Ammonia
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- Benefits of Online Chemistry Analyzers
- ChemScan UV-2150 Process Analyzer (Measures one parameter with up to 4 Sample Lines)
- Chemscan UV-4100 Process Analyzer (Measures up to 4 Parameters with 1 or 2 Sample Lines)
- ChemScan UV-6101 Process Analyzer (Measures up to 8 Parameters with up to 8 Sample Lines)
ChemScan® Application Summary
Ammonia Feed Control (Chloramination)
Statement of the Problem
Many utilities want to control a chloramination process by using existing chlorine residual analyzers in combinatin of with an analyzer able to detect free ammonia at trace concentration in the presence of chloramine. Up to the point of maximum monochloramine formation, a free ammonia residual will be present. This represents a fraction of the total ammonia present in the water, most of which is combined with chlorine. (For a more complete discussion, see the Application Summary entitled "Water Chloramination Process Control".)
Control Strategy
A 5 to 1 or less weight ratio of Cl2 to NH3-N will suppress the decomposition of monochloramine into dichloramine or trichloramine in water. If a modest free ammonia residual is maintained along with a target combined chlorine concentration after chloramine formation, the process can be maintained with chloramine concentrations near the monochloramine peak but not past this peak into the zone where chloramine decomposition begins to occur.
Apparatus
ChemScan® Process Analyzers can be used to detect free ammonia, while compensating for the presence of combined ammonia, turbidity and other chemicals. Spectrophotometric methods are used for the analysis. Expanded path length flow cells can also be used which are capable of detecting free ammonia at a fraction of a part per million, if desired.
Wastewater Chloramination Process Control
Statement of the Problem
Chloramination of wastewater is difficult to control because of the variable concentration of ammonia that may be present in wastewater that has not been fully nitrified during the treatment process. The ammonia concentration is rarely proportionate to the flow rate, thus making flow paced control an unreliable strategy.
Process Control Strategy
Under variable ammonia conditions, one strategy is to monitor incoming ammonia (prior to a chlorine addition point) and use this information to feed forward a desired addition value for chlorine which has been stochiometrically calculated to produce a desired monochloramine concentration. A second sample point at or after the point of chlorine addition is used to verify that the desired monochloramine concentration is being achieved and that the set point for free ammonia following chloramine formation is also as desired (zero or at some minimum value). The desired monochloramine concentration is selected based on the concentration and contact time necessary to assure disinfection of the wastewater.
Apparatus
ChemScan® Process Analyzers are designed to detect free ammonia, chloramine or both in wastewater from one or more points in the treatment process.
The ChemScan® ammonia method detects ammonia in the form of NH3 by adjusting sample pH using a hydroxide solution and injecting a surplus of hypochlorite in the form of a bleach solution, forming a monochloramine that can be detected directly by the ChemScan® analyzer.
Monochloramine is detected directly in wastewater at a standard pH of 6-9, without the need for reagents or pH buffer.
An alternate method of chloramine analysis injects a pH buffer to force monochloramine into the di- or tri-chloramine state, and compares the difference in absorbance spectra before and after the pH change.