Tel: +44 (0) 1726 879800

www.partech.co.uk

Dissolved Oxygen

Applications• Wastewater Treatment Plants

– Used in activated sludge tanks for the control of nitrification strength • Surface Water Monitoring

– Oxygen measurement in rivers, lakes or seas as an indicator of the water quality.

• Water Treatment– Intake Protection– Reservoir Water Quality

• Fish Farms– Oxygen measurement and regulation for optimum living and growth conditions

Inlet- Dissolved Oxygen

Inlet works

Storm Water

Activated Sludge- Dissolved Oxygen Tertiary

River- Dissolved

Oxygen

Product Application – Wastewater Treatment

oooooooooooooooooo

oooooooooooooooooo

oooooooooooooooooo

oooooooooooooooooo

oooooooooooooooooo

oooooooooooooooooo

oooooooooooooooooo

oooooooooooooooooo

oooooooooooooooooo

oooooooooooooooooo

oooooooooo

From Primary Settlement

Aeration tank

Aeration System

Clarifier

To Outfall or Tertiary Treatment

Sludge Recirculation Excess sludge extraction

• Activated sludge is a biochemical process for treating sewage and industrial wastewater that uses air (or oxygen) and microorganisms to biologically oxidize organic pollutants, producing a waste sludge (or floc) containing the oxidized material.

• The oxygen reacts with ammonia to form nitrate (nitrification process).

• Atmospheric air or pure oxygen is bubbled through primary treated sewage (or industrial wastewater) and combined with organisms to develop a biological floc which reduces the organic content of the sewage

• The combination of raw sewage and biological mass is commonly known as Mixed Liquor.

Simplified Diagram of Activated Sludge System

Air is forced into the aeration basins, it increases the activity of the micro organisms and helps keep the organic waste thoroughly mixed

Oxygen is added to the aeration basin to enhance the nitrification process by providing oxygen to combine with ammonia to form nitrates

Micro organisms must have at least 0.1 to 0.3mg/l DO. Plants maintain the DO to 2 mg/l. If the DO is less than 2mg/l the bugs in the centre of the floc may die as the bugs on the outside of the floc use up the DO first. If this happens the floc breaks up and settles poorly

When the DO comes too high it wastes energy. The aeration process takes between 30-60% of the total electrical power in a WwTW. Automated aeration process using DO according to the ESEPA may reduce energy costs by 50%.

Also adds benefit of mixing, bring the bugs, oxygen and nutrient together. This keeps the floc suspended and prevents it from settling

Why Measure Dissolved Oxygen?

Platform over aeration process

Over aerated process with inaccessible

probesSample point is

critical

Find• Representative

sample point of the process

• Well mixed sample• Safe to reach

sensors

Avoid• Dead Zone• Extreme Turbulence• Area next to Aerator• Hazardous access to

sensor• Reaching over

handrails

Ensure Success – Pick Your Location?

Outlet

RAS

Inlet

Aerator

Aerator

Aerator

Where should the DO sensor go?

Oxidation Ditch

Oxidation Ditch

Outlet

RASInlet

Aerator

Aerator

Aerator

Here

Not representativeNot

fully mixed

False High

Good Balance

Technologies

Active Membrane with Luminescent Molécules on an Inerte Material

Inert Membrane allows DO molecules to pass into the electrolyte

The Sensing Environment for an Optical Cell consist of an optical arrangement where the membrane is excited by an LED to cause a luminescent response. The oxygen reacting with the surface of the membrane causes the luminescent properties to change and hence DO can be monitored.VariationsLED Wavelength: Green or BlueMembrane MaterialMembrane Life

Sensors Technologies - ComparisonsThe Sensing Environment for a Galvanic Cell consists of a cathode and anode surrounded by an electrolyte. The oxygen passing through the membrane reacts with the electrolyte generating a potential difference proportional to the concentration of dissolved oxygen. Variations:Clarke Cell – electrolyte is consumed and sensing heads needs replacing.Mackereth Cell – electrolyte is not consumed and no sensor replacement is required.Membrane MaterialsElectrolyte CompositionAnode/Cathode Materials

