Series A15/81 Dissolved Sulfide Monitor
from Analytical Technology

Sulfides can be found naturally in well water and can build up in wastewater collection systems due to anaerobic conditions that are frequently occur. They are also used in mercury removal processes and are frequently found in tanning wastes. In drinking water systems, sulfides cause taste and odor problems. In wastewater systems, they can cause damage to concrete structures in collection systems and contribute to odor problems in treatment facilities. Measurement of dissolved sulfide concentrations has been done primarily by the use of analyzers employing selective ion electrodes (SIE) for sensing. While providing adequate sensitivity, SIE based systems require frequent zero and span adjustments to maintain measurement accuracy. Because of this, most SIE based monitoring systems are relatively expensive and require frequent service.

ATI's Model A15/81 Dissolved Sulfide Monitor provides an improved method for measuring sulfides in solution. Rather than using an SIE sensor, the A15/81 employs a polargraphic H2S gas sensor that is isolated from the sample. The result is a system that can operate continuously on many types of water and wastewater streams with minimal maintenance and adjustment.

The A15/81 Monitor takes a unique approach to the measurement of sulfide in solution. In operation, a small amount of sample is pumped into the system and mixed with acid. In acidic solution hydrosulfide and sulfide ions (HS- and S-2) are converted to hydrogen sulfide according to the following reaction: The mixed sample flows into a special chamber where the hydrogen sulfide is stripped from the sample. A sensor located in the gas stream measures the released H2S concentration and displays the results in terms of equivalent sulfide ion concentration in mg/l. Because sulfide measurements are often made in samples of poor quality, fouling of analytical system has been a major concern. An important feature of the A15/81 system is the fact that the sensor never comes in contact with the sample. Only the gas stream containing the stripped H2S reaches the sensor. The result is a system that will continue to function, regardless of the quality of the sample. The only requirement is that large particulate be strained from the sample. The analytical system will easily pass particulate as large as 100 microns, so only course screening is required.

A15/81 Sulfide Monitors consist of three seprate components, a chemistry module where the sample is pH adjusted for measurement, an inlet overflow assembly where raw sample is delivered to the system and an electronic readout containing the sulfide concentration display, analog output and alarm contacts. Readout modules are available in either wall mount NEMA 4X or general purpose panel mount versions. A 20' interconnecting cable is supplied to connect the monitor to the chemistry module, and separation can be increased to a maximum of 100' if required. An optional stainless steel system panel is available for mounting all components and providing a convenient shelf for reagent bottles.

Sample is connected to the overflow assembly using 1/4" id flexible tubing. Recommended sample flow rate is 3-30 gallons per house (0.2-2 LPM). While the monitor uses only a small fraction of this sample, higher flow keeps sample delivery times a minimum. Excess sample simply overflows into a drain chamber. A 1/2" id hose barb is provided for connection of drain tubing.

Sulfide monitoring systems are extremely easy to operate and maintain. Acid usage for pH adjustment in the chemistry module is inexpensive and consumption is limited to one gallon every 40 days. Peristaltic pumps used for sample and acid use long life tubing that requires replacement every 6 months. Pump heads are designed for easy tube changes, requiring about 10 minutes to replace both tubes. The sulfide gas sensor requires no maintenance other than an occasional visual inspection to ensure that no deposits have collected on the sensing membrane.

Monitoring sulfides in solution using the gas stripping technique provides extremely high measurement sensitivity. Monitoring samples down to low ppb levels can be done easily. Because the gas sensor is very stable, monthly zero and span checks are all that is needed. A separate port is provided to feed distilled water of sulfide standard when required, without disrupting normal sample inlet flow.

Features

• Sulfide Measurement: Sulfide ion is measured selectively by conversion to hydrogen sulfide
• Gas Phase Sensing: Measurement is made without contact between sample and sensor, eliminating the potential for sensor fouling.
• Alphanumeric LCD: Provides sulfide display, alarm status indication and all configuration information.
• Two Control Relays: Relays are programmable for setpoint, deadband and time delay. Relays offer pulse frequency and pulse width modulation control modes in addition to simple on/off control for direct chemical feed pump modulation.
• Isolated Output: Programmable 4-20 mA output span from 0-0.2 ppm to 0-20.00 ppm full scale. Output may also be inverted if required.
• High Sensitivity: Capable of measuring down to 5 ppb

Download a copy of the Model A15/81 Dissolved Sulfide monitor literature

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AFC International, Inc.
PO Box 894, DeMotte, IN 46310
715 SW Almond St, Ste C, DeMotte, IN 46310
800-952-3293 219-987-6825 Fax 219-987-6826
eMail: sales@afcintl.com

Last Revised: 1/23/07