With nearly 3,000 small-scale animal carcass incinerators
in the UK, Alan Collings reports on an independent study to
assess the impact of their atmospheric emissions
The UK has around 2,600 small-scale animal carcass incinerators,
located at sites such as farms, rendering plant, pet crematoria,
hunt kennels and some veterinary practices.1 In February 2001, the
Department for Environment, Food and Rural Affairs (Defra) contracted
Netcen to measure and review atmospheric emissions from small-scale
animal carcass incinerators (or those processing less than 50kg.h-1
animal remains). The aim of the study was to keep the Government
informed as progress is made on the amendment of the EU Animal Waste
Directive (90/667/EEC). The specific objectives of the study were
to: measure emissions from the incinerators; identify options for
improvements; and make recommendations on best available techniques
(BAT).
WORK PROGRAMME
In order to determine current practices and technology for the incineration
of animal carcasses in small incinerators, and to determine information
available on the emissions from such incinerators, an information
search on current literature was undertaken. A representative set
of 11 sites was selected, which covered factors such as manufacturer,
age, specification (with and without afterburners), feedstock and
maintenance. The ages of the incinerator units ranged from five
months to six years, with a median age of 12 months. A test protocol
was developed to determine emissions of eight pollutants using reference
methods:
- sulfur dioxide (SO2);
- hydrogen chloride (HCl);
- oxides of nitrogen (NOx);
- total particulate matter (TPM);
- carbon monoxide (CO);
- carbon dioxide (CO2);
- volatile organic compounds (VOCs); and
- dioxins/furans.
The impact on air quality was assessed both nationally and locally
in terms of the contribution to total UK emissions and the local
pollutant concentration. Alternative scenarios to the current on-farm
incineration were then considered to establish whether any potential
improvements could be made and to help develop BAT.
EUROPEAN COMPARISONS
In order to identify the information available on the performance
and emissions from the incinerators, each of the incinerator manufacturers
was contacted. An extensive database and web search was also undertaken
to identify information about similar incineration facilities across
Europe.
Although small-scale animal carcass incinerators are used in other
European countries, and the US, the environmental performance of
the machines is not well known. UK usage appears to be far more
intensive and subject to less regulation than elsewhere in Europe.
This situation however, is due to change with the introduction of
the EU Animal By-Products Regulation, which will harmonise regulatory
controls on small carcass incinerators across Europe. In France,
for example, domestic pets are incinerated at small private pet
crematoria, which incinerate animals from several sources. Cattle
are incinerated in large specialised incinerators, while small animals
such as chickens are collected from farms in a public service and
burnt in a centralised and controlled incinerator.
The use of these incinerators appears to be prohibited in Austria,
Belgium and Germany where animal remains are sent instead to larger
centrally located incineration facilities. In Sweden, there are
a small number of small on-farm incinerators, which have been approved
by the Swedish Board of Agriculture. Regulations apply to the operation
of the units, and a specific hygiene programme must be drawn up
and followed by the operator. The operator must also keep and maintain
records of incinerator operations for at least two years.
MEASUREMENTS
In order to identify 14 sites for a visual assessment, a telephone
survey was carried out, whereby sites were selected to provide a
representative cross-section of the installed equipment and feed
stock. The next step involved site reconnaissance visits so that
up to 11 suitable incinerators could be chosen for monitoring.
A protocol to measure emissions from the animal carcass incinerators
was developed from reference test methods used for assessing emissions
from industrial processes. A number of possible ways of testing
were assessed and a set of procedures were developed which would:
ensure reliable results from each of the sites, with a minimum deviation
from standard methods; and produce a safe system of work that considered
the operating temperatures of the incinerators and other hazards.
A continuous emission monitoring system was also set up to determine
NOx, SO2, CO, CO2 and O2 emission concentrations. Best practice
for sampling particulate and dioxins/furans involves employing a
multipoint, isokinetic, sampling strategy because variation in particle
size and particulate concentrations across a sampling plane can
be significant. Although the reference test method adopted for particulate
and dioxins/furans sampling allows single point sampling at small
ducts (diameters <0.35m) it can lead to high uncertainty (>10
per cent).
