essential requirements for a low-emission operation of ... · the following requirements for a low...

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November 2014

Essential requirements for a low-emission

operation of composting facilities

The following requirements for a low emission operation of composting facilities have been identi-

fied, taking into account the State of the Art of Composting guideline (BMLFUW 2005) and best

practice examples of Austrian composting facilities. On the one hand, the requirements from the

State of the Art of Composting guideline have partly been put into concrete terms, and on the

other hand additional requirements have been included. Where the State of the Art of Composting

guideline contains additional requirements which are not listed in the following, these require-

ments also have to be considered.

The requirements are designed for composting facilities which fall within the scope of the Indus-

trial Emissions Directive (IED, 2010/75/EC). In accordance with Annex I of the IED (point 5.3)

these include biological treatment facilities for recovery with a capacity of more than 75 tonnes

per day. Since the declaration about capacity in Austria is often laid down in terms of annual ton-

nage in the relevant authorisation permits, it will be necessary, in individual cases, to consult the

competent authority to determine whether a waste treatment facility falls within the scope of the

IED.

The specified requirements also provide guidance for small facilities and their low-emission oper-

ation according to state of the art technology.

The aim of composting is to produce compost which is rich in humic substances and nutrients.

The decomposition of organic substances is not a primary concern.

Apart from the in-house documentation of the process stages and process management, compli-

ance with the requirements should be checked by external experts on a regular basis – at least

once a year. Such external checks should be carried out by authorised specialists or a specialist

agency and include, with a view to the specified requirements, in particular:

- Inspection of the facility and the operational management of equipment,

- Traceability of waste streams (inputs, outputs, notes),

- Checking of in-house quality management, especially

o operating logs and operational documentation as well as

o available measurement results or measurement registrations.

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A) General requirements

A1) Storage of Materials

Subsoil requirements:

In general, areas with a firm, liquid-tight base need to be provided for the delivery, storage and in-

termediate storage of waste materials, with the exception of structured woody materials (e.g. gar-

den and park waste and wood chips) in a raw or chopped-up state, which can also be stored on

open topsoil. [1]

Roofing/housing requirements:

In areas where annual precipitation exceeds 1,300 mm and if, at the same time, at least one of

the following criteria applies, a roof or a housing/encapsulating structure will be necessary for de-

livery, storage and intermediate storage facilities [1]:

- Storage for 9 months or more

- Percentage of N rich materials (e.g. organic containers with large quantities of kitchen

waste, wet food waste, sewage sludge) greater than 25 % (v/v) (annual mean)

This shall not apply to separate areas dedicated to the takeover and storage of structural woody

material (e.g. garden and park waste and wood chips).

Any areas with housing elements or encapsulated areas have to be equipped with exhaust air

capturing and treatment systems (for exhaust air treatment requirements see A8).

Poorly structured materials such as

- biogenic household wastes (organic waste containers),

- kitchen wastes from restaurants and the food industry,

- fresh green waste and

- other non-woody materials with a high water content

are not suitable for long-term storage due to their high water content. These materials have

a high potential for leachate water formation and tend to rot quickly. In open storage they

therefore have to be treated/mixed each working day.

Rapid and/or immediate processing reduces odour emissions as well as leachate water for-

mation, which also constitutes a source of odour emissions. In addition, emissions of me-

thane and ammonia are reduced [7].

If materials are not processed/mixed each working day, potential delivery, storage and in-

termediate storage areas for poorly structured materials need to be housed/encapsulated

and equipped with exhaust air collection and treatment units.

For optimum rotting conditions, materials should be processed each working day in case of

housed/encapsulated storage, too. Acidification of the rotting material – and thus delays in

rotting – can thus also be prevented.

Structured materials such as

- woody waste from autumn and winter cuts and

- tree and brush cuttings from gardens and parks

mainly accrue seasonally. In order to have a sufficient amount of structured materials availa-

ble, parts of these materials should be stored over longer periods of time. On account of low

water contents, high air pore volumes and thus low putrescence propensities, open storage

is possible.

