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Published online 25 May 2007
Published in J Environ Qual 36:1061-1068 (2007)
DOI: 10.2134/jeq2006.0326
© 2007 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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TECHNICAL REPORTS

Waste Management

Environmental Impact Evaluation of Feeds Prepared from Food Residues Using Life Cycle Assessment

Akifumi Oginoa,*, Hiroyuki Hirookab, Atsuo Ikeguchia, Yasuo Tanakaa, Miyoko Wakia, Hiroshi Yokoyamaa and Tomoyuki Kawashimaa

a National Institute of Livestock and Grassland Science, 2 Ikenodai, Tsukuba, Ibaraki 305-0901, Japan
b Graduate School of Agriculture, Kyoto Univ., Sakyo-ku, Kyoto 606-8502, Japan

* Corresponding author (aogino{at}affrc.go.jp)

Received for publication August 20, 2006.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
There is increasing concern about feeds prepared from food residues (FFR) from an environmental viewpoint; however, various forms of energy are consumed in the production of FFR. Environmental impacts of three scenarios were therefore investigated and compared using life cycle assessment (LCA): production of liquid FFR by sterilization with heat (LQ), production of dehydrated FFR by dehydration (DH), and disposal of food residues by incineration (IC). The functional unit was defined as 1 kg dry matter of produced feed standardized to a fixed energy content. The system boundaries included collection of food residues and production of feed from food residues. In IC, food residues are incinerated as waste, and thus the impacts of production and transportation of commercial concentrate feeds equivalent to the FFR in the other scenarios are included in the analysis. Our results suggested that the average amounts of greenhouse gas (GHG) emissions from LQ, DH, and IC were 268, 1073, and 1066 g of CO2 equivalent, respectively. The amount of GHG emissions from LQ was remarkably small, indicating that LQ was effective for reducing the environmental impact of animal production. Although the average amount of GHG emissions from DH was nearly equal to that from IC, a large variation of GHG emissions was observed among the DH units. The energy consumption of the three scenarios followed a pattern similar to that of GHG emissions. The water consumption of the FFR-producing units was remarkably smaller than that of IC due to the large volumes of water consumed in forage crop production.

Abbreviations: DH, production of dehydrated FFR by dehydration • DM, dry matter • FFR, feed prepared from food residues • FU, functional unit • g CO2 eq., g of CO2 equivalent • GHG, greenhouse gas • IC, disposal of food residues by incineration • LCA, life cycle assessment • LQ, production of liquid FFR by heating • MC, moisture content • ME, metabolizable energy


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
FROM the viewpoint of environmental protection and resource conservation, there is increasing concern about the recycling of food residues. Utilization of food residues as animal feed represents a high level of recycling, and it also has significance as a means of increasing the feed self-sufficiency rate. In Japan, the food-recycling law enforced in 2001 has promoted the use of food residues for animal feeding. Japanese law allows food residues containing meats that were originally processed for human consumption to be fed to pigs, while the use of animal proteins including fish meal for ruminants has been completely banned. Many studies evaluating the nutritional characteristics of feeds prepared from food residues (FFR) have been conducted, and have reported positive findings (Westendorf et al., 1998; Myer et al., 1999; Farhat et al., 2001). Furthermore, Sancho et al. (2004) reported that food residues after thermal treatment at a temperature of at least 65°C for 20 min were sufficiently sanitary based on microbiological analyses, and the nutritional parameters of the product remained suitable for its use as animal feed. Feeding liquid feed to pigs is a practice that has been used for many years (Cumby, 1986), and its effectiveness has been investigated (Lawlor et al., 2002; Canibe and Jensen, 2003). Among FFR methods, liquid FFR appears to be effective at taking advantage of the high moisture content (MC) of food residues, while dehydrated FFR have the advantage of being dispensed in a manner similar to commercial formula feeds. However, before extensive promotion takes place, FFR practices need to be evaluated in terms of their environmental impact, as various forms of energy are consumed in the production of FFR. While the environmental impacts of food waste treatments, such as composting and biogasification, have been evaluated (Hirai et al., 2001; Mendes et al., 2003; Lundie and Peters, 2005), there has been no evaluation of the environmental impacts of producing FFR.

Life cycle assessment (LCA) is a type of integrated environmental impact assessment, and its methodology has been internationally standardized (ISO, 1997, 1998). Recently, several studies have reported that LCA can be used to assess animal production, including the production of dairy cattle (Haas et al., 2001; de Boer, 2003; Hospido et al., 2003), beef cattle (Ogino et al., 2004; Casey and Holden, 2006), and pigs (Basset-Mens and van der Werf, 2005). Life cycle assessment has also been used in the evaluations of food waste treatments mentioned above. For all of these reasons, LCA seemed suited for use in evaluating the environmental impacts of FFR production.

In this study, LCA was used to evaluate and compare greenhouse gas (GHG) emissions, as well as the energy consumption and water consumption, involved in liquid and dehydrated FFR production and food residue incineration, as indices of the environmental impacts of these various practices.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
The LCA concept consists of four major stages: (i) goal and scope definition, i.e., system description, (ii) life cycle inventory, (iii) life cycle impact assessment, and (iv) interpretation. The details of the first three stages are described in this section, and the interpretation is presented in the Discussion section.

System Description
To evaluate the environmental impacts of producing FFR, three scenarios were compared using LCA: producing liquid FFR by heating (LQ), producing dehydrated FFR by dehydration (DH), and disposal of food residues by incineration (IC). Incineration was the control scenario because incineration is the major method of food residue disposal in Japan. Figure 1 presents the three food residue treatment and utilization systems analyzed in this study. Feeds prepared from food residues were assumed to be given to pigs in this study; this is presently their major use due to the risk of contaminated animal protein in ruminants and the suitability of pigs for liquid feeding. The system boundaries included collection of food residues and production of FFR. In LQ, collected food residues are processed by mixing, with addition of water if needed, and sterilization with heat. In DH, collected food residues are processed by heating and dehydration. On the other hand, in IC, food residues are incinerated as waste, and thus the impacts of the production and transportation of commercial concentrate feeds equivalent to the absent FFR are added to the estimate. Because most of the feeds for Japanese pig production are imported mainly from the USA, it was assumed that the feeds were produced in the USA and imported to Japan. The functional unit (FU) was defined as 1 kg dry matter (DM) of produced feed with a metabolizable energy (ME) content of 16.4 MJ kg–1, which is equivalent to that of the commercial concentrate feeds, and then the amount of each produced FFR was standardized with its ME content to calculate the environmental impacts per FU. The FFR-producing units investigated in this study took food residues for free or rather received disposal fees, and thus food residues could be regarded as waste with no economic value, and their environmental loads could be disregarded. The environmental loads associated with the production of capital goods, such as the plants for FFR production and the trucks for collection of food residues, were also not taken into account. Global warming, energy consumption, and water consumption were the environmental impact categories used in the present study. Accordingly, GHG emissions and the energy and water consumption of all the processes in each scenario were investigated.


Figure 1
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  		Fig. 1. Description of the systems of food residue utilization or disposal investigated in this life cycle assessment (LCA) study.

 
Life Cycle Inventory
Data collection was based on site investigations, studies in the literature, and LCA software databases. Site investigations for data collection on two (LQ) and three (DH) FFR-producing units were conducted. Summaries of the units are presented in Tables 1 and 2. Units A and B produce liquid FFR, and Units C, D, and E produce dehydrated FFR. Unit A uses kitchen and food-factory wastes to produce liquid FFR with the addition of water. Unit B produces liquid FFR on a smaller scale, using solid and liquid food-factory wastes with the addition of a small amount of water. Unit C produces dehydrated FFR by steam heating and removes the odor generated during dehydration using a catalytic deodorizing device run on electric power. Unit D produces dehydrated FFR by frying and drying food residues under reduced pressure to evaporate the water from them; then, surplus edible oil derived from the food residues are recycled as fuel oil. Unit E utilizes the waste heat of an adjacent incinerator of industrial waste for dehydrating food residues. The environmental loads of the waste heat were not taken into account because Unit E and the adjacent incinerator are located in a remote region, and no facility in the surrounding area has the potential to utilize waste heat.


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  		Table 1. Summary of the investigated business units producing liquid FFR.{dagger}

 

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  		Table 2. Summary of the investigated business units producing dehydrated FFR.{dagger}

 
In regard to the chemical composition of FFR, the ether extract (EE, %DM), crude protein (CP, %DM), ash (%DM), and neutral detergent fiber (NDF, %DM) content were 13.2, 18.2, 3.0, and 3.1, respectively, for Unit B; 5.2, 21.6, 12.1, and 4.5, respectively, for Unit C based on site investigations; and 9.4, 14.1, 1.9, and 0.2, respectively, for Unit E based on the report of Takahashi et al. (2006). The digestible energy (DE, kcal kg–1 DM) and CP (%DM) content of FFR were 4423 and 17.2 for Unit A (Kawashima, unpublished data), and 3665 and 23.4 for Unit D (NARO, 2002). The gross energy (GE, kcal kg–1), DE (kcal kg–1), and ME (kcal kg–1) content of FFR were calculated using these values and Eq. [1 Go–3] adopted by the National Research Council (NRC, 1998):

Formula 1[1]

Formula 2[2]

Formula 3[3]

The databases of the LCA software JEMAI-LCA (JEMAI, 2000) and SimaPro (PRe Consultants, 2003) were used to calculate GHG emissions from the production and combustion of fossil fuels, consumption of electricity, and transport. The environmental loads from FFR production were determined by multiplying the unit emissions for electricity and each fuel by the consumption of electricity and each fuel obtained by the site investigations, respectively. For the environmental loads from food residue collection, in the case of Units A and D, for which fuel consumption data were available (125 and 157 kg d–1 of diesel oil, respectively), GHG emissions were determined by multiplying unit emissions for diesel oil by the amounts of diesel oil consumption. Otherwise, GHG emissions were determined by multiplying unit emissions for diesel oil by transport distance (Table 1) and unit consumptions of diesel oil for transport. The transport distances by 2-, 4-, and 10-t trucks were 179, 146, and 171 km d–1, respectively, for Unit B, and those by 2- and 3-t trucks were 316 and 288 km d–1, respectively, for Unit C. Unit consumptions of diesel oil for transport by 2-, 3-, 4-, 6-, and 10-t trucks were 0.104, 0.116, 0.128, 0.167, and 0.237 kg km–1, respectively (JEMAI, 2000).

For the IC scenario, the amount of fuel consumed to collect food residues was calculated as the average of those values for the FFR-producing units. For the amount of electricity consumed in the incinerator, the value reported by Hirai et al. (2001) was used. The amount of fuel consumed to incinerate food residues was calculated from the quantity of heat required to evaporate water included in food residues as follows:

Formula 4[4]
where QW is the quantity of heat required to evaporate water (kcal kg–1), W is the amount of water included in 1 kg of food residues (kg), CH (1.1) is the coefficient for maintaining high temperature and suppressing smoke, CE (0.63) is the coefficient of thermal efficiency of the incinerator (Tchobanoglous et al., 1993), QF (3327 kcal) is the quantity of heat per 1 kg DM of food residues (Tchobanoglous et al., 1993), and QO (8874 kcal L–1) is the net heating value of heavy oil (EDMC, 2002). In the IC scenario, common food residues were assumed; thus, the MC of food residues was assumed to be 788 g kg–1 from the average among food residues of the investigated units, excluding that of Unit E, which had a much lower MC than those used in the other units.

The commercial concentrate feeds equivalent to FFR were assumed to be 54% corn, 26% sorghum, and 20% soybean meal, based on the composition of commercial formula feeds to meet the nutrient requirements of growing-finishing pigs according to the feeding standard for swine (NARO, 2005). The DE (kcal kg–1 DM) and CP (%DM) content of the commercial concentrate feed were 4007 and 18.1 based on those of the ingredients (NARO, 2002), and the ME content was calculated as described above. The environmental loads of production in the USA and transport to Japan were estimated as reported by Ogino et al. (2004). Pollutants emitted from the production of the commercial feed were determined as follows using data on the amounts of fuels and agricultural materials consumed in the production of each crop (Pimentel, 1980):

Formula 5[5]
where PA is the emission of pollutant A from the production of commercial feed (g kg–1 feed), Fij is the consumption of fuel j in the production of commercial feed ingredient i (MJ kg–1 feed), GAj is the emission coefficient of pollutant A from the production and combustion of fuel j (g MJ–1), Li is the consumption of electricity in the production of commercial feed ingredient i (kWh kg–1 feed), MA is the emission coefficient of pollutant A from electricity production and consumption (g kWh–1), i is the commercial feed ingredient (corn, sorghum, or soybean), and j is the fuel (gasoline, diesel, LP gas, natural gas, or indirect energy). The weighted average of the coefficient of each fuel, based on the amount of consumption in the USA in 2000 (EIA, 2003), was used as the emission coefficient of pollutant A from indirect energy, which is consumed to produce agricultural materials such as chemical fertilizers or pesticides. As for N2O emissions from the production of chemical nitrogen fertilizer, the proportion of NO3–N to the total nitrogen in chemical fertilizer was determined as 9.49% based on the statistics of fertilizer use (USDA, 2005), and 1.58% of the nitrogen amount in nitric acid was assumed to be emitted as N2O during the production of nitric acid (IPCC, 1997). As for N2O emissions from the field of feed production, 0.60% of the nitrogen amount in chemical fertilizer applied to the corn and sorghum fields and 0.73% of that on soybean fields were assumed to be emitted as N2O (MOE, 2003).

Environmental loads from the commercial feed transport to Japan were determined by multiplying the unit emission by the product of the feed weight and transport distance. The marine transport distance from the USA was determined as 18180 km from New Orleans to Nagoya, which includes the river freight involved in transporting the feed down the Mississippi River; the distances between these cities were based on the JNOA distance chart (JNOA, 1990). The distance of land transport (trucking) in the USA was defined as 200 km.

The energy consumptions of the processes in each scenario were calculated using the amounts of fuel and electricity consumptions determined in the calculation of GHG emissions. Water consumption of FFR production including food residue collection were determined using the data of total water consumption for each FFR-producing unit obtained by the site investigations. Some data on water consumption were corrected in response to the amount of FFR production at the time, because they were belatedly obtained. Water was used in the units for steam boilers, washing FFR-producing plants and trucks for food residue collection, and so on. The volumes of water consumed during the production of commercial concentrate feed were determined by the water demand for each crop reported by Oki and Kanae (2004), and the water consumption during import to Japan were determined using the inventory data of SimaPro (PRe Consultants, 2003). For the amount of water consumed in the food residue incineration, including the collection of food residues, the value reported by CAT (2006) was used.

Life Cycle Impact Assessment
In the impact assessment, the data of the life cycle inventory are interpreted in terms of their environmental impact. The environmental loads (emissions) are sorted and assigned to specific environmental impact categories, then multiplied by equivalency factors for each specific load and impact category. Thereafter, all weighted environmental loads included in the impact category are added and the environmental impact is obtained. In this study, the contribution of the system for utilization and treatment of food residues to the environmental impact category of global warming was examined. The global warming potential (GWP), an index for estimating the global warming contribution due to atmospheric emission of GHGs, was computed according to the CO2–equivalent factors defined by IPCC (2001): CO2, 1; CH4, 23; and N2O, 296. These factors were set based on a time horizon of 100 yr.

Simulation of Transport Distance of the Produced Feeds
The transport of FFR for LQ and DH, and the commercial feed for IC to pig farms, was not included in the system boundaries because the transport distance of feeds to pig farms varies case by case. In particular, the destinations of the feeds are difficult to identify if dehydrated FFR is used as an ingredient in formula feeds. The MC of the feeds are, however, quite different among liquid FFR, dehydrated FFR, and the commercial feed, and thus the effects of transport distance of the feeds on the environmental impact were simulated and evaluated. In the simulation, the environmental impacts were investigated assuming that 10-t trucks were used for the transportation, and that the transport distance was 50, 100, 150, or 200 km. The transport distances were expressed as a one-way distance to pig farms, while the GHG emissions were calculated on the basis of round-trip distance.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The GHG emissions of each scenario were investigated, and the results are shown in Table 3. The average amounts of GHG emissions from LQ and DH were 268 and 1073 g of CO2 equivalent (g CO2 eq.), respectively, and the amount of GHG emissions from IC was 1066 g CO2 eq. The amount of GHG emissions from LQ units was remarkably small, less than 30% of that from IC. In contrast, the average amount of GHG emissions from DH was nearly equal to that from IC. Comparing the GHG emissions of LQ and DH, those from the collection of food residues were somewhat greater for LQ than for DH; however, those from the production of FFR were far greater for DH than for LQ. In LQ, the GHG emissions from the collection of food residues and those from the production of FFR were not very different. But in DH, particularly Units C and D, the amount of GHG emissions derived from the fuel consumption required to dehydrate food residues was large. For IC, the amount of GHG emissions from the production of commercial feed was the largest, followed by that derived from fuels consumed in the incineration of food residues. Of the LQ units, Unit B emitted about 1.5 times the amount of GHGs emitted by Unit A. The amounts of GHG emissions derived from fuels consumed in the production of FFR were about the same or slightly smaller than those from the collection of food residues in the two units. For DH units, the amount of GHG emissions from Unit C was the greatest, followed by Unit D, and that from Unit E was smallest. The amounts of GHG emissions derived from fuels consumed in the production of FFR accounted for a large percentage of the total GHG emissions, especially in Units C and D.


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  		Table 3. Greenhouse gas emissions from each business unit under the LQ and DH scenarios and the IC scenario.{dagger}

 
The proportion of CO2 to the total GHG emissions of the FFR-producing units was between 80 and 96%, and N2O accounted for most of the remaining part of the GHG emissions. The amount of N2O emissions from the production of commercial feed in IC was relatively large (76.6 g CO2 eq.); it was largely derived from nitrogen in the chemical fertilizer applied to fields. The amounts of N2O emissions derived from fuels, especially natural gas, consumed in the production of FFR were also large.

The energy consumptions of each unit and IC scenario are shown in Table 4. The average energy consumptions of LQ, DH, and IC were 3.9, 16.7, and 14.5 MJ, respectively. The energy consumption of LQ was remarkably small. In contrast, the average energy consumption of DH was higher than that of IC, and some DH units consumed especially large amounts of energy.


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  		Table 4. Energy consumption of each business unit under the LQ and DH scenarios and the IC scenario.{dagger}

 
The water consumptions of each unit and IC scenario are shown in Table 5. The average water consumptions for LQ, DH, and IC were 2.9, 5.1, and 1034.6 L, respectively. The LQ and DH units consumed much smaller amounts of water than IC. In IC, most of the water was consumed in the process of producing commercial feed.


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  		Table 5. Water consumption each business unit under the LQ and DH scenarios and the IC scenario.{dagger}

 
Figure 2 shows the results of the simulation evaluating the effects of transport distance on the GHG emissions for liquid FFR, dehydrated FFR, and commercial feed for IC. As the theoretical transport distance became longer, the amount of GHG emissions from LQ units increased at a higher rate than those of the other scenarios. However, even when the produced FFR was assumed to be transported 200 km to farms, LQ units still emitted less than half the GHGs emitted by the other scenarios, with the exception of Unit E.


Figure 2
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  		Fig. 2. The effects of transport distance of the produced feeds for each unit of LQ and DH scenarios and IC scenario on greenhouse gas (GHG) emissions. FFR, feed prepared from food residues; LQ, production of liquid FFR by heating; DH, production of dehydrated FFR; IC, disposal of food residues by incineration; A and B, LQ units; C, D, and E, DH units. The functional unit was defined as 1 kg dry matter of produced feed with a fixed metabolizable energy content.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
The LCA analysis of the scenarios for the treatment of food residues revealed that remarkably less GHGs were emitted by liquid FFR production. For DH, the average amount of GHG emissions from the units investigated in this study were about the same as that for IC; however, a large variation in the GHG emissions was observed among the DH units, and two of the three had an even larger environmental impact than IC. The enormous amounts of fuel consumed in the production of FFR by DH, i.e., for the dehydration of food residues, were responsible for the large amount of GHG emissions. By comparison, no large fuel consumption was required in the incineration process of IC because the dried food residues functioned as a heat source. In other words, all of the heat required to dehydrate food residues in DH had to be added from the outside.

In terms of the individual DH units (Table 3), a large amount of the GHGs were emitted from FFR production in Unit C because all of the heat to dehydrate food residues came from fossil fuels. In addition, the amount of GHG emissions from electricity was larger than that of the other units, mainly because a deodorizing device with electrical power was used. Although Unit D emitted a smaller amount of GHGs as a whole than Unit C, the amount of GHG emissions from fuels consumed in the production of FFR in Unit D was similar to that in Unit C. This result was obtained despite the fact that the surplus edible oil derived from food residues was recycled as fuel oil; about one third of the recycled fuel oil fuel was used for deodorization by combustion. The amount of GHG emissions from Unit E was the smallest of the three DH units. This unit's fuel consumption was suppressed because Unit E utilized the waste heat from an adjacent industrial waste incinerator for dehydration of food residues. Furthermore, no deodorization was necessary because of the location of Unit E in a remote region and the sanitary management of food residues. Our results implied that producing FFR by dehydration would not lead to reduction of GHG emissions without efforts such as recycling of waste heat or fuels or reduction of the energy consumed for deodorization. Production of FFR by dehydration, however, has the advantage of increasing the feed self-sufficiency rate, which is very low in Japan, and attention should be paid to this point.

In terms of the results for each LQ unit, the amount of GHG emissions from Unit B was larger than that from Unit A (about 1.5 times). The most evident reason was that the GHG emissions from the transport of food residues were higher in Unit B because large amounts of liquid food residues such as milk and whey were used, and the transport distance was longer. Second, more fuel was required to heat food residues in Unit B, probably because Unit B is located in Hokkaido, a northern and colder region in Japan.

The results of the simulation evaluating the effects of transport distance of the produced feeds indicated that LQ units emitted smaller amounts of GHGs, even when the produced FFR was transported 200 km to farms. Only Unit E had a level of GHG emissions similar to that of the LQ units. Thus, the environmental loads of the transport of produced feeds were smaller than that of the production of feeds despite the fact that the transport volume of FFR in LQ was larger.

The energy consumptions of each scenario and of each unit showed a pattern similar to that of the GHG emissions; however, the average energy consumption for DH was higher than that for IC despite the fact that the averages of DH and IC had similar emissions of GHGs. This appeared to be because IC had the some amount of N2O emissions, while most of the GHG emitted from DH was CO2, which was closely related to fossil fuel energy. Non-CO2 GHGs, such as N2O and methane, contributed to global warming to some extent for agricultural products, in contrast to industrial products, for which CO2 accounted for most of the total GHG emissions (Brentrup et al., 2004; Ogino et al., 2004, 2007).

The water consumptions for LQ and DH were far smaller than that for IC. In IC, most of the water consumed was for the production of forage crops. Agriculture is considered a major consumer of water resources (Shiklomanov and Rodda, 2003) due to evapotranspiration of water from cropland originally derived from precipitation and irrigation (Oki and Kanae, 2006). The variation of water consumption among FFR-producing units appeared to be mainly affected by the water efficiency of steam boilers.

Since LQ does not require evaporation of moisture in food residues but only heating for sterilization at a temperature of 70 to 80°C, much less energy was consumed, and thus far fewer GHGs were emitted compared to DH. The liquid FFR in the present study was sufficiently sanitary because it was prepared through heat treatment. As described above, Sancho et al. (2004) reported that food residues after thermal treatment at a temperature of at least 65°C for 20 min were sufficiently sanitary, and nutritional parameters of the product remained suitable.

Liquid FFR requires a liquid feeding system; thus, it is harder to introduce to farms than dehydrated FFR. Use of FFR, however, leads to cost reduction for feeds, and thereby reduces overall costs. In contrast, farmers can feed dehydrated FFR to swine without modifying the feeding system or dehydrated FFR can be mixed with commercial formula feed. However, LQ produces FFR using a smaller amount of fuels as described above and consequently at a smaller fuel cost than DH.

Comparisons between LCA studies must be qualified by stating that LCA studies by different authors are likely to involve enormously different assumptions, and that relative results within an LCA study are far more meaningful than absolute results. Still, it is reasonably informative to compare our LCA results for LQ as a food waste treatment with those found for other food waste treatment processes. In their household-based LCA study, Lundie and Peters (2005) reported that the amounts of GHG emissions from treatment with a food waste processor, home composting with aerobic or anaerobic conditions, centralized composting, and landfilling with municipal waste per the average amount of food waste produced by a household in 1 yr (182 kg) were 13, 0.30, 273, 52, and 82 kg CO2 eq., respectively. LQ had better or equivalent environmental performance than all of these treatments, except for home composting under an aerobic condition. Lundie and Peters (2005) also reported energy consumptions ranging from 40 to 661 MJ per FU and water consumptions ranging from 10 to 2335 kL per FU for different food waste management options. LQ consumed less energy and all FFR-producing units consumed less water than these food waste management options when the production of feed equivalent to FFR was taken into account, although it was not clear how the compost produced in the composting options was treated.

Mendes et al. (2003) used LCA to evaluate the environmental impacts of biological treatment processes of the biodegradable fraction in municipal solid waste, and reported that GHG emissions from biogasification and composting with biofiltration were less than 50 kg CO2 eq. per ton of waste. Hirai et al. (2001) also used LCA to evaluate the environmental impacts of food waste treatments, such as composting and biogasification, and reported GHG emissions ranging from –10 to 130 kg CO2 eq. per ton of waste. The estimate for GHG emissions from LQ is smaller than those from all of these food waste treatments when the production of feed equivalent to FFR is taken into account. Compost made directly from food residues comes to compete with the compost made from animal waste in countries with a high density of animals, such as Japan. Therefore, it enhances the effective recycling of biomass that food residues are given as feed to animals and their manure is composted and applied to farmlands.

The animal industry has recognized the necessity of taking action on environmental problems. The present study indicates that liquid FFR has a remarkably reduced environmental impact compared with the treatment of food residues as waste. These results provide helpful information on the utilization of food residues and the promotion of these practices.


   ACKNOWLEDGMENTS
 
This research was supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS). We would also like to thank Dr. Tabara and Mr. Hishinuma, National Inst. of Advanced Industrial Science and Technology (AIST), for their advice, and the persons who participated at the site investigations for their significant contributions to the data collection.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 





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