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A novel bioconversion for value-added products from food waste using Musca domestica
Waste Management xxx (2016) xxx–xxx
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A novel bioconversion for value-added products from food waste using Musca domestica Yi Niu a, Dong Zheng a, Binghua Yao b, Zizhe Cai a, Zhimin Zhao a, Shengqing Wu a, Peiqing Cong c, Depo Yang a,⇑ a b c
School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China College of Animal Science, South China Agricultural University, Guangzhou 510642, China State Key Laboratory of Bio-control, School of Life Science, Sun Yat-Sen University, Guangzhou 510006, China
a r t i c l e
i n f o
Article history: Received 27 February 2016 Revised 27 August 2016 Accepted 14 October 2016 Available online xxxx Keywords: Food waste Bioconversion Musca domestica Maggot protein Maggot oil Biodiesel
a b s t r a c t Food waste, as a major part of the municipal solid waste has been generated increasingly worldwide. Efficient and feasible utilization of this waste material for productivity process is significant for both economical and environmental reasons. In the present study, Musca domestica larva was used as the carrier to conduct a bioconversion with food waste to get the value-added maggot protein, oil and organic fertilizers. Methods of adult flies rearing, culture medium adjuvant selection, maggot culture conditions, stocking density and the valorization of the waste have been explored. From the experimental results, every 1000 g culture mediums (700 g food waste and 300 g adjuvant) could be disposed by 1.5 g M. domestica eggs under proper culture conditions after emergence in just 4 days, 42.95 ± 0.25% of which had been consumed and the culture medium residues could be used as good organic fertilizers, accompanying with the food waste consumption, 53.08 g dried maggots that contained 57.06 ± 2.19% protein and 15.07 ± 2.03% oil had been produced. The maggot protein for its outstanding pharmacological activities is regarded as a good raw material in the field of medicine and animal feeding. Meanwhile, the maggot oil represents a potential alternative feedstock for biodiesel production. In our study, the maggot biodiesel was obtained after the procedure of transesterification reaction with methanol and the productivity was 87.71%. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Waste as a major problem globally becomes more and more significant in both developed and developing countries. Food waste which includes unconsumed food that is discarded by food processing industries, retailers, restaurants, and consumers(Huang et al., 2015), is the single largest component of the waste stream worldwide. For its high contents of biodegradable organic compounds and moisture (75–85%), food waste readily decomposes, followed by generating foul smell and sometimes leading to illness under natural environments (Moon et al., 2009). According to the data from the Food and Agriculture Organization of the United Nations (FAO), there are 1.3 billion tons of food waste produced every year, around one-third of food produced for human consumption globally (Gustavsson, 2011). In contrast to current ⇑ Corresponding author at: School of Pharmaceutical Science, Sun Yat-sen University, Guangzhou Higher Education Mega Center, Guangzhou, China. E-mail address: [email protected] (D. Yang).
large-scale production, amount of this food waste found no efficient uses different from landfill or first-generation recycling practices (such as animal feed, composting and incineration) (Lin et al., 2013). However, incineration and landfill are two crucial sources of greenhouse gas emission (Camobreco et al., 1999), animal feed and composting with food waste that will increase the risks of occurrence of animal related diseases and the pollution of the surface and underground water (Uncu and Cekmecelioglu, 2011). Waste is a resource rather than problem, The McKinsey Global Institute announced that food waste ranked third of fifteen identified resources with productive opportunities (Dobbs.R 2011). Consequently, it is an urgent issue of finding more sustainable, efficient and economic competitive methods for food waste recycling. Bioconversion, due to its environmentally friendly, sustainable, and renewable properties, is considered to be one of the most promising methods to deal with food waste. Some scholars have conducted the bioconversion using earthworm and Black Soldier Fly and they all obtained visible results in vary degrees (Nguyen et al., 2015; Wani et al., 2013).
http://dx.doi.org/10.1016/j.wasman.2016.10.054 0956-053X/Ó 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Niu, Y., et al. A novel bioconversion for value-added products from food waste using Musca domestica. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.10.054
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Y. Niu et al. / Waste Management xxx (2016) xxx–xxx
Musca domestica (Linnaeus) (Diptera: Muscidae) is a kind of holometabolous insects with morphologically distinct stages of egg, larva (maggot), pupa and adult (Roger, 2002). The larva of M. domestica are fond of organic wastes such as rotten organisms, rubbish, and animal waste, thus food waste is an eligible feed for them. Unlike many pests that consume waste, Musca domestica has many outstanding advantages as following: firstly with their strong adaption to environment and not easily infected, M. domestica exhibits a large geographic distribution, thriving in temperatures ranging from 20 °C to 35 °C in areas like Australia, the Pacific, Africa, the Americas and Asia. Without the species introduction, the food waste consumption can be achieved. Secondly, Musca domestica has highly reproductive ability, fast growth and short lifecycle. Each M. domestica female can lay totally approximately 500 eggs during its entire life. The lifecycle of them is about 15 days, they can usually survive 7–8 generations per year, and even 20 generations under proper conditions. Year-round breeding could be achieved through artificial feeding circumstance. Last but not least accompanying with the consumption of waste, more valuable and worthy production has been produced. The dried maggots have 55% crude protein and 15% fat. Maggot protein is a good substitute of fish meal in livestock (Satoh et al., 2010), due to its noticeable pharmacological activities. It has also been regarded as a promising medicinal material. In our study the maggot oil as a new material for biodiesel has been proved to be viable. Therefore we can prospect that the bioconversion for value-added products (such as maggot protein and biodiesel) from food waste using Musca domestica is universal, efficient and with high economic and environmental values. Food waste, on account of its high viscosity and humidity, is not suitable for rearing maggots directly, in which some low-cost adjuvant should be added. In the present study, we have examined the impact of different adjuvant on the Musca domestica larval development, assessed the maggots’ capacity of reducing food waste. The protein as well as oil increment of maggots have been valued. Meanwhile, the elementary analysis of the maggot fatty acid and preparations of maggot biodiesel have been done. 2. Materials and methods 2.1. Rearing of the adult flies The Musca domestica in our research was captured from wild in Zhongshan, China and identified by Professor Hong PANG, department of life science, Sun Yat-sen University. Every 5000 adults were reared in one 50 ⁄ 50 ⁄ 50 cm mesh cage (0.2 mm pore size) with a stocking density of approximate 2.8 cm3 per fly. M. domestica colonies were maintained on a diet of 2:2:1 sugar powdered: milk: hen egg at 25 °C with a photoperiod of 12:12 (L:D) h cycle. Small white bags filled with soggy wheat bran and brown sugars (4:1) were placed in the colony cages as oviposition medium. Every other 12 h, the concentrated eggs were collected and inoculated into different culture mediums. 2.2. Examined the impact of different adjuvant on the larval development Food waste described in this paper was obtained daily from three different sites, a Chinese restaurant, a western restaurant and a breakfast shop in Zhongshan, China. They were dehydrated with strainers (75% moisture content) followed by mixing and shattering uniformly for backup. Four kinds of low-cost offcuts were chosen as the adjuvant of food waste: millet bran, wholeplant corn silage, wheat bran and sawdust, which were all dried and crushed coarsely. The study subjects were divided into four
