HKD/N m3) as a diesel substitute. These savings are comparatively higher than turning the biogas into heat and electricity (0.19 EUR/N m3 or 1.94 HKD/N m3 in a combined heat and power plant, 0.143 EUR/N m3 or 1.46 HKD/ N m3 for electricity-only production). Biogas fuelled cars can be imported by the HKSAR Government for the implementation of biogas fuel for vehicle use in Hong Kong. Biogas fuelled cars are currently factory-made by several major car manufacturers such as Mercedes-Benz, Volkswagen, Ford and Volvo. The biogas fuel can be firstly used by the government service cars in the various government departments, since the
Please cite this article in press as: Woon, K.S., Lo, I.M.C. A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.03.022
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Table 1 Key parameters of the biogas upgrading technologies. Biogas upgrading technology
Energy requirement (kWh/m3 of upgraded biogas)
Methane losses (%)
Technical availability per year (%)b
Cost of upgraded biogas (HKD/m3)g,j
Methane concentration in the product gas stream (by volume %)h
Pressure swing adsorption
2a
94
2.39i
>98
<2a
96
1.38i
>98
Amine scrubbing
0.5–0.6a 0.240b 0.335c 0.285d 0.300a 0.200b 0.430c 0.391d 0.646c 0.126d
<0.1a
91
1.56
>99.8
Membrane separation
0.769c 0.378e
>10f
98
2.02i
98
Water scrubbing
a b c d e f g h i j k
Example of city/country applying the technologyk – Bachenbülach, Switzerland (1996) – Helsingborg, Sweden (2002) – Linköping, Sweden (1997) – Lille, France (2007) – Borås, Sweden (2002) – Stavenger, Norway (2009) – Berthierville, Canada (2003) – Bruck an der Leitha, Austria (2008)
Adapted from Persson (2007). Adapted from Beil and Hoffstede (2009). Adapted from Berndt (2006). Adapted from Günther (2007). Adapted from Miltner et al. (2008). Adapted from Dirkse (2008). Adapted from de Hullu et al. (2008). Adapted from Bauer et al. (2013). The cost is associated to plants with an output of between 200 and 300 N m3/h upgraded biogas. Currency exchange rate: 1 HKD to 0.11 EUR. Number in the bracket indicates the beginning year of operation.
Table 2 Fuel consumption for each vehicle categorya. Type of fuel
Fuel consumption (kg/100 km) Light good vehicle (LGV)
Petrol Diesel Biogas fuel
6.93 5.95 6.19
Heavy good vehicle (HGV)b d
N/A 31.40 34.65
Busc N/Ad 44.84 48.28
Note: a Adapted from NSCA (2006). b HGV is based on 38 tonnes articulated truck. c Bus is based on 88-seats double deck bus. d N/A stands for not applicable.
HKSAR Government is not required to deal with any private companies for its implementation. For example, the HKSAR Government can introduce biogas refuse collection vehicles for the Food and Environmental Hygiene Department. Through the use of biogas refuse collection vehicles, it promotes a sustainable closed-loop system in the food waste management framework in Hong Kong. This is because the food wastes are turned into biogas fuel for the biogas refuse collection vehicles that collect these food wastes. Besides, the HKSAR Government can introduce biogas fire trucks for the Fire Services Department, biogas ambulances for the Department of Health, and even biogas police cars for the Hong Kong Police Force. The use of biogas fuel for vehicle use can be extended to private cars. Hafeez (2013) stated that the biogas generated from 1 kg of food waste equals to about 0.13 l petrol. This biogas allows a private car, with an engine size of 2501– 3500 cc and an average consumption of 14 l/100 km (EMSD, 2013), to drive 0.93 km/kg treated food waste. Considering the 1080 tpd food waste treated in phase 2 or later phases of OWTFs, it is estimated that about 140,600 l petrol will be produced daily. Assuming the private car is travelled 100 km/day, the biogas fuel generated from food waste can be used to fuel approximately 10,000 private cars/day (about 2.2% of the total private cars in Hong Kong), helping to reduce the CO2 emissions by about 80,000 tonne/year (about 1.1% of the total emitted amount by
the transport sector in Hong Kong in 2011). To encourage the use of biogas fuelled cars by the Hong Kong public, the HKSAR Government can provide incentive and tax reductions if biogas fuelled cars are bought by the users. To further enhance the use of biogas fuel, the HKSAR Government can negotiate with the Hong Kong city bus (e.g. Kowloon Motor Bus) and taxi companies in order to promote the use of biogas fuel in public transport. 5.1. Application of food waste as renewable biogas fuel for vehicle use in other countries The use of biogas fuel produced from food waste has been extensively adopted by some European cities such as Linköping and Stockholm in Sweden, Lille in France, and Oslo in Norway. Table 3 summarizes the production and distribution of biogas, as well as the biogas vehicles in use in these respective cities. For example, a biogas plant in Linköping has an annual treatment capacity of 100,000 tonnes food waste, produces 4.7 million m3 of upgraded biogas fuel that is used in 89 public buses and over 1000 personal cars (IEA, 2005; Martin, 2009). In Linköping city, food waste produces sufficient biogas fuel for about 6% of registered vehicles, including the fleet of city buses and taxis (Cleantech Östergötland, 2014). Fig. 3 shows some of the photos of the biogas fuelled personal cars and biogas fuelled public buses, as well as the biogas filling stations in Linköping city. The distribution networks for biogas in Linköping are well-developed. The distribution networks connect the refueling stations with the production plants via biogas grid, hence minimising road bound transportation. A series of economic incentives, such as no tax on biogas as vehicle fuel, lower tax on biogas fuelled vehicles, exclusion from city gate tolls for biogas vehicles, and even free parking for biogas vehicles, have been promulgated by the Swedish Government in order to promote the use of biogas fuel in private cars (NSCA, 2006). To promote the development of biogas fuel for vehicle use, the European Commission has established an initiative called the Biogasmax project to reduce reliance on fossil fuels and reduce
Please cite this article in press as: Woon, K.S., Lo, I.M.C. A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.03.022
