Drying solid fractions of animal manure and digestate to produce commercial fertilisers

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ManuREsource2013

International conference on Manure management and valorization

December 5-6, 2013 Bruges, Belgium

Drying solid fractions of

animal manure and digestate to produce commercial fertilisers

Giuseppe Moscatelli, Giuseppe Bonazzi, Sergio Piccinini, Paolo Mantovi

Research Centre on Animal Production CRPA, Reggio Emilia, Italy

Progetto Equizoo-CR Iniziativa svolta nell’ambito del Programma regionale di ricerca in campo agricolo 2010-2012 con il contributo finanziario di:

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Aim of the work

To test the feasibility of a new treatment line for drying solid fractions from slurry or digestate

NEW

TREATMENT LINE

to obtain a product with a lower water content and volume, stabilized, easier to handle and sold in

bags as commercial fertiliser.

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LIBERA

The new treatment line

Has been developed by VOMM SpA company (Milan, Italy).

It is a turbo technology, based on the creation of a thin film of material in high turbulence by means of a turbine rotating inside a static horizontal chamber.

The chamber is jacketed and a thermal fluid, such as thermal oil, keep the temperature constant inside the machine.

It is possible to work in a closed circuit, to avoid any

atmospheric emission.

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Drying equipment (closed circuit)

Developer VOMM SpA Milan (Italy)

2-Turbine dryer

3-Cyclone 4-Scrubber 5-Chiller

7-Air heating

6-Air blower

1-Doser

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Scheme of the process

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Drying equipment - dried material

Turbine dryer

Cyclone

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Pelletizer - pellets

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Materials and methods

Six types of solid fractions were tested in the pilot plant:



3 from digestate (dairy cattle manure + energy crops), separated by a screw press

(22%, 18%, 14% Total Solids)



2 from dairy cattle slurry, separated by a screw press (19%, 16% Total Solids)



1 from dairy cattle slurry, separated by a drum press

(18% Total Solids)

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Materials and methods

Drying process parameters set in the experiments:

−

Temperature of thermal oil: 270 °C

−

Temperature jacket chamber IN: 240-250 °C

−

Temperature air flow IN: 190 °C

−

Temperature air flow OUT: 125 °C

−

Volume air flow: 645 Nm

³

/h

−

Load rate material to be dried: 75 kg/h

−

Rotary blade system: 850 rpm

−

Contact time of the material in the rotating turbine: 20 sec

−

Temperature condensate fraction OUT: 30 °C

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Characteristics of solids (IN and OUT)

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Characteristics of solids (IN and OUT)

Total Solids [%] Nitrogen [%] Phosphorus [%]

IN OUT IN OUT IN OUT

Digestate 1 22 88 0.43 1.62 0.19 0.71

Digestate 2 18 83 0.40 1.41 0.17 0.70

Digestate 3 14 82 0.34 1.44 0.13 0.61

Average 84 0.39 1.49 0.16 0.67

Cattle slurry 1 19 88 0.37 1.40 0.10 0.49

Cattle slurry 2 16 86 0.39 1.40 0.10 0.47

Cattle slurry 3 18 90 0.41 1.62 0.08 0.35

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Characteristics of water condensate

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Characteristics of water condensate

pH TSS Total N Ammonia-N Total P COD [-] [mg/kg] [mg/kg] [% TKN] [mg/kg] [mg O₂/kg]

Digestate 1 9.4 110 638 94 11.2 1876

Digestate 2 9.5 60 807 97 6.5 1154

Digestate 3 9.5 30 742 99 6.1 1044

Average 9.5 60 729 97 7.9 1358

Cattle slurry 1 9.6 10 691 99 1.8 800

Cattle slurry 2 9.5 10 845 99 1.7 850

Cattle slurry 3 9.4 10 667 99 1.8 244

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UF & RO equipment (lab scale)

UF and RO module by GE Water and Process Technologies UF: Membrane at 20 µm – Model Purtrex PX20-20

1^st step RO: high pressure (30 bar) – Membrane Model WW- 8040HP polymer customized spiral-wound configuration

resistent to organic fouling

2^nd step RO: low pressure (15 bar) for high retention capacity

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UF & RO results

pH TSS Ammonia-N Total P COD EC

[-] [mg/kg] [mg/kg] [mg/kg] [mg O₂/kg] [μS/cm]

Water

condensate IN

9.5 ¹

5.3 ² 40 718 4.8 995 5670

Retentate OUT 5.5 240 8181 178 4454 45400

Permeate OUT 6.2 12 1.9 0.08 23 37

Limit values ³ 5.5-9.5 80 11.6 10 160

1, 2: before (1) and after (2) acidification

3: Italian legislative decree 152/2006, Section 3, Tab 3, All.5

- the large volume of permeate can be discharged into surface water as the limits set by water protection law are respected;

- the small volume of the concentrate (retentate) should be added to the new solid

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Conclusions and perspectives

Drying manure solid fractions in a closed circuit plant, avoiding ammonia and dust emissions by recirculation of the air flow, is technically feasible;

The recovery of thermal energy from CHP hot gases in a biogas plant, to heat the turbo dryer, may be of interest;

UF and RO can be applied to purify condensate water from the drying process;

Utilising manure surplus as a source of N and P and other

nutrients to produce fertilisers, helps reducing the environmental pressure in areas with high livestock density. This approach

could also contribute to create a market of recycled materials in the frame of a sustainable green economy.

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What should be done

An evaluation of:

 the investment and running costs, to verify the economical sustainability of the proposed treatment line (considering the possible value of the pellet);

 reliability and operational management costs of UF and RO process;

 the possibility to recycle the retentate from RO in the turbo- dryer, in order to increase the N content in the pellet.

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