WasteChain

Inspiration

India's informal waste economy moves an estimated 60% of all recycled material through ragpickers, kabadiwalas, and small aggregators — yet none of it shows up in official EPR (Extended Producer Responsibility) records. Producers pay for "verified recycling" on the basis of trust, not data. The result: well-documented fraud (weight shaving, ghost manifests, rebagging) and zero credit flowing back to the people doing the actual work.

We wanted to know: what if every kilogram of waste came with a tamper-evident receipt — from the moment a ragpicker picked it up to the moment a recycler melted it down?

What it does

WasteChain is a real-time traceability network for informal recycling.

• SHA-256 hash-chained ledger — every pickup, handoff, weighing, and recovery writes a record whose hash includes the previous record's hash. Change one row and every row downstream breaks.
• Multi-stage flow tracking — Stage 1 (ragpicker recovery) → Stage 2 (truck/door pickup) → Stage 3 (transfer-station weighing) → Stage 4 (recycler handoff). Every stage carries GPS, photo, and weight.
• 5-pattern anomaly engine — automatically detects REBAG_SUSPICION, WEIGHT_SHAVING, TEMPORAL_INCONSISTENCY, DENSITY_VIOLATION, and REPUTATION_FARMING.
• Multi-tenant org tree — Zone → Ward, ZP → Taluk → GP. Arbitrary nesting for any urban or rural admin structure.
• EPR carbon impact — every verified recovery is converted to CO₂e avoided using PWM 2022 emission factors, producing audit-ready credit claims.
• Real QR + GPS + photo capture — no mock data; the workflow page fires real API calls against a running Postgres-backed FastAPI service.

How we built it

• Backend: FastAPI + SQLAlchemy 2.0 + Pydantic v2, deployed on Render with free Postgres
• Frontend: React 18 + Vite + TypeScript + Tailwind + Leaflet, deployed on Vercel
• Hash chain: custom Python service that hashes the canonical JSON of each record + previous_hash. A ChainState singleton handles backdated / offline-synced writes deterministically.
• QR: qrcode (generate) + html5-qrcode (scan) — works on any modern mobile browser over HTTPS
• Maps: Leaflet + OpenStreetMap tiles
• Anomaly engine: pure-SQL temporal queries + Python heuristics, no ML required (judges can read the code in 5 minutes)

Challenges we ran into

• Hash-chain integrity across backdated seed inserts — solved with a ChainState singleton that lets us inject historical data without breaking ordering.
• Postgres vs SQLite drift in production — SQLite tolerated a circular foreign key between batches and ragpicker_recoveries; Postgres rejected it. Fixed with use_alter=True plus a schema-nuke fallback in the seed routine.
• Leaflet panes leaking through React modals — Leaflet uses z-index 400+ on its own panes. Fixed with a global override and bumping every modal to z-1000.
• Render free tier cold start (~30-50s) after 15 minutes idle — mitigated with a /healthz warm-up before demos.
• Multi-tenant org tree — needed arbitrary nesting depth (Zone→Ward and ZP→Taluk→GP behave differently). Solved with a self-referential parent_id and a recursive CTE for the org explorer.

Accomplishments we're proud of

• Built an end-to-end production-deployed system in a hackathon — not a Figma demo.
• The hash chain genuinely works: tamper any row in the DB and the verifier flags the exact break point.
• 7 deployed organizations, 25+ users, real GPS streaming, real photo hashing, real QR scanning — every button on the live workflow page hits the real backend.
• Multilingual UI (English / Hindi / Kannada) — informal-economy users don't all speak English.

What we learned

• Trust isn't a feature you add at the end. It has to be in the schema from row one.
• Postgres surfaces every modeling sin SQLite forgives. Test on the production DB engine from day one.
• The hardest part of waste traceability isn't the cryptography — it's getting the data into the chain in the first place. That's why our UX is one-tap for every stage.

What's next

• Mobile app wrapping the PWA for offline-first capture in low-connectivity rural areas
• Government EPR portal integration (one API call submits a verified manifest)
• Reputation-staked microcredit for ragpickers, using on-chain recovery volume as the credit score

Built With

• fastapi
• github
• html5-qrcode
• jwt
• leaflet.js
• openstreetmap
• postgresql
• pydantic
• python
• qrcode
• react
• render
• sha-256
• sqlalchemy
• tailwindcss
• typescript
• vercel
• vite