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Table 3 Summary of some European cities that have adopted the biogas fuel for vehicle use. Country
City
Inhabitants
Sweden
Linköping
0.14 million
– A biogas plant with an annual treatment capacity of 100,000 tonnes food waste, producing 4.7 million m3 of upgraded biogas fuel – 12 public biogas filling stations as of 2005
Swedenb
Stockholm
0.91 million (municipality area)
Franceb
Lille
1.1 million
Norwayc
Oslo
0.59 million
– 11 biogas refueling station as of 2007 – As the demand is exceeded the Stockholm’s biogas production capacity, supply of biogas is bought from city of Linköping and Västerås (distributed via lorry) – An Organic Recovery Center (ORC) with an annual treatment capacity of 108,000 tonnes of food waste, producing 4 million m3/year of biogas – The waste collection truck depot and bust depot are located next to the ORC (i.e. minimise the distance of distribution via dedicated pipeline) – A biogas plant located in Nes, Romerike treats 50,000 tonnes/ year of food waste, producing 14,000 m3/day of upgraded biogas
a
a b c
Production and distribution
Use in vehicles – All the diesel buses in operation have been replaced by biogas fuelled buses since 2002 – The world’s first biogas train with operated range of 600 km (between Linköping and Västervik) became operational in Linköping in 2005 – There are over 1000 personal cars and 89 public buses fuelled by biogas as of 2008 – 25 heavy duty vehicles including 16 waste collection vehicles and 9 public buses – 80 light duty vehicles (e.g. taxis and personal cars) – 10 heavy duty waste collecting biogas vehicles as of 2009 – 289 gas-driven buses (fuelled by a mixture of upgraded biogas and compressed natural gas) as of 2009 (80% of all buses in the city) – 135 municipal buses are operated by biogas fuel as of 2013
Information is summarized and adapted from IEA (2005) and Martin (2009). Information is summarized and adapted from Pädam et al. (2010). Information is summarized and adapted from Wärtsilä (2014).
(i)
(ii) Biogas fuelled car capable of running on biogas fuel and petrol
(iii)
(iv)
Fig. 3. Photos of (i) biogas fuelled car; (ii) biogas fuelled car filling station; (iii) biogas fuelled public bus; and (iv) biogas fuelled bus filling station in Linköping city, Sweden.
greenhouse gas emissions by providing information on more efficient production, distribution and use of biogas fuel in the transport sector (Biogasmax, 2010). A network of biogas-related large scale demonstrations has been created on certain countries (e.g. Sweden, France, Switzerland, etc.) with the purpose of sharing experience in terms of best practice in managing urban transportation. Through the introduction of biogas fuel from food waste, it provides welfares to the local community both economically and environmentally. This is because the resources used are from local food waste, and the end-use is in vehicles from the local community.
6. Conclusions A food waste management framework is proposed for separating, collecting, and valorizing the food waste effectively in Hong Kong. The benefits and ways of implementation of the optic bag system in Hong Kong are explained in this paper. It is expected that the simplicity of the optic bag system can render a less behavioural change of householders, and thus to encourage the Hong Kong public to implement food waste separation at source. This paper also discusses the conversion of food waste to biogas as a renewable energy source, particularly to the potential application as
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biogas fuel for vehicle use in Hong Kong. Through the implementation of the proposed framework, the framework can hopefully provide a simple yet effective approach to food waste separation at source, and promote the sustainable use of food waste as a renewable energy in urban cities like Hong Kong. References AQSIQ, Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China, 2014. Quarantine Access Procedures for Agricultural Products to be Imported to China for the First Time. (accessed 20.08.14). Bauer, F., Hulteberg, C., Persson, T., Tamm, D., 2013. Biogas Upgrading – Review of Commercial Technologies. Svenskt Gastekniskt Center AB, Malmö, Sweden. Beil, M., Hoffstede, U., 2009. Biogasmax: overview on biogas upgrading technologies. In: European Biomethane Fuel Conference, Göteborg, Sweden. Berndt, A.S., 2006. CarboTech Engineering GmbH, Intelligent Utilisation of Biogas – Upgrading and Adding to the Grid, Jönköping, Sweden. Biogasmax, 2010. 2006/2010 The Synthesis, European Commission, Lille Métropole, France. Book, J., 2014. Global Sustainable Cities Network (GSCN): Experience from the Tekniska verken/City of Linköping’s Long Term Ownership and Management of Municipal Waste, Tekniska Verken, Linköping, Sweden. Cleantech Östergötland, 2014. The Twin Cities of Sweden – Linköping and Norrkoping. (accessed 10.06.14). DARD, Department for Agricultural and Rural Development of the United Kingdom, 2013. Food and Feed Businesses. (accessed 3.10.14). de Hullu, J., Maassen, J., van Meel, P., Siamak, S., Vaessen, J., Bini, L., Reijenga, J., 2008. Biogas Upgrading: Comparing different Techniques. Eindhoven University of Technology, The Netherlands. Dirkse, E.H.M., 2008. Biogas Upgrading Using the DMT TS-PWS Technology, DMT Environmental Technology, Heerenveen, the Netherlands. EMSD, Electrical and Mechanical Services Department, 2013. Transport – Energy Consumption Indicator. (accessed 14.02.15). Envac, 2014. Optical sorting plant. (accessed 10.12.14). EPA, Environmental Protection Administration of Taiwan, 2014a. Collection of Municipal Solid Waste by All Organizations, Solid Waste Statistics, Taiwan. EPA, Environmental Protection Administration of Taiwan, 2014b. Properties of Municipal Solid Waste, Solid Waste Statistics, Taiwan. Francis, A., Bell, H., 2008. The Impact of Transport: Sustainable Transport Report. BioRegional Consulting Ltd., Surrey, The United Kingdom. Günther, L., GmbH Presentation, D.G.E., 2007. Purification of Biomethane using Pressureless Purification for the Production of Biomethane and Carbon Dioxide. Innogas, Finland. Hafeez, M.H., 2013. Comparison of Solid Waste Management between Oslo (Norway) and Lahore (Pakistan), Department of International Environment and Development Studies, Norwegian University of Life Sciences, Master Thesis.
