final report market expectations and requirements …...market expectations and requirements for...

Final Report

Market expectations and

requirements for digestate

Market expectations and requirements for digestate – what are the options?

Project code: OMK006-003 Research date: March – June 2012 Publication Date: March 2013

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Written by: Principal authors: Claire King, Paul Bardos and Stephen Nortcliff (r3 Environmental Technology Ltd), with support from Antony Chapman, Simon Collett (Pell Frischmann Consulting Engineers Ltd) and Ursula Kepp.

Front cover photography: Land restoration site.

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Market expectations and requirements for digestate 3

Executive summary

The Government’s Anaerobic Digestion Strategy and Action Plan (Defra 2011a) focuses on removing the barriers to developing the anaerobic digestion (AD) industry in the UK, one of which covers digestate use. The aim of this project has been to investigate what users of digestate products require in terms of product characteristics and what expectations they have of quality. Another aim is to inform digestate producers of the opportunities and barriers that exist in these prospective markets. The project ran concurrently with WRAP reviews on Digestate distribution models (project number OMK006-001) and Assessment of enhancement techniques for digestate (project number OMK006-002) (WRAP, 2012f). The scope of this work included both current and likely end-use of primary sources of digestate; whole digestate and separated solid fibre and liquor products. The focus was on digestate produced from source segregated waste, principally from food waste (either PAS110 (BSI, 2010) and ADQP (EA, 2009b) compliant or not), but it also included products from the anaerobic digestion of non-source segregated waste (for example, Mechanically-sorted Biological Treatment (MBT) of municipal waste to produce CLO (compost like output), sewage sludge to produce biosolids and co-digestates. The project undertook both a literature review and survey, building on previous reports on new markets for digestates (WRAP, 2010 and WRAP 2011b) and current field trials work by WRAP across a number of sectors (WRAP 2012b). These, together with project team knowledge, formed the basis of identifying potential digestate end-use and, market sectors. The main focus of the work was to ascertain the particular characteristics required from source-segregated waste digestate pertinent to each sector and product, through an opinion gathering survey. Although currently representing the single most significant market for digestate, agriculture, was excluded as a sector from this survey, since it forms the focus of specific (and separate) WRAP market development activity. Forty-five people were contacted and sixty-six interviews carried out across a range of eight end-uses and fourteen sectors. The aim was to speak to informed stakeholders who are working with either digestates or other recycled materials. 54 % of the interviews were carried out with those who had some practical experience of using digestate; 12 % had worked with biosolids, 12 % with MBT outputs and 47% with PAS100 compost. A summary of the feedback from the survey has been formalized into the table below:

Review of respondents to digestates (whole, solid and liquor) for crop end-uses: awareness, attractiveness, ease of use and barriers Group Sub-group Awareness

of digestates

in sector

Attractiveness

of digestates to

sector

Ease of

use

Existing

applications

Possible

applications

Barriers

Field grown

horticulture

Vegetables Possibly on

some

vegetables

Soil improver

(whole or

solid)

Trees (top fruit

nursery stock)

Soil improver

(whole or

solid)

Soft fruit Liquor

Land

restoration

Biomass Trial Soil improver

(whole or

solid)


Forestry Trial Soil improver

(whole or

solid)

Industrial spoil

reclamation

Trial Soil improver

(whole or

solid)

Urban green space Soil improver

(whole or

solid)

Forestry

Conventional

forests

Soil improver

(whole or

solid)

Amenity

Landscape Soil improver

(whole or

solid)

Grass

parks/(roadsides)

Liquor

Liquid feed

for Sports

Turf

Pitches Trial Liquor

Fine turf -golf Trial Liquor

Soil

manufacture

Amenity

Land restoration

Trial Solid

Container

production

horticulture

Professional &

Amateur

Constituent

of peat free

growing

media

Dried

fertiliser

pellets

Various

Horticulture

Dried product

Key Awareness (excluding trial managers) some respondents were not aware of AD outputs.

Respondents foresaw possible digestate applications in their sector with prompting.

Respondents were aware of products or trials in their sector using digestates.

Attractiveness Some major barriers to or concerns over digestate use foreseen by some respondents. Potential applications (after discussion).

Products could readily be used.

Ease of use Niche opportunities, specialist users, pre-treatment of digestate needed.

Wider opportunities but needing pre-treatment of digestate.

Potential or actual applications no pre-treatment needed.

Barriers Some barriers mentioned.

Many barriers mentioned.

“Show-stoppers”, i.e. no use possible.

From an analysis of the survey, a number of potential applications for digestate use were identified. They have been grouped into two blocks (illustrated below): Those that show greatest potential for use as they are more suited to the application and have fewer technical problems to overcome; and those that show some potential for use. In some cases UK use or trials are already underway, whereas in other cases it is an emerging market application, and this is indicated in the right-hand column.


End-use and sectors that show the greatest potential for digestate use

Land restoration i.e. soil forming or soil improvement for degraded or marginal land (see glossary) Key benefits:

Acknowledged benefits of organic matter and nutrients.

Need for physical soil improvement.

High nitrogen can boost early growth.

Supplies other major and minor nutrients.

It can be used in its current form as a whole digestate or solid fibre.

Tolerate variability in amount and balance of nutrients.

Often economically attractive to users under current pricing.

Problems to be overcome:

Odour.

Some sites require PAS110 compliance.

Further possible enhancements:

Further aerobic stabilisation to reduce odour.

Reduced water content to improve material handling characteristics.

UK

use

or tria

ls u

nd

erw

ay

Organic component for soil manufacture Key benefits:

Provide organic component for soil manufacture.

Provide nutrients which may be beneficial when mixed and with other constituents.

PAS110 compliance ensures PTEs, pathogens and organic contaminants are monitored and kept within safe levels.


Digestate’s physical characteristics can make it difficult to mix with mineral soil components.

Odour.

Soluble salts would need to be appraised.


Reduced water content e.g. more efficient method of dewatering and/or further drying.


Co-composting with green waste would improve physical consistency and make a friable product.

Po

ten

tial a

nd

em

erg

ing

ap

plic

atio

ns


Field grown horticulture Key benefits:

Supply readily available nitrogen fertiliser (whole digestate).

Supply organic matter as soil improver beneficial on light/medium horticultural soils (fibre digestate).

It can be used in its current form as a whole or fibre digestate.



Concern over pathogens on edible crops. Confidence in pathogen control essential.

UK

use

or tria

ls u

nd

erw

ay

Production of pelleted organic fertiliser Key benefits:

Nutrient content to produce a fertiliser product.

Slow release form of nitrogen suitable for some uses e.g. amenity sector

Organic fertiliser.

Green credentials: produced from recycled product.



Energy cost of thermal drying.

Odour.


Further enhancements:

Thermal drying.

Po

ten

tial a

nd

em

erg

ing

ap

plic

atio

ns


Other end-uses that show some potential for digestate use

Liquid fertiliser for turf Key benefits:

Good balance of nitrogen relative to phosphate and potash.

High readily available nitrogen content to boost growth.

PAS110 ensures pathogens, PTEs and organic contaminants are monitored and kept within safe levels.

Environmentally friendly product.


Odour.

Solid fraction may cause blockage of spray equipment especially where dilution is required.

High soluble salts need to be appraised.

The need for a consistent product.



Further nutrient stripping may be needed to separate unwanted salts such as sodium or chloride.

UK

use

or tria

ls u

nd

erw

ay

Component of growing media Key benefits:

Provide peat alternative as growing media constituent.

PAS110 ensures pathogens, PTEs and organic contaminants are monitored and kept within safe levels.


Odour.

Digestate’s physical characteristics can make it difficult to mix with other growing media constituents.

Nutrient levels too high – particularly ammonium.


Possible herbicide contamination.



Co-composting with green waste probably essential to improve physical, chemical and biological characteristics.

Po

ten

tial a

nd

em

erg

ing

ap

plic

atio

ns


Thermal conversion This market provides an opportunity for digestates that are unsuitable for application to land. Key benefits:

Potential good calorific value.


Too wet - uncertainity over calorific value and materials’ classification.

Unknown compositional value of materials: cadmium, mercury and chlorine.

Further enhancements:

Reduced water content e.g. more efficient method of dewatering and/or further drying.

Heavy metal stripping.

