Waste Water Review
Introduction:
The waste water from the refinery is discharged into the Mississippi river at a single outlet. The flow
through this outlet (called Pond Flow) was measured by using a Parshall Flume and recorded by the PI
system under the PI tagname: 94FI0434. The waste water was monitored for the following pollutants.
1.BOD
2.COD
3.Oil & Grease
4.TSS
5.Sulfide
6.Phenol
7.Chromium & Chromium-6
8.Mercury
9.Ammonia (NH3)
10.Nitrates
The concentration of the pollutants in the discharge water was obtained through laboratory analysis and the
same recorded in laboratory bench sheets. For the purposes of the review the calculations for the following
pollutants were checked for accuracy.
1.
COD
2.
Oil & Grease
3.
TSS (Total Suspended Solids)
4.
Nitrates
Six months were chosen at random from the years 1997-99 and the total emissions calculations for the
above four pollutants for those months was checked. The following months were chosen for the review of
calculations
October 1997
January 1998
June 1998
June 1999
July 1999
September 1999
In the review the pond flow (measured by the Parshall Flume) was multiplied with the daily average
pollutant concentrations to obtain the daily emission of the pollutant. This was summed over the entire
month to get the total emissions for the month.
Total emissions kg/day = Pond Flow (MM Gal/day) x Concentration of Pollutant (mg/L) x 3.78 (L/Gal)
The monthly emissions calculated in the review were compared with the values reported by FHR. The
values reported by FHR were obtained from the emissions calculation files of the respective months. For
the calculations review the pond flow and concentration data was taken from the FHR emission
calculations file and were assumed accurate.
As part of the review the pond flow and the pollutant concentration data were also checked for their
accuracy. Three days per month were chosen for the six months mentioned above i.e., a total of 18 days
were chosen from the six months. The pond flow data was obtained from the PI system and compared with
the data used in the FHR emission calculation files. Further calibration data for the Parshall Flume were
also obtained to substantiate that the accuracy of the device. Similarly, laboratory bench sheets for the four
pollutants were obtained for these 18 days and the concentration data was compared with the data used in
the FHR emission calculation files. The 18 days chosen for the data review are:
1.
October 1997 : 22nd , 23rd , 27th
2.
January 1998 : 1st , 13th , 26th
3.
June 1998 : 19th , 27th , 28th
4.
June 1999 : 12th , 26th , 27th
5.
July 1999 : 1st , 12th , 19th
6.
September 1999 : 5th , 17th , 27th
Review of Pond Flow Data:
The device 94ME048 is the flow device through which the entire waste water flow from the plant passes
through. The flow measuring device is a paschall flume. The flume measures the level of liquid and
computes the total flow. The flume is periodically calibrated. As part of the review it was verified that the
flume was calibrated regularly during the review months. Table 1 lists the maximum % error found in the
flume readings during each calibration.
Table 1: Calibration of Parshall Flume
Max % diff bet
Date of Calibration
readings bef
and aft calib
10/06/97
0.6%
10/10/97
-2.5%
10/16/97
-1.0%
10/22/97
-3.6%
10/29/97
0.0%
01/09/98
-2.0%
01/16/98
3.6%
01/23/98
1.4%
01/30/98
0.0%
06/03/98
-8.2%
06/10/98
-4.4%
06/19/98
2.8%
06/24/98
1.2%
06/01/99
-0.8%
06/08/99
-7.8%
06/15/99
-3.0%
06/22/99
2.8%
06/29/99
2.8%
07/07/99
-0.4%
07/12/99
2.4%
07/19/99
-25.4%
07/27/99
-10.2%
09/07/99
0.0%
09/14/99
-1.6%
09/21/99
-14.6%
09/27/99
13.0%
The % difference in the readings before and after calibration suggests that there is significant loss of
accuracy between two calibrations. This could lead to significant under or over estimation of the amount of
waste water discharged.
The actual pond flow data for the 18 days listed in the previous section was obtained from the PI system
using the PI tagname 94FI0434. Table 2 lists the data from the PI database and compares it with
what was used in the FHR emission calculation files.
