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Effectively all Irish biosolids go to farmland, and that route is narrowing faster than a replacement can be built. Redrock Bioenergy made a submission to the Uisce Éireann National Bioresources Strategy consultation arguing for one focused strengthening of the draft: plan advanced thermal conversion as real capacity at the regional Bioresource Centres, complete the treatment chain on one site, and judge every route on what it destroys and recovers rather than on the volume it removes.

The submission was made to a public consultation and is published here in full. Download the submission (PDF), or read the argument below.

The position we start from

Redrock's core business returns nutrients to farmland. We develop anaerobic digestion, and we regard biofertiliser as the right destination for organic residues where the material is clean and a landbank exists. Nothing in the submission is an argument against land application in principle. The argument is that the test should be the contaminant profile of the material, not the disposal route in the abstract. Where there is a landbank and no persistent pollutant load, spreading is the better outcome and it recovers nutrient value that destruction would forgo. Where a persistent pollutant load is present, spreading transfers the liability to soil instead of resolving it. Wastewater sludge sits on the second side of that line, because it inherits whatever the sewer catchment collects.

Three things worth adding to the challenge set

The draft Strategy identifies the pressure on the agricultural outlet accurately. We would sharpen it in three ways.

Source control is a genuine good, and it cannot close the gap on its own. Catchment interventions reduce the load arriving from identifiable point sources, and they protect and can expand the landbank for clean material. They do not reach diffuse and legacy inputs, infiltration, atmospheric deposition or contaminated ground draining to sewer, so the annual sludge flow does not fall to a spreadable floor however long control runs. Source control is also specific to the contaminant it targets: microplastics and pharmaceutical residues persist whatever a PFAS restriction achieves. Source control and a destruction endpoint are complementary, not alternatives.

The narrowing of the land route should be planned for, not absorbed as a surprise. Australia is the leading indicator. On the release of the draft PFAS national management plan, a major water utility suspended land application and began evaluating on-site thermal treatment. The lesson is in the sequence, not the destination: a tightening regime moved that utility off land before a replacement route existed, and a replacement takes years to specify, consent and build.

Not every thermal route destroys a contaminant; some only move it. This is the point on which any destruction pathway is most reasonably challenged, and it is correct. Thermal treatment at lower or incompletely controlled conditions can break a long-chain PFAS molecule into shorter-chain PFAS and other fluorinated fragments distributed across the solid residue, the aqueous condensate and the offgas. The parent compound leaves the measured matrix without being mineralised. The right response is not to set thermal conversion aside, but to define destruction precisely and hold every route to that definition, ours included.

Define destruction, then apply it evenly

Destruction should mean complete mineralisation, evidenced on a fluorine mass balance in which the aqueous and solid legs close to inorganic fluoride against stated detection limits, with the gas-phase leg explicitly bounded rather than assumed closed. There is at present no validated total-organofluorine stack method for any thermal route, so the gas phase is a debit held open against every route, and no route should be credited with complete gas-phase mineralisation until a method exists. Defined that way, the partial-transformation concern stops being a blanket objection and becomes a discriminating test.

From that definition follow five technology-neutral selection criteria: destruction toward mineralisation rather than removal of the parent compound; phosphorus recovery weighted by the form the residue leaves in; net energy contribution to the works; acceptance of wet dewatered cake without a dedicated drying step; and suitability for distributed deployment at the Bioresource Centre itself. The first three are the outcome the Strategy is trying to buy. The last two separate the routes that deliver it on site from the routes that deliver it only after drying the feed or only at a single distant facility.

Complete the chain on one site

Aggregation is right for the digestion step, and dewatering at satellite sites and hauling to a regional centre concentrates sludge to the scale digestion and thermal conversion both need. Our recommendation concerns what happens after digestion. Once the sludge has been aggregated and digested, the residue should be treated and destroyed on that same site rather than bulked, dried and hauled a second time to a separate central facility. A second leg adds cost, carbon and haulage risk, puts a contaminant-bearing material back on the road network without treating it, and forfeits the energy integration in which biogas upgrading, thermal conversion and phosphorus recovery each feed the next.

A final movement remains in either case, because the phosphorus-bearing residue leaves for recovery. The point is its scale. Digestion has already destroyed much of the volatile fraction, so the inorganic fraction of the digested dry solids typically runs in the order of 30 to 50 per cent, and advanced digestion pushes it towards the upper end. A biosolid dried above 90 per cent dry matter carries essentially the whole of those dry solids out of the gate, and pays for the drying first. Destroying at the hub means only the residue leaves. On a dry-solids basis, and on the mineral-residue route, that is a reduction in the order of 50 to 70 per cent, and the character of the movement changes as much as its size: a concentrated product movement to a recovery offtake rather than a bulk waste movement to a disposal point.

Why not simply incinerate

The most reasonable challenge to all of this is that high-temperature combustion already destroys the organic and pathogen load at scale today. We take it seriously. Proven-at-scale operation is a real advantage that a first-of-kind route has to earn against, and it is not something we ask a regulator to set aside. Our narrower point is that a closed total-fluorine balance on the gas leg has not been demonstrated for any thermal route, combustion included, so criterion (a) is a threshold every route must clear on evidence rather than a contest that can be scored today.

Among the routes that clear it, the question becomes what destroying the load costs. Combustion needs the feed dried or held at high dry matter, and the latent heat of the evaporated water leaves with the vapour and is hard to recover. That penalty is largest on exactly the feed these centres produce, since a digested cake has already exported its readily combustible volatiles as biogas and is therefore less likely to combust autothermally. A mono-incinerator's minimum economic size may also exceed a single centre's tonnage, which re-imposes centralisation and a second haul. On phosphorus we are careful not to over-claim: recovery from incineration ash is proven at commercial scale and recovery from a supercritical-water mineral residue is not, so that criterion is at best neutral on current evidence and we do not rest the comparison on it.

The eight recommendations

What we asked for, and what we did not

Redrock is developing a supercritical fluid gasification module, which is the route the Strategy's long list calls hydrothermal gasification. We declared that interest plainly, and the one place we named it was to ask that it be reconsidered within the viable technology set, on the same evidence-gated terms as any other route, rather than screened out before the evidence exists. We accept screen-out if the evidence does not support it.

We sought no procurement advantage, exclusivity or commitment. The at-scale demonstration on Irish sludge offered at R7 would be funded and delivered independently, its evidence criteria published openly and technology-neutrally, and its data, methods and results contributed to the common evidence base on equal terms whatever the outcome. The five selection criteria follow from the estate's own energy-neutrality and transport obligations, not from our technology, and we would propose the same five whatever route we were developing.

Redrock Bioenergy develops anaerobic digestion and advanced thermal treatment for wet and contaminated organic residues across Ireland, the United Kingdom and Australia. To discuss biosolids treatment or the demonstration programme, contact info@redrockbioenergy.com.

This page summarises a submission made to a public consultation on 22 July 2026 and reflects the position and evidence base at that date. It is not a design, procurement or investment recommendation. Process performance, energy balance and residue characteristics are site and feedstock specific.