Overview

Tunisia is the world’s second largest olive oil producer. Pressing the crop leaves behind roughly 254,000 tonnes of solid residue and 950,000 cubic metres of olive mill wastewater a year, most of it left in open evaporation pools where it seeps into soil and groundwater. Regenerative SARL is building a facility at Nabeul to convert that residue, along with manure and other organic waste, into biochar, compost, biostimulants and biogas.

The Subnational Climate Fund (SCF) is providing technical assistance, to the project. SCF first commissioned a pre-feasibility study, now complete, which confirmed that stable biochar can be produced from olive mill residue and produced the first measured estimate of its carbon removal potential. In July 2026 SCF approved a second package covering a feasibility study and an environmental and social study. The project remains at pre-feasibility stage and no investment decision has been taken.

The Challenge

Olive mill wastewater, known locally as margine, is rich in polyphenols and toxic if untreated. The prevailing practice is to leave it in open pools to evaporate. Tunisia generates a further 3.5 million tonnes of agricultural waste a year, much of it dumped or burned in the open, contributing to soil degradation, water contamination and biodiversity loss. Agricultural emissions in Tunisia were around 4,597 ktCO2e in 2010 and are projected to reach 6,053 ktCO2e by 2030.

The same sector is also running short of soil. Heavy reliance on synthetic fertiliser has depleted microbial life and soil structure, leaving crops more exposed to drought and erosion. Converting the waste into soil amendments addresses both problems at once, but Tunisia has no operational national standard for biochar application, no domestic carbon sequestration methodology and no mandatory treatment requirement for olive mill wastewater. A project attempting this has to build its own compliance case.

Technical Assistance

The SCF Technical Assistance Facility, led by the International Union for Conservation of Nature (IUCN) in collaboration with Catalytic Finance Foundation and Gold Standard, has supported the project in two stages.

Stage 1: Pre-feasibility study

Approved in May 2025 to test whether olive mill residue could be converted into a usable biochar. What it found:

• Pyrolysis trials produced stable biochar from margine residue, reproducibly at around 550 degrees Celsius with a 30% yield.
• The material is suitable as a soil amendment, with stability indicators inside international certification thresholds, though further optimisation is recommended to maximise carbon permanence.
• The product pathway is compatible with Tunisian agricultural regulation, and alignment with international standards offers a route towards certification.
• A preliminary cradle-to-gate life cycle assessment put net carbon storage at approximately 393 tCO2e a year from around 600 tonnes of biochar at planned scale. The feedstock already identified in the region offers a clear pathway to scale, with a potential of up to 20,000 tonnes of biochar and carbon removal potential increasing proportionally

Stage 2: Feasibility study

Approved with an affordability analysis added and broadened value-chain scope. Which pyrolysis configuration suits the feedstock, and what that does to capital and operating assumptions.

• How the wider value chain holds together, from feedstock sourcing through processing to end use.
• Who the customers are, what they will pay, and whether they will commit in writing.
• Whether the products are affordable to the farmers they are aimed at, and at what price point adoption breaks down.
• How the biochar, compost and biostimulants actually perform in Tunisian field conditions, and what that is worth to a farmer.

Stage 2: Environmental and social study

Study running alongside the feasibility study:

• Whether the project is ready for certification under the Puro.earth biochar methodology and the World Biochar Certificate, and where the gaps are.
• Whether feedstock sourcing, production processes and biochar quality controls stand up to scrutiny.
• Whether the carbon removal calculations are robust enough to support a certification claim.
• Which environmental, social, health and safety risks could affect implementation, certification or investment readiness.
• Whether monitoring, traceability and management systems are adequate, and what corrective action is needed.

Neither study replaces the full environmental and social impact assessment required before any investment decision.

There can be no guarantee that the investment will be completed on the terms described or implied above, that SCF will be able to successfully invest in such project or that impact targets will be achieved.