chew_2015

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).


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


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


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


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


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


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


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


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)


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)


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

chew_2015

Documents

energy use

levels of nitrogen

use of digestate

swedish government

swedish population

swedish agriculture

levels of phosphorus

andxes nitrogen