Composting Facility Odour Assessments
Specialist odour impact assessments and H4 Odour Management Plans for open windrow and in-vessel composting facilities across the UK. EA-recognised methodology delivered personally by a chartered specialist.
Composting and Green Waste: An Inherently Odorous Process
Composting is one of the most inherently odorous industrial activities regulated in the UK. The biological breakdown of green waste, food waste and biosolids generates a complex cocktail of volatile organic compounds, reduced sulphur compounds, amines and short-chain fatty acids — many of which have very low odour thresholds and can be detected by neighbours at concentrations measured in single odour units per cubic metre. Combined with the long process times, large surface areas and seasonally variable feedstocks involved, this makes composting a sector where rigorous, regulator-recognised odour assessment is essential rather than optional.
Malcolm Pounder CEnv MIAQM leads every composting odour assessment personally, working to the Environment Agency's H4 Odour Management Guidance, the current IAQM Guidance on the Assessment of Odour for Planning and using FIDOL principles (Frequency, Intensity, Duration, Offensiveness, Location) when characterising likely effects. Whether you are bringing forward a new in-vessel composting facility, expanding an existing open windrow operation, supporting an EA permit variation or responding to a complaint cluster, we have the technical depth to deliver.
For new sites we typically combine an IAQM-methodology planning assessment with H4-compliant dispersion modelling, and state the biofilter outlet performance the model relies on, so the planning team, the EA permitting officer and the design engineer all see the same coherent technical story. Design and sizing of the biofilter stay with the design engineer.
Our Composting Facility Odour Services
Planning, permitting and operational odour support for composting and biowaste sites across the UK.
IAQM & H4 Odour Assessment
Full odour impact assessment to the current IAQM odour guidance and EA H4 methodology for new composting facilities, throughput increases and feedstock changes. Source potential characterised from sector-recognised emission datasets, receptor sensitivity rated against IAQM categories, and significance concluded in line with both planning and permitting expectations.
Odour Management Plans
Site-specific Odour Management Plans to satisfy the EA H4 framework and discharge planning conditions. Source inventory, biofilter operating regime, action triggers, complaints procedure, FIDOL-based monitoring protocol and corrective-action ladder — written in operational language compost site staff can actually use day-to-day.
Biofilter Performance in the Model
For in-vessel composting hall extract, the dispersion model uses the captured air volume and outlet odour concentration from your design engineer's biofilter specification, and the report states the outlet performance the conclusions rely on. We check that the biofilter on the drawings is the biofilter the model assumes; design, sizing and specification stay with your design engineer or contractor.
Monitoring & Complaint Response
FIDOL-based perimeter monitoring programmes, complaint cluster analysis with meteorological back-trajectory work, biofilter inlet/outlet olfactometry sampling oversight and rapid-response complaint investigations. Used in routine compliance, in defence against statutory nuisance allegations and in negotiation with EA officers during enforcement reviews.
Common Scenarios
Composting is one of the most regulator-scrutinised waste sectors in the UK, and odour assessments are a near-universal requirement. We are routinely commissioned across the full life cycle of a composting facility, from feasibility through to operational support and enforcement defence.
Engaging early is almost always cost-effective: site layout, building enclosure, biofilter sizing and feedstock acceptance all influence the achievable odour outcome, and adjusting them on the drawing board costs an order of magnitude less than retrofitting after complaints emerge.
- New open windrow facilities
- New in-vessel composting (IVC)
- EA permit variations
- Throughput increases
- Feedstock changes (e.g. adding food waste)
- Site relocations
- Complaint cluster investigations
- Enforcement notice response
Frequently Asked Questions
Do composting facilities need an odour assessment?
Yes. Both open windrow and in-vessel composting facilities require an odour impact assessment as part of any planning application, and an Odour Management Plan as part of the Environment Agency Environmental Permit. Composting of biowaste over 35 tonnes per day is a Schedule 1 Part A(1) activity under the Environmental Permitting Regulations 2016, and the EA's H4 Odour Management Guidance applies regardless of throughput. Because compost feedstocks (green waste, food waste, sludge) are highly odorous, the regulator and LPAs both expect a substantive, modelling-based assessment for any new or expanded site.
What is the H4 odour framework?
H4 is the Environment Agency's Horizontal Guidance Note on Odour Management for Permitted Facilities. It sets out the regulator's expectations for source identification, risk assessment, monitoring and mitigation at IPPC and Environmental Permitting sites including composting facilities. It requires operators to demonstrate BAT (best available techniques) for odour control, produce a site-specific Odour Management Plan, monitor for nuisance and respond to complaints in a documented way. The H4 framework is the EA's primary tool for assessing acceptability and for setting and enforcing permit conditions.
What is the difference between open and in-vessel composting odour?
Open windrow composting (typically green waste only) generates odour from the surfaces of the windrows themselves — particularly during turning operations — and emits over a very large area which is hard to capture and treat. In-vessel composting (often used for food waste and ABPR Cat 3 materials) takes place inside enclosed vessels or tunnels, with all process air captured and routed through a biofilter and sometimes a scrubber. In-vessel systems are inherently more controllable from an odour perspective and can be sited closer to receptors, whereas open windrow facilities typically require a much larger separation distance to sensitive land uses.
Do you design or size biofilters?
No. Biofilter design, sizing and specification are for the process designer or contractor. Our assessment uses the captured air volume and outlet odour concentration from their specification in the dispersion model, and states the outlet performance the conclusions rely on, so the biofilter on the drawings is the one the model assumes.
How much does a composting facility odour assessment cost?
Fees depend on scale, the number of sensitive receptors and whether the site is open windrow, in-vessel or hybrid. A typical planning-stage IAQM odour impact assessment with H4-compliant dispersion modelling is in the low-to-mid four figures. A full Odour Management Plan to support an EA permit application or variation is similar. Combined planning-plus-permit packages attract a small discount. We provide fixed-fee quotes following a short scoping conversation, with no hidden extras.