Environ Sci Pollut Res DOI 10.1007/s11356-015-4668-3
BIOLOGICAL WASTE AS RESOURCE, WITH A FOCUS ON FOOD WASTE
Investigation of the available technologies and their feasibility for the conversion of food waste into fish feed in Hong Kong Jack Y. K. Cheng 1 & Irene M. C. Lo 1
Received: 30 December 2014 / Accepted: 6 May 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract Food waste is the largest constituent of municipal solid waste in Hong Kong, but food waste recycling is still in its infancy. With the imminent saturation of all landfill sites by 2020, multiple technologies are needed to boost up the food waste recycling rate in Hong Kong. Conversion of food waste into animal feeds is prevalent in Japan, South Korea, and Taiwan, treating over 40 % of their recycled food waste. This direction is worth exploring in Hong Kong once concerns over food safety are resolved. Fortunately, while feeding food waste to pigs and chickens poses threats to public health, feeding it to fish is considered low risk. In order to examine the feasibility of converting food waste into fish feed in Hong Kong, this paper investigates the market demand, technical viability, feed quality, regulatory hurdles, and potential contribution. The results show that a significant amount of food waste can be recycled by converting it into fish feed due to the enormous demand from feed factories in mainland China. Two conversion technologies, heat drying and black soldier fly bioconversion, are studied extensively. Black soldier fly bioconversion is preferable because the end-product, insect powder, is anticipated to gain import approval from mainland China. The authors suggest further research efforts to speed up its application for food waste recycling in urban cities.
Keywords Animal feed . Black soldier fly bioconversion . Fish feed . Food waste . Heat drying . Waste valorization Responsible editor: Philippe Garrigues * Irene M. C. Lo [email protected] 1
Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China
Introduction Hong Kong is facing a serious waste challenge since all the existing landfills will be saturated by 2020. As food waste represents the largest portion of municipal solid waste, eliminating food waste can alleviate the landfill pressure substantially. In Hong Kong, merely 0.6 % of food waste is recycled (HKEPD 2014), which is far behind other developed places in Asia such as South Korea (95 %), Taiwan (31 %), and Japan (25 %) (LegCo 2013; EPA 2014a, b; MOE 2014). Therefore, there is an urgent need to apply multiple technologies for food waste valorization to boost the recycling rate. After investigating the proportions of food waste recycling methods in South Korea, Taiwan, and Japan, it was revealed that more than 40 % of the food waste is processed into swine, poultry, and fish feeds to partly substitute the conventional feed ingredients. Table 1 provides summary statistics on their food waste recycling rates and a breakdown of their recycling methods. The question is whether Hong Kong can improve its food waste recycling through animal feed production. However, recycling food waste into animal feeds requires caution because food waste can be a medium for spreading contagious diseases. To mitigate public health risks, the European Commission has prohibited this practice since 2002 as stated in Regulation (EC) No. 1774/2002. Four notifiable diseases have been identified, namely foot and mouth disease, swine fever, highly pathogenic avian influenza, and transmissible spongiform encephalopathies (TSEs) (DARD 2013). These infectious disease outbreaks have caused severe economic loss, massive culling of animals, and even human deaths. In consideration of the previous unpleasant experiences battling bird flu and swine flu crises, the Hong Kong Government is unlikely to support the conversion of food waste into swine and poultry feeds for the sake of public health. Furthermore, feeding food waste to pigs and chickens
Environ Sci Pollut Res Table 1 Food waste recycling rates in South Korea, Taiwan, and Japan with a breakdown of the recycling methods
Food waste recycling rate (%) Recycled as animal feeds (%)a Recycled as compost (%) Recycled as other products (%)b Source a
South Korea
Taiwan
Japan
94.70 40.55 49.52 9.93 LegCo 2013
30.92 71.38 28.43 0.19 EPA 2014a, b, c
24.58 46.77c 39.05c 14.18c MOE 2014
Animal feeds include swine, poultry, and fish feed
b
Other products include methane gas for electricity generation and water heating, as well as oil and fat products such as biodiesel and printing inks c
Values shown only represent the commercial and industrial sector in Japan as the breakdown in the domestic sector is not available
can result in TSEs because this group of fatal degenerative brain diseases is caused by intraspecies recycling, which refers to the feeding of animals with proteins from the same species (e.g., feeding pork to pigs). Due to the complex composition of mixed food wastes, it would be difficult to avoid intraspecies recycling, and manual separation of pork and chicken meat would not be cost-effective. As a result, feeding food waste to pigs and chickens is neither safe nor practical. Fortunately, none of these four notifiable diseases are related to fish (DARD 2013). Moreover, according to Regulation (EC) No. 56/2013, feeding food waste to fish does not raise any concern over compliance with intraspecies recycling. Even though food waste may contain fish protein, the inclusion of fish protein in fish diets has been practised effectively for a long time and is believed to have a negligible TSE risk. As it is safe to turn food waste into fish feed, it is worth investigating further whether this can be adopted in Hong Kong to improve food waste recycling. The objectives of this paper are to (i) evaluate the market demand for new fish feed in local and export markets; (ii) screen the available technologies for converting food waste into fish feed to identify the suitable ones for Hong Kong; (iii) review previous feeding studies that use fish feed produced from food waste in the diet; (iv) assess the regulatory hurdles in selling the fish feed abroad; (v) quantify the amount of food waste required for meeting the market demand to evaluate its significance for food waste recycling in Hong Kong; and finally (vi) discuss the technical challenges and suggest further research directions. It is hoped that this study can serve as a useful reference for policymakers, industry players, and academic researchers to explore the potential of fish feed production as an effective means for food waste recycling.
Market demand for new fish feed in local and export markets As the goal of recycling is to turn wastes into valuable resources, market demand for end-products is crucial. This
paper covers the market demand in both local and export markets because fish feed is a commonly traded commodity and thus should not be limited to domestic sales. Among all export markets, mainland China is chosen as the sole focus because of its dominant share, which accounts for 62 % of global aquaculture production (FAO 2014a). Together with Hong Kong’s proximity to mainland China, it would be sensible for local fish feed producers to consider exporting the fish feed to mainland China. Domestic sales are often preferred due to low transportation cost and few regulatory hurdles. However, the market demand for fish feed in Hong Kong is limited, estimated at around 10 tonnes per day (tpd). The potential buyers are the fish farm owners since there is no feed factory in Hong Kong. There are three main sources of fish feed in Hong Kong, namely traditional vegetarian feed, pellet feed, and trash fish (AFCD 2009). The traditional vegetarian feed includes wheat bran, rice bran, weed, soy dregs, flour, and peanut cakes, which are suitable for freshwater fish. Pellet feed is made from grinding baked trash fish, fish oil, vitamins, and binder and is suitable for both freshwater and marine species. Trash fish refers to the small fish that are caught unintentionally during fishing activities and are suitable for marine fish. For these three types of fish feed, the traditional vegetarian feed and pellet feed have become more expensive in recent years due to the increasing prices of feed ingredients. The supply of trash fish has become limited after the trawling ban in Hong Kong in 2012. As a result, the fish farm owners are prone to switch to alternative feed sources. Relatively, the market demand for fish feed in mainland China is very significant and amounts to about 40,000 tpd (DMANFQ 2010). The target buyers are the fish feed manufacturers, which face increasing pressure due to rising feed cost. Fish meal, one of the important fish feed ingredients that is derived from fresh raw fish or fish trimmings, has tripled in price within a decade. Figure 1 illustrates a clear upward trend in fish meal price in the recent decade. This drives the feed factories to look for low-cost alternatives for fish meal replacement. Currently, more than 2000 tpd of fish meal is
Environ Sci Pollut Res
Fishmeal price (US$/ tonne)
2500
2000
1500
1000
500
0 Jul-04
Jul-06
Jul-08
Jul-10
Jul-12
Jul-14
Fig. 1 Trend in the fish meal price during 2004–2014. Data adapted from World Bank (2014)
imported to mainland China (OECD-FAO 2014). If the fish feed produced from food waste can be exported to mainland China to substitute fish meal at a competitive price, its market demand would be huge. In fact, one of the fish feed ingredients in the list of approved imported feed materials of mainland China, sandworm, is produced by feeding food waste like rapeseed dregs or soybean oil cake and has already been allowed to be imported to mainland China from North Korea (AQSIQ 2015).