UK

use

or tria

ls u

nd

erw

ay


Contents

1.0 Introduction and aims ................................................................................ 16 2.0 Approach .................................................................................................... 17

2.1 Survey approach........................................................................................... 18 2.2 Survey method ........................................................................................ 20

3.0 Nature of digestates ................................................................................... 21 3.1 Organic Waste management in the UK ....................................................... 21 3.2 What is anaerobic digestion? ..................................................................... 21 3.3 Feedstocks .............................................................................................. 21 3.4 AD processes ........................................................................................... 21 3.5 Digestate quality ...................................................................................... 22

3.5.1 Biosolids (sewage sludge) ............................................................... 22 3.5.2 Source segregated wastes (specifically including food waste) ............. 22 3.5.3 Non-source segregated waste: Mechanical Biological treatment (MBT) 23 3.5.4 Non-waste derived digestates (purpose grown crops and manures).... 24

3.6 Comparing digestates with composts ......................................................... 24 3.7 Separation of digestate and further enhancements ..................................... 24 3.8 Digestate and nutrient content .................................................................. 25 3.9 Other analyses ......................................................................................... 26

4.0 Currently available digestates and their end-uses ..................................... 27 4.1 Digestates from waste .............................................................................. 27 4.2 Biosolids (sewage sludge) ......................................................................... 28

5.0 Results ........................................................................................................ 29 5.1 Breakdown of survey respondents ............................................................. 29 5.2 General response of sectors ...................................................................... 30 5.3 Analysis of survey by end-use and sector ................................................... 34

5.3.1 Group 1 - Application to Field grown horticulture .............................. 34 5.3.2 Group 2 - Application to Land Restoration sites ................................. 35 5.3.3 Group 3 - Application to Forestry ..................................................... 37 5.3.4 Group 4 - Application to Amenity land .............................................. 38 5.3.5 Group 5 - Use of liquor as a liquid feed ............................................ 39 5.3.6 Group 6 - Use as an organic constituent for soil manufacture............. 41 5.3.7 Group 7 - Use as a peat replacement in growing media ..................... 41 5.3.8 Group 8 - Dried pelleted fertiliser .................................................... 43 5.3.9 Group 9 – Thermal conversion of digestate ...................................... 44 5.3.10 Group 10 - Fibre-board for the construction industry ......................... 44

5.4 Cross cutting issues .................................................................................. 45 5.4.1 What are the benefits of using digestates? ....................................... 45 5.4.2 What are the main features you would like to see? ........................... 45 5.4.3 Are there any problems you foresee? ............................................... 46 5.4.4 Other issues that arose from the survey ........................................... 47

6.0 Conclusions ................................................................................................ 48 6.1 End-use and sectors that show the greatest potential for digestate use ........ 48 6.2 Other end-uses that show some potential for digestate use ......................... 50 6.3 Possible threats for marketing digestates ................................................... 51

6.3.1 Understanding market requirements ................................................ 51 6.3.2 Public perception ........................................................................... 51 6.3.3 Geographical limitations of a bulky product ...................................... 52

7.0 Recommendations ...................................................................................... 52 Appendix 2 Broader issues .................................................................................. 64

European perspective ........................................................................................... 64 Sustainability criteria ........................................................................................... 66


Glossary

ADBA Anaerobic Digestion and Biogas Association

AEBIOM European Biogas Association

AfOR Association for Organics Recycling

Animal by-Products (ABPR) Products of animal origin

AD Anaerobic digestion

ADQP Anaerobic Digestate Quality Protocol. End od waste criteria for the production and use of quality outputs from anaerobic digestion of source segregated wastes

Biodegradable Capable of undergoing biologically mediated decomposition

Biofertiliser

Biofertiliser is the name adopted for quality digestates that meets the ADQP and PAS110 specification

Biofertiliser Certification Scheme The scheme which regulates the production of biofertiliser (ADQP and PAS110)

Biogas Mixture of gases produced by anaerobic digestion

Biomass Any living or recently dead plant or animal material

Biosolids Treated sewage sludge

Biowaste Animal and vegetal waste arising from households, commerce and the food manufacturing industry

Biomethane Pure methane produced from Biogas

CHP Combined heat and power

Co-digestion A process whereby one or more waste types are digested in a mixture, in order to enhance digester efficiency and increase biogas yield

Co-digestate Amended sewage sludge digestates

CLO Compost like output, biologically stabilised material produced by an MBT facility (may also be referred to as grey compost or biocompost

CNG Compressed natural gas


CQP Compost Quality Protocol. End of waste criteria for the production and use of quality outputs from the composting of source segregated wastes

Digestate Nutrient-rich material left following anaerobic digestion. Often referred to as whole digestate

Digestate fibre Fibrous fraction of material derived by separating the coarse fibres from the whole digestate

Digestate liquor The remaining liquid from whole digestate after treatment to remove fibre (solids)

Digestate whole Material resulting from an anaerobic digestion process that has not undergone post-digestion separation

Digestate materials Whole digestate resulting from anaerobic digestion process, and any subsequently separated fibre or liquor. Includes any separated fibre that undergoes a subsequent aerobic stabilisation phase, without addition of further materials

Digester The tank in which anaerobic digestion takes place

Dry solids Measure of solids content within the digestate. Defined as the % of mass remaining after drying at 105°C

Electrical conductivity A measure of the total salt concentration of a solution. Measured in dSm-1

EC JRC European Commission Joint Research Centre

FACTS Fertiliser Advisers Certification and Training Scheme

Feedstock The material that is put into the digester

Fertiliser A substance added to soil to make it more fertile

Digestate fibre The solid part of digestate, usually mechanically separated from the whole digestate

Gate fee Charge levied upon a given quantity of waste received at a Waste processing facility

GHG Green house gases that trap heat in the atmosphere contributing to climate change

Inorganic Material of mineral origin such as metal or glass


Land restoration This includes:- 1. Land reclamation (the recovery of

land from a brownfield or under-utilised state to make it suitable for reuse achieved through the stabilisation, contouring, maintenance, conditioning, reconstruction and revegetation of land).

2. Land remediation (the process of making a site fit for purpose through the destruction, removal or containment of contaminants).

3. Soil conditioning (see below)

Manures Organic matter, including farm animal waste used as organic fertiliser in agriculture

MBT Mechanical Biological Treatment – combination of mechanical and biological treatments for extracting recyclables from mixed household waste

Mesophilic Organisms that grows best in moderate temperatures

Methane A colourless, odourless gas with the formula CH4

PAS110 Specification for digestate derived from the anaerobic digestation of source segregated biodegradable material, so that they meet end of waste crtiteria

PTE Potentially Toxic Element. Element that has the potential to be toxic to humans, flora or fauna

Organic Material which comes from animal or plant sources

Quality Protocol A Quality Protocol gives guidance on how to recover waste, remove it from the regulatory regime and relevant regulations

REA Renewable Enery Association

RHS Royal Horticultural Society

ROC Renewables Obligation Certificate

Sludge Residual, semi-solid material left from sewage treatment processes

Soil improver/soil conditioner Material added to soil in situ primarily to maintain or improve its physical properties, and which may improve its chemical or biological properties


SRF Solid Recovered Fuel

Source segregated Materials of the types and sources specified that are stored, collected and not subsequently combined with any other wastes, or any potentially polluting or toxic materials or products, during treatment or storage (before or after treatment)


Acknowledgements

R3 environmental technology ltd would like to thank the many people who gave their time participating in the telephone survey and acknowledges the support of David Tompkins, Jacks Guinness and other WRAP colleagues, especially in developing contacts with stakeholder groups.