Shredded or chopped-up structured material in intermediate storage, in the form of table or

trapezoid windrows, must not be higher than 3.5 m. As shredded structured material, too, is

subject to continuous decomposition, caution should be taken to guarantee the required gas

exchange, e.g. by way of adequate grain size (shredding ratio).

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Relevant other legal requirements such as fire protection issues need to be considered on

an individual basis.

Municipal sewage sludges are characterised by relatively high water contents. Any further

water logging on account of precipitation thus needs to be avoided. Sewage sludges need to

be stored in such a way as to allow adequate draining of the precipitation water (windrow

type; fleece-covered, if necessary). For storage periods exceeding 4 weeks, interim storage

areas for sewage sludges must be covered with a roof.

As a rule, potential storing of sewage sludges serves the purpose of optimised material

management and bridging of periods of time until the required quantities and mixing partners

- in the sense of process control of the main composting process - are available. Processing

for the intensive (active) rotting stage needs to be carried out as early as possible.

Solid fermentation residues1 are characterised by high water content and a high potential

of odour emissions. Fermentation residues not subjected to an aerobisation process pursu-

ant to the requirements under B32 ideally need to be processed/mixed every working day. In

case of prolonged storage (longer than 72 hours) of fermentation residues not undergoing an

aerobisation process, housing/encapsulation needs to be provided.

Uncontrolled stockpiling, storage and decomposition of unselected materials are not recognised

as a state of the art of composting technique [1].

A2) Rapid Windrow Formation

Upon handover and receipt, the feedstock should enter the biological treatment process as soon

as possible by windrow formation. Conditions for ideal oxygen supply need to be created by way

of adequate material blending, windrows geometry and by adapting turning intervals accordingly.

Adding of about 5 – 10 % (v/v) of old compost can foster rapid formation of humic substances as

well as the integration of volatile carbon and nitrogen compounds [1]. Fine compost elements are

also added by admixing screen overflow.

Requirements concerning the admixing of structured materials are defined under the special re-

quirements given in item B. In general, structured ligneous materials have a wide C/N ratio and

are thus apt to increase the C/N ratio in the rotting mixture.

A3) Turning equipment

In order to guarantee a low-emission operation in open composting during the active/intensive rot-

ting stage, the only admissible procedure is the use of homogenised turning equipment (turning

machine) [3]. Turning of the post-rotting (curing stage) material by way of wheel-loaders is admis-

sible.

A4) Controlled Variable: Water Content

Microorganisms are able to take up nutrients as well as oxygen in soluble form only. A sufficient

degree of humidity, particularly during the initial and intensive/active rotting stage, is thus indis-

pensable. The optimum degree of humidity decreases in the course of the decomposition pro-

cess.

1 Fermentation residues from wet fermentation must always be dewatered for composting; whether fermentation res-

idues from dry fermentation need to be dewatered depends on the process. Depending on the dewatering process, dewatered fermentation residues have a DM content of about 20 to 35 %. 2 Provided the share of fermentation residues in the overall input of a batch is less than 20 % (m/m).

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Water contents of organic feedstock may vary considerably. Pure kitchen or vegetable wastes, for

example, have a fresh mass water content of 80 – 95 %.

Water contents of mixtures rich in kitchen wastes and poor in structure, for example, ideally range

between 45 – 50 % in the moist mass; for more structured mixtures richer in fibrous green waste,

moist mass water contents range between 45 – 60 %. [2]

During processing, the materials have to be adequately blended. The water contents of the waste

mixture for windrow formation should not exceed 65 – 70 %.

In case of excessive water content (> 70 %), aeration is limited, which may cause slightly anaero-

bic conditions and thus methane formation. If the water content is too low (< 30 %), uptake and

transport of nutrients are impaired, which slows down the composting process. In case of water

contents below 30 %, the degradation process is largely inhibited; below 20 %, it will cease entire-

ly.