Anode Cathode

Receiver Emitter

The cell is cylindrical in construction, the anode is so constructed as to give the maximum surface area to improve response.(the type 3 electrode –used for sewage applications has an iron anode)

The membrane may be of polyethylene, silicone rubber, PTFE, or any membrane showing good permeability to oxygen. In this cell the oxygen reacts with the metal anode and ceramic cathode generating a current, which is directly proportional to the partial pressure of the oxygen passing through the membrane. It is in effect an electrochemical cell. The electrode has a high temperature coefficient but a thermistor is built into the cell to give temperature compensation over a range from +2 to +40˚C. The signal is amplified and displayed either as concentration or percentage saturation.

Dissolved Oxygen Sensors Technologies – Galvanic Membrane

Compare a good optical sensor and a good galvanic sensor and there is little to choose between them.

• Optical has a shorter response time (5 times faster than galvanic) and can monitor in static water.

• Optical Membrane caps can have a short life.– 12 – 18 month enforced replacement for some.

• Good Galvanic sensors will last 3+ years between refurbishments.

Does the Sensing Technology Matter?

Good Optical and Galvanic sensors work• Choose a good sensor, the principal of operation is only part of

the decision.• Correct installation is key to success.

Maintenance is required and must be included in operating budgets• New monitors need to be quickly integrated into operator and

technicians work programmes, not left until they fail.• Or use the supplier/ICA contractor to look after the equipment.• Consider who will do the calibration, cleaning and servicing of

the instrument.

Product Information

OxyTechw 2 ™ OPT• Dissolved Oxygen & Temperature Sensor• Optical Luminescent Technology• Applications

• Activated Sludge Control

OxyTechw 2 ™ GAL• Dissolved Oxygen• Galvanic principle.• Applications.

• Activated Sludge Control• Exceptional resistance to damage. Long term

stability of 3 years without need for sensor replacement or membrane replacement

Fast response – Minimal Maintenance

Sensors – Dissolved Oxygen

• Provides self cleaning action on face of sensor

• Prone to ragging and fats/grease

Floating Ball

• Places sensor below the surface.

• Prone to ragging

Rigid staff

• Ragging falls off by moving sensor

• Places the sensor below the surface

• Provides self cleaning action on face of sensor

Flexible Shaft

Sensors Installation & Cleaning

7300w 2 Monitor/ControllerMultiple Sensors• 1 or 2 into the base unit• Upto 8 using expansion boxes• Any w² sensor is compatible with the monitor

Graphic Display with trending• Easy to configure• Multiple language ability

Flexible control and monitoring options• Profibus output – anticipated late 2011• Triple Validation option• Dosing control and datalogging available on request

Example of a Dissolved Oxygen Application

Example of connection layout for 7300w2(1 or 2 sensors)

Example of connection layout for 7300w2(1 to 8 sensors)

Portable OptionGalvanic Sensor

• Self Polarising and Self Temperature Compensated

No warm up time, short response time• 90% of end value in less than 20 seconds

Automatic Calibration and self check

1400 hours from one 9V alkaline battery• Approximately 2 years with 1 hour use per day

Large easy to read graphical LCD display

Tel: +44 (0) 1726 879800

www.partech.co.uk

Andrew Wallace -Field Sales EngineerMobile: 0777 815 0118Email: andrew@partech.co.uk

Angus Fosten -Sales and Marketing DirectorMobile: 0776 846 5581Email: angus@partech.co.uk

Clive Teobald -Sales EngineerMobile: 0796 601 3446Email: clive@partech.co.uk

Derek Bourne -Export Sales and Marketing DirectorMobile: 0780 857 2573Email: derek.bourne@partech.co.uk

Jan Johnson -Sales AdministratorEmail: jan@partech.co.uk