However, the emissions from these incinerators were expected to
vary significantly with time. The degree of variation in concentration
across the sampling plane was not expected to be as significant
as the variation in concentration over the duration of the burn.
As a result, a single point sampling was used. Experimental results
for the incinerators tested (table 1) showed that the presence of
afterburners made a significant difference to the emission concentrations
of some pollutants, and consequently results are grouped according
to presence or absence of this technology. The results in table
1 demonstrate a large variation in concentrations of most pollutants
between the incinerators tested. Units fitted with afterburners
generally gave rise to significantly less emissions for nearly all
the pollutants measured, with the exception of NOx. Increased emission
of NOx is consistent with the higher heat input into the incinerator
from the afterburner.
The determined dioxin and furan concentrations are generally low,
with about half the incinerators indicating compliance with EU waste
incineration directive (WID) limits. The dioxins data for all the
incinerators show close agreement when the expected uncertainty
of +/- 50 per cent in the reported data is considered. The range
of emission releases over a typical operating cycle for each incinerator
is shown in table 2.
However, even incinerators equipped with an afterburner but poorly
operated and/or maintained (for example overloaded) can give rise
to much greater emissions of most pollutants than a simpler design,
not equipped with an afterburner, but carefully operated. For example,
concentrations of particulates CO and VOC at site 8 are significantly
higher than for most of the other incinerators monitored, although
this incinerator is equipped with an afterburner. This demonstrates
the need for plant operators to be properly trained in the use and
maintenance of the equipment. Carbon dioxide emissions are primarily
governed by the carbon content of fuel burned and the wastes incinerated,
with combustion efficiency an additional factor. Similarly SO2 emissions
are directly proportional to the sulfur content of the fuel used
and waste incinerated.
EMISSION LIMITS AND BENCHMARKS
At present there are no emission limits in the UK which are applicable
to small (<50kg.h-1) incinerators. However, there are a number
of similar, although larger scale activities under local authority
air pollution control, which provide benchmark release limits. In
addition, WID defines mandatory maximum release limits for all other
incineration plant.2 While it is highly unlikely that current small-scale
incinerators will comply with all the WID limits, they are an important
benchmark as future revisions of process guidance notes will need
to reflect the WID limits.
For most incinerators, the measured pollutant emission concentrations
are higher than several of the emission limit values, including
many of the less exacting limit values. This is not surprising,
as small animal remains incinerators are currently unregulated (except
for nuisance and smoke issues). Site 1 was unusual in meeting emission
standards for larger animal remains incinerators and crematoria.
However, the incinerator at this site produced the highest NOx emission
concentration. Emission of HCl was higher than some of the other
units tested but, HCl emissions from unabated plant are dependent
on the composition of the waste materials and fuel. Dioxin and furan
emissions were generally very low for all the incinerators monitored
and several of the units tested demonstrated compliance with the
WID limit of 0.1ng.ITEQ.m-3. However, the emission limits set within
the WID are significantly exceeded for all the other pollutants
measured.
CONTRIBUTION TO TOTAL UK EMISSIONS
The UK national atmospheric emissions inventory (NAEI), will be
updated for 2001 in summer 2003 to include the estimated annual
emissions of each pollutant from small animal carcass incinerators.3
The total emissions from the small incinerators were taken from
the results of the incinerators monitored. It has been assumed that
a total of 2,600 units were in use and that each unit operates for
an average of 35 hours per week for 52 weeks per year (ie 1,820
operational hours per annum). While the emissions from small carcass
incinerators are not currently accounted for directly within the
NAEI, it is likely that fuel combustion emissions are. The results
from this study demonstrate that the contribution of emissions from
small carcass incinerators to the national total is very low at
less than 0.2 per cent for all the measured pollutants. Emissions
of several pollutants from the incinerators are significant when
compared with the totals provided for agriculture.