A5) Controlled variable: C/N ratio

Microbiologically degradable sources of carbon and nitrogen must be available at a balanced ra-

tio. An excess of readily available nitrogen (C/N < 15 - 20:1) may induce great losses in the form

of ammonia as well as nitrous oxide formation. A C/N ratio of (20) 25 - 35 (40) : 1 can be as-

sumed as a target ratio for the feedstock mixture. [1]

A6) Controlled variable: Temperature

Temperature has a significant impact upon emissions. In the interest of a low-emission operation

and quality development (favourable environment for microbial degradation and the development

of humic substances), self-heating of the composting mixture in the course of exothermal aerobic

material degradation must be managed and controlled. Temperatures exceeding 55/60 °C over

an extended period of time (longer than necessary for thermal hygienisation) impair the process.

At and beyond approximately 65 °C, the biological species spectrum narrows considerably. This,

again, slows down the degradation and transformation velocity and induces the formation of un-

desired and potentially odour-intensive metabolic products. Along with the danger of partial or

complete dry-stabilisation of the composting mixture, the formation of aggregates rich in humic

substances is inhibited. Composting systems which systematically maintain temperatures above

70 °C for several days do not comply with good practice and state of the art composting.

Thus, temperatures during the intensive rotting stage need to be reduced rapidly below 70°C by

taking adequate measures such as irrigation, turning, reduction of windrow height and volume,

enhanced aeration in active aeration, addition of old compost or clayey soil.

Temperatures during the intensive rotting stage should exceed 70 °C for a period of a few days

only.

However, limiting the temperature range during the thermophilic stage of composting can be

achieved by way of adequate material blending at an early stage, upon windrow formation.

As soon as the temperature of the compost mixture no longer lastingly exceeds 40/45°C, the pro-

cess enters the curing stage [1]. Higher temperatures over brief periods of time immediately after

the turning process are possible and admissible [3]. Turning intervals and thus heat losses/water

losses need to be reduced during the curing stage. [1].

With regard to the curing stage, nitrous oxide formation is particularly relevant. It occurs below

ranges of 40 – 45 °C with a maximum at about 30 °C [9].

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A7) Internal Process Monitoring

The requirements regarding internal process monitoring given below are mainly part of the docu-

mentation of a low-emission operation. Selecting one of the parameters does thus not guarantee

the technically correct management and control of a facility in each and every case.

In housed/encapsulated process management, the following process parameters need to

be monitored per tunnel and/or formed batch over the entire intensive/active rotting stage:

- temperature at the windrow core

- temperature of exhaust air ahead of biofilter (in order to prevent overheating of the bio-

filter, among other reasons)

- oxygen content of the exhaust air from intensive/active rotting

Oxygen contents need to be measured continuously to regulate aeration.

In forced-aeration reactor systems, the oxygen content in the exhaust air from closed reac-

tors as control parameter should not fall below 14 % (v/v) [1].

In open process management, the following process parameters need to be measured and

documented per formed batch each working day during the first 4 weeks of the inten-

sive/active rotting stage:

- Temperature at the windrow core

- Oxygen (O2) concentration at the windrow core

- Carbon dioxide (CO2) concentration at the windrow core

- Methane (CH4) concentration at the windrow core

Open process management with forced aeration does not fall under this regime. In this case,

measurements of the concentrations of oxygen (O2), methane (CH4) and carbon dioxide

(CO2) at the windrow core need to be carried out, if possible, during aeration intermissions

(in case of intermittent aeration), twice a week during the intensive/active rotting stage until

the end of forced aeration. Measurements need to be documented. Temperatures need to

be measured and documented each working day.

Measurement points must be set for each 300 m³ of formed batch. In general, at least two

measurement points need to be defined per batch.

Example: For a triangular windrow cross-section with a windrow height of 2.5 m, a windrow

base width of 5 m and windrow length of 100 m, measurements at a minimum of three

measurement points will be required.

Beginning with the 5th week of the intensive/active rotting stage as well as upon the end of

forced aeration, these parameters need to be measured and documented up to the moment

when process temperatures fall permanently below < 40/45 °C twice a week per batch.

The measurement points must be placed at a minimum of 30 cm above the windrow base and/or

30 cm below the windrow surface. Measurements must be made before turning. Measured values

must be documented batch-wise.