Technology screening for converting food waste into fish feed in Hong Kong As the market demand for new fish feed exists, the next step is to select technologies that are suitable for a modern city like Hong Kong, and at the same time produce fish feed of high Table 2
quality. Table 2 provides an assessment of the potential conversion technologies. Nine technologies are identified from the relevant literature for screening, namely direct feeding, heat sterilization, heat drying, fermentation, algal production, aquatic weed production, earthworm production, housefly bioconversion and black soldier fly bioconversion. After taking into account the hygiene, land requirement, and ecological aspects, many technologies are not suitable for Hong Kong. Direct feeding, heat sterilization, and fermentation fail to guarantee that feeds are free of pathogens. Algal production and aquatic weed production require massive water bodies, which do not exist in Hong Kong. The earthworm species most often used for decomposing organic waste is a foreign invasive species that can threaten the native species. The housefly has long been known to be a disease carrier, and thus, mass rearing of houseflies cannot be tolerated in an urban city. After the elimination, only heat drying and black soldier fly bioconversion are considered applicable in Hong Kong. Heat drying assures feed safety as pathogenic viruses, bacteria, and mould can be inactivated under prolonged heat exposure and low water content. As for black soldier fly bioconversion, this fly species is safe to use since it can be found locally and does not disturb human beings or spread diseases (FAO 2013). Its end product, insect powder, also undergoes heat drying to achieve sterilization. Hence, the feasibility of these two technologies for converting food waste into fish feed was the focus of this study. Heat drying is a conventional method and is easy to operate. It applies warm and dry air to lower the moisture content down to approximately 10 %. This technology has been adopted in countries such as Japan and South Korea. For
Technology assessment for the conversion of food waste into fish feed in Hong Kong
No
Technology
Viability
Justifications
1 2 3
Direct feeding Heat sterilization Heat drying
No No Yes
Untreated food waste may carry pathogens (Polprasert 2007). Due to the high moisture content of food waste, it can spoil easily. It ensures feed safety because the prolonged heat exposure inactivates most pathogenic viruses and the low water content inhibits mould and bacterial growth.
4
Fermentation
No
5 6 7
Algal production Aquatic weed production Earthworm production
No No No
8 9
Housefly bioconversion Black soldier fly bioconversion
No Yes
Fermented food waste is semi-liquid, messy and smelly, which is inconvenient for feeding and storage. Drying of fermented food waste can improve its physical properties, but there is insufficient research data on the effect of feeding dried fermented food waste on fish growth performance. It requires a large area of land (Polprasert 2007). It requires a large area of land (Polprasert 2007). Earthworms suitable for food waste processing are foreign invasive species, which can be detrimental to the local ecosystem. Housefly is a notorious disease vector that is not acceptable in Hong Kong. Black soldier fly is safe to use because it is a local species and does not disturb human beings or spread diseases (FAO 2013). Through the bioconversion process, food waste is converted into insect biomass, which can also be processed into dried insect powder for the ease of usage and transportation as well as sterilization.
Environ Sci Pollut Res
instance, the maximum treatment capacity is 255 tpd in Yokohama, Japan (FAO 2014b). The end-product is a food waste powder that weighs about one-fifth of the original weight since the moisture content of food waste is around 80 %. In Japan, food waste powder can be registered as an Becofeed^ under the Japan Scientific Feed Association (Sugiura et al. 2009). Due to the complex composition of food waste, its crude protein level can fluctuate significantly, ranging from 3.0 to 37.7 %. On an industrial scale, the variation can be reduced to 19.8–25.8 % by collecting food waste from multiple sources such as school canteens, food factories, and convenience stores (Sayeki et al. 2001). While this may not be nutritious enough for high trophic level fish like carnivorous and omnivorous fish, its protein level is adequate for low trophic level fish like herbivorous and forage fish, which has a protein requirement of 18–23 %. Mo et al. (2014) demonstrated that using food waste powder for feeding big head carp and grass carp can yield a comparable result to commercially manufactured feed. Black soldier fly bioconversion refers to the use of the black soldier fly, Hermetia illucens (Diptera: Stratiomyidae) for converting food waste into insect biomass. Young larvae of the black soldier fly are reared continuously to consume the food waste. When the larvae become mature, they will be harvested, dried, and milled into insect powder. This technology has been commercialized in the USA, Canada, the Netherlands, and South Africa. For example, the maximum treatment capacity is 110 tpd in Cape Town, South Africa (Packham 2014). The insect powder produced can have a protein level of 39.5–59.2 % subject to the larval diet (Nguyen 2010). In South Africa, the insect powder is standardized to a minimum of 50 % protein level and has been approved by the Department of Agriculture, Forestry and Fisheries of the Republic of South Africa (AgriProtein 2014a, b). Its high and consistent protein level is desirable as a fish meal substitute for carnivorous fish such as grouper and sea bass, which requires a dietary protein level of over 38 % in their diets. Yet, this technology requires a high degree of technical Table 3
Fish feeding trials using fish feeds produced from food waste Although crude protein level is a useful parameter for assessing the nutritional adequacy of fish feed, the feed buyers are also concerned about the actual fish growth and costeffectiveness when making purchase decisions. These two factors can be determined through feeding studies by measuring specific growth rate (SGR) and feed conversion ratio (FCR), respectively. The SGR measures the daily growth rate of the fish, which is expressed by the equation SGR=[ln (W2) −ln (W1)]×100 %/ΔT where W1 is the initial weight (in grams), W2 is the final weight (in grams), and ΔT is the duration of the experiment (in days). A high SGR is desirable because it implies that the fish grow rapidly. The FCR refers to the amount of feed required to grow a kilogram of fish. A low FCR is preferable since it suggests reduced feed input, which may translate into feed cost savings. Several fish feeding trials have been conducted to evaluate the effect of replacing fish meal with the food waste powder produced by heat drying. The results of these feeding trials are summarized in Table 4. Bake et al. (2009) assessed the potential of using food industry wastes as a fish meal substitute in
Comparison of economic attractiveness between heat drying and black soldier fly bioconversion
Conversion rate (wet food waste: dry fish feed) Amount of fish feed produced from 100 t of food waste (tonne) Market value of fish feed (US$/tonne) Fish feed revenue gained from 100 tonnes of food waste (US$) a
expertise since it involves insect rearing processes, including fly breeding, fly egg laying, larvae feeding, and pupation (Newton et al. 2005). In order to evaluate the economic attractiveness of these two technologies, an economic analysis is conducted based on the conversion rates and market values of the two fish feeds (Table 3). For every 100 t of food waste recycled, heat drying generates revenue of US$2000–2600, whereas black soldier fly bioconversion generates US$8600. The latter delivers a higher economic return because the insect powder produced by black soldier fly bioconversion can be sold 10 times higher than the food waste powder produced by heat drying. The high market value of insect powder can be attributed to its consistently high crude protein level.
Heat drying
Black soldier fly bioconversion
5:1a 20 (food waste powder) 100–130c 2000–2600
15.7:1b 6.37 (insect powder) 1,350d 8,600
Since food waste contains about 80 % moisture content, the conversion rate is around 5:1
b
The largest plant for black soldier fly bioconversion in South Africa is reported to have a treatment capacity of 110 tpd (Packham 2014) and produce 7 tpd of insect powder (AgriProtein 2014a) c
EPA 2005
d
AgriProtein 2014a
Environ Sci Pollut Res Table 4
Effect of replacing fish meal with the food waste powder produced by heat drying in various fish diets
Fish species
Diet
Tilapia
Specific growth rate (%) Feed conversion ratio Reference
0 % food waste powder (control) 20 % fish meal substituted with food waste powdera Orange-spotted grouper 0 % food waste powder (control) 10 % fish meal substituted with food waste powderb 20 % fish meal substituted with food waste powderb 30 % fish meal substituted with food waste powderb 40 % fish meal substituted with food waste powderb Giant grouper 0 % food waste powder (control) 50 % fish meal substituted with food waste powderb 100 % fish meal substituted with food waste powderb Tilapia 0 % food waste powder (control) 50 % fish meal substituted with food waste powderb 100 % fish meal substituted with food waste powderb
8.65 8.37 6.22 5.88 5.88 5.10 4.65 5.24 3.95 1.75 5.02 4.34 3.66
0.76 0.76 1.34 1.34 1.27 1.66 1.78 1.39 1.82 5.13 1.46 2.63 3.79
Bake et al. 2009 Hsieh 2010
Hsieh 2010
Hsieh 2010
a
The source comes from food industry wastes, including leftover food from convenience stores, food waste residues discharged during food processing, hotel waste, restaurant cooking waste, tofu waste, and bread production waste. The crude protein content is 19.73 %
b
The source comes from restaurant waste in the National Taiwan Ocean University. The crude protein content is 38 %
the diet of tilapia. The results showed that the FCR remained unchanged from the control when 20 % of fish meal was substituted by food industry wastes. However, the SGR dropped as a result of lower feed intake. Similar findings were also reported in Hsieh (2010) that the FCR was maintained while the SGR was reduced when 20 % of fish meal was replaced by restaurant wastes in the diet of orange-spotted grouper. Hsieh (2010) also evaluated the SGR and FCR at high fish meal substitution rates beyond 30 % in the diets of orange-spotted grouper, giant grouper, and tilapia and found that both SGR and FCR were adversely affected in these fish species. From these results, the maximum substitution rate of food waste powder in fish diets is suggested to be 20 %. One should note that the food waste powder has to be economical to compensate for the decrease in SGR at a 20 % substitution rate. Partial replacement of fish meal with the insect powder produced by black soldier fly bioconversion has been studied in various feeding studies. Table 5 provides a summary of the fish feeding trials. Newton et al. (2005) replaced fish meal and soybean meal with insect powder in channel catfish diets at 0, 7.5, 15, 22.5, and 30 %. The results revealed that there were no significant differences in both the SGR and the FCR up to a 30 % substitution rate. St-Hilaire et al. (2007) investigated the inclusion of insect powder in the diet of rainbow trout for fish meal replacement at three different levels of 0, 25, and 50 %. It was found that the FCR and SGR were negatively affected at a 50 % substitution rate, but changed only slightly at 25 %. Kroeckel et al. (2012) evaluated different fish meal substitution levels with defatted insect powder in juvenile turbot diets at 0, 17, 33, 49, 64, and 76 %. The FCR was not affected at a 17 % substitution rate as compared to the control diet, but increased when a greater percentage of insect powder was
applied. From these results, it is believed that the suitable fish meal substitution rate of insect powder in fish diets falls within 17–30 %.