groups, each group contained prepared food waste (700 g) and one kind of adjuvant (300 g) that mentioned above (Group1: wheat bran, G2: millet bran, G3: whole-plant corn silage and G4: sawdust). All the groups were mixed uniformly and kept the humidity at 70–80% with tap water, pH at 5–7 and the temperature at 25– 30 °C. Every group was inoculated with 0.8 g M. domestica eggs (13,000 larva). After the eggs hatching, the culture medium was stirred evenly every other 6 h at the premise of keeping the whole system ventilating. After four-day rearing, the third instar larva was harvested and analyzed. All procedures were performed with at least three independent replicates. 2.3. Assessing the maggots’ capacity of reducing food waste Different quantities of M. domestica eggs including 0.5 g (8000 eggs), 0.75 g (12,000 eggs), 1 g (16,000 eggs), 1.25 g (20,000 eggs), 1.5 g (24,000 eggs) and 2 g (32,000 eggs) were inoculated in 700 g food waste and 300 g wheat bran. The rearing methods as employed in 2.2 were used. After four-day cultivating, the even weight of single maggot was assessed, the maggots and culture medium were separated and dried in the oven (60 °C), then weighted respectively (on account of the variation water content of the fore and aft culture mediums, we adopted dried culture mediums weight to calculate the culture medium consumption rate here). The protein and oil content of the larva had also been evaluated. 2.4. Analysis 2.4.1. Determination of protein, oil consent of larva and nutrient evaluation of the adjuvant Fresh third instar larva were put into boiling water for instant death, dried in an oven at 60 °C for 24 h, and crushed into powder. The method of Kjeldahl nitrogen determination was used to determinate the content of protein of larva, KJELTEC 8400 Auto Kjeldahl Nitrogen Analysis (FOSS. Denmark) was used in our study. The oil extraction was carried out using a soxhlet extractor with n-hexane as solvent for 8 h, following with a recovered process using a rotary evaporator at 50 °C under vacuum. Oil was warmed at 80 °C for 2 h to remove the excess moisture then weighted to determine the oil contents. Fiber and ash contents were analyzed with the method of acid and alkali digestion by the Fibertec2010 (FOSS. Denmark). Carbohydrate contents were the rest material contents after getting rid of the other three factors. Protein, oil, carbohydrate, fiber and ash of the adjuvant had been evaluated in our study. 2.4.2. Maggot fatty acid composition analysis The maggot fatty acid composition was analyzed with a Finnigan GC–MS system equipped with a DB-5 MS column (30 m ⁄ 0.25 mm ⁄ 0.25 lm) and FDI. Helium was used as the carrier gas at a flow rate of 1.0 ml/min and a pressure of 100 kPa. The oven temperature was set at 210 °C for 15 min. Electron ionization mode (ionization energy of 70 eV) was used for GC–MS detection. The injector and MS transfer temperatures were both set at 250 °C. The scanning mass range selected was 29–500 m/z. A sample volume of 1.0 lL was injected into the column with the split ratio of 1:30 (EN14103, 2003). Data were managed with Xcalibur software with the NIST mass spectra library database. 2.5. Preparation of maggot biodiesel Fresh third instar larvae were put into boiling water for instant death, dried in an oven at 60 °C for 4 h, and crushed into powder. The powder was then immersed in five times amount of nhexane for fat extraction for 12 h. The extraction was recovered by using a rotary evaporator at 50 °C under vacuum. Oil was
Please cite this article in press as: Niu, Y., et al. A novel bioconversion for value-added products from food waste using Musca domestica. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.10.054
Y. Niu et al. / Waste Management xxx (2016) xxx–xxx
warmed at 80 °C for 2 h to remove the excess moisture. Then the obtained maggot oil (MO) was subjected by an acid pretreatment to lower the acid value. Maggot oil and methanol were added to a flask in a ratio of 1:8 with an amount of sulfuric acid (1 wt% MO) and then were heated at 70 °C for 2 h. The mixture was allowed to settle for 2 h, and the methanol-water fraction in the top layer was removed. The oil phase was washed with distilled water until a neutral pH was achieved. This procedure was followed by the removal of the residual methanol by rotary evaporation (Leung et al., 2012). The pretreated maggot oil was heated to the desired temperature in an oil bath before starting the reaction. KOH (Potassium hydroxide) was used as catalyst. Experiments were performed under the conditions referred to the paper of Zhuoxue Li et al. that methanol to oil molar ratios was at 6:1, catalyst concentrations of KOH was 1.4 (weight%), reaction temperature was 55 °C and reaction time was30 min. Agitation intensity (200 rpm) was kept constant throughout the whole course of experiments. When the reaction had proceeded for the desired duration, the reaction flask was transferred to ice to stop and then centrifugated at 3000 rpm for 5 min. The upper layer was separated and washed with 70 °C deionized water until it reached neutrality. After a process of drying, housefly larva methyl esters (biodiesel) was obtained (Li et al.,2012). 3. Results and discussion 3.1. Adult fly rearing The adults stocking density is approximate 2.8 cm3 per fly, which is described in the paper of Cickova et al. (2012). Appropriate temperature as well as sufficient illumination is very important for oviposition of adult flies. We found that neither a high (>35 °C) nor a low (<20 °C) temperature is suitable for flies to lay eggs and in dim light the amount of eggs would be reduced as well. So we maintained the housefly colonies at 25 °C and gave additional light during cloudy days. Generally brown sugar and milk are the usual food for adult flies, during our rearing, hen egg was added to their diet, for the reason that protein is the very nutrition for females generating eggs. Flies laid the largest quantity of eggs during the second week after emergence. At the peak of oviposition, we could collect 10 g eggs (160,000 eggs) from one cage within 12 h. Four weeks after emergence we removed and executed the old flies. In consideration of females’ preferring whiteness, white bags were used to collect eggs in the M. domestica colony. 3.2. The impact of different adjuvant on the larval development The viscosity and humidity of food waste are extremely high, and its moisture content can reach 70–80%. For being photophobic, the larva will drill into the culture medium. Highly viscous food waste cannot provide sufficient air for maggots. Therefore food waste is not suitable for rearing maggots directly and we should add some low-cost adjuvant into it. Wheat bran, millet bran, whole-plant corn silage and sawdust were selected as candidates with the reason that they are all easy-accessed, low-cost and large-outputted. In addition to the bioconversion of food waste into valuable products, we hope to find a new significant usage of these remnants. We assessed the dried maggots’ production, protein and oil contents as well as the even weight of each larva from four groups (by mean of weighting 100 fresh maggots then deducing the even weight of each larva). The results were shown in Fig. 1. All the parameters were the means of three parallel testing. From the results we can find group 1 (700 g food waste and 300 g wheat bran) provide the highest production of maggots, the rank of even weight of each larva is also the first one. At the
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Fig. 1. The larva quality parameters of four different culture mediums, Group1: wheat bran, G2: millet bran, G3: whole-plant corn silage and G4: sawdust. Datas are expressed as the means ± standard error of mean (SEM).
