Farm anaerobic digestion: feedstock and traffic evidence

The first question on a farm anaerobic digestion application is whether the use is still agriculture in planning terms. Appearance comes later. A digester fed from the holding, returning digestate to the same land, sits close to agriculture. One importing feedstock from thirty miles away and exporting gas to the grid is an industrial or waste use, wherever it happens to stand.

Councils decide that question on the feedstock catchment evidence, and applicants who treat it as a formality lose control of the whole application.

Agricultural or industrial in planning terms

Section 336 of the Town and Country Planning Act 1990 defines agriculture, and development reasonably necessary for the purposes of agriculture on a holding is treated differently from a commercial energy installation.

Three factors tip the balance:

• Where the feedstock comes from. Predominantly from the holding points towards agriculture. Substantial imports from other farms or from food processors point away.
• Where the output goes. Digestate spread on the holding is agricultural. Gas or electricity sold into the grid at scale is not, though a modest export does not by itself change the character.
• The scale of the plant relative to the farm. A digester sized to the slurry of the resident herd reads differently from one sized to the local maize market.

Permitted development rarely helps. Part 6 of Schedule 2 to the GPDO 2015 covers agricultural buildings on units of 5 hectares or more, with prior approval for siting, design and external appearance, subject to floorspace limits. A small slurry digester serving the holding is occasionally argued through it. A commercial plant with clamps, tanks, a gas upgrading skid and a weighbridge is not, and trying it usually costs six months.

Say plainly in the Planning Statement which characterisation you are arguing for and why. Officers are far more receptive to an honest description of an industrial use in a rural location than to an agricultural label that does not survive the first question.

Feedstock catchment and the evidence to produce

This is the heart of the application, and it should be a table rather than a paragraph.

For each feedstock give the material, the annual tonnage, the origin by farm or supplier, the road distance, the number of vehicle movements it generates and the months of the year it arrives. Total it. Then show the proportion arising on the holding and the proportion imported.

Back it with the supply agreements or heads of terms, redacted for price if necessary. A statement that feedstock will come "mainly from the local area" is worth nothing, and the council will condition a restriction anyway, so you may as well write the restriction you can live with.

Two practical points. Maize and wholecrop arrive in a short harvest window, which concentrates traffic into a few weeks rather than spreading it. And the mix changes over the life of the plant, so build headroom into any tonnage condition or you will be back with a section 73 application in three years.

Traffic, and the lanes the traffic uses

Plant of this kind generates articulated deliveries, tractor and trailer movements, digestate tankers and occasional abnormal loads during construction.

The highway authority will look at the route from the strategic network to the site, not just the access. Single track lanes with passing places, a hump-backed bridge, a village street with no footway and a school on it, all feature more often in the refusal reasons than the access itself does.

A Transport Statement is usually the right document at farm scale, with a full assessment where movement numbers are high. It should give the daily and peak-week movement profile by vehicle type, the routing strategy, swept path drawings for the largest vehicle at the access and at any pinch point, and visibility splays measured on site rather than taken from a drawing.

Offer routing as a condition, with a written routing agreement and a driver briefing. Councils accept those where the operator can show who enforces them.

Digestate, odour and the permit

Digestate storage is sized in months, not litres. Where the holding lies in a nitrate vulnerable zone, the storage period required by the rules governing organic manures applies, and that usually means several months of covered capacity.

Cover it. An open lagoon or an uncovered tank is the single biggest source of odour complaints from these plants, and a cover also reduces ammonia loss and rainfall dilution. The visual consequence is a taller structure, which brings the landscape question forward.

On the regulatory side, a plant treating waste feedstock needs an environmental permit from the Environment Agency, and standard rules permits exist for anaerobic digestion. Plants using only crops and manures from the holding may follow a different route. Establish which applies before you fix the feedstock list, because the answer changes the planning description of development.

Odour is dual-regulated in the same way ammonia is. The permit controls the operation, and the council still has to be satisfied that the use is acceptable in its location. An Odour Assessment covering the clamps, the reception area, the digestate store and the emergency flare is what answers that. Councils expect a suitably qualified author and professional review is strongly advised. The interaction between scale, odour and screening plays out much as it does for poultry units.

Landscape, and what the tanks actually look like

Digester tanks, gas domes and silage clamps are large, pale and geometric, and they sit in landscapes that have nothing else like them. A flare stack adds a vertical element visible at night.

Handle it directly. A Landscape and Visual Impact Assessment with winter viewpoints, photomontages from the nearest public rights of way and a section through the site against the existing farm buildings does more than any amount of text about screening. Grouping the plant with the existing farmstead, rather than putting it in a clean field for construction convenience, is usually the single most effective mitigation.

Colour matters more than people expect. A dark recessive finish on tanks and cladding changes how the group reads from a distance, and it costs almost nothing at specification stage.

Grid connection and the things it drags in

The connection is a planning matter even when it is someone else's.

An electrical connection may run for kilometres to reach a suitable point, and the cable route crosses land, hedgerows, watercourses and possibly archaeology. Works by a statutory undertaker have their own permitted development rights, so the cable may not need permission, but the trenching still affects hedgerows and protected species and it still has to be programmed.

Gas to grid needs an entry unit, a propane injection facility in many cases, and a kiosk near the main. Show the connection point and the route on the application drawings even where consent for them is not being sought, because a scheme whose connection is undeliverable is a scheme that will not be built.

Illustrative example. A 500 kilowatt plant on a 240 hectare arable and dairy holding proposes 60 per cent of feedstock from the farm, 30 per cent from two neighbouring farms within four miles and 10 per cent imported. The council conditions the tonnage and the origin, restricts deliveries to weekdays between 07:00 and 18:00, requires a routing agreement, and requires the digestate store to be covered. The figures are illustrative.

Conditions to expect, and to draft first

Councils commonly condition feedstock type and tonnage, the proportion arising off the holding, delivery hours, vehicle routing, an odour management plan, a landscape and ecological management plan, external colour finishes, lighting, and restoration of the site if the plant ceases operating.

Draft your own versions and offer them. A condition you have written is one you can comply with, and a restriction on feedstock origin that you proposed is far easier to vary later than one imposed against your objection. Broader diversification questions, including where the line sits between farming and a separate business use, are covered in the piece on farm diversification into workshops and offices.

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.

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