Report

1.0 Introduction and aims Anaerobic digestion is a means of treating organic materials, including biowastes, in the absence of oxygen to yield methane and a digestate (e.g. AEBIOM 2009, ADBA, 2012 and Al Seadi, 2008). The most commonly used digestion system in the UK is wet mesophilic digestion operating between 25°C and 40°C. Other less common systems include dry digestion, which uses a feedstock with very high dry solids content and thermophilic digestion, which operates at higher temperatures (50°C - 60°C). Digestate derived from mesophilic disgestion is typically a slurry-like consistency and it can be used directly (whole) or mechanically separated into a solid fibre product and a liquor (further detail is given in Section 3.5). Un-dewatered (whole) digestate, solid fibre and liquor are all considered primary digestates and are investigated in this report. The Government’s Anaerobic Digestion Strategy and Action Plan (Defra, 2011a) focusses on removing the barriers to developing the anaerobic digestion (AD) industry, one of which covers digestate use. This action plan was predicated on a view that AD is the best technology currently available for treating source-segregated food waste in particular. One of the barriers identified in the AD Strategy is the need for markets for the quality digestate produced from such AD plants. In order to develop strong sustainable outlets for digestate, operators will need to adopt a market focused approach to distributing digestate products. Currently the majority of digestate is being used on agricultural land but there is a need to understand, in broader terms, what the markets require from digestate across a range of end-use and sectors. The aim of this project has been to investigate what users of digestate products require in terms of product characteristics, and what expectations they have of quality. Another aim of this work is to inform the producers of the opportunities and barriers that exist in these prospective markets. The project investigated:

Current and likely end-use of primary sources of digestate; whole digestate and separated

solid fibre and liquor products.

The use of these products across a range of sectors, for example, land restoration, field-

grown horticulture, amenity landscape, sports turf, growing media, soil manufacture and

as a solid recovered fuel, to ascertain the particular requirements pertinent to each

sector.

Different categories of digestate. The focus will be on digestate produced from source

segregated waste, principally from food waste (either PAS110 - Publically Available

Standard 110 (BSI, 2010) and ADQP - Anaerobic Digestate Quality protocol (EA, 2009b)

compliant or not), but also include products from the anaerobic digestion of non-source

segregated waste (for example, Mechanically-sorted Biological Treatment (MBT) of

municipal waste to produce CLO (compost like output)) and sewage sludge to produce

Biosolids. In addition co-digestates will be referenced.

Initially the project undertook a literature review building on previous reports on new markets for digestates (WRAP, 2010 and WRAP 2011b) and current work by WRAP across a number of sectors (WRAP 2012b). From these sources and project team experience a list was drawn up of products and sectors (excluding agriculture). This formed the basis of the main focus of the project, an opinion survey targeting end-use and potential end-use across the range of sectors. The survey approach is described in more detail in Section 2.1. It was found that experience of digestate use is still relatively low in these sectors, therefore, the


survey was directed at informed stakeholders who may have worked with digestates or were familiar with similar recycled organics. Digestate producers were not directly included in the contact group,since the the study aims to provide them with information of the needs of potential customers. This work ran concurrently with WRAP reviews on Digestate distribution models (Project number OMK006-001) and Assessment of enhancement techniques for digestate (Project number OMK006-002), (WRAP, 2012f). 2.0 Approach This section describes the project strategy, in particular the survey approach. It includes some technical detail about anaerobic digestion. However, the general principles for AD and the types and characteristics of digestate are summarised in Section 3. The project identified the end products of digestate and the market sectors in which they may be used (excluding agriculture), with the aim of identifying stakeholders who could be interviewed to seek their views on the benefits and concerns of using digestates or digestate based products. Alongside this the types and quantities of digestate were described. One of the aims of this was to produce a number of examples of digestate quality; the dry matter and nutrient content, and basing quality criteria on those underpinning PAS110 (BSI, 2010) and the ADQP (EA, 2009b). These worked examples were used to facilitate discussion during the opinion based survey (see Figure 1). The analysis of the survey identified opportunities for digestate use.

Figure 1 Project approach

Digestate can be grouped according to feedstock input as this affects the type of digestate produced and the way it can be used. Four broad categories are recognised in this report. In addition co-digestates are considered briefly:

Biosolids (sewage sludge).

Source segregated wastes (specifically including food waste).


Non-source segregated wastes e.g. MBT outputs (CLO).

Non-waste derived digestates (purpose grown crops and manures).

The focus of this report was to obtain new information on the rapidly expanding production of digestate from source segregated waste and was broadly an information gathering exercise targeted at end-users and potential end-users of these digestates. Non-source segregated waste (MBT output) was also considered but to a lesser extent. The work is set in the context of the water industry’s established anaerobic digestion of sewage sludge, where digested biosolids provide a benchmark for a range of products to different end-uses. There is an extensive bibliography of biosolids use in restoration, forestry and agriculture and about the thermal conversion of biosolids (Sterritt and Lester, 1980; Wolstenholme, 1992 and Fytili and Zabaniotou, 2008) and the use of biosolids in horticultural and retail sectors may be limited because of consumer resistance. Therefore this project was directed towards understanding market sector expectations for the more novel digestates from source segregated biowastes. Digestates derived from purpose grown crops and digestates produced and used on farm are not classified as waste products and not considered in the scope of this report because they are not seeking other markets. However, farm manures and purpose grown crops may also be used as additional feedstocks for source segregated wastes at off-farm plants. 2.1 Survey approach Initially a list of end-uses was developed from previous reports on new and developing markets for digestates (WRAP, 2010 and WRAP, 2011b), and the background knowledge of the project team. The investigation started with the relatively few sectors designated for use under the ADQP (EA 2009b), (see Section 3.5) i.e. field grown horticulture, land restoration and forestry. Agriculture is also a designated market sector where the majority of digestate currently is used, but this is not included as it is the focus of specific (and separate) WRAP market development activity. This work seeks to extend and explore other current or likely end-uses extending to other land applications in the amenity landscape and sports turf sectors. More specialised uses in horticulture included: components of growing media for container production, manufactured soil, and liquid feeds. Solid fuel recovery and fibreboard for the construction industry were also investigated. It was acknowledged that the same end-use may have different requirements across different industry sectors, so sectoral needs would also have to be addressed. For example, whole digestate may be used as a fertiliser in the land restoration sector or in field grown horticulture or in natural forests. The land restoration sector may be split into further sub-sectors, for example urban greenspace or semi-natural habitat, each having different views on what is required. Through further discussions with consultants, and researchers involved with digestate trials, the list was developed and product/sectoral combinations listed so that the current and most likely end-uses and sectors for use were identified (Table 1).


Table 1 Current and potential end-uses for digestates

Product Sector Sub-sector

Whole digestate fertiliser

Land restoration Forestry Semi natural habitat Urban greenspace Biomass for energy

Biomass for energy

Field horticulture Vegetables

Nursery trees/ Top Fruit

Forestry

Solid (fibre) digestate soil improver

Land restoration Forestry Semi natural habitat Urban greenspace Biomass for energy

Biomass for energy

Forestry

Field horticulture Vegetables

Nursery trees/ Top fruit preplanting

Landscape

Solid (fibre) digestate organic amendment in growing media

Horticulture Amateur Professional

Solid (fibre) digestate organic amendment in soil manufacture

Landscape Amenity Land restoration Turf manufacture

Solid (fibre) digestate solid recovered fuel

Fuel industry

Solid (fibre) digestate in production of fibre board

Construction

Liquor digestate fertiliser

Sports Turf Amenity sports turf Golf courses

Horticulture Amateur fertiliser Soft fruit Hydroponics/aquaculture

Dried solid (fibre) digestate pellets

Horticulture Amateur Landscape Sports Turf Vegetables Fruit

Fertilisers produced through intensive processing e.g. ammonia stripping and struvite production

Horticulture

The next step was to identify the stakeholders to represent each use and sector. As there is little general use of digestates in many of the sectors to be investigated it was necessary to interact with informed stakeholders who may have worked with digestates or similar recycled


organics, principally composted materials. These included people with varying levels of knowledge and included consultants (as representatives of end-users and working on other WRAP projects) and manufacturers of specialist products, such as fertilisers and growing media, as well as practitioners “on the ground” such as growers, groundsmen, landscape contractors and others. The organisations contacted are listed in Appendix 1. A series of informal interviews was held focusing on:

How users and potential users perceive digestates.

What the potential benefits to using digestates might be.

What barriers or fears might restrict use.

Which are the key quality characteristics that would be essential if digestates are to

comply with existing specifications in the various sectors.

2.2 Survey method Interviewees were contacted initially through an introductory email setting the context and stating the aims of the project. This was followed up with a telephone conversation. The phone interviews had a general structure to allow the collation of data around the themes of benefits, problems and the key features required of digestates. To facilitate discussions about the nature of digestates, worked examples for whole, fibre and liquor digestate were calculated. This enabled realistic discussion around likely nutrient levels and consistency (dry solids content), and allowed users to compare digestates with products already in use and understand where potential uses might lie. Discussions were interviewee led, and although a basic information template was followed, did not ask a formal set of questions. The survey asked the following questions to all interviewees:

What might the benefits be of using digestate (why are you buying it)?

