How Alkalinity Aects Nitrification How AlkalinityUse alkalinity profiling Aects in wastewater operations to control How Alkalinitybiological Affects activity and optimize Nitrification process control Use alkalinityNitrification profiling in wastewater operations to control biological activityUse alkalinity and profilingoptimizeBY MARY EVANSin wastewater ANDprocess GARY SOBER operations control to control biological activity and optimize process control BY MARY EVANS AND GARY SOBER The Water Environment Federation’s new Operations Challenge operations, there are three forms of oxygen available to laboratory event will determine alkalinity needs to facilitate bacteria: dissolved oxygen (O2), nitrate ions (NO3-), and 2 nitrification. Operators will evaluate alkalinity and ammonia by sulfate ions (SO4 -). Aerobic metabolisms use dissolved analyzing a series of samples similar to those observed in water oxygen to convert food to energy. Certain classes of aerobic resource recovery facilities. bacteria, called nitrifiers, use ammonia (NH3) for food instead of carbon-based organic compounds. This type of This event will give operators an understanding of how aerobic metabolism, which uses dissolved oxygen to convert alkalinity works in the wastewater treatment process to facilitate ammonia to nitrate, is referred to as “nitrification.” Nitrifiers are nitrification, as well as the analytical expertise to perform the the dominant bacteria when organic food supplies have tests onsite. This provides the real-time data needed to perform been consumed. calculations, since these analyses typically are performed in a laboratory that can present a delay in the data. pH VS NITRIFICATION RATE AT 68 ºF What is alkalinity? The alkalinity of water is a measure of its capacity to neutralize acids. It 100 also refers to the buffering capacity, orpH VS NITRIFICATION90 RATE AT 68 ºF the capacity to resist a change in pH. 80 For wastewater operations, alkalinity 70 is measured and reported in terms of 100 60 equivalent calcium carbonate (CaCO ). 90 3 50 Alkalinity is commonly measured to 80 a certain pH. For wastewater, the 40 measurement is total alkalinity,70 which 30 is measured to a pH of 4.5 SU.60 Even 20 though pH and alkalinity are 50related, 10 there are distinct differences between 40 % of Max Nitrification Rate these two parameters and how they 0 30 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 can affect your facility operations. 20 pH Alkalinity and pH 10 FIGURE 1. pH versus nitrification rates at 68ºF (maximum nitrification rate occurs at 8.0–8.5 pH) Alkalinity is often used as% of Max Nitrification Rate an indicator 0 Source: EPA-625/4-73-004a, Revised Nitrification and Denitrification Facilities Wastewater Treatment, of biological activity. In wastewater6.0 6.5 7.0 U.S.7.5 Environmental8.0 Protection8.5 Agency9.0 Technology9.5 Transfer10.0 Seminar. pH FIGURE 1. pH versus nitrification rates at 68ºF (maximum nitrification rate occurs at 8.0–8.5 pH) Source: EPA-625/4-73-004a, Revised NITRIFICATION Nitrification and Denitrification ACTIVITIES Facilities Wastewater AT PHTreatment, 7.2 AND BELOW U.S. Environmental Protection Agency Technology Transfer Seminar. pH Activity NITRIFICATION ACTIVITIES7.2 AT PH 7.2 AND BELOW 1.00 7.0 0.83 pH Activity 6.8 0.67 7.2 6.6 1.00 0.50 7.0 6.4 0.83 0.34 6.8 6.2 0.67 0.17 6.6 0.50 FIGURE 2. Measurement of nitrification activity at a pH of 7.2 and lower 6.4 Source: EPA-625/4-73-004a Revised Nitrification0.34 and Denitrification Facilities Wastewater Treatment, U.S. Environmental Protection Agency Technology Transfer Seminar. 6.2 0.17 FIGURE 2. Measurement of nitrification activity at a pH of 7.2 and lower Source: EPA-625/4-73-004a Revised Nitrification and Denitrification Facilities Wastewater Treatment, U.S. Environmental Protection Agency Technology Transfer Seminar. “In addition, nitrification is pH- sensitive and rates of nitrification will decline significantly at pH values below 6.8. Therefore, it “In addition, nitrificationis important is pH- to maintain an sensitive and rates ofadequate nitrification alkalinity in the aeration will decline significantlytank to atprovide pH pH stability and values below 6.8. Therefore,also to provide it inorganic carbon is important to maintainfor nitrifiers.” an adequate alkalinity in the aeration tank to provide pH stability and also to provide inorganic carbon for nitrifiers.” “When measuring total alkalinity, the endpoint reflects how much alkalinity would be available at a pH of 4.5. At higher pH values of 7.0 to 7.4 SU, where wastewater “When measuring total alkalinity, operations are typically conducted, the endpoint reflects how much not all alkalinity measured to a pH alkalinity would be available at of 4.5 is available for use. This a pH of 4.5. At higher pH values is a critical distinction for the of 7.0 to 7.4 SU, where wastewater bioavailability of alkalinity.” operations are typically conducted, not all alkalinity measured to a pH of 4.5 is available