HKEB, Hong Kong Environment Bureau, 2014. A Food Waste and Yard Waste Plan for Hong Kong 2014-2022. HKEPD, Hong Kong Environmental Protection Department, 2013a. Strategic Landfills. (accessed 27.06.14). HKEPD, Hong Kong Environmental Protection Department, 2013b. Organic Waste Treatment Facilities. Hong Kong. IEA, International Energy Agency, 2005. 100% Biogas for urban transportin Linköping, Sweden: Biogas in Buses, Cars and Trains, IEA Bioenergy Task 37, Paris, France. LegCo, Legislative Council of the Hong Kong Special Administrative Region, 2013. Report of the Delegation of the Panel on Environmental Affairs on the Duty Visit to the Republic of Korea to Study its Experience on Waste Management. (accessed 5.01.15). LegCo, 2014. Item for Public Works Subcommittee of Finance Committee, Organic Waste Treatment Facilities Phase 1, PWSC(2014-15)1, Hong Kong. Martin, M., 2009. The ‘‘Biogasification’’ of Linköping: A Large Technical Systems Perspective. Linköping University, Sweden. Mepex, 2014. Optical Bag Sorting Plant: Prequalification for a Turnkey Contract of Electro-mechanical Delivery. 426-940. E0001.A02. Skien, Norway. Miltner, M., Makaruk, A. Harasek, M., 2008. Application of Gas Permeation for Biogas Upgrade – Operational Experiences of Feeding Biomethane into the Austrian Gas Grid. In: 16th European Biomass Conference and Exhibition, Valencia, Spain. MOE, Ministry of the Environment of Japan, 2012. Generation of Food Waste and Treatment Status, Environmental Statistics 2008, Japan. Murphya, J.D., McKeoghb, E., Kielyb, G., 2004. Technical/economic/environmental analysis of biogas utilization. Appl. Energy 77 (4), 407–427. NSCA, National Society for Clean Air and Environmental Protection, 2006. Biogas as a Road Transport Fuel: An Assessment of the Potential Role of Biogas as a Renewable Transport Fuel, Brighton, United Kingdom. OptiBag, 2014. Financial: Rational and Cost-effective Waste Management. (accessed 10.09.14). Pädam, S., Waluszewski, D., Rehnlund, B., Hugosson, B. 2010. Biomethane Vehicles in Five European Cities, Biogasmax Integrated Project. RTD Contract No: 019795, European Commission. Papacz, W., 2011. Biogas as vehicle fuel. J. KONES Powertrain Transport 18 (1), 403– 410. Patterson, T., Esteves, S., Dinsdale, R., Guwy, A., 2011. An evaluation of the policy and techno-economic factors affecting the potential for biogas upgrading for transport fuel use in the UK. Energy Policy 39, 1806–1816. Persson, M., 2007. Biogas upgrading and utilisation as a vehicle fuel. In: Proceedings of the Future of Biogas in Europe III, University of Southern Denmark. Tekniska verken, 2012. Extract and Free Translation of the Annual Report 2012, Linköping, Sweden. Wärtsilä, 2014. Wärtsilä Biogas Liquefaction Plant EGE Biogas, Wärtsilä Corportion, Oslo, Norway. Yliopisto, J., 2013. D5.1 – Evaluation of Potential Technologies and Operational Scales Reflecting Market Needs for Low-cost Gas Upgrading Systems. VALORGAS: Valorisation of Food Waste to Biogas, Grant Agreement No.: 241334, Seventh Framework Programme Theme Energy: Biowaste as Feedstock for 2nd Generation. European Union.
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A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong Kok Sin Woon, Irene M.C. Lo ⇑ Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Biogas fuel Collection Food waste Optic bag Separation Waste valorization
a b s t r a c t Hong Kong is experiencing a pressing need for food waste management. Currently, approximately 3600 tonnes of food waste are disposed of at landfills in Hong Kong daily. The landfills in Hong Kong are expected to be exhausted by 2020. In the long run, unavoidable food waste should be sorted out from the other municipal solid waste (MSW) and then valorized into valuable resources. A simple sorting process involving less behavioural change of residents is, therefore, of paramount importance in order to encourage residents to sort the food waste from other MSW. In this paper, a sustainable framework of food waste collection and recycling for renewable biogas fuel production is proposed. For an efficient separation and collection system, an optic bag (i.e. green bag) can be used to pack the food waste, while the residual MSW can be packed in a common plastic bag. All the wastes are then sent to the refuse transfer stations in the conventional way (i.e. refuse collection vehicles). At the refuse transfer stations, the food waste is separated from the residual MSW using optic sensors which recognize the colours of the bags. The food waste in the optic bags is then delivered to the proposed Organic Waste Treatment Facilities, in which biogas is generated following the anaerobic digestion technology. The biogas can be further upgraded via gas upgrading units to a quality suitable for use as a vehicle biogas fuel. The use of biogas fuel from food waste has been widely practiced by some countries such as Sweden, France, and Norway. Hopefully, the proposed framework can provide the epitome of the waste-to-wealth concept for the sustainable collection and recycling of food waste in Hong Kong. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction The disposal of mounting municipal solid waste (MSW) is an imminent problem for Hong Kong society. Currently, Hong Kong relies mainly on landfills for MSW disposal. In 2012, approximately 9000 tonnes of MSW were disposed of in the landfills every day. It is anticipated that the current three strategic landfills in Hong Kong, namely South East New Territories, North East New Territories, and West New Territories, will reach their maximum capacities by 2020 (HKEPD, 2013a). Of the 9000 tonnes of MSW disposed of at landfills, about 3600 tonnes is food waste, representing the largest waste component of MSW in Hong Kong. Food waste in Hong Kong generally refers to the organic waste generated during food production and processing, wholesale and retail preparation, after meal leftovers, and expired foods. The food waste per capita in Hong Kong is comparatively higher than those of other Asian cities of similar economic status. For example, the food waste per capita in Hong Kong is about 2 times higher than ⇑ Corresponding author. Tel.: +852 23587157; fax: +852 23581534. E-mail address: [email protected] (I.M.C. Lo).
