Halfway through a sugar beet processing campaign (September through May), a Midwest refinery noticed that something was wrong with its wastewater processing system. The plant discharge was within the limits of its NPDES permit parameters, but the chemical oxygen demand (COD) readings from its 8.9-million-gallon anaerobic digester were very different at the top, center, and bottom of the digester. The system engineer suspected that the mixers were not operating properly.
Without functional mixing, the digester was unable to process the refinery’s high-COD wastewater. To fix the problem, the facility’s processing and engineering team decided to repair the mixing blades in the digester at the end of the campaign.
The digester was emptied and cleaned during the process, which removed all active biology from the tank. After maintenance was completed, the anaerobic digester needed to be reseeded to begin properly processing high-COD wastewater.
Initially, using activated sludge from a neighboring sugar refinery’s anaerobic digester was suggested as a method for seeding the repaired digester. This process would involve hauling thousands of gallons of activated sludge at an estimated cost ranging from $70,000 to $100,000.
In addition to the cost, seeding with activated sludge from another facility would be highly time-consuming and risky. The sludge could introduce unknown foreign contaminants into the newly cleaned and repaired system. This could cause unpredictable treatment issues in the future.
The plant began seeking alternative options, which led it to BioLynceus®. The BioLynceus® team suggested reseeding with ProBiotic Scrubber® II (PBII). This live culture treatment would supply the digester with a diverse microbial community and provide the company with a more cost-effective, easier-to-transport, and more reliable solution.
PBII was added to the digester along with the facility’s high-strength COD wastewater to restart the system. After four days of PBII treatment, the digester was producing methane consistently, indicating that the microbial community was properly processing the influent COD.
Seeding the digester with PBII saved the refinery time and money because sludge hauling was not necessary to restart the system.
Figure 1. Cumulative biogas produced per 1000 pounds influent
COD was calculated for an anaerobic digester at an industrial
wastewater plant from November to March during three sugar
refinery production campaigns. PBII was used to seed the anaerobic
digester at the end of campaign
1. Treatment continued through
campaigns two and three. The values displayed were calculated by
summing the biogas produced divided by the COD loading.
An additional benefit of treatment with PBII was that the quantity of methane produced was much higher than before treatment (Figure 1). The average increase in biogas production during the second and third campaigns was 13 cfs per 1,000 lbs of COD.
These results were also attributed to cleaning out the digester and repairing the mixers before implementing the product. The methane produced was used as a cleaner energy source to help operate the drying kilns.
With BioLynceus®, the anaerobic digester was restarted with less financial burden than would have been associated with using activated sludge, and the biogas produced by the digester provided the refinery with a stable energy source.
BioLynceus® ProBiotic Scrubber®II is a cost-effective program for digestor start-up.