In some published articles, it was mentioned that feeding while decanting from the surface helps the granulation process, but wouldn't that affect the effluent quality being mixed with the feed? Especially in a high height to diameter ratio reactor.
I am not sure exactly how it was done in those studies. But from my experience, if the decanting is done from the surface or near the surface, the feeding can be done from the bottom. That is to say, the influent can be pumped in at a port as low as possible, preferably at the bottom of the column reactor, and the influent water flows upward through the sludge bed during feeding. This will expose the sludge to very high OLR for a short time, which might help granulation. Plus, if the reactor has a high H/D ratio, and the feeding is done not too quickly, presumably the mixing will be less of a problem.
Hi Yi Zhang! Thank you for your answer. I understand that slow feeding will help with avoiding mixing. But won't that prevent the selection process of the denser granules? Cause after settling, the biomass sits well below the top effluent port and the slow up-flow is not enough to lift sludge.
The turbulance during feeding is not significant, compare to that provided by aeration and/or mixing during the reaction phase. Part of the reason is that the feeding time is usually very short, like several minutes, while the aeration phase lasts several hours. So prolonging the feeding from say 2 min to 10 min wouldn't make that much of a difference.
What I meant is granulation is mainly achieved by selecting fast settling particles. If the effluent port is at the top of the reactor, won't that prevent this selection process? As the upflow of feed is not enough to lift light flocs.
Yes, what you say is right. That's why I said I didn't now exactly how it was done. To my knowledge, the reactors usually have volumetric exchange ratios from 0.33-0.67. That's to say, every cycle 1/3~2/3 of the reactor's volume will be decanted. For this purpose, the effluent port is usually located in the middle section of the reactor. However, it is possible, though troublesome, to install a mobile effluent port, which moves down with the liquid surface when the liquid is being discharged.
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