those in Singapore and South Korea. In addition, the food waste recycling rate is low in Hong Kong (0.6%), which is far below compared to other urban cities in Asia such as South Korea (95%), Taiwan (31%) and Japan (25%) (MOE, 2012; LegCo, 2013; EPA, 2014a,b). The current practice of disposing food waste at landfills is not a sustainable approach in Hong Kong, as it incurs fast depletion of landfill space, generates odour nuisance, and produces greenhouse gases and leachates, thus causing severe adverse environmental problems. A landfill ban on organic waste has been practiced by a few countries. In South Korea and Sweden, a banning disposal of food waste at landfills has been imposed since 2005. In Germany, zero disposal of biodegradable municipal waste at landfills has been reported since 2006. Similarly in Norway, a landfill ban on biodegradable waste was enforced in 2009. Meanwhile, the accelerating human population growth and growing global energy demand in the society have stimulated rigorous research efforts to valorize waste to resource in order to meet such global targets. The security of supply energy may likely become an increasingly important aspect of decision making for developing a sustainable city. Due to these circumstances, unavoidable food
http://dx.doi.org/10.1016/j.wasman.2015.03.022 0956-053X/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Woon, K.S., Lo, I.M.C. A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.03.022
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waste should be collected systematically and valorized to a valueadded product for advancing environmental sustainability and economic development.
2. Proposed framework of food waste collection and recycling for renewable biogas fuel in Hong Kong Among the 3600 tonnes of food waste generated daily, domestic households give rise to about 2500 tonnes, while around 1100 tonnes come from food associated with commercial and industrial (C&I) sources (HKEB, 2014). Assuming that the food waste collection rates of domestic household and C&I sectors are 50% in the future, the total food waste collection rate in Hong Kong is about 1800 tonnes per day (tpd). This amount renders a massive challenge to society if the collected food waste is not recycled and valorized to a value-added product, as far as possible. A systematic food waste separation and collection system, together with environmentally friendly food waste valorization technologies is, therefore, imperative in order to form a sustainable food waste management framework in Hong Kong. In light of this need, a sustainable framework of food waste collection and recycling for valorizing the food waste to renewable biogas fuel is proposed in this study. The proposed framework is established in consideration of the food waste collection and recycling systems in certain cities such as Oslo in Norway, Linköping in Sweden, and Lille in France, as well as with reference to the food waste management environment and community needs in Hong Kong. The proposed framework of the food waste collection and recycling for the food waste valorization in Hong Kong is shown in Fig. 1, and consists of three parts: (i) food waste separation at source and collection; (ii) food waste valorization to value-added products; and (iii) other MSW treatment. It is hoped that the proposed framework can also act as a reference for other urban cities that face a food waste disposal dilemma similar to Hong Kong’s environmental conditions.
3. Proposed optic bag system for food waste separation and collection at source in Hong Kong Source separation is a critical step in dealing with the increasing problem of food waste in society prior to transporting the food waste to various recycling facilities. In Hong Kong, most of the food waste, particularly the food waste from domestic households, is not sorted out from other types of MSW prior to discarding in the three strategic landfills. Residents, nevertheless, are responsible for separating the food waste from the other MSW produced in their home. If the residents fail to sort the food waste at source, the food waste will be contaminated and cannot then be recycled. A complicated sorting process in households, however, can discourage the residents from sorting their waste. A less behavioural change of the public is needed for the collection and separation of food waste. This is important to reduce any changes that might affect the lifestyle of the public and minimise potential impacts on the livelihoods of the public. In addition, the food waste collection system should be reasonably practicable built based upon the existing waste management system. By doing so, the public will not be required to travel to a new place or change their daily routine substantially for the sorting of food waste, and thus be more willing to take part in separating food waste at source. As such, a simple sorting process needing less behavioural change by residents is a key part in order to motivate the residents to sort the food waste from the other MSW. In order to achieve this objective, food waste and other types of MSW can be efficiently separated via an optic bag system.
