Field and Laboratory Tests to Evaluate Nitrification

Transcription

1 Field and Laboratory Tests to Evaluate Nitrification KIMBERLY GUPTA, PE PORTLAND WATER BUREAU CO- AUTHOR: ERIK ENGLEBERT AWWA PNWS KENNEWICK, MAY 4, 2017

2 Presentation Outline Overview of Portland s System Background on Nitrification PWB s Nitrification Monitoring Program Hach SL1000 Field Instrument Evaluation

3 Portland Water Bureau Overview Serves approximately 966,000 people approximately 25% of Oregon 19 wholesale customers which comprise approximately 42% of system demand

4 Portland s Distribution System 180 pressure zones 70 storage tanks 39 pumping plants Over 2000 miles of distribution pipeline Over 220 water quality sampling stations

5 Nitrification Overview Nitrification is the bacteriological oxidation of ammonia to nitrate via a two step process 1 st Step: ammonia to nitrite + NH 3 + O 2 NO H + +2e - 2 nd Step: nitrite to nitrate + NO H 2 O NO H + +2e -

6 Why Do We Care About Nitrification? Nitrifying bacteria can survive and proliferate under conditions typically observed in chloraminated water distribution systems Nitrification can adversely affect water quality and indirectly affect regulatory compliance There are control strategies that utilities can implement to decrease nitrification Decreased ph Decreased alkalinity Increased R2A Decreased Cl Nitrification High (or low) free ammonia Increased nitrite Increased nitrate

7 Source to Tap Nitrification Raw Water Ammonia in source water Treatment Optimized chlorine to ammonia ratio Emerging mitigation strategies Distribution System DS optimization

8 Monitoring for Nitrification Ammonia oxidizing and nitrite oxidizing bacteria can be analyzed via culturing, serological or molecular methods Complex, time consuming, and potentially expensive As a result we look for indicators of nitrification Nitrite Nitrate Free ammonia HPC R2A Chlorine ph

9 PWB Historic Nitrification Monitoring Nitrification Study Determined that nitrification does occur at MRT sites in PWB s system and can extend into the late fall 2011 Tank Monitoring Study 2012 Monitored a subset of tank sites for chlorine, free ammonia, temperature, nitrite and nitrate TCR Site Study If ph or chlorine residual fell below chronic limits in two consecutive samples or acute limits in one sample at TCR sites, the site qualified for nitrification monitoring Present Pilot Monitoring Plan and Action Plan New approach to nitrification monitoring ATP Evaluation Annual Nitrification Monitoring and Action Plan Changes annually depending on system results

10 2013 Nitrification Program Goal More Holistic Approach Programmatic shift away from sampling only in problem areas New objective: sample in all areas hydraulically connected to the problem area to see where the problem is starting

11 Parameters Monitored Lab Nitrite Nitrate HPC-R2A Free ammonia Field Chlorine residual ph Temperature ORP ATP (2013 only)

12 Nitrification Triggers and Control Strategies Targets and action levels were developed for chlorine residual, nitrite, nitrate, ph, and HPC-R2A A toolbox of control strategies was developed to reduce water age and improve the cleanliness of the system

13 Information Dissemination Provided key personnel with data as it became available Auto generated weekly s with parameters that exceeded triggers Bi-weekly meetings with stakeholders to discuss results and make operational decisions

14 Control Strategies Developed a toolbox of control strategies to reduce water age and improve the cleanliness of the system Ensure optimization of chlorine and ammonia injection points Increase sampling Adjust pumping operations Lower tank operating levels Unidirectional flushing Conventional flushing

15 Control Strategies Control measures continued: Drain and clean tanks ahead of schedule Take storage out of service Install mixers if tanks are stratified Increased the chloramine target leaving the treatment plant R2A (cfu/ml) R2A in AH Tank 0 Apr-13 Nov-13 May-14 Dec-14 Jul-15 Jan-16 AH Dip AH Outlet Mixer Installed

16 Conclusions from the 2013 Nitrification Study Nitrification ramped up in the late summer and extended into the late fall Having monitoring data in a timely manner was key! Even though all of the control strategies were effective, once nitrification was underway, it was very difficult to stop Proactive steps to delay/stop the rate of nitrification were essential

17 2014- Present Nitrification Program As a result, PWB takes a proactive approach to water quality and nitrification management before the nitrification season starts: Prepare a new monitoring and action plan each year that takes into account the previous year s water quality results Seasonally adjust chloramine target Take several tanks out of service (seasonally) Lower operating levels/begin deep cycling a number of critical tanks Change regulator settings to increase demand on certain parts of the system

18 2014- Present Nitrification Program Install chlorine residual analyzers as needed (installed chlorine residual analyzers at 7 key tanks in 2014) UDF program targets flushing in pressure zones that had water quality issues in the previous year Adjust spot flushing schedules Deploy an autoflusher Time pumping operations

19 Nitrification Monitoring Results Late September 2013 Late September 2016

20 Field Equipment Tests Another goal of the nitrification program is to continue looking for mechanisms to gain information faster about what is happening in the system Reliable field tests are always best (near real time data) Additional bonus of offsetting workload for our in-house lab In the past, we have not have not had much success with testing for free ammonia or nitrate in the field Before utilizing a new piece of equipment, we generally do a side by side study to evaluate its precision and accuracy before deploying

