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Nutrient recovery and emissions of ammonia, nitrous oxide and methane from animal manure in Europe: effects of manure treatment technologies Yong Hou, Gerard L. Velthof, Jan Peter Lesschen, Igor G. Staritsky, and Oene Oenema Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b04524 • Publication Date (Web): 06 Dec 2016 Downloaded from http://pubs.acs.org on December 10, 2016

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Environmental Science & Technology

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Nutrient recovery and emissions of ammonia, nitrous oxide and methane from

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animal manure in Europe: effects of manure treatment technologies

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Yong Hou∗,†, Gerard L. Velthof‡ , Jan Peter Lesschen‡, Igor G. Staritsky‡, Oene Oenema†,‡

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†

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Wageningen, Gelderland, The Netherlands

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Department of Soil Quality, Wageningen University & Research, P.O. Box 47, 6700 AA,

‡

Wageningen Environmental Research, Wageningen University & Research, P.O. Box 47, 6700 AA,

Wageningen, Gelderland, The Netherlands

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Corresponding Author:

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∗

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[email protected];

Phone: +31 (0)317-485083; fax +31 (0)317-426101; e-mails: [email protected];

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ACS Paragon Plus Environment


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Abstract

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Animal manure contributes considerably to ammonia (NH3) and greenhouse gas (GHG)

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emissions in Europe. Various treatment technologies have been implemented to reduce

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emissions and to facilitate its use as fertilizer, but a systematic analysis of these technologies

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has not yet been carried out. This study presents an integrated assessment of manure treatment

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effects on NH3, nitrous oxide (N2O) and methane (CH4) emissions from manure management

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chains in all countries of EU-27 in 2010 using the MITERRA-Europe model. Effects of

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implementing twelve treatment technologies on emissions and nutrient recovery were further

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explored through scenario analyses; the level of implementation corresponded to levels

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currently achieved by forerunner countries. Manure treatment decreased GHG emissions from

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manures in EU countries by 0-17% in 2010, with the largest contribution from anaerobic

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digestion; the effects on NH3 emissions were small. Scenario analyses indicate that increased

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use of slurry acidification, thermal drying, incineration and pyrolysis may decrease NH3 (9-

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11%) and GHG (11-18%) emissions; nitrification-denitrification treatment decreased NH3

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emissions, but increased GHG emissions. The nitrogen recovery (% of nitrogen excreted in

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housings that is applied to land) would increase from a mean of 57% (in 2010) to 61% by

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acidification, but would decrease to 48% by incineration. Promoting optimized manure

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treatment technologies can greatly contribute to achieving NH3 and GHG emission targets set

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in EU environmental policies.

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NH3, N2O, CH4

Animal housing

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Storage & treatment

Application to land

(Abstract art)

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INTRODUCTION

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Animal manure is a main source of plant-available nutrients, but also a major source of

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emissions of ammonia (NH3) and the greenhouse gases (GHG) - nitrous oxide (N2O) and

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methane (CH4). Manure from animal production is responsible for about 40% of the global

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anthropogenic NH3 and N2O emissions.1,2 Approximately 35-40% of global anthropogenic

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CH4 emissions are associated with the livestock sector (about 6% from manure management

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and the remaining from enteric fermentation).3 In Europe, animal manures contribute about 65%

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to the total anthropogenic NH3, 40% to N2O and 10% to CH4 emissions.4–7 Farm animals

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excreted 9.7 Tg N and 1.7 Tg P in the 27 member states of European Union (EU-27) in 2010,

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equivalent to about 95% and 160% of the total use of mineral N and P fertilizers.8,9

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Emissions of NH3, N2O and CH4 may occur simultaneously from different sources of

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manure management systems that typically include animal houses, manure storages, manure

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application to land and droppings from grazing animals in pastures. Introducing a

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management measure may have interactive effects on emissions of these gases from a specific

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source; it may also influence emissions downstream in the system and hence the nutrient

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recovery from the manure.10–12 The management chain from manure production up to its final

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use needs to be considered when assessing effects of measures on gaseous emissions and

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nutrient recycling and recovery.

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Manure treatment technologies have been increasingly applied in practice in Europe during

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the last few decades, driven by the specialization/intensification of animal production and the

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tightened enforcement of EU environmental policies.13 Manure treatment creates management

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opportunities to better use the nutrients and organic matter in manure. Treatment may induce

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changes in physical, chemical and/or biological properties of the manure and hence influence

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emissions of NH3 and GHG throughout the management chain. An inventory of manure

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processing activities in the EU member states reported that 7.8% of manure produced in the

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EU was processed in 2010, but with large variations among countries (range 0-35%).14 While

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the increased implementation of manure treatment is in general lauded as an environmental

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success,15 there is a need for systematic assessment of the impacts of manure treatment on

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environmental factors to provide guidance to further development of manure management

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strategies.