same time this group is the very culture medium that cultivated the maggots with the highest content of protein and oil. To explain this phenomenon, the nutrition analysis (protein, oil, carbohydrate, fiber and ash) of the adjuvant had been done (Table 1). Based on the available data, we can find wheat bran had the highest protein and fat content and lowest content of fiber and ash. Previous study showed that fat is the most consumed nutrients in the maggot diet, followed by protein and carbohydrate accounts for just a small part of the total depletion and there is hardly any consumption of fiber and ash (Lin Bai et al., 2007). Therefore it could be known that wheat bran is the most eligible adjuvant of the four. Besides the nutrition supply, proper content and different variety of fiber of adjuvant is the main influential factor of cultivation. Appropriate content of fiber can raise the air permeability of the culture mediums. However, excessive fiber especially binding with lignin will not only prevent the leaching of nutrients but also increase the losses of water and heat for its lower hydrophily than protein and sugar. Thus it will change the humidity and temperature of culture mediums, which are the two essential factors of maggot rearing. Even though millet bran and whole-plant corn silage can offer nutrition to maggots to some extent, they cannot provide relatively stable culture circumstances. The culture result was not successful as group1. Consequently we hypothesized that wheat bran may be an eligible adjuvant of food waste to culture housefly maggots. 3.3. The maggots’ capacity of reducing food waste and ability of protein and oil increment The dried maggot productions, culture medium consumption rates and even single larva weights under different inoculum densities (Table 2) were compared. It turned out that the dried maggot production and culture mediums consumption would increase along with the raise of inoculums density. This trend became flat gradually when the inoculums density was higher than 1.5 g/kg. Meanwhile the even single larva weight decreased accompanying the increase of inoculums density (Figs. 2–4). More than 40% culture mediums could be consumed by M. domestica larva. It could be shown that when the inoculums density was increased, substituting for the accruing of consumption rates was the decrease of even single larva weight, which indicated the food waste culture medium contained 40 45% nutriments that could be consumed by maggots and the optimal quantity of housefly eggs for success-
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Table 1 Nutrition analysis of four culture medium adjuvants.
Protein (%) Fat (%) Carbohydrate (%) Fiber and ash (%)
Wheat bran
Millet bran
Whole-plant corn silage
Sawdust
14.4 ± 0.30 3 ± 0.24 71.8 ± 0.18 10.8 ± 0.24
8.6 ± 0.15 5.76 ± 0.28 60.14 ± 0.31 25.5 ± 0.11
5.7 ± 0.26 3.2 ± 0.22 72.8 ± 0.5 18.3 ± 0.19
1.5 ± 0.13 1.1 ± 0.33 26.2 ± 0.26 71.2 ± 0.27
Table 2 Parameters of cultivation under different inoculums densities. Inoculums density (g/kg)
Production (g/kg)
Consumption rate (%)
Single larva weight (mg)
0.5 0.75 1 1.25 1.5 2
32.69 ± 1.03 42.66 ± 0.92 45.28 ± 1.21 45.7 ± 0.80 53.08 ± 0.96 55.81 ± 0.65
38.74 ± 0.43 38.53 ± 1.31 37.26 ± 0.78 41.05 ± 1.47 42.95 ± 0.25 43.49 ± 1.31
21.42 ± 1.01 19.57 ± 0.77 16.66 ± 0.74 12.65 ± 0.25 11.59 ± 0.69 10.27 ± 0.93
Fig. 4. Even single larva weights under different inoculum densities, datas are expressed as the means ± standard error of mean (SEM).
Fig. 2. Dried maggot productions under different inoculum densities, datas are expressed as the means ± standard error of mean (SEM).
ful bioconversion was 1.5 g (24,000 eggs)/kg for food waste with wheat bran. From the available data, 1.5 g eggs of M. domestica after hatching could deal with 1 kg culture medium which meant they could dispose 700 g food waste and 300 g wheat bran in four days, among which 410 g culture medium was consumed and the food residues were finally turned into high quality organic manure that could be used to fertilize the crops (Haug, 1993). In our experiments, 6 g eggs could obtained from one 0.125 m3 cage of housefly adults averagely per day, thus one cage of housefly could deal with 2.8 kg food waste every four days. Disposition of 1 ton food waste just need a space of 44.64 m3 and four days. The protein and fat contents have been tested in our study, and all the groups of maggots contained the content of protein and fat, 57.06 ± 2.19% and 15.07 ± 2.03% respectively. For rearing in filthy and decaying niches without viral or bacterial infections, a variety of researches about the maggot proteins had been done. Scholars found the effects of antioxidant, antibacterial, antifungal (Fu et al., 2009)and in vitro antitumor properties (Cao et al., 2010) of the protein extracts from housefly larvae successively. In addition to the great medical values, for the maggot protein’s good pharmacological activities and balance of amino acid content, it was regarded as a good substitute of fish meals in the field of animal breeding. In order to ascertain the safety of the protein of food waste cultural maggots, we had determined the content of the aflatoxin-B1 with colloidal gold test strip and aflatoxin-B1was not detected in maggot (<10 ppm). The oil of maggots was another kind of product, according to the analysis of its fatty acid composition (showed in 2.3), it could be found that the oil of maggots would be a feasible resource for biodiesel production. After the reaction of transesterification with methanol, the housefly larva methyl esters had been produced.
Fig. 3. Culture mediums consumption under different inoculums densities, datas are expressed as the means ± standard error of mean (SEM).
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Y. Niu et al. / Waste Management xxx (2016) xxx–xxx Table 3 Ingredients and relative contents of maggot fatty acid. Number
Retention time/min
Ingredient
Molecular formula
Relative content/%
1 2 3 4 5 6 7 8 9 10 11 12 13 14
2.09 2.46 2.93 2.99 3.75 4.48 4.65 4.91 6.41 7.95 8.15 8.71 9.2 11.22
Lauric acid Tridecoic acid Myristoleic acid Myristic acid Pentadecanoic acid Hexadecadienoic acid Palmitoleic acid Palmitic acid Heptadecanoic acid Linoleic acid Oleic acid Stearic acid Alpha-Linolenic Acid Arachic acid
C12H24O2 C13H26O2 C14H26O2 C14H28O2 C15H30O2 C16H28O2 C16H30O2 C16H32O2 C17H34O2 C18H32O2 C18H34O2 C18H36O2 C18H30O2 C20H40O2
1.21 0.08 0.64 5.96 2.51 0.4 17.4 27.14 0.65 13.45 24.54 5.01 0.36 0.09
Table 4 Fuel properties of biodiesel from housefly (Musca domestica L.) larva oil. Property
Test method
Biodiesel from HLO
ASTM D6751
EN14214
Density (kg/m3) Viscosity (mm2/s) Flash point (°C) Water content (mg/kg) Acid value (mg KOH/g) Cold filter plugging point (°C) Sulfated ash content (%) Sulfur content (mg/kg) Copper strip corrosion Cetane number
ASTM ASTM ASTM ASTM ASTM ASTM ASTM ASTM ASTM ASTM
875.0 4.14 164 <0.03 0.17 4 0.004 nd 1a 55
–a 1.9–6.0 93 min 0.03 max 0.50 max –a 0.02max 0.05max No.3max 47 min
860–900 3.5–5.0 120 min 0.05 max 0.50 max –b 0.02 max 10max No.1 min 51 min
D5002 D445 D93 D95 D664 D6371 D874 D4294 D130 D613
nd Not detected. a Not specified. b Not specified. EN 14214 uses time and location-dependent values for the cold filter plugging point instead.
