FUNDAMENTALS OF NITRIFICATION 2016 So. Cal. Water Education Seminar Orange, California – August 10, 2016 Hélène Baribeau, Ph.D., P.E. Agenda • Background • Problems caused by nitrification • Regulatory compliance • Causes and triggers: – Water quality conditions – Distribution system characteristics, and operational practices • Nitrification indicators Nitrosomonas Wolfe et al., AEM, 56:2:451, 1990 Agenda • Nitrification may be occurring in 63% of water providers that use monochloramine • 48% of utilities have experienced nitrification (2004 survey): – 25% are responding to nitrification ≥2 times per summer “If you don’t – Not all systems are monitoring think you have specifically for nitrification nitrification, you (sample numbers, frequency, haven’t looked locations, water quality parameters) hard enough!” Nitrification is + ‐ + • AOB: NH4 + 3/2 O2 → NO2 + H2O + 2 H ‐ ‐ NOB: NO2 + 1/2 O2 → NO3 ‐ • Incomplete nitrification: NH3 → NO2 ‐ • Complete nitrification: NH3 → NO3 • No single microorganism can oxidize ammonia to nitrate Monochloramine decomposition AOB NOB Monochloramine Ammonia Nitrite Nitrate + ‐ ‐ (NH2Cl) (NH3 / NH4 ) (NO2 ) (NO3 ) Nitrification is • Two unrelated groups of bacteria: – AOB: Nitroso‐ • Nitrosomonas, Nitrosococcus, Nitrosospira, Nitrosovibrio, Nitrosolobus • Also ammonia‐oxidizing Archaea – NOB: Nitro‐ • Nitrobacter, Nitrospina, Nitrococcus, Nitrospira • Limited information regarding genera/species in drinking water distribution systems, and identification depends on methods used • Wide variety of characteristics and differences: – Shape, pigments, cell wall, flagella, reproduction... Nitrification is Responsible for Regulations, Effects of Nitrification Problems High levels of nitrite (and nitrate) Decrease in disinfectant residuals SWTR, TCR May allow bacterial growth, does not protect the DS against contaminations High HPCs, potential presence coliforms SWTR, TCR and E. coli, cell lysis consumes chloramine Decrease in pH, dissolved oxygen, and Lead and Copper Rule alkalinity May enhance corrosion Tastes and odors, particles Customer complaints “Free chlorine burn” DBPRs Nitrification and Regulations • Regulated as Inorganic Contaminants: ‐ – Nitrate MCL: 45 mg/L NO3 (10 mg/L N) Nitrite MCL: 1 mg/L N Nitrite + nitrate MCL: 10 mg/L N – At entry points to the distribution system: • Increases in nitrite/nitrate in the distribution system? Nitrosomonas Watson et al., Bergey’s Manual of Systematic Bacteriology, 1989 Nitrification and Regulations • Difficult to exceed MCLs due to nitrification: • Low Cl2:NH3 ratio, high free ammonia concentration, high chloramine residual • Many other challenges encountered before (e.g., loss in disinfectants, microbial growth, …) Nitrification and Regulations • Bacteriological quality determined by the (Revised) Total Coliform Rule (TCR): • Collect x samples per week/month (based on system size and type) • Coliforms (fecal coliforms or Escherichia coli) • Chlorine residual • MCL violation if: • > y% of samples are positive for total coliforms (based on system size and type) • Repeat sample is positive for fecal coliforms (FC) or E. coli • Following a FC+ or E. coli +, a repeat sample is TC+ • Revised TCR Nitrification and Regulations • Minimum residual set by Bacteriological Quality (Surface Water Treatment Rule, SWTR): • Entry points: Disinfectant “shall not be <0.2 mg/L for >4 hours in any 24‐hour period” • Distribution system: • Disinfectant “cannot be undetectable in >5% of samples in a month for any 2 consecutive months” • “HPC 500 ≤ CFU/mL is deemed to have detectable residual disinfectant” • Maximum residual set by the Stage 1 and Stage 2 Disinfectants and Disinfection Byproduct Rules (≤ MRDLs) Nitrification and Regulations • Minimum residual • Maximum residual set by the Stage 1 and Stage 2 Disinfectants and Disinfection Byproduct Rules: • Running Annual Average (RAA) of quarterly averages • Monochloramine MRDL: 4.0 mg/L Cl2 Free chlorine MRDL: 4.0 mg/L Cl2 Chlorine dioxide MRDL: 0.8 mg/L ClO2 • DBP MCLs (chlorine burn): • THM4: 0.080 mg/L • HAA5 (ClAA, Cl2AA, Cl3AA, BrAA, Br2AA): 0.060 mg/L CAUSES AND TRIGGERS OF NITRIFICATION Triggers of Nitrification Distribution system Water quality characteristics, operation • Substrate (free ammonia) • Water age • Monochloramine residual • Sediments, biofilms • Chlorine‐to‐ammonia ratio (system cleanliness) • • Temperature Corrosion • • pH, alkalinity Darkness • Organic material (treatment processes) Triggers – Ammonia • Obligate chemolithotrophs: – Carbon dioxide (CO2) as carbon source – Inorganic substrates as energy source: • AOB: Ammonia + (NH3 may be the preferred source over NH4 ) • NOB: Nitrite – Some exceptions: • Organic substrates (Nitrobacter) → Slower growth • Organic material is not a food source, but affects chloramine stability → Ammonia release → Food • (Phosphorus is needed for nitrifier growth) Triggers – Chloramine • Chloramine degradation (decay and demand) Releases ammonia Food for AOB • Monochloramine stability is affected by: – Formation conditions: • Monochloramine dose (faster decay at higher doses) • Chlorine‐to‐ammonia ratio (faster decay at higher ratios) • pH (faster decay at low pH) – Decay reaction (auto‐decomposition): ‐ + 3 NH2Cl → N2 + NH3 + 3 Cl + 3 H – Monochloramine demand: Triggers – Chloramine • Monochloramine demand: – Microorganisms and biofilms – Corrosion products and tubercles – Organic material – Inorganic material: • Nitrite • Bromide Vikesland et al., Water Research, 37:7:1766, 2001 Triggers –Cl2:NH3 Ratio • Desirable: 4.5:1 to 5:1 – Less ammonia available upon chloramine degradation – But monochloramine degrades faster at higher ratios • As monochloramine decays, the Cl2:NH3 ratio decreases Triggers – Temperature • Range: 4‐60°C Optimum: 20‐35°C (25‐30°C) • Typically: >15°C • Duel effect of temperature: – Nitrifiers growth rate increases with temperature – Chloramine decomposition increases with temperature Vikesland et al., Water Research, 37:7:1766, 2001 Triggers –pH • Optimum: 6.5 to 8.5: .05 ) 1 – 7.5 to 8.0 for AOB .04 7.6 to 7.8 for NOB .03 • Dual effect of pH: .02 – Affect nitrifying bacteria .01 – Affect chloramine stability 0.0 (chloramines are more Specific Growth rate (h - 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 stable at higher pH) pH • pH decreases during nitrification in low‐alkalinity waters May increase corrosion Triggers – Alkalinity, DO • ~7.1 g alkalinity CaCO3 consumed per 1 mg NH3‐N • Dissolved oxygen (DO): – Aerobic microorganisms + – AOB: 3.2 mg O2 per mg NH4 ‐N oxidized ‐ NOB: 1.1 mg O2 per mg NO2 ‐N oxidized – Some exceptions: • Low oxygen concentrations • Facultative aerobes Nitrococcus mobilis Watson et al., Bergey’s Manual of Systematic Bacteriology, 1989 Inhibitors of Nitrification • Metals: – Nickel, chromium, iron, aluminum, zinc, lead, manganese – Copper: • Low levels may enhance nitrifier growth (<10 μg/L) • High levels are toxic to nitrifiers (>100 μg/L) • Cyanides • Phenols, mercaptans, thiourea • Halogenated compounds: e.g., THMs, perchlorate Inhibitors of Nitrification • THMs can delay the onset of nitrification: – AOB can biodegrade THMs through cometabolism, with production of compounds that are toxic to AOB • Brominated THMs are particularly toxic to nitrifiers Speitel et al., Journal AWWA, 103:1:69, 2011 Triggers –Water Age • Nitrification generally occurs at high water age: – Lower monochloramine residual • Distribution system characteristics: – Dead‐ends: • By design • Closed valves – Storage facilities: • Poorly cycled or mixed • Common inlet/outlet – Oversized pipes – Multiple pressure zones Triggers – Corrosion • Nitrification can occur in pipes of any materials, however… – Corrosion tubercles can harbor microorganisms – Corrosion tubercles consume disinfectants: + 2+ 3+ + ‐ ½ NH2Cl + H + Fe → Fe + ½ NH4 + ½ Cl – Corrosion control practices can affect nitrifiers because they need phosphorous to grow – Benefits of corrosion control outweigh its drawbacks Golden State Water Company Triggers – Darkness • Nitrifiers are inhibited by light, but not fully inactivated by it • NOB may be more sensitive than AOB • Recovery from inhibition in darkness • Photo‐inhibition and recovery depend on: • Illumination intensity • Attenuation properties of water • Water circulation (exposure of microorganisms) AWWA, Opflow 2010 INDICATORS AND MONITORING OF NITRIFICATION Nitrification Indicators • No ideal method to identify and enumerate nitrifiers: Advantages Disadvantages Culturing • Relatively easy • Underestimate counts techniques • Enumeration • Difficult to identify species possible • Long incubation time Microscopy • Faster than • Initial isolation required and serological culturing • Large diversity requires techniques techniques different antibodies Molecular • Identification • Large diversity requires methods possible different primers/probes • Fastest • Complex; not readily usable by water utilities Nitrification Indicators • Monitoring based on indicators: • Substrates: Ammonia (free), and nitrite • Products: Nitrite, and nitrate • Chloramine residual • HPCs • Temperature, pH Nitrospina gracilis, • Drawbacks of indicators: Watson et al., 1989 Indicators are the results of nitrification; They do not predict nitrification Trends are system dependent Trends may be due to factors other than nitrification Summary • Carried out by various bacteria that belong to different groups, different characteristics • Potential causes are numerous, including water quality, and distribution system characteristics and operations • Favorable growth conditions of nitrifiers are similar to those observed in distribution systems • Lack of simple, quantitative and rapid methods for identification and enumeration ‐ ‐ – Monitored via indicators (NH3, NO2 , NO3 , NH2Cl) Thank you! Hélène Baribeau, Ph.D., P.E. (714) 488‐0496 [email protected].