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Few studies have assessed N and GHG emissions from the animal production systems at

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country and the EU-27 levels.16–18 Manure treatment techniques are usually not considered in

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these large-scale studies, and as a consequence their environmental impacts have not been

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systematically addressed. Although a large number of laboratory and pilot experiments have

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been carried out to analyze NH3 and GHG emissions from processed manures, most of them

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focused on a specific gas/substance or emission source.10,19,20 Whole-farm (or life cycle)

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assessments were mostly conducted based on specific farm-scale characteristics. Manure

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management systems and the implementation of NH3 abatement measures (e.g. low-emission

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stables, storage systems and application methods) vary greatly among farms and

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countries.21,22 These farm and country-specific contexts may influence the performance of

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manure treatment technologies. There is as yet little information about the potential effects of

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manure treatment technologies in the EU. In particular, there is insufficient understanding of

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possible synergistic and antagonistic effects of manure treatment on emissions of NH3, N2O

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and CH4 and on nutrient recovery.

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The objective of this study is to assess the contribution of various manure treatment

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techniques to emissions of NH3, N2O and CH4 from animal manure in all member states of

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the EU-27 during 2010 (the latest year for which most activity data from statistics are

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available), using the model MITERRA-Europe.11,16 Further, the whole-chain impact potentials

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of treatment technologies on gaseous emissions and nutrient recovery were explored through

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scenario analyses. An uncertainty analysis was also executed.

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MATERIALS AND METHODS

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System boundary. The whole management chain from ‘animal excretion, in-house and

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outdoor manure storage, manure treatment, application of manure to land, and deposition of

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urine and faeces in pastures during grazing’ in the EU-27 was considered in this study. The

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system boundary, the main flows of nutrients embodied in animal manures and the possible

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manure treatment techniques are illustrated in Figure 1.11,14,16 The system includes the faeces

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and urine from grazing animals deposited in pastures (31% of total N excretion in 2010; Table

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S1) and the faeces and urine produced by housed animals. Excreta from housings are applied

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to agricultural land after a period of storage in either liquid or solid form, or in some cases are

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treated by certain technologies.

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The main treatment technologies currently applied in Europe are solid-liquid separation,

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anaerobic digestion, acidification, biological aerobic N removal (i.e. nitrification-

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denitrification), composting, (thermal or bio-) drying and incineration.14 The use of a

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particular technology depends on manure form (e.g. liquids, slurry and solid manure). Treated

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manure products are typically returned to land, as fertilizers or soil amendments.14,15 Several

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NH3 mitigation measures have also been adopted (see details in supporting information), but

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the implementation level largely varied between countries.18

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Emission sources. Emissions of NH3, N2O and CH4 from the manure management chain

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were quantified at country and EU-27 level for 2010. Animal categories include the main

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categories in Europe, i.e. dairy cows, other cattle, pigs, poultry, sheep and goats.16 Emission

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sources include NH3, N2O and CH4 from animal manure in housing, manure storage and

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treatment systems, and NH3 and N2O from manure applied to land and deposited in pastures

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(Figure 1). As the present study focuses on manure management, enteric CH4 emissions were

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not considered (see details in supporting information and Figure S1).

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MITERRA-Europe and data sources. For calculations, the model MITERRA-Europe

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was used. MITERRA-Europe is an integrated environmental assessment model which

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calculates the N and P losses and GHG emissions on a deterministic and annual basis, using

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statistical data of agriculture at EU country and regional levels.11,16 Country specific NH3

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emission factors (EFs) are based on information from the GAINS model, and quantification of

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N2O and CH4 emissions are based on IPCC guidelines.22,23

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The N and P excretion for each animal category and country was quantified on the basis of

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a three-year average (2009-2011) using the nutrient balance of feed intake and animal

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production.8 Quantification of NH3 and GHG emissions are based on nutrient excretion

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coefficients and respective emission factors. Data about manure management systems (i.e.

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animal grazing, daily spreading, liquid and solid based systems) were sourced from national

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GHG inventory reports (NIRs) to UNFCCC.21 Data about the degree of implementation of

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NH3 mitigation measures and their abatement efficiencies were obtained from GAINS22,23 and

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supplemented with information from NH3 mitigation guidance (UNECE) and review

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articles.10,24–27

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The IPCC default N2O-N EFs were adopted to quantify emissions of N2O from manure

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management systems, application and deposition.28 To calculate CH4 emissions, country-

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specific methane conversion factors (MCFs) for each animal category and manure

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management system were obtained from NIRs to UNFCCC and considered the allocation of

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manure management systems among climate zones. Calculations, nutrient excretion data

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(Table S1) and emission factors (Table S2) are detailed in supporting information (SI).

