COD value of inflent (substrate and innoculum ) is much LOWER than for samples I tested subsequently during lab scale anaerobic digestion. COD is expected to decrease continuously during the digestion process. Is there any explanation for why this isnt so?
I assume you are measuring COD in dissolved form (i.e. after filtering).
During the startup phase (or at anytime), some MLSS (Biosolids) degrade and could contribute effluent COD. in this case effluent COD can be higher than influent COD.
there are other reasons. if you can share more information about the operation conditions and COD analytical methods, we can discuss more.
I agree with @Amila Abeynayaka basically.
If you give more information about your system (substrate, bioengineering parameters of operation, ....) more explanations of your question can be found.
Best regards
Vit
Thank you so much Amila Abeynayaka and Vit Mateju .
I use preconsumer foodwaste as substrate and second stage digester effluent as inoculum.
My reactor is operating at mesophilic temperature (37 degrees C), also under anaerobic conditions. The reactor is also connected to a selective cation exchange membrane system that removes ammonia simultaneously during the digestion process and exchanges the ammonium ions in the digester with potassium ions in a draw solution.
I use the HACH kits to analyse COD ( mercury sulfate, potassium dichromate, and sulfuric acid as reagents), samples are heated at 150 degrees for 2hours and a spectrophotometer to measure absorbance.
Olutooni Ajayi thanks for the Indo.
A. How do you pretre the sample before analyze? For example do you filter it to remove suspended solids? Or your effluent sample contains suspended solids?
B. Which phase you are tuning? Just startup, or you change the feed conditions, or did you add some biomass recently to the system?
C. Do you have values of VSS in the reactor? (And I fluent and effluent).
Amila Abeynayaka
A. I usually blend and homogenize my mixture (substrate and foodwaste) just before I start up the experieent. So, I dont filter them before analysis. From the most recent solids test, the effluent contains less than 1% of suspended solids.
B. I set up the experiment about a week ago so its just starting out. No change in feed or biomass at any point throughout the whole experiment duration.
C. Yes I have VSS values for both influent and effluent in the reactor and they are both less than 1% of the total sample weight.
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