By introducing the optic bag system, food waste will be packed in an optic bag (e.g. a bag in green colour), while the residual MSW will be packed in a common plastic bag or a pre-paid designated bag if MSW charging scheme is implemented by the Hong Kong Special Administration Region (HKSAR) Government. The optic bag comes in two sizes, which are 10 l size with 270 mm width 130 mm depth 480 mm height and 30 l size with 300 mm width 220 mm depth 640 mm height (Mepex, 2014). All the packed wastes will still be disposed of at the existing collection bins or rubbish chutes. By doing so, it will avoid the need for the households and C&I sectors to reconfigure the waste storage space in their properties. All the wastes will then be collected by the refuse collection vehicles and transported to the respective refuse transfer stations in Hong Kong. As such, no changes to collection routines are required. It is observed that the optic bag is comparatively thicker than the common plastic bag used in Hong Kong. In Oslo, Norway, the optic bag remains intact in the optical sorting plant after it is transported via refuse transfer vehicles. The refuse transfer vehicles used in Oslo are of similar configuration (i.e. with rear compactor) to those in Hong Kong. Hence, it is believed that the optic bag will not be damaged when it arrives at the refuse transfer stations in Hong Kong. Upon arrival at the refuse transfer stations, all the waste bags will be unloaded into a receiving pit. At this point, the optic bags have yet to be separated from the other bags. All the bags will then be sent to a main conveyor belt, in which an optic sensor technology will be used to sort the bags. The green colour of the optic bag allows the optical camera in the sorting plant to identify and sort the optic bag from the other plastic bags automatically. When an optic bag of green colour (i.e. food waste) is detected, a signal will be sent to push the green bag off the main conveyor belt to a second belt. An Enviflex system (i.e. an automatic bag-opener and breaker of food waste) can be employed to separate the collected food waste from the optic bag. In the system, a hydraulically driven roller will be used to open the optic bag. The optic bag will be pulled in a long strip and the food waste will be broken into pieces of approximately 35–50 mm. The food waste and the optic bag will then be screened for separation. Finally, the food waste will be compacted and containerized in purposely built containers and then transported to various food waste recycling facilities for further treatment. Meanwhile, the other residual MSWs such as plastics and papers, which are packed in common plastic bags, will be sent to a proposed advanced incineration facility. After combustion, the heat generated will be used in a steam turbine for generating electricity. The HKSAR Government is going to launch the MSW charging scheme based on a quantity-based system. According to this system, the waste charge could be introduced through the mandatory use of pre-paid designated garbage bags. The optic bag can be assigned as one of the pre-paid designated garbage bags for packaging food waste (the cost of an optic bag is about 0.1 Swedish Krona (SEK) or 0.1 Hong Kong Dollar (HKD) based on Swedish case), while the other pre-paid designated garbage bags can be used for the disposal of other types of MSW. To promote the implementation of optic bag system in Hong Kong, the HKSAR Government should work hand-in-hand with local industry, consumers and communities. It can be done through education by fostering positive behaviour change along with legislation, such as mandatory use of optic bag for packaging food waste or food waste disposal ban in strategic landfills. 3.1. Applications of optic bag system in other countries The optic bag system has been applied in several countries especially in European countries such as Sweden and Norway. An optical sorting plant can be constructed in many different forms
Please cite this article in press as: Woon, K.S., Lo, I.M.C. A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.03.022
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(i) Food waste separation at source and collection
Food waste
Other MSW
Packed in an optic bag (i.e., green bag)
Packed in a common plastic bag or designated bag if MSW charging is launched
Discard at existing collection bins or rubbish chutes Deliver to refuse transfer stations via refuse collection vehicles Unload all waste bags into a receiving pit. The waste bags are sent to a main conveyor belt
Separate the food waste and other MSW using optic sensor installed in the refuse transfer station
Food waste
Other MSW
To assorted food waste recycling facilities
To proposed advanced incineration facility
Compost, swine feed, fish feed
Renewable biogas
Electricity, city gas
Recovered energy
Biogas fuel for vehicle use
(ii) Food waste valorization to value-added products
Electricity
(iii) Other MSW treatment
Fig. 1. Proposed framework of food waste collection and recycling for food waste valorization in Hong Kong.
and configurations in order to meet the specific requirements. Typically, the capital cost of an optical sorting plant with an annual treatment capacity of around 30,000 tonnes for the sorting of two fractions (i.e. optic bag and other residual waste bags) is about 30 million SEK or 29 million HKD, based on a plant in Sweden in 2011 (OptiBag, 2014). In Linköping, Sweden, the optic bag system has also been operated by a waste collection company called Tekniska verken. About 80% of the domestic households in this city have adopted the optic bag system (Book, 2014). Fig. 2 illustrates a simplified flow diagram for separating the optic bag from other bags in an optical sorting plant operated by the Tekniska verken company. Based on the performance of the optical sorting plant, the food waste fraction can be collected with a high level of purity, with an
optimum separation efficiency of 98% (Tekniska verken, 2012). Optic bags that are not detected accurately or any loose materials that pass through the optical sorting system are treated as residual fractions. In Oslo, Norway, the Haraldrud sorting plant has adopted optic bag sensor technology since 2009. The plant handles approximately 150,000 tonnes/year of food waste and is currently the world’s largest optical sorting facility for separating food waste from other household wastes (Envac, 2014). Experience from this city suggests that the residents quickly accept this type of waste sorting system. Other examples of optical sorting plants with two fractions (i.e. food waste and other residual wastes) can be found in cities such as Södertälje and Borås in Sweden, Øras and Mo i Rana in Norway, and Jakobstad in Finland.
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Optic bag (i.e., green bag)
All bags are dumped into a receiving pit
All bags are sent to a conveyor belt
Optic bags and common plastic bags are separated using an optic sensor
Optic bags with food waste are collected in a container Fig. 2. Simplified process flow diagram of an optical sorting plant in Linköping city, Sweden.
4. Valorization of food waste to value-added products in Hong Kong In order to promote the waste-to-wealth concept, collected food waste should be valorized to a value-added product after the separation and collection processes. After separating and collecting the food waste efficiently, the sorted food waste can be sent to various food waste recycling facilities and recycled as a source of valuable material or as a source of renewable energy in the case of Hong Kong. As a source of valuable material, the food waste can be valorized as compost or animal feed such as swine feed and fish feed. As a source of renewable energy, the food waste can be converted into electricity, city gas (i.e. heating fuel for cooking purpose), and biogas fuel for vehicle use.