Regulatory hurdles in selling fish feed to mainland China The feed industry is highly regulated in most countries because it can affect animal and human health. If the fish feed fails to gain approval from the authority, the sales potential can be greatly reduced regardless of its price or nutritional value. Consequently, particular attention should be paid to the regulatory requirements in the export market. In mainland China, two regulatory bodies are involved for feed import, which are the Ministry of Agriculture (MoA) and the General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ). Approvals from both sides are prerequisites to import feed into mainland China. In order to verify the possibility of selling fish feed to mainland China, it is vital to understand the roles of the MoA and AQSIQ. The MoA is responsible for the administration and supervision of feed and feed additives. Before gaining approval from the MoA, any application has to undergo a scientific assessment on feed safety, efficacy, and environmental impact by the National Feed Assessment Committee. Meanwhile, the AQSIQ is involved in certification and standardization for quality control of imported goods. Based on their responsibilities and assessment criteria, the possibility of importing fish feed to mainland China is analyzed. Regarding the food waste powder produced by heat drying, its import can pose a serious threat to the public health since it can cause intraspecies recycling when used in the production
Environ Sci Pollut Res Table 5
Effect of replacing fish meal with the insect powder produced by black soldier fly bioconversion in various fish diets
Fish species
Diet
Specific growth rate (%)
Feed conversion ratio
Reference
Channel catfish
0 % insect powder (control) 7.5 % fish meal and soybean meal substituted with insect powdera 15.0 % fish meal and soybean meal substituted with insect powdera 22.5 % fish meal and soybean meal substituted with insect powdera 30.0 % fish meal and soybean meal substituted with insect powdera 0 % insect powder (control) 25 % fish meal substituted with insect powderb 50 % fish meal substituted with insect powderb 0 % defatted insect powder (control) 17 % fish meal substituted with defatted insect powderc 33 % fish meal substituted with defatted insect powderc 49 % fish meal substituted with defatted insect powderc 64 % fish meal substituted with defatted insect powderc 76 % fish meal substituted with defatted insect powderc
1.70 1.84 1.79 1.54 1.70 3.09 2.92 2.73 1.73 1.53 1.43 1.19 0.94 0.63
2.20 1.87 1.96 2.55 2.31 1.18 1.22 1.47 0.76 0.76 0.82 0.86 0.98 1.21
Newton et al. 2005
Rainbow trout
Turbot
St-Hilaire et al. 2007
Kroeckel et al. 2012
a
The insect powder was produced from dried black soldier fly prepupae raised on swine manure, with a crude protein level of 43.2 %
b
The insect powder was produced from dried black soldier fly prepupae raised on swine manure, with a crude protein level of 43.6 %
c
The insect powder was obtained from a commercial producer (Hermetia Futtermittel GbR, Baruth/Mark, Germany). The diet fed to the larvae is unknown. The crude protein of the defatted insect powder is 54.1 %
of other animal feeds in the feed factory, which can be difficult to monitor. Bian et al. (2009) also stressed the TSE risk involved when animals are fed with food waste. Owing to the concern over TSE transmission risk, it is anticipated that the National Feed Assessment Committee of the MoA is likely to raise an objection. From the perspective of the AQSIQ, food waste powder is difficult to be standardized because of its complex composition and unstable source. Bian et al. (2009) explain that the homogeneity of feed is vital for standardization to control quality and prevent hazards. In fact, almost all feed ingredients listed in the Catalogue of Feed Materials of China are homogeneous products. In addition, according to BThe Administrative Measures on New Feeds and New Feed Additives^ in mainland China, a new feed ingredient has to be a single feed, meaning that the source should originate from a single type of plant, animal, microbe, or mineral. As the nature of food waste powder does not fit this definition, the AQSIQ is unlikely to grant import approval for the food waste powder. As for the insect powder produced by black soldier fly bioconversion, it mitigates the concern over intraspecies recycling because it is safe to feed insect protein to pigs, chickens, and fish. Moreover, insect powder has a high and stable protein level that makes it a viable alternative to fish meal. Furthermore, the Food and Agriculture Organization of the United Nations also recommends the feed industry to seriously consider its use as animal feed (FAO 2013). Since insect powder can meet the feed safety and efficacy criteria of the National Feed Assessment Committee, the MoA may accept its application for feed import. For the AQSIQ, insect powder is a material that can be easily standardized since it
belongs to a single feed. Furthermore, a category for Binsect and processed insect products^ has already existed in the Catalogue of Feed Materials of China. Therefore, this new insect powder can be included in the catalogue easily. With the ease of standardization and certification, insect powder tends to receive little objection from the AQSIQ as feed quality can be controlled properly. From the regulatory perspective, it is found that insect powder is more likely to be authorized in mainland China, whereas food waste powder tends to be rejected. As feed safety, feed quality, and quality control are universally important around the world, this may also have reference values for other countries.
Potential contribution to food waste recycling in Hong Kong In order to quantify the potential contribution of fish feed production to food waste recycling in Hong Kong, the amounts of food waste required to meet the market demand for new fish feed are calculated in Table 6 by the formula: F=D×S×C, where F is the amount of food waste required (in tpd), D is the market demand for fish feed (in tpd), S is the suitable substitution rate of new fish feed in fish diets, and C is the conversion rate from wet food waste to dry fish feed. By selling the fish feed locally, the amounts of food waste required through heat drying and black soldier fly bioconversion are 10 and 39 tpd, respectively. Considering that the amount of food waste in Hong Kong is about 3300 tpd, the
Environ Sci Pollut Res Table 6
Amount of food waste required to meet the market demand for fish feed in Hong Kong and China Hong Kong
Market demand for fish feed (tpd) Type of new fish feed Substitution rate of new fish feed in fish diets Market demand for new fish feed (tpd) Conversion rate (wet food waste: dry fish feed) Amount of food waste required to meet market demand (tpd)
D
10 Food waste powder S 20%b DxS 2 C 5:1e F=D×S×C 10
China 2687a Insect powder Food waste powder 25%c 20%b 2.5 n/ad f 15.7:1 5:1e 39 n/ad
Insect powder 25%c 672 15.7:1f 10560g
It is mentioned in section BMarket demand for new fish feed in local and export markets^ that feed manufacturers in mainland China are searching for fish meal substitutes. Therefore, the value here only represents the amount of fish meal imported to mainland China, instead of the total fish feed demand. The value can be obtained from OECD-FAO (2014) a
b
A substitution rate of 20 % food waste powder in fish diets is selected based on the feeding trial results of Bake et al. (2009) and Hsieh (2010), which show insignificant changes in feed conversion rate. For details, please refer to section BFish feeding trials using fish feeds produced from food waste^
c
The suitable fish meal substitution rate of insect powder in fish diets falls within 17–30 % based on the feeding trial results of Newton et al. (2005), StHilaire et al. (2007), and Kroeckel et al. (2012), which show insignificant changes in fish growth performance and feed conversion rate. A median of 25 % is selected for calculation. For details, please refer to sectionBFish feeding trials using fish feeds produced from food waste^ It is mentioned in section BRegulatory hurdles in selling fish feed to mainland China^ that the food waste powder is unlikely to be authorized for import into mainland China. Therefore, the calculation is omitted
d
e
Since food waste contains about 80 % moisture content, the conversion rate is around 5:1
f
The largest plant for black soldier fly bioconversion in South Africa is reported to have a treatment capacity of 110 tpd (Packham 2014) and produce 7 tpd of insect powder (AgriProtein 2014a) g This value exceeds the total amount of food waste in Hong Kong, which is 3337 tpd (HKEPD 2014). It means that mainland China can absorb all the supply even if all the food waste in Hong Kong is converted into fish feed
contribution appears to be insignificant. The export of food waste powder into mainland China is not under consideration since its possibility is ruled out in section BRegulatory hurdles in selling fish feed to mainland China.^ Fortunately, the export of insect powder into mainland China can improve food waste recycling in Hong Kong substantially. This is because, if insect powder is accepted by mainland China and used to replace imported fish meal, it requires 10,560 tpd of food waste to meet the demand, which already exceeds the total amount of food waste in Hong Kong. In other words, mainland China can absorb all the supply even if all the food waste in Hong Kong is converted into fish feed. Moreover, there are markets other than mainland China looking for fish meal replacement. According to OECD-FAO (2014), while mainland China was the largest fish meal importer in 2013, accounting for 36 % of the total world’s imports, Japan (8 %) and Norway (7 %) also accounted for a large share. Nevertheless, even though black soldier fly bioconversion may be able to convert all food waste into resources in Hong Kong, it should be emphasized that not all food waste can be recycled by one technology. This is because the treatment capacity depends on various factors, for instance, the government’s target recycling rate and the infrastructure. The Hong Kong Government plans to build a network of around five to six Organic Waste Treatment Facilities (OWTFs) between 2014 and 2024 with a total recycling capacity of about 1300–1500 tpd, and it has been decided that the first two facilities (OWTF phase 1 and OWTF phase 2) will adopt
anaerobic digestion for treating 500 tpd of food waste (HKEB 2014). As a result, the maximum food waste treatment capacity using black soldier fly bioconversion in Hong Kong is 800–1000 tpd.
