I went looking for a pelletiser that wasn't there

Why the undefined product-manufacturing stage matters to the Glan Devon bio-fertiliser proposal

I began with what seemed like a narrow technical question:

How will the proposed Glan Devon facility actually turn dried biosolids and mineral fertiliser into a durable, homogeneous pellet?

The development application says the dried biosolids will be blended with mineral fertilisers and then processed through a “pelletiser or granulator”, after which the material will be screened for size consistency.

That sounds straightforward.

It is not.

Pelletisation and granulation are not necessarily equivalent process descriptions. The terms sometimes overlap in industry usage, but they can involve materially different product-forming mechanisms, equipment, additives, recycle circuits and environmental outputs.

The choice can affect whether the feed is compressed through a die, extruded, agglomerated using moisture or binder, layered around a core, coated with mineral nutrients or subjected to some form of chemical conditioning before the final particle is formed.

The problem is that the public application does not identify which process is proposed.

Appendix 1 shows a processing line—but not the process that makes the product

The application does contain an overall process flow diagram.

Appendix 1 identifies several relevant items, including:

• biosolids and mineral-fertiliser storage;

• an agitated mixer and another mixer;

• milling or crushing equipment;

• a belt dryer;

• a screen separator;

• a crusher;

• a cooling screw;

• conveyors;

• bagging;

• finished-product storage;

• generic chemical and ammonia storage;

• and some air-handling and filtration infrastructure.

That is important context. The entire facility is not entirely an empty black box. But the central product-forming operation remains unresolved.

The written process description says the blended material enters a “pelletiser or granulator.” Yet neither a pelletiser nor granulator is identified in the equipment schedule. Nor is another item expressly described as performing that function.

The diagram shows equipment around the product-forming stage without clearly showing the unit operation that converts the mixed feed into the claimed pelletised or granulated fertiliser.

That creates a direct documentary gap:

The written description relies on a pelletiser or granulator, but the process diagram does not identify one.

It would be improper to guess whether one of the mixers, the dryer, the crusher or some unlabelled or omitted item performs that task.

Thus, the application does not provide a complete, process-specific flowsheet for the fertiliser-manufacturing circuit.

The middle of the process remains a functional black box. That is a problem.

“Blend and pelletise” describes an ambition, not a manufacturing process

A physical process can produce a reasonably uniform compound fertiliser pellet. The components do not necessarily have to be chemically dissolved or reacted. But successful solids homogenisation requires deliberate engineering.

The biosolids and mineral inputs may need to be:

• reduced to suitable particle sizes;

• accurately dosed;

• mixed sufficiently to control local variation;

• conditioned to a suitable moisture and temperature;

• bound or agglomerated;

• formed into particles;

• dried or cured;

• cooled;

• screened;

• and tested before release.

The finished particles must then remain intact through conveying, bagging, storage, trucking, unloading and agricultural use.

The application identifies mixers, but does not provide the information needed to assess whether the mixing and forming system can produce the claimed product.

It does not establish:

• the physical form of the mineral fertiliser;

• the feed particle-size specifications;

• the separate duties of the two mixers;

• mixing times or control methods;

• the product-forming mechanism;

• binder or granulating-liquid requirements;

• formulation tolerances;

• pellet or granule structure;

• or the required degree of chemical uniformity.

A bulk recipe of approximately equal dry masses does not demonstrate that every finished particle—or every physical fraction of the finished product—contains approximately equal proportions.

What sort of particle is being proposed?

Several materially different products could all be described loosely as “blended and pelletised”. A compound pellet might contain finely divided biosolids and mineral fertiliser dispersed through one bound matrix. A coated granule might have a biosolids-rich core with mineral fertiliser concentrated in an outer layer. A layered agglomerate might develop different compositions through its radius or between particle sizes. A bulk blend might retain distinguishable biosolids-derived and mineral particles. A reaction granule might involve dissolution, hydrolysis, precipitation or other chemical treatment before final particle formation.

These are not cosmetic distinctions.

They determine what happens when particles crack, abrade, dissolve, screen differently or break during transport.

If a homogeneous compound pellet breaks cleanly, the fragments may remain reasonably representative of the original formulation. If a coated particle breaks, the coating and core may separate into chemically different fractions.

