Token Hierarchy

The MassID → Certificate → Credit lifecycle and relationships in the Carrot token system.

From physical waste to tradeable credits

The Carrot Network transforms verified recycling work into environmental assets through a layered token system. Each layer builds on the one before it, creating an unbreakable chain of evidence from physical waste to purchasable credits.

The hierarchy has five layers:

MassID — A verified batch of waste (material type, weight, chain of custody from Waste Generator to Recycler). Implemented as a soulbound NFT (ERC-721).
Certificate (GasID or RecycledID) — Represents a verified environmental outcome when MassIDs pass methodology verification at an accredited facility. Implemented as a soulbound NFT.
Credit — A tradeable unit of verified environmental impact where 1 credit = 1 metric ton. Minted automatically when certificates are created, in a matching amount. Each methodology issues credits under its own on-chain symbol (e.g. BOLD Recycling issues C-BIOW, BOLD Carbon (CH₄) issues C-CARB.CH4 for methane). Implemented as a fungible ERC-20 token — issued and transacted in any amount, including fractions.
CreditPurchaseReceipt — A soulbound NFT minted when credits are purchased. Provides immutable proof that the transaction occurred.
CreditRetirementReceipt — A soulbound NFT minted when credits are retired. Provides permanent proof that the environmental offset has been claimed.

How the layers connect

Each layer in the hierarchy references the one below it, creating full traceability:

Layer	Token	Standard	Transferable?	What it proves
Tracking	MassID	ERC-721	No (soulbound)	Physical waste was collected, sorted, and transported
Certification	GasID / RecycledID	ERC-721	No (soulbound)	Environmental impact was verified by dMRV
Tokenization	TRC / TCC (e.g. `C-BIOW`, `C-CARB.CH4`)	ERC-20	Yes (fungible)	1 token = 1 metric ton of verified impact
Purchase	`CreditPurchaseReceipt`	ERC-721	No (soulbound)	Credits were purchased with USDC payment
Retirement	`CreditRetirementReceipt`	ERC-721	No (soulbound)	Credits were permanently burned and claimed

All tokens are deployed on-chain.

Why soulbound?

All NFTs in the Carrot token system are soulbound — they cannot be transferred between wallets. This is a deliberate design choice:

Tamper-proof audit trail — Since tokens cannot be moved, the provenance chain from waste to credit is permanent and verifiable.
No speculative trading — MassIDs and certificates represent verified physical work, not speculative assets. Preventing transfers ensures they remain tied to their original context.
Custody via the Vault — All soulbound NFTs are held by the Vault smart contract, which manages custody on behalf of the network.

Only credits (ERC-20 tokens) are transferable, because they are the layer designed for market activity — purchasing, holding, and retiring environmental offsets.

Two credit paths

The hierarchy produces two independent credit types, each representing a different environmental outcome. Each path is driven by a different methodology framework that processes MassIDs independently:

Recycling path

MassID → RecycledID → Tokenized Recycling Credit (TRC)

Proves that waste material was physically recycled. Tokenized Recycling Credits (TRC) use a unit of 1 metric ton of certified recycled material and are minted proportionally to each certificate's verified quantity. The BOLD Recycling methodology issues TRCs with the on-chain symbol C-BIOW; other recycling methodologies may use different symbols. TRCs are material-specific — glass TRCs represent recycled glass, plastic TRCs represent recycled plastic.

Carbon path

MassID → GasID → Tokenized Carbon Credit (TCC)

Proves that greenhouse gas emissions were avoided by recycling instead of landfilling. Tokenized Carbon Credits (TCC) use a unit of 1 metric ton of CO₂-equivalent avoided and are minted proportionally to each GasID certificate's verified quantity. The BOLD Carbon (CH₄) methodology issues TCCs with the on-chain symbol C-CARB.CH4 (methane); other carbon methodologies may use different symbols. A carbon methodology calculates the emissions difference between the recycling scenario and the baseline landfill scenario directly from the MassID data.

The same MassID can back both a RecycledID and a GasID, since each certificate is issued by an independent methodology framework — a recycling methodology verifies the physical recycling outcome, while a carbon methodology quantifies the emissions avoided.

End-to-end traceability

The token hierarchy enables full traceability from retired credit back to physical waste:

Credit retirement → CreditRetirementReceipt → Credit (e.g. C-BIOW, C-CARB.CH4) → Certificate (RecycledID or GasID) → MassID → Physical waste batch with chain of custody

This traceability is publicly verifiable through the Carrot Explorer and any blockchain block explorer such as PolygonScan. Any auditor, regulator, or interested party can trace a retired credit back through every layer to the specific waste batches and recycling participants that produced it.

Learn about certificates · Learn about credits · Learn about purchasing · Learn about retirement