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A Method to Determine Biodegradable Dissolved Organic Nitrogen in Water Tanush Wadhawana, Halis Simseka, Murthy Kasia, Kristofer Knutsonb, John McEvoyc, Birgit Pruessc and Eakalak Khana* Department of Civil Engineering, North Dakota State University, Fargo, ND 58108, USA b Moorhead Water Treatment Plant, Moorhead, MN 56561-0779, USA c Department of Veterinary and Microbiological Sciences, North Dakota State University, Fargo, ND 58108, USA Abstract Dissolved organic nitrogen (DON) consists of biodegradable and non-biodegradable portions. The presence of biodegradable organic nitrogen in finished water can support bacterial growth in the water distribution system. To prevent bacterial growth, water treatment facilities rely on the use disinfectants, which further reacts with DON to form toxic disinfection byproducts (DBPs). One strategy for removing DON (biodegradable) is the use of biofilters. However, in order to study the removal of DON from the water, it is essential to be able to quantify the biodegradable and/or non-biodegradable portions. The objective of this study was to develop a method to determine the biodegradable portion of DON (BDON). The principle behind the method was the ability of bacteria to ammonify BDON. The amount of BDON was determined by measuring DON before and after incubation. A BDON method developed in this study was successfully applied on samples collected from different locations of a water treatment plant. BDON concentrations were about 50, 30, 40 and <10 g N/L in influent, before ozonation, after ozonation and treated effluent samples, respectively. To determine BDON, a minimum incubation period of 14 days was required. Biofilters in the treatment plant were able to remove 87% of the BDON in ozonated water.

a

2011 IWA Specialty Conference on Natural Organic Matter, Costa Mesa, CA, USA, July 27-29, 2011, www.nwri-usa.org\nom2011.htm

Introduction Dissolved organic nitrogen (DON) is a part of natural organic matter which is present in all drinking water supplies. DON consists of biodegradable dissolved organic nitrogen (BDON) and non-biodegradable dissolved organic nitrogen (NBDON). The presence of BDON along with biodegradable organic carbon (BDOC) in finished water can support bacterial growth in the water distribution system. The bacterial growth can lead to undesirable clogging of the distribution system or an outbreak of a pathogenic bacterium. To prevent bacterial growth in the distribution system, water treatment facilities rely on the use disinfectants such as chlorine or chloramine. These disinfectants are known to react with dissolved organic matter to produce toxic disinfection by-products (DBPs). Trihalomethanes (THMs) and haloacetic acids (HAAs) are the common DBPs. Recent studies on DBPs have shifted their focus from THMs and HAAs to nitrogen containing disinfectant by products (N-DBPs) including haloacetonitriles, halonitromethanes, haloacetamide and nitrosoamines. The N-DBPs formation from DON in the presence of hypochlorite, monochloramines and chlorine gas has been reported (Lee et al. 2007). However, it is not yet known if BDON or NBDON portions of DON form N-DBPs. In order to completely understand the role of DON in formation of N-DBPs in drinking water, determining BDON and NBDON is very important. This knowledge will help in fine tuning existing water facilities to achieve complete removal of BDON and NBDON and prevent the formation of N-DBPs in the treatment plant. This study deals with developing a method to determine BDON in water. The method developed was adopted from the BDON test used for wastewater (Khan et al. 2009). The principle behind the method was the ability of bacteria to ammonify BDON. The amount of BDON was determined by measuring DON before and after incubation. The development focused on the incubation time and type of water samples. Research methodology Sample collection and BDON method description Water samples were collected from four different stages of the Moorhead Water Treatment Plant, Minnesota (Figure 1). They were collected on three different occasions, 3 to 4 weeks apart. Both BDON and BDOC were measured on the same set of samples. BDOC was measured to check the potency of the inoculum. The samples were filtered through a 0.22 µm pore size cellulose acetate membrane and the filtrate was measured for DON and DOC (initial DON and DOC). Three hundred milliliters of each filtrate were inoculated with 2 ml of 5% mixed liquor suspended solids obtained from the Moorhead Wastewater Treatment Plant, Moorhead, Minnesota. The mixture was incubated at 25°C in dark amber bottles. The mixed culture from the wastewater treatment plant was used as an inoculum to provide a broad range of bacterial species to thrive on the dissolved organic matter over a period of time. The incubation periods for BDON and BDOC analyses were 0, 2, 7, 14, 21, and 28 days, at which the samples were sacrificed (for final DON and DOC analyses). Figure 2 shows a flow chart describing the BDON/BDOC procedure.