Table 2 : Comparison of flow data from PI and FHR emission calculation files
Date
Flow Data
Flow Data used in
% Diff
Flow Data
% Diff
From PI
FHR files
between
of previous
between
MMgal/day
MMgal/day
cols 2 & 3
day from PI
cols 3 & 5
MMgal/day
10/22/97
3.09
3.21
3.9%
3.04
5.6%
10/23/97
3.16
3.14
- 0.6%
3.09
1.6%
10/27/97
2.94
2.79
- 5.1%
2.67
4.5%
1/1/98
5.15
4.71
- 8.5%
-
1/13/98
4.37
4.48
2.5%
4.36
2.8%
1/26/98
4.97
5.16
3.8%
5.07
1.8%
6/19/98
4.93
4.81
- 2.4%
4.81
0.0%
6/27/98
6.00
5.78
- 3.7%
5.59
3.4%
6/28/98
6.77
6.19
- 8.6%
6.00
3.2%
6/12/99
3.57
4.47
25.2%
4.56
-2.0%
6/26/99
5.52
5.52
0.0%
5.55
-05%
6/27/99
5.14
5.49
6.8%
5.52
-0.5%
7/1/99
2.68
3.10
15.7%
-
7/12/99
3.24
3.14
3.1%
3.23
-2.8%
7/19/99
4.66
2.65
-43.1%
2.67
-0.7%
9/5/99
2.79
3.5
25.4%
3.50
0.0%
9/17/99
3.51
3.84
9.4%
3.82
0.5%
9/27/99
3.04
3.14
3.3%
3.23
-2.8%
It was noticed that the flow data of the previous day from the PI system matched better with the flow data
in the FHR files. For example, the flow data for 7/19/99 in the FHR files matches closely with the flow data
for 7/18/99 (previous day) from the PI system. This suggested that there might have been a shift in the data
set by a day.
Review of Concentration Values of Pollutants (COD, TSS and Oil & Grease) :
The concentrations of the various pollutants are measured through laboratory analysis and recorded in Lab
Bench Sheets. Three days were chosen (at random) from each of the six review months. The concentration
values of COD, TSS and Oil & Grease that were used in the emission calculation files were checked on
these days to verify that they agreed with the values listed in the Lab Bench Sheets. The following errors
that were found.

For example, 1.3 mg/L was rounded off to 1 and 1.5 mg/L was rounded off to 2. This lead to
unnecessary loss of accuracy.
Nitrates Emission :
The calculation for nitrates in the waste water differs from that of the rest of the pollutants.
Nitrogen is present in waste water as ammonia. The waste water undergoes a process called nitrification
which breaks down the ammonia into first nitrides and then to nitrates. Both ammonia and the nitrates were
reported under waste water emissions. In the case of nitrates, the amount of nitrates depends on whether
there was little, partial or complete nitrification.
In 1997 and 1998, engineering estimates of the
concentration of nitrates were used to compute the nitrate emissions.
Complete Nitrification
16.5 mg/L
Partial Nitrification
8 mg/L
Little Nitrification
0.8 mg/L
Note : The validity of these engineering assumptions could not be ascertained
Average Nitrate Concentration 
where
N1  16.5  N 2  8  N 3  0.8
mg / L
12
N1 – number of months of complete nitrification
N 2 – number of months of partial nitrification
N 3 – number of months of little nitrification
In 1999, 14 sample tests were conducted to determine nitrate concentration and the average value was
14.81 mg/L.
Total Nitrate discharged lb/yr = (Average Nitrate Conc mg/L) x (Annual average Discharge Mgal) x 8.34
The summary of the review calculations are given in Table 3.
Table 3: Summary of Nitrate Emissions
Flow (MG/yr)
Average
Nitrate Emissions
Concentration
lb/yr
(mg/L)
1997
1431
7.02
371074.0
1998
1450
11.82
672100.4
1999
1500
14.81
821224.6