Sparta’s Biogas Production Soars with New Digester Mixing System

A Wisconsin wastewater treatment plant has seen a 25% increase in biogas production since installing Landia's innovative GasMix system.

In Sparta, which is situated midway between Milwaukee and Minneapolis, a large-scale improvement at the wastewater treatment plant (WWTP) anaerobic digestion (AD) process greatly increased efficiency.

Two digesters with capacities of 334,000 gallons (1,264m³) and 183,000 gallons (693m³) respectively formerly limited biogas production due to rags, grit and debris buildup.

That was resolved with the integration of Landia's GasMix system, now offering full mixing of the tanks' contents. From a solid and dependable Landia Chopper Pump—developed in 1950 and strategically placed venturi nozzles, all mechanical components are externally accessible, simplifying maintenance and reducing downtime.

“A long time coming but worth the wait“
Ed Hanson, Wastewater Treatment Plant Manager for Sparta, had to say:
“Our old, straightforward mix system only blew air up in the digesters that wasn't very efficient. And we couldn't get to it to do repairs or maintenance without draining down the tanks. This will put you offline for a while that nobody wants when we are trying to produce biogas.“.

In the end, the old mixing setup was struggling; merely delivering some modest recirculation with very little actual mixing taking place. Once it was time to drain down the first digester and install the Landia GasMix we found an immense quantity of debris within.

Sparta's WWTP, which was commissioned in the 1950s, is serving 10,000 individuals in the ‘Bicycling Capital of America'. The facility treats effluent from a big dairy, large food processor, landfill leachate and haulier septic waste. Minimal pre-treatment and screening have not hindered the plant from having greatly improved mixing capabilities.

A close fit – slick installation

“Installation of the Landia GasMix was a breeze,” added Hanson. “Landia were present to help at each stage especially as this was a close and tricky challenge with little scope for the new mixing arrangement. We had to move some of our recirculation pumps.

When we installed the new system, we could see right away that the Landia GasMix created a lot of turbulence and worked very well scavenging off the top of the digester. Everything went according to plan so we proceeded half a year later and fitted a second Landia GasMix on our second digester. 

Although it was a challenge with the space constraints we have on this part of the plant everything went together and the new blending system has been running flawlessly with no issues at all.”

Increased methane production and efficiency

Heat generated as a result of the AD process is now used to generate the ideal digester temperatures, and the gas-solids mixing by GasMix system enhances volatile solids destruction and generates biogas.

“We've certainly seen that our gas bills aren't as extreme as they were last year and we're much more environmentally friendly now,” Hanson said. “We have very long cold winters down here so with the old mixing system you could see everything drop back to zero as the temperature dropped but since our upgrade the gas lasts much much longer. We can see that a lot more methane is being produced and faster.“

Simpler maintenance and value-added digestate

Compared to the original configuration, when mixing ingredients were housed within the digesters themselves, all parts of the new system are externally mounted. This allows Hanson and his four-member crew to do simple visual and auditory checks and make adjustments, as required.

“Easy to maintain and we also get a good quality end-product digestate,” Hanson concluded. This provides the farms in the county with some very valuable nitrogen as a fertiliser and it also saves them money, which is always a plus. We're now looking at how we can get it to be more consistent so there is less water and more product. We're messing around with getting the compaction levels just right so that it is easier for the farmers to apply to land.

“The new blending system was an eternity in coming but has proved well worth it. We're now producing biogas like we should because the sludge from the digester is being properly blended by the Landia GasMix.”

For more information visit: www.landiaworld.com