The ammonia nitrogen level in the effluent from the AO process is higher than that in the inlet water
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The wastewater in question is the scalding wastewater from gelatin factories (derived from pigskin and cowhide). The treatment process involves: mechanical screen – air flotation tank – sedimentation tank – Tank A (equipped with packing) – Tank O (equipped with packing) – secondary sedimentation tank. After three months of operation, the ammonia nitrogen level has not decreased. Previously, they used only air flotation followed by sedimentation, but the environmental agency deemed this approach insufficient, so we carried out the necessary modifications. The COD level in the effluent from the air flotation process was 1000, while the ammonia nitrogen level was 30. However, after the AO process, the COD level in the effluent was still around 100, but the ammonia nitrogen level rose to 80. During the National Day holiday, the plant owner invited an engineer from the neighboring municipal sewage treatment plant to take a look. The engineer raised several issues: 1. Our external recirculation rate is too low (100% recirculation is required from the sludge tank to tank A); 2. Internal recirculation isn’t necessary (previously, 200% recirculation occurred from the end of tank O to the beginning of tank A); 3. An impeller needs to be added to tank A; 4. Sludge should be removed more frequently. Then, their plant sent over a small amount of sludge (about 1 ton) and insisted on doing this for 10 days ； Since many different methods didn’t work, I followed his approach. It’s the third day now, and the situation is improving; these days the COD level is 20 and the ammonia nitrogen level is 50, which is still on the high side. Now the environmental protection agency is pressing the owner to carry out the inspection; otherwise the factory will have to close. The owner is very anxious and keeps pushing me, it’s a real headache! ! ! Please give me some advice. I also have some other questions: 1. Does the external reflux need to be of such a large volume, and must it occur 24 hours a day? (The water supply is not continuous; it’s about 9 hours per day.) 2. Is it really not necessary to turn on internal recirculation? (Shouldn’t the nitrification solution be recirculated for denitrification?) If internal recirculation is to be used, for how long and at what intensity? (PS: Currently, the sludge volume in tank O is acceptable – SV30 is at 30%, DO is between 2 and 3, and PH is between 7.5 and 8. The sludge is earthy-yellow in color and has an earthy odor; however, the floc particles are not very large, and the sludge remains somewhat fine and dispersed. Some sludge will end up in the effluent from the secondary sedimentation tank.) Thank you all!
I’m also looking into the same issue. I’m using the A2O process for coking wastewater; please get in touch if you find any results. Thanks.
This post was last edited by ifay2011 on 2015-10-13 09:02. Since there is improvement, let’s follow what the engineer next door does: lol. 1 hour of water supply per day – what about the rest of the time? Should we use air aeration? That’s not good for the sludge, right? Is it possible to reduce the water inflow volume so as to ensure continuous water supply for 24 hours, or to supply water at intervals while still maintaining a balanced load throughout the day? In that case, the relevant parameters would need to be adjusted. Has Pool 2 been equipped with a flow promoter according to the advice of the engineer next door? This is very important; if not, the sludge will settle in Pool 2. In such a case, it might be better to simply return the water to Pool O. Is there any requirement regarding total nitrogen in the effluent? If not, it’s possible to turn it off (although it’s recommended to keep it on). The engineer next door seems to think that since ammonia nitrogen isn’t being nitrified, what’s the point of recycling the water? Once the ammonia nitrogen level drops, internal recirculation can be considered; the recirculation ratio is usually 200–400%. There’s no rush – wait a few more days. Nitrifying bacteria have a long generation cycle; it takes about a week to determine whether the adjustments have been effective. Since there is improvement, continue with these measures for a few more days. 5 If the pH of pool O drops significantly, be sure to supplement alkalinity. Personal opinion, for reference only.