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Emissions of GHG, including N2O and CH4, were converted to CO2-equivalent (CO2-eq),

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considering the global warming potential of 25 and 298 times of that of CO2 for CH4 and N2O

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emissions, respectively. Indirect N2O emissions were not considered, and thus what is

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reported here should be considered as minimum estimates.

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Emissions from manure treatment. A ‘manure treatment’ module was developed to

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assess environmental effects of the main treatment technologies in the manure management

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chain (Figure 1). Information on the use of treatment techniques in each country in 2010 was

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derived from an inventory report on manure treatment activities and NIRs to UNFCCC.14,21

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Calculations and parameters (Table S3) related to emissions (NH3, N2O and CH4) from

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manure treatment, storage and field application (treated manure), and nutrient recovery are

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detailed in SI. Specific characteristics of referenced technologies are as follows:

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Solid-liquid separation. Three groups of mechanical separator were included: i) screw and

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filter pressing, ii) non-pressurized filtration and iii) centrifugation and sedimentation. Their

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separation efficiencies (i.e. the mass of a nutrient element in separated solid fraction,

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expressed as % of the mass of this element in raw slurry) varied from 10-33% for N and 15-

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69% for P. Separation efficiencies were higher when flocculates and multivalent cations

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(coagulation-flocculation) were added (Table S3). It is assumed that separation was near the

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source of production, i.e. the slurry removed from housing was not stored prior to separation.

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Slurry acidification. Acidification involves the daily addition of concentrated acid (e.g.

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sulfuric acid) to the slurry under slatted floors within housing, to lower the pH to 5.5. A

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fraction of the acidified slurry is transferred to an exterior storage tank without further

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treatment.29,30 The average NH3 abatement efficiency was 65% in housing, 83% in outdoor

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storage and 40% during application; a reduction of 87% for CH4 emissions from housing and

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storage systems was found.10,29,30

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Anaerobic digestion. Anaerobic digestion of animal slurry in EU is dominantly operated

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under mesophilic conditions.14 Biogas production from slurry was quantified as function of

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volatile solid inputs, CH4 yield and biogas composition.31 Biogas is considered to be

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composed of 55-65% CH4 and 35-45% CO2, depending on the country. Leakage is assumed

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as 1% of the gross biogas production.32 Liquid and solid fractions were produced from

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digested slurry when mechanical separators were used for post treatment.

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Nitrification-denitrification treatment. This technology includes a separation unit (pre-

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treatment), a nitrification-denitrification process (with liquid fractions as input) and a

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settlement/separation unit (post-treatment). The resulting sludge and liquid effluent (post-

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treatment) and solid fractions (pre-treatment) are stored before application. Emission factors

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during treatment and storage were derived from studies conducted in Belgium, France and the

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Netherlands, where this technique has been applied (Table S3).25,33–36

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Composting. Solid manure and solid fractions separated from slurry are used for

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composting.14 Emissions of NH3 from composting were considered to be 52% higher on

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average than those from conventional storage, whereas emissions of CH4 (71%) and N2O

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(49%) were lower on average; these percentages were derived from a meta-analysis study.27

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Thermal drying. Poultry manure and separated solid fractions are dried at temperate of 80-

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150 oC and commonly pelletized as post treatment.14 Gaseous emissions from the dryer must

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be recovered to avoid NH3 emissions. Consequently, an air scrubber was assumed to be

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installed with an average NH3 abatement efficiency of 85%.14,37 Methane emissions were

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assumed to be negligible under aerobic conductions.

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Bio-drying. This technique is used to treat poultry manure and solid fractions separated

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from slurry to reduce moisture content (by 40-60%) and to facilitate transport. This technique

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has not been widely used in EU.14 Emissions of NH3 are assumed to be increased (by 121%)

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relative to static piling due to the forced aeration.27 Changes in N2O and CH4 emissions due to

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aeration were not always consistent, therefore EFs for static piling were assumed to apply for

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these systems.27

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Incineration. Industrial-scale incineration of poultry manure exists in several EU countries

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(the Netherlands and UK), with the net energy surplus being used for electricity

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generation.14,38 The gases released from this process (with gas cleaning installation) mainly

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consist of CO2 and N2, while other emissions (NH3, N2O, NOx and CH4) are minor or

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negligible.38 Ash residues contain all P input from feedstocks and no or a limited fraction (less

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than 2%) of the C and N input.38–41

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Emissions from application of manure. Emissions of NH3 and N2O following the

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application of (treated and untreated) manure were estimated from their N contents and the

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specific EFs. Calculations and emission factors (Table S2 and Table S3) are detailed in SI.