4.1. Valorization of food waste to compost, swine feed and fish feed There are a few companies currently practicing the aforementioned conversion of food waste into different valuable materials in Hong Kong, such as Kowloon Bay Pilot Composting Plant (turning food waste to compost), Green Environmental Kitchen Residue Recycle Limited and Hong Kong Organic Waste Recycling Centre (turning food waste into swine feed), and Kowloon Biotechnology
Limited (turning food waste to fish feed). In addition, a food waste processing plant in the Hong Kong Ecopark with a treatment capacity of 200 tpd is expected to be commissioned in 2015 in order to produce high protein fish feed. In Asian countries such as South Korea, Taiwan and Japan, more than 40% of the food waste is processed into compost, swine feed, and fish feed to partly substitute for chemical fertilizers and conventional feed ingredients. There are, however, some challenges in valorizing food waste to compost, swine feed, and fish feed in Hong Kong. The recycling of food waste into compost, swine feed, and fish feed in Hong Kong is low mainly due to the diminishing agricultural and fisheries industries. Hence, the current food waste recycling rate in Hong Kong is relatively lower compared to these Asian countries. It is projected that the demands for compost, swine feed and fish feed in Hong Kong are only about 340 tpd, 170 tpd, 10 tpd of food waste, respectively. For the valorization of food waste to swine feed, it is not encouraged by the Agriculture, Fisheries and Conservation Department of the HKSAR Government. This is because recycling of food waste into animal feed requires caution due to the fact that food waste can be a medium for spreading contagious diseases. Some notifiable diseases, namely foot and mouth disease, swine fever, highly pathogenic avian influenza, and transmissible spongiform encephalopathies (TSEs), have been identified in the conversion of food waste to
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animal feed processes (DARD, 2013). To avoid disease transmission, the European Commission has prohibited this practice since 2002, as stated in Regulation (EC) No. 1774/2002. Meanwhile, the export of feed products to the other countries or regions, such as mainland China can be difficult, mainly due to license and regulatory hurdles. For example, a feed factory license from the HKSAR Government is necessary in order to apply for a feed import license from the Ministry of Agriculture of the Chinese Central Government (AQSIQ, 2014). Due to these challenges, it is not feasible to valorize all collected food waste to compost, swine feed, and fish feed in Hong Kong. 4.2. Renewable biogas generation from proposed Organic Waste Treatment Facilities As abovementioned, the local market for compost, swine feed, and fish feed can only account for about 520 tpd of food waste. Based on the assumed food waste collection rate of 1800 tpd and the market demand of compost, fish feed, and swine feed in Hong Kong, there is still about 1280 tpd of collected food waste that remains to be recycled. In this context, the feasibility of valorizing the food waste into sources of renewable energy should be explored. The HKSAR Government has recently published a government report entitled ‘‘A Food Waste and Yard Waste Plan for Hong Kong 2014–2022’’. In the report, the HKSAR Government envisages that Hong Kong needs to build a network of Organic Waste Treatment Facilities (OWTF) in different locations between 2014 and 2024 in order to recycle food waste. In the OWTF, the food waste will undergo an anaerobic digestion process, producing biogas that can be recovered for energy generation. Two phases of the OWTFs have been proposed by the HKSAR Government. Phase 1 and phase 2 of the OWTFs are planned to be located at Siu Ho Wan in North Lantau Island and Shaling at North District of New Territories, respectively. For OWTF phase 1, it is expected that 200 tpd of food waste will be treated, while 300 tpd of food waste will be treated by OWTF phase 2. The design and construction of OWTF phase 1 began in 2014 and it is expected to be commissioned in 2016. Meanwhile, the design and construction of OWTF phase 2 will begin in 2015 and it is projected to be commissioned in 2017 (HKEPD, 2013b). However, it should be pointed out that the proposed OWTFs phase 1 and phase 2 are only able to accommodate 500 tpd food waste. Hence, it is expected that 3 or 4 more OWTFs, each with a proposed capacity of 200–300 tpd, need to be constructed in order to consume the remaining 780 tpd food waste (i.e. after the demand of compost, swine feed, fish feed, phase 1 and 2 of OWTFs). For OWTF phase 1, the biogas produced from the OWTF will be used as a renewable energy for electricity generation. It is estimated that about 14 million kW h/year of surplus electricity can be generated from the OWTF phase 1 and sent to the power grid, which is adequate for use by 3000 households (HKEPD, 2013b). The energy recovery system in the OWTF is beneficial to food waste recycling. This is attributed to the fact that it reduces the amount of fossil fuels in the fuel mix for electricity generation in Hong Kong, thus reducing the environmental pollution and greenhouse gas emissions. Nevertheless, the HKSAR Government is obligated to collaborate with the power companies in Hong Kong (i.e. China Light & Power and Hong Kong Electric) in employing the electricity generated from the OWTF. Negotiations with the power companies in transmitting the excess electricity to the grid are necessary and there is a possibility that the power companies might not want the electricity generated from the OWTF. In addition, a combined heat and power (CHP) will be used to generate the electricity in the OWTF. The efficiency of electricity generated by the CHP, nonetheless, is expected to be low and the heat produced
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will not be applied in Hong Kong. Besides converting the biogas into electricity, another alternative is to valorize the biogas to city gas and to use for cooking in domestic households. The conversion of biogas to city gas, however, faces the same challenge as turning biogas into electricity. The HKSAR Government also needs to negotiate with the Hong Kong and China Gas Company Limited (i.e. Towngas company) in using the biogas. Hence, there is also a possibility that the Towngas company might not want to be involved in the purchase of biogas produced from the OWTF.