What are the main features you would like to see from such a material?

Are there any problems that you think might arise out of using digestates?

Supplementary questions were asked of those who had more detailed knowledge. These were explored as introduced by the interviewee:

Which nutrients were important?

Was it important to have a specific amount of any given nutrient?

If so, were nutrients available in the required amounts?

Were the major nutrients present in the correct ratios?

What benefits did the organic matter give?

Physical consistency – what was needed?

Odour , how bad and frequent was it?

Physical contaminants – which ones and limits?

Chemical contaminants metals – which ones and limits?

Chemical contaminants organic – which ones and limits?

Pathogens – which ones and limits?

Sodium, electrical conductivity and scorch concerns.

The worked examples (average nutrient content of the digestate types under discussion) were sent to those who expressed an interest for further comment. It proved difficult to find many well-informed stakeholders in some sectors, e.g. the construction industry. This, together with the large range of end-uses and sectors meant that some categories had few consultees.


The survey findings were collated and summarised across end-use to draw out general themes and then each end-use/sector was discussed separately with any additional user requirements and perceptions that were commented on and any regulatory conditions pertinent to that sector. 3.0 Nature of digestates 3.1 Organic Waste management in the UK The overall approach to organic waste management across the UK was established in the Defra Waste Strategy (Defra, 2000) with subsequent revisions for England (Defra 2007, 2011b), Scotland (Scottish Government, 2010) and Wales (Welsh Government, 2012). These strategy documents are a national response to the requirements of the EU Waste Framework Directive (EU 2008), which set recycling targets for Member States. The EU target set for the UK as a whole is 50% by 2020. The Scottish Government has set a recycling target of 70% by 2025 with zero waste as its ultimate goal, and The Welsh Government, currently in the process of developing its waste guidance, is also proposing a recycling target (including food waste) of 70% by 2025. In addition, the EU Landfill Directive (EU, 1999) requires the reduction of the quantity of organic waste being sent to landfill; the UK target is a reduction to 35% of the quantity of waste to landfill in 1995, by 2020. These policy drivers are increasing the need to develop and extend the recycling of organic materials. 3.2 What is anaerobic digestion? Anaerobic digestion is the process whereby micro-organisms decompose organic material (feedstock) in the absence of oxygen (in sealed airtight containers) to produce a mixture of methane and carbon dioxide called biogas which is used to generate electricity, gas or heat or used as a biofuel – and a residual solid or liquid product called digestate or biofertiliser (e.g. AEBIOM 2009, ADBA, 2012 and Al Seadi, 2008). The potential and rates of biogas production rely on feedstock and AD methodology, and are dealt with in other reports e.g. the Biogas Handbook (Al Seadi et al., 2008) and websites (e.g.NNFCC, 2012b). Digestates are the subject of this report. 3.3 Feedstocks Feedstock to an AD plant can be a single input or a mixture of inputs from a wide range of animal, plant and organic waste substrates. Short chain hydrocarbons such as sugars degrade more readily than longer chain hydrocarbons. Woody materials that contain long chain hydrocarbons such as lignin are unsuitable. Animal manures, sewage effluent, plant material, food waste, food processing residues and textiles are all possible feedstocks (e.g. Lukehurst et al., 2010 and EA, 2009b). The nature of the anaerobic digestion process is such that most of the nutrient quality of the feedstock material remains in the digestate residues. They are therefore a valuable source of stable organic material and nutrients. Feedstock also influences the amount and type of any potentially toxic elements (PTEs) and other non-degradable contaminants (Al Seadi et al., 2008 and Lukehurst et al., 2010). 3.4 AD processes AD plants use either dry, wet, or liquid digestion technology dependant on feedstock materials.

Liquid digestion describes very low solids systems (less than 2% dry matter) which are

typically operated for effluents with high concentrations of soluble organic material e.g.

effluent from food production and wash waters.

Wet digestion operates at less than 12 % dry matter and is applied to materials such as

sewage sludge, food residues, farm manures and soft green waste, and also in some MBT

systems.


Dry digestion operates at greater than 25% dry matter, and is used for municipal waste

and green waste.

The amount of water after digestion is almost the same as at the point of input to the digester. The principal AD approach currently in use in the UK is the wet digestion method producing low organic matter slurry of typically 5 to 7 % dry solids. Further description and summary of AD methods are given on the biogas –info website, the official information portal on anerobic digestion (biogas-info, 2012). 3.5 Digestate quality The characteristics and opportunities for use of the categories of digestate listed in Section 2 are described here: 3.5.1 Biosolids (sewage sludge) The anaerobic digestion of sewage effluent has been the long standing practice of the water treatment industry and – once processed post-digestion – produces a range of materials known as biosolids. Sludge production is a necessary part of sewage treatment; about 70% is thickened and undergoes anaerobic digestion producing a digested liquid. This is often further de-watered to produce a solid digested cake and a liquid, which is recycled back to the sewage treatment works (occasionally with some pre-treatment). The digestate cake can be used directly or further treated through conditioning with lime (lime stabilised), or dried to a high dry matter content (thermally dried). When biosolids are applied to agricultural land the terms of The Safe Sludge Matrix (Water UK /ADAS, 1998), The Sludge Use in Agriculture Regulations 1989 (SI, 1989) and The Code of Practice for Agricultural Use of Sewage Sludge (Defra, 2006b) are followed. The Safe Sludge Matrix relates the type of biosolid that can be applied to different agricultural and horticultural crops, and the time intervals allowed between application and harvest. The Sludge Use in Agriculture Regulations 1989 and The Code of Practice for Agricultural Use of Sewage Sludge state that the sludge and the soil must be tested for a range of potentially toxic elements (PTEs) and pH. (PTEs include zinc, copper, nickel, cadmium, lead, mercury, chromium, molybdenum, selenium, arsenic and fluoride). This ensures that there are maximum permissible concentrations of PTEs in soil and a maximum permissible average quantity of PTEs in the sludge applied over a 10 year period. The Regulations and Code of Practice also cover other areas relating to environmental protection. Adequate records of use must also be kept relating to analysis of soil and sludge and timing and rate of application. 3.5.2 Source segregated wastes (specifically including food waste) A range of source segregated feedstocks including animal manures, food waste and food processing residues are fed into the AD system. The goal of source segregation is to limit the input of potential contaminants such as heavy metals (Amlinger et al, 2004). In the UK at the moment, the primary digestate output is whole digestate. Digestates produced from source segregated waste can be recognised as products rather than regulated as treated wastes if they are made from source segregated wastes and comply with the ADQP (EA, 2009b). This protocol specifies end of waste criteria for the production of quality outputs from anaerobic digestion of source segregated biodegradable waste once it has been applied to land. It stipulates (1) allowable waste streams (feedstocks), (2) the method to produce quality product – i.e. compliant with PAS110 (BSI, 2010), and (3) requires that the intended use is in a designated market sector to be specified (see below). Regulation in Scotland compared to the rest of the UK only requires certification to PAS110 to be considered as fully recovered.


Opportunities therefore exist for digestate produced to this protocol to be marketed as a quality product with defined standards relating to contaminants, toxins and pathogens, thereby re-assuring markets and guaranteeing outlets for digestate. (1) Allowable Feedstocks: These largely come from the agricultural and food processing

and wood processing and textiles industries, meeting certain quality criteria (EA, 2009b). In Scotland there is no definitive list of acceptable feedstocks, they include but are not confined to those listed in the Quality Protocol for anerobic digestates (SEPA, 2012). Wastes can be included providing they are beneficial to the process (e.g. they provide good biogas potential) and will not adversely affect the operation of the process or the quality and use of the final digestate.

(2) PAS110 (BSI, 2010): The PAS is the UK’s baseline specification for digestate quality,

allowing producers to demonstrate consistent production of safe material. In Scotland, digestates independently certified to PAS110 may be regarded as products, and not subject to environmental regulation when transported or used. In the other UK nations, PAS110 digestates must also meet the requirements of the AD Quality Protocol (ADQP) to be regarded as products. The ADQP lists acceptable input materials and allowable markets. The specification stipulates the analyses/ tests required to achieve a minimum quality of digestate, including the method of testing and maximum upper limits permissible for the following:

Pathogens (human and animal indicator species).

