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 1 v. 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 1
Outline of Presentation Chloramination Nitrification 3 Chloramines 4 2
The chemicals of interest - O H H Cl Cl Chlorine Cl Cl O O – Regardless of gas or other source, in water it is hypochlorite ion and hypochlorous acid Ammonia H H H H N N – “Free Available” ammonia H H Inorganic (what is being dosed) Organic (what is in some source water) H N Chloramines: Mono-, Di-, Tri- H Cl – Monochloramine is what we want 5 Yuefeng Xie’s Bar Theory of chloramination This chlorine molecule walks into Cl a bar… – At first, there are lots of free available ammonia molecules…. N Later, a chlorine molecule walks into a bar… – And all the free available ammonia molecules were used up… 6 3
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 2 + 3 Cl - + 3 H + + H 2 O 7 Breakpoint curve Total Chlorine = The sum of the Free Total Chlorine Species active chlorine Ammonia species Mono- chloramine Free Chlorine Dichloramine Trichloramine Cl 2 :N mass ratio 5:1 7.6:1 8 4
Breakpoint curve: Question What CAN you measure? Total and Species (mg/L) – Using normal equipment Chlorine Residuals: Free Ammonia Free Mono- Chlorine chloramine Cl 2 :NH 3 -N (Chlorine to Ammonia-Nitrogen mass ratio) 9 Nitrification 10 5
Nitrification Nitrification happens when bacteria called nitrifiers ‘eat’ ammonia, then nitrite, to form nitrite, then nitrate. Nitrification causes loss of residual chloramines. 11 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 2 - + 3H+ + 2e - - + H 2 O NOB NO 3 - + 2H+ +2e - NO 2 6
Nitrification in the environment Nitrosomonas bacteria Nitrobacter bacteria (AOB) uses up ammonia (NOB) uses nitrite and makes NITRITE to make NITRATE Wastew ater NITRATE effluent BUILD UP Run off Fish excreta and urine NITRITE (NO 2 - ) NITRATE (NO 3 - ) AMMONIA Gases PLANT Plant FERTILIZER remnants ANAEROBIC BACTERIA Nitrification in a pipe Reactions Nitrobacter bacteria happen in Nitrosomonas bacteria (AOB) uses AMMONIA (NOB) uses NITRITE biofilm to produce NITRITE to produce NITRATE NITRATE Naturally occurring BUILD UP Added - ) - ) AMMONIA NITRITE (NO 2 NITRATE (NO 3 Decomposition of chloramines 7
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 Comparison of a Utility's operations during normal and nitrification events. 8
NAP Workshops 17 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. 9
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 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 10
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. 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 11
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 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. 12
Comparison of a Utility's operations during normal and nitrification events. 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 13
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. 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. 14
Nitrification Action Plan Example Example: Nitrification Action Plan Chloramine-Effectiveness Sample Suite Yellow Flag Red Flag Site Chemical Goal Trigger Actions Trigger Actions Total / Mono 4.2 3.5 1) Verify results 3.0 1) Verify results Entry Point Free 2) Check and adjust dose 2) Adjust dose 0.01 0.2 0.3 Till levels return to normal Till levels return to normal ammonia Total / Mono 2.0 1.5 1) Verify results 1.0 1) Verify results Average 2) Measure nitrite and nitrate 2) Measure nitrite and nitrate Free Water Age 0.3 +/- 20% +/- 50% ammonia 3) Adjust dose 3) Adjust dose Total / Mono 1.0 0.7 4) Identify affected area (check 0.5 4) Identify affected area upstream and downstream) (check upstream and 5) Flush area downstream) High Water 6) Flush dead ends 5) Flush area Free Age 0.5 +/- 20% +/- 50% Till levels return to normal ammonia 6) Flush dead ends 7) Convert to Free Chlorine Till levels return to normal Nitrite/Nitrate Yellow Flag Red Flag Site Chemical Baseline Trigger Actions Trigger Actions 1) Verify results 1) Verify results +/- 20% +/- 50% Nitrite 0.025 2) Identify source changes 2) Identify affected area (<0.02 or >0.03) (<0.013 or >0.05) Entry Point IF confirmed-modify BL 3) Flush Nitrate 1.5 >1.7 >2.0 3) Identify area, 4) Perform free chlorine burn Till levels return to normal 4) Flush area Till levels return to normal +/- 20% +/- 50% Source Nitrite 0.025 (<0.02 or >0.03) (<0.013 or >0.05) water(s) Nitrate 1.5 >1.7 >2.0 +/- 20% +/- 50% Blended Nitrite 0.025 (<0.02 or >0.03) (<0.013 or >0.05) water Nitrate 1.5 >1.7 >2.0 Take-home Message 15
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 16
Recommend
More recommend