Evaluations of measured values of the gas composition at the windrow core need to be based on

the median value of all individual measured values obtained during the intensive/active rotting

stage of one year. Evaluations are thus not made batch-wise. In this way, the influence of tem-

perature fluctuations over the year (reduced chimney effect at high temperatures) can to be taken

into account.

Within the scope of external monitoring, measured values of CH4, O2 and the sum of O2 + CO2 al-

so need to be considered.

In open composting, as opposed to housed/encapsulated process management, monitoring of

airborne emissions is not possible. Measuring gas concentrations and temperatures at the wind-

row core serves the purpose of documenting a technically correct composting process in a trace-

able manner.

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A8) Exhaust air management

Exhaust air streams from housed/encapsulated areas as well as exhaust air streams from open

processes with forced aeration (suction ventilation) need to be cleaned. Biofilters are adequate

cleaning units for the reduction of odours. Biofilters must be operated pursuant to ÖWAV Rule

Sheet 513, in order to keep odour as well as NMVOC emissions as low as possible. However, the

use of comparable cleaning units such as bioscrubbers is also admissible.

Along with the effect of ammonia as an air pollutant, high raw gas ammonia concentrations may

impair and/or inhibit odour reduction in the biofilter and cause increased ammonia emissions.

In order to avoid the formation of nitrous oxide in the biofilter upon ammonia reduction, in case of

increased ammonia concentrations, the raw gas must be conducted via an acid scrubber for am-

monia separation before introduction into the biofilter. Ammonia concentrations above 50 ppm are

relevant; concentrations above 200 ppm lead to a significant short-term impairment of the filter ef-

fect [4]. Thus, for ammonia concentrations above 50 ppm in the raw gas, acid scrubbers are ex-

pedient in order to prevent biofilter acidification and/or odour problems. NH3 separation in the acid

scrubber is generally highly effective (up to 95 %).

Exhaust air temperatures ahead of introduction into the biofilter need to be retained at a range of

5 – 40 °C. [12]. Exhaust air temperatures which are too high require exhaust air cooling.

A9) Confectioning/Screening

The screening process may result in increased dust and bioaerosol emissions when the compost

is too dry.

In order to avoid excessively dry compost, the water content during the curing stage needs to be

(cautiously) raised as needed. However, excessive humidification is to be avoided.

In general, the water content is to be regulated in such a way as to avoid relevant dust emissions

on the one hand, while preventing adverse effects upon screening performance on the other. Fog

sprays effectively bind dust and germs in the screening process.

A10) Mechanical Manipulation of Matured Composts

Considering that matured composts, too, are still aerobic, biologically active materials, screenings

below 15 mm and pile heights above about 2.5 m need regular turning in order to allow for the re-

quired oxygen supply. The turning frequency essentially depends upon the residual microbial ac-

tivity. Depending on the degree of maturity, turning frequencies of 3 – 4 weeks generally meet this

requirement. [1]

A11) Waste Water Management

Press water, process water, scrubbing water and condensate accruing up to the complete hygien-

isation of the compost material must only be used for humidification provided a process-induced

hygienisation of the entire compost material, including added process waters, is guaranteed [6].

Storage and composting areas must be shaped in such a way as to allow for rapid discharge of

press, process and precipitation surface water and to prevent water logging in the area of the

windrow base. Correspondingly, the requirements for slopes, depending upon windrow height,

annual precipitation and the existence of roofing and/or integrated aeration and discharge chan-

nels, need to be observed.

7/16

Minimum longitudinal slope (%) for composting areas depending upon precipitation rate, windrow

height, roofing and aeration as well as discharge systems; (no transverse slope), based upon [1]

Minimum slopes

for windrow sys-

tems [in %]

open

annual precipitation

(mm)

roofed With aeration/drain

tubes below windrows*

<450 450-900 >900

Triangular wind-

rows 1 % 2 % 3 % 1 % 1 %

Trapezoid/ table

windrows

Not state of the art

of technique 1 % 1 %

* In case of composting on slab with submerged drain/aeration tubes, the site is not required to have a slope. However, the

drain-off of water must be guaranteed also in case of heavy precipitation and at maximum capacity utilization.