Stability tests (volatile fatty acids, residual biogas potential).

PTEs.

Physical contaminants.

The following tests also have to be declared but without upper limits specified:

pH.

Total Nitrogen.

Total Phosphorus.

Total Potassium.

Ammoniacal nitrogen.

Water soluble chloride.

Water soluble sodium.

Dry matter.

Loss on ignition.

(3) Designated market sectors: The current designated market sectors for digestates (whole, solid fibre or liquor) are agriculture, forestry, soil/field-grown horticulture and for solid fibre digestate only, land restoration.

3.5.3 Non-source segregated waste: Mechanical Biological treatment (MBT) MBT consists of mechanical sorting which removes ‘dry’ (non-biodegradable) recyclables, and a subsequent biological treatment of the organic ‘fines’ which may be an aerobic decomposition or AD process (Cameron et al., 2008) and typically also includes subsequent downstream mechanical processing. This method is used for non-source segregated waste feedstock such as residual municipal waste; the output is sometimes called Compost-Like Output (CLO) or biocompost. As a ‘mixed-source waste digestate’ it may only be applied to land under Environment Agency permit (EA, 2012b) and (SI, 2010 replacing SI 2007).


3.5.4 Non-waste derived digestates (purpose grown crops and manures) Digestates derived from purpose grown crops and digestates produced and used on farm are not classified as waste products and not considered in the scope of this report, although farm manures and purpose grown crops may also be used as feedstocks for source segregated wastes at off-farm plants (EA, 2012c). 3.6 Comparing digestates with composts The availability of quality composts through compliance with the CQP (Compost Quality Protocol (EA, 2012a) and PAS100 (BSI, 2011a) has raised awareness of waste recycling of organic materials. Care needs to be taken in comparing digestates with composts because the nature of the two processes, create different products (e.g. Bardos, 2005, and WRAP, 2011d). These differences are summarised in Table 2.

Table 2 Comparison of the effects of aerobic composting and anaerobic digestion

Issue Compost Digestate

Heat Large release of heat Small release of heat

Water Water lost through evaporation, especially in systems with forced aeration

Water retained

C cycle Carbon largely converted to carbon dioxide

Carbon converted to methane and CO2

Ammonium content Ammonium lost by volatilisation or leaching

Ammonium contained (but may be lost during storage and application)

Readily Available Nitrogen Low levels of plant available nitrogen (Defra, 2010)

High levels of plant available nitrogen

Stability Mature composts usually microbially stable

Often microbially unstable as dispatched from operating facilities

Odour Soil like odour Occasionally unpleasant odour

Potentially Toxic Elements (PTEs)

Dependant on feedstock: specified under PAS100

Dependant on feedstock: specified under PAS110

Persistent organic pollutants

See note (a) See note (a)

Gaseous emissions from storage and use

Little, possibly CO2 Emissions of methane and ammonia (especially from uncontained storage) Lukehurst et al. 2010

Bioaerosols Potential hazard from compost agitation during storage and use (EC JRC 2011). See note (b)

Uncertain, suggested by EC JRC (2011). See note (b)

Note (a) WRAP consider the likelihood of organic pollutants to be low for PAS100 and PAS110 materials (Amlinger et al, 2004). Hence the PAS100 and PAS110 specifications do not include limits for organic pollutants. Note(b) EC JRC Technical report - first working document. 3.7 Separation of digestate and further enhancements Whole digestate can be separated into a higher solids (fibre) fraction and liquor (see section 4.2). This process partitions the nutrients, with the soluble nutrients largely following the partition of the water. Typically this results in relative enrichment of the solids fraction with phosphorus and the liquor with ammonium-nitrogen and potassium. Whereas the nutrient


content of whole digestate is largely governed by the feedstock composition, the nutrient content of the separated fractions is largely influenced by the method of separation. The separation efficiency varies considerably between different mechanisation systems (Lukehurst et al. 2010). The moisture content of the solid fibre is also determined by the method of separation; for example, a screw or belt press produces lower dry matter content than the decanter centrifuge method. A range of other digestate enhancement technologies are reviewed in WRAP project OMK006-002 (WRAP, 2012f). At present in the UK there has been little development beyond dewatering, to produce solid fibre and liquor. However in the Biosolids sector, thermal drying to produce fertiliser pellets occurs, and Struvite production is being developed (see section 4). 3.8 Digestate and nutrient content The nutrient composition of the whole digestate is largely dependent on feedstock, so that nutrient concentrations can vary quite considerably. The range of nitrogen, phosphate and potash for food waste digestate is given in Table 3.

Table 3 Range in nitrogen phosphate and potash in food based whole digestate

Total N Total P2O5 Total K2O

Minimum value (kg/t) 3.5 0.25 1.0

Maximum value (kg/t)

7.9 1.50 2.75

Note: derived from (WRAP, 2011b and WRAP 2011d) The worked example used in the survey calculated digestate nutrient values for digestates derived from source segregated food waste (see table 4). These were based on averaged data for N, P and K, and dry solids of whole digestate derived from data summarised in WRAP reports (WRAP, 2011b and WRAP 2011d), and is based on many analyses taken from nine AD producers. Analyses of separated fibre and liquor are calculated from Separation Efficiency values (Lukehurst et al. 2010) and given in (Table 4). Data for food based digestate is compared with biosolids, MBT output and green compost in Table 5. Generally, food-based digestates are produced from high protein feedstocks, and are rich in nitrogen, with something in the region of 80% of the total nitrogen in the readily plant-available form (WRAP, 2012d). This compares to 40% of readily available nitrogen in biosolid digested liquid (Defra, 2010) and 16% of readily available nitrogen in MBT output (Taylor et al , 2010). This contrasts with green compost where a very small proportion is plant available,


digestate (a)

Fibre (b) 21 1.5 0.35 0.23 0.42

Liquor (b) 2.1 0.44 0.06 0.22 0.42

Note (a) derived from reports (WRAP, 2011b and WRAP 2011c) (b) Calculated from Separation Efficiency Values (Lukehurst et al. 2010)

Table 5 Nutrient values from a range of digestates

Digestate Dry solids (%)

Total N (kg/m3 or kg/t)

Total P2O5 (kg/m3 or kg/t)

Total K2O (kg/m3 or kg/t)

Readily available N (kg/m3 or kg/t)

Whole digestate (a)

3.2 5.57 0.60 2.0 4.63

Biosolid digested liquid (b)

4 2.0 3.0 0.1 0.8

Biosolid digested cake (b)

25 11.0 18.0 0.6 1.6

Biosolid lime stabilised (b)

40 8.5 26.0 0.8 0.9

Biosolid composted (b)

60 11.0 6.0 3.0 0.6

Biosolid thermally dried (b)

95 40.0 70.0 2.0 2.0

MBT output (c)

40 6.4 3.6 1.9 -

Green compost (b)

60 7.5 3.0 5.5


Table 6 Results of analyses from whole digestate samples

Test Result

PTE PAS110 compliant except for one which exceeded the limit for zinc and one which exceeded the limit for lead.

