"Less than 2% of the nutrients in urban food waste are currently recovered for compost or transformed into useful products — while farms on a city's outskirts desperately need affordable, sustainable fertilizer."

— Yara International & Ellen MacArthur Foundation, Nutrient Upcycling Alliance, 2020
The problem

A third of all food produced never reaches a plate

Globally, 50–70% of household solid waste is organic kitchen material — vegetable trimmings, fruit peels, eggshells, coffee grounds, tea leaves. Instead of being processed, the vast majority ends up in landfills where it decomposes anaerobically, releasing methane — a greenhouse gas 28× more potent than CO₂ over a century. Meanwhile, urban farms like Mareso's rooftop project need exactly what that waste contains: stable, affordable, organic nutrition for the soil.

⅓
Of global food produced never reaches the table
25%
Of landfill space occupied by food waste globally
<2%
Of urban food-waste nutrients currently recovered as fertilizer
The science of kitchen waste

What's actually in that bag of scraps?

Research published in the International Journal of Science and Research Archive (Mahmud & Omar, 2025) confirms that common kitchen discards carry a surprisingly complete nutrient profile — enough to meaningfully replace synthetic fertilizers in a rooftop growing system.

🍌
K: 0.7–0.8%
Banana & fruit peels
Highest in potassium — supports flowering and fruiting. Decomposes quickly; ideal for fast-turn compost batches.
🥕
N: 0.3–0.6%
Vegetable scraps
Rich in nitrogen, phosphorus and magnesium. Controls soil pH and improves microbial activity — essential for leafy growth.
🥚
Ca: 30–40%
Eggshells
An exceptional calcium source. Balances soil pH, strengthens root structure. Crush before adding to speed absorption.
☕
N: 3–5%
Coffee grounds & tea leaves
Among the highest nitrogen concentrations of any kitchen waste. Stimulates beneficial soil microbes and improves aeration.
Relative nitrogen content — common kitchen waste materials
% N by fresh weight basis · Source: Mahmud & Omar, IJSRA 2025; values represent mid-range of reported intervals
High nitrogen (≥1%) Mid-range (0.3–1%) Low (<0.3%)
Nitrogen: Tea leaves 4%, Rice husk 0.75%, Vegetables 0.45%, Papaya 0.45%, Coffee 0.35%, Eggshells 0.2%, Banana 0.11%
The solution

Mareso's closed-loop rooftop system

At the Mareso Regenerative Rooftop Farm, food waste never leaves the system. Organic scraps from meals are collected and processed on-site at the dedicated compost zone (Zone 5 in the farm layout), producing organic fertilizer that feeds back into the multi-layer food forest (Zone A) and the climate-controlled growing zone (Zone B) — closing the loop between the dining table and the harvest.

This mirrors the ambition of Yara International's Nutrient Upcycling Alliance in London — a partnership between Yara and Veolia that has demonstrated city food waste can supply 350,000 hectares of peri-urban farmland with certified organic fertilizer pellets. Mareso brings this circular logic down to the household and neighbourhood scale.

MRS Regenerative Rooftop Farm — aerial layout showing Zone A Food Forest, Zone B Climate-Controlled Growing, compost zone, solar panels and water harvesting
MRS Regenerative Rooftop Farm — Zone A (Food Forest · Open) · Zone B (Climate-Controlled Growing) · Zone 5 (Compost) · Solar & Water Harvesting
Methods

Three composting methods for your rooftop

  • 01

    Traditional composting — 3 to 6 months

    Mix organic scraps (peels, vegetables, eggshells) with dry carbon material (dry leaves, sawdust, shredded paper) in a ~25:1 C:N ratio. Turn weekly to aerate. Produces odour-free compost well-suited to the enclosed Zone 5 bay in Mareso's rooftop layout. Best for steady, high-volume output across seasons.

    🥦
    Kitchen
    scraps
    Peels, veg,
    eggshells
    +
    🍂
    Dry carbon
    material
    Leaves,
    sawdust
    →
    🔄
    Mix & turn
    weekly
    25:1 C:N
    ratio
    →
    🌱
    Rich
    compost
    3–6 months
  • 02

    Vermicomposting with red wigglers — 4 to 8 weeks

    Eisenia fetida worms consume kitchen scraps and excrete castings — gram-for-gram the most nutrient-dense organic amendment available. No odour, compact footprint, fast turnaround. The castings dramatically improve soil water-retention and microbial life, making them ideal for container-grown rooftop beds.