Facilities may deviate from the above requirements for longitudinal slopes provided the compost-

ing areas have additional transverse slopes that are drained via infiltration structures between the

windrows. These infiltration structures must have a longitudinal slope of a minimum of 0.5 %.

Minimum transverse and minimum longitudinal slopes (%) for composting areas depending upon

precipitation rates, windrow height, roofing and aeration as well as discharge systems

Minimum slope

for windrow sys-

tems [in %]

open

annual precipitation

(mm)

roofed With aeration/drain

tubes below windrows *

<450 450-900 >900

Triangular wind-

rows

Transverse

slope

1 % 2 % 3 % 1 % 1 %

Triangular wind-

rows

Longitudinal

slope

0,5 % 0,5 % 1 % 0,5 % 0,5 %

Trapezoid/ Table

windrows

Transverse

slope


of technique 1 % 1 %

Trapezoid/ Table

windrows

Longitudinal

slope


of technique 0,5 % 0,5 %

* In case of composting on slab with submerged drain/aeration tubes, the site is not required to have a slope. However, the

drain-off of water must be guaranteed also in case of heavy precipitation and at maximum capacity utilization.

In the takeover and interim storage areas for freshly delivered material from organic waste con-

tainers or other materials with high water content, attention must be paid to a rapid discharge of

leachate and precipitation water; logging of press and precipitation water under stored biowaste

needs to be avoided.

Collection tanks for waste waters must be lastingly impermeable and without overflow. The vol-

ume of the collection tank is to be dimensioned in such a way as to reliably hold precipitation wa-

ters from a one in five year 48 hour rainfall event, along with the average leachate (0.028 m³/m² of

sealed area) [1].

Calculations can be modelled upon the supplementary sheet of ÖKL-Baumerkblatt 24a.

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B) Special Requirements

In the following, special requirements for the composting of materials from organic waste contain-

ers, sewage sludges, fermentation residues, and green waste (cf. B1-B4) will be defined, supple-

menting the general requirements.

Blending of the above materials shall be carried out as follows:

More than 20 % (m/m) of materials from organic waste containers3, with fermentation residues and/or

sewage sludge accounting for less than 20% each:

B1) Requirements for the composting of organic waste container materials

More than 20 % (m/m) of sewage sludge, with fermentation residues accounting for less than 20%:

B2) Requirements for the composting of sewage sludges

More than 20 % (m/m) of fermentation residues:

B3) Requirements for the composting of fermentation residues

More than 80 % (m/m) of green waste (highly structured materials such as tree and shrub cuttings, ma-

terials from green belts or strips along highways and roads; herbaceous material from organic waste

containers, etc., not including grass and lawn cuttings):

B4) Requirements for the composting of green waste

The corresponding specific requirements (B1, B2, B3 or B4) need to be applied for every batch.

If mixtures of organic waste container materials and/or sewage sludges and/or fermentation resi-

dues are not covered, the following procedures need to be observed:

In case of varying mass fractions: The requirements (B1-B3) of the waste accounting for the

highest mass fraction are to be applied.

In case of equal mass fractions: requirements are to be applied in the following order:

fermentation residue > sewage sludge > organic waste container material.

As to the choice of which special requirements apply, it is not only the collection system (e.g. col-

lection of organic waste container material) that is decisive. Based on adequate investigation /

documentation / evidence, it may also be the actual composition of the collected waste that is the

decisive factor in the choice of the applicable requirements.

3 Fine fraction of material from organic waste containers.

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B1) Requirements for the Composting of Materials from Organic Waste Containers

Mixing ratios / feedstock mixture [3] (see the following examples)

Minimum share of structured material*

m/m (mass) (v/v) volume

Rural organic waste

containers4

15 % share of structured material5

per m³ of rural organic waste container

0.5 m³ of structured material* (1 / 0.5)

Urban organic waste

containers6

25 % share of structured material

per m³ of urban organic waste con-

tainer 1 m³ of structured material* (1 /

1)

*Admitted structured materials are woody wastes such as tree and shrub cuttings. The share of structured

material needs to be increased correspondingly if no screen overflow is admixed.