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Emission factors were obtained from review articles (e.g. meta-analysis) and experimental

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studies (data sources are shown in SI). Impacts of manure application approaches that result

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in low NH3 emissions, such as immediate incorporation, injection of manure and band

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spreading, were quantified according to abatement efficiencies (see details in SI).

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Defining scenarios. Effects of treatment technologies on emissions of NH3, N2O and CH4

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from manure, and the N and P flows in the manure management chain of the EU-27 were

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further examined through scenario analyses. The assessment focuses on exploring the whole

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management chain impacts and the interactions between gas emissions when treatment

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technologies are implemented. Scenarios are summarized in Table 1. Twelve scenarios (S1-12)

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with alternative treatment technologies were compared with the reference case of no manure

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treatment.

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For all scenarios, it is assumed that an equivalent of 20% of total manure (N) collected

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from animal houses in each country was processed. For all technologies, the same amount of

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treated manure are considered, thus allowing technology comparison. The assumption of 20%

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implementation generally corresponds to the upper bound of the current use of specific

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treatment in EU countries. For example, 11% of total slurry produced was acidified in

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Denmark in 2010,14 and nearly 20% in 2015. In Italy, 24% of total slurry was treated by solid-

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liquid separation.14 Anaerobic digestion was applied to 13-24% of pig and cattle slurry in

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Germany and 20-35% in Italy as well as 30% of pig slurry in Cyprus.21 Nearly one third of

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chicken manure in the Netherlands was incinerated in 2010 and 15% in UK.14,38

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Scenarios include increased implementation of single treatment technologies (S1-9) and

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advanced combination of technologies (S10-12). For scenarios with raw slurry as feedstock

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(S1-5, S10-12), treatment technologies were considered to be applied to slurry removed from

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animal houses, with the exception for acidification (S4, S10) that is applied to slurry in the

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houses (i.e. before removal). For scenarios with solid manure as feedstock, technologies were

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applied to solid manure removed from houses. The amount of treated slurry or solid manure is

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assumed to be equivalent to 20% of total manure (i.e. the sum of slurry and solid manure, in

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terms of N) removed. However, the total amount of treated slurry or solid manure in a few

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countries can be less than 20% of total manure removed, because the specific manure form

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assumed to be treated was insufficiently produced (e.g in Bulgaria, Poland and Slovenia

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where slurry manure accounted for less than 15% of total manure produced; Table S1).

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Although pyrolysis of solid manure studies have been conducted, this technique has not yet

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been commercially implemented in Europe.14 In scenario (S9), slow pyrolysis of manure at a

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temperature of 600°C was considered with the purpose of producing a stabilized biochar. The

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mass (C, N and P) balance in pyrolysis is detailed in SI (Table S3). Three treatment systems

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with combinations of technologies were designed (S10-12) based on literature.42,43 In scenario

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S10, slurries acidified in housing (as S4) are separated by decanter centrifuge before outdoor

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storage. In scenario S11, slurries removed from housing are separated (as S2), and then the

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liquid fractions are acidified and the solid fractions are pyrolyzed. In scenario S12, all

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anaerobically digested slurries (as S3) are assumed to be acidified and immediately separated

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(centrifuge).

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Uncertainty analysis. Uncertainty analysis was carried out to achieve insight in how

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variation in the key parameters in the model affected the results, using a Monte Carlo (MC)

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based method.44 Six groups of parameters were included in this analysis: i) animal numbers, ii)

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nutrient excretion, iii) emissions from housing and manure storages (e.g. emission factors), iv)

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manure treatment and v) manure application as well as vi) manure treatment activity data.

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Parameter uncertainty is shown in Table S4. The model output uncertainty in response to

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uncertainty of the parameters was quantified for the year 2010, the reference (without manure

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treatment) and the scenarios (1000 MC runs each). The difference in emissions between the

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reference and each treatment scenario was statistically analyzed by comparing the MC

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simulating outputs, using Tukey’ Honestly Significant Difference (HSD) test at the 0.05

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significance level with the 95% confidence interval. In addition, the uncertainty contribution

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of the six parameter groups to the overall uncertainty was analyzed for the year 2010.