Technical challenges and future research directions While converting food waste to fish feed is feasible in Hong Kong, several important technical issues remain unresolved. Taking the example of a pilot bioconversion site in a rural area of Hong Kong, which used black soldier fly bioconversion to convert 100 kg of food waste into insect protein for fish feeding every day. The site was divided into two zones, namely the larva zone and the adult fly zone. In the larva zone, the black soldier fly larvae were held in multiple plastic trays with dimensions of 60 cm by 42 cm by 12 cm. Each tray held at most 1 kg of larvae and 2 kg of food waste. In the adult fly zone, the adult flies were kept in a greenhouse to mate and lay eggs so that new generations were born to continue the bioconversion process. The daily routine of the workers was to feed shredded food waste into each tray, harvest the mature larvae out from the tray, add new pupae to the adult fly zone, and take new eggs from the adult fly zone to the larva zone. Two major technical challenges were identified that may deter it from being scaled up: (1) automation of labor-intensive processes for higher cost-effectiveness and (2) improved process control for higher process reliability and efficiency.
Environ Sci Pollut Res
It was observed that the production in this pilot site was time-consuming and unproductive. For example, one worker had to spend the whole morning shredding 100 kg of food waste and feeding it manually to 36 trays, and the whole afternoon harvesting the mature larvae by hand sieving. Sometimes when the food residue became large granules and could not be easily sifted out, the worker had to separate the mature larvae out by handpicking. The same problem is also described in Amatya (2009) where they had to spend 10 h a week in Texas handling merely 13 kg of organic waste. Such a low-technology, labor-intensive operation can dramatically increase the production cost and become a bottleneck for scaling up. Consequently, it is necessary to make the processes more automatic and use machinery to replace human labor. Otherwise, it would incur a prohibitive labor cost in a modern city like Hong Kong. In addition, the process control in this pilot site is inadequate. For instance, the temperature often rose from 25 °C to above 40 °C within an hour after larval feeding, leading to a high larval mortality rate. Tomberlin et al. (2009) revealed that when black soldier fly larvae are reared at 27 and 30 °C, the survival rate averages at 74–97 %. Yet, when the temperature is increased to 36 °C, the survival rate of black soldier fly larvae is only 0.1 %. This explains why the pilot site did not have a healthy colony for food waste treatment. Furthermore, as the ambient temperature changes throughout the year, the performance of the black soldier fly larvae can fluctuate greatly. Newby (1997) reported in his field trials in Queensland, Australia, that the food consumption rate of the black soldier fly larvae declines with temperature and stops at 15 °C. As a result, waste reduction efficiency is much lower in cold weather. In order to maintain high process reliability and efficiency, it is therefore essential to exercise stringent process controls with a proper reactor design to ensure that the temperature can be effectively maintained within an optimal range. Last but not least, there still remain some uncertainties concerning the chemical hazards in the insect powder derived from food waste like bioaccumulation and biomagnification of harmful substances. Diener (2010) and Bank (2014) have determined the bioaccumulation factors of some heavy metals in black soldier fly larvae fed on contaminated chicken feed pellets and fresh human feces, respectively. Nevertheless, there are other contaminants that deserve attention such as aflatoxin and pesticides. In view of the chemical contaminations found in trash fish and compound feeds in mainland China (Guo et al. 2009), if insect powder contains low levels of contaminants, its inclusion in fish diets can be beneficial to the public health.
Conclusions This paper has evaluated the feasibility of converting food waste into fish feed in Hong Kong based on analyses of
market demand, technical viability, feed quality, regulatory hurdles, and potential contribution. It is found that a significant amount of food waste in Hong Kong can be recycled by producing fish feed for export to mainland China. Two conversion technologies, heat drying and black soldier fly bioconversion, are studied at great length, and the latter is found to be more viable. This is because the insect powder produced by black soldier fly bioconversion has a better chance of being authorized in mainland China, whereas the food waste powder produced by heat drying is unlikely to be accepted. It is hoped that food waste recycling in urban cities can be significantly improved through further research on black soldier fly bioconversion.
References AFCD, Agriculture, Fisheries and Conservation Department of Hong Kong (2009) Series 1: Fish Feed Management. Good Aquaculture Practices booklets. https://www.afcd.gov.hk/english/fisheries/fish_ aqu/fish_aqu_techsup/fish_feed_management.html. Accessed 31 Mar 2015 AgriProtein (2014a) Nature's natural feed ingredients. http://www. agriprotein.com/docs/agriprotein-brochure.pdf. Accessed 24 Oct 2014 AgriProtein (2014b) MagmealTM, Sustainable feed ingredients. http:// agriprotein.com/docs/agriprotein-magmeal.pdf. Accessed 24 Oct 2014 Amatya P (2009) Economics of Black Soldier Fly (Hermetia Illucens) in Dairy Waste Management. Dissertation, Tarleton State University AQSIQ, General Administration of Quality Supervision, Inspection and Quarantine of China (2015) Product list of approved imported feed materials and additives. http://dzwjyjgs.aqsiq.gov.cn/zwgk/slaq/ jjsljtjj/zrmd/201212/t20121225_335617.htm. Accessed 31 Mar 2015 (in Chinese) Bake GG, Akimoto A, Endo M, Takeuchi T (2009) Evaluation of recycled food waste as a partial replacement of fishmeal in the diets for first feeding Nile tilapia Oreochromis niloticus. Fish Sci 75(5): 1275–1283 Bank IJ (2014) To assess the impact of black soldier fly (Hermetia illucens) larvae on faecal reduction in pit latrines. Dissertation, London School of Hygiene &Tropical Medicine Bian R, Dai C, Zhang L, Wang J, Su Q, Feng M et al (2009) Analysis of feed use problem after the meal kitchen garbage harmless treatment. Feed China 9:26–30 (in Chinese) DARD, Department for Agricultural and Rural Development of UK (2013) Food and feed businesses. http://www.dardni.gov.uk/index/ animal-health-and-welfare/animal-by-products/animal-by-productsgeneral-guidance/food-and-feed-businesses.htm. Accessed 3 Oct 2014 Diener S (2010) Valorisation of Organic Solid Waste using the Black Soldier Fly, Hermetia illucens, in Low and Middle‐Income Countries. Dissertation, the Swiss Federal Institute of Aquatic Science and Technology (Eawag) DMANFQ, Dutch Ministry of Agriculture, Nature and Food Quality (2010) The Animal Feed Chain in China Opportunities to Enhance Quality and Safety Arrangements EPA, Environmental Protection Administration of Taiwan (2005) Visit to Japan on recycling technologies for food waste and bulky items.
