Nitrification Action Plans (NAPs)

Transcription

1 Directed Assistance Module (DAM) 8: Nitrification Action Plans (NAPs) Developed by the TCEQ Water Supply Division (WSD) Texas Optimization Program (TOP) Presented by the WSD Financial, Managerial, and Technical (FMT) Capacity Development Contractor v. 2 1

2 Outline of NAP DAM Presentation: Brief overview Six workshops 1. Sample Sites 2. Monitoring Frequency 3. Methods 4. Goals, baselines, and triggers 5. Actions 6. Communication strategies 2

3 Outline of Presentation Chloramination Nitrification 3

4 Chloramines 4

5 The chemicals of interest Chlorine H Cl Regardless of gas or other source, in water it is hypochlorite ion and hypochlorous acid Ammonia Free Available ammonia H O Inorganic (what is being dosed) Organic (what is in some source water) Chloramines: Mono-, Di-, Tri- Cl Monochloramine is what we want N H N H H - H O Cl N H 5

6 Yuefeng Xie s Bar Theory of chloramination Cl This chlorine molecule walks into a bar At first, there are lots of free N available ammonia molecules. Later, a chlorine molecule walks into a bar And all the free available ammonia molecules were used up 6

7 Chloramine chemistry HOCl + NH 3 NH 2 Cl + H 2 O NH 2 Cl + HOCl NHCl 2 + H 2 O 2 NH 2 Cl NHCl 2 + NH 3 NHCl 2 + HOCl NCl 3 + H 2 O 2 NH 2 Cl + HOCl N Cl H + + H 2 O 7

8 Breakpoint curve Total Chlorine Species Free Ammonia Monochloramine Dichloramine Total Chlorine = The sum of the active chlorine species Free Chlorine Trichloramine Cl 2 :N mass ratio 5:1 7.6:1 8

9 Breakpoint curve: Question What CAN you measure? Chlorine Residuals: Total and Species (mg/l) Using normal equipment Free Ammonia Monochloramine Free Chlorine Cl 2 :NH 3 -N (Chlorine to Ammonia-Nitrogen mass ratio) 9

10 Nitrification 10

11 Nitrification Nitrification happens when bacteria called nitrifiers eat ammonia, then nitrite, to form nitrite, then nitrate. Nitrification causes loss of residual chloramines. 11

12 The chemicals of interest Normal chloramine reactions, in the monochloramine zone: HOCl + NH 3 NH 2 Cl + H 2 O 2 NH 2 Cl NHCl 2 + NH 3 Nitrification NH 3 + O 2 AOB NO H+ + 2e - NO H 2 O NOB NO H+ +2e -

13 Nitrification in the environment Wastewater effluent Run off AMMONIA Fish excreta and urine Nitrosomonas bacteria (AOB) uses up ammonia and makes NITRITE NITRITE (NO 2- ) Nitrobacter bacteria (NOB) uses nitrite to make NITRATE NITRATE BUILD UP NITRATE (NO 3- ) Gases Plant remnants PLANT FERTILIZER ANAEROBIC BACTERIA

14 Nitrification in a pipe Nitrosomonas bacteria (AOB) uses AMMONIA to produce NITRITE Nitrobacter bacteria (NOB) uses NITRITE to produce NITRATE Reactions happen in biofilm Added Naturally occurring NITRATE BUILD UP AMMONIA NITRITE (NO 2- ) NITRATE (NO 3- ) Decomposition of chloramines

15 Nitrification is an imbalance There is a balance between how fast the chloramines can kill ( inactivate ) the bacteria and how fast the bacteria can regrow. Nitrification is a problem when that balance shifts to where the bacteria are eating ammonia and growing too fast for the monochloramines to kill all of them. 15

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17 NAP Workshops 17

18 A Nitrification Action Plan is like a Monitoring Plan It includes 1. A sample site map, 2. Sample schedules, 3. Analytical methods, 4. Site-specific goals, baselines, and trigger levels, 5. Actions, and 6. Communication strategies.

19 DAM Workshops This DAM includes a workshop for each element of the DAM. As you go through each workshop, note follow-up actions that you will need to complete later. 19

20 Workshop 1. NAP sites NAP sample sites: Represent sources, entry points, average and high water age in all pressure planes. Can be the same as coliform sites But they don t have to be. Critical control points A point where control can be applied and is essential to prevent or eliminate nitrification EG: Before booster chloramination

21 Workshop 2. Monitoring frequency NAP monitoring must be done weekly, May be done more frequently. Small systems, <750 people or 250 cnx. Monitor monochloramine and ammonia with every weekly total chlorine sample. Large systems, select sites at low, average and high water age for weekly sampling.

22 3a. Sample collection method Water representing the main Not stagnant water in the sample line Use the calculated flush time (CFT) Based on volume and flow Flush just two (2) pipe-volumes Don t overflush Consider building a hydrant and tap sampler

23 3b. Analytical methods Total chlorine: Use EPA approved method Monochloramine, ammonia, nitrite, nitrate EPA does not have approved methods. Achieve the required accuracy Document on the List of Analytical Methods (LAM) Attach to Monitoring Plan

24 4. Goals/baselines and trigger levels Nitrification is controlled by defining what normal is and looking for trends that are abnormal. Therefore, initial data must be analyzed to define normal levels, And additional data must be analyzed or hypothetical levels must be projected for levels that are a concern: trigger levels.

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26 Workshop 5. Actions! Preventive action: Routine operating conditions Do this even when your levels are ok Corrective: Trigger 1 Intermediate--Do this when levels are not quite ok Corrective: Trigger 2 Do this when nitrification is bad

27 Most preventive and corrective actions overlap Preventive and corrective actions: Verify results. Flush. Dose chlorine and ammonia correctly. Minimize water age. Operational corrective action: Temporary conversion to free chlorine.

28 Workshop 6. Communication strategies Make sure that all communication pathways are robust: Standard operating procedures Chain of command for action approval Notification of other PWSs, customers, TCEQ as needed.

29 Entry Point Average Water Age All Sites Example: Chloramine-Effectiveness Nitrification Sample Suite Action Plan Site Chemical Goal Far Reaches Total / Yellow Flag Red Flag Trigger Actions Trigger Actions 1) Verify results 1) Verify results 2) Check and adjust 2) Adjust dose dose Mono Ammonia Total / Mono Ammonia 0.5 +/- 20% +/- 50% Total / Mono downstream) 0.5 Ammonia 0.9 +/- 20% +/- 50% Site Chemical Baseline Nitrification Action Plan Example 1) Verify results 2) Measure nitrite and nitrate 3) Adjust dose 4) Identify affected area (check upstream and 5) Flush area 6) Flush dead ends Till levels return to normal Nitrite/Nitrate Yellow Flag Red Flag Trigger Actions Trigger Actions Nitrite 1) Verify results 1.23 > 1.5 > 2 2) Identify source changes IF confirmed-modify BL 3) Identify area, Nitrate /- 20% +/- 50% 4) Flush area Till levels return to normal 1) Verify results 2) Measure nitrite and nitrate 3) Adjust dose 4) Identify affected area (check upstream and downstream) 5) Flush area 6) Flush dead ends 7) Convert to Free Chlorine Till levels return to normal 1) Verify results 2) Identify affected area 3) Flush 4) Perform free chlorine burn Till levels return to normal

30 Take-home Message

31 Take-home Message Chloramines are an important tool. They can help maintain residuals, and Avoid unwanted disinfection byproducts. Nitrification is a potential risk of chloramination. Nitrification can be detected and controlled using a Nitrification Action Plan

32 Thanks! Any Questions? 32