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A: High levels of yeast in wastewater cause undesirable effects including bulking due to interfloc bridging, discoloring the effluent, and/or producing malodors. Yeast can be filamentous or budding, which are sometimes seen as tetrads under the microscope. The most well-known condition to promote the growth of yeast in wastewater is low pH (prefer pH 5.6), however their growth is also enhanced by high BOD to Nitrogen and High BOD to phosphorous ratios, generally indicating nutrient-limiting conditions.
Under aerated conditions with high BOD (primarily composed of simple sugars such as sucrose, maltose, glucose, and fructose, or carbohydrates) yeast proliferates rapidly, converting these easy-to-use substrates into biomass and causing an increase in sludge volume and/or total suspend solid levels.(Under anaerobic conditions the biomass of yeast does not increase, but they produce alcohols and low molecular weight acids.) Due to the increased surface area of filamentous yeast, they are able to scavenge nutrients more easily than bacteria and are able to withstand low nitrogen levels, often needing only half as much as required by most bacteria.
Q: What Strategy Do You Recommend for Controlling Yeast in a Biological Process?
A:
- Raise the pH above pH 7 to favor the growth of bacteria.
- Add our VitaStim Low F:M to promote the growth of floc forming bacteria and outcompete the slower-growing organisms. (For more information, read the case history below.)
- Maintain good F/M and make sure nitrogen and phosphorous levels are balanced sufficiently. We can help you with this.
Case History
This Midwestern city operates a 1 MGD activated sludge plant. One day they called us because their plant was not settling in the aeration basins or in the digestors; their digestors were full and they could not haul solids to the fields for another month. What filament had invaded their wastewater plant?
Pictures of actinomycetes from sample brought back on slide - stained with crystal violet, viewed under 1000x magnification.
Yeast can be seen budding in the middle of the slide.
A consultant had made a common mistake, identifying it as Nocardia. We asked them if there was a food processing company in town. Sure enough, there was. We went to the food processing company and found a small wastewater plant that had been overtaken by actinomycetes and yeast.
In the municipal plant we started to add VitaStim Low F:M. We found if we added 30#’s into their aerobic digestor and then turned the digestor off for the night, in the morning the actinomycetes and yeast were gone and the digestor settled. This bought time. In the food processing plant we started adding VitaStim Low F:M and adjusted ammonia and phosphorous levels, and the plant came back quickly. Essentially, we outcompeted the yeast and actinomycetes.
If you have issue with either of these give us a call or email us, we will help you recover.
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