Generally, the following rule applies: the higher the windrows, the greater the required free

pore volume.

Intensive rotting stage: windrow geometry, turning frequency, aeration and

composting time [3]:

- Composting of materials from organic waste containers

Windrow height

upon batch

formation

Maximum

windrow

cross-

section7

Maximum

width of

windrow

base

Minimum turning

frequency/week

Forced aeration

required8

Reference

value: in-

tensive rot-

ting time

Up to 1.5 m 3 m2 3m

1/week Yes 7 WE

several times No 7 WE

1.5 ‐ 1.8 m 3 ‐ 4 m2 3.5 m

1/week Yes 7 WO


1.8 ‐ 2.2 m 4 ‐ 6 m2 4.5 m

1/week Yes 8 WE

several times No* 9 WE

2.2 ‐ 2.5m 6 ‐ 7.5 m2 5 m

several times Yes 8 WE

1/week Yes 10 WE

*… operation without forced aeration possible in case of high share of structured material only

Higher shares of structured materials and lower windrow cross-sections allow for longer turn-

ing intervals, provided there is a sufficient amount of moisture and the moisture is homoge-

neously distributed. Excessive turning frequencies may disturb the creation of a chimney ef-

fect in passively aerated windrows.

For actively aerated table or trapezoid windrows, the same turning frequencies and intensive

rotting times shall apply as in triangular windrows, corresponding to the windrow heights.

Unaerated table or trapezoid windrows during the intensive rotting stage are not state of the

art composting.

In areas with high precipitation ranges, windrows should have minimum heights of 1.5 m in

order to reduce the danger of water logging during the curing stage. During the cold season,

too, a minimum height of 1.5 m is a necessary condition to prevent windrows from cooling

down to a degree preventing the required hygienisation.

4 Bulk density of rural organic waste container: 0.5 t/m³. 5 Bulk density of tree and shrub cuttings (shredded): 0.25 – 0.35t/m³. 6 Bulk density of rural organic waste container: 0.75 t/m³. 7 Maximum windrow cross-section: calculated mean value of semi-circle area and area of triangle 8 Definition of "forced aeration": ventilation of the composting process supported by ventilators (fans) and ventilation

pipes/vents.

10/16

Curing stage: windrow geometry, aeration and turning frequency [2]

During the curing stage (temperatures lastingly < 40/45 °C), the oxygen demand is signifi-

cantly lower than during the intensive rotting stage. Nevertheless, attention needs to be giv-

en to sufficient gas exchange, and water logging on account of watering (irrigation) or precip-

itation needs to be avoided. Thus, as well as on account of the fact that at the curing stage

structural stability has already declined, passively aerated table and trapezoid windrow sys-

tems with pile heights > 2.50 m without forced aeration are not recommended.

In order to guarantee the required gas exchange as well as sufficient homogenisation, wind-

rows need to be turned on a regular basis (about every 2 – 4 weeks), (with or without forced

aeration).

Depending upon the nature and composition of the feedstock materials (i.e. share of struc-

tured material and C/N ratio), the management intensity during the curing stage and the de-

sired compost quality, the required curing stage times will vary.

11/16

B2) Requirements for the Composting of Sewage Sludges

Sewage sludges nave a narrow C/N ratio of 8-12:1 and thus qualify as N sources [1]. Their struc-

ture and energy contents (C content), however, are very low, which calls for high amounts of car-

bon-containing, structurally stable material (e.g. tree and shrub cuttings) to achieve low levels of

odour and emissions during composting.

Mixing ratios / feedstock mixture [3] (following are examples)

Minimum share of structured material

m/m (mass) (v/v) volume

Blending with straw9

Minimum of 20 % of straw

per m³ of sewage sludge 2.5 – 3 m³ of straw

(1 / 2.5 – 3.0)

Screen flow-back does not accrue and can thus not

be considered.

