When HCL was added into the yeast tank, foaming starts to form aggressively and gets thicken when pH drops to around 5.4-5.6. The appearance of bubbles is different to that before HCL was added. Please refer to the file attached on the bubbles appearance before and after HCL was added. The supplier of yeast gave the optimum range to be 5-5.5 so we tried to decrease the pH using HCL. However, the pH continues to rise again after 2 days. Does that mean the yeast is dead or could anyone suggest the possible reasons and solution of the problem?
For your information, the DO currently is around 0.3mg/L and the SOUR is around 8. Currently, the yeast tank is extremely low in nitrogen but the pH keeps increasing so we couldn't add in urea to provide nitrogen as nutrients for the yeast. That was the reason why we added in HCL, hoping to decrease the pH to the optimum range so we could add in urea to provide nutrient.
Also, the yeast tank smells really bad which means it's anaerobic. We maximised the aeration rate but the DO remains around 0.3mg/L. The removal efficiency is around 60%.
Anyone who has an idea of what is going on and could help on this issue, please drop your thoughts. Thank you.
Hi Ging Wong,
First of all, which kind of wastewater has been treated in your tank is important. If COD or BOD is to high, oxygen consumption will be high. You know yeasts can achieve fermentations and products of fermentations are generally acids. For example purivic, butiric, lactic etc. So, if yeast achieve fermentation we expect acidic environment. I think there is no enough fermentation in your tank. If you expect aerobic fermentation (sometimes it can be limited) you can try increase oxygen conc. in tank. Please give additional information about influent wastewater.
Dear Ging Wong,
Of course glyserol, methanol and citric acid have COD for chemical oxidation and have BOD for biological oxidation. 10000-20000 ppm are very high for biological degradation under aerobic conditions. Even aerobic bacteria can not do this. At least 2.0 mg/L oxygen and enough organisms should be exist in the tank. Most probable you can not supply 2.0 mgO2/L under this conditions. Most of all, what is your aim? Is supply %98 COD removal rate? You can not do this under this conditions. I think you should add nutrients for supply full feeding of organisms. If I were you I would use Anaerobic- aerobic sequential reactor with nutrients for successful treatment. However if you wonder performance of yeast on wastewater we should talk about more.
The problem currently for yeast tank is the odour problem, the foaming problem and the pH increasement few days after addition of HCL. Today, the colour of yeast tank changed to black... the aeration is of maximum but the DO still arnd 0.3mg/L... The design removal efficiency is 85%. We do wish to increase the COD removal rate but the problems to solve currently are those i mentioned. Do you have any thoughts on how should we do? We wish to put in urea but the pH keeps increasing in yeast tank so how should we cope with this? We do have an activated sludge after yeast tank so the COD of effluent to be discharged still in the spec.
Thank you very much for your time..
Dear Ging, my educated guess would be that some long-chain fatty acids, LCFA - derived through the palm oil-based biodiesel production - would act as surfactants in your yeast process.
Additionally, the pH decrease - due to HCl dosing - would protonate LCFAs, thereby increasing their hydrophobicity - a factor that can enhance the foaming.
It would be useful to make observation on the foam using microscopy - you may find filamentous bacteria/fungie stabilising the foam.
The smell is probably caused by the digestion of the foam - so I would try to remove the foam, and hope that would reduce the nuisance.
Finally, try to check and remove any submerged part from the effluent outlet, preventing foam to leave the reactor.
Good luck and please, do not forget to evaluate the usefuleness of this answer using the green/orange arrows.
Benedek
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