biogas from slaughterhouse waste

8/2/2019 Biogas From Slaughterhouse Waste

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Biogas from slaughterhouse waste:

towards an energy

self-sufficient industry

BIOGAS IN THE SOCIETYInformation from IEA BIOENERGY

TASK 37 Energy from biogas and

landfill gas

SUMMARYUsing the biogas from animal by-products (ABP)digestion, the St Martin slaughter facility can covermost of its heat demand and some of the electrici-ty requirements. In combination with heat from ageothermal power plant, the slaughterhouse fullycovers its demand on thermal energy by renewableenergy.The combined slaughterhouse/biogas plant is loca-ted at St.Martin/Innkreis in the North-West of

Austria. This biogas plant is processing all animalby-products which may not be further utilized suchas blood, hind gut, stomach content and fat scrub-ber content. The electricity produced from biogas isfed into the national power grid and the heat isdelivered to the slaughtering facility. The specificload profile of the slaughterhouse showed thatonly during 35% of time the heat produced by theCHP could directly be consumed in the slaughter-house. Therefore, a hot water storage tank servesas buffer to match th steady heat production withthe heat demand of the slaughterhouse. Thus near-ly all of the heat produced in the biogas plant is

used in the slaughterhouse covering 80% of itsenergy demand.

Photo 1: Biogas plant

IEA Bioenergy Task 37

Anaerobic digestion of slaughterhouse wastes

(animal by-products).

80% of the heat demand in the slaughterhouse

is covered by the biogas driven CHP.

A hot water storage tank uncouples heat supply

from heat production.

In combination with geothermal energy the complete heat

demand of the slaughterhouse is covered by renewable energy.

Reduction of disposal costs.

Production of a valuable fertilizer.


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BACKGROUND

After the European Union banned rendered animal prote-ins from the feed chain in 1999, the costs for the treat-ment of Animal By-Products (ABP) increased considerably.Since the ABP-Regulation (Reg. (EC) No. 1774/2002) defi-ned new treatment possibilities and laid down corre-sponding processing parameters, new pathways for theutilisation of slaughterhouse wastes were opened. Somebiogas plants in the agro-industrial sector are usingpasteurised ABP as co-substrates together with manure,catering waste and other energy crops. The biogas plantin St. Martin is operated only with ABP deriving predomi-nantely from the adjacent pig slaughtering facility.

The slaughterhouse that owns and operates also thebiogas plant slaughters approx. 2,000 pigs a day. Thereis a bovine slaughtering facility nearby and its ABPs arealso available for digestion in the biogas plant,but except for rumen content are actually not used inthe biogas plant due to capacity restrictions.Anaerobic digestion of animal by-products allows to sup-ply heat to the slaughtering facility and to reduce thedisposal-costs of the pig slaughtering facility. After theimplementation of a hot water storage tank 80% of theheat demand is covered. The remainder is covered byheat from a geothermal facility. The digestate is given offto surrounding farmers as a valuable fertilizer.

BIOGAS PLANTOperationThe plant design corresponds to the classical concept ofan agricultural biogas plant (Photo 1): two main fermen-ters of 600 m3 resp. 1,000 m3, a secondary fermentationtank (without heating, 1,000 m3 ) and a storage tank(3,200 m3) were constructed (Photo 2).The biogas plant is operated with selected fractions ofthe pig slaughtering process such as pig blood, mincedhind gut including content and fat from dissolved

air flotation. According to the European Directive(1774/2002 EC) the material is crushed to a maximumparticle size of 12 mm.The substrate is pumped from the slaughterhouse to abuffer tank and subsequently pasteurised (70 C/60 min).Before feeding , the substrate is cooled to 55C in orderto minimise a possible damage of the bacterial biomassin the biogas fermenter. In average approx. 20m3 ofslaughterhouse wastes per day are fed in parallel to thetwo digesters (Table 1). The biogas formed allows a pro-duction of approx. 4.7 MWh/d of electricity and 7 MWh/dof heat.Rumen content from the neighbouring cattle slaughter-house is delivered to the biogas plant and fed through afeeding screw directly into the smaller digester.Both digesters are operated at mesophilic temperatures(35 C). Higher fermentation temperatures will increasethe amount of undissociated ammonia (NH3 ) in the

system, which is believed to be the toxic form of ammo-nia-nitrogen for micro-organisms. Therefore a higher fer-

mentation temperature would increase the instability ofthe micro-biological community. Depending on the sub-strate composition ammonia-nitrogen levels vary bet-ween 4.5 and 7.5 g/L.Blood (as the main source of nitrogen) is added in func-tion of the ammonia concentration in the digesters. Highlevels of ammonia lead to high concentrations of volatilefatty acids, indicating a poor microbiological activity andleading to foaming problems. If fermentation problemsoccur anaerobic sludge (from a near-by sewage sludgedigester) is used to dilute the fermenter content and re-inoculate the process. During disturbances blood is notused as substrate and is treated in a rendering plant untilthe stability of the digestion process has recovered.