    🥬
    Kitchen
    scraps
    Veg, fruit,
    coffee
    →
    🪱
    Red wigglers
    digest
    Eisenia fetida
    in worm bin
    →
    💧
    Worm
    castings
    4–8 weeks
    →
    🌿
    Richer soil
    microbes
    No odour
    compact
    Most nutrient-dense organic amendment available — ideal for container beds on rooftops
  • 03

    Black Soldier Fly (BSF) — 2 to 4 weeks

    BSF larvae decompose organic waste at extraordinary speed and produce high-grade compost. The harvested larvae are 40–44% protein — a secondary output usable as aquaculture supplement or poultry feed. Currently being commercialised by Vietnamese biotech startups and under active research at the Institute of Tropical Biology, HCMC.

    🗑️
    Organic
    waste
    Any kitchen
    scraps
    →
    🦟
    BSF larvae
    decompose
    Fastest
    method
    →
    🌱
    High-grade compost
    For soil & beds
    🐟
    Larvae biomass
    40–44% protein · aquaculture feed
    Fastest
    2–4
    weeks
    Dual-output system: compost for the farm + high-protein biomass for aquaculture
Comparison

Organic compost vs. chemical fertilizer

Evidence from lab-verified field trials — including MicrobeBio, BioFerti, Waypoint Analytical (Report #17-333-0009) and Rock River Laboratory — consistently shows organic bio-fertilizers outperform chemical fertilizers on every long-term metric that matters for a living rooftop ecosystem.

Chemical (NPK / Urea)
Fast-acting but short-lived
Depletes soil nutrients over time
Kills beneficial soil microbes
High fossil fuel cost to manufacture
Runoff pollutes local waterways
Price tied to global commodity markets
Organic compost from kitchen waste
Slow-release, season-long nutrition
Regenerates and builds soil structure
Feeds symbiotic microbial ecosystem
Sequesters carbon in the soil
Enhances soil water-retention capacity
Near-zero cost from kitchen waste
Real-world progress

Where does the world stand?

A landmark reference: Massachusetts (USA) mandated organic waste diversion for any business generating ≥1 ton/week from 2014. The law generated 900+ jobs and added $77 million to state GDP. South Korea collects a pay-by-weight fee on landfilled food waste, driving 70%+ diversion. Vietnam has no equivalent law yet, but momentum is building from the ground up.

Netherlands
85%
Japan
78%
South Korea
70%
USA (mandated states)
42%
SE Asia average
~12%
% of urban organic waste managed through composting, biogas, or recovery systems

Vietnam — current landscape 2025

No mandatory organic-waste diversion law exists yet, but dozens of urban farm and composting initiatives are active across HCMC, Hanoi and Da Lat. District 7 and Thu Duc pilot programmes distribute compost bins to households. Several premium residential buildings now operate centralised on-site compost facilities. BSF commercialisation is under active research at the Institute of Tropical Biology. The Mareso Rooftop Farm is among the first projects in Vietnam to integrate composting directly into a closed-loop rooftop growing system — making it a regional reference model.

Key takeaways

What this means for you

  • A 20-litre bin is enough to start

    A household of four generates 0.5–1 kg of organic kitchen waste per day. After 6–8 weeks of vermicomposting, that's enough fertilizer to sustain 5–8 m² of rooftop growing area — no large capital investment required to begin.

  • C:N ratio is the single most important technical variable

    Kitchen scraps are nitrogen-rich (green). Balance with carbon-rich (brown) materials: dry leaves, sawdust, shredded paper. Target a 25:1 C:N ratio for fast, odour-free decomposition. Getting this wrong is the number one reason home composting fails.

  • Avoid meat, dairy and cooking oils

    These decompose anaerobically, generating odour and attracting pests. For a rooftop or balcony compost system, restrict inputs to vegetables, fruit peels, eggshells, coffee grounds and tea leaves — consistently high success rate, minimal odour.

  • This is an economic model, not just an environmental gesture

    Self-produced organic fertilizer can cut 60–80% of input costs for a rooftop farm. At commercial scale — as demonstrated by Yara International's Nutrient Upcycling Alliance in London — city food waste can supply 350,000 ha of peri-urban farmland with certified organic fertilizer pellets, creating jobs and new supply chains throughout.