IMPACT ON LOCAL AIR QUALITY
A simple model for short and medium range dispersion of pollutants
into the atmosphere was used to calculate annual average concentrations
in the surrounding area.4 A typical combined plume and stack height
was assumed to be 10m and concentrations of pollutants were calculated
at various distances from the incinerator using the mean emissions
of pollutants from the 11 incinerators monitored. The model outputs
are presented in table 3.
Ground level concentrations of all the pollutants examined fall
off rapidly with distance from the point of emission. In general,
most of these incinerators are located in rural areas, typically
at distances greater than 200m from centres of population and with
no, or few, additional major emission sources.
The model however, does not address potential high-ground level
concentrations from poor dispersion conditions, in which there is
potential for the grounding of the plume. Such conditions could
also arise where siting of the incinerator or stack height is inadequate.
For example, a higher concentration may arise due to the plume impinging
on adjacent buildings (including livestock sheds). The concentration
in the area surrounding the incinerator must be within the national
air quality standards (NAQS). Table 4 summaries the standards and
the estimated percentage contribution of the modelled emissions
to the limits/targets. A small carcass incinerator would typically
contribute less than 0.5 per cent to the pollutant concentration
limits in the area outside a 1km radius of the incinerator. Most
of the standards are expressed as eight or 24-hour means and few
of the incinerators have a combustion cycle greater than eight hours.
EVALUATING BAT
The study considered three scenarios in its analysis of what may
be considered to be BAT:
- diversion of animal waste from farms to a centralised, large animal
waste incinerator;
- replacement of current small carcass incinerators with the lowest
emission model found from the measurements taken; and
- business as usual case (for comparison).
The evaluation is based on potential emission improvements achieved
through these scenarios. The likely costs and animal health risks
of the scenarios however, have not been considered as these aspects
were beyond the scope of the study. The analysis of the first two
scenarios is shown below. In order to simplify the first scenario
- diversion of animal waste from farms to a centralised, large animal
waste incinerator - several assumptions have been made:
- the central incinerator complies with the concentration limits
for new plant in the waste incineration directive;
- the average distance from the central incinerator to a typical
farm is 50km (100km round trip);
- animal carcasses are collected, on average, once a week; and
- the vehicle used is a diesel fuelled light goods vehicle (LGV).
Table 5 compares the WID limits with the mean concentrations of
pollutants measured, together with an evaluation of the degree of
abatement that would be required to meet the WID standards, and
the estimated emission savings through meeting these standards.
The table also shows an estimate of the emissions associated with
the transport of the animal carcasses to a central incinerator.
The figures show that, in comparison with emissions from incineration,
the emissions from the transport of remains are negligible.
The largest potential emissions abatement (above 90 per cent) is
for VOCs, CO and particulate matter, and these emissions are all
directly a function of combustion efficiency. A reduction of about
75 per cent in emissions of acid gases (HCl and SO2) is also predicted,
although this will be at the expense of the consumption of neutralisation
reagents and the formation of residues which are generally sent
to landfill. Interestingly, emissions of NOx may increase through
the use of a large central facility.
In the second scenario - replacement of current small carcass incinerators
with the lowest emission model found from the measurements taken
- the impact on emission is assessed by comparing emissions resulting
from the replacement of all the small carcass incinerators with
the least polluting incinerator. While it is possible that a better
overall environmental performance may be achieved by other incinerators
not assessed in the study, the use of the "best" performing
example in this survey as a benchmark at least identifies achievable
standards.
The selected incinerator (site 1 - see table 1) does not show the
best performance for all the pollutants. This approach however,
is considered to be better than defining a hybrid incinerator performance
that may not be achievable in practice. The results of the analysis
are presented in table 6.
