Reliable, Representative & Relevant The 3 R’s for online ... · • GSE - Use of caustic dosing with the GSE to release ammonia from solution to gas phase • Minimal interferences

Innovation in Environmental & Process Technology

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Reliable, Representative & Relevant

The 3 R’s for online waste water measurement



Two very different analyser design approaches to

ensuring reliable, representative and relevant dataA. PBS Insitu auto-calibrating ammonia monitor

B. Lar Quick Cod / Toc Ultra High temp oxidation

PBS

Insitu

Ammonia

Lar Quick COD Ultra



Typical causes of sampling errors –

taken from discussion of Water & Steam sampling issue – Jonas, Power

engineering May 2005

Causes of Sampling Errors (in Order of Priority/Impact)

• Sample withdrawal...

• - not representing sampled stream (wall effects, stratification, not

isokinetic, mixing, etc.)

• - not representing all phases (solid, liquid, gas)

• Deposition in sample line (could also result in plugging)

• Deposit release (leading to spikes)

• High pressure drop resulting in insufficient sample flow

• Changes in sample flow rate

• High sample temperature (causing pH and conductivity errors)

• Chemical reactions in sample lines or coolers (oxygen reduction, etc.)

• Deposition in the pressure reducing device



Typical causes of sampling errors

Causes of Sampling Errors (in Order of Priority/Impact)

• Dissociation of water in the pressure reducing device - forming O2 +

H2 (high pressure and temperature water)

• Leakage of cooling water into the sample - leaking sample cooler

• Corrosion of the sampling system - generation of corrosion products

• Filters in the sampling system interfere with sampling suspended

solids

• Sorption on sample tubing and suspended oxides removes a portion of

monitored chemical species

• Leakage of air into grab sample container increases O2 and

conductivity, reduces pH, possible introduction of bacteria)

• Dissolution or precipitation and plating-out of metal species in the

sample tubing and containers



Representative• Flowsampler – example 1

• High Flow – Iso 5667-14 – Isokinetic sampling

• Aprox 1 m/sec

• No requirement of filtration


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IsoKinetic Sampling



Representative• Flowsampler

• High Flow

• 1 m/sec

• No requirement of filtration



Representative• Flowsampler

• Influence of filtration

Sample Analyser

with filter

Lar Quick

TOC Ultra

1 53.4 110

2 ➢ 50 122

Airport Site TOC

measurement

Ultrafiltration for Uv TOC analyser

Lar Quick TOC Ultra gave results

double the Uv TOC



RepresentativePBS , or Process Buoy, In-situ – example 2

• Measuring settled activated sludge



RepresentativePBS In-situ – example 2

• Measuring settled activated sludge


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Solenoid valve opens

permitting sample to fill

settling chamber

Solenoid valve

reopens permitting

supernatant to fill

measurement

chamber

Ammonia is measured with

gas-selective probe

Sludge /solids settles for pre

programmed time period

Reagent is

added to

increase

pH>11.5 and

convert NH4

(Ammonium) to

NH3 (Ammonia)

Sample is mixed


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Relevant – Example 1• Ammonia - PBS

• Uses a GSE –Minimal effect of interferences

• Only volatile amines effect the GSE probe

• The Ammonium electrode is effected by interferences such as

Potassium

• Electrode membrane is prone to drift and fouling

ISE

Ion Selective

Electrode

GSE

Gas Sensing

Electrode



Relevant – Example 1• Ammonia - PBS

• GSE - Use of caustic dosing with the GSE to release ammonia from

solution to gas phase

• Minimal interferences and probe is kept clean

ISE GSE



Relevant Filtration installed to protect the analyser from fouling often results in

changing the nature of sample being measured

• Ammonia can be reduced by slime build up resulting in local

nitrification / de-nitrification


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Relevant- Example 2• Measuring throughout the WWTP process with the Lar Quick COD analyser



Relevant• COD – Lar Quick COD Ultra

• Oxygen demand method close to dichromate oxygen demand method

• Speed of response

Typical Ratio of TOC v COD in

waste water in various industries


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RelevantUsing an analysis technique developed for clean water for waste water often

doesn’t perform as well as expected – e.g. Uv TOC oxidation

• Incomplete measurement

• Require lots more chemicals

• Slows the response so that spills can be missed


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RelevantUsing an analysis technique developed for clean water for waste water often

doesn’t perform as well as expected

• Poor recovery efficiencies – effects of high salt

• Can require significant dilution – slows response and leads to

inaccuracies


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How hot is 1200 oC


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Quick COD Ultra Method –Oxygen Demand rather than CO2 Production



RelevantCOD – Lar Quick COD Ultra

• Speed of response



Reliable

Others - Achieved ? With add on’s :• Filters

• Ultrasonics

• Air cleaning

• Chemical cleaning

• Wipers



Reliable• A design approach - Minimise contact between the mechanics of the

analyser and the waste water material itself

• PBS insitu – use of air to fill and remove the sample

• Lar Quick COD Ultra – use of XY robot

• Autocheck / Autocalibrate

• Calibration is always needed when measuring waste water.

PBS

Insitu

Ammonia

Quick COD Ultra


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Typical installations

Sample Handling Capability Crucial !

Zoogloea Biological slime is typical in final effluent


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Solenoid valve opens

permitting sample to fill

settling chamber

Solenoid valve

reopens permitting

supernatant to fill

measurement

chamber

Ammonia is measured with

gas-selective probe

Sludge /solids settles for pre

programmed time period

Reagent is

added to

increase

pH>11.5 and

convert NH4

(Ammonium) to

NH3 (Ammonia)

Sample is mixed


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Reliable• Complicated sample paths through small tubes bring reliability issues


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Reliable• Complicated sample paths through small tubes bring reliability issues


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Lar Quick COD Ultra :



Summary:• Understanding the nature of the waste water itself and designing the

analyser to take this into account can result in Relevant,

Representative and Reliable data

• The PBS and the Quick COD Ultra are both very similar and very

different in the way this is achieved

PBS

Insitu

Ammonia

Quick COD Ultra


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Any Questions ?

Documents

Reliable, Representative & Relevant The 3 R’s for online ... · • GSE - Use of caustic dosing with the GSE to release ammonia from solution to gas phase • Minimal interferences