E.coli PAS110 compliant Salmonella spp None detected Plant pathogens clubroot and potato blight None detected

Stability PAS110 compliant for Volatile Fatty Acids and residual biogas potential with the exception of one sample

Physical contaminants PAS110 compliant

Organic compound contaminants Very low or below the limit of detection

Biochemical Oxygen demand (average) c. 5000 mg/L pH (range) 8.2 – 8.5

Water soluble chloride (average) 2750 mg/L

Water soluble sodium (average) 1480 mg/L

Water soluble boron (average) 1.63 mg/L

4.0 Currently available digestates and their end-uses 4.1 Digestates from waste The fastest growth in new AD plants in the UK is in the waste-fed sector. From just 17 AD and 9 MBT sites in 2009 (WRAP, 2011e) , the WRAP/NNFCC report on Anaerobic Digestion infrastructure in the UK (WRAP, 2012c) states that there were 44 waste fed plants with a capacity to handle 3.7 million tonnes of material per year, on 30 September 2011. The waste-fed plants take a variety of feedstocks including both source-segregated and non-segregated feedstocks , including municipal food waste, industrial food processing waste, abattoir waste, sewage effluent, crops and farm waste either singly or in mixtures. 31 of these plants are non-industrial commercial scale operations accepting waste from outside sources and 13 are industrial processing waste from their own activities. Since then, the number of plants has increased to 63 operational waste-fed sites (Feb 2013) with a handling capacity of 4.7 million tonnes. Designated market sectors for ADQP compliant digestate are agriculture, field-grown horticulture, forestry and land restoration (EA, 2009b). In 2010, 100% of whole digestate and 99% of solid digestate was used in agriculture, while 1% of solid digestate was used in land restoration. Almost none was used in soil grown horticulture or forestry (WRAP 2012d). In a recent survey of AD plants, 12 out of 21 have installed digestate separators although they may not be used at full capacity (WRAP, A). A small proportion of AD plants have attained end of waste status to date (Biofertiliser Certification Scheme). This is a young and developing part of the industry where many of the plants have been operating for less than one year and so few strategies for marketing digestate have been developed (WRAP, A). The dominant outputs for CLO’s from MBT facilities in the UK are envisaged as re-use on previously developed land (primarily one off applications), as a waste derived fuel or as a pretreatment step for landfill, (Bardos, 2005 and Bardos et al ., 2007). The use of CLOs for agricultural purposes is currently not supported although the Environment Agency has set out conditions for limited field trials (EA, 2009c).


4.2 Biosolids (sewage sludge) The water industry (2010) produced a total of 1.46 Mt (dry solids) of sewage sludge in 146 plants, of which 66% was treated by anaerobic digestion to produce digested sludge, (Water UK, 2011). The majority of this (80%) is applied to agricultural land, 14% is sent to thermal destruction (mostly with energy recovery), 3% to land reclamation, 1% to landfill and the remaining 2% to other uses including aerobic composting. In some regions all or nearly all the sewage sludge produced goes to agriculture, reflecting the proximity of a suitable agricultural land base (Anglian, Northumbrian, Severn Trent, South-west and Wessex Water). Energy recovery for power production is greatest in Yorkshire, Scottish and Thames Water, (Table 7). Scottish Water also sends a significant amount (15%) to land reclamation (Water UK, 2011). Application of biosolids to agricultural land is recognised as the Best Practicable Environmental Option in most circumstances by the EU and the UK government (Water UK, 2010).

Table 7 The end-uses for biosolids

Water Authority

Agriculture Land reclamation

Landfill Thermal Destruction

Other

Anglian 99 1

N Ireland 74 3 3 15 6

Northumbrian 100

Scottish 38 15 1 44 3

Severn Trent 100

South west 100

Southern 91 6 3

Thames 59 9 39 1

United Utilities 79 21

Welsh 88 5 8

Wessex 100

Yorkshire 39 4 2 48 7

Total 80 3 1 14 2

Most biosolids are applied to land as sludge products, but thermally-dried biosolid granules are sold as a fertiliser in some regions e.g. Southern Water’s Bestway Granules (Southern Water, 2012). The water industry sees the need to expand markets in new sectors and is developing new products. For example a post-digestion process where biosolid sludge is co-composted with green waste to produce a soil improver or a constituent in soil manufacture in the landscape sector is being developed at some plants, as at Anglian Water’s Great Billing Plant and at Yorkshire Water’s Esholt Plant where it is further treated by ‘phytoremediation’. These products may attain individual end of waste specification through the Environment Agency. Following the success of an experimental unit, a plant is currently planned to produce magnesium ammonium phosphate (struvite) fertiliser in the Thames Water region.


5.0 Results 5.1 Breakdown of survey respondents Forty-five people were contacted and sixty-six interviews carried out across a range of eight end-uses and fourteen sectors. The aim was to speak to informed stakeholders who are working with either digestates or other recycled materials. 54 % of the interviews were carried out with those who had some practical experience of using digestate; 12 % had worked with Biosolids, 12 % with MBT outputs and 47% with PAS100 compost. The different stakeholder groups brought different insights into the survey. The largest stakeholder group were the consultants (sectoral advisers), who not only represented the end-users and their interests but were well-informed about potential developments that may affect their clients. Direct end-users were able to reflect the practical daily management issues that might arise from using digestates. The trials managers were actively involved with field experiments using digestates and provided an informed technical base, which also helped to identify the most promising end-uses. The manufacturers represented specialised uses for processing digestates for a range of products for professional and amateur use (e.g. growing media, liquid and solid fertilisers and fuel). The breakdown of the number of interviews undertaken across each stakeholder group is shown in Figure 2.

Figure 2 Number of interviews across stakeholder groups.

The majority of the interviews were conducted within the land-based and horticulture sectors. Two other areas were investigated, solid fuel recovery and the production of fibreboard as a wood substitute for the construction industry. These two are excluded from the general analysis and reported separately under end-use (Sections 5.3.9 and 5.3.10). The summary of the number of interviews undertaken according to end-use and sector are given in Table 8. The table excludes interviews from the fuel and construction sectors.

21%

40%

24%

15%

End-user

Consultant - sectoral advisers

Field trials managers

Manufacturer - processor of digestate


Table 8 Number of interviews conducted across end-use and sector

5.2 General response of sectors The data was collated into groups and subgroups, in order to be able to review and analyse the findings (see Table 9).

Respondents

Soil

impro

ver

solid

Liq

uid

fert

whole

Solid

fert

dried s

olid

Liq

uid

feeds-liq

uor

Gro

win

g m

edia

solid

Soil

manufa

ctu

re s

olid

Horticulture general 3 1 2 1 7

Fruit 1 1

Vegetables 1 2 3

Nursery stock 2 2

Amenity sports turf 1 1 6 8

Amenity turf 2 2 2 6

Amenity public landscape 2 1 3 4 10

Amateur 1 1 1 3 6

Forestry 1 1

Biomass 3 1 4

Land restoration 10 2 1 1 14

23 7 8 12 6 6 62


Table 9 Grouping of results according to end-use and sector

Group Sub group Group 1 Application to Field grown horticulture

Field grown horticulture Vegetables Fruit and nursery stock

Group 2 Application to Land Restoration sites

Forestry Biomass production Reclamation of industrial spoil

Group 3 Application to Forestry

Conventional forests Biomass production

Group 4 Application to Amenity land

Amenity landscape Amenity turf

Group 5 Use of liquor as a liquid feed

Amenity turf Sports turf Soft fruit Nursery stock Amateur

Group 6 Use as an organic constituent for soil manufacture

Landscape Land restoration

Group 7 Use as a peat replacement in growing media

Amateur Professional

Group 8 Dried pelleted fertiliser

Field grown horticulture Amenity landscape/ turf Sports turf Amateur

Group 9 Solid recovered fuel (SRF)

Group 10 Fibre-board for the construction industry

The variety of applications across different groups resulted in different responses in relation to digestate use, the awareness of digestates, how suited they were for a specific use and the number of problems that might be encountered. Some sectors could use the products in the raw state with no pre-treatment, others required some improvement or with a small degree of change such as providing a drier solid product, whereas others required considerable further treatment. These findings for digestate for crop end-uses are summarised in Table 9. A brief synopsis of some of the major findings is given here according to sector and end-use, with a fuller text in Section 5.3.

Field grown horticulture could be viewed as an extension of use from the agriculture

sector, where whole, liquor and fibre digestates are used on a field scale. However a

number of barriers were mentioned for use on horticultural edible crops, despite the

awareness of their nutrient value.


Land restoration. This sector was aware of the benefits of organic materials to restore

land and saw the supply of organic matter and nutrients provided by digestates as a

positive benefit. There seemed to be a greater enthusiasm for use of digestates in this

sector, and the suggestion that digestates could be used in their raw state as whole or

solid digestate.

Amenity landscape. This sector was less aware of the characteristics of digestates

although well aware of the broader context of using organic materials as peat

replacements for a range of uses. The greatest interest was in use as a component in soil

replacement in general landscape use or restored land in urban green space, although

there were problems to overcome requiring further treatment, for example to reduce

water content and high ammonium content.

Sports turf. There was less awareness of digestates, but considerable interest in using a

nitrogen feed with green credentials. There were a number barriers to overcome relating

to use in close proximity to the public. Odour would not be acceptable and there were

concerns over high salt content (electrical conductivity).

