# How is the carbon footprint of a fermentation-made API different from a synthetic one?

Canonical: https://senseible.earth/answers/fermentation-api-carbon-footprint

A fermentation API's footprint is driven by utilities: electricity for aeration and agitation, steam for sterilisation, and chilling, run for days per batch. A synthetic API's footprint is driven more by solvents, reagents and starting materials. Fermentation also releases biogenic CO2 from the microbes, which is reported separately.

## Where the emissions sit in a fermentation route

- Aeration and agitation: air compressors or blowers and fermenter agitators run around the clock for the whole batch. This is often the largest electricity load.
- Sterilisation: steam to sterilise the medium, fermenters and lines before each batch, from a coal, furnace oil, PNG or biomass boiler.
- Cooling: chillers and cooling towers remove the heat the microbes give off.
- Downstream processing: filtration, extraction, ion exchange, crystallisation and drying. Solvent use here is real but usually smaller per kg than in multi-step synthesis.
- Media: sugar or glucose, soybean meal, corn steep liquor and other nutrients, each with an agricultural footprint.

## Biogenic CO2 from the fermenter

Microbes convert sugar to biomass, product and CO2. The CO2 in the exhaust air comes from plant-based carbon, so it is biogenic. Report it as a separate figure, outside the fossil total, and do not leave it out silently.

The fossil carbon in the medium, if any, and the energy used to run the fermenter stay in the main result.

## Waste is a bigger line than in synthesis

Fermentation leaves large volumes of spent broth and mycelium. If they go to anaerobic treatment, methane can escape; if they go to land or a biogas plant, say so. Effluent treatment electricity also scales with broth volume.

Include the route you actually use and keep the disposal manifests or contracts as evidence.

## Why the PLI scheme makes this question common

The Department of Pharmaceuticals' PLI scheme for KSMs, drug intermediates and APIs (2020) has a separate category for fermentation-based products such as Penicillin G. New domestic plants supplying formulators that answer to EU buyers get asked for a per kg footprint early. The method is the same cradle-to-gate approach under ISO 14067 or the GHG Protocol Product Standard; what changes is which lines dominate.

## Illustrative fermentation campaign of 1,000 kg API

- Electricity for aeration, agitation, chilling and recovery: 3,00,000 kWh x 0.710 = 2,13,000 kg CO2
- Coal for sterilisation and process steam: 1,50,000 kg x 2.42 = 3,63,000 kg CO2
- Energy per kg API: (2,13,000 + 3,63,000) / 1,000 = 576 kg CO2
- Add media, solvents and waste treatment with their own factors per kg
- Fermenter exhaust CO2 from sugar: reported as a separate biogenic figure

Quantities are illustrative assumptions for one campaign. Allocate plant utilities to the campaign with a documented key such as fermenter hours.

## What Senseible does here

Senseible reads electricity bills and boiler fuel invoices and applies 0.710 kg CO2 per kWh and IPCC 2006 fuel factors, giving the utility totals that dominate a fermentation route. Media and solvent purchases go to the Scope 3 supplier evidence trail with their quantities.

- [API carbon footprint per kg (synthetic)](https://senseible.earth/answers/api-carbon-footprint-per-kg)
- [Allocating factory electricity to products](https://senseible.earth/answers/how-to-allocate-factory-electricity-to-products)
- [Product carbon footprint calculator](https://senseible.earth/calculators/product-carbon-footprint)

Sources: [ISO 14067:2018, Carbon footprint of products](https://www.iso.org), [GHG Protocol Product Life Cycle Accounting and Reporting Standard (2011)](https://ghgprotocol.org/standards), [2006 IPCC Guidelines, Volume 2 Energy (fuel CO2 defaults)](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html)

Last reviewed 2026-10-18.