I am looking for some ideas and/or feedback on chemical phosphorus removal in a small RBC system.

The plant has three primary settling tanks prior to the RBC. The RBC effluent goes to a clarifier, the RAS is pumped to the 2nd of the 3 primary tanks. Clarifier effluent passes thru a roto-strainer prior to the clearwell and is then pumped up the hill for sub-surface disposal. Solids are trucked off-site periodically thru the year. The plant design peak flow is 300 m3/d and our summer peak flows are ~120 m3/d. This is a seasonal resort area and our winter flows average ~15 m3/d. The Total P levels spike in the summer to 7-9 mg/L and far exceed our permit of < 1 mg/L.

Currently alum is dosed into the effluent side of the RBC. Not quite sure of the dosing rate right now, I will add when I calculate it.

I am considering trying ferric chloride, liquid alum, ferric sulphate, and PAC. I need a robust system as the plant is not monitored daily. Also, I have newer and inexperienced operators to monitor the system.

Finally, the BOD and TSS on the final effluent is < 10 / <10. I have sent in a sample recently for dissolved P as well as Total P. I know the solids handling is terrible in this sytem and am sorting that out as well. Any suggestions regarding the chemical P removal are appreciated.

You might check out sodium aluminate, however, it does require being kept relatively warm at all times during storage otherwise it will crystallize.  But it does precipitate out phosphorus.  I have seen it do this in primary basins along with the primary sludge. 

~Eric

I have heard that lanthanum compounds can be used very effectively for P removal.

David Wichern, aka "Dedalus"

Dedalus Environmental

You may want to look at primary clarifier eff. P conc. as well as the inf. P  Establishing sol P vs. TP is good idea too.  it might help in calculating dose more accurately.  But...<1 P limit means you've got to shoot for 0.5 mg/l P at sec clar eff. and calculating dose at that low a level can't be done accurately.  trial and error, jar tests on Pri Eff highly recommended. 

Depending on conditions in Pri clar 1,2,3 you will get P release under anaerobic conditions.  More frequent solids removal may help lower P conc and you might want to do that before chemical addition to maximize process first then find out what chem needs are.  Good Luck!

Hi

Just wanted to update everyone. The alum dosage has been between 30 -50 mg/L and ~ 90% of the Total P is dissolved. I have managed to reduce the Total P to ~ 2 mg/L using the alum with low flows throughout the system (< 40 m3/day). I am switching to a PAC in the next month to reduce my dosing rate in anticipation of higher average daily flows. The next step it seems is a decent solids removal program, although my options are limited to removal by vac truck.

All suggestions are appreciated. So often a new set of eyes (or another brain) sees things out of place we have become conditioned to.

Thanks,

TMc.

It seems to me that you have old sludge;just increase your wasting.

Just be mindful of how much you waste; espciall if you are trying

to nitrify.