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RESULTS

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Manure management chain in 2010. Effects of manure treatment on NH3 and non-CO2

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GHG emissions were relatively small in 2010 (Figure 2). Approximately 6% of total N

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excreted by housed animals was treated in the EU-27; countries with excretion being treated

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above this EU average were typically in the EU-15 (except Cyprus; Table S1). Manure

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treatment altered GHG emissions in a range of -17% to 1% at country level, and on average

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by -4% at the EU-27 level. These reductions were mainly associated with anaerobic digestion

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use (Figure 2). Germany, Italy, Denmark, Spain, and the Netherlands had the largest GHG

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abatement due to manure treatment, sharing 89% of the EU-27 total abatement. In these five

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countries, anaerobic digestion abated GHG emissions from manure in a range of 1% (in Spain)

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to 9% (in Germany). Acidification abated 5% of GHG emissions in Denmark, separation 5%

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in Italy, and composting nearly 3% in Spain (Figure 2).

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Effects of treatment techniques on NH3 emissions were minor in most EU-27 countries

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(Figure 2). Reduction in NH3 emissions was relatively large in Denmark due to acidification

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(5%), in Belgium (4%) due to nitrification-denitrification treatment, and in Netherlands and

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UK (2-3%) due to incineration.

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Total NH3 emissions from the manure management chain in the EU-27 were 2.5 Tg N and

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GHG emissions were 86.9 Tg CO2-eq in 2010 (Figure 2a). The amounts of N and P excreted

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in housings that were applied to land (corrected for NH3 emissions) were 57% (a range of 52-

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68% among countries; Table S1) and 98%, respectively (Table 2).

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Scenario analyses - NH3 and GHG emissions. Scenarios with increased implementation

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of manure treatment technologies (20% of all manure produced in housings) in the EU-27

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were compared with the reference (without manure treatment; Figure 3).

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Increased implementation of slurry separation by screw press (S1) or decanter centrifuge

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(S2) decreased total GHG emissions by 8% and 12%, respectively. This reduction is due to

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decreased CH4 emissions from storage; the greater reduction from decanter centrifuge is

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related to the larger fraction of storage of separated solid manure. However, total NH3

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emissions changed only marginally. Increased adoption of anaerobic digestion (S3) decreased

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total GHG emissions by 19% (due to a reduction of 17% in CH4 emissions), while NH3

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emissions were minimally affected. Increased implementation of acidification (S4) decreased

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both NH3 emissions (mainly from housing and storage) and GHG emissions by 10% and 18%,

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respectively. Nitrification-denitrification treatment (S5) decreased both NH3 emissions from

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storage and treatment systems (by 3%) and from manure applied to land (5%). Emissions of

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N2O increased by 28% due to nitrification-denitrification treatment, which was partly off-set

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by lower CH4 emissions (18%). Nitrification-denitrification use resulted in an increase of 6%

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in total GHG emissions from the manure management chain (Figure 3).

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Composting of solid manure (S6) slightly changed total NH3 emissions. Increased

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emissions during composting were offset by lower emissions following application of

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compost to land. Composting decreased GHG emissions by 7% relative to the reference.

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Thermal drying (S7), incineration (S8) and slow pyrolysis (S9) of solid manure decreased

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both NH3 (9-11%) and GHG emissions (11-12%). In these three scenarios (S7-9), decreased

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GHG emissions were due to reduction in both CH4 emissions from storage systems and N2O

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emissions from fields relative to the reference; NH3 emissions also decreased during manure

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storage and land application (Figure 3).

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Acidification followed by separation of acidified slurry (S10) decreased NH3 and GHG

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emissions similarly to acidification use alone (S4). Centrifuge separation followed by

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acidification of liquid fractions and pyrolysis of solid fractions (S11) decreased NH3

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emissions by 7% and GHG emissions by 20%. Anaerobic digestion in combination with

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acidification and centrifuge (S12) had lower NH3 emissions compared to anaerobic digestion

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alone (S3), and had similar reduction potential of GHG emissions (Figure 3).

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Scenario analyses – nutrient recovery and content. The amount of total N applied to

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land, in terms of percentage of total N excreted in housing in the EU-27 increased from 57%

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to 60-61% due to acidification treatment (S4, S10, S12; Table 2). Nitrogen recovery however

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decreased to 48% with incineration (S8) and to 52% with nitrification-denitrification (S5) and

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slow pyrolysis (S9). Other technologies changed N recovery only marginally (Table 2).

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The N recovery of treated manure varied from 2% (incineration) to 87% (acidification).

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The N/P ratio varied from 3.4 to 10.7 in liquid manure products from treatment, compared to

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a mean of 3.5 in raw slurry. For solid manure products, the N/P ratio ranged from 0.1 to 3.2 in

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comparison to 3.0 for raw solid manure (Table 2).

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Uncertainty. The uncertainty (expressed as coefficient of variation) was 16% for total NH3

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emissions, 20% for GHG emissions and 6% for the N recovery in 2010. Emission factors for

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manure in housing and storage are the main factor contributing to the overall uncertainty in

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total NH3 emissions (70%) and GHG emissions (39%). Manure application emission factors

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contributed 50% to the overall GHG emission uncertainty. Manure treatment activity data and

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associated emission parameters contributed less than 1% to the overall emission uncertainty in

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2010 (Figure S2).