Environ Sci Pollut Res http://report.nat.gov.tw/ReportFront/report_detail.jspx?sysId= C09403724. Accessed 10 Aug 2014 (in Chinese) EPA, Environmental Protection Administration of Taiwan (2014a) Collection of municipal solid waste by all organizations. Solid waste statistics EPA, Environmental Protection Administration of Taiwan (2014b) Properties of municipal solid waste. Solid waste statistics EPA, Environmental Protection Administration of Taiwan (2014c) Impact of food waste recycling over the years. http://www.epa.gov. tw/ct.asp?xItem=25301&ctNode=33183&mp=epa. Accessed 20 Dec 2014 (in Chinese) FAO, Food and Agriculture Organization of the United Nations (2013) Edible insects: Future prospects for food and feed security. Rome FAO, Food and Agriculture Organization of the United Nations (2014a) The State of World Fisheries and Aquaculture 2014. Rome FAO, Food and Agriculture Organization of the United Nations (2014b) Reducing waste and recycling leftovers for animal feed. Sustainability pathways Guo Y, Yu HY, Zhang BZ, Zeng EY (2009) Persistent halogenated hydrocarbons in fish feeds manufactured in South China. J Agric Food Chem 57(9):3674–3680 HKEB, Hong Kong Environment Bureau (2014) A Food Waste and Yard Waste Plan for Hong Kong 2014-2022. Hong Kong HKEPD, Hong Kong Environment Protection Department (2014) Monitoring of solid waste in Hong Kong 2012, Waste reduction statistics and data Hsieh M-J (2010) Effects of fish meal replacement by kitchen waste on the growth and body composition of tilapia (Oreochromis nilotica × Oreochromis aurea), giant grouper (Epinephelus lanceolatus) and orange-spotted grouper (Epinephelus coioides). Dissertation, National Taiwan Ocean University Kroeckel S, Harjes A-GE, Roth I, Katz H, Wuertz S, Susenbeth A et al (2012) When a turbot catches a fly: Evaluation of a pre-pupae meal of the Black Soldier Fly (Hermetia illucens) as fish meal substitute Growth performance and chitin degradation in juvenile turbot (Psetta maxima). Aquaculture 364-365:345–352 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. http://www.legco.
gov.hk/general/english/sec/duty_v/yr12-16/ea20130401.htm. Accessed 2 Aug 2014 Mo WY, Cheng Z, Choi WM, Man YB, Liu Y, Wong MH (2014) Application of food waste based diets in polyculture of low trophic level fish: Effects on fish growth, water quality and plankton density. Marine Poll Bull 85(2):803–809 MOE, Ministry of the Environment of Japan (2014) Generation of food waste and treatment status, Environmental Statistics 2012 Newby R (1997) Use of soldier fly larvae in organic waste management. In: Proceedings of the ‘Compost 97’ Conference, 14–15 July 1997, Griffith University, Brisbane, Australia Newton L, Sheppard C, Watson DW, Burtle G, Dove R (2005) Using the black soldier fly,Hermetia illucens, as a value-added tool for the management of swine manure. Phase 2 Report, Development of environmental superior technologies. NC State University. http:// www.cals.ncsu.edu/waste_mgt/smithfield_projects/phase2report05/ phase2report.htm. Accessed 7 Aug 2014 Nguyen H (2010) Decomposition of organic wastes by black soldier fly larvae. LAP Lambert Academic Publishing, Saarbrücken, Germany OECD-FAO, Organization for Economic Co-operation and Development and Food and Agriculture Organization of the United Nations (2014) OECD-FAO Agricultural Outlook 2014-2023 Packham C (2014) Insect farms: Investors see big profits in thinking small. Reuters News Polprasert C (2007) Organic waste recycling: technology and management, 3rd edn. IWA Publishing, London Sayeki M, Kitagawa T, Matsumoto M, Nishiyama A, Miyoshi K, Mochizuki M et al (2001) Chemical composition and energy value of dried meal from food waste as feedstuff in swine and cattle. Anim Sci J 72(7):34–40 (in Japanese) St-Hilaire S, Sheppard C, Tomberlin JK, Irving S, Newton L, McGuire MA et al (2007) Fly prepupae as a feedstuff for rainbow trout, oncorhynchus mykiss. J World Aquacult Soc 38(1):59–67 Sugiura K, Yamatani S, Watahara M, Onodera T (2009) Ecofeed, animal feed produced from recycled food waste. Vet Ital 45(3):397–404 Tomberlin JK, Adler PH, Myers HM (2009) Development of the black soldier fly (Diptera: Stratiomyidae) in relation to temperature. Environ Entomol 38(3):930–934 World Bank (2014) Global Economic Monitor (GEM) Commodities, World DataBank
BIOLOGICAL WASTE AS RESOURCE, WITH A FOCUS ON FOOD WASTE
Investigation of the available technologies and their feasibility for the conversion of food waste into fish feed in Hong Kong Jack Y. K. Cheng 1 & Irene M. C. Lo 1
Received: 30 December 2014 / Accepted: 6 May 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract Food waste is the largest constituent of municipal solid waste in Hong Kong, but food waste recycling is still in its infancy. With the imminent saturation of all landfill sites by 2020, multiple technologies are needed to boost up the food waste recycling rate in Hong Kong. Conversion of food waste into animal feeds is prevalent in Japan, South Korea, and Taiwan, treating over 40 % of their recycled food waste. This direction is worth exploring in Hong Kong once concerns over food safety are resolved. Fortunately, while feeding food waste to pigs and chickens poses threats to public health, feeding it to fish is considered low risk. In order to examine the feasibility of converting food waste into fish feed in Hong Kong, this paper investigates the market demand, technical viability, feed quality, regulatory hurdles, and potential contribution. The results show that a significant amount of food waste can be recycled by converting it into fish feed due to the enormous demand from feed factories in mainland China. Two conversion technologies, heat drying and black soldier fly bioconversion, are studied extensively. Black soldier fly bioconversion is preferable because the end-product, insect powder, is anticipated to gain import approval from mainland China. The authors suggest further research efforts to speed up its application for food waste recycling in urban cities.
Keywords Animal feed . Black soldier fly bioconversion . Fish feed . Food waste . Heat drying . Waste valorization Responsible editor: Philippe Garrigues * Irene M. C. Lo [email protected] 1
Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China
Introduction Hong Kong is facing a serious waste challenge since all the existing landfills will be saturated by 2020. As food waste represents the largest portion of municipal solid waste, eliminating food waste can alleviate the landfill pressure substantially. In Hong Kong, merely 0.6 % of food waste is recycled (HKEPD 2014), which is far behind other developed places in Asia such as South Korea (95 %), Taiwan (31 %), and Japan (25 %) (LegCo 2013; EPA 2014a, b; MOE 2014). Therefore, there is an urgent need to apply multiple technologies for food waste valorization to boost the recycling rate. After investigating the proportions of food waste recycling methods in South Korea, Taiwan, and Japan, it was revealed that more than 40 % of the food waste is processed into swine, poultry, and fish feeds to partly substitute the conventional feed ingredients. Table 1 provides summary statistics on their food waste recycling rates and a breakdown of their recycling methods. The question is whether Hong Kong can improve its food waste recycling through animal feed production. However, recycling food waste into animal feeds requires caution because food waste can be a medium for spreading contagious diseases. To mitigate public health risks, the European Commission has prohibited this practice since 2002 as stated in Regulation (EC) No. 1774/2002. Four notifiable diseases have been identified, namely foot and mouth disease, swine fever, highly pathogenic avian influenza, and transmissible spongiform encephalopathies (TSEs) (DARD 2013). These infectious disease outbreaks have caused severe economic loss, massive culling of animals, and even human deaths. In consideration of the previous unpleasant experiences battling bird flu and swine flu crises, the Hong Kong Government is unlikely to support the conversion of food waste into swine and poultry feeds for the sake of public health. Furthermore, feeding food waste to pigs and chickens
Environ Sci Pollut Res Table 1 Food waste recycling rates in South Korea, Taiwan, and Japan with a breakdown of the recycling methods
Food waste recycling rate (%) Recycled as animal feeds (%)a Recycled as compost (%) Recycled as other products (%)b Source a
South Korea
Taiwan
Japan
94.70 40.55 49.52 9.93 LegCo 2013
30.92 71.38 28.43 0.19 EPA 2014a, b, c
24.58 46.77c 39.05c 14.18c MOE 2014
Animal feeds include swine, poultry, and fish feed
b
Other products include methane gas for electricity generation and water heating, as well as oil and fat products such as biodiesel and printing inks c
Values shown only represent the commercial and industrial sector in Japan as the breakdown in the domestic sector is not available
can result in TSEs because this group of fatal degenerative brain diseases is caused by intraspecies recycling, which refers to the feeding of animals with proteins from the same species (e.g., feeding pork to pigs). Due to the complex composition of mixed food wastes, it would be difficult to avoid intraspecies recycling, and manual separation of pork and chicken meat would not be cost-effective. As a result, feeding food waste to pigs and chickens is neither safe nor practical. Fortunately, none of these four notifiable diseases are related to fish (DARD 2013). Moreover, according to Regulation (EC) No. 56/2013, feeding food waste to fish does not raise any concern over compliance with intraspecies recycling. Even though food waste may contain fish protein, the inclusion of fish protein in fish diets has been practised effectively for a long time and is believed to have a negligible TSE risk. As it is safe to turn food waste into fish feed, it is worth investigating further whether this can be adopted in Hong Kong to improve food waste recycling. The objectives of this paper are to (i) evaluate the market demand for new fish feed in local and export markets; (ii) screen the available technologies for converting food waste into fish feed to identify the suitable ones for Hong Kong; (iii) review previous feeding studies that use fish feed produced from food waste in the diet; (iv) assess the regulatory hurdles in selling the fish feed abroad; (v) quantify the amount of food waste required for meeting the market demand to evaluate its significance for food waste recycling in Hong Kong; and finally (vi) discuss the technical challenges and suggest further research directions. It is hoped that this study can serve as a useful reference for policymakers, industry players, and academic researchers to explore the potential of fish feed production as an effective means for food waste recycling.
