Anaerobic digestion or biomass plant on a farm: permission

An anaerobic digestion or biomass plant on a farm almost always needs full planning permission, and it is refused far more often on lorry movements and odour than on the principle of renewable energy. The two questions that decide the application are whether the plant is properly part of the farming enterprise or an industrial operation on farmland, and whether the local lane network can carry the feedstock traffic. Answer those with evidence and the rest of the case is manageable.

Whether the plant counts as agricultural development

Agricultural permitted development under Part 6 of Schedule 2 to the General Permitted Development Order 2015 covers buildings and operations reasonably necessary for agriculture on the unit. A digester that processes only slurry and crops grown on the holding, and uses the gas on the farm, can sometimes sit within that description.

Most plants do not. Once the operation imports feedstock from other farms or from food waste collections, or exports gas or electricity commercially, it stops being agriculture within the meaning of section 336 of the Town and Country Planning Act 1990 and becomes an industrial process. That distinction sets the application route, the fee and the policy tests that follow.

Where the answer is uncertain, resolve it deliberately rather than by assumption. A pre-application enquiry, or an application for a lawful development certificate on the agricultural point, costs far less than an enforcement notice after the tanks are built. Farm diversification arguments help here in the same way they do for a farm shop and the diversification test, but they do not convert an industrial process into agriculture.

Feedstock, HGV movements and the highway evidence

Traffic is the objection that arrives first and lasts longest. A digester needs feedstock delivered and digestate removed, and both move by tractor and trailer or by articulated lorry on roads that were not built for them.

The transport evidence needs to cover the whole picture.

1. Annual tonnage in and out, converted to vehicle movements by season, with the peak week identified rather than the average.
2. The routes those vehicles will use, with swept path analysis at every pinch point, junction and bridge.
3. Existing traffic counts on the affected lanes, taken in a neutral month.
4. Any passing places, verge protection or junction improvement needed, and how it would be secured.
5. Whether a routing agreement is offered, and how it would be enforced.

On a scheme of any scale this belongs in a Transport Assessment rather than a short note. Highway authorities take routing agreements seriously and will want them tied down by condition or obligation, because a promise about which way lorries turn is worth nothing if it cannot be enforced.

Odour and bioaerosols

Odour is the objection that turns a parish against a scheme. Digestate stores, feedstock reception, silage clamps and the digester itself all release odour, and reception buildings are the usual mitigation because they allow air to be captured and treated.

An odour assessment should identify sources, characterise them, model dispersion to the nearest sensitive receptors and set out the mitigation that keeps predicted exposure acceptable. The Institute of Air Quality Management publishes the guidance most practitioners work to, and the local environmental health officer will read the report closely.

Bioaerosols are a separate issue and matter most where feedstock includes green waste or food waste. The Environment Agency applies screening distances around composting and digestion facilities, and where sensitive receptors fall inside them a bioaerosol risk assessment is expected. That work belongs with the permit application as much as the planning one, and the two assessments should not contradict each other.

The Odour Assessment page sets out what that report covers, and the mitigation logic is close to the extraction and abatement arguments used for a hot food takeaway, scaled up.

Environmental permitting alongside planning

Planning permission and an environmental permit are separate consents from separate regulators, and neither guarantees the other. Most digestion plants need a permit under the Environmental Permitting (England and Wales) Regulations 2016, either a standard rules permit or a bespoke one depending on capacity, feedstock and location.

Councils are entitled to assume that pollution control matters will be handled by the permitting regime, and national policy says so. That does not make odour irrelevant to planning, because the acceptability of the location remains a planning judgement, and applicants who tell a committee that odour is a matter for the Environment Agency usually regret it.

Landscape, lighting and built form

A digester is a cluster of tall tanks, a gas holder, a flare stack, silage clamps and hardstanding. On open farmland that reads as industrial development, so the design case has to work.

Practical moves that help: siting against an existing farm building group rather than in an open field, using dark recessive colours on tanks, keeping the flare as low as the safety case permits, and planting structural hedgerow and tree belts that will screen at maturity. The Design and Access Statement is where that reasoning is set out.

Lighting deserves its own attention in a dark rural area. Specify luminaires, mounting heights, aiming and controls, and design to the Institution of Lighting Professionals guidance for the relevant environmental zone. A lighting condition is nearly certain, so it is better to write the scheme than to inherit one.

Digestate storage and spreading

Digestate is a valuable fertiliser and a regulatory liability. Storage capacity has to match the closed periods when spreading is not permitted, and slurry and digestate stores are regulated under the silage, slurry and agricultural fuel oil rules as well as by the permit.

Set out the storage volume, the months of cover it provides, the spreading area available and how the land bank was calculated. Where the plant sits in a nitrate vulnerable zone, the closed periods and application limits are tighter, and an under-sized store is a common reason for a refusal or a difficult condition.

Common refusals on traffic and odour

Look across refused rural digestion schemes and the reasons repeat. Feedstock lorries on unsuitable single track lanes. Odour sources too close to dwellings without enclosure. Digestate storage sized for an optimistic spreading calendar. Tanks sited in open landscape rather than against an existing farmstead.

Each of those is fixable at design stage and expensive to fix at appeal. So commission the traffic and odour work before the layout is fixed, not after.

PlanScope drafts the Planning Statement around your scheme details, flags where evidence is missing and shows which specialist reports a rural energy proposal usually triggers.

This is general guidance, not legal advice. Check the position with your local planning authority, the Environment Agency or a qualified professional before relying on it.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.