Blending with shrub

cuttings10

Minimum of 30 % of shrub

cuttings

per m³ of sewage sludge 1.5 – 2 m³ of shrub cuttings

(1 / 1.5 – 2.0)

Factor 1.5 can be applied only if the screen overflow

is being considered,

otherwise, factor 2.0 shall apply.



- Composting of Sewage Sludges

Windrow height

upon batch

formation

Maximum

windrow

cross sec-

tion11

Maximum

width of wind-

row base

Minimum turning

frequency/week

Forced aeration

required12

Reference

value: inten-

sive rotting

time

Up to 1.5 m 3 m2 3m

1/week Yes 8 WE


1.5 ‐ 1.8 m 3 ‐ 4 m2 3.5 m

1/week Yes 8 WE


1.8 ‐ 2.2 m 4 ‐ 6 m2 4.5 m

1/week Yes 9 WE


2.2 ‐ 2.5m 6 ‐ 7.5 m2 5 m


1/week Yes 10 WE



ing intervals, provided there is a sufficient amount of moisture and moisture is homogene-

ously distributed. Excessive turning frequencies may disturb the creation of a chimney effect

in passively aerated windrows.




art composting.

9 Pile density for straw (loose): 0.08 t/m³; density sewage sludge: 0.8 – 1.0 t/m³.

10 Pile density for tree and shrub cuttings (shredded): 0.25 – 0.35 t/m³.

11 Maximum windrow cross-section: calculated mean value of semi-circle area and area of triangle. 12 Definition of "forced aeration": ventilation of the composting process supported by ventilators (fans) and ventilation

pipes/vents.

12/16














aeration).




13/16

B3) Requirements for the Composting of Fermentation Residues

Mixing ratios / feedstock mixture

Depending upon the feedstock material of fermentation and/or the material mix during aero-

bisation, it may be necessary to add further structured material. The share of structure-

forming materials (shredded material, screen overflow, structured material in fermented

waste, material admixed during aerobic conditions, etc.) in the material mix should, depend-

ing on the nature of the structured material, have a total share of structured material of 60 –

75 % (v/v).

Aerobisation

When composting fermentation residues, adequate aerobic conditions need to be generated

rapidly upon discharge, regardless of the achieved degree of stabilisation. In particular with

a view to odour emissions, fast ending of methane formation and oxidation of the reductive N

degradation products (NH3/N2O formation potential) has to be achieved [1].

Composting of fermentation residues from wet fermentation requires dehydration in any

case; dehydration of dry fermentation residues is process-dependent. Depending upon the

dehydration process, dehydrated fermentation residues have a DM content of about

20 – 30 %. Depending upon the consistency of solid fermentation residues, admixing of

structured material may be necessary.

Solid fermentation residues need to be subjected to aerobisation in housed/encapsulated

areas/facilities over a period of 8 – 10 days soon after exiting the biogas facility. During this

process good ventilability must be guaranteed for the fermentation residues (admixing of

structured material, low pile height, etc.). The exhaust air captured from the

housed/encapsulated areas needs to be cleaned (cf. requirements under A8).

Aerobisation need not be carried out at the site of the composting facility but may also be

carried out at the site of the biogas facility, for example.

The requirement for the aerobisation of fermentation residues in housed/encapsulated areas

does not need to be observed if the share of fermentation residues in the total input of a

batch accounts for less than 20 % (m/m) and the batch itself contains a sufficient amount of

structured material.



- Composting of Fermentation Residues

Windrow height

upon batch

formation

Maximum

windrow

cross-

section13

Maximum

width of

windrow

base

Minimum turning

frequency/

week

Forced aeration

required14

Reference

value: in-

tensive rot-

ting time

Up to 1.5 m 3 m2 3m

1/week Yes 8 WE


1.5 ‐ 1.8 m 3 ‐ 4 m2 3.5 m

1/week Yes 8 WE


1.8 ‐ 2.2 m 4 ‐ 6 m2 4.5 m

1/week Yes 9 WE


2.2 ‐ 2.5m 6 ‐ 7.5 m2 5 m


1/week No 10 WE


13 Maximum windrow cross-section: calculated mean value of semi-circle area and area of triangle. 14 Definition of "forced aeration": ventilation of the composting process supported by ventilators (fans) and ventilation

pipes/vents.