Market demand for new fish feed in local and export markets As the goal of recycling is to turn wastes into valuable resources, market demand for end-products is crucial. This
paper covers the market demand in both local and export markets because fish feed is a commonly traded commodity and thus should not be limited to domestic sales. Among all export markets, mainland China is chosen as the sole focus because of its dominant share, which accounts for 62 % of global aquaculture production (FAO 2014a). Together with Hong Kong’s proximity to mainland China, it would be sensible for local fish feed producers to consider exporting the fish feed to mainland China. Domestic sales are often preferred due to low transportation cost and few regulatory hurdles. However, the market demand for fish feed in Hong Kong is limited, estimated at around 10 tonnes per day (tpd). The potential buyers are the fish farm owners since there is no feed factory in Hong Kong. There are three main sources of fish feed in Hong Kong, namely traditional vegetarian feed, pellet feed, and trash fish (AFCD 2009). The traditional vegetarian feed includes wheat bran, rice bran, weed, soy dregs, flour, and peanut cakes, which are suitable for freshwater fish. Pellet feed is made from grinding baked trash fish, fish oil, vitamins, and binder and is suitable for both freshwater and marine species. Trash fish refers to the small fish that are caught unintentionally during fishing activities and are suitable for marine fish. For these three types of fish feed, the traditional vegetarian feed and pellet feed have become more expensive in recent years due to the increasing prices of feed ingredients. The supply of trash fish has become limited after the trawling ban in Hong Kong in 2012. As a result, the fish farm owners are prone to switch to alternative feed sources. Relatively, the market demand for fish feed in mainland China is very significant and amounts to about 40,000 tpd (DMANFQ 2010). The target buyers are the fish feed manufacturers, which face increasing pressure due to rising feed cost. Fish meal, one of the important fish feed ingredients that is derived from fresh raw fish or fish trimmings, has tripled in price within a decade. Figure 1 illustrates a clear upward trend in fish meal price in the recent decade. This drives the feed factories to look for low-cost alternatives for fish meal replacement. Currently, more than 2000 tpd of fish meal is
Environ Sci Pollut Res
Fishmeal price (US$/ tonne)
2500
2000
1500
1000
500
0 Jul-04
Jul-06
Jul-08
Jul-10
Jul-12
Jul-14
Fig. 1 Trend in the fish meal price during 2004–2014. Data adapted from World Bank (2014)
imported to mainland China (OECD-FAO 2014). If the fish feed produced from food waste can be exported to mainland China to substitute fish meal at a competitive price, its market demand would be huge. In fact, one of the fish feed ingredients in the list of approved imported feed materials of mainland China, sandworm, is produced by feeding food waste like rapeseed dregs or soybean oil cake and has already been allowed to be imported to mainland China from North Korea (AQSIQ 2015).
Technology screening for converting food waste into fish feed in Hong Kong As the market demand for new fish feed exists, the next step is to select technologies that are suitable for a modern city like Hong Kong, and at the same time produce fish feed of high Table 2
quality. Table 2 provides an assessment of the potential conversion technologies. Nine technologies are identified from the relevant literature for screening, namely direct feeding, heat sterilization, heat drying, fermentation, algal production, aquatic weed production, earthworm production, housefly bioconversion and black soldier fly bioconversion. After taking into account the hygiene, land requirement, and ecological aspects, many technologies are not suitable for Hong Kong. Direct feeding, heat sterilization, and fermentation fail to guarantee that feeds are free of pathogens. Algal production and aquatic weed production require massive water bodies, which do not exist in Hong Kong. The earthworm species most often used for decomposing organic waste is a foreign invasive species that can threaten the native species. The housefly has long been known to be a disease carrier, and thus, mass rearing of houseflies cannot be tolerated in an urban city. After the elimination, only heat drying and black soldier fly bioconversion are considered applicable in Hong Kong. Heat drying assures feed safety as pathogenic viruses, bacteria, and mould can be inactivated under prolonged heat exposure and low water content. As for black soldier fly bioconversion, this fly species is safe to use since it can be found locally and does not disturb human beings or spread diseases (FAO 2013). Its end product, insect powder, also undergoes heat drying to achieve sterilization. Hence, the feasibility of these two technologies for converting food waste into fish feed was the focus of this study. Heat drying is a conventional method and is easy to operate. It applies warm and dry air to lower the moisture content down to approximately 10 %. This technology has been adopted in countries such as Japan and South Korea. For
Technology assessment for the conversion of food waste into fish feed in Hong Kong
No
Technology
Viability
Justifications
1 2 3
Direct feeding Heat sterilization Heat drying
No No Yes
Untreated food waste may carry pathogens (Polprasert 2007). Due to the high moisture content of food waste, it can spoil easily. It ensures feed safety because the prolonged heat exposure inactivates most pathogenic viruses and the low water content inhibits mould and bacterial growth.
4
Fermentation
No
5 6 7
Algal production Aquatic weed production Earthworm production
No No No
8 9
Housefly bioconversion Black soldier fly bioconversion
No Yes
Fermented food waste is semi-liquid, messy and smelly, which is inconvenient for feeding and storage. Drying of fermented food waste can improve its physical properties, but there is insufficient research data on the effect of feeding dried fermented food waste on fish growth performance. It requires a large area of land (Polprasert 2007). It requires a large area of land (Polprasert 2007). Earthworms suitable for food waste processing are foreign invasive species, which can be detrimental to the local ecosystem. Housefly is a notorious disease vector that is not acceptable in Hong Kong. Black soldier fly is safe to use because it is a local species and does not disturb human beings or spread diseases (FAO 2013). Through the bioconversion process, food waste is converted into insect biomass, which can also be processed into dried insect powder for the ease of usage and transportation as well as sterilization.
Environ Sci Pollut Res
instance, the maximum treatment capacity is 255 tpd in Yokohama, Japan (FAO 2014b). The end-product is a food waste powder that weighs about one-fifth of the original weight since the moisture content of food waste is around 80 %. In Japan, food waste powder can be registered as an Becofeed^ under the Japan Scientific Feed Association (Sugiura et al. 2009). Due to the complex composition of food waste, its crude protein level can fluctuate significantly, ranging from 3.0 to 37.7 %. On an industrial scale, the variation can be reduced to 19.8–25.8 % by collecting food waste from multiple sources such as school canteens, food factories, and convenience stores (Sayeki et al. 2001). While this may not be nutritious enough for high trophic level fish like carnivorous and omnivorous fish, its protein level is adequate for low trophic level fish like herbivorous and forage fish, which has a protein requirement of 18–23 %. Mo et al. (2014) demonstrated that using food waste powder for feeding big head carp and grass carp can yield a comparable result to commercially manufactured feed. Black soldier fly bioconversion refers to the use of the black soldier fly, Hermetia illucens (Diptera: Stratiomyidae) for converting food waste into insect biomass. Young larvae of the black soldier fly are reared continuously to consume the food waste. When the larvae become mature, they will be harvested, dried, and milled into insect powder. This technology has been commercialized in the USA, Canada, the Netherlands, and South Africa. For example, the maximum treatment capacity is 110 tpd in Cape Town, South Africa (Packham 2014). The insect powder produced can have a protein level of 39.5–59.2 % subject to the larval diet (Nguyen 2010). In South Africa, the insect powder is standardized to a minimum of 50 % protein level and has been approved by the Department of Agriculture, Forestry and Fisheries of the Republic of South Africa (AgriProtein 2014a, b). Its high and consistent protein level is desirable as a fish meal substitute for carnivorous fish such as grouper and sea bass, which requires a dietary protein level of over 38 % in their diets. Yet, this technology requires a high degree of technical Table 3
Fish feeding trials using fish feeds produced from food waste Although crude protein level is a useful parameter for assessing the nutritional adequacy of fish feed, the feed buyers are also concerned about the actual fish growth and costeffectiveness when making purchase decisions. These two factors can be determined through feeding studies by measuring specific growth rate (SGR) and feed conversion ratio (FCR), respectively. The SGR measures the daily growth rate of the fish, which is expressed by the equation SGR=[ln (W2) −ln (W1)]×100 %/ΔT where W1 is the initial weight (in grams), W2 is the final weight (in grams), and ΔT is the duration of the experiment (in days). A high SGR is desirable because it implies that the fish grow rapidly. The FCR refers to the amount of feed required to grow a kilogram of fish. A low FCR is preferable since it suggests reduced feed input, which may translate into feed cost savings. Several fish feeding trials have been conducted to evaluate the effect of replacing fish meal with the food waste powder produced by heat drying. The results of these feeding trials are summarized in Table 4. Bake et al. (2009) assessed the potential of using food industry wastes as a fish meal substitute in
Comparison of economic attractiveness between heat drying and black soldier fly bioconversion
Conversion rate (wet food waste: dry fish feed) Amount of fish feed produced from 100 t of food waste (tonne) Market value of fish feed (US$/tonne) Fish feed revenue gained from 100 tonnes of food waste (US$) a
expertise since it involves insect rearing processes, including fly breeding, fly egg laying, larvae feeding, and pupation (Newton et al. 2005). In order to evaluate the economic attractiveness of these two technologies, an economic analysis is conducted based on the conversion rates and market values of the two fish feeds (Table 3). For every 100 t of food waste recycled, heat drying generates revenue of US$2000–2600, whereas black soldier fly bioconversion generates US$8600. The latter delivers a higher economic return because the insect powder produced by black soldier fly bioconversion can be sold 10 times higher than the food waste powder produced by heat drying. The high market value of insect powder can be attributed to its consistently high crude protein level.
