A Method to Determine Biodegradable Dissolved Organic Nitrogen ...

Tanush Wadhawan 1 , John McEvoy 2 , and Eakalak Khan 1
1
Civil Engineering Department
2
Veterinary and Microbiological Sciences Department
North Dakota State University
Fargo , North Dakota
USA

Outlines
•Introduction
•Research justification and objective
•Methodology
•Results and discussion
•Conclusions
•Ongoing work
•Acknowledgements

Introduction
• Dissolved organic carbon (DOC) and dissolved
organic nitrogen (DON) are parts of natural organic
matter (NOM).
• DOC = Biodegradable DOC (BDOC) + Non-BDOC
• BDOC = DOC that can be mineralized by bacteria.
• BDOC in finished water can support undesirable
bacterial growth in water distribution system.

Introduction
• DON = Biodegradable DON + Non-BDON
(BDON)
(NBDON)
• BDON = DON that can be mineralized
(ammonified) by bacteria.
• BDON in finished water can support undesirable
bacterial growth in the water distribution system.
• BDON could lead to nitrification.
Organic N NH 3 -N NO 2 -N NO 3 -N

Introduction
• To prevent bacterial regrowth, treatment plants
add disinfectants such as chlorine or chloramines.
• Disinfectants + NOM disinfectant by-products
(DBPs).
• Trihalomethanes and haloacetic acids are the
common DBPs.
• But focus has shifted towards nitrogen containing
DBPs including haloacetonitriles,
halonitromethanes, haloacetamide and
nitrosoamines.

Introduction
• N-DBP formation from DON in the presence of
hypochlorite, monochloramines and chlorine gas
has been reported.
• BDON or NBDON is a precursor for N-DBP?
• This knowledge will help in controlling formation
of N-DBPs in treatment plants.
• Controlling BDON in finished water will help in
minimizing nitrification.

Research Justification
• Before being able to control BDON (or NBDON),
need to be able to determine it.
Objective
• To develop a method for measuring BDON in
water.

Methodology
• Adopted from the BDON test for wastewater.
• BDON in wastewater can reduce oxygen and
support algal growth in receiving waters.
• The method was based on the ability of bacteria to
ammonify DON.
• DON reduction before and after incubation with
mixed culture inoculum.

Methodology
• BDON measurement in wastewater is easier than
in drinking water.
• The concentration of organics in drinking water is
very low.
• Finding correct type of inoculum.
• Finding adequate incubation time.
• Finding sensitive analytical methods for
nitrogen determination.

Methodology
DON = TDN – DNH 3 -N – DNO 2 -N – DNO 3 -N
DON = DTKN – DNH 3 -N
TDN = Total dissolved nitrogen
DTKN = Dissolved total Kjehldahl nitrogen
D = Dissolved

Water sample (300 mL)
0.22 µm pore size membrane filter
Filtrate DON measurement (DON i
)
2 mL
inoculum 20°C and aerated every 12 hrs
of 5%
diluted Incubation
MLSS bottle
Sacrificed at 2, 7, 14, 21 and 28
days
DON measurement (DON f
)
BDOC was also measured.

Methodology
• No direct method to measure DON.
• DON = TDN – DNH 3 -N – DNO 2 -N – DNO 3 -N
Sulfanilamide Napthylethylenediamine
DNO 2 -N
Diazo compound
Colored azo dye
543 nm
0.01-2.5 µg/l

Methodology
DNO 3 -N
DNH 3 -N
(Cd-Cu reduction)
0.05-45 µg/l
(Oxidized with NaClO in alkali)
0.04-10 µg/l
DNO 2 -N
TDN
(Oxidized with K 2 S 2 O 8 )
2.0-40 µg/l
DNO 3 -N

Methodology
• BDON = [(DON i – DON f )]
• BDON 2 = [(DON 0 – DON 2 )]
• BDON 7 = [(DON 0 – DON 7 )]
• BDON 14 = [(DON 0 – DON 14 )] …

Methodology
• Samples from Moorhead Water Treatment Plant
(WTP), Moorhead, Minnesota.
• 4.1 MGD.
• Three sets of samples collected three consecutive
weeks.
• Triplicate analyses.

Red River 1 Coagulating/
Well 3 Softening Unit
2 4
Reservoirs
8
Distribution
System
9
Moorhead WTP
7
Clear Well
6
Ozone
Chamber
5
Biological
Filters
3, 4, 5 and 6 - Sampling locations

Coagulated and Softened Water
Characteristics
Parameters Average±standard deviation Range
DOC (mg/L) 4.18±0.60 3.43-5.48
UV absorbance at 254 nm (1/cm) 0.043±0.004 0.037-0.054
Specific UV absorbance (L/mg
1.04±0.18 0.75-1.45
C.m)
Dissolved oxygen (mg/L) 8.91±0.08 8.83-9.04
Alkalinity (mg/L as CaCO 3 ) 70.05±12.35 42-94
Hardness (mg/L as CaCO 3 ) 89.73±6.83 76-110
pH 11.21±0.25 10.63-11.67
Turbidity (NTU) 0.10±0.02 0.07-0.13

TDN (mg/L)
Results
TDN through incubation
1.46
1.44
1.42
1.40
1.38
1.36
1.34
1.32
1.30
0 10 20 30
Incubation time (days)
River
Before ozonation
After ozonation
Treated effluent

TDN (mg/L)
Results
TDN
1.50
1.45
1.40
1.35
1.30
1.25
1.20
River
Before
ozonation
After ozonation Treated effluent

DON (mg/L)
Results
River
0.94
0.93
0.92
0.91
0.90
0.89
0.88
0.87
0 5 10 15 20 25 30
Incubation time (days)

DON (mg/L)
Results
Before ozonation
0.59
0.58
0.58
0.57
0.57
0.56
0.56
0.55
0 5 10 15 20 25 30
Incubation time (days)

DON (mg/L)
Results
After ozonation
0.61
0.60
0.59
0.58
0.57
0.56
0.55
0 5 10 15 20 25 30
Incubation time (days)

DON (mg/L)
Results
Treated effluent
0.44
0.44
0.44
0.43
0.43
0.43
0.43
0.43
0.42
0 5 10 15 20 25 30
Incubation time (days)

BDON (ug/L)
Results
BDON
60.0
50.0
40.0
30.0
River
Before ozonation
After ozonation
Treated effluent
20.0
10.0
0.0
0 2 7 14 21 28
Incubation time (days)

BDOC (mg/l)
Results
BDOC
1.2
1.0
0.8
Influent
Before ozonation
After ozonation
Treated effluent
0.6
0.4
0.2
0.0
2 7 14 21 28
Incubation time (days)

Conclusions
• A method for determining BDON in water was
developed.
• The method was based on DON reduction during
incubation with mixed bacterial culture.
• DON was determined based on the difference
between TDN and inorganic nitrogen species
combined.
• To determined DON, nitrogen species involved
were converted to NO 2 -N.

Conclusions
• Incubation time of 14 days is adequate.
• The developed method was successfully tested
with water samples.
• More work on the limitations of the method.

Ongoing Work
• Using standard organic nitrogen samples to
determine:
• Detection limit
• Accuracy
• Precision
• Using pure culture inoculum:
• Pseudomonas putida KT2440

Acknowledgments
• Kristofer Knutson – Moorhead Water Treatment
Plant
• Ruchi Joshi – Undergraduate Research Assistant
• Halis Simsek – Ph.D. Candidate
• Murthy Kasi – Ph.D. Candidate

Thank you.
Questions?
E-mail: eakalak.khan@ndsu.edu