Growing media for container production. This manufacturing industry is very aware

and pro-active in trialling a wide range of possible peat replacements. Digestate is not an

obvious candidate for peat replacement and would need considerable further treatment

for example co-composting to produce a more marketable material.

Soil manufacture. Use of solid fibre digestate as an organic component of

manufactured soil has less stringent requirements than use in growing media for

container production. Problems relating to handling, odour and salt content need to be

addressed.

Note: With regard to amateur use of digestate or digestate based products further discussion is given under the appropriate sector, for example for use as a liquid feed or for use as a peat replacement in growing media. Solid Recovered Fuel and Fibreboard are treated separately in Sections 5.3.9 and 5.3.10.


Table 10 Review of respondents to digestates (whole, solid and liquor) for crop end-uses: awareness, attractiveness, ease of use and barriers Group- taken

from Table 7

Sub-group Awareness

of digestates

in sector

Attractiveness

of digestates to

sector

Ease of

use

Existing

applications

Possible

applications

Barriers

Field grown

horticulture

(group 1)

Vegetables Possibly on

some

vegetables

Soil improver

(whole or

solid)

Trees (top fruit

nursery stock)

Soil improver

(whole or

solid)

Soft fruit Liquor

Land

restoration

(group 2)

Biomass Trial Soil improver

(whole or

solid)

Forestry Trial Soil improver

(whole or

solid)

Industrial spoil

reclamation

Trial Soil improver

(whole or

solid)

Urban green space Soil improver

(whole or

solid)

Forestry

(group 3)

Conventional

forests

Soil improver

(whole or

solid)

Amenity

(group 4)

Landscape Soil improver

(whole or

solid)

Grass

parks/(roadsides)

Liquor

Liquid feed

for Sports

Turf

(group5)

Pitches Trial Liquor

Fine turf -golf Trial Liquor

Soil

manufacture

(group 6)

Amenity

Land restoration

Trial Solid

Container

production

horticulture

(group 7)

Professional &

Amateur

Constituent

of peat free

growing

media

Dried

fertiliser

pellets

(group 8)

Various

Horticulture

Dried product

Key Awareness (excluding trial managers) some respondents were not aware of AD outputs. respondents foresaw possible digestate applications in their sector with prompting.

respondents were aware of products or trials in their sector using digestates.

Attractiveness some major barriers to or concerns over digestate use foreseen by some respondents. potential applications (after discussion). products could readily be used.

Ease of use niche opportunities, specialist users, pre-treatment of digestate needed. wider opportunities but needing pre-treatment of digestate.

potential or actual applications no pre-treatment needed

Barriers some barriers mentioned. many barriers mentioned. “show-stoppers”, i.e. no use possible.


5.3 Analysis of survey by end-use and sector The results are further analysed by group and subgroup; each being reported in turn and showing: Regulatory framework. Technical boundary conditions. User requirements and perceptions (in italics). 5.3.1 Group 1 - Application to Field grown horticulture Field vegetables are included in this group although it may be considered as a natural extension to the use of digestates in agriculture.

Group 1 Field grown horticulture

REGULATORY AND STANDARDS FRAMEWORK Nitrate Vulnerable Zones The use of manures and other organic materials applied to horticultural/agricultural land is regulated by the Nitrate Vulnerable Zones (NVZ) rules (Defra 2009a), to protect the wider environment from diffuse pollution of nitrogen from agricultural land. NVZs cover 62% of agricultural land in England, 14% in Scotland and 4% in Wales. Even outside these zones, voluntary Codes of Good Agricultural Practice apply (Defra, 2009b and Scottish Executive, 2005) and these require the same practice for nitrogen and organic manures on a voluntary basis. The following points taken from the NVZ codes guide the use of digestates on agricultural land, restricting amounts, timing and areas where digestate may be spread:

Nitrogen fertiliser applications must be in accordance with crop requirement and a full management plan made to account for soil nitrogen supply in organic manures and manufactured nitrogen fertiliser.

There is an individual field limit of 250kg/ha total nitrogen from organic manures per year, including on and off farm products such as biosolids and digestates.

There are closed periods when manures with a high readily available nitrogen over 30% (includes liquid digested biosolids and digestates) cannot be spread to land. They extend from 1 August to 15 January and are dependent on soil type and cropping.

Manures cannot be spread on areas or in circumstances where there is a high risk of nitrate loss. For example within 10m of surface water or on land that is frozen, snow-covered or waterlogged.

Liquid digested biosolids must be incorporated within 24 hours of application unless applied by injection or band spreader.

Prohibition of the use of MBT output Compost-like outputs from MBT of mixed source municipal waste cannot be applied to agricultural land used for the growing of food or fodder crops or any land likely to grow food or fodder crops in the future – except under experimental circumstances where the harvested crops are subsequently destroyed (EA, 2012d).

TECHNICAL BOUNDARY CONDITIONS Fertiliser requirement Fertiliser requirements are low for fruit and nursery stock, and so amounts required are less than for arable crops or vegetables, whereas some field grown vegetables such as brassicas are suited to high available nitrogen applications. The low phosphate of source segregated food -waste digestates (Table 4) may be beneficial in areas where soil phosphorus indices are already high. Use in accordance with COGAP and NVZ regulations would limit use in closed periods, which are longer for sandy soils often used for vegetable growing (due to the greater risk of nitrate leaching in such soils).


Avoidance of microbial contamination Guidelines for growers to reduce the risk of microbial contamination of ready to eat crops (fruit and vegetables) are produced by the Food Standards Agency (FSA 2009). Batch-stored or treated manures may only be applied before drilling and planting; (controls are more stringent for fresh manure). The Safe Sludge Matrix (BRC/WaterUK/ADAS 1998) for conventional (anaerobically digested) sludge is more rigorous, with a 12 month interval between application and harvest for vegetables, and a 30 month interval for salads. There is also a 10 month interval for enhanced treated sludges. PAS 110 requires pasteurisation as a default position for waste-fed AD facilities. An ongoing WRAP project with Cranfield University is developing a new “safe digestate matrix” for biofertilisers to mirror the existing Safe Sludge Matrix. This will be critical in ensuring digestate use in the field horticulture sector. The use of digestates on certified organic produce Organic Farmers and Growers (OF&G) allow the use of composts and digestates on certified organic land provided the only food waste feedstock is source segregated household food waste and the product is PAS110 compliant. Non-organic slurry can be used as an input provided it is from animals that have access to pasture during the growing season and the livestock system must be non-GM. The grower must notify OF&G of its use (OF&G, 2012).

USER REQUIREMENTS AND PERCEPTIONS FROM THE SURVEY Sub-group: Field vegetables: Due to the closeness of the producer to the consumer compared to arable farming interviewees expressed concerns over the way the retailer and ultimately the consumer would view the use of digestate if they saw it as a “waste” product with potential to contaminate fresh food produce. There were strong concerns over the possibility of pathogens transfer. Sub-group: Field grown fruit,fruit and hardy ornamental nursery stock (woody perennial shrubs and trees grown for the garden and landscape market): Little interest was shown by this sector as these crops have low nutrient requirements and as they are perennial crops digestate could only logistically be used pre-planting. Granular fertiliser is more easily applied.

5.3.2 Group 2 - Application to Land Restoration sites Land may be restored to a variety of planting; forestry, semi-natural vegetation, urban greenspace or even biomass production. Current WRAP trials are investigating a range of impoverished industrial sites where they are comparing the use of compost, digestate and a mixture of both (WRAP, 2012b).

Group 2: Application to restored land

REGULATORY AND STANDARDS FRAMEWORK Restored land is a designated end-use for (fibre) digestates under the ADQP (EA, 2009b), so the door is already open for extended use, which at present is very low. Other waste-based digestates (source-segregated or non source-segregated) may be applied to non-agricultural land under The Environmental Permitting Regulations (England and Wales) (SI 2010 and EA 2012b). A code of practice for the use of sludge, compost and other recycled organic materials for land reclamation (SNIFFER, 2010a, 2010b) requires that any application of recycled organic material must be made according to available good practice, should not cause harm to the


environment and should not exceed an appropriate rate for the land in question, which would be classified as disposal of a waste material.