The potential increase in UK NOx emissions would be less than 0.03
per cent. There may be low NOx burner technology available for the
burners used on these incinerators which would help mitigate the
NOx emissions. However, the availability of such technology for
such small burners is not known. Improvement to combustion chamber
design (for example improved refractory design) may also allow a
reduction in the fuel requirement, and as a result a reduction in
NOx emission. The potential VOC and CO emission reduction is in
excess of 99 per cent and the particulate reduction would be about
86 per cent, which compares well with scenario 1.
SUMMARY OF BAT REVIEW
The evaluation shows that significant reductions in atmospheric
emissions are achievable with an optimised small incinerator. Although
the improvements in HCl or SO2 acid gas emissions would not match
those achievable with a larger facility and overall NOx emissions
would be higher, the reductions in other emissions would be similar
to those indicated for the large central facility. This evaluation
shows that the use of an on-site incinerator with afterburner could
represent BAT for animal remains disposal. The use of large central
incineration facilities would allow supervision through an existing
regulatory framework. The continued use of small on-site incinerators
would require development of a type approval scheme or other supervision
measures. Upgrading or renewing the incinerator population to match
the best achievable in this survey is part of the recommendation
of BAT. However, it should also include other technical and management
improvements.
RISK ASSESSMENT NEEDED
Significant reductions in emissions to atmosphere are achievable
with an optimised small incinerator, and the use of an on-site incinerator
with afterburner could represent BAT for animal remains disposal.
The BAT review also included recommendations on furnace design,
operation and management. Improvements could be made in housekeeping,
storage and handling of animal remains, fuels use and storage, residue
disposal, operating temperature, loading and operator training.
A type approval system for small incinerators is recommended to
minimise the opportunity for installation of more polluting designs.
With the exception of oxides of nitrogen, plant fitted with afterburners
generally produce less emissions than incinerators without. Several
of the incinerators perform well against the benchmark releases
provided in current guidance for animal remains incinerators prescribed
for local authority air pollution control. Dioxin emission concentrations
surveyed were less than 1ng.ITEQ.m-3 with several incinerators meeting
the WID limit of 0.1ng.ITEQ.m-3. The results from this study demonstrate
that the contribution of emissions from small carcass incinerators
to the UK national total is very low at (or less than) 0.2 per cent
for all the measured pollutants. For pollutants given NAQS targets,
a small carcass incinerator would typically contribute less than
0.5 per cent to each of the total pollutant concentration limits
in the area outside a 1km radius of the incinerator.
Where diseased animal carcasses are being incinerated, poor combustion
may not completely destroy the diseased material and the resulting
particle emissions could provide a transport mechanism for disease
to other animals via direct inhalation or ingestion of material
deposited on to pasture. However, alternatives to on-farm incineration,
involving the collection of material for disposal at a larger centralised
site, may cause problems through the spread of disease from farm
to farm. Ultimately, the study recommends that a risk assessment
is undertaken to ensure that the final choice of disposal methods
for animal remains addresses both environmental and animal health
issues. Alan Collings is technical manager in the emission monitoring
team at Netcen (an operating division of AEA Technology plc). E-mail:
alan.collings@aeat.co.uk
References
1 Peirson, S. (2001). Confidential report to: Dr Ian Davidson, Rural
Marine and Environmental Division Ministry of Agriculture Fisheries
and Food, Nobel House, 17 Smith Square, London, SW1A 2HH. An assessment
of the numbers and types of small carcass incinerators (<50kg/hour)
currently in use in the UK. ADAS Hollyshaw House, Hollyshaw Lane,
Leeds, LS15 7BD.
2 Directive 2000/76/EC of the European Parliament and of the council
of 4 December 2000 on the incineration of waste.
3 Goodwin, JWL et al. (2001). UK emissions of air pollutants 1970
- 1999.
4 Clarke, R.H. (1979). A model for short and medium range dispersion
of radionuclides released to
the atmosphere. NRPB-R91. National Radiological Protection Board,
Harwell, Didcot, Oxon, OX11 0RQ.
To access the full report, visit the Defra National Air Quality
Archive at: www.airquality.co.uk/archive/index.php.
A summary of the test procedures used by Netcen can also be obtained
from the website.