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The differences in emissions between reference and scenarios were statistically significant,

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except for S1-3 (separation techniques and anaerobic digestion; regarding NH3 emissions) and

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for S6 (composting; both NH3 and GHG emissions) (Figure 3).

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DISCUSSION

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Manure treatment in EU. Anaerobic digestion and solid-liquid separation are the most

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popular treatment technologies in Europe. Anaerobic digestion was estimated to have the

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largest contribution to overall GHG mitigation of all treatment technologies (Figure 2).

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Germany and Denmark have been most successful in promoting anaerobic digestion. The

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success is due to national government support (e.g. investment support for construction and

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subsidies on bioenergy delivery) and the enforcement of EU environmental regulations (e.g.

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Nitrates Directive, Renewable Energy Directive).45 The Danish government proposed a target

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of using 50% of the manure produced for renewable energy by 2020. This target would

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essentially be met through an expansion of biogas plants.46 Slurry separation has been adopted

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by livestock farms in many countries of EU-27 (particularly Italy and Portugal), which

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decreased GHG emissions (Figure 2). The reduction is achieved by lowering CH4 emissions

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from storage of separated solid fractions.12 Also, it was assumed that the slurry was not stored

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prior to separation, thus the reported GHG reduction due to separation can be the maximum

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estimates. Anaerobic digestion and slurry separation did not change NH3 emissions

334

significantly (Figure 2).

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Adoption of treatment technologies except anaerobic digestion and solid-liquid separation

336

was concentrated in a few specific countries, therefore their contributions were limited at the

337

EU-27 level. Slurry acidification with the purpose of NH3 abatement is only used in Denmark,

15



338

which also reduced CH4 emissions from slurry.10 The CH4 emission reduction is attributed to

339

the inhibition of methanogenesis due to acidic conditions and high concentrations of sulphate

340

(which is an electron acceptor) and sulphide (which is toxic).47,48 Poultry manure incineration

341

is used in the Netherlands and UK. There is evidence that CH4 and N2O emissions from

342

manure incineration are negligible, and the electricity production ‘saves’ emissions by

343

replacing fossil fuel combustion.38 Composting occurs in many countries on small scale units.

344

A meta-analysis indicates that composting tends to variably decrease N2O and CH4 emissions

345

compared to conventional static storage of solid waste.27 Although manure treatment is still

346

marginally used in Europe, many techniques (e.g. anaerobic digestion, acidification,

347

incineration) significantly contribute to decreases in GHG and/or NH3 emissions. Therefore, it

348

is important to take manure treatment into account for national emission inventories.

349

Implications of scenario analyses. Scenario analyses indicate that processing 20% of the

350

total manure produced from housings would decrease NH3 emissions by 0 to 11% and alter

351

GHG emissions by -20 to +6% from animal manure in the EU-27, relative to the reference

352

(Figure 3). Both NH3 and GHG emissions strongly decreased in scenarios with acidification

353

(S4, S10-12), and to a lesser extent with thermal drying (S7), incineration (S8) and pyrolysis

354

(S9) (Figure 3).

355

Manure N is a major source (81%) of NH3 emissions from agriculture in Europe.49 It has

356

been reported that implementation of an optimal combination of NH3 mitigation measures

357

(covered manure storages, low-emission application, etc.) would decrease total NH3

358

emissions in the EU-27 by 316 Gg N.18 Results suggest that processing 20% of the total

359

manure production from housings would have comparable emission abatement (180-275 Gg

360

N; S4-5, S7-12). A number of manure treatment technologies (e.g. slurry acidification,

361

incineration, pyrolysis) approaching the reported level may also have potential to mitigate

16


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362

GHG emissions (Figure 3). Conventional NH3 abatement measures minimally affect or

363

increase GHG emissions.11,18

364

Nitrification-denitrification treatment increased GHG emissions due to increased N2O

365

emissions from the reactor, despite CH4 emission reductions (Figure 3). Emissions of N2O

366

from nitrification-denitrification ranged from 1 to 20% of the slurry N input.25,34–36 The IPCC

367

default N2O EFs for raw slurry storage have a much smaller range: 0-0.5%.28 Emissions of

368

N2O from nitrification-denitrification treatment may be decreased by increasing the residence

369

time of the slurry in the denitrification reactor or by a better controlling molasses addition

370

(through measurement of the redox potential).35,50 Minimizing unwanted side effects is

371

especially important for Brittany (France) and Flanders (Belgium) where nitrification-