21 Hach SL1000 Hach SL1000 is simple to use multi-parameter field instrument Uses Chemkeys rather than vials and reagent packets Can monitor for up to 4 Chemkey parameters for colorimetric analysis at once Space for 2 probes Limited opportunity for operator error List of analytes that can theoretically be tested by this instrument: Free/total ammonia, free/total chlorine, monochloramine, nitrite, alkalinity, copper, hardness, iron Goal was to evaluate efficacy for the following: Nitrification field monitoring Process control

22 Hach SL1000 vs Lab Methods Comparison Methodology Comprehensive test for 3 analytes Free ammonia (NH 3 -F) Total ammonia (NH 3 -T) Monochloramine (NH 2 Cl) Preliminary test for 2 analytes Nitrite (NO 2 ) Chlorine (Cl) Tested across range of concentrations Similar to system conditions

23 Hach SL1000 vs Laboratory Methods: Free/Total Ammonia Lab test conducted with Timberline Ammonia Analyzer (TI-001) MRLs: Timberline = 0.01mg/L SL1000 = 0.05mg/L Tested spiked levels in DI and tap water Each spike level tested in triplicate Spiking levels Deionized water: 0.01, 0.02, 0.03, 0.05, 0.1, 0.2, 0.3 mg/l Tap water: ambient (no spike), 0.01, 0.02, 0.05, 0.1, 0.2 mg/l Results combined for analysis

24 Hach SL1000 vs Lab: Free Ammonia Results Test results were significantly different (p= <0.05) SL1000 had slightly lower variation but no significant difference between the methods Mean difference = Comparison Timberline SL1000 p value Different Results? N/A N/A <0.05* Standard Deviation N/A Different variance between spiking levels? Yes Yes <0.05 / <0.05 NH 3 _F R² = R 2 = NH3_F by SL NH3_F by Timberline

25 Hach SL1000 vs Lab: Total Ammonia Test results were significantly different (p= <0.05) SL1000 had lower variation and this did not vary based on spiking level Mean difference = Comparison Timberline SL1000 p value Different Results? N/A N/A <0.05 Standard Deviation N/A Different variance between spiking levels? NH 3 _T Yes No <0.05 / >0.05 R² = R 2 = NH3_T by SL NH3_T by Timberline

26 Hach SL1000 vs Lab: Monochloramine Lab test conducted with amperometric titration (SM 4500-Cl D) MRLs Amperometric titration = 0.01mg/L SL1000 = 0.04mg/L Tested spiked levels in deionized water Each spike level tested in duplicate due to method volume constraints Spiking levels: 0.1, 0.5, 1.0, 1.5, 1.75, 2.0, 2.25, 2.7 mg/l

27 Hach SL1000 vs Lab: Monochloramine Test results were not significantly different (p= >0.05) No difference in variation between methods Mean difference = Comparison Timberline SL1000 p value Different Results? No No >0.05 Standard Deviation N/A Different variance between methods 3 No No >0.05 NH 2 Cl 2.5 R² = R 2 = NH2_Cl by SL NH2Cl by Timberline

28 Hach SL1000 vs Lab: Total Chlorine Lab test conducted with amperometric titration (SM 4500-Cl D) 2014 preliminary study did side by side tests with lab Only compared side by side results, rather than performance against known standard

29 Hach SL1000 vs Lab: Total Chlorine Test results were not significantly different (p= >0.05) No difference in variance between methods (p=>0.05) Limited sample set so not enough samples to do standard deviation or variance by standard set R 2 = Comparison Lab Std Method SL1000 p value Different Results? No No >0.05 Cl_T SL1000 Result 3.5 R² = Laboratory Result

30 Hach SL1000 vs Lab: Nitrite Lab test conducted according to SM4500-NO 3 -F MRLs are the same SM4500-NO 3 -F = 0.005mg/L, SL1000 = 0.005mg/L Compared two data sets 2014 preliminary study did side by side tests with lab Most spike levels tested in duplicate Spiking levels: 0.005, 0.01, 0.05, 0.12, 0.15, 0.2 mg/l Lab & SL1000 field data from 2016 Nitrification Monitoring

31 Hach SL1000 vs Lab Methods: Nitrite Test results using standard solutions were not significantly different (p= >0.05) Limited sample set so did not have enough samples to do standard deviation or variance Mean difference = R 2 = Comparison Lab Std Method SL1000 p value Different Results? No No >0.05 NO2 NO2 by SL R² = NO2 by Standard Method

32 Hach SL1000 vs Lab Methods: Conclusions Meets criteria we look for when evaluating new methods for field testing Provides near real time results Reproducibility of results Accuracy acceptable for field tests More work needs to be done, but the SL1000 appears to be an effective method for testing for several nitrification parameters in the field While SL1000 statistically differs from lab method for some analytes, plotted results & R squared values provide confidence that results provide a good estimate of actual values

33 Next Steps SL1000 Comprehensive testing free/total chlorine, nitrite Yearlong comparison of SL1000 to lab methods to test for any seasonal matrix effects for monochloramine, free/total ammonia, free/total chlorine Test other relevant Chemkeys as they become available Test out other field kits/analysis methods as they become available!

34 Questions? Contact information Kimberly Gupta, PE Portland Water Bureau