Dissolved Oxygen. Tel: +44 (0)

Transcription

1 Dissolved Oxygen Tel: +44 (0)

2 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

3 Product Application Wastewater Treatment Activated Sludge - Dissolved Oxygen River - Dissolved Oxygen Tertiary Inlet - Dissolved Oxygen Storm Water Inlet works

4 Simplified Diagram of Activated Sludge System From Primary Settlement Aeration tank To Outfall or Tertiary Treatment ooooooooooooooooooo ooooooooooooooooooo ooooooooooooooooooo ooooooooooooooooooo ooooooooooooooooooo ooooooooooooooooooo ooooooooooooooooooo ooooooooooooooooooo ooooooooooooooooooo ooooooooooooooooooo Clarifier Aeration System 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.

5 Why Measure Dissolved Oxygen? 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

6 Ensure Success Pick Your Location Platform over aeration process Over aerated process with inaccessible probes Sample 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

7 Oxidation Ditch Aerator Inlet RAS Aerator Outlet Aerator Where should the DO sensor go?

8 Oxidation Ditch Aerator Inlet RAS Aerator Outlet Not representative Not fully mixed Good Balance False High Aerator Here

9 Technologies

10 Sensors Technologies - Comparisons 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. Variations LED Wavelength: Green or Blue Membrane Material Membrane Life The 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 Materials Electrolyte Composition Anode/Cathode Materials Active Membrane with Luminescent Molécules on an Inerte Material Inert Membrane allows DO molecules to pass into the electrolyte Receiver Emitter Anode Cathode

11 Dissolved Oxygen Sensors Technologies Galvanic Membrane 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.

12 Does the Sensing Technology Matter? 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 month enforced replacement for some. Good Galvanic sensors will last 3+ years between refurbishments. 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.

13 Product Information

14 Sensors Dissolved Oxygen 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

15 Sensors Installation & Cleaning Floating Ball Rigid staff Provides self cleaning action on face of sensor Prone to ragging and fats/grease Flexible Shaft Places sensor below the surface. Prone to ragging Ragging falls off by moving sensor Places the sensor below the surface Provides self cleaning action on face of sensor

16 7300w 2 Monitor/Controller Multiple 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

17 Example of a Dissolved Oxygen Application

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

19 Example of connection layout for 7300w 2 (1 to 8 sensors)

20 Portable Option Galvanic 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

21 Angus Fosten - Sales and Marketing Director Mobile: angus@partech.co.uk Derek Bourne - Export Sales and Marketing Director Mobile: derek.bourne@partech.co.uk Andrew Wallace - Field Sales Engineer Mobile: andrew@partech.co.uk Jan Johnson - Sales Administrator jan@partech.co.uk Clive Teobald - Sales Engineer Mