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Resources, Conservation and Recycling 95 (2015) 114
Contents lists available at ScienceDirect
Resources, Conservation and Recycling
jo ur nal home p age: www.elsev ier .com/ locate / resconrec
Full length article
Environ odin agric
Yoon LinPer-Andea Swedish Univ Uppsb Swedish Insti
a r t i c l
Article history:Received 3 ApReceived in reAccepted 22 N
Keywords:Biogas producLCADigestateFertilizerFood waste
treatment
l imp. Thised, pethod), potck. Ul fertishowe im
However, acidication and eutrophication caused by digestate
handling and the cadmium content ofdigestate should still be
considered.
2014 Elsevier B.V. All rights reserved.
1. Introdu
Food waagriculture.compensatedoing this isEuropean Uin organic
f2013). The ducing cereIn conventichemical feagriculture,e.g.
pelletiz
An alterby both concally digestchemical feseveral envin the
prodthe efuen
CorresponE-mail add
http://dx.doi.o0921-3449/ ction
ste contains plant nutrients mainly originating from To maintain
its fertility, agricultural land needs to bed for the loss of these
nutrients. One obvious way of
to recycle them back to arable land, in line with both thenion
(EU) waste hierarchy and the principles of ecologyarming, as this
promotes reuse and recycling (IFOAM,need for external plant
nutrients is large for farms pro-als and vegetables for the market
(Doltra et al., 2011).onal agriculture this need is normally
covered by usingrtilizers. However, their use is not allowed in
organic
which leads to the use of more expensive fertilizers,ed meat
meal.native fertilizer rapidly becoming more widely usedventional
and organic farmers in Sweden is anaerobi-ed food waste (Avfall
Sverige, 2013). Compared withrtilizer, digested food waste
fertilizer ought to haveironmental advantages, as high quality
energy is gaineduction process and the nutrients are preserved
withint, i.e. the digestate. On the other hand, production of
ding author. Tel.: +46 1867 2209.resses: [email protected],
[email protected] (Y.L. Chiew).
chemical fertilizer is energy intensive, contributing about 56%
toindirect energy use in Swedish agriculture (Ahlgren, 2009) andxes
nitrogen from the atmosphere, thus increasing the amountof nitrogen
in the biosphere. Chemical fertilizer production thusincreases the
global ows of nitrogen and phosphorus at a timewhen the levels of
nitrogen have already exceeded the safe plan-etary boundaries and
the levels of phosphorus are about to doso (Rockstrm et al., 2009).
Use of pelletized meat meal fertilizerrecycles nitrogen and
phosphorus and does not increase theirglobal ows, but has the
disadvantage that it is relatively energydemanding (Spngberg et
al., 2011).
Use of digestate also contributes to carbon sequestration,
asdigestate organics are incorporated into the soil. The
productionof biogas is the reason why anaerobic digestion of food
wasteis rapidly increasing in Sweden, by 25% between 2009 and
2011(Energimyndigheten, 2012a). Recently, the Swedish parliament
seta national goal that by 2018, 40% of all food waste should be
treatedin such a way that both nutrients and energy are recovered,
i.e. thatit is digested (Swedish Government, 2012).
The Swedish population is exposed to high levels of cadmium(Cd),
resulting in adverse effects on both skeleton and kidney tis-sues.
The main exposure routes are through food and smoking.Food cadmium
intake is high, partly due to high levels of cadmiumin Swedish
agricultural soils. The maximum level in fertilizers inSweden to
prevent this situation deteriorating further has been
rg/10.1016/j.resconrec.2014.11.0152014 Elsevier B.V. All rights
reserved.mental impact of recycling digested foultureA case
study
Chiewa,, Johanna Spngberga, Andras Bakyb,rs Hanssona, Hkan
Jnssona
ersity of Agricultural Sciences, Department of Energy and
Technology, Box 7032, 750 07tute of Agricultural and Environmental
Engineering, Box 7033, 750 07 Uppsala, Sweden
e i n f o
ril 2014vised form 7 September 2014ovember 2014
tion
a b s t r a c t
This study assessed the environmentafood waste as fertilizer in
agriculturewhere the food waste was incineratSweden and life cycle
assessment muse, global warming potential (GWPto farmland and use
of phosphate ronegative results than use of chemicaphosphate rock.
Sensitivity analyses energy use and better for GWP if som waste as
a fertilizer
ala, Sweden
acts of recycling the plant nutrients in anaerobically digested
was compared with the impacts of using chemical fertilizer,roducing
heat. The study site was a biogas plant in centralology was used.
The impacts studied were primary energyential acidication,
potential eutrophication, cadmium owse of digested food waste as
fertilizer proved to have largerlizer in all categories assessed
except use of non-renewableed that the scenarios were comparable in
terms of primaryprovements in the anaerobic digestion system were
made.
-
2 Y.L. Chiew et al. / Resources, Conservation and Recycling 95
(2015) 114
estimated at 12 mg Cd per kg phosphorus (KEMI, 2011).
Meetingthis level is a challenge for all recycled fertilizers.
Manure con-tains about 815 mg Cd per kg phosphorus (KEMI, 2011) and
foodwaste around 35 mg (Jnsson et al., 2005). Chemical fertilizers
usedin Sweden (KEMI, 201input to thewaste, largeand therefo
Earlier ltion of foowaste treatCour JansenBerglund, 2Khoo et
al.tion of foodin terms of and Astrup,ies have rebenecial tCour
Jansendigestate ha
Several shave reportcontributiotive GWP (eJansen, 201energy
recoFruergaard tribute to Gand Berglucation in sobetween
inBerglund, 2to include ing and euteutrophicatbiogas prodon
acidicaduction (Be2011). The macidicationby either ofincluded,
mstudy incluof digestatefor conventfrom an orgSweden.
2. Method
LCA met(ISO, 2006)
2.1. Goal an
The goalment and rto comparethe digestatdigestion reproduced
unario, chem
land, and the same amount of food waste as was source
separatedin the DF scenario was incinerated, producing heat.
2.2. Functional unit
funnd sn anound fokg punal u
bags in thinan
pact
imphicatmpor004)s wene (Cxideng whicateth
as tlyinge of plso a
stem
proc biogissioolds
and sere ed tted wject fry of
a sundl
peried in
heatttomal fe
nctio chemed inted, a
tem
od w
d waauraouse005)he comostly contain around 36 mg Cd per kg
phosphorus1). However, chemical fertilizers give a net cadmium
soil, while recycled fertilizers, such as manure and foodly
recycle cadmium previously taken up from the soilre should not
increase the level in the long run.ife cycle assessment (LCA)
studies on anaerobic diges-d waste have mainly focused on assessing
differentment alternatives at the level of city (Bernstad and la,
2011; Kirkeby et al., 2006) or country (Brjesson and007; Fruergaard
and Astrup, 2011; Kim et al., 2013;, 2010). A few LCA studies have
shown that incinera-
waste is a better alternative than anaerobic digestionthe
environmental impact (Kim et al., 2013; Fruergaard
2011; Brjesson and Berglund, 2007). Other LCA stud-ported that
anaerobic digestion of food waste is morehan incineration (Khoo et
al., 2010; Bernstad and la, 2011). However, in those studies
infrastructure andndling were not included.tudies (Kim et al.,
2013; Brjesson and Berglund, 2007)ed that anaerobic digestion of
food waste gives a netn to GWP. Other studies have reported a net
nega-.g. Fruergaard and Astrup, 2011; Bernstad and la Cour1;
Poeschl et al., 2012). Incineration of food waste forvery is often
reported to avoid GWP (Kim et al., 2013;and Astrup, 2011), but
sometimes reported to con-WP (Bernstad and la Cour Jansen, 2011;
Brjesson
nd, 2007). The results on eutrophication and acidi-me previous
studies showed no signicant differencecineration and digestion of
food waste (Brjesson and007; Kirkeby et al., 2006), but these
studies seemed notdigestate handling, which is where the main
acidify-rophying emissions occur. Other studies showed thation
(included as nutrient enrichment) was greater foruction than for
incineration of food waste and resultstion were greater for
incineration than for biogas pro-rnstad and la Cour Jansen, 2011;
Fruergaard and Astrup,ain reasons for these differences in
eutrophication and
impacts were that digestate storage was not included the studies
compared and that nitrogen leaching wasainly causing
eutrophication. In contrast, the presentded infrastructure and
assessed the handling and use
from anaerobic digestion of food waste as a fertilizerional or
organic farming. The study was based on dataanically certied
anaerobic digestion plant in central
ology
hodology was used according to ISO 14040 and 14044. System
description and data used are provided below.
d scope
of this study was to assess the impacts on the environ-esources
of using digested food waste as fertilizer and
these impacts with those of using chemical fertilizer. Ine
fertilizer (DF) scenario, food waste was digested, thesidues spread
as fertilizer on arable land and the biogassed as vehicle fuel. In
the chemical fertilizer (CF) sce-ical fertilizer was manufactured
and spread on arable
Thedling anitrogeThe amdigesteof 254 functiopaper lected
contam
2.3. Im
Theeutropmost iet al., 2egoriemethaphur owarmiEutrop2001
mculatedmultiptor. Uswere a
2.4. Sy
Thefrom aThe emhousehliquid tions wupgradtaminawet
rerecoveducingwas lafor thecollectducingand bochemicthe future
ofincludneglec
3. Sys
3.1. Fo
Fooas restfrom het al., 2from tctional unit (FU) assessed was
the production, han-preading of a fertilizer containing 1 kg
plant-availabled 0.20 kg phosphorus after spreading on arable
land.t of phosphorus was based on the composition of theod waste
after spreading. The collection and treatmentre food waste from
households was also included in thenit. This corresponded to 266 kg
food waste (includingand contaminants such as stones, plastic etc.)
being col-e DF scenario and 259 kg in the CF scenario (includingts
but not paper bags).
categories
act categories of global warming, acidication andion were
evaluated, as these have been shown to betant for organic
fertilizers (Spngberg, 2014; Brentrup. Emissions to air and water
affecting these impact cat-re estimated, e.g. emissions of carbon
dioxide (CO2),H4), nitrous oxide (N2O), nitrogen oxides (NOx),
sul-s (SOx), ammonia (NH3)and phosphate (PO43). Globalas quantied
using a 100-year perspective (IPCC, 2006).ion and acidication were
quantied using the CMLod (Guine et al., 2002). The primary energy
was cal-he cumulative energy demand (Ecoinvent, 2010) or by
the energy carriers used by their primary energy fac-hosphate
rock and the ow of cadmium to arable landssessed.
boundaries
esses and activities included are shown in Fig. 1. Dataas plant
in central Sweden were used for the DF scenario.ns from collection
of source-separated food waste from, production and use of biogas,
storage, handling of theolid digestates, and handling and disposal
of reject frac-included. The biogas produced from food waste waso
vehicle fuel, replacing natural gas. Food waste con-ith plastic,
wood, textiles etc. ended up in the dry and
ractions. The dry reject fraction was incinerated, with heat,
and the wet reject fraction was composted, pro-bstrate for soil
production. The heavy reject fractionled. The data used in this
scenario were average dataod 20102012. In the CF scenario, the food
waste was
a mixed household waste fraction and incinerated, pro- that
replaced average Swedish district heating. The y
ash generated were sent to landll. In this scenario,rtilizer was
used to fertilize arable land and thus fullnal unit. European data
were used for the manufac-ical fertilizer. The infrastructure of
both scenarios was
the study. Leakage of nitrogen from arable land wass this was
considered to be similar for both scenarios.
description and data used
aste characteristics
ste was collected from households and businesses suchnts and
industries, in approximate proportions of 82%holds and 18% from
restaurants and industries (Jnsson. The composition of food waste
treated was calculatedmposition of food waste from households,
restaurants
-
Y.L. Chiew et al. / Resources, Conservation and Recycling 95
(2015) 114 3
Fig. 1. System l fertidashed line bo aste prod. = produc
and industrHowever, fo(Table 1).
3.2. Digesta
3.2.1. CollecThe food
in 12 munilected in anbag holdersholders to vshows the aused for
footo househo
Table 1Dry matter con
Waste fracti
Dry matter (Volatile solidC-tot, biologN-tot P-tot Cd
a G. Hagskolb Jnsson etc Data on D
Sundqvist et a boundaries and processes included in the
digestate fertilizer (DF) and chemicaxes. Box in light grey
involves no treatment. Note that different amounts of food w
tion.
ies, in paper bags glued with starch for the DF scenario.r the
CF scenario paper bags and glue were not included
te fertilizer scenario
tion and transportation of food waste waste was collected from a
total of 155,273 householdscipalities in central Sweden. The food
waste was col-
open, ventilated system based on paper bags placed in in the
kitchen. Full paper bags were brought by house-entilated waste bins
in or close to the house. Table 2mount of paper bags, paper bag
holders and waste binsd waste collection. The paper bags
distributed yearly
lds were 9-L paper bags (98.5%), while restaurants and
tent, volatile solids and composition of food waste.
on Units Food waste + paperbagsc
Food waste
DM) content % Of wet weight 30.1 28.7a
s (VS) % Of DM 90.1 90.1a
ical % Of DM 48.3 48.9b
% Of DM 2.4 2.6a
% Of DM 0.30 0.32a
% Of DM 1.3E 05 1.2E 05b
d (pers. comm. 2014). al. (2005).M, VS, C-tot, N-tot, P-tot and
Cd for the paper bags were taken froml. (1999).
schools usehouseholdsties. The rewere not in120140 L 400 L for
mtrade. Accobins used wsizes. The pbins, as we
Table 2Amount of papfuel consumpt
Paper bags Paper bag hoWaste bins Food waste Fuelconsumptio
a Waste colbiodiesel (K. P
b Waste collused was a mmetres, 1 m3 a
c Trucks andiesel blendedlizer (CF) scenarios. Avoided processes
and products are shown inwere collected in the two scenarios (see
Section 2.2). Abbreviations:d larger paper bags of 22 L (0.9%) and
45 L (0.6%). The used paper bag holders distributed by the
municipali-staurants and trade used their own facilities and
thesecluded in the study. Five sizes of waste bins were used,and
190 L for single households and 240 L, 370 L andulti-households,
recycling houses and restaurants andrding to the municipal
authorities, 76.4% of the wasteere 120140 L, 21.3% were 240 L and
2.3% were otherroduction of paper bags, paper bag holders and
wastell as the transportation involved during distributing
er bags used, paper bag holders, waste bins, food waste
collected andion during collection of food waste.
Units Amount
19449,000lders 140,025
58,201collected [t y1] 14,823
nCollection Diesel [L y1]a 56,941
Biogas [N m3 yr1]b 48,134Transport (fromve stations to thebiogas
plant)c
Diesel [L y1] 11,953
lection trucks used 49% pure diesel and 51% diesel blended with
5%ettersson, pers. comm. 2013).ection trucks in one municipality
used biogas as vehicle fuel. The gasixture of 70% biogas and 30%
natural gas. Units: N m3 (Normal cubict 10 kPa and 0 C).d trailer
used Swedish average diesel mix: 17% pure diesel and 83%
with 5% biodiesel (Energimyndigheten, 2012b).
-
4 Y.L. Chiew et al. / Resources, Conservation and Recycling 95
(2015) 114
them, are described in an Appendix to this paper (Tables A1 and
A2).The food waste was collected once every two weeks in
residen-tial districts (single household), while in apartment
building areas(multi-households) it was collected every week using
waste col-lection trucwaste collemass of foomass of wareloading
stity) for furthfrom reloadassuming thing from thfood waste diesel
and bby the emis
3.2.2. DigesOn aver
with 30.1%unloaded itaminationmechanicalmixed withized for 1
haround 40
tate leavingsolid digestdigestate, i.
Of the arinspection obiowaste (8erated for e(1254 t) of t(69 t)
as he(mixture ofused for soiand sand an
The subsincluding pgrease separesources uand chemic2011, 2012to
their magreen electr(K. Pettersstrict heatin11,917 m3 oand fresh
wfor the biog
On averbefore lossto their meproductionin Appendixthe total
me
3.2.3. UpgrThe biog
from food plant, purimethane gaupgrading pused in
theproduction
electricity and 7106 m3 water were used. Due to interruptions
inthe upgrading process, on average 1.2% of methane gas was used
ina gas engine or was torched. In total, the system produced
vehiclefuel containing 1301,000 N m3 methane gas from food waste
and
bagsl gasr upg
Dispo biow
werort a
conort e% of to Ualcul
whilted fed be Sw
weta, wh. Theammh con013)al fe
g we comous e% nitn wa
of tal niject st wf asht of t 17.
replchatest. Av
(ANtroge
use ed. Tand (ing omiss
(IPCnspoissiocurree lanng st
Diges tont 1.4
the eir ch
lique tan
2000ks with two compartments. Fuel consumption for foodction was
estimated by allocating it in relation to thed waste collected,
which was about 25% of the totalste collected. The food waste was
transported to veations, where it was reloaded to trucks (2840 t
capac-er transport to the biogas plant. The distance travelleding
stations to the biogas plant varied from 30 to 71 km,e trucks made
a round trip and were empty on return-
e plant. The emissions from collection and transport offrom
municipalities were calculated from the amount ofiogas fuel used,
as described in Table 2, by multiplyingsions data described in
Appendix (Tables A1 and A2).
tion and biogas productionage, 14,823 t per year of
source-separated food waste
DM arrived at the digestion plant (Table 2). It wasn the
reception hall and visually inspected for con-. If it passed this
inspection, the paper bags werely shredded, passed through a
mechanical screen and
tap and reject water to a slurry. This was pasteur- at 70 C
before entering a digestion reactor running atC with a hydraulic
retention time of 20 days. The diges-
the reactor partly owed to centrifuges producing aate (29% DM)
and partly left the plant as non-dewaterede. as a liquid digestate
(4% DM).riving food waste, 6.58% (976 t) did not pass the visualr
the initial screen. This dry reject mainly consisted of4.5%) and
some plastics, wood etc. (15.5%). It was incin-nergy recovery. In
the preparation of the slurry, 8.46%he arriving food waste ended up
as wet reject and 0.46%avy reject. The wet reject consisted of
organic material
oating food waste, bres, etc.). It was composted andl
production. The heavy reject mainly consisted of stonesd was
landlled.trate in the reactor consisted of 12,525 t of food
wasteaper bags after pre-treatment, 2235 t of sludge fromrators and
2085 t of silage. Data on the amount ofsed by the biogas plant
(electricity, heat, freshwaterals) were collected from
environmental reports (SVAB,) and allocated to the different
substrates accordingss, i.e. 77% to the food waste. The plant used
3777 GJicity consisting of 99% hydropower and 1% wind poweron,
pers. comm. 2013) and 5634 GJ heat from the dis-g network of the
municipality. The biogas plant usedf tap water for preparation of
the slurry. The chemicalsater used in the biogas plant and data on
infrastructureas plant are described in Appendix (Table A1).age,
1406,304 N m3 of methane gas were producedes and this was allocated
to the substrates accordingthane production potential. Thus 84% of
the methane
was allocated to food waste and paper bags (Table A3). Methane
losses from the biogas plant were 4.94% ofthane produced (SVAB,
2011, 2012).
ading and use of biogasas produced, containing 1320,811 N m3
methane gaswaste and paper bags, was sent to the upgradinged and
compressed to vehicle quality biogas with 97%s. About 1.5% of the
methane gas was lost from thelant (SVAB, 2011). Losses of methane
gas and resources
upgrading plant were allocated according to methane. For the
upgrading process, an average of 2873 GJ
paper naturadata fo
3.2.4. The
reject)transpfor thetranspand 9088 km were
c1998),estimaallocataverag
Theat Istrnology0.8 kg the aset al., 2chemicpostinDuringas
gaseand 74nitrogegen 6%The totwet recomporatio oamouning thawouldno
leacomponitrate35% nienergyincludin Finlspreadoxide e(tot-N)
Trathe emthis ocand thweighi
3.2.5. One
in aboudue toand th
Thestoragand in. The vehicle fuel was used in city buses,
replacing. Emissions from production and use of natural gas
andrading plants are described in Appendix (Table A1).
sal of reject fractionsaste (dry reject) and all the organic
materials (wet
e assumed to be food waste and the emissions fromnd treatment of
these rejects were included. However,taminants (e.g. plastics,
metal, textile, wood), only themissions were included. The dry
reject was incineratedthis fraction was sent 71 km to Avesta and
10% was sentppsala. The heat recovered, slag and y ash producedated
using the ORWARE incineration model (Bjrklund,e the resources used
and the emissions generated wererom an environmental report
(Vrmevrden, 2013) andased on heat produced. The recovered heat
replacededish district heating.
reject was transported 43 km to the composting plantich uses
semi-permeable membrane composting tech-
wet reject contained 9.2 kg total nitrogen (tot-N) andonium
nitrogen (NH4N) on a wet weight basis andtent was about half that
in the food waste (Carlsson. The compost was used for production of
soil, replacingrtilizer. Data on energy use and emissions during
com-t reject were described in Appendix (Tables A1 and A4).posting,
94 kg nitrogen per tonne of dry reject were lostmissions, estimated
as 15% nitrous oxide, 11% ammoniarogen gas from the denitrication
process. Ammoniums estimated to be 1% of total nitrogen and nitrate
nitro-
otal nitrogen in the mature compost (Sonesson, 1996).trogen in
compost was calculated from total nitrogen inminus nitrogen losses.
The phosphorus content of theas estimated to be 0.2% of total
solids, based on the
content in the wet reject (Carlsson et al., 2013). Thechemical
fertilizer replaced was calculated by assum-5% of the total
nitrogen content in the nished compostace chemical fertilizer
(Odlare et al., 2000). Assuming
during composting, the phosphorus remained in theoided chemical
fertilizer components were ammonium) and triple superphosphate
(TSP), with a content ofn and 21% phosphorus, respectively. The
emissions andfrom production and spreading of these fertilizers
werehe production of both compounds was assumed to beTable A2).
Data on emissions and energy use from theperation were taken from
Lindgren et al. (2002). Nitrousions were calculated as 1% (N2ON) of
applied nitrogenC, 2006).rt of the heavy reject to landll was
included, whilens from landlling this fraction were not included,
asd in both scenarios. The distance between biogas plantdll was
approximately 2.7 km, including a stop at theation.
tate handlingne of food waste entering the digestion process
resulted
t of liquid digestate and 0.2 t of solid digestate (Table
3),dilution with tap water. The yearly amounts
producedaracteristics can be found in Table 3.id digestate fraction
was stored in a 3000 m3 concretek covered with a plastic roof
beside the biogas plant
m3 satellite storage tanks made of plastic and with a
-
Y.L. Chiew et al. / Resources, Conservation and Recycling 95
(2015) 114 5
Table 3Total amounts, dry matter content, volatile solids and
nutrient concentrations of the two digestate fractions.
Amounta [t] DMb [%] VSb [%] Ntotb [kg t1 wet weight] NH4Nb [kg
t1 wet weight] Ptotb [kg t1 wet weight]
Liquid fraction 20,843 4.3 3.0 4.3 3.6 0.4Solid fractio
a Average pb Calculation ers. co
oating rootainer besidno roof) beincluded, asless of the dwas 15
km apers. commin Appendixto be spreadfraction in aactivities w
During organic subAmmonia ebe the sametom ll-up,solid manuliquid
digespH 7.5 anduid digestatfrom storagmanure, buuid digestatmethane
afof liquid digspreading sspreading nused. Indiretized NH3Nwere
only sions are newhile ammtotal storagabout 46 su91 summer
3.3. Chemic
3.3.1. CollecFood wa
collected an(used shopppose and thAs no separin this scentotal
weighneeded. Thibins were re240 L wasteever, 370 L aDF
scenariowaste, onlyallocated tolection routthe DF scenassumed
totrucks were
ort wationsala,nerat
Incinavered to. Thetion, not
and 1aries
shop) th
g valasteodel itialls cohis mof foo
formciumableing tationly ret proe Swling a
Dispo y ainerand fes w(Tabl
ash
Plant planed to
totalus sthe diers norusal fe
dmiun 2319 28.8 20.9 8.2
roduced 20102012 (SVAB, 2011; G. Hagskld, pers. comm. 2013).s
based on digestate analysis 20102012 and ORWARE simulation (G.
Hagskld, p
f beside the eld. The solid fraction was stored in a con-e the
biogas plant and on a concrete pad (about 30 m2,side the eld. The
production of the container was not
this was assumed to be used for other purposes regard-igestate
production. The average distance to the farmnd the transport was
done weekly by lorry (G. Hagskld,. 2013). Data on materials and
transport can be found
(Tables A1 and A2). The liquid fraction was assumed in spring by
band spreading equipment and the solidutumn by solid manure
equipment. Data on spreadingere taken from Lindgren et al.
(2002).storage and after spreading, digestate, just as
otherstrates, emits methane, nitrous oxide and ammonia.missions
when storing liquid digestate were assumed to
as when storing liquid manure under roof and with bot- and those
when storing solid digestate as when storingre (Table A4). For
ammonia emissions after spreadingtate, emissions after spreading of
liquid manure with
7.9 were used for interpolation to the pH of the liq-e, 7.6
(Rodhe et al., 2013). The nitrous oxide emissionse of liquid
digestate were also based on data for liquidt adjusted for the
difference in NH4N/tot-N ratio of liq-e compared with liquid
manure. Data on emissions ofter spreading of liquid manure were
used for spreadingestate. No data were found on ammonia emissions
afterolid digestate and therefore data for emissions
afteron-digested solid manure, incorporated after 4 h, werect
nitrous oxide emissions were calculated as 1% of vola-
(IPCC, 2006). Emissions of nitrous oxide and methanecalculated
for storage during summer, as these emis-gligible during winter
according to Rodhe et al. (2013),onia emissions were accumulated
emissions over thee period. Average storage time for liquid
digestate wasmmer days and 137 winter days and for solid
digestate
days and 91 winter days.
al fertilizer scenario
tion and transportation of food wasteste was put together with
residual waste in plastic bags,d transported to an incineration
plant. Used plastic bagsing bags) were assumed to be employed for
this pur-erefore no environmental load was allocated to them.ate
waste bins were needed to collect the food wasteario, the waste
bins were reduced, i.e. only 37% of thet of waste bins in the DF
scenario was estimated to bes was estimated by assuming that 120 L
and 140 L wasteplaced by 190 L and 240 L waste bins, and that 190 L
and
bins were replaced by 370 L and 400 L waste bins. How-nd 400 L
waste bins were assumed to be same as in the. Since the waste bins
were used for collection of mixed
25% of the weight of waste bins in the CF scenario was
transpincinerto Uppto inci
3.3.2. On
reloadAvestaproducsideredstonesboundplasticTable 1heatinfood
wtion mwas inue gaUsing ttonne in thethe calused (Taccordincinerand
onon heaaveraglandl
3.3.3. The
the incholm) distanctively bottom
3.3.4. The
assum50% ofpreviorus in tfertilizphosphchemic
3.4. Ca the food waste (K. Pettersson, pers. comm. 2012). Col-es
for food waste were assumed to be the same as inario. Emissions
from waste collection trucks were also
be the same, even though one-compartment collection used instead
of two-compartment versions. However
The foodet al., 2005)39 mg Cd pesome cadmstudy was a3.4 2.4
mm. 2012; Bjrklund, 1998).
as changed, as the food waste was assumed to go to the plants at
Avesta and Uppsala (90% to Avesta and 10%
the same distribution as for the dry reject fraction
sention).
eration of food waste and replaced district heatage, 14,416 t of
food waste (without paper bags) were
transport trucks and sent to the incineration plant in
incineration plant has ue gas condensation, but no
of electricity. Only incineration of food waste was con- the
incineration of contaminants such as 0.5% sand and.0% wood and
textiles, as these were outside the system
. As the food waste was collected in non-ventilated usedping
bags, it had a lower dry matter content (28.7%; seean in the DF
scenario, and thus both higher and lowerues were reduced, to 6091
and 4117 MJ per tonne of, respectively. Due to lack of data, the
same incinera-as calibrated for Avesta was used. However, this
modely developed for the incinerator in Uppsala, which
hasndensation and only heat recovery (Bjrklund, 1998).odel, heat
production was calculated to be 5326 MJ perd waste. Air and water
emissions and use of resources
of electricity, ammonia (for ue gas cleaning) and hydroxide,
sodium hydroxide and activated hydroxide
A1) when incinerating food waste were all calibratedo the 2012
environmental report for the Avesta waste
process which, like Uppsala, has ue gas condensationcovers heat
(Vrmevrden, 2013). Allocation was basedduction. The heat generated
from food waste replacededish district heat. The data for
incineration plant andre presented in Table A1.
sal of bottom ash and y ashnd bottom ash from food waste were
transported fromation plant in Avesta to landll in Hgbytorp
(Stock-rom Uppsala to the landll in Hovgrden (Uppsala). Theere
measured to be about 122 km and 44 km, respec-e A2). Data on the
emissions from landlling y and
were taken from the SPINE report (CPM, 2013).
availability and chemical fertilizer productiont available
nitrogen content of the liquid digestate was
be 80% of total nitrogen and that of the solid digestate
nitrogen (Delin et al., 2012; Svensson et al., 2004). As inudies
(Bernstad and la Cour Jansen, 2011), all phospho-gestate was
assumed to be plant available. The chemicaleeded to supply 1 kg
plant available nitrogen and 0.20 kg, according to the FU, were
produced and spread as thertilizer in Section 3.2.4.
m content of digestate and chemical fertilizer waste contained
37 mg Cd per kg phosphorus (Jnsson, while the food waste and paper
bag mixture containedr kg phosphorus, due to the paper bags also
containingium. The cadmium level of the chemical fertilizer in
thisssumed to be 3 mg per kg phosphorus, the content of the
-
6 Y.L. Chiew et al. / Resources, Conservation and Recycling 95
(2015) 114
Fig. 2. Primar Rejectby incineratio
majority offrom the Ko
3.5. Potenti
When cathere is thusphere. Cartype, tempecarbon addposted
wetbottom ashIn the CF scecontributeddigestate anadded to soies
(BernstaFor the bot2% of the inassumed tomately as stfor
centurie
4. Results
4.1. Primar
The DF sper FU, i.e. The upgradand rejects primary enupgrading
ocollection ofor productdling used
io ge. This1358eat
con of primaiowationr FU
prody energy use for the digestate fertilizer (DF) and chemical
fertilizer (CF)scenarios. n of the dry reject and composting of the
wet reject.
the phosphate rock used in Sweden, which originatesla Peninsula
(Yara, 2010).
al carbon sequestration
rbon is added to soil sequestration can take place, ands a
reduction in the carbon dioxide entering the atmo-bon sequestration
is complex, depending on e.g. soilrature, microbial activity, etc.
In the DF scenario, the
ed to arable land with digestate, the carbon in the com- reject
fraction for soil production and the carbon in the
scenarper FUduced from henergyper FUtotal pating bproduc7 MJ
pe
The remaining after incineration of dry reject was
included.nario, only the bottom ash remaining after
incineration
to carbon sequestration. The carbon sequestration ofd compost
was estimated to be 7% of the total carbonil in a 100-year
perspective, based on previous stud-d and la Cour Jansen, 2012;
Lund Hansen et al., 2006).tom ash going to landll, all the carbon
in the ash, i.e.itial carbon in the food waste (Bjrklund, 1998),
was
be sequestered, as this was considered to be approxi-able as the
carbon in charcoal, which can be sequestereds (Fowles, 2007).
and discussion
y energy use
cenario had a net primary energy balance of 283 MJit avoided
more primary energy than it used (Fig. 2).ed biogas avoided use of
870 MJ primary energy per FUhandling avoided use of 41 MJ per FU,
while 276 MJ ofergy per FU were used at the plant for digestion
andf the biogas. In addition, 330 MJ per FU were used forf the
source-separated biowaste. Of this, 76% was usedion and
distribution of the paper bags. Digestate han-22 MJ per FU.
Compared with the DF scenario, the CF
productionand transpoand the resfood waste more in ter1.09.
4.2. Global
The net per FU for for the CF savoided (Fitributed 28leakage
waproductionthat procesemissions f36%. The csource-sepawith the
latribution oThese largesions due tcity buses (s handling denotes
heat production and chemical fertilizers avoided
nerated more primary energy, with a balance of 784 MJ was due to
incineration of the food waste, which pro-
MJ of heat. As Swedish district heat is partly generatedpumps
and waste heat from industries, the primaryversion factor was less
than 1 (0.79). This led to 1073 MJrimary energy being avoided by
the incineration. Thery energy use for collecting, transporting and
inciner-ste was about 73 MJ per FU, while chemical fertilizer
and handling used 43 MJ per FU and ash handling used.uction of
kraft paper, i.e. the material used for paper bag
, was about 64% of the primary energy used in collectionrtation
and 20% was used for distributing the paper bagst for production of
the bags. The biogas produced fromand paper bags replaced 870 MJ of
natural gas, which isms of the primary energy, as the conversion
factor was
warming potential (GWP)
impact on global warming potential was 8.4 kg CO2 eqthe DF
scenario, while it was 17.1 kg CO2 eq per FUcenario, i.e. emissions
of 17.1 kg CO2 eq per FU wereg. 3). Biogas production and digestate
handling con-.5 and 19.0 kg CO2 eq per FU, respectively. Methanes
the main factor causing GWP emissions from biogas, contributing
about 75% of the total GWP emissions fors. Of the GWP from
digestate handling, nitrous oxiderom storage of the solid digestate
contributed most,ontribution from the collection and transport of
therated food waste was also large, 16.6 kg CO2 eq per FU,rgest
contribution, 51%, from the production and dis-f the kraft paper
bags used for food waste collection.
contributions were partly balanced by avoided emis-o the
upgraded biogas replacing natural gas as fuel for57.8 kg CO2 eq),
but also partly due to the treated reject
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Y.L. Chiew et al. / Resources, Conservation and Recycling 95
(2015) 114 7
Fig. 3. Global warming potential for the digestate fertilizer
(DF) and chemical fertilizer (CF) scenarios. Rejects handling
denotes heat production and chemical fertilizersavoided by
incineration of the dry reject and composting of the wet
reject.
fractions replacing chemical fertilizer and Swedish district
heat.In the CF scenario, the emissions were small for food waste
col-lection and transport, incineration and ash handling. The
largestcontributiocal fertilizesmall in th
avoided by the heat produced by incineration, but most of
theavoided heat caused relatively low GWP, from biofuel, heat
pumpsetc. However, the avoided GWP was large enough to give a
net
e balance, 17.1 kg CO eq per FU. Carbon sequestrationntrib
Fig. 4. Potentiby incinerationn was from the production and
handling of chemi-r. The avoided greenhouse gas emissions were
alsoe CF scenario. Large amounts of primary energy were
negativalso co4.6).al acidication for the digestate fertilizer
(DF) and chemical fertilizer (CF) scenarios. Rejec of the dry
reject and composting of the wet reject.2uted somewhat to GWP in
both scenarios (see Sectionts handling denotes heat production and
chemical fertilizers avoided
-
8 Y.L. Chiew et al. / Resources, Conservation and Recycling 95
(2015) 114
Fig. 5. Potent nariosavoided by inc
4.3. Potenti
The potfor the DF amounts, nthe digestacation (0.52after
spread0.10 kg SOalso led to collection aemissions fcesses in ththat
can cahydrogen c
4.4. Potenti
As for awere one ofnario (0.13 and transpoeq per FU) (bags used.
(0.02 kg Pnario was oin the CF scFU). In theproduction
4.5. Flows o
The DF sIn addition,phosphorusthe CF sce
ate n is
ownarion thers st of poruse levers, 2io, wial eutrophication for
the digestate fertilizer (DF) and chemical fertilizer (CF)
sceineration of the dry reject and composting of the wet
reject.
al acidication
ential acidication was about 0.58 kg SO2 eq per FUscenario,
while the CF scenario avoided insignicantet 0.02 kg SO2 eq per FU
(Fig. 4). In the DF scenario,te handling contributed most to the
potential acidi-
kg SO2 eq per FU), mainly due to ammonia emissionsing the liquid
digestate. The avoided fuel contributed2 eq in the DF scenario and
handling of reject fractionsa small amount being avoided. This was
followed bynd transport (0.02 kg SO2 eq per FU), mainly due to
phosphnitroge
TheDF scebased ofertilizcontenphosphaveragfertilizscenarrom the
production of paper bags (71%). All the pro-e CF scenario emitted
small amounts of the compoundsuse acidication, e.g. nitrogen
oxides, sulphur dioxide,hloride and ammonia.
al eutrophication
cidication, ammonia emissions in digestate handling the main
contributors to eutrophication in the DF sce-kg PO43 eq per FU).
The contribution from collectionrtation of food waste was fairly
small (0.02 kg PO43
Fig. 5), and was mainly due to production of the paperAvoided
emissions mainly came from the avoided fuelO43 eq per FU). The
total eutrophication in the CF sce-nly 8% of that in the DF
scenario. The largest contributionenario came from incineration
(0.01 kg PO43 eq per
CF scenario, the incineration of food waste for heat avoided
0.007 kg PO43 eq per FU.
f phosphorus, nitrogen and cadmium
cenario provided fertilizer with renewable phosphorus. the
compost from the wet reject avoided use of 0.02 kg
from non-renewable phosphate rock per FU, whilenario used 0.20
kg phosphorus from non-renewable
used 17.0 madded withthus did noother hand,the cadmiuommends
afertilizers.
4.6. Potenti
The carbwas estimacomposteddry reject gwaste incincarbon seqand
landl
Table 4Mass balance f(DF) scenario.
Liquid digesSolid digestaTotal . Rejects handling denotes heat
production and chemical fertilizers
rock. For the ow of nitrogen, a mass balance forgiven for the DF
scenario in Table 4.
of cadmium to arable land per FU was 8.6 mg for the and 0.6 mg
for the CF scenario. For comparison, resultse average level of 6 mg
Cd per kg phosphorus of chemicalold in Sweden (KEMI, 2011) and the
median cadmiumhosphorus fertilizers used in Europe of 87 mg Cd per
kg
(Nziguheba and Smolders, 2008) were calculated. If theel of Cd
content in Sweden had been used for chemical.3 mg Cd would have
been added to the soil in the CFhile if a European median chemical
fertilizer had been
g Cd would have been added. However, the cadmium
the digestate mainly originated from arable land andt cause much
further accumulation in the soil. On the
it is important to consider the importance of decreasingm
content in arable soil and thus KEMI (2011) rec-
maximum level of 12 mg Cd per kg phosphorus for
al carbon sequestration
on content in the waste products in the DF scenarioted to be 5.7
kg per FU in digestate, 4.0 kg per FU in the
wet reject fraction for soil production and 1.8 kg in theoing to
incineration. The carbon content of the fooderated in the CF
scenario was 31.8 kg per FU. Potentialuestration in the DF scenario
(with digestate, compostled slag) was about 0.7 kg, while it was
0.6 kg carbon
or the nitrogen ow (kg total nitrogen FU1) of the digestate
fertilizer
At start Storage Spreading Nitrogen to eld
tate 1.33 0.01 0.17 1.15te 0.28 0.07 0.03 0.18
1.61 0.08 0.20 1.33
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Y.L. Chiew et al. / Resources, Conservation and Recycling 95
(2015) 114 9
Table 5Results of the sensitivity analyses for the digestate
fertilizer (DF) and chemical fertilizer (CF) scenarios.
Primary energy use[MJ FU1]
GWP[kg CO2 eq FU1]
Acidication[kg SO2 eq FU1]
Eutrophication[kg PO43 eq FU1]
Cd [mg]
CF scenarioRecent technReplacing CF
DF scenario Recent technReduction o
plant and BAT (CH4 los
upgradingSwedish ave
upgradingSwedish ave
upgradingReplacing usReplacing pa
assuming 50% reductio50% increase
Potential of cBAT for biogUsed plasticSwedish heaEmissions
fr
Total reducti
Result of imp
in the CF scdecrease inyear perspeassumptionemitted froalso
formedbased on than undereslarge part oyears was n
4.7. Sensitiv
To test thfew changetion of moschemical femeal fertilizing from
muSwedish avand (4) diesthe sensitivfood waste system;
(6)upgrading; tivity analy
In the CFincinerationwhich has aused 196 Mto have an ciency of
8gas condenwas assumeper tonne oequal the av
incin (Bjhe put tht foupplieimilnd nded prod784 17.1 ology for
incineration plant 875 5.6
production with MMF production 587 18.0
283 8.4 ology for incineration plant (dry reject) 290 9.2
f 50% in methane leakage from biogasupgrading plant
312 7.0
s 0.13% in biogas plant and 0.27% in)
349 21.3
rage electricity mix in biogas and plants
196 9.1
rage district heating in biogas and plants
367 5.3
e of diesel 80 17.1 per bag with used plastic shopping bagssame
amount of reject
470 4.5
n in emissions from digestate handling 251 2.7 in emissions from
digestate handling 304 17.7
ombined improvements for DF scenarioas and upgrading plants 67
29.7
shopping bag 187 4.0 t replaces Vsters heat 84 3.2om digestate
(50%) 32 5.8
on 306 42.6
rovements 589 34.2
enario (with landlled slag), which would represent a GWP of 2.6
and 2.3 kg CO2 eq, respectively, in a 100-ctive (see Fig. 3). The
GWP was estimated based on the
that only carbon dioxide emissions would have beenm the soil and
could thus be larger if methane were. The potential GWP of carbon
sequestration given wase amount left in the soil after 100 years
and was thustimate. The fact that the emissions are delayed from af
the initial carbon degraded in the soil during the 100ot taken into
consideration.
plants as heattions, t12%, bamounwere anario, sby 3% aof
avoitricity ity analysis and uncertainty
e sensitivity of some assumptions made in the study, as in the
scenarios were made one at a time: (1) applica-t recent technology
for incinerating food waste; (2) thertilizer in CF scenario was
replaced with pelletized meater; (3) the 100% renewable electricity
and district heat-nicipality used by the biogas plant were replaced
with
erage electricity and Swedish average district heating;el as
fuel was replaced instead of natural gas. In addition,ity to
various improvements in anaerobic digestion ofwas investigated,
such as: (5) the food waste collection
reduction of methane losses in biogas production andand (7)
emissions from digestate handling. The sensi-sis results are shown
in Table 5.
scenario, the data on resource use and emissions for the plant
were taken from the Avesta incineration plant,
ue gas condensation system but only recovers heat. ItJ
electricity per tonne of food waste and was assumedincineration
efciency of 91% and a condensation ef-0%. Recent technology for an
incinerator without uesation, i.e. data on a waste incinerator in
Gothenburg,d. The electricity consumption of this plant was 19 MJf
food waste. The energy generated was assumed toerage proportions of
energy produced at Swedish waste
GWP impacSwedish diselectricity mlarge fractiolow GWP imcation
are ito waste inefciency, b
Pelletizetilizer usedslaughterhostudy was pmal By-Proet al.,
2011)meal fertilizanimal fat, mon way tmeat meal ated. This oand
incinerstudy, 12.5 were needethe functioizer was avin the CF scrst
degrad0.02 0.01 0.60.01 0.01 0.01 0.02 0.6
0.58 0.13 8.60.58 0.13 0.58 0.13
0.57 0.13
0.58 0.13
0.59 0.13
0.59 0.13 0.55 0.11
0.31 0.07 7.80.91 0.20 9.4
0.01 0.00 0.03 0.02 0.01 0.00
0.27 0.06 0.8
0.31 0.08 0.8
0.27 0.05 7.8
erating household waste, i.e. 18% as electricity and 82%rklund,
1998; CPM, 2013). As a result of these assump-rimary energy balance
in the CF scenario increased bye avoided GWP was smaller, about 33%
of the originalnd for the CF scenario. When the same assumptionsd
for incinerating the dry reject fraction in the DF sce-ar
tendencies were found, i.e. primary energy increasedet GWP
increased by 9% due to the smaller contributionGWP from the dry
reject. The reason was that the elec-uced avoided average Swedish
electricity mix with a low
t factor, only 43% of the GWP impact factor of averagetrict
heating (0.025 kg CO2 eq/MJ). Half of the Swedishix is generated by
nuclear power (51%) and anothern comes from hydro power (40%). Both
of these havepacts and the impacts on acidication and eutrophi-
nsignicant. Application of the most recent technologycineration
will thus provide benets in terms of energyut not in terms of the
environmental impact.d meat meal fertilizer (MMF) is a common type
of fer-
in organic farming in Sweden. It is produced fromuse waste. The
meat meal fertilizer product in thisroduced by drying and
pelletizing slaughter waste, Ani-duct Category 2, under Swedish
conditions (Spngberg. Included in the analysis were the production
of a meater and the avoided use of fossil fuel oil, as a similar
fuel,is co-produced in meat meal production. A more com-o treat
slaughter waste is to incinerate it. Thus, whenfertilizer is
produced, another fuel needs to be inciner-ther fuel was assumed to
be biofuel and its productionation were included. To full the
functional unit of thekg meat meal fertilizer, containing 0.38 kg
phosphorus,d. As the amount of phosphorus was greater than innal
unit of this study, use of 0.18 kg phosphate fertil-oided.
Treatment of food waste was by incineration, asenario. Sequestered
carbon was estimated based on aation of 80% of the organic matter,
corresponding to the
-
10 Y.L. Chiew et al. / Resources, Conservation and Recycling 95
(2015) 114
plant available nitrogen content of meat meal (Spngberg et
al.,2011). Of the remaining amount of carbon, 7% was assumed to
besequestered (Bernstad and la Cour Jansen, 2012; Lund Hansen et
al.,2006).
Meat meenergy thanenergy balafor the origthe productcal
fertilizerfor meat meutrophicatfrom the mwere the m
The metcontributedthese plantin the methreduce GWenergy to
beplants and u0.13% for th2013). If thi67 MJ more
If the paproductionThe amounthe collectiamount of o8%, as it
wproductionpaper bagsmary energby almost 4tions remaibe reduced
If the biotricity mix, would be abon acidicadistrict heabetter
for pthe impactseutrophicat
If the upprimary eneefciency oGWP impaccity buses cication
imphave less bereplacing d
The datagreat impacpotential euto energy uamount of fwere
calculand spreadidigestate, aa more temmicrobial a
The impstorage andrespectivelyin food was
amount of food waste to collect, transport and treat, but also a
dif-ference in the amount of energy produced from the treatment.
Intotal, these impacts affected the results in both a negative and
pos-itive way for both scenarios. The largest impact of changing
the
ons fP, wut 68missn anspecd. Thte wced
the d be nangeabou10% w
nera
resucan bose aact. systeor thvide
methwed er, it
mass ashant fd wa
DF fractnergwevebag d thDF s, 6% oscena% of pophi
collt, anntallals inc. shre unng ofof ms on. Thiethan
to deonsi
emir pHgrads onom tat syucedal fertilizer production used
slightly larger amounts of chemical fertilizer production, so the
total primarynce was somewhat less favourable for meat meal
thaninal CF scenario. Due to the replacement of fossil fuels,ion of
meat meal fertilizer caused less GWP than chemi-
production and thus the net result for GWP was bettereal
fertilizers than chemical fertilizer. The results forion and
acidication did not change, as eld emissionseat meal fertilizer and
the chemical fertilizer, whichain contributors to these categories,
were similar.hane gas losses in the biogas plant and upgrading
plant
about 27 kg CO2 eq per FU. The total methane losses ins were
measured to be about 6.4%. A reduction of 50%ane losses in the
biogas and upgrading plants would
P by 16 kg CO2 eq per FU, and allow 30 MJ more primary gained.
With best available technology (BAT) for biogaspgrading plants, the
methane losses can be reduced toe biogas plant and 0.27% for the
upgrading plant (Gthe,s were to be achieved, the DF scenario would
generate
primary energy and avoid 21 kg CO2 eq per FU.per bags were
replaced with used plastic bags, both the
and distribution of kraft paper bags would be avoided.t of waste
bins used and the transportation routes inon system would be
approximately the same, but therganic matter to the reactor would
decrease by about
ould no longer include paper bags. The methane gas would also
decrease by 8%. The DF scenario without
for collection of food waste would improve the pri-y balance by
about 66%, and the GWP would be reduced7%, provided that the food
waste lost with reject frac-ned the same. Acidication and
eutrophication would
slightly compared with the original DF scenario.gas and
upgrading plants used average Swedish elec-
the primary energy use would be 86 MJ higher, the GWPout 0.6 kg
CO2 eq higher and there would be no effectstion and eutrophication.
On the other hand, if Swedishting were used, the scenario results
would be 96 MJrimary energy use and 3.6 kg CO2 eq better for
GWP,
on acidication would be slightly worse and those onion would be
insignicant.graded biogas were to be used for replacing diesel,
thergy replaced would be 203 MJ lower, due to the higherf engines
using diesel compared with natural gas. Thets would be 8.6 kg CO2
eq higher. The use of diesel inould also slightly increase the
acidication and eutroph-acts compared with natural gas. The DF
scenario wouldnet in all impact categories if the biogas were used
foriesel.
used on emissions from storage and spreading had at on the
results, since they contributed directly to GWP,trophication and
potential acidication and indirectlyse. This was because any
nitrogen loss increased theood waste needed to be digested to full
the FU. Resultsated for a reduction of 50% in all emissions from
storageng, representing better management in the handling ofnd for
an increase in the emissions of 50%, representingperate scenario
with a warmer climate and thus higherctivity and emissions.act on
the results from changing the emissions from
spreading resulted in larger and smaller amounts,, of food waste
needing to be treated per FU. This changete needed to full the FU
involved a difference in the
emissiof GWby abooxide eicatio46%, rereduceopposiinuenbut
byshouldalso ching by about
4.8. Ge
The(LCA) to chotal impof the made fcially ewaste,sis shoHowevon
theter andimportthe foo
Thereject mary eeq. Hopaper lowereto the energythe CF than 5of
eutr
Theefcienronmemateribags etlines ahandlisions impactTable 5and
mshownment creduceature oand upimpactseen frtrict heis prodrom
storage and spreading could be seen in the resultshere a 50%
reduction lowered the total GWP balance%. This was mainly due to
the large impact of nitrousions, which is a strong climate gas. The
results for acid-d eutrophication were also reduced, by about 47
andtively, when emissions from digestate handling weree results on
primary energy use were affected in theay to the other results, as
this impact was not directlyby changes in the emissions from
storage and spreading,ecreased amount of food waste treated per FU.
Here itoted that the results for a comparable CF scenario would
as the amount of food waste treated changed, increas-t 10% when
the emissions increased and decreasing byhen the emissions
decreased.
l discussion
lts of this study demonstrate that life cycle assessmente used
as a support tool for farmers when they want
fertilizer that helps them reduce their environmen-The life
cycle methodology illustrates the importancem boundaries set for
the study and the assumptionse processes included. In this case
study, this was espe-nt for the local conditions specied for
collection of foodane losses at the biogas plant etc. The
sensitivity analy-
how important these specications were for the results. was a
challenge to collect sufcient high-quality data
balance of material, nutrients, dry matter, organic mat- in the
reactor. Getting these balances correct provedor the amount and
composition of the digestate fromste, and thus for the emissions
from the digestate.scenario beneted from resource recovery from
theions, i.e. incineration of dry reject generated 7 MJ pri-y per
tonne food waste treated and avoided 218 kg CO2r, infrastructure
included in the DF scenario, such as
holders, waste bins and biogas and upgrading plants,e benets of
that scenario. Of the factors contributingcenario, such
infrastructure represented 5% of primaryf GWP, 2% of acidication
and 3% of eutrophication. Forrio, waste bins, incinerator and
landll represented lessrimary energy, 11% of GWP, 16% of
acidication and 24%cation.ection system should be scrutinized to
make it mored collection in used plastic bags might be an envi-
y favourable option. However, aspects such as better paper bags,
more efcient distribution of the paper
ould also be considered, and improvements along thesederway in
the municipalities studied here. Improved
digestate, e.g. storage and spreading, to reduce emis-ethane,
nitrous oxide and ammonia would reduce
GWP, acidication and eutrophication, as shown ins could be
achieved by e.g. using a gasproof storage covere collection from
the digestate storage. This has beencrease the environmental
impacts of digestate manage-derably (Poeschl et al., 2012). Other
potential means tossions from digestate include e.g. lowering the
temper-
of the digestate to inhibit microbial activity. The biogasing
plants currently use green electricity to reduce the
GWP. This is an environmentally wise choice, as can behe
sensitivity analysis. The biogas plant also uses the dis-stem of
the municipality (0.06 kg CO2 eq per MJ), which
by use of more fossil fuels than the average Swedish
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Y.L. Chiew et al. / Resources, Conservation and Recycling 95
(2015) 114 11
district heat (0.03 kg CO2 eq per MJ). If the municipality were
tochange to producing its district heat with a similar mix as the
aver-age Swedish mix, the GWP for the DF scenario would decrease
by3 kg CO2 eq per FU. A change to using meat meal fertilizer
instead ofchemical fertilizer would not alter the results
signicantly (Table 5).
For the DF scenario, it is important to optimize the biogas
yieldby reducing methane losses, which have currently been reduced
to2.3% at biogas and upgrading plants. Furthermore, it is
importantto optimize the fuel replaced, as this study showed
improvementsin terms of primary energy, GWP, acidication and
eutrophicationwhen natural gas was replaced rather than diesel. It
is also inter-esting to note that when energy recovered by
incineration replaceselectricity, a larger amount of primary energy
can be avoided butless GWP is avoided, due to Swedish electricity
production relyingmainly on hydro and nuclear power, with low
emissions of GWP.Swedish district heat production uses just small
amounts of fos-sil fuels but relatively more than electricity
production. Thus, ifGWP is prioritized, then heat production should
be preferred overelectricity and maximized by ue gas
condensation.
If BAT for methane leakage in biogas and upgrading plants wereto
be applied, paper bags eliminated in the collection system
anddigestate mnet approx.CO2 eq GWthan the CFalthough accantly
high
One largfrom storagmethane andigestate we.g. total ntate.
Methaalso based odigestate, ebased on stin composiammonia coing the
digeestimate. Anicantly lo1% gure uSwedish stusions over aunder
summunder Swedand ammonafter spread
the liquid digestate. One way to reduce these emissions could
thusbe to mix the solid and liquid digestate and to handle it as a
liquiddigestate with a slightly higher dry matter content.
The use of digested food waste in this study gave a
largernegative impact for all categories studied than using
chemical fer-tilizers and incineration of the food waste. However,
consideringthe potential improvements mentioned earlier in the
discussion,digestate could be better than chemical fertilizer in
terms of GWP.From the perspective of plant nutrient recycling, the
nutrients inthe food waste, including micronutrients and organic
matter, arelost in the incineration process and the nutrient loop
is not closed. Aconsequence of this is that non-renewable
phosphorus sources areneeded. To move towards more sustainable
agriculture, we needto close the nutrient loops to a larger extent.
Thus, digestion offood waste for use as fertilizer is an
interesting option. However,as this study showed, the digestion
system needs to be improvedif it is to compare favourably with a
system with incineration andchemical fertilizer. For organic
farming, digestate is an interestingfertilizer, especially when
considering that manure handling alsocauses emissions contributing
to acidication and eutrophication.The cadmium content of the
digestate should be considered, as it is
ely h
clus
his c was, lowthaner. If sfullyer inock.atioow
wled
s stud numcienccFe
dix A
s app, infrales A
Table A1Inventory data
Material/pro
Paper bags27 MJ
Kraft paper Glue
Potato starchPaper bag pr
Paper bag hPolypropyleInjection mo ers is
bag h
Waste bins 3 kg, E), 20
High-densityanagement improved, the DF scenario could generate a
560590 MJ primary energy and avoid about 2034 kgP (Table 5). This
would make the DF scenario better
scenario for GWP and comparable for primary energy,idication and
eutrophication would still be signi-
er for the DF scenario.e uncertainty in this study is the
estimated emissionse and spreading of the digestate. Our estimates
ofd nitrous oxide emissions from storage of the solidere based on a
study on dewatered sewage sludge withitrogen content about 1.8
times that of solid diges-ne emissions from spreading of solid
digestate weren a study on sewage sludge. All emissions from
liquid
xcept for nitrous oxide emissions from spreading, wereudies on
digested liquid manure, which also differedtion, although the
emissions were adjusted based onntent. For direct nitrous oxide
emissions from spread-
state the default value of IPCC was used, which is a rough
Swedish study on digested liquid manure showed sig-wer results,
0.1% N2ON of tot-N, compared with thesed by IPCC (2006). However,
the study period in thedy was only 72 days, whereas IPCC estimates
the emis-
year. Furthermore, the Swedish study was conducteder conditions
and thus these emissions might be lowerish conditions. It was also
shown that the nitrous oxideia emissions from the solid digestate
at storage anding were signicantly higher per kg nitrogen than
for
relativ
5. Con
In tof foodenergycation fertilizsuccesfertilizphate
racidicmium
Ackno
Thi(Granttural SMary M
Appen
Thicesses
Tab
for the input materials, processes and infrastructures in the
study.
cess/infrastructure Description/assumption/weight
19 g kraft paper and 0.50.6 g glue Electricity consumption for
production 1 paper bag is 0.0Swedish conditions 100 g potato starch
in 375 g water
oduction
olders 0.173 kg polypropylene (PP), 10-year life span ne (PP)
European average ulding Electricity consumption for production of
paper bag hold
0.27 kW h and input PP is 0.247 kg to produce 1 kg paper
120 L, 140 L, 190 L, 240 L, 370 L, 400 L are 9.9 kg, 10.6 kg,
1and 22 kg, respectively. High-density polyethylene (HDP
polyethylene(HDPE) European average igh in relation to the
recommendations by KEMI (2011).
ions
ase study, use of chemical fertilizers and incinerationte proved
to make a better net contribution to primaryer the GWP and cause
less eutrophication and acidi-
digestion of the food waste and use of the digestate
asimprovements in the digestion system are implemented, digestate
as fertilizer could be better than chemical
terms of lowered GWP and use of non-renewable phos- However, it
would still cause more eutrophication andn than chemical fertilizer
use. The relatively large cad-
with digested food waste should be considered.
gements
y was funded by the Swedish Research Council Formasber
2007-1683) and the Swedish University of Agricul-es. We thank Vafab
Milj AB for the data support ande for the English revision.
. Appendix
endix contains inventory data on input materials, pro-structure
and all transport included in the study.1A4.
Reference for emissions
San Sac (n.d.), G. Wallin (pers. comm., 2013). L. Zanders (pers.
comm., 2013)
Korsns (2011)Avebe Adhesives (2010), C. Hansson (pers.comm.,
2013)Ecoinvent (2010)Ecoinvent (2010)
K. Pettersson (pers.comm., 2013)Ecoinvent (2010)
an estimatedolder material.
Ecoinvent (2010), R. Ferm (pers. comm., 2012)
14.4 kg, 19 kg-year life span
PWS Nordic (n.d.)
Ecoinvent (2010)
-
12 Y.L. Chiew et al. / Resources, Conservation and Recycling 95
(2015) 114
Table A1 (Continued)
Material/process/infrastructure Description/assumption/weight
Reference for emissions
Injection moulding To produce 1 kg waste bin material, the input
HDPE plastics were assumed tobe 1.06 kg and the energy consumption
5.33 MJ of Germany medium voltageelectricity production.
Ecoinvent (2010)
Electricity 99% Hydro and 1% wind Gode et al. (2011)Swedish
electricity mix Ecoinvent (2010)
Heat District heating of municipality of Vsters MlarEnergi
(2013)Swedish district heating Gode et al. (2011), Vattenfall
(n.d.)
Chemicals used in biogas plant Products and amounts K.
Pettersson (pers.comm., 2013)Lubricant oil Lubricant oil, at plant;
Mineral: 1030 kg year1 and synthetic: 1549 kg year1 Ecoinvent
(2010)Degreaser Fatty acid, from vegetable oil, at plant; 103 kg
year1 Ecoinvent (2010)
Naphtha, at regional storage; 27 kg year1 Ecoinvent
(2010)Ethanol Ethanol from ethylene, at plant; 163 kg year1
Ecoinvent (2010)Glycol Ethylene glycol, at plant; 511 kg year1
Ecoinvent (2010)Petrol Petrol, low sulphur, at regional storage;
175 kg year1 Ecoinvent (2010)Sodium hydroxide Sodium hydroxide, 50%
in H2O, production mix, at plant; 2153 kg year1 Ecoinvent
(2010)Iron(III) chloride Iron(III) chloride, 40% in H2O, at plant;
124,200 kg year1 Ecoinvent (2010)Nitrogen gas Nitrogen liquid; 800
kg year1 Ecoinvent (2010)
Fresh waterproduction
Products and amounts used at biogas plant SVAB (2011 and
2012)Lime, hydrated, packed, at plant; 3.1 kg Ecoinvent
(2010)Carbon dioxide liquid, at plant; 1.7 kg Ecoinvent
(2010)Electricity, low voltage, production NORDEL, at grid; 230
MJ(63.9 kW h) Ecoinvent (2010)
Vehicle fuelDiesel/diesel blend 5% biodiesel Production and
utilization Gode et al. (2011)Natural gas Production and
utilization Gode et al. (2011)
Fuel consumption: 0.46 m3 km1 Uppenberg et al. (2001)Biogas
Production and utilization Gode et al. (2011)
City buses of municipality of Vsters Biogasmax (2010)Fuel
consumption: 0.52 m3 km1 Biogasmax (2010)
Biogas plant Anaerobic digestion plant (biowaste), 25 years for
life span; 1 p Ecoinvent (2010)
Upgrading plants 25 Years for life span; 1 p Ecoinvent
(2010)Amount of material inputs was taken from Valorgas (n.d.) and
adjusted.Cement, at plant; 4333 kg Ecoinvent (2010)Sand; 8667 kg
Ecoinvent (2010)Tap water; 1000 kg Ecoinvent (2010)Steel,
unalloyed, at plant; 11,000 kg Ecoinvent (2010)Fibre glass, at
plant; 5 kg Ecoinvent (2010)Natural rubber-based sealant, at plant;
5 kg Ecoinvent (2010)PE, granulate, at plant; 25 kg Ecoinvent
(2010)Torch efciency: 90% UNFCCC (2010)
Composting wet reject Energy consumption: 0.2 MJ kg1 input
material, Swedish electricity mix Khner (2001)Fertilizer AN
production Best available technology (BAT) Brentrup and Pallire
(2008)Fertilizer TSP production Average European production data
for 2006 Davis and Haglund (1999)
Digestate storage and spreading Life time 30 years by eld, 50
years at plantLiquid storage at plant Concrete, normal, at plant;
168 m3 Ecoinvent (2010)
Reinforcing steel, at plant; 5.6 t Ecoinvent
(2010)Polyvinylchloride, regional storage; 3.7 t Ecoinvent
(2010)
Liquid storage at eld Excavationhydraulic digger; 1000 m3
Ecoinvent (2010)Bottom lining HDPE, granulate, at plant; 1.6 m3
Ecoinvent (2010)Roof polyvinylchloride, regional storage; 1.1 m3
Ecoinvent (2010)Concrete, normal, at plant; 4.3 m3 Ecoinvent
(2010)
Solid storage at eld Concrete, normal, at plant; 10.9 m3
Ecoinvent (2010)
Chemicals used inincineration plant
Lime, hydrated, at plant; 88.0 t year1 Ecoinvent (2010)Sodium
hydroxide, 50% in H2O, production mix, at plant; 3935 kg year1
Ecoinvent (2010)Ammonia, liquid; 28.1 t year1 Ecoinvent
(2010)Activated carbon, at plant; 1263 kg year1 Ecoinvent
(2010)
Incinerator plant Municipal waste incineration plant; 1 p, 40
years for life span Ecoinvent (2010)
Landlling facility Slag compartment; 1 p, 35 years for life span
Ecoinvent (2010)
-
Y.L. Chiew et al. / Resources, Conservation and Recycling 95
(2015) 114 13
Table A2Transport included in the study.
Transport Means of transportation Distance [km] Reference for
emissions
Paper factory to paper bag factory Included in Krsnas dataPaper
bag toDistributionbag in muni 1
iesel a
Paper bag hoPaper bag hoWaste bins f
DistributionCollection ofReload statiobiogas plant L km
pty).Dry/wet/heaDigestate froChemical ferproduct (froFly ash
(AveBottom ash
a Distance eb Estimated
Table A3Methane-form
Substrate
Source-sepaSludge fromSilage
Table A4Emissions valu
CompostingWet reject
StorageLiquid digesSolid digesta
SpreadingLiquid digesSolid digesta
a Kehres (20b Field studyc Karlsson ad Field studye Field studyf
IPCC (2006
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Environmental impact of recycling digested food waste as a
fertilizer in agricultureA case study1 Introduction2 Methodology2.1
Goal and scope2.2 Functional unit2.3 Impact categories2.4 System
boundaries
3 System description and data used3.1 Food waste
characteristics3.2 Digestate fertilizer scenario3.2.1 Collection
and transportation of food waste3.2.2 Digestion and biogas
production3.2.3 Upgrading and use of biogas3.2.4 Disposal of reject
fractions3.2.5 Digestate handling
3.3 Chemical fertilizer scenario3.3.1 Collection and
transportation of food waste3.3.2 Incineration of food waste and
replaced district heat3.3.3 Disposal of bottom ash and fly ash3.3.4
Plant availability and chemical fertilizer production
3.4 Cadmium content of digestate and chemical fertilizer3.5
Potential carbon sequestration
4 Results and discussion4.1 Primary energy use4.2 Global warming
potential (GWP)4.3 Potential acidification4.4 Potential
eutrophication4.5 Flows of phosphorus, nitrogen and cadmium4.6
Potential carbon sequestration4.7 Sensitivity analysis and
uncertainty4.8 General discussion
5 ConclusionsAcknowledgementsAppendix A AppendixReferences