Red River 1 . Well 2 3 . . Reservoirs 8 . Distribution System 7 .

Coagulating/ Softening Unit

4 .

Ozone Chamber 5 . Biological Filters

Clear Well 6 .

3, 4, 5 and 6 Sampling location 9 . Figure 1. Schematic representing treatment train for Moorhead WWTP.

Figure 2. Flow chart representing the experimental procedure. DON, BDON, NBDON, DOC and BDOC determinations DON was determined from the difference between TDN and the sum of inorganic N as shown in equation 1. BDON was calculated from the difference between final DON (DONT) and initial DON (DONI) according to equation 2. NBDON is equal to DONT. DOC was analyzed according to the procedure described in APHA et al. (1998), using a total organic carbon analyzer (Tekmar-Dohrmann model Phoenix 8000). BDOC was calculated based on the difference between final DOC (DOCT) and initial DOC (DOCI) according to equation 4. DON = TDN ­ (NH4++ NO3- + NO2-) BDON = (DONI ­ DONT) NBDON = DONT (1) (2) (3)

BDOC = (DOCI ­ DOCT)

(4)

Nitrite analysis For measuring nitrite (NO2-), the Standard Method 4500-NO2- B. Colorimetric Method was used (APHA et al. 1998). NO2- in samples is diazotized with sulfanilamide and coupled with N-(1-naphthyl)-ethylenediamine dihydrochloride. The reaction forms a highly colored azo dye which is then measured spectrophotometrically at 543 nm using a 1 cm path length cuvette. The method has a detection range of 5-1000 g NO2- N/L. Nitrate analysis Nitrate (NO3-) was measured using the Standard Method 4500-NO3- E. Cadmium Reduction Method (APHA et al. 1998). NO3- is reduced quantitatively to NO2- in the presence of cadmium and nitrite is measured using the method described above. The detection range for this method is 10-1000 g NO3- N/L. Ammonia analysis Ammonia (NH3) was measured using the Standard Method 4500-NH3 F. Phenate Method (APHA et al. 1998). Indophenol, a blue compound is formed due the reaction between NH3, hypochlorite and phenol. This reaction is catalyzed by sodium nitroprusside. Indophenol is measured spectrophotometrically at 640 nm using a 1 cm path length cuvette. Total dissolved nitrogen analysis Total dissolved nitrogen (TDN) was oxidized to NO3- using the persulfate oxidation method under alkaline conditions. Six hundred and sixty six microliters of the oxidizing reagent were added to 5 ml of samples. The oxidizing reagent was prepared by dissolving 45 g of potassium persulfate and 27 g of boric acid into 315 ml of 1 M sodium hydroxide, and the final volume was brought up to 900 ml with distilled water. The sample and oxidizing reagent mixture was autoclaved for 30 min at 121°C and 15 lb/in2 pressure. Concentration of NO3- converted from TDN was measured with the cadmium reduction method (described above). Results and discussion For calibration purposes, standard curves were obtained for NO2-, NO3- and NH3 by plotting absorbance of standards against concentrations. Figure 3 shows that there were strong linear correlations between the concentrations of all the nitrogen species and absorbency. The correlation coefficients and regression equations for NO2-, NO3- and NH3, obtained were 0.9997, 0.9909 and 0.9838, and y=0.0383x, y=0.0035x and y=0.0139x, respectively. Linear ranges for NO2-, NO3- and NH3 concentrations versus absorbency were 0-100 g NO2- N/L, 0-150 g NO3N/L, and 0-200 g NH3 N/L, respectively.

