Rules of Thumb in Biomass Fermentation TEAs. Part 1: Capex Big Picture

A few basic principles for calculating biomass fermentation capex can be useful shortcuts, allowing various stakeholders to quickly compare the costs of production for different technologies.

How to compare the Capex per production capacity of a facility?

• Capex mainly comprises equipment, building and installation costs

• Building and installation can be estimated via Lang factor (see below)

• Factories Capex per Capacity production can cost from $2,000 to $10,000 / ton-per-annum (tpa)

• Calculating this value for a new facility will give a point of reference

• A facility equipment includes fermentor and downstream processing (DSP) (e.g. centrifuges, filters, dryers)

A back-of-the-envelope calculation can tell you the Capex:

Eq. [1]

Capex = (fermentation volume x (unit fermentor cost + DSP unit cost)) x lang factor

• Unit fermentor cost can range from $2,000 /m3 to $15,000/ m3. A useful baseline value in single-cell protein (whole biomass) systems is around $10,000/m3. Hereafter, fermentor volume is always referring to working volume (which is about 80% of the total reactor volume). 

• The lang factor represents costs of installation and other items and ranges between 2 and 4. 

• DSP unit cost can be roughly estimated as a factor of the fermentor cost between $3,000 to $10,000 / m3 of fermentation volume.

For example for hypothetical Acme Bio:   

Capex = (fermentation volume x (unit fermentor cost + DSP unit cost )) x lang factor 

Capex =   (100 m3 x ($10,000/m3+ $15,000/m3 )) x 3

Capex = 100 x 25,000 x 3 = $7.5M

The ratio of unit fermentor cost / DSP unit cost is given as 0.67 here, and will vary depending on the relative complexity of the fermentation versus downstream processing.

The facility capacity in ton per annum (tpa) can be easily estimated:

Eq. [2]

Capacity = Vp x fermentor volume x uptime% x 8760 hr/y x retention%  x 1 ton / 1000 kg

Where Vp is volumetric productivity in units of cell dry weight kg/m3/hr. Vp is commonly used in continuous mode fermentation. For batch mode, Vp is equivalent to titre divided by batch duration. Vp mostly ranges from 1 to 5 kg/m3/hr on an industrial scale. Values above this number are possible but unlikely in scaled up systems. Retention is the amount of dry product retained after DSP relative to dry biomass output from the fermentor, which can be ~60% for food and 90% for feed. Uptime is the hours the fermentor is running per year considering time needed for cleaning and resets which ranges from 75% to 95%, and 8760 is the hours in a years.

Example for Acme Bio.

Capacity = 3 kg/m3/y x 100 m3 x  7900 hr/y x 90%  x 1 ton / 1000 kg

 Capacity = 2370 tpa = 2.4 ktpa

Thus the example Acme Bio has apex / capacity of $ 7.5 M / 2.4 ktpa = $3125 / tpa

The following graph shows how the Capex per Capacity varies with Vp.

Unit Capex of fermentor vs production capacity

Lets compare this to some real world data.

Table highlights the $ per m3 of total facility capacity for the real life companies

Company	Product	Scale m3	Capacity ktpa	Capex adjusted, M$ (2025)	$/m3 total facility	$/tpa	$/m3/month
ICI ref	feed	1,500	50	590	395,000	12,000	1,600
Quorn ref	food	350	12	260	734,000	21,000	3,100
Solar Foods ref*	food	2000	15	148	74,000	9,000	308
Enifer ref	food	150	3	34	227,000	11,000	945

*est. Note Vp is 1 to 1.5 kg/m3/hr, another ref gives 317M Capex

Based on the above data, we can estimate the Vp for ICI:

Vp = Capacity  / (fermentor volume x 90% uptime x 8760 hr/y x retention)

Vp = 50,000 tons/y / (1500 m3 x 90% x 8760 hr/y x 90% x 1 ton / 1000 kg)  

Vp = 50,000 / 10,643 = 4.7 kg / m3 / h

Furthermore, if we assume a DSP cost of $15 000/m3 scale, lang factor 3.5, we can estimate the Capex.

Capex = (fermentation volume x (unit fermentor cost + DSP unit cost)) x lang factor 

Capex = $ 590 M

Capacity = Vp x fermentor volume x 90% uptime x 8760 hr/y x retention

Assuming Lang factor at 3.5, and DSP unit cost at 15000 $/m3:

Unit fermentor cost = Capex/Lang factor/fermentation volume - DSP unit cost =

= 100 000 $/m3

This indicates that for ICI, unit DSP or fermentor costs or Lang were higher than usual.

The $/m3/month values in the table can be compared to typical CMOs costs for users. CMO user costs are in the order of magnitude of $4000 /m3 / month for biomass fermentation and $6000 / m3/ month for precision fermentation. Thus, the use of CMOs has a significant premium, as a tradeoff for not needing upfront capital expenditure from the user.

Would you like us to share Rules of Thumb on the costs of equipment in downstream processing (e.g centrifuges, spray dryers, rotary drum dryers) next ?

For DSP, normalised unit costs can be used as heuristics for TEAs. Cleary selection of appropriate equipment is key.

Graph showing a relationship between scale of centrifuge and its cost. m3 here refers to the input flow to the centrifuge.