Provides Real Time

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Nov 5, 2013 (3 years and 9 months ago)

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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

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

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

<
----

Calibrated Properly
-----
>

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 0.1
-

50
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


Measuring Chamber


Electrodes


Valves


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


Bi
-
directional RS 232

The End