From: "Palazzolo, Michael A." <Michael.Palazzolo@alcoa.com>

To: David Putney/RTP/USEPA/US@EPA

Date: 04/28/2011 03:30 PM

Subject: RE: PAL ICR for Massena East

David,

We may need to discuss this further. There is no sludge that leaves the scrubber 

on a continuous basis like a typical FGD system. This scrubber uses a sodium 

bicarbonate solution and there is only a continuous scrubber blowdown stream that 

consists of sodium bicarbonate solution (containing dissolved sodium sulfate) and a 

minimal amount of solids. The solids do not immediately get separated from the 

blowdown stream for disposal. The blowdown gets combined with other site 

industrial wastewaters prior to any removal of solids. So, solids removed during 

treatment are not representative of solids in the scrubber.

There is some material that collects very slowly in the bottom of the scrubber sump 

over a six month period. This material we call a “sludge” and it only gets removed 

when we shut down the scrubber for maintenance to clean it. 

We are proposing to sample only the continuous scrubber blowdown stream in 

response to the 114 request. This stream, which includes solids and liquids from 

the scrubber, is essentially the same liquid that would escape the demister at the 

top of the scrubber and be emitted from the stack. Will this work for you? How will 

you use total metals in the blowdown stream (mg/liter of blowdown) to calculate 

metals composition of stack PM emissions?

Mike

________________________________________________________

From: Putney.David@epamail.epa.gov [mailto:Putney.David@epamail.epa.gov] 

Sent: Thursday, April 28, 2011 2:18 PM

To: Palazzolo, Michael A.

Subject: PAL ICR for Massena East

Mike,

As we discussed earlier today, see the contractors' thoughts on the need to test the scrubber sludge and 

blowdown in red and blue text below:

I tend to think in terms of mass balances. In the dry scrubber/baghouse situation we can look at 

the composition of the baghouse dust and use it to represent the composition of the particulate 

that escapes the baghouse--then apply this composition to the PM limit in their permit to estimate 

emissions for risk purposes. In the dry scrubber/wet scrubber situation we should look at the 

weighted average of all of the streams that are discharged from the wet scrubber. I think that is 

the blowdown (which I thought someone said was recycled back to the wet scrubber after 

settling and never discharged, in which case it could be ignored) and the sludge hauled off. The 

composition of the sum of what leaves, on a weighted dry basis, represents the composition of 
the material that escapes the wet scrubber. We then apply that composition to the PM permit 

limit. The short answer is, if both of the streams leave the plant, we need data, including masses 

of each stream that leave the plant in any given year. 

All of this logic is imperfect but it is reasonable, as well as being relatively cheap and relatively 

fast.

I agree....if the scrubber sludge and the water both leave the plant (are not recycled in the 

process) then we need the HAP metal concentration in both, as well as the mass flow rate of both 

at the sampling points. For example, suppose the water in the scrubber is 100 gpm, but 90 gpm 

are recycled, and only 10 gpm leave the plant. We need the metals concentration of that 10 gpm. 

An example calculation would be 10 gpm at 8.33 lb/gal is 83.3 lb/minute, times 0.5 ppm of that 

water being hexavalent chromium equals 83.3 x 0.0000005 = 4.16 x 10-5 lb/min hexavalent 

chromium in the water.

Now let’s say 10 lb/minute (dry basis) of scrubber sludge are also leaving, and that the 

concentration is also 0.5 ppm. Therefore, the lb/min of hex chrome in the scrubber sludge are 10 

X 0.0000005 = 5 x 10-6 lb/minute of hexavalent chromium in the sludge.

So the total hex chrome leaving is 4.66 x 10-5 lb/minute, in 10 lb/minute (dry basis) of material. 

So the ppm on a dry basis is now 0.466 ppm. We should multiply their particulate emissions by 

0.466 ppm, instead of just the concentration in the water or in the sludge.

David Putney, Environmental Engineer

U.S. Environmental Protection Agency

Office of Air Quality Planning and Standards

Sector Policies and Programs Division

109 T.W. Alexander Drive, RTP, NC 27711

Mail Drop D243-02

Ph: (919) 541-2016 Fax: (919) 541-3207

Email: putney.david@epa.gov