TECHNICAL BOUNDARY CONDITIONS Frequently restored soils are physically, chemically and biologically degraded and there is considerable advantage in using bulky organic materials over chemical fertilisers (Kilbride 2006), particularly in improving physical attributes which affect the air and water balance, but also in providing the full range of nutrients (some of which are slow release) and in increasing microbial activity. MBT output (CLO) has been shown to improve biomass yield, increase soil water holding capacity and decrease bulk density when used at two limestone quarry reclamation sites (Rollett et al., 2010). Potential disadvantages include the immobilisation of nitrogen when the C:N ratio is above 25, nitrogen losses to the environment and the possible increase in potentially toxic elements (PTEs) either through their introduction into the soil with the product or in some cases through the mobilisation of existing PTEs by the organic amendment. The effect of organic matter on trace element mobility appears to be highly case specific, as in some cases dissolved organic compounds and colloids from composts may increase the mobility of trace elements (McCarthy & Zachara, 1989 and Su:brim project , 2008). Guidance for the use of different organic amendments including on brownfield sites for woodland establishment, forestry and grassland is given in Forest Research Best Practice Guide 6 (Kilbride, 2006).

USER REQUIREMENTS AND PERCEPTIONS FROM THE SURVEY The majority of this group commented on fibre digestate but also on whole digestate and as an amendment of imported soil material. The benefits were seen as a valuable source of organic matter (77%) and to supply nutrients (62%). The most frequently mentioned concern was odour (46%) and high salt content (23%). 23 % mentioned public concerns. Site managers (particularly if in close proximity to the public ( for example restored land used as urban greenspace) were concerned that the public would not like its use if it had the appearance of containing waste. This might include odour or physical appearance, for example if the material contains plastic. Several mentioned that “sewage sludge” had a negative image and they would not like digestate to be associated with it in the public’s mind. 38% specifically mentioned PAS110 compliance as a necessary requirement, showing that this sector is looking for a regulated material which can be trusted to be low in contaminants, pathogens and PTEs. Three users of separated digestate fibre said there were problems with the handling of the material, which was too wet and sticky, adhering to machinery and difficult to mix in to the soil. It needed to be at least “stackable” and a minimum dry matter content of 30% was required by one respondent . The exact nutrient content was not critical because their low input nutrient systems were able to tolerate a range of N, P and K content, although there was concern that too much of the nitrogen was readily available and liable to losses through volatilisation, leaching and when wet, by denitrification. Whole digestate or separated liquor could also be useful to irrigate establishing plants on very droughty land or reclaimed industrial spoil. Further comments under Section 5.3.4 Amenity Sector also have relevance to urban green space.


5.3.3 Group 3 - Application to Forestry

Group 3- Application to Forestry sub-group conventional forests

REGULATORY AND STANDARDS FRAMEWORK The UK Forestry Standard (UKFS) is the reference standard for sustainable forest management in the UK (Forestry Commission, 2011). The UKFS, supported by its series of Guidelines, outlines the context for forestry in the UK, sets out the approach of the UK governments to sustainable forest management, defines standards and requirements, and provides a basis for regulation and monitoring (Forestry Commission, 2011). It has a statutory legal requirement to produce and implement a forest plan for sustainable forest management where the forest soils’ fertility should be maintained to safeguard the soils’ character and productive potential. The use of sewage sludge is permitted provided it causes ecological improvement and is applied in accordance with the Sludge Act as specified in UKFS Requirements section Forests and Soil (Forestry Commission, 2011 page 40). The regulatory authority must be consulted prior to the application of any waste to forest soils, including sewage sludge and composts. In addition the Forestry Commission complies with the Forest stewardship council (FSC) international independent certification scheme (FSC, 1996). Principle 6 on environmental impact states that “forest management shall conserve biological diversity and its associated values, water resources, soils and unique and fragile ecosystems and landscapes and by so doing maintain the ecological functions and integrity of the forest”. It thus tends towards low inputs and is unlikely to see the use of waste products as beneficial.

TECHNICAL BOUNDARY CONDITIONS The use of biosolids (liquid and cake) and composts have been shown to improve foliar nutrition and forest productivity without adverse effects on the environment (Moffat, 2006). However the greatest use of organic wastes has not been in conventional forestry but in the establishment of woodland on reclaimed land to improve soil and soil-forming materials.

USER REQUIREMENTS AND PERCEPTIONS FROM THE SURVEY Forests are considered natural ecosystems tending towards low inputs, and there has not been a great uptake of organic wastes such as biosolids by foresters. There are difficulties in applying bulky materials to tree-stands once established. Opportunities for pre-planting are limited due to the long-term crop nature of forests.

Group 3 - Application to Forestry sub-group biomass production

REGULATORY AND STANDARDS FRAMEWORK Nitrate vulnerable zones on agricultural land (see Group 1 - Application to Field grown horticulture)

TECHNICAL BOUNDARY CONDITIONS Fertiliser requirement Biomass production is usually carried out on agricultural land where the phosphorus and potassium fertility is high and applications of phosphate and potash are not required above soil indices of 1 and 2 respectively (Defra 2010). Relatively small amounts of nitrogen are required (50 – 100 kg/ha/a) where the soil nitrogen supply index is 2 or below, compared to other arable crops. Application is during May and therefore outside the NVZ closed periods (Defra 2010). Application of nitrogen in the first year of establishment potentially increases


nitrate run-off and should be avoided. Fertilisation can be delayed to the third year (McKay 2006). These all point to the fact that only small amounts of fertiliser are needed and at infrequent intervals and so would only be a route for relatively small quantities of digestate.

USER REQUIREMENTS AND PERCEPTIONS FROM THE SURVEY Nutrients and organic matter inputs were seen as positive but all required PAS110 compliance and respondents were concerned about odour. There are potential difficulties in applying digestate to the growing crop. 5.3.4 Group 4 - Application to Amenity land Amenity horticulture includes land primarily used for recreation, pleasure, visual enhancement and environmental protection rather than for the production of economic crops. The landscape sector responded quickly to the phasing out of peat, with 95% of alternatives in use by 1999 (DETR, 2000). PAS100 compost is widely accepted and this is the type of product that is required for use as a soil improver.

Group 4 - Application to Amenity land (as a soil improver)

REGULATORY AND STANDARDS FRAMEWORK PAS110 digestate may be applied to soil grown horticulture under the ADQP (EA, 2009b). Waste-based digestates (source-segregated or non source-segregated) may be applied to non-agricultural land under The Environmental Permitting Regulations (England and Wales) (SI 2010 and EA 2012b).

TECHNICAL BOUNDARY CONDITIONS Survey respondents highlighted technical guidance for composts which they are familiar with. Essential requirements for use as a soil improver are the Compost QP (EA, 2012a) and PAS100 (BSI, Jan 2011), together with additional requirements given in Compost Specifications for the Landscape Industry (Landscape Institute (LI), 2003). This document is currently available on the WRAP website but in the long term will be obtainable through subscription from NBS, Landscape section. These set out additional criteria for pH, electrical conductivity, moisture content, organic matter content, particle size and C:N ratio (Table 11). This is the current standard and landscape contractors are unlikely to accept anything less. Electrical conductivity and pH impact directly on plant growth and may cause scorch and poor growth. Moisture content and organic matter affect handling properties and the product is required in an easily spreadable form. A product that gives a slow release of nitrogen is preferred to give sustained growth over a long time period.

Table 11 Soil improvement for general landscaping.; planting beds, tree shrub and herbaceous planting, turf establishment (Taken from LI, 2003)

Horticultural parameters Units of measure Recommended range

pH pH units (1:5 water extract) 7.0 – 8.7

Electrical conductivity µS/cm (or mS/m) (1:5 water extract)

2000 (200)

Moisture content %m/m of fresh weight 35 – 55

Organic matter content % dry weight basis >25

Particle sizing % m/m of air-dried sample passing the selected mesh aperture size

99% pass 25 mm screen 99% pass 10 mm screen

C:N ratio 20:1 maximum


Digestate is likely to be unsuitable as a replacement for use as a surface mulch, not only because of its low dry mattercontent, high nutrient value and odour (LI, 2003) but also because of potential volatilisation losses from high ammonium levels when applied to the surface of soil (Defra, 2009b).

USER REQUIREMENTS AND PERCEPTIONS FROM THE SURVEY These respondents voiced a range of opinions relating to the quality of the product. Its use in the public

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