If the ingredients remain as discrete particles or poorly integrated agglomerates, mineral-rich and biosolids-rich material may behave differently during screening, storage and use. The application does not identify the intended particle architecture.

Screening creates separate streams

The application says the product will be screened for size consistency. The process diagram also depicts a screen separator, crusher and connected conveyors. That means classification and some form of reprocessing have at least been contemplated. But the relevant streams are not clearly identified or quantified.

The diagram does not establish:

• which stream is the correctly sized product;

• which stream is undersize;

• which is oversize;

• what material enters the crusher;

• where crushed material reports;

• whether undersize is recycled;

• whether fines are recycled or removed;

• whether any material leaves as reject;

• or how much material circulates internally.

The presence of a screen and crusher does not close the circuit. It merely confirms that distinct physical fractions may be produced. That makes their composition and destination important.

The missing circulating load

This is where my mining background became unexpectedly useful. A screened pelletising or granulation circuit can behave much like a closed crushing and classification circuit.

Fresh feed enters.

On-size product leaves.

Off-size material may be crushed, remixed or returned to the product-forming stage.

Some material may repeatedly fail to report to the acceptable product stream.

In mining, persistent oversize material circulating through a process is often called scats. The same basic problem can arise here. A large internal recycle load can increase:

• mixer, conveyor, screen and crusher duty;

• dust generation;

• equipment wear;

• power use;

• material residence time;

• storage requirements;

• and the amount of material exposed to repeated drying or handling.

The saleable-product rate does not necessarily describe the actual tonnage handled internally. The DA provides no quantified fresh-feed, product, recycle or reject balance for this circuit. It does not identify a one-pass product yield or normal and maximum recycle inventory. Nor does it clearly identify how material that cannot be technically or lawfully recycled indefinitely will be removed. The process needs a defined route for persistent oversize, contaminated material, nonconforming batches and other unrecoverable solids. That removal could be continuous, periodic or event-based.

But it must exist. Otherwise yesterday’s failed product simply becomes part of tomorrow’s feed.

Where is the product-release circuit?

Bagging and finished-product storage do not constitute a quality-control system. A manufacturing process needs to distinguish between:

• material still being processed;

• conforming product;

• material awaiting test results;

• material suitable for rework;

• and material that must be rejected.

That requires a defined product specification. The public application does not appear to provide specifications for matters such as:

• particle-size distribution;

• moisture;

• bulk density;

• crush strength;

• abrasion or durability;

• maximum fines;

• nutrient tolerances;

• variation between batches;

• variation between size fractions;

• storage stability;

• or contaminant compliance.

Nor is there a visible test–hold–release–reject–reprocess circuit. Without that system, it is difficult to determine:

• when material becomes finished product;

• how failed batches are identified;

• how much material may accumulate in quarantine;

• whether repeated reprocessing is permitted;

• or what happens to material that cannot be made compliant.

Those questions go beyond commercial product quality. They affect the amount of waste, dust, reprocessing, storage and transport generated by the facility.

The contaminant question follows the physical fractions

The proposed process includes mixing, screening, crushing and material recycling. Those operations can create distinct physical fractions. The DA provides no evidence demonstrating that nutrients, biosolids content and contaminants remain acceptably distributed between those fractions. That does not prove that PFAS, metals or microplastics will become enriched in fines, oversize or recycled material. It means the question is unanswered.

Metals may associate with different mineral, organic or ash-rich phases.

PFAS may be associated differently with organic solids, proteins, moisture and other material properties.

Microplastics are themselves discrete particles with varying sizes, densities and shapes.

If different screen or handling fractions contain different proportions of biosolids, mineral fertiliser, ash, coating or binder, their chemistry may also differ.

A bulk composite analysis could report an acceptable average while failing to describe:

• fines;

• crushed oversize;

• recycled material;

• dust-collection residues;

• or persistent rejects.

The required evidence is therefore not simply another average product assay. It is a material and constituent balance showing where each relevant component reports through the actual process.

The End of Waste pathway remains unclear

The project’s central claimed transformation is:

regulated biosolids → manufactured fertiliser resource

But that transition is not created by a label.

