Hello all,
I have been running 8 MECs using a potentiostat for one month now. The potential I have fixed on the anode is 0.4 V against ref (Ag/AgCl). The 8 MECs are 4 duplicates of different anode materials. Each electrode has a surface area of 4.5 cm squared.
There are clear differences in currents between the different materials, but all of them have not increased substantially at all - they just seem to oscillate over time, with a minor net increase from day 1 to now.
The feed I am using is primary effluent from a domestic wastewater treatment plant - the COD concentration feed has ranged between 300-420 mg/L thus far. The systems were run in batch for 5 days with wastewater and sodium acetate (with a total COD concentration of 600 mg/L) and have since been running in flow through mode since the batch phase ended. The MECs have an anodic chamber of 50 mL with a HRT of 10 hours.
Has anybody had experience with this kind of feeding process? Thus far, the COD levels have consistently fallen (values below 100 mg/L) once processed in the MECs. Should the HRT be reduced? Could the bugs need a higher organic loading rate?
Any help, suggestions or further questions would all be welcomed!
Dan
Thank you for the answer Bandi - The current I am actually getting is in the micro amps! I should add that I am using a battery separator (Entek) so the resistance across the system is likely to be higher than with an open chamber system.
I could give much comment, but I do not know whether you would get it. How strong is your background in electrochemistry? What do you consider the most difficult book/chapter of a book on electrochemistry that you read? (I have a bachelor degree in physical chemistry, have a phd on the corrosion of dental alloys, published on the measurement of the electrical potentials of dental restorations; I am also familiar with redox processes such as occur in oxidative phosphylation such as by the mitochondrion)
It is interesting. Dr Juan is right. Please discuss more about the experimental set up of yours.
Hi All,
Thank you very much for all the interest.
In brief:
Anodes/working electrodes: are made from carbon fibre felt and graphite felts - depends on MEC
Cathodes/counter: stainless steel meshes
Feedstock: Batch phase was a combination of wastewater and sodium acetate (0.5 g / L) with a total COD of 600 mg / L. After batch phase, the cells have been run with real wastewater collected and used only when fresh, at an HRT of 10 hours. The HRT as of yesterday (one month of continuous flow through mode has passed) has since been lowered to 5 hours as COD tests post treatment had very low COD remaining (the average COD input has been between 300-400 mg / L. This is because of the use of real wastewaters, so the COD content cannot be controlled - but this is desired).
The working electrode has had a fixed 0.4 V using a Dropsens 8000u potentiostat.
Resistance across all electrodes, current collectors and wires is less than 1 ohm when tested before set up.
Best,
Dan
Hi All,
Update; with the increased flow rate (and therefore reduced Hydraulic retention time) there was an initial drop in the quality of the effluent which over time has again improved. There has not really been a significant improvement in current (I am still using primary effluent with a COD between 300-450 mg L). There was a bit of a spike when the higher concentration COD wastewater was fed to the reactors.
Would switching to a power supply instead of a potentiostat be advisable?
Best,
Dan
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