Heat drying
Black soldier fly bioconversion
5:1a 20 (food waste powder) 100–130c 2000–2600
15.7:1b 6.37 (insect powder) 1,350d 8,600
Since food waste contains about 80 % moisture content, the conversion rate is around 5:1
b
The largest plant for black soldier fly bioconversion in South Africa is reported to have a treatment capacity of 110 tpd (Packham 2014) and produce 7 tpd of insect powder (AgriProtein 2014a) c
EPA 2005
d
AgriProtein 2014a
Environ Sci Pollut Res Table 4
Effect of replacing fish meal with the food waste powder produced by heat drying in various fish diets
Fish species
Diet
Tilapia
Specific growth rate (%) Feed conversion ratio Reference
0 % food waste powder (control) 20 % fish meal substituted with food waste powdera Orange-spotted grouper 0 % food waste powder (control) 10 % fish meal substituted with food waste powderb 20 % fish meal substituted with food waste powderb 30 % fish meal substituted with food waste powderb 40 % fish meal substituted with food waste powderb Giant grouper 0 % food waste powder (control) 50 % fish meal substituted with food waste powderb 100 % fish meal substituted with food waste powderb Tilapia 0 % food waste powder (control) 50 % fish meal substituted with food waste powderb 100 % fish meal substituted with food waste powderb
8.65 8.37 6.22 5.88 5.88 5.10 4.65 5.24 3.95 1.75 5.02 4.34 3.66
0.76 0.76 1.34 1.34 1.27 1.66 1.78 1.39 1.82 5.13 1.46 2.63 3.79
Bake et al. 2009 Hsieh 2010
Hsieh 2010
Hsieh 2010
a
The source comes from food industry wastes, including leftover food from convenience stores, food waste residues discharged during food processing, hotel waste, restaurant cooking waste, tofu waste, and bread production waste. The crude protein content is 19.73 %
b
The source comes from restaurant waste in the National Taiwan Ocean University. The crude protein content is 38 %
the diet of tilapia. The results showed that the FCR remained unchanged from the control when 20 % of fish meal was substituted by food industry wastes. However, the SGR dropped as a result of lower feed intake. Similar findings were also reported in Hsieh (2010) that the FCR was maintained while the SGR was reduced when 20 % of fish meal was replaced by restaurant wastes in the diet of orange-spotted grouper. Hsieh (2010) also evaluated the SGR and FCR at high fish meal substitution rates beyond 30 % in the diets of orange-spotted grouper, giant grouper, and tilapia and found that both SGR and FCR were adversely affected in these fish species. From these results, the maximum substitution rate of food waste powder in fish diets is suggested to be 20 %. One should note that the food waste powder has to be economical to compensate for the decrease in SGR at a 20 % substitution rate. Partial replacement of fish meal with the insect powder produced by black soldier fly bioconversion has been studied in various feeding studies. Table 5 provides a summary of the fish feeding trials. Newton et al. (2005) replaced fish meal and soybean meal with insect powder in channel catfish diets at 0, 7.5, 15, 22.5, and 30 %. The results revealed that there were no significant differences in both the SGR and the FCR up to a 30 % substitution rate. St-Hilaire et al. (2007) investigated the inclusion of insect powder in the diet of rainbow trout for fish meal replacement at three different levels of 0, 25, and 50 %. It was found that the FCR and SGR were negatively affected at a 50 % substitution rate, but changed only slightly at 25 %. Kroeckel et al. (2012) evaluated different fish meal substitution levels with defatted insect powder in juvenile turbot diets at 0, 17, 33, 49, 64, and 76 %. The FCR was not affected at a 17 % substitution rate as compared to the control diet, but increased when a greater percentage of insect powder was
applied. From these results, it is believed that the suitable fish meal substitution rate of insect powder in fish diets falls within 17–30 %.
Regulatory hurdles in selling fish feed to mainland China The feed industry is highly regulated in most countries because it can affect animal and human health. If the fish feed fails to gain approval from the authority, the sales potential can be greatly reduced regardless of its price or nutritional value. Consequently, particular attention should be paid to the regulatory requirements in the export market. In mainland China, two regulatory bodies are involved for feed import, which are the Ministry of Agriculture (MoA) and the General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ). Approvals from both sides are prerequisites to import feed into mainland China. In order to verify the possibility of selling fish feed to mainland China, it is vital to understand the roles of the MoA and AQSIQ. The MoA is responsible for the administration and supervision of feed and feed additives. Before gaining approval from the MoA, any application has to undergo a scientific assessment on feed safety, efficacy, and environmental impact by the National Feed Assessment Committee. Meanwhile, the AQSIQ is involved in certification and standardization for quality control of imported goods. Based on their responsibilities and assessment criteria, the possibility of importing fish feed to mainland China is analyzed. Regarding the food waste powder produced by heat drying, its import can pose a serious threat to the public health since it can cause intraspecies recycling when used in the production
Environ Sci Pollut Res Table 5
Effect of replacing fish meal with the insect powder produced by black soldier fly bioconversion in various fish diets
Fish species
Diet
Specific growth rate (%)
Feed conversion ratio
Reference
Channel catfish
0 % insect powder (control) 7.5 % fish meal and soybean meal substituted with insect powdera 15.0 % fish meal and soybean meal substituted with insect powdera 22.5 % fish meal and soybean meal substituted with insect powdera 30.0 % fish meal and soybean meal substituted with insect powdera 0 % insect powder (control) 25 % fish meal substituted with insect powderb 50 % fish meal substituted with insect powderb 0 % defatted insect powder (control) 17 % fish meal substituted with defatted insect powderc 33 % fish meal substituted with defatted insect powderc 49 % fish meal substituted with defatted insect powderc 64 % fish meal substituted with defatted insect powderc 76 % fish meal substituted with defatted insect powderc
1.70 1.84 1.79 1.54 1.70 3.09 2.92 2.73 1.73 1.53 1.43 1.19 0.94 0.63
2.20 1.87 1.96 2.55 2.31 1.18 1.22 1.47 0.76 0.76 0.82 0.86 0.98 1.21
Newton et al. 2005
Rainbow trout
Turbot
St-Hilaire et al. 2007
Kroeckel et al. 2012
a
The insect powder was produced from dried black soldier fly prepupae raised on swine manure, with a crude protein level of 43.2 %
b
The insect powder was produced from dried black soldier fly prepupae raised on swine manure, with a crude protein level of 43.6 %
c
The insect powder was obtained from a commercial producer (Hermetia Futtermittel GbR, Baruth/Mark, Germany). The diet fed to the larvae is unknown. The crude protein of the defatted insect powder is 54.1 %
of other animal feeds in the feed factory, which can be difficult to monitor. Bian et al. (2009) also stressed the TSE risk involved when animals are fed with food waste. Owing to the concern over TSE transmission risk, it is anticipated that the National Feed Assessment Committee of the MoA is likely to raise an objection. From the perspective of the AQSIQ, food waste powder is difficult to be standardized because of its complex composition and unstable source. Bian et al. (2009) explain that the homogeneity of feed is vital for standardization to control quality and prevent hazards. In fact, almost all feed ingredients listed in the Catalogue of Feed Materials of China are homogeneous products. In addition, according to BThe Administrative Measures on New Feeds and New Feed Additives^ in mainland China, a new feed ingredient has to be a single feed, meaning that the source should originate from a single type of plant, animal, microbe, or mineral. As the nature of food waste powder does not fit this definition, the AQSIQ is unlikely to grant import approval for the food waste powder. As for the insect powder produced by black soldier fly bioconversion, it mitigates the concern over intraspecies recycling because it is safe to feed insect protein to pigs, chickens, and fish. Moreover, insect powder has a high and stable protein level that makes it a viable alternative to fish meal. Furthermore, the Food and Agriculture Organization of the United Nations also recommends the feed industry to seriously consider its use as animal feed (FAO 2013). Since insect powder can meet the feed safety and efficacy criteria of the National Feed Assessment Committee, the MoA may accept its application for feed import. For the AQSIQ, insect powder is a material that can be easily standardized since it
belongs to a single feed. Furthermore, a category for Binsect and processed insect products^ has already existed in the Catalogue of Feed Materials of China. Therefore, this new insect powder can be included in the catalogue easily. With the ease of standardization and certification, insect powder tends to receive little objection from the AQSIQ as feed quality can be controlled properly. From the regulatory perspective, it is found that insect powder is more likely to be authorized in mainland China, whereas food waste powder tends to be rejected. As feed safety, feed quality, and quality control are universally important around the world, this may also have reference values for other countries.