Under Queensland’s End of Waste framework, resource status depends on an applicable End of Waste Code or approval and compliance with its quality and use conditions. The public documents do not clearly establish:

• whether the existing Biosolids End of Waste Code covers the hybrid biosolids–mineral product;

• whether a project-specific approval is required;

• the exact point at which the material becomes a resource;

• the status of intermediate mixed material;

• the status of material sent through the screen or crusher;

• the status of failed batches;

• or the destination of material that cannot become compliant product.

Physical segregation would not automatically turn an entire product batch back into waste. But neither can every intermediate, rejected or reprocessed stream be assumed to retain resource status merely because it remains inside a facility intended to manufacture fertiliser.

The EoW pathway must follow the actual material—not the intended label.

ERA 7 makes the undefined process more important

The proposal includes ERA 7—Chemical Manufacturing.

Queensland’s regulatory definition is broad enough to include fertiliser manufacturing and the combining, processing or reacting of materials. That broad category does not define the actual plant. It does not tell the assessor whether the final process will involve:

• dry compression;

• extrusion;

• wet granulation;

• steam conditioning;

• coatings;

• liquid nutrient solutions;

• chemical binders;

• acids or alkalis;

• anti-caking agents;

• dust suppressants;

• or some other process aid.

Appendix 1 shows generic chemical and ammonia storage infrastructure. But the substances, quantities, capacities, functions and dosing points relevant to fertiliser manufacture are not defined. It would be an inference to assume that the depicted chemical tanks are used as binders, fertiliser additives or part of the product-forming process.

The proper conclusion is narrower and more serious:

The chemical and additive envelope associated with the product-forming component of ERA 7 has not been defined.

Different product-forming routes could materially affect:

• chemical inventories;

• tank and bunding requirements;

• dust and vapour sources;

• wastewater;

• washdown;

• residual chemicals;

• fire and incompatibility hazards;

• emissions;

• and off-specification material.

These are not vendor-selection details. They are part of the environmental impact envelope.

SARA has identified parts of the wider problem

SARA’s further-advice notice has already raised questions about matters including:

• waste types and variability;

• waste-acceptance criteria;

• rejected loads;

• residue and ash testing;

• storage of wet and processed materials;

• storage of fertiliser additives and finished product;

• fugitive emissions from drying, blending and conveying;

• ammonia, VOCs, odour and dust;

• PFAS in emissions and condensate;

• and PFAS monitoring in the final fertiliser and at application locations.

That confirms that these are not merely academic product-development concerns. They are matters relevant to the environmental assessment. But the central product-forming operation remains unresolved.

The notice does not appear to settle:

• what the pelletiser or granulator actually is;

• how the product is formed;

• what additives or chemicals it requires;

• how screen fractions are handled;

• what circulating load is expected;

• or how failed product is tested, quarantined, reprocessed or rejected.

Why this matters to planning

The issue is not whether every bolt, motor and pipe must be selected before approval. Detailed engineering can refine a process after approval. But the basic process must first be defined well enough for the assessor to understand:

• what development is being authorised;

• which substances may be used;

• what infrastructure is required;

• what emissions and wastes may arise;

• how failure is managed;

• and what limits need to be imposed.

Conditions can regulate a known process envelope. They can identify permitted feedstocks and additives, set maximum quantities, limit equipment and storage, define monitoring points, control emissions, restrict recycle inventories and require reject-management arrangements. They cannot meaningfully control an unidentified product-forming operation through a general instruction to design something compliant later. You cannot assess what has not been described. And you cannot meaningfully condition an operating envelope that has not been defined.

The central finding

Nothing in this analysis establishes that a durable, homogeneous biosolids–mineral fertiliser pellet cannot be manufactured. It probably can (but it may not be easy).

The issue is that the Glan Devon DA does not presently establish:

• which manufacturing method will be used;

• where the product-forming operation appears in the flowsheet;

• what additives and conditioners it requires and how they will be handled;

• how its classified and recycled streams are managed;

• how product conformity is tested;

• what happens when production fails;

• or how every resulting stream fits within the environmental and End of Waste frameworks.

Appendix 1 shows parts of a processing line. It does not show, define or close the process that makes the claimed product.

The entire facility is not a black box but The critical product-forming part of ERA 7 is.

Once that distinction is recognised, the omission no longer looks like unfinished equipment selection.

It looks like a missing process definition at the centre of the application.

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