Fig. 5. Process Map and results of the bioconversion of food waste using M. domestica.
3.4. Analysis of maggot fatty acid composition by GC–MS Through analysis by GC–MS, we obtained the ingredients and relative contents of housefly larva fatty acid, which is shown in Table 3. Those could be found that palmitic acid (27.14%), oleic acid (24.54%), palmitoleic acid (17.40%), linoleic acid (13.45%) and myristic acid (5.96%) are the main ingredients of the maggot fatty acid. Most fatty acid of the M. domestica larva contain 16–18 carbon chain, which is similar to the composition of petroleum. Comparing with the ingredients of plant oil that was usually used for biodiesel production such as palm oil and wine stone oil. It is demonstrated that maggot fatty acid is analogous to them.
Previous study suggested that the major factor contributes to the price of biodiesel is the feedstock, which accounts for nearly 80% of the price (Sharma et al., 2008). Therefore, ideal resources should fulfill the requirements of large production scale and low production cost (Singh and Singh, 2010). In our study, maggots were fed with food waste and low-cost wheat bran. The highly reproductive ability of M. domestica ensured large production of maggot oil. Consequently, it can be deemed that as the valueadded product of food waste via bioconversion of M. domestica, maggot oil is a promising material of biodiesel.
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3.5. Yield and fuel properties of HLMEs The process of acid pretreatment had lowered the acid value into 0.71 mg KOH/g, conversion of the maggot oil could continue with the base-catalyzed transesterification. Under proper conditions, the maximum yield of housefly larva methyl esters (HLMEs) from maggot oil was 87.71%. The dried maggots in our research contained 15.07 ± 2.03% oil, thus the yield of the M. domestica larva biodiesel was 13.21 ± 1.78% from dried maggots. The fuel properties of refined HLMEs were determined and reported in Table 4. The physical and fuel properties of HLMEs such as density (875.0 kg/m3), kinematic viscosity (4.14 mm2/s), flash point (164 °C), cetane number (55) were comparable to those of ASTM D 6751 and EN 14214. Other properties of purified biodiesel such as, acid value, sulfur content, sulfated ash content, copper strip corrosion, water content were met to the European and American standards for biodiesel fuel. One of the major problems associated with the use of biodiesel is its poor low temperature flow property due to chemical properties of the raw housefly larva oil (HLO), consisting of 43.1% saturated fatty acid. This can be improved via using additives such as depressants, flow improvers, winterization etc., alternatively, the fuel can be used in warm-temperature climates or in the summer season only (Cvengroš and Cvengrošová, 2004). At this point, a new system of food waste disposition had been established. In our system 1 ton food waste could be disposed in just 4 days. Furthermore, the whole bioconversion could produce 379 kg fresh maggots which could provide about 43.26 kg protein and 11.43 kg oil. Through further processing, protein drugs and biodiesel which are with more economical values could be obtained. The whole working scheme of the bioconversion could be observed in Fig. 5. All the materials in this system were readily-accessible and low-cost. The space required for the system was really small (disposing 1ton food waste only needed 44.64 m3). In addition, the conditions of the bioconversion were easier control, in Guangdong province of China where are with the subtropical monsoon climate, 8 months disposition without any temperature supplement can be achieved. Except small amounts of organic emissions, this processing would produce little pollution to the environment. Consequently, it can be suggested that the present system is economic, environmentally friendly and with high value added. 4. Conclusion Bioconversion as a new conception for food waste disposition has drawed increasingly attentions in the field of environmental protection and resources. In our present study, housefly had been selected as the carrier for the bioconversion. Besides its outstanding ability of food waste consumption, the products were also estimable. Protein and oil were the two main value-added products here. Their contents were 57.06 ± 2.19% and 15.07 ± 2.03% respectively. From the experimental results, the eligible adjuvant was likely to be wheat bran and the optimal quantity of housefly eggs was 1.5 g (24,000 eggs)/kg for food waste with wheat bran. Under proper culture conditions the efficiency of food waste consumption and productivity of increments via the bioconversion by the housefly were encouraging. In addition, the biodiesel production with maggot oil had been explored in our study. The maximum yield
of housefly larva methyl esters (HLMEs) from maggot oil was 87.71%. In the future studies, the process of biodiesel production with housefly larva would be further optimized. The food residues of the maggot would be further explored, more experiments about its fertilization qualities would be started. Additionally, more studies on the safety of the maggot protein would be explored. References Camobreco, V., Ham, R., Barlaz, M., Repa, E., Felker, M., Rousseau, C., Rathle, J., 1999. Life-cycle inventory of a modern municipal solid waste landfill. Waste Manage. Res. 17, 394–408. Cao, X., Huo, Z., Lu, M., Mao, D., Zhao, Q., Xu, C., Wang, C., Zeng, B., 2010. Purification of lectin from larvae of the fly, Musca domestica, and in vitro anti-tumor activity in MCF-7 cells. J. Insect Sci. (Online) 10, 164. Cickova, H., Pastor, B., Kozanek, M., Martinez-Sanchez, A., Rojo, S., Takac, P., 2012. Biodegradation of pig manure by the housefly, Musca domestica: a viable ecological strategy for pig manure management. PLoS ONE 7, e32798. Cvengroš, J., Cvengrošová, Z., 2004. Used frying oils and fats and their utilization in the production of methyl esters of higher fatty acids. Biomass Bioenergy 27, 173–181. Dobbs, R.O.J., Thompson, F., Brinkman, M., Zornes, M., 2011. Resources Revolution: Meeting the World’s Energy, Materials, Food, and Water Needs. McKinsey Global Institute, McKinsey & Company. EN14103, 2003. Fat and Oil Derivatives-Fatty Acid Methyl Esters (FAME) – Determination of Ester and Linolenic Acid Methyl Ester Contents. European Committee for Standardization, Brussels, Belgium. Fu, P., Wu, J., Guo, G., 2009. Purification and molecular identification of an antifungal peptide from the hemolymph of Musca domestica (housefly). Cell. Mol. Immunol. 6, 245–251. Gustavsson, J., Cederberg, C., Sonesson, U., van Otterdijk, R., Meybeck, A., 2011. Global Food Losses and Food Waste: Extent, Causes and Prevention. FAO, Rome, Italy. Haug, R.T., 1993. The Practical Handbook of Compost Engineering[J]. Lewis Publishers Boca Raton. Huang, H., Singh, V., Qureshi, N., 2015. Butanol production from food waste: a novel process for producing sustainable energy and reducing environmental pollution. Biotechnol Biofuels 8, 147. Leung, D., Yang, D., Li, Z., Zhao, Z., Chen, J., Zhu, L., 2012. Biodiesel from Zophobas morio larva oil: process optimization and FAME characterization. Ind. Eng. Chem. Res. 51, 1036–1040. Li, Z., Yang, D., Huang, M., Hu, X., Shen, J., Zhao, Z., Chen, J., 2012. Chrysomya megacephala (Fabricius) larvae: a new biodiesel resource. Appl. Energy 94, 349– 354. Bai, Lin., Li, X., Zhang, Lin., Wang, Yachao., Yong, Gu., 2007. Study on the conversion regulation of nutriment and energy of pig manure disposed by Musca domestica. Chin. J. Anim. Sci. 43, 59–62. Lin, C.S.K., Pfaltzgraff, L.A., Herrero-Davila, L., Mubofu, E.B., Abderrahim, S., Clark, J. H., Koutinas, A.A., Kopsahelis, N., Stamatelatou, K., Dickson, F., Thankappan, S., Mohamed, Z., Brocklesby, R., Luque, R., 2013. Food waste as a valuable resource for the production of chemicals, materials and fuels. Current situation and global perspective. Energy Environ. Sci. 6, 426. Moon, H.C., Song, I.S., Kim, J.C., Shirai, Y., Lee, D.H., Kim, J.K., Chung, S.O., Kim, D.H., Oh, K.K., Cho, Y.S., 2009. Enzymatic hydrolysis of food waste and ethanol fermentation. Int. J. Energy Res. 33, 164–172. Nguyen, T.T., Tomberlin, J.K., Vanlaerhoven, S., 2015. Ability of black soldier Fly (Diptera: Stratiomyidae) Larvae to recycle food waste. Environ. Entomol. 44, 406–410. Roger, D.M., 2002. 14–Muscid Flies (Muscidae). Med. Vet. Entomol., 279–301 Satoh, S., Haga, Y., Wakayama, T., Yamaguchi, K., Akiyama, T., 2010. Use of maggot meal for substitution of fish meal in rainbow trout diets. Sharma, Y.C., Singh, B., Upadhyay, S.N., 2008. Advancements in development and characterization of biodiesel: a review. Fuel 87, 2355–2373. Singh, S.P., Singh, D., 2010. Biodiesel production through the use of different sources and characterization of oils and their esters as the substitute of diesel: a review. Renew. Sustain. Energy Rev. 14, 200–216. Uncu, O.N., Cekmecelioglu, D., 2011. Cost-effective approach to ethanol production and optimization by response surface methodology. Waste Manage. 31, 636– 643. Wani, K.A., Mamta, Rao, R.J., 2013. Bioconversion of garden waste, kitchen waste and cow dung into value-added products using earthworm Eisenia fetida. Saudi. J. Biol. Sci. 20, 149–154.
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Waste Management journal homepage: www.elsevier.com/locate/wasman
A novel bioconversion for value-added products from food waste using Musca domestica Yi Niu a, Dong Zheng a, Binghua Yao b, Zizhe Cai a, Zhimin Zhao a, Shengqing Wu a, Peiqing Cong c, Depo Yang a,⇑ a b c
School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China College of Animal Science, South China Agricultural University, Guangzhou 510642, China State Key Laboratory of Bio-control, School of Life Science, Sun Yat-Sen University, Guangzhou 510006, China
a r t i c l e
i n f o
Article history: Received 27 February 2016 Revised 27 August 2016 Accepted 14 October 2016 Available online xxxx Keywords: Food waste Bioconversion Musca domestica Maggot protein Maggot oil Biodiesel
a b s t r a c t Food waste, as a major part of the municipal solid waste has been generated increasingly worldwide. Efficient and feasible utilization of this waste material for productivity process is significant for both economical and environmental reasons. In the present study, Musca domestica larva was used as the carrier to conduct a bioconversion with food waste to get the value-added maggot protein, oil and organic fertilizers. Methods of adult flies rearing, culture medium adjuvant selection, maggot culture conditions, stocking density and the valorization of the waste have been explored. From the experimental results, every 1000 g culture mediums (700 g food waste and 300 g adjuvant) could be disposed by 1.5 g M. domestica eggs under proper culture conditions after emergence in just 4 days, 42.95 ± 0.25% of which had been consumed and the culture medium residues could be used as good organic fertilizers, accompanying with the food waste consumption, 53.08 g dried maggots that contained 57.06 ± 2.19% protein and 15.07 ± 2.03% oil had been produced. The maggot protein for its outstanding pharmacological activities is regarded as a good raw material in the field of medicine and animal feeding. Meanwhile, the maggot oil represents a potential alternative feedstock for biodiesel production. In our study, the maggot biodiesel was obtained after the procedure of transesterification reaction with methanol and the productivity was 87.71%. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Waste as a major problem globally becomes more and more significant in both developed and developing countries. Food waste which includes unconsumed food that is discarded by food processing industries, retailers, restaurants, and consumers(Huang et al., 2015), is the single largest component of the waste stream worldwide. For its high contents of biodegradable organic compounds and moisture (75–85%), food waste readily decomposes, followed by generating foul smell and sometimes leading to illness under natural environments (Moon et al., 2009). According to the data from the Food and Agriculture Organization of the United Nations (FAO), there are 1.3 billion tons of food waste produced every year, around one-third of food produced for human consumption globally (Gustavsson, 2011). In contrast to current ⇑ Corresponding author at: School of Pharmaceutical Science, Sun Yat-sen University, Guangzhou Higher Education Mega Center, Guangzhou, China. E-mail address: [email protected] (D. Yang).
large-scale production, amount of this food waste found no efficient uses different from landfill or first-generation recycling practices (such as animal feed, composting and incineration) (Lin et al., 2013). However, incineration and landfill are two crucial sources of greenhouse gas emission (Camobreco et al., 1999), animal feed and composting with food waste that will increase the risks of occurrence of animal related diseases and the pollution of the surface and underground water (Uncu and Cekmecelioglu, 2011). Waste is a resource rather than problem, The McKinsey Global Institute announced that food waste ranked third of fifteen identified resources with productive opportunities (Dobbs.R 2011). Consequently, it is an urgent issue of finding more sustainable, efficient and economic competitive methods for food waste recycling. Bioconversion, due to its environmentally friendly, sustainable, and renewable properties, is considered to be one of the most promising methods to deal with food waste. Some scholars have conducted the bioconversion using earthworm and Black Soldier Fly and they all obtained visible results in vary degrees (Nguyen et al., 2015; Wani et al., 2013).
http://dx.doi.org/10.1016/j.wasman.2016.10.054 0956-053X/Ó 2016 Elsevier Ltd. All rights reserved.