372

denitrification treatment has been implemented to decrease the manure N surplus.33

373

Increasing the efficiency of manure N and P use as fertilizer is economically beneficial

374

because it reduces the reliance on chemical fertilizers. However, scenarios with nitrification-

375

denitrification (S5), incineration (S8) and slow pyrolysis (S9) have an estimated low recovery

376

fraction available for land application (Table 2). These technologies cannot be considered

377

sustainable from a resource use efficiency point of view, as they convert the majority of N

378

(about 65% to 100%) to a form (dinitrogen gas) that can no longer be used for

379

fertilization.25,38 During these treatments (S5, S8-9), a significant fraction of the carbon in the

380

manure is also lost, reducing the organic matter input to soil. In the manure incineration

381

scenario (S8), the N loss equals to 8% of mineral N fertilizer consumed in EU in 2010. In

382

livestock-rich regions that produce more manure N than crops need, these technologies may

383

help lower N surpluses. Acidification (S4, S10, S12) increased manure N recovery and the

384

N/P ratios because of the saving of N from volatilization (Table 2). Slurry acidification

385

increases the N fertilizer equivalent value by about 25% compared to raw slurry.30,51

17



386

Phosphate rock is a non-renewable resource scarce in EU where more than 95% of mineral

387

P fertilizer is imported.52 For all manure treatment scenarios, the total P recovery estimates

388

did not decrease (Table 2). Nevertheless, the P availability for crops (in terms of first year P

389

fertilizer equivalent value) varied from less than 20% for ash residues to 80%-100% for

390

acidified slurry or separated liquid fractions.15 Manure treatment generates manure products

391

that vary in N/P ratios (0.1-10.7; Table 2). The use of slurry separation resulted in liquid

392

fractions with higher N/P ratios and solid fractions with lower N/P ratios than untreated

393

manure (Table 2), because of the higher separation efficiency of P than that of N.53 The large

394

fraction of N in manure was emitted during incineration and the amount of P remained

395

constant during incineration, which leads to low N/P ratios in ash. The ash as a PK fertilizer is

396

odorless and sterile and has a lower mass and volume than raw manure, which is suitable for

397

export to regions with a high P demand.38 Therefore, manure treatment provides opportunities

398

to tailor manure products to better meet specific crop nutrient demands.

399

Green energy production from anaerobic digestion and incineration of manure is a potential

400

pathway to achieving the EU Renewable Energy target; at least 27% of the total energy needs

401

come from renewables by 2030.54 Green energy can reduce CO2 emissions by replacing heat

402

and electricity produced from fossil fuels. Net energy production from anaerobic digestion

403

(S3) is estimated at 1.7-2.8 Mtoe (Million Tonnes of Oil Equivalent), assuming an energy

404

surplus of 50-80% in biogas plants used for heat and electricity cogeneration.12,32 5.5-8.7 Tg

405

CO2-eq would be avoided, assuming an emission factor of 0.074 kg CO2 MJ-1 on average for

406

power production from fossil fuel (21% coal, 46% petroleum and 33% gas) in the EU-

407

27.9,12,32 The avoided CO2 emission is equivalent to 6-10% of GHG emissions estimated for

408

the manure management chain in the EU-27 in 2010.

409

These scenario analyses illustrate that manure treatment technologies can mitigate GHG

410

and/or NH3 emissions from the manure management chain. Increasing use of these

18


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411

technologies may contribute to achieving the NH3 emission targets of the National Emission

412

Ceiling Directive (Directive 2001/81/EC), and GHG emission targets of the Kyoto Protocol

413

and Paris Agreement on Climate Change.55 Slurry acidification, incineration and pyrolysis are

414

manure treatment technologies that reduce both NH3 and GHG emissions. Acidification

415

increases N recovery, whereas incineration and pyrolysis can be used to reduce manure N

416

surpluses in regions with high animal density. Solid-liquid separation produces manure

417

products with diverse N and P contents, which enable farmers to better meet crop-specific

418

nutrient demands. Combining anaerobic digestion with acidification or with other NH3

419

mitigation measures (for storage of digested slurry) is needed to achieve abatement of both

420

GHG and NH3 emissions.

421

422

ASSOCIATED CONTENT

423

Supporting Information Available: Detailed description of model calculations, data sources,

424

and uncertainty analyses, and supporting figures and tables as mentioned in the text. This

425

material is available free of charge via the Internet at http://pubs.acs.org.

426

ACKNOWLEDGMENTS

427

This research has received funding from the People Programme (Marie Curie Actions) of the

428

European Union’s Seventh Framework Programme FP7/2007-2013/under REA grant

429

agreement no 289887. The results and conclusions achieved reflect only the author’s view and

430

the Union is not liable for any use that may be made of the information contained therein.

