Civil Engineering Department

Transcription

1 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

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

3 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.

4 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

5 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.

6 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.

7 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.

8 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.

9 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.

10 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

11 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.

12 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 µg/l

13 Methodology DNO 3 -N DNH 3 -N (Cd-Cu reduction) µg/l (Oxidized with NaClO in alkali) µg/l DNO 2 -N TDN (Oxidized with K 2 S 2 O 8 ) µg/l DNO 3 -N

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

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

16 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

17 Coagulated and Softened Water Characteristics Parameters Average±standard deviation Range DOC (mg/l) 4.18± UV absorbance at 254 nm (1/cm) 0.043± Specific UV absorbance (L/mg 1.04± C.m) Dissolved oxygen (mg/l) 8.91± Alkalinity (mg/l as CaCO 3 ) 70.05± Hardness (mg/l as CaCO 3 ) 89.73± ph 11.21± Turbidity (NTU) 0.10±

18 TDN (mg/l) Results TDN through incubation Incubation time (days) River Before ozonation After ozonation Treated effluent

19 TDN (mg/l) Results TDN River Before ozonation After ozonation Treated effluent

20 DON (mg/l) Results River Incubation time (days)

21 DON (mg/l) Results Before ozonation Incubation time (days)

22 DON (mg/l) Results After ozonation Incubation time (days)

23 DON (mg/l) Results Treated effluent Incubation time (days)

24 BDON (ug/l) Results BDON River Before ozonation After ozonation Treated effluent Incubation time (days)

25 BDOC (mg/l) Influent Before ozonation After ozonation Treated effluent Results BDOC Incubation time (days)

26 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.

27 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.

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

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

30 Thank you. Questions?