Adding value to digestate: landscaping, regeneration and horticultural sector trials.

18th European Biosolids & Organic Resources Conference 19-20th Nov 2013

Jacks Guinness – WRAP Project Manager

What I’ll cover…

Background and context

Work to develop markets for digestate

Landscape & Regeneration

Horticulture

Conclusions

About WRAP

WRAP’s vision is a world without waste, where resources are used sustainably. We help businesses, individuals and communities reap the benefits of reducing waste, developing sustainable products and using resources in an efficient way.

Why is WRAP involved?

Policy drivers – AD Strategy and Action Plan

Closing the loop

Digestate – key for closing the nutrient recycling loop

Reduces use of primary resources/fertilisers - phosphate is a finite resource

Market model

Supply Demand Sustainable Market

Volume

Location

Product/Price

End user requirements

Supply Digestate volumes

2012 tonnage (actual)

2016 tonnage (predicted)

Waste fed AD sites 678, 465 1,891,825

Location 122 operational facilities (68 Waste fed, 54 Farm fed) Proximity to markets

Addressing the barriers

Developing the market for digestate by:

Building safe and secure markets

Promoting and developing BSI PAS110 specification

Building skills and knowledge – operators and end users

Obtaining evidence on digestate benefits – research and field trials

Investigating new markets and opportunities

Demand - what end-users want

Consistency

Low risk

Fitness for purpose

CONFIDENCE/ TRUST

AD risk assessment

Clostridium botulinum Herbicides in

digestate

Impact of pasteurisation on

pests and diseases

Compost/digestate data

Biofertiliser matrix

Odour/ammonium

Demonstrating digestate safety and fitness for purpose

Flavour/odour taints

Food Standards Agency/Crop Assurance schemes e.g. Red Tractor

Promoting and developing quality products – BSI PAS110

Transforming ‘waste’ digestates into ‘products’

12 operators certified to BSI PAS110

Certified tonnage = 437,900 tonnes pa (registered throughput)

Under review www.biofertiliser.org.uk

Why use digestate?

Nutrients N, P, K, S, Mg Trace elements

Organic matter (fibre)

Can save money

Reduce carbon footprint

At present almost all digestate is used in agriculture - experiments under DC-Agri

Most UK digestates are low dry matter (<10%)

Can be separated

– Fibre

– Liquor

Different fractions have different nutrient profiles

– Different potential uses

– Different potential markets

Developing digestates

Other potential markets

Brownfield site restoration – soil improvement (growing energy crops)

Soil manufacture

Turf establishment

Sports and amenity turf maintenance

Horticultural applications

Establishing energy crops on brownfield land

– Fibre/whole digestates (compost)

Fertilising energy crops on brownfield land

– Whole and liquor digestates

Fertiliser for turf growing and maintenance uses

– Liquor digestates

Informing future reviews of allowable markets within ADQP

All projects will have an associated knowledge exchange programme

L & R Field experiments 2012 -2014

Using digestate as a biofertiliser for established short rotation coppice (SRC) willow

Burntstump - restored landfill site in

Nottinghamshire growing SRC willow for the last two years

Trial investigates the use of digestate as a biofertiliser to improve crop yields using specialised irrigation equipment within the plantation

Trial will investigate effects on:

SRC willow yields

Soil physical, chemical and biological properties

Using digestate as a sport and amenity turf fertiliser Examines the use of liquid fraction

digestate as a fertiliser for sports and amenity turfs

Replicated research trials at Cranfield University and the Sports Turf Research Institute

Investigating turf quality, soil health & practical application

Using digestate to establish perennial grasses for AD feedstock

2 sites: Landfill site (Essex) and Quarry (Leics)

Grasses grown on sub-soil bunds at the edge of operational areas

Compost applied to improve soils prior to planting

Whole digestate then applied and repeated at intervals

Potential benefits: low cost, diversification for operators

Findings to date

Fibre useful as a soil improver - limited quantities available

Early evidence of yield increases

Liquors good nutrient source but dilute and need ultra filtering to avoid blockages on standard spraying and spreading equipment

Digestate behaves like fertiliser but application rates need to be managed carefully to avoid problems e.g. scorching, high conductivity

Can be difficult to handle

Odour a barrier to use on sports and amenity turf

Horticulture feasibility trials

Exploring the potential for quality digestate:

As an addition to wood/bark chips to create viable growing media blends

As a liquid feed for containerised strawberry production

In soil-less hydroponic trials for tomatoes

Use of the fibre in container composts

Questions to answer:

– What are the constraints?

– Can these be overcome?

– Are there business benefits?

– Should the ADQP be changed?

Bark admixtures Formulation and testing of novel organic growing media using quality digestates for the production of containerised plants. Bark + other sustainable materials + digestates = novel growing media

Making the admixtures The main selection criteria were EC, structure

and consistency (not too wet or too dry)

Standard ingredients trialled

The final admixtures:

60% bark, 30% wood fibre, 10% top soil + digestate

Trial

Controls (industry standards)

Peat-based control (PC)

Peat-free control (bark & wood fibre based BC)

4 digestates – each with 5 admixtures

5 replicates = 110 plants per trial

Plants grown were cyclamen, fern and pine

Monitored regularly for growth & plant health

Results

Cyclamen

Large variability in plants

Flowers were produced in all treatments

Corms all healthy (except 1) and of similar weights

All plants grew and senesced at approx the same time

Ferns

Potential for liverwort control using admixtures

No significant differences for the number of fern fronds and frond length

No significant difference in the root:shoot ratio in any of the treatments

Highest % of digestate (1000ml in 5 lit of mix) showed reduced foliage quality & reduction in total plant weight

Pines No differences – foliage quality good for all treatments

And no significant differences in: Growth Quality Fresh weight Dry weight

Strawberry cultivation – liquid feed

Can quality digestate be used as a nutrient source for trickle irrigation in strawberries to replace conventional nutrient solutions used in commercial production?