Potential contribution to food waste recycling in Hong Kong In order to quantify the potential contribution of fish feed production to food waste recycling in Hong Kong, the amounts of food waste required to meet the market demand for new fish feed are calculated in Table 6 by the formula: F=D×S×C, where F is the amount of food waste required (in tpd), D is the market demand for fish feed (in tpd), S is the suitable substitution rate of new fish feed in fish diets, and C is the conversion rate from wet food waste to dry fish feed. By selling the fish feed locally, the amounts of food waste required through heat drying and black soldier fly bioconversion are 10 and 39 tpd, respectively. Considering that the amount of food waste in Hong Kong is about 3300 tpd, the
Environ Sci Pollut Res Table 6
Amount of food waste required to meet the market demand for fish feed in Hong Kong and China Hong Kong
Market demand for fish feed (tpd) Type of new fish feed Substitution rate of new fish feed in fish diets Market demand for new fish feed (tpd) Conversion rate (wet food waste: dry fish feed) Amount of food waste required to meet market demand (tpd)
D
10 Food waste powder S 20%b DxS 2 C 5:1e F=D×S×C 10
China 2687a Insect powder Food waste powder 25%c 20%b 2.5 n/ad f 15.7:1 5:1e 39 n/ad
Insect powder 25%c 672 15.7:1f 10560g
It is mentioned in section BMarket demand for new fish feed in local and export markets^ that feed manufacturers in mainland China are searching for fish meal substitutes. Therefore, the value here only represents the amount of fish meal imported to mainland China, instead of the total fish feed demand. The value can be obtained from OECD-FAO (2014) a
b
A substitution rate of 20 % food waste powder in fish diets is selected based on the feeding trial results of Bake et al. (2009) and Hsieh (2010), which show insignificant changes in feed conversion rate. For details, please refer to section BFish feeding trials using fish feeds produced from food waste^
c
The suitable fish meal substitution rate of insect powder in fish diets falls within 17–30 % based on the feeding trial results of Newton et al. (2005), StHilaire et al. (2007), and Kroeckel et al. (2012), which show insignificant changes in fish growth performance and feed conversion rate. A median of 25 % is selected for calculation. For details, please refer to sectionBFish feeding trials using fish feeds produced from food waste^ It is mentioned in section BRegulatory hurdles in selling fish feed to mainland China^ that the food waste powder is unlikely to be authorized for import into mainland China. Therefore, the calculation is omitted
d
e
Since food waste contains about 80 % moisture content, the conversion rate is around 5:1
f
The largest plant for black soldier fly bioconversion in South Africa is reported to have a treatment capacity of 110 tpd (Packham 2014) and produce 7 tpd of insect powder (AgriProtein 2014a) g This value exceeds the total amount of food waste in Hong Kong, which is 3337 tpd (HKEPD 2014). It means that mainland China can absorb all the supply even if all the food waste in Hong Kong is converted into fish feed
contribution appears to be insignificant. The export of food waste powder into mainland China is not under consideration since its possibility is ruled out in section BRegulatory hurdles in selling fish feed to mainland China.^ Fortunately, the export of insect powder into mainland China can improve food waste recycling in Hong Kong substantially. This is because, if insect powder is accepted by mainland China and used to replace imported fish meal, it requires 10,560 tpd of food waste to meet the demand, which already exceeds the total amount of food waste in Hong Kong. In other words, mainland China can absorb all the supply even if all the food waste in Hong Kong is converted into fish feed. Moreover, there are markets other than mainland China looking for fish meal replacement. According to OECD-FAO (2014), while mainland China was the largest fish meal importer in 2013, accounting for 36 % of the total world’s imports, Japan (8 %) and Norway (7 %) also accounted for a large share. Nevertheless, even though black soldier fly bioconversion may be able to convert all food waste into resources in Hong Kong, it should be emphasized that not all food waste can be recycled by one technology. This is because the treatment capacity depends on various factors, for instance, the government’s target recycling rate and the infrastructure. The Hong Kong Government plans to build a network of around five to six Organic Waste Treatment Facilities (OWTFs) between 2014 and 2024 with a total recycling capacity of about 1300–1500 tpd, and it has been decided that the first two facilities (OWTF phase 1 and OWTF phase 2) will adopt
anaerobic digestion for treating 500 tpd of food waste (HKEB 2014). As a result, the maximum food waste treatment capacity using black soldier fly bioconversion in Hong Kong is 800–1000 tpd.
Technical challenges and future research directions While converting food waste to fish feed is feasible in Hong Kong, several important technical issues remain unresolved. Taking the example of a pilot bioconversion site in a rural area of Hong Kong, which used black soldier fly bioconversion to convert 100 kg of food waste into insect protein for fish feeding every day. The site was divided into two zones, namely the larva zone and the adult fly zone. In the larva zone, the black soldier fly larvae were held in multiple plastic trays with dimensions of 60 cm by 42 cm by 12 cm. Each tray held at most 1 kg of larvae and 2 kg of food waste. In the adult fly zone, the adult flies were kept in a greenhouse to mate and lay eggs so that new generations were born to continue the bioconversion process. The daily routine of the workers was to feed shredded food waste into each tray, harvest the mature larvae out from the tray, add new pupae to the adult fly zone, and take new eggs from the adult fly zone to the larva zone. Two major technical challenges were identified that may deter it from being scaled up: (1) automation of labor-intensive processes for higher cost-effectiveness and (2) improved process control for higher process reliability and efficiency.
Environ Sci Pollut Res
It was observed that the production in this pilot site was time-consuming and unproductive. For example, one worker had to spend the whole morning shredding 100 kg of food waste and feeding it manually to 36 trays, and the whole afternoon harvesting the mature larvae by hand sieving. Sometimes when the food residue became large granules and could not be easily sifted out, the worker had to separate the mature larvae out by handpicking. The same problem is also described in Amatya (2009) where they had to spend 10 h a week in Texas handling merely 13 kg of organic waste. Such a low-technology, labor-intensive operation can dramatically increase the production cost and become a bottleneck for scaling up. Consequently, it is necessary to make the processes more automatic and use machinery to replace human labor. Otherwise, it would incur a prohibitive labor cost in a modern city like Hong Kong. In addition, the process control in this pilot site is inadequate. For instance, the temperature often rose from 25 °C to above 40 °C within an hour after larval feeding, leading to a high larval mortality rate. Tomberlin et al. (2009) revealed that when black soldier fly larvae are reared at 27 and 30 °C, the survival rate averages at 74–97 %. Yet, when the temperature is increased to 36 °C, the survival rate of black soldier fly larvae is only 0.1 %. This explains why the pilot site did not have a healthy colony for food waste treatment. Furthermore, as the ambient temperature changes throughout the year, the performance of the black soldier fly larvae can fluctuate greatly. Newby (1997) reported in his field trials in Queensland, Australia, that the food consumption rate of the black soldier fly larvae declines with temperature and stops at 15 °C. As a result, waste reduction efficiency is much lower in cold weather. In order to maintain high process reliability and efficiency, it is therefore essential to exercise stringent process controls with a proper reactor design to ensure that the temperature can be effectively maintained within an optimal range. Last but not least, there still remain some uncertainties concerning the chemical hazards in the insect powder derived from food waste like bioaccumulation and biomagnification of harmful substances. Diener (2010) and Bank (2014) have determined the bioaccumulation factors of some heavy metals in black soldier fly larvae fed on contaminated chicken feed pellets and fresh human feces, respectively. Nevertheless, there are other contaminants that deserve attention such as aflatoxin and pesticides. In view of the chemical contaminations found in trash fish and compound feeds in mainland China (Guo et al. 2009), if insect powder contains low levels of contaminants, its inclusion in fish diets can be beneficial to the public health.
Conclusions This paper has evaluated the feasibility of converting food waste into fish feed in Hong Kong based on analyses of
market demand, technical viability, feed quality, regulatory hurdles, and potential contribution. It is found that a significant amount of food waste in Hong Kong can be recycled by producing fish feed for export to mainland China. Two conversion technologies, heat drying and black soldier fly bioconversion, are studied at great length, and the latter is found to be more viable. This is because the insect powder produced by black soldier fly bioconversion has a better chance of being authorized in mainland China, whereas the food waste powder produced by heat drying is unlikely to be accepted. It is hoped that food waste recycling in urban cities can be significantly improved through further research on black soldier fly bioconversion.
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