14/16


ing intervals, provided there is a sufficient amount of moisture and moisture is homogene-

ously distributed. Excessive turning frequencies may disturb the creation of a chimney effect

in passively aerated windrows.




art composting.














aeration).




15/16

B4) Requirements for the Composting of Green Waste (highly-structured materials such as

tree and shrub cuttings, materials from green belts or strips along highways and roads;

herbaceous material from organic waste containers, etc.)

Green waste (highly structured materials such as tree and shrub cuttings, materials from green

belts or strips along highways and roads; herbaceous material from organic waste containers,

etc., not including grass and lawn cuttings) have a higher structural share (air pore volume). Its

organic substance is available for microbial decomposition only to a minor extent. Thus, in green

waste composting, the oxygen demand is lower.

Intensive rotting stage: Windrow geometry, turning frequency

Green waste should be composted in triangular windrows with a total height not exceeding

3 m and a total base width not exceeding 6.5 m.

In order to guarantee the required gas exchange as well as sufficient homogenisation, the

windrows need to be turned once a week during the intensive rotting stage. If the measured

value of methane is below 5% and the windrow is sufficiently homogenous, the time intervals

between turning the windrows can be extended. Gas measurements at the windrow core

(O2, CO2, and CH4) should be carried out, notwithstanding the requirements under A7, at

least twice a week during the intensive rotting stage over the first 4 weeks, and once a week

thereafter.

Curing stage: windrow geometry, turning frequency








rows need to be turned on a regular basis (about every 2 – 4 weeks).

16/16

C) References

(1) Stand der Technik der Kompostierung des BMLFUW

(2) Grundlagenstudie Stand der Technik der Kompostierung des BMLFUW

(3) „Handzettel für Kompostanlagenbetreiber – Mindeststandards einer ordnungsgemäßen

Kompostierung“ der ARGE Kompost & Biogas

(4) ÖWAV -Regelblatt 518 „Anforderungen an den Betrieb von Kompostierungsanlagen“

(Austrian Water and Waste Management Association)

(5) KGVÖ Regelblatt Nr. 12 Österreichisches Kompost-Gütesiegel; KGVÖ Anerkennungs-

und Überwachungsverfahren auf Basis: Kompost VO, Ö-Normen S 2206-1, S2206-2,

ONR 192206, Richtlinie „Stand der Technik“

(6) ÖNORM S 2205 Technische Anforderungen an Kompostierungsanlagen zur Verarbei-

tung biogener Abfälle

(7) Betrieb von Kompostierungsanlagen mit geringen Emissionen klimarelevanter Gase;

Bundesgütegemeinschaft Kompost e.V.

(8) CUHLS , C. 2001 Schadstoffbilanzierung und Emissionsminderung bei der mecha-

nisch-biologischen Abfallbehandlung, Veröffentlichung des Instituts für Siedlungswas-

serwirtschaft und Abfalltechnik der Universität Hannover (Heft 114), Hannover 2001

(9) KETELSEN, K. 2011 Kurzgutachten zur Frachtbegrenzung für Emissionen aus der

MBA

(10) TRIMBORN, M., GOLDBACH, H., CLEMENS, J., CUHLS, C., BREEGER, A., 2003.

Reduktion von klimawirksamen Spurengasen in der Abluft von Biofiltern auf Bioabfall-

behandlungsanlagen. Band 14 der Bonner Agrikulturchemischen Reihe, Abschlussbe-

richt zum Forschungsvorhaben AZ.: 15052 der Deutschen Bundesstiftung Umwelt (Os-

nabrück)

(11) ÖKL-Baumerkblatt 24a 1993 (Austrian Council for Agricultural Engineering and Rural

Development - Austrian construction sheet for agricultural composting sites)

(12) ÖWAV Regelblatt 513: Betrieb von Biofiltern (Austrian Water and Waste Management

Association)

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