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Musca domestica (Linnaeus) (Diptera: Muscidae) is a kind of holometabolous insects with morphologically distinct stages of egg, larva (maggot), pupa and adult (Roger, 2002). The larva of M. domestica are fond of organic wastes such as rotten organisms, rubbish, and animal waste, thus food waste is an eligible feed for them. Unlike many pests that consume waste, Musca domestica has many outstanding advantages as following: firstly with their strong adaption to environment and not easily infected, M. domestica exhibits a large geographic distribution, thriving in temperatures ranging from 20 °C to 35 °C in areas like Australia, the Pacific, Africa, the Americas and Asia. Without the species introduction, the food waste consumption can be achieved. Secondly, Musca domestica has highly reproductive ability, fast growth and short lifecycle. Each M. domestica female can lay totally approximately 500 eggs during its entire life. The lifecycle of them is about 15 days, they can usually survive 7–8 generations per year, and even 20 generations under proper conditions. Year-round breeding could be achieved through artificial feeding circumstance. Last but not least accompanying with the consumption of waste, more valuable and worthy production has been produced. The dried maggots have 55% crude protein and 15% fat. Maggot protein is a good substitute of fish meal in livestock (Satoh et al., 2010), due to its noticeable pharmacological activities. It has also been regarded as a promising medicinal material. In our study the maggot oil as a new material for biodiesel has been proved to be viable. Therefore we can prospect that the bioconversion for value-added products (such as maggot protein and biodiesel) from food waste using Musca domestica is universal, efficient and with high economic and environmental values. Food waste, on account of its high viscosity and humidity, is not suitable for rearing maggots directly, in which some low-cost adjuvant should be added. In the present study, we have examined the impact of different adjuvant on the Musca domestica larval development, assessed the maggots’ capacity of reducing food waste. The protein as well as oil increment of maggots have been valued. Meanwhile, the elementary analysis of the maggot fatty acid and preparations of maggot biodiesel have been done. 2. Materials and methods 2.1. Rearing of the adult flies The Musca domestica in our research was captured from wild in Zhongshan, China and identified by Professor Hong PANG, department of life science, Sun Yat-sen University. Every 5000 adults were reared in one 50 ⁄ 50 ⁄ 50 cm mesh cage (0.2 mm pore size) with a stocking density of approximate 2.8 cm3 per fly. M. domestica colonies were maintained on a diet of 2:2:1 sugar powdered: milk: hen egg at 25 °C with a photoperiod of 12:12 (L:D) h cycle. Small white bags filled with soggy wheat bran and brown sugars (4:1) were placed in the colony cages as oviposition medium. Every other 12 h, the concentrated eggs were collected and inoculated into different culture mediums. 2.2. Examined the impact of different adjuvant on the larval development Food waste described in this paper was obtained daily from three different sites, a Chinese restaurant, a western restaurant and a breakfast shop in Zhongshan, China. They were dehydrated with strainers (75% moisture content) followed by mixing and shattering uniformly for backup. Four kinds of low-cost offcuts were chosen as the adjuvant of food waste: millet bran, wholeplant corn silage, wheat bran and sawdust, which were all dried and crushed coarsely. The study subjects were divided into four
groups, each group contained prepared food waste (700 g) and one kind of adjuvant (300 g) that mentioned above (Group1: wheat bran, G2: millet bran, G3: whole-plant corn silage and G4: sawdust). All the groups were mixed uniformly and kept the humidity at 70–80% with tap water, pH at 5–7 and the temperature at 25– 30 °C. Every group was inoculated with 0.8 g M. domestica eggs (13,000 larva). After the eggs hatching, the culture medium was stirred evenly every other 6 h at the premise of keeping the whole system ventilating. After four-day rearing, the third instar larva was harvested and analyzed. All procedures were performed with at least three independent replicates. 2.3. Assessing the maggots’ capacity of reducing food waste Different quantities of M. domestica eggs including 0.5 g (8000 eggs), 0.75 g (12,000 eggs), 1 g (16,000 eggs), 1.25 g (20,000 eggs), 1.5 g (24,000 eggs) and 2 g (32,000 eggs) were inoculated in 700 g food waste and 300 g wheat bran. The rearing methods as employed in 2.2 were used. After four-day cultivating, the even weight of single maggot was assessed, the maggots and culture medium were separated and dried in the oven (60 °C), then weighted respectively (on account of the variation water content of the fore and aft culture mediums, we adopted dried culture mediums weight to calculate the culture medium consumption rate here). The protein and oil content of the larva had also been evaluated. 2.4. Analysis 2.4.1. Determination of protein, oil consent of larva and nutrient evaluation of the adjuvant Fresh third instar larva were put into boiling water for instant death, dried in an oven at 60 °C for 24 h, and crushed into powder. The method of Kjeldahl nitrogen determination was used to determinate the content of protein of larva, KJELTEC 8400 Auto Kjeldahl Nitrogen Analysis (FOSS. Denmark) was used in our study. The oil extraction was carried out using a soxhlet extractor with n-hexane as solvent for 8 h, following with a recovered process using a rotary evaporator at 50 °C under vacuum. Oil was warmed at 80 °C for 2 h to remove the excess moisture then weighted to determine the oil contents. Fiber and ash contents were analyzed with the method of acid and alkali digestion by the Fibertec2010 (FOSS. Denmark). Carbohydrate contents were the rest material contents after getting rid of the other three factors. Protein, oil, carbohydrate, fiber and ash of the adjuvant had been evaluated in our study. 2.4.2. Maggot fatty acid composition analysis The maggot fatty acid composition was analyzed with a Finnigan GC–MS system equipped with a DB-5 MS column (30 m ⁄ 0.25 mm ⁄ 0.25 lm) and FDI. Helium was used as the carrier gas at a flow rate of 1.0 ml/min and a pressure of 100 kPa. The oven temperature was set at 210 °C for 15 min. Electron ionization mode (ionization energy of 70 eV) was used for GC–MS detection. The injector and MS transfer temperatures were both set at 250 °C. The scanning mass range selected was 29–500 m/z. A sample volume of 1.0 lL was injected into the column with the split ratio of 1:30 (EN14103, 2003). Data were managed with Xcalibur software with the NIST mass spectra library database. 2.5. Preparation of maggot biodiesel Fresh third instar larvae were put into boiling water for instant death, dried in an oven at 60 °C for 4 h, and crushed into powder. The powder was then immersed in five times amount of nhexane for fat extraction for 12 h. The extraction was recovered by using a rotary evaporator at 50 °C under vacuum. Oil was