431

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432

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571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592

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593

Table 1. Description of manure treatment scenariosa Scenarios

594

Origins of feedstock

Brief description of treatment systems

Manure products Liquid form Solid form S1: Screw press Slurry (cattle, pigs) Screw press; LF, SF are not treated further LF (liquid fraction) SF (solid fraction) S2: Decanter centrifuge Slurry (cattle, pigs) Decanter centrifuge; LF, SF are not treated further LF SF S3: Anaerobic digestion (AD) Slurry (cattle, pigs) Mesophilic digesters Digestate; LF of digestate SF of digestate S4: Acidification (Acid) Slurry (cattle, pigs) Acidifying slurry in housing and storage Acidified slurry S5: Nitrification-denitrification Slurry (cattle, pigs) Nitrification-denitrification b Effluents Sludge; SF S6: Composting Solid (cattle, pigs, poultry) Composting Compost S7: Thermal drying Solid (cattle, pigs, poultry) Thermal drying, with air scrubbers Dried pellets Ash residues S8: Incineration Solid (cattle, pigs, poultry) Pre-drying and incineration S9: Pyrolysis Solid (cattle, pigs, poultry) Slow pyrolysis operated at ~600 °C Biochar S10: Acid-centrifuge Slurry (cattle, pigs) Acidification -> centrifuge Acidified LF Acidified SF S11: Centrifuge-Acid, pyrolysis Slurry (cattle, pigs) Centrifuge -> acidification (LF); pyrolysis (SF) Acidified LF Biochar S12: AD-Acid-centrifuge Slurry (cattle, pigs) Anaerobic digestion -> acidification -> centrifuge Acidified digested LF Acidified digested SF a Parameter inputs (e.g. emissions factors) are shown in supporting information (e.g. Table S3). b Decanter centrifuge is considered as pre-treatment unit.

595

24


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596

Table 2. Amounts of nitrogen (N) and phosphorus (P) in manure applied to land, expressed in percent of the amounts of N and P excreted in

597

housing (i.e. N and P recovery), in the EU-27 in 2010 and in scenariosa All manure (treated and untreated) N recovery P recovery (%) (%)

598 599 600

Treated manure N recovery (%)

P recovery (%)

N/P ratio in manure productsb

Liquid form Solid form In 2010 57 98 -c 3.5 (untreated) 3.0 (untreated) Scenarios: single technique, slurry S1: Screw press 58 98 63 100 3.6 2.0 S2: Decanter centrifuge 58 98 61 100 7.5 1.2 S3: Anaerobic digestion (AD) 58 98 62 100 3.4; 5.0 1.2 S4: Acidification (Acid) 61 98 87 100 4.4 S5: Nitrification-denitrification 52 98 33 100 8.6 2.9; 1.1 Scenarios: single technique, solid manure S6: Composting 58 99 60 100 3.2 S7: Thermal drying 58 99 57 100 3.1 S8: Incineration 48 99 2 100 0.1 S9: Pyrolysis 52 99 25 100 2.1 Scenarios: combined techniques, slurry S10: Acid-centrifuge 61 98 84 100 10.7 1.5 S11: Centrifuge-Acid, pyrolysis 57 98 61 100 9.7 0.5 S12: AD-Acid-centrifuge 60 98 74 100 10.0 1.4 a Emissions of ammonia were subtracted from the N in applied manure for calculating the N recovery. b Manure products from respective treatment technologies are explained in Table 1 (liquid manure products from AD include digested slurry and liquid fraction separated from digestate; solid manure products from nitrification-denitrification include sludge and solid fraction separated from slurry). c Not applicable.

601

25



602

Figure 1. Schematic representation of the manure management chain with manure treatment

603

technologies (highlighted in grey) discussed in this study. The arrows indicate the main flows

604

of manure products. The clouds show emission sources of ammonia (NH3), nitrous oxide

605

(N2O) and methane (CH4) from animal manure.

606

Figure 2. Emissions of ammonia (NH3), nitrous oxide (N2O) and methane (CH4) from

607

manure management chains in countries of EU-27 in 2010 (a), and estimated effects of

608

current manure treatment on NH3 and greenhouse gas (GHG) emissions by comparing

609

situations with and without treatment (b) (positive = increased emission; negative = emission

610

mitigation).

611

Figure 3. Changes in emissions of nitrous oxide (N2O) and methane (CH4) (upper panel) and

612

in ammonia (NH3) emissions (bottom panel) from the manure management chain following

613

the implementation of manure treatment scenarios, relative to a situation without manure

614

treatment (see text and Table 1). (-)/(+) indicates significant difference (lower/higher; P

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