Nitrogen Recovery Increasing Fermentation StabilityA pronaunced dependency between the ammonia-con-centration and the biogas-yield was observed. With incre-asing ammonia concentrations degradation rate andmethane production decreased while volatile fatty acidsconcentrations increased.In laboratory experiments the performance of the full-scale plant was simulated. Increasing of the C:N-ratio byadding another carbon source did not improve gas pro-duction. However, removing of ammonia lead to a better

performance of the process. The specific methane yieldcould be increased up to 20% with the additional benefitof a lower volatile fatty-acids concentration indicating amuch more stable fermentation process.

Odour EmissionProcessing of slaughterhouse waste requires an efficientexhaust air treatment. Due to odour emissions in thebeginning of the operation, a new concept of odourreduction was developed (Figure 1). The plant had to beadapted by several measures:The digestate storage tank (originally planed as an open

BIOGAS IN THE SOCIETYInformation from IEA BIOENERGY TASK 37 Energy from biogas and landfill gas

Photo 2: Biogas plant, Fermenter and Desulphurisation-column (in the front)


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tank) was covered with pre-fabricated concrete sectionsin a gas tight manner.

Odour emissions of the storage tank could not be treatedin a bio-filter system with good results due to a highcontent of non degradable gases in the exhaust air.Initially the fresh substrate was conveyed with a com-pressed air transportation system from the slaughter-house to the storage tank located at the biogas plant. Tominimise exhaust air the transportation system wasreplaced by pumps and the storage tank was closedhermetically and connected to the biogas collectionsystem.The exhaust air from the processing hall was divided intoa stream with high odour nuisances (deriving from thepasteurisation and cooling unit) and a stream with lowodour emissions (delivery of rumen content and generalexhaust air in the hall). The high mass flow of lowcharged exhaust air is treated directly in a bio-filtersystem and the small air flow charged with a high odourload is pre-treated in an alkali-scrubber before beingdischarged to the bio-filter system.The high ammonia- and H2S-content in the biogas causedhigh SOx and NOx-emissions in the exhaust gas of theCHP. After installing an external desulphurisation unit(packed column operated at low pH-values, Photo 2) theconcentrations of H2S and NH3 in the biogas are reducedsubstantially. Based on this improved biogas quality the

engine of the CHP could be equipped with a catalyticconverter in order to reduce NOx and CO-concentrationsin the exhaust gas.

Demand site management of heatProvided the biogas plants are fed continuously, methane

is produced at a constant rate. The produced electricitymay be delivered steadily to the national power grid.However, the thermal energy produced by the CHP could

fully be used during one third of the time only. Animalsare slaughtered during working days in two 8 hour shifts,from 2 am to 6 pm. During that time (60%) there is apeak heat consumption of the slaughtering facility excee-ding heat production from the CHP plant.

With a hot-water storagetank, of a capacity of200 m3 (Photo 3) heat pro-duction is uncoupled fromheat consumption. Hence,heat produced on a con-stant rate in the CHP maybe transferred from periodsof low energy demand inthe slaughterhouse to timeswith a demand exceedingproduction. As a result,

nearly all the produced heatfrom the CHP is used in theslaughterhouse, coveringapprox 80% of the energy-demand. The rest is coveredby a geothermal powerplant (Figure 2).

BIOGAS IN THE SOCIETYInformation from IEA BIOENERGY TASK 37 Energy from biogas and landfill gas

Figure 1: Concept of odour emission control

Photo 3: Hot wateraccumulator (200 m)

Table 1: Average substrate mass streams (measured over 339 days)

Figure 2: Energy-Flow chart, connection of the biogas plantto the slaughtering facility

monitoring over339 days

Flotation at (dislo-ved air fotation )

Pig Blood Hind gut o pig(incl. content)

Bovine RumenContent

Anaerobic Sludge(Sewage digestion)

Days of feeding 314

[m/d]

278

[m/d]

314

[m/d]

160

[m/d]

21

[m/d]

Average per feeding day

Average over monitoring period

6.15

5.62

3.69

2.98

5.12

5.10

10.0

3.77

19.0

1.02


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CONTACTS

Bioenergy Plant

Rudolf Grofurtner GmbH

A- 4973 St.Martin/I, Diesseits 236

www.grossfurtner.at

Biogas Research & Consulting Group

Institute for Environmental Biotechnology,

IFA-Tulln

3430 Tulln, Konrad Lorenz Str. 20

www.codigestion.com

biogas from slaughterhouse waste

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