5. Valorization of food waste to renewable biogas fuel for vehicle use in Hong Kong More alternatives should be explored in order to utilize the biogas generated from the OWTF. For OWTF phase 1, the biogas generated after the anaerobic digestion process has been proposed to be used as electricity (LegCo, 2014). Nevertheless, the use of biogas generated from the OWTF phase 2 is yet to be confirmed. In view of the caveats encountered when turning the food waste into electricity or city gas in Hong Kong, the biogas generated from the phase 2 or later phases of OWTF is recommended to be upgraded to a quality suitable for use as a vehicle biogas fuel. Using advanced biogas upgrading technologies, the methane (50–70% by volume in raw biogas) and carbon dioxide (25–45% by volume in raw biogas) can be separated effectively and efficiently, turning the biogas into biogas fuel for vehicle use. There are a lot of existing biogas upgrading technologies available in the market, such as pressure swing adsorption, water scrubbing, amine scrubbing, and membrane separation. Table 1 shows some of the key parameters (e.g. energy requirement, methane losses, technical availability per year, etc.) of various biogas upgrading technologies. Yliopisto (2013) reported that water scrubbing is the most suitable process for most large-scale systems (>100 N m3 biogas/h), while membrane separation system appears to be most suitable for smallscale systems (<100 N m3 biogas/h). Sweden is considered the most advanced country in terms of the application of biogas upgrading technologies. Currently, there are 32 biogas upgrading plants in Sweden located in cities such as Stockholm, Linköping, Falkenberg, and Göteborg (Patterson et al., 2011). By using biogas fuel from food waste, it reduces the use of imported fossil fuel supplies, as well as significantly providing lower emissions of greenhouse gases, nitrogen oxides and particles, compared to petrol and diesel fuel. Papacz (2011) reported that biogas-fuelled vehicles can reduce greenhouse gas emissions by between 75% and 200% compared with fossil fuels. Francis and Bell (2008) stated that each bus running on biogas fuel in Linköping, Sweden, contributes to reducing CO2 emissions by 90 tonnes/year and NOx emissions by 1.2 tonnes/year. Table 2 shows the consumption of different types of fuels for light good vehicles, heavy good vehicles, and buses. For a travel distance of 100 km, the consumption of biogas fuel is about 10.6% less compared to petrol. In view of economic perspective, Murphya et al. (2004) highlighted that the use of biogas fuel for vehicle use has the potential to save 0.39 EUR/N m3 (3.99 HKD/N m3) as a petrol substitute and 0.28 EUR/N m3 (2.87 HKD/N m3) as a diesel substitute. These savings are comparatively higher than turning the biogas into heat and electricity (0.19 EUR/N m3 or 1.94 HKD/N m3 in a combined heat and power plant, 0.143 EUR/N m3 or 1.46 HKD/ N m3 for electricity-only production). Biogas fuelled cars can be imported by the HKSAR Government for the implementation of biogas fuel for vehicle use in Hong Kong. Biogas fuelled cars are currently factory-made by several major car manufacturers such as Mercedes-Benz, Volkswagen, Ford and Volvo. The biogas fuel can be firstly used by the government service cars in the various government departments, since the
Please cite this article in press as: Woon, K.S., Lo, I.M.C. A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.03.022
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Table 1 Key parameters of the biogas upgrading technologies. Biogas upgrading technology
Energy requirement (kWh/m3 of upgraded biogas)
Methane losses (%)
Technical availability per year (%)b
Cost of upgraded biogas (HKD/m3)g,j
Methane concentration in the product gas stream (by volume %)h
Pressure swing adsorption
2a
94
2.39i
>98
<2a
96
1.38i
>98
Amine scrubbing
0.5–0.6a 0.240b 0.335c 0.285d 0.300a 0.200b 0.430c 0.391d 0.646c 0.126d
<0.1a
91
1.56
>99.8
Membrane separation
0.769c 0.378e
>10f
98
2.02i
98
Water scrubbing
a b c d e f g h i j k
Example of city/country applying the technologyk – Bachenbülach, Switzerland (1996) – Helsingborg, Sweden (2002) – Linköping, Sweden (1997) – Lille, France (2007) – Borås, Sweden (2002) – Stavenger, Norway (2009) – Berthierville, Canada (2003) – Bruck an der Leitha, Austria (2008)
Adapted from Persson (2007). Adapted from Beil and Hoffstede (2009). Adapted from Berndt (2006). Adapted from Günther (2007). Adapted from Miltner et al. (2008). Adapted from Dirkse (2008). Adapted from de Hullu et al. (2008). Adapted from Bauer et al. (2013). The cost is associated to plants with an output of between 200 and 300 N m3/h upgraded biogas. Currency exchange rate: 1 HKD to 0.11 EUR. Number in the bracket indicates the beginning year of operation.
Table 2 Fuel consumption for each vehicle categorya. Type of fuel
Fuel consumption (kg/100 km) Light good vehicle (LGV)
Petrol Diesel Biogas fuel
6.93 5.95 6.19
Heavy good vehicle (HGV)b d
N/A 31.40 34.65
Busc N/Ad 44.84 48.28
Note: a Adapted from NSCA (2006). b HGV is based on 38 tonnes articulated truck. c Bus is based on 88-seats double deck bus. d N/A stands for not applicable.
