Digester Mixing on Track for Californian AD Facility

Biogas Energy have built an anaerobic digestion (AD) facility at North State Rendering in Oroville, California that is already paying dividends, with uninterrupted biogas generating electricity, fuelling trucks and running boilers.

“For a rendering plant, biogas is a natural fit”, says Brian Gannon of Biogas Energy. “North State Rendering were looking for ways to cut costs, secure new waste supply contracts, and improve wastewater treatment, so creating their own on-site biogas facility was a wise move.  Modifying the anaerobic digestion process to integrate with a rendering plant took some fine tuning, including a very positive modification to the digester’s mixing system, but now, we can see how we got it right”.

From the reception area, the material is pumped into two tanks (40’ diameter by 24’ high), where the first acid-forming phase of the biogas production process takes place.

These heated tanks contain bacteria that break down the material and prepare it for the main digester tank, which stands 64’ tall. When the material is ready, it is pumped into the main digester where biogas-producing bacteria get to work. 

Brian Gannon continued: “We had been using submersible propeller mixers inside our main digester, but with our re-design of the tank, we switched to a new system that meets all of our needs. One of the main issues with submersible digester mixing systems is that the equipment is inside the tank, which from a maintenance point of view is a nightmare. The downtime caused by having to open the digester to lift the mixers out for repairs and maintenance caused serious process interruptions and safety issues.

“We now have a Landia digester mixing system, which is mounted externally, so maintenance is much easier. Even during commissioning when the AD biology was at a delicate stage, we were able to carry out some tweaks without any interruption whatsoever to the biogas production process. With submersible mixers we would have had to start over again, which would have been very expensive and used up a ton of manpower.

“The anaerobic digestion facility is designed to process a very wide range of feedstock”, he said, “so its pumps and mixers have to cope. The Landia chopper pumps, which form part of the GasMix system, are absolute troopers. They just keep on working. We wouldn’t be achieving what we are now without them”.

Comprising two 30-HP chopper pumps and a self-aspirating system that reduces solids to produce more methane in a much shorter time period, Landia’s GasMix (designed specifically for AD/biogas) is easy to regulate and also offers significant energy savings because it only has to run for a maximum of 30 per cent of the installed capacity.

“We generate enough electricity to power the entire North State Rendering plant,” added Brian.  “Heat from the generator is also used to heat the digesters, so we’re able to optimise energy efficiency”.

Brian Gannon concluded:  “For Biogas Energy, our experience at North State Rendering and the introduction of Landia’s GasMix digester mixing system means that we can help our clients generate renewable energy with a system that maximises production while facilitating operations and maintenance”.