Case Study: H₂S Cut from 172 ppm to 47 ppm at Calgren Renewable Fuels, Pixley, California
At Calgren Renewable Fuels in Pixley, California — a renewable fuels facility in the Central Valley — ON2 containerized oxygen plants supply oxygen for biological H₂S removal. The result is not a modeled projection — it's read directly off the facility's field gas analyzer: hydrogen sulfide down from 172 ppm to 47 ppm, roughly a 73% reduction, with the process running continuously. The photos and analyzer readings from this installation are published on our renewables page.
The result: 172 ppm to 47 ppm, on the customer's own analyzer
The most credible number in any case study is the one the customer measures themselves. At this facility, the field gas analyzer showed H₂S at 172 ppm before treatment and 47 ppm with ON2 oxygen injection supporting biological desulfurization — a reduction of roughly 73%. No chemical dosing, no scavenger media, no consumable purchases: the H₂S is removed biologically, with controlled oxygen from an on-site ON2 plant as the only input.
About the facility: one of California's most integrated dairy RNG systems
Calgren operates one of the most integrated dairy digester / renewable natural gas systems in California, centered at its Pixley campus in Tulare County. Biogas from a cluster of nearly 20 dairy manure digesters at local family dairies is gathered by pipeline to Calgren's central upgrading facility, cleaned to pipeline quality, and injected into the SoCalGas utility system as transportation fuel — Calgren reports production of more than 1,200,000 MMBtu of RNG per year. This is not a pilot: it's a mature, expanding operation where gas quality directly determines revenue, and where ON2 oxygen supports the desulfurization step.
The installation: containers beside the process towers, no building
The ON2 ROCS containerized plants sit directly beside the facility's process towers — outdoors, on a pad, with no dedicated building. Each container arrives as a complete plug-and-play oxygen plant and is supported by ON2 directly, with real-time in-container monitoring visible to the operator. Because the plants are modular, capacity was matched to the facility's gas volume and can be expanded if the process grows.
Specifications that match biogas requirements
ON2 containerized oxygen plants deliver 90–95% oxygen purity — the range typically specified for biological desulfurization — with delivery pressure adjustable from 0 to 50 psi to match your digester headspace or injection point. The insulated, climate-controlled container is engineered for year-round outdoor operation from −50°C to +50°C, proven in deployments from Yellowknife, Canada to New Delhi, India.
Buy it or lease-to-own
ON2 offers direct purchase or lease-to-own over 5 or 7 years, so the oxygen plant can be matched to your project's capital plan instead of the other way around. Either way you deal with a single manufacturer — we understand your project, design the system, then build, ship, and commission it. ON2 has been building oxygen systems since 1984, with every system manufactured in the USA.
About this case study
This page is published by ON2 Systems Inc. for informational purposes. The H₂S measurements shown were taken from field gas analyzer readings at the installation site. References to Calgren Renewable Fuels describe an actual installation and publicly reported information about the facility; they do not constitute an endorsement, sponsorship, or testimonial by Calgren Renewable Fuels. All company names and trademarks are the property of their respective owners.
What's included
- 90–95% oxygen purity for biological desulfurization
- Delivery pressure adjustable from 0 to 50 psi
- Proven outdoor operation from −50°C to +50°C
- Plug-and-play containerized plant — no building required
- Runs on demand; standby when oxygen isn't needed
- Direct purchase or lease-to-own over 5 or 7 years
Frequently asked questions
How much did the oxygen plant reduce H₂S at the California facility?
The facility's own field gas analyzer showed H₂S reduced from 172 ppm to 47 ppm — roughly a 73% reduction — with ON2 on-site oxygen supporting biological desulfurization, and no chemical dosing or scavenger media.
What oxygen purity do ON2 plants deliver for biogas desulfurization?
ON2 containerized oxygen plants deliver 90–95% oxygen purity, the range typically specified for biological hydrogen sulfide removal in anaerobic digesters. Purity and flow are confirmed against your gas volume and composition during quoting.
Can we lease the oxygen plant instead of buying it?
Yes. ON2 offers lease-to-own over 5 or 7 years alongside direct purchase, so you can spread the cost into predictable payments and keep capital available for the rest of the project.
Want the same reading on your analyzer?
Send us your biogas flow and H₂S concentration and we'll size an on-site oxygen plant for your facility — purchase or lease-to-own.