HKSAR Government is not required to deal with any private companies for its implementation. For example, the HKSAR Government can introduce biogas refuse collection vehicles for the Food and Environmental Hygiene Department. Through the use of biogas refuse collection vehicles, it promotes a sustainable closed-loop system in the food waste management framework in Hong Kong. This is because the food wastes are turned into biogas fuel for the biogas refuse collection vehicles that collect these food wastes. Besides, the HKSAR Government can introduce biogas fire trucks for the Fire Services Department, biogas ambulances for the Department of Health, and even biogas police cars for the Hong Kong Police Force. The use of biogas fuel for vehicle use can be extended to private cars. Hafeez (2013) stated that the biogas generated from 1 kg of food waste equals to about 0.13 l petrol. This biogas allows a private car, with an engine size of 2501– 3500 cc and an average consumption of 14 l/100 km (EMSD, 2013), to drive 0.93 km/kg treated food waste. Considering the 1080 tpd food waste treated in phase 2 or later phases of OWTFs, it is estimated that about 140,600 l petrol will be produced daily. Assuming the private car is travelled 100 km/day, the biogas fuel generated from food waste can be used to fuel approximately 10,000 private cars/day (about 2.2% of the total private cars in Hong Kong), helping to reduce the CO2 emissions by about 80,000 tonne/year (about 1.1% of the total emitted amount by
the transport sector in Hong Kong in 2011). To encourage the use of biogas fuelled cars by the Hong Kong public, the HKSAR Government can provide incentive and tax reductions if biogas fuelled cars are bought by the users. To further enhance the use of biogas fuel, the HKSAR Government can negotiate with the Hong Kong city bus (e.g. Kowloon Motor Bus) and taxi companies in order to promote the use of biogas fuel in public transport. 5.1. Application of food waste as renewable biogas fuel for vehicle use in other countries The use of biogas fuel produced from food waste has been extensively adopted by some European cities such as Linköping and Stockholm in Sweden, Lille in France, and Oslo in Norway. Table 3 summarizes the production and distribution of biogas, as well as the biogas vehicles in use in these respective cities. For example, a biogas plant in Linköping has an annual treatment capacity of 100,000 tonnes food waste, produces 4.7 million m3 of upgraded biogas fuel that is used in 89 public buses and over 1000 personal cars (IEA, 2005; Martin, 2009). In Linköping city, food waste produces sufficient biogas fuel for about 6% of registered vehicles, including the fleet of city buses and taxis (Cleantech Östergötland, 2014). Fig. 3 shows some of the photos of the biogas fuelled personal cars and biogas fuelled public buses, as well as the biogas filling stations in Linköping city. The distribution networks for biogas in Linköping are well-developed. The distribution networks connect the refueling stations with the production plants via biogas grid, hence minimising road bound transportation. A series of economic incentives, such as no tax on biogas as vehicle fuel, lower tax on biogas fuelled vehicles, exclusion from city gate tolls for biogas vehicles, and even free parking for biogas vehicles, have been promulgated by the Swedish Government in order to promote the use of biogas fuel in private cars (NSCA, 2006). To promote the development of biogas fuel for vehicle use, the European Commission has established an initiative called the Biogasmax project to reduce reliance on fossil fuels and reduce
Please cite this article in press as: Woon, K.S., Lo, I.M.C. A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.03.022
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Table 3 Summary of some European cities that have adopted the biogas fuel for vehicle use. Country
City
Inhabitants
Sweden
Linköping
0.14 million
– A biogas plant with an annual treatment capacity of 100,000 tonnes food waste, producing 4.7 million m3 of upgraded biogas fuel – 12 public biogas filling stations as of 2005
Swedenb
Stockholm
0.91 million (municipality area)
Franceb
Lille
1.1 million
Norwayc
Oslo
0.59 million
– 11 biogas refueling station as of 2007 – As the demand is exceeded the Stockholm’s biogas production capacity, supply of biogas is bought from city of Linköping and Västerås (distributed via lorry) – An Organic Recovery Center (ORC) with an annual treatment capacity of 108,000 tonnes of food waste, producing 4 million m3/year of biogas – The waste collection truck depot and bust depot are located next to the ORC (i.e. minimise the distance of distribution via dedicated pipeline) – A biogas plant located in Nes, Romerike treats 50,000 tonnes/ year of food waste, producing 14,000 m3/day of upgraded biogas
a
a b c
Production and distribution
Use in vehicles – All the diesel buses in operation have been replaced by biogas fuelled buses since 2002 – The world’s first biogas train with operated range of 600 km (between Linköping and Västervik) became operational in Linköping in 2005 – There are over 1000 personal cars and 89 public buses fuelled by biogas as of 2008 – 25 heavy duty vehicles including 16 waste collection vehicles and 9 public buses – 80 light duty vehicles (e.g. taxis and personal cars) – 10 heavy duty waste collecting biogas vehicles as of 2009 – 289 gas-driven buses (fuelled by a mixture of upgraded biogas and compressed natural gas) as of 2009 (80% of all buses in the city) – 135 municipal buses are operated by biogas fuel as of 2013
Information is summarized and adapted from IEA (2005) and Martin (2009). Information is summarized and adapted from Pädam et al. (2010). Information is summarized and adapted from Wärtsilä (2014).
(i)
(ii) Biogas fuelled car capable of running on biogas fuel and petrol
(iii)
(iv)
Fig. 3. Photos of (i) biogas fuelled car; (ii) biogas fuelled car filling station; (iii) biogas fuelled public bus; and (iv) biogas fuelled bus filling station in Linköping city, Sweden.
greenhouse gas emissions by providing information on more efficient production, distribution and use of biogas fuel in the transport sector (Biogasmax, 2010). A network of biogas-related large scale demonstrations has been created on certain countries (e.g. Sweden, France, Switzerland, etc.) with the purpose of sharing experience in terms of best practice in managing urban transportation. Through the introduction of biogas fuel from food waste, it provides welfares to the local community both economically and environmentally. This is because the resources used are from local food waste, and the end-use is in vehicles from the local community.
6. Conclusions A food waste management framework is proposed for separating, collecting, and valorizing the food waste effectively in Hong Kong. The benefits and ways of implementation of the optic bag system in Hong Kong are explained in this paper. It is expected that the simplicity of the optic bag system can render a less behavioural change of householders, and thus to encourage the Hong Kong public to implement food waste separation at source. This paper also discusses the conversion of food waste to biogas as a renewable energy source, particularly to the potential application as
Please cite this article in press as: Woon, K.S., Lo, I.M.C. A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.03.022
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biogas fuel for vehicle use in Hong Kong. Through the implementation of the proposed framework, the framework can hopefully provide a simple yet effective approach to food waste separation at source, and promote the sustainable use of food waste as a renewable energy in urban cities like Hong Kong. References AQSIQ, Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China, 2014. Quarantine Access Procedures for Agricultural Products to be Imported to China for the First Time.
HKEB, Hong Kong Environment Bureau, 2014. A Food Waste and Yard Waste Plan for Hong Kong 2014-2022. HKEPD, Hong Kong Environmental Protection Department, 2013a. Strategic Landfills.
Please cite this article in press as: Woon, K.S., Lo, I.M.C. A proposed framework of food waste collection and recycling for renewable biogas fuel production in Hong Kong. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.03.022