Ammonia Analyzer Provides Real Time Process Control Capability PWO Operator Seminar – February 22, 2002 Greg Farmer - Littleton / Englewood WWTP Gary Girolimon - Ted Miller and Associates

Littleton / Englewood WWTP Process Schematic

Before Automating Process Control Diurnal ammonia variations led to:  Breakpoint chlorination  Inconsistent fecal coliform counts

Benefits  Dial in Final Effluent Ammonia Concentration  Centrate Return Timing Feedback  Maximize Nitrifying Trickling Filter (NTF) Efficiency  More Consistent Fecal Coliform Counts Through Control of Ammonia to Chlorine Ratio  Only 2-3 hours/month Maintenance

Ammonia Control

Nitrifying Trickle Filters

NTF Effluent Ammonia Control Modes By-Pass Valve Control  24 / 7 Effluent ammonia goal is 2.0 mg/l  Valve opens incrementally when ammonia is below 2.0 mg/l  Valve closes incrementally when ammonia above 2.0 mg/l Pump Control  If ammonia level increases above 7.0 mg/l, NTF pump speeds increase  When ammonia falls below 5.0 mg/l pump speeds decrease.  Pumps cannot go below a preset speed so that the minimum hydraulic loading is maintained.

By-Pass Valve Control If the analyzer detects ammonia level below the set point, the by- pass valve opens incrementally. If the analyzer detects ammonia levels above the set point, the by-pass valve closes incrementally.

By-Pass Valve Operation Ammonia > Valve closes when ammonia level increases above set point of 2 mg/l. Valve opens when ammonia level decreases below set point of 2 mg/l. < Valve position Nitrate >

Pump Speed Control If the analyzer detects ammonia levels below a set point the NTF pumps speeds decrease. Pump speed cannot go below a selected value so that the minimum hydraulic loading is maintained. If the analyzer detects ammonia levels above a set point the NTF pump speeds increase.

Pump Speed Control Operation By-pass valve Position > < NTF Pump Output Nitrate > < Ammonia

Chlorination

Controlled Chlorine to Ammonia Ratio

Fecal Coliform Counts

Analyzer Accuracy

Instrument Accuracy Analyzer vs. Lab Instrument values are extracted daily at 8:00 am and logged to the historical data server. Operators collect a sample near the analyzer at ~8:00 am for analysis by the lab.

Final Effluent Ammonia vs. STIP Daily Average

Nitrate Buoy Recalibrated During Regular Maintenance - Suspect Poor Quality 3 rd party Reagent

ISCO/STIP Process Buoy

STIP Process Buoy  Operates by being placed directly in wastewater (even activated sludge)  Separate buoys for ammonium and nitrate

STIP Process Buoy  Follows EPA approved methods of analysis  Operates in a batch analysis mode with typical analysis times of 3 to 5 minutes  Measuring range of mg/l as N for both nitrate and ammonium

Method of Analysis - General  Solenoid valve opens permitting sample to fill settling chamber via hydrostatic pressure  Sludge settles for pre programmed time period  Ammonium and nitrate measured with ion selective electrodes (ISE)  Solenoid valve reopens permitting supernatant to fill measurement chamber

Method of Analysis - NH 4 N  Caustic (NaOH) added till pH>11.5  Ammonium is converted to Ammonia (gas)  Ammonia measurement taken with gas selective electrode

Method of Analysis - NO 3 N  Conductivity sensor used to add reagent (ion suppression) to adjust ionic strength of solution  Concentration measured with nitrate selective electrode

Method of Analysis - Schematic

Calibration  Buoy calibration is done using three step standard addition method  Calibrated automatically once per day

Buoy Bulkhead Layout

Process Buoy In Open Position  Shows Settling Chamber Settling Chamber Measuring Chamber Measuring Chamber Electrodes Electrodes Valves Valves Amplifiers Amplifiers

Process Buoy Without Stainless Steel Housing

Controller  One controller can operate two buoys  LCD screen displays current reading and graph of last 6- hours of operation  Outputs: 4-20 mA 4-20 mA Bi-directional RS 232 Bi-directional RS 232

The End