Control (industry standard) and 6 digestates trialled, grow bags with trickle irrigation.

Assessed for foliage colour and quality, fruit quality and dry weight of plants

Nitrogen availability

The digestates contained 10 - 25 times too much mineral N; all in the form of ammonium

Digestates were diluted (up to 51 times) to achieve 120mg/l total mineral nitrogen

Some nitrate is required so diluted digestates were amended to provide:

60% ammonium-N (from digestate)

40% nitrate-N (from amendment)

Establishment

Strawberries planted end of Jan 2013

Feeding started three weeks later

Digestate (day 18) Control

Total fruit yield at harvest

Average fruit weight at harvest

Conclusions

Diluted and amended digestates can successfully be used to produce a fertigated strawberry crop

Fruit yield and quality yield are (mostly) maintained (under experimental conditions)

Digestate based fertilisation has the potential to significantly reduce overall fertiliser cost.

The cost saving is 1% or less of the produce crop value

Potting compost blends – fibre & green waste compost

Key study questions:

• Will plants survive in composts free of peat and containing significant AD Fibre mixed with composted green waste?

• How will this range of compost blends perform in comparison to established retail formulations?

• How will these novel compost mixtures perform under near commercial growing environments and practices?

Findings

• Inclusion of a composting phase after mixing of digestate & GWC is necessary

• AD Fibre can be reliably incorporated as a growing media component up to at least 50% by volume

• AD fibre used in this study did not require pH adjustment or nutrient leaching prior to use in order to produce commercially satisfactory levels of growth in the majority of instances.

• The physical structure blends appeared stable over 3 months

• average bulk density values of the blends were higher than control composts but may lend water holding benefits for some needs

• Further work needed to assess optimum irrigation management

• Its potential may be as a bulk replacement or / and as a slow release fertilizer source

Aim: Determine feasibility of using liquid digestate as nutrient medium for hydroponic solution. Digestates used: 2 derived from food waste (FW1 and FW2) (PAS110) and 1 from cattle dung (CD). Crops grown: Tomato and lettuce – focus here is tomatoes. System used: Open system (does not recirculate). Potential problem: High ammonium concentration.

Tomatoes

Tomatoes – Set-up

Set-up: Series of closed trials using Moneymaker and Super Sweet 100. Whole digestates were diluted and replaced weekly. Solutions were topped up as required and tubs aerated.

Tomatoes – Digestate dilutions

FW1 FW2 CD

Total-N (mg/L) 4327 6912 3359

Ammonium (mg/L) 4227 6654 2846

Nitrate (mg/L) 100 258 513

Excess total-N (x) 38 (30)* 61 (48) 30 (23)

Ammonium (% of total) 98 92 85

Diln. needed (x) 374 (294) 589 (462) 252 (198)

Nitrate amendment required (mg/L) 101 (129) 102 (129) 100 (127)

N-required pre-flowering (mg/L) 113

N-required post-flowering (mg/L) 144

* Where there are two sets of numbers, those outside the brackets refer to pre-flowering solutions and those within brackets refer to post-flowering solutions.

Findings

average weight per tomato statistically the same across treatments. Total yield was the same across all treatments. No significant differences Differences in total number of tomatoes were. The standard solution (INO)

generally yielded more, but the same number as for FW1 (statistically). trend towards smaller tomatoes from plants grown in the standard

inorganic solution – may explain similarity in overall yield despite more tomatoes being produced by those plants

System is feasible & can offer some potential savings especially if nutrients are re-circulated and nitrification issue is cracked.

Overall Findings – Hort Trials

Currently not a permitted use – EA permit /exemption required

Recommend using PAS110 QP - compliant digestates

Growing media - fibre demonstrates good potential

Useful nutrients

Different kinds can be difficult to handle

Hydroponics – high N content

Needs substantial dilution to substitute for conventional fertigation solutions

But system feasible if nitrification cracked

Handling and odour issues may be present

Further work recommended

Recent publications

• ‘Digestate enhancement & treatment’ (Nov 2012) • Identification & review of technologies &

treatment for a wide range of digestates • ‘Market expectations and requirements

for digestate’ (March 2013) • End user product needs

Recent publications – contd.

• ‘Evidence for digestate use in different UK markets: an annotated bibliography’ (June 2013) • Published evidence on digestate

benefits

• ‘Digestate distribution models’ (Aug 2013)

• Looked at different organic recycling industry supply/distribution models to provide information to AD industry

Conclusions

Digestate can be a very valuable resource but has to be managed carefully

We’ve come along way but there is still more to do

Operators need to understand their products and potential markets

Proven enhancement technologies needed to develop products if new markets are to be viable

Further work needed to develop the case for digestate use in potential new markets

Thank you www.wrap.org.uk

www.wrap.org.uk/landscaping

www.wrap.org.uk/horticulture

jacks.guinness@wrap.org.uk