3.5 3.0 A543 nm 2.5 2.0 1.5 1.0 0.5 0.0 0 NO2 3.0 2.5 A650 nm 2.0 1.5 1.0 0.5 0.0 0 50 100 150 NH3 ( g N/L) y = 0.0139x R² = 0.9838 50

-(ug

0.6 0.5 y = 0.0383x R² = 0.9997 0.4 0.3 0.2 0.1 y = 0.0035x R² = 0.9909

a

100 N/L)

0.0 0 50

-

b

100 150 NO3 ( g N/L)

c

200

Figure 3. Standard curves for (a) NO2-, (b) NO3- and (c) NH3. Before incubation, TDN was 1.33 mg/L in the influent and increased to 1.42 mg/L in the before ozonation water samples. This was because the water treatment facility adds ammonia to their water in order to prevent bromate formation. In after ozonation samples, a slight decrease in TDN was observed. However, after filtration (the treated effluent), the TDN increased again (Figure 4). This can be due to the release of soluble microbial products during biofiltration. 1.50 1.45 TDN (mg/L) 1.40 1.35 1.30 1.25 1.20 River Before ozonation After ozonation Treated effluent

Figure 4. TDN of four stages in the water treatment plant.

Figure 5 shows that the amount of BDON in all of the samples increased with increasing incubation period. No BDON exertion was observed in influent and effluent for first two days; however, there was some BDON exertion in the before (3 g N/L) and after (30 g N/L) ozonation water samples. After 14 days of incubation more than 50 g N/L of BDON was exerted in the influent sample. Lowest levels of BDON removal were observed in the treated samples. Biofilters in the treatment plant were able to remove 87% of the BDON. 60.0 50.0 BDON (ug N/L) 40.0 30.0 20.0 10.0 0.0 7 14 21 28 Incubation time (days) Figure 5. BDON measurement of water samples from four stages of the Moorhead Water Treatment Plant over the incubation time of 28 days. DON concentrations in the water samples throughout the incubation period corresponding to the BDON results in Figure 5 are shown in Figure 6. As seen in Figure 6a, DON in the influent and effluent samples did not change in the first 2 days corresponding to no BDON exertion. For all four types of samples, the majority of DON reduction took place in the first 14 days which consequently is a minimum time required for BDON determination. BDOC exertion was observed until the incubation time of 21 days after which it reached a steady state indicating the inoculum was potent (data not shown). 0 2

River Before ozonation After ozonation Treated effluent

0.94 0.93 DON (mg N/L) 0.92 0.91 0.90 0.89 0.88 0.87 0 0.61 0.60 DON (mg N/L) 0.59 0.58 0.57 0.56 0.55 0 10 20 Incubation times (days) 30 10 20 30

0.59

a

0.58 0.58 0.57 0.57 0.56 0.56 0.55 0 0.44 0.44 0.44 0.43 0.43 0.43 0.43 0.43 0.42 0 10 20 Incubation times (days) 10 20

b

30

c

d

30

Figure 6. DON concentration throughout the incubation period (a) Influent water, (b) Before ozonation, (c) After ozonation, (d) Treated effluent. Figure 7 shows that the TDN values did not change much after incubation. This indicates the balance of N throughout the incubation and the reliability of the developed BDON method. 1.45 1.40 1.35 1.30 1.25 10 15 20 Incubation time (days) Figure 7. TDN over the incubation period. 0 5 River Before ozonation After ozonation Treated effluent 25 30

TDN (mg N/L)

Conclusions A method to determine BDON in drinking water was developed in this study and was successfully applied to samples collected from different locations of a water treatment plant. BDON concentration varied from 1 to 50 g N/L in influent, before ozonation, after ozonation and treated effluent samples. To determine BDON, a minimum incubation period of 14 days was required. Biofilters in the treatment plant were able to remove 87% of the BDON. Future work on testing inocula from different sources and applications of the method on standard organic nitrogen compounds to determine its accuracy and precision is recommended. Acknowledgements The authors would like to thank Department of Veterinary and Microbiological Sciences and Department of Civil Engineering, NDSU for funding the project. References APHA, AWWA, and WEF. (1998). Standard Methods for the Examination of Water and Wastewater 20th ed., Washington, D.C. Khan, E., Awobamise, M., Jones, K., Murthy, S. (2009). Method development for measuring biodegradable dissolved organic nitrogen in treated wastewater. Water Environmental Research, 81, 779-787. Lee, W., Westerhoff, P., Croue, J-P. (2007). Dissolved organic nitrogen as a precursor for chloroform, dichloroacetonitrile, n-nitrosodimethylamine, and trichloronitromethane. Environmental Science and Technology, 41, 5485-5490.

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