for use. This is a critical distinction for the bioavailability of“operation alkalinity.” of a biological process depends on steady-state conditions” “operation of a biological“operation process of a biological process depends on steady-statedepends conditions” on steady-state conditions” “alkalinity is the key to steady- state operations.” “operation of a biological“sufficient process amount of alkalinity can depends on steady-stateprovide conditions” for improved performance and expanded treatment capacity” “alkalinity is the key to steady- state operations.” “sufficient amount of alkalinity can ® provide forGALLON improved performance FOR GALLON, THIOGUARD andPROVIDES expanded treatment MORE capacity BIOAVAILABLE” ALKALINITY THAN ANY OTHER OPTION AVAILABLE. GALLON FOR GALLON, THIOGUARD® PROVIDES MORECLICK BIOAVAILABLE TO LEARN ALKALINITY MORE ABOUT HOW THIOGUARD® CAN HELP YOU! THAN ANY OTHER OPTION AVAILABLE. CLICK TO LEARN MORE GALLONABOUT HOWFOR GALLON, THIOGUARD® CAN HELP YOU! PROVIDES MORE BIOAVAILABLE ALKALINITY GALLONTHAN ANYFOR OTHERGALLON, TREATEMENT AVAILABLE. PROVIDES MORECLICK BIOAVAILABLE HERE TO FINDALKALINITY OUT MORE! THAN ANY OTHER TREATEMENT AVAILABLE. CLICK HERE TO FIND OUT MORE! How Alkalinity Aects Nitrification Use alkalinity profiling in wastewater operations to control biological activity and optimize process control BY MARY EVANS AND GARY SOBER pH VS NITRIFICATION RATE AT 68 ºF 100 90 80 70 60 50 40 30 20 10 % of Max Nitrification Rate 0 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 pH FIGURE 1. pH versus nitrification rates at 68ºF (maximum nitrification rate occurs at 8.0–8.5 pH) Source: EPA-625/4-73-004a, Revised Nitrification and Denitrification Facilities Wastewater Treatment, U.S. Environmental Protection Agency Technology Transfer Seminar. Further processes include denitrification, or anoxic metabolism, which occurs NITRIFICATION ACTIVITIES AT PH 7.2 AND BELOW when bacteria utilize nitrate as the source of oxygen and the bacteria use pH Activity nitrate as the oxygen source. In an anoxic environment, the nitrate ion is converted 7.2 1.00 to nitrogen gas while the bacteria converts the food to energy. Finally, 7.0 0.83 anaerobic conditions will occur when dissolved oxygen and nitrate are no 6.8 0.67 longer present and the bacteria will obtain oxygen from sulfate. The sulfate is 6.6 0.50 converted to hydrogen sulfide and other sulfur-related compounds. 6.4 0.34 6.2 0.17 Alkalinity is lost in an activated sludge process during nitrification. During nitrification, 7.14 mg of alkalinity as FIGURE 2. Measurement of nitrification activity at a pH of 7.2 and lower Source: EPA-625/4-73-004a Revised Nitrification and Denitrification Facilities Wastewater Treatment, CaCO3 is destroyed for every milligram U.S. Environmental Protection Agency Technology Transfer Seminar. of ammonium ions oxidized. Lack of carbonate alkalinity will stop nitrification. In wastewater treatment, it is critical to maintain pH in a In addition, nitrification is pH-sensitive and rates of nitrification range that is favorable for biological activity. These optimum will decline significantly at pH values below 6.8. Therefore, conditions include a near-neutral pH value between 7.0 and it is important to maintain an adequate alkalinity in the 7.4. Effective and efficient operation of a biological process aeration tank to provide pH stability and also to provide depends on steady-state conditions. The best operations require inorganic carbon for nitrifiers. At pH values near 5.8 to 6.0, “In addition, nitrification is pH- conditions without sudden changes in any of the operating the rates may be 10% to 20% of the rate at pH 7.0. A pH of variables.sensitive If andkept ratesin a steady of nitrification state, good flocculating types of 7.0 to 7.2 is normally used to maintain reasonable nitrification microorganismswill decline willsignificantly be more numerous. at pH Alkalinity is the key to rates, and for locations with low-alkalinity waters, alkalinity is steady-state operations. The more stable the environment for added at the water resource recovery facility to maintain values below 6.8. Therefore, it the microorganisms, the more effectively they will be able acceptable pH values. The amount of alkalinity added depends is important to maintain an to work. In other words, a sufficient amount of alkalinity on the initial alkalinity concentration and amount of NH4-N canadequate provide alkalinity for improved in the performanceaeration and expanded to be oxidized. After complete nitrification, a residual alkalinity treatmenttank to capacity.provide pH stability and of 70 to 80 mg/L as CaCO3 in the aeration tank is desirable. If this alkalinity is not present, then alkalinity should be added to also to provide inorganic carbon How much alkalinity is needed? the aeration tank. for nitrifiers.” To nitrify, alkalinity levels should be at least eight times the Why is alkalinity or buffering important? concentration of ammonia in wastewater.