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warmed at 80 °C for 2 h to remove the excess moisture. Then the obtained maggot oil (MO) was subjected by an acid pretreatment to lower the acid value. Maggot oil and methanol were added to a flask in a ratio of 1:8 with an amount of sulfuric acid (1 wt% MO) and then were heated at 70 °C for 2 h. The mixture was allowed to settle for 2 h, and the methanol-water fraction in the top layer was removed. The oil phase was washed with distilled water until a neutral pH was achieved. This procedure was followed by the removal of the residual methanol by rotary evaporation (Leung et al., 2012). The pretreated maggot oil was heated to the desired temperature in an oil bath before starting the reaction. KOH (Potassium hydroxide) was used as catalyst. Experiments were performed under the conditions referred to the paper of Zhuoxue Li et al. that methanol to oil molar ratios was at 6:1, catalyst concentrations of KOH was 1.4 (weight%), reaction temperature was 55 °C and reaction time was30 min. Agitation intensity (200 rpm) was kept constant throughout the whole course of experiments. When the reaction had proceeded for the desired duration, the reaction flask was transferred to ice to stop and then centrifugated at 3000 rpm for 5 min. The upper layer was separated and washed with 70 °C deionized water until it reached neutrality. After a process of drying, housefly larva methyl esters (biodiesel) was obtained (Li et al.,2012). 3. Results and discussion 3.1. Adult fly rearing The adults stocking density is approximate 2.8 cm3 per fly, which is described in the paper of Cickova et al. (2012). Appropriate temperature as well as sufficient illumination is very important for oviposition of adult flies. We found that neither a high (>35 °C) nor a low (<20 °C) temperature is suitable for flies to lay eggs and in dim light the amount of eggs would be reduced as well. So we maintained the housefly colonies at 25 °C and gave additional light during cloudy days. Generally brown sugar and milk are the usual food for adult flies, during our rearing, hen egg was added to their diet, for the reason that protein is the very nutrition for females generating eggs. Flies laid the largest quantity of eggs during the second week after emergence. At the peak of oviposition, we could collect 10 g eggs (160,000 eggs) from one cage within 12 h. Four weeks after emergence we removed and executed the old flies. In consideration of females’ preferring whiteness, white bags were used to collect eggs in the M. domestica colony. 3.2. The impact of different adjuvant on the larval development The viscosity and humidity of food waste are extremely high, and its moisture content can reach 70–80%. For being photophobic, the larva will drill into the culture medium. Highly viscous food waste cannot provide sufficient air for maggots. Therefore food waste is not suitable for rearing maggots directly and we should add some low-cost adjuvant into it. Wheat bran, millet bran, whole-plant corn silage and sawdust were selected as candidates with the reason that they are all easy-accessed, low-cost and large-outputted. In addition to the bioconversion of food waste into valuable products, we hope to find a new significant usage of these remnants. We assessed the dried maggots’ production, protein and oil contents as well as the even weight of each larva from four groups (by mean of weighting 100 fresh maggots then deducing the even weight of each larva). The results were shown in Fig. 1. All the parameters were the means of three parallel testing. From the results we can find group 1 (700 g food waste and 300 g wheat bran) provide the highest production of maggots, the rank of even weight of each larva is also the first one. At the
3
Fig. 1. The larva quality parameters of four different culture mediums, Group1: wheat bran, G2: millet bran, G3: whole-plant corn silage and G4: sawdust. Datas are expressed as the means ± standard error of mean (SEM).
same time this group is the very culture medium that cultivated the maggots with the highest content of protein and oil. To explain this phenomenon, the nutrition analysis (protein, oil, carbohydrate, fiber and ash) of the adjuvant had been done (Table 1). Based on the available data, we can find wheat bran had the highest protein and fat content and lowest content of fiber and ash. Previous study showed that fat is the most consumed nutrients in the maggot diet, followed by protein and carbohydrate accounts for just a small part of the total depletion and there is hardly any consumption of fiber and ash (Lin Bai et al., 2007). Therefore it could be known that wheat bran is the most eligible adjuvant of the four. Besides the nutrition supply, proper content and different variety of fiber of adjuvant is the main influential factor of cultivation. Appropriate content of fiber can raise the air permeability of the culture mediums. However, excessive fiber especially binding with lignin will not only prevent the leaching of nutrients but also increase the losses of water and heat for its lower hydrophily than protein and sugar. Thus it will change the humidity and temperature of culture mediums, which are the two essential factors of maggot rearing. Even though millet bran and whole-plant corn silage can offer nutrition to maggots to some extent, they cannot provide relatively stable culture circumstances. The culture result was not successful as group1. Consequently we hypothesized that wheat bran may be an eligible adjuvant of food waste to culture housefly maggots. 3.3. The maggots’ capacity of reducing food waste and ability of protein and oil increment The dried maggot productions, culture medium consumption rates and even single larva weights under different inoculum densities (Table 2) were compared. It turned out that the dried maggot production and culture mediums consumption would increase along with the raise of inoculums density. This trend became flat gradually when the inoculums density was higher than 1.5 g/kg. Meanwhile the even single larva weight decreased accompanying the increase of inoculums density (Figs. 2–4). More than 40% culture mediums could be consumed by M. domestica larva. It could be shown that when the inoculums density was increased, substituting for the accruing of consumption rates was the decrease of even single larva weight, which indicated the food waste culture medium contained 40 45% nutriments that could be consumed by maggots and the optimal quantity of housefly eggs for success-
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Table 1 Nutrition analysis of four culture medium adjuvants.
Protein (%) Fat (%) Carbohydrate (%) Fiber and ash (%)
Wheat bran
Millet bran
Whole-plant corn silage
Sawdust
14.4 ± 0.30 3 ± 0.24 71.8 ± 0.18 10.8 ± 0.24
8.6 ± 0.15 5.76 ± 0.28 60.14 ± 0.31 25.5 ± 0.11
5.7 ± 0.26 3.2 ± 0.22 72.8 ± 0.5 18.3 ± 0.19
1.5 ± 0.13 1.1 ± 0.33 26.2 ± 0.26 71.2 ± 0.27
Table 2 Parameters of cultivation under different inoculums densities. Inoculums density (g/kg)
Production (g/kg)
Consumption rate (%)
Single larva weight (mg)
0.5 0.75 1 1.25 1.5 2
32.69 ± 1.03 42.66 ± 0.92 45.28 ± 1.21 45.7 ± 0.80 53.08 ± 0.96 55.81 ± 0.65
38.74 ± 0.43 38.53 ± 1.31 37.26 ± 0.78 41.05 ± 1.47 42.95 ± 0.25 43.49 ± 1.31
21.42 ± 1.01 19.57 ± 0.77 16.66 ± 0.74 12.65 ± 0.25 11.59 ± 0.69 10.27 ± 0.93
Fig. 4. Even single larva weights under different inoculum densities, datas are expressed as the means ± standard error of mean (SEM).
Fig. 2. Dried maggot productions under different inoculum densities, datas are expressed as the means ± standard error of mean (SEM).
ful bioconversion was 1.5 g (24,000 eggs)/kg for food waste with wheat bran. From the available data, 1.5 g eggs of M. domestica after hatching could deal with 1 kg culture medium which meant they could dispose 700 g food waste and 300 g wheat bran in four days, among which 410 g culture medium was consumed and the food residues were finally turned into high quality organic manure that could be used to fertilize the crops (Haug, 1993). In our experiments, 6 g eggs could obtained from one 0.125 m3 cage of housefly adults averagely per day, thus one cage of housefly could deal with 2.8 kg food waste every four days. Disposition of 1 ton food waste just need a space of 44.64 m3 and four days. The protein and fat contents have been tested in our study, and all the groups of maggots contained the content of protein and fat, 57.06 ± 2.19% and 15.07 ± 2.03% respectively. For rearing in filthy and decaying niches without viral or bacterial infections, a variety of researches about the maggot proteins had been done. Scholars found the effects of antioxidant, antibacterial, antifungal (Fu et al., 2009)and in vitro antitumor properties (Cao et al., 2010) of the protein extracts from housefly larvae successively. In addition to the great medical values, for the maggot protein’s good pharmacological activities and balance of amino acid content, it was regarded as a good substitute of fish meals in the field of animal breeding. In order to ascertain the safety of the protein of food waste cultural maggots, we had determined the content of the aflatoxin-B1 with colloidal gold test strip and aflatoxin-B1was not detected in maggot (<10 ppm). The oil of maggots was another kind of product, according to the analysis of its fatty acid composition (showed in 2.3), it could be found that the oil of maggots would be a feasible resource for biodiesel production. After the reaction of transesterification with methanol, the housefly larva methyl esters had been produced.
Fig. 3. Culture mediums consumption under different inoculums densities, datas are expressed as the means ± standard error of mean (SEM).
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Y. Niu et al. / Waste Management xxx (2016) xxx–xxx Table 3 Ingredients and relative contents of maggot fatty acid. Number
Retention time/min
Ingredient
Molecular formula
Relative content/%
1 2 3 4 5 6 7 8 9 10 11 12 13 14
2.09 2.46 2.93 2.99 3.75 4.48 4.65 4.91 6.41 7.95 8.15 8.71 9.2 11.22
Lauric acid Tridecoic acid Myristoleic acid Myristic acid Pentadecanoic acid Hexadecadienoic acid Palmitoleic acid Palmitic acid Heptadecanoic acid Linoleic acid Oleic acid Stearic acid Alpha-Linolenic Acid Arachic acid
C12H24O2 C13H26O2 C14H26O2 C14H28O2 C15H30O2 C16H28O2 C16H30O2 C16H32O2 C17H34O2 C18H32O2 C18H34O2 C18H36O2 C18H30O2 C20H40O2
1.21 0.08 0.64 5.96 2.51 0.4 17.4 27.14 0.65 13.45 24.54 5.01 0.36 0.09
Table 4 Fuel properties of biodiesel from housefly (Musca domestica L.) larva oil. Property
Test method
Biodiesel from HLO
ASTM D6751
EN14214
Density (kg/m3) Viscosity (mm2/s) Flash point (°C) Water content (mg/kg) Acid value (mg KOH/g) Cold filter plugging point (°C) Sulfated ash content (%) Sulfur content (mg/kg) Copper strip corrosion Cetane number
ASTM ASTM ASTM ASTM ASTM ASTM ASTM ASTM ASTM ASTM
875.0 4.14 164 <0.03 0.17 4 0.004 nd 1a 55
–a 1.9–6.0 93 min 0.03 max 0.50 max –a 0.02max 0.05max No.3max 47 min
860–900 3.5–5.0 120 min 0.05 max 0.50 max –b 0.02 max 10max No.1 min 51 min
D5002 D445 D93 D95 D664 D6371 D874 D4294 D130 D613
nd Not detected. a Not specified. b Not specified. EN 14214 uses time and location-dependent values for the cold filter plugging point instead.
Fig. 5. Process Map and results of the bioconversion of food waste using M. domestica.
3.4. Analysis of maggot fatty acid composition by GC–MS Through analysis by GC–MS, we obtained the ingredients and relative contents of housefly larva fatty acid, which is shown in Table 3. Those could be found that palmitic acid (27.14%), oleic acid (24.54%), palmitoleic acid (17.40%), linoleic acid (13.45%) and myristic acid (5.96%) are the main ingredients of the maggot fatty acid. Most fatty acid of the M. domestica larva contain 16–18 carbon chain, which is similar to the composition of petroleum. Comparing with the ingredients of plant oil that was usually used for biodiesel production such as palm oil and wine stone oil. It is demonstrated that maggot fatty acid is analogous to them.
Previous study suggested that the major factor contributes to the price of biodiesel is the feedstock, which accounts for nearly 80% of the price (Sharma et al., 2008). Therefore, ideal resources should fulfill the requirements of large production scale and low production cost (Singh and Singh, 2010). In our study, maggots were fed with food waste and low-cost wheat bran. The highly reproductive ability of M. domestica ensured large production of maggot oil. Consequently, it can be deemed that as the valueadded product of food waste via bioconversion of M. domestica, maggot oil is a promising material of biodiesel.
Please cite this article in press as: Niu, Y., et al. A novel bioconversion for value-added products from food waste using Musca domestica. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.10.054
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3.5. Yield and fuel properties of HLMEs The process of acid pretreatment had lowered the acid value into 0.71 mg KOH/g, conversion of the maggot oil could continue with the base-catalyzed transesterification. Under proper conditions, the maximum yield of housefly larva methyl esters (HLMEs) from maggot oil was 87.71%. The dried maggots in our research contained 15.07 ± 2.03% oil, thus the yield of the M. domestica larva biodiesel was 13.21 ± 1.78% from dried maggots. The fuel properties of refined HLMEs were determined and reported in Table 4. The physical and fuel properties of HLMEs such as density (875.0 kg/m3), kinematic viscosity (4.14 mm2/s), flash point (164 °C), cetane number (55) were comparable to those of ASTM D 6751 and EN 14214. Other properties of purified biodiesel such as, acid value, sulfur content, sulfated ash content, copper strip corrosion, water content were met to the European and American standards for biodiesel fuel. One of the major problems associated with the use of biodiesel is its poor low temperature flow property due to chemical properties of the raw housefly larva oil (HLO), consisting of 43.1% saturated fatty acid. This can be improved via using additives such as depressants, flow improvers, winterization etc., alternatively, the fuel can be used in warm-temperature climates or in the summer season only (Cvengroš and Cvengrošová, 2004). At this point, a new system of food waste disposition had been established. In our system 1 ton food waste could be disposed in just 4 days. Furthermore, the whole bioconversion could produce 379 kg fresh maggots which could provide about 43.26 kg protein and 11.43 kg oil. Through further processing, protein drugs and biodiesel which are with more economical values could be obtained. The whole working scheme of the bioconversion could be observed in Fig. 5. All the materials in this system were readily-accessible and low-cost. The space required for the system was really small (disposing 1ton food waste only needed 44.64 m3). In addition, the conditions of the bioconversion were easier control, in Guangdong province of China where are with the subtropical monsoon climate, 8 months disposition without any temperature supplement can be achieved. Except small amounts of organic emissions, this processing would produce little pollution to the environment. Consequently, it can be suggested that the present system is economic, environmentally friendly and with high value added. 4. Conclusion Bioconversion as a new conception for food waste disposition has drawed increasingly attentions in the field of environmental protection and resources. In our present study, housefly had been selected as the carrier for the bioconversion. Besides its outstanding ability of food waste consumption, the products were also estimable. Protein and oil were the two main value-added products here. Their contents were 57.06 ± 2.19% and 15.07 ± 2.03% respectively. From the experimental results, the eligible adjuvant was likely to be wheat bran and the optimal quantity of housefly eggs was 1.5 g (24,000 eggs)/kg for food waste with wheat bran. Under proper culture conditions the efficiency of food waste consumption and productivity of increments via the bioconversion by the housefly were encouraging. In addition, the biodiesel production with maggot oil had been explored in our study. The maximum yield
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Please cite this article in press as: Niu, Y., et al. A novel bioconversion for value-added products from food waste using Musca domestica. Waste Management (2016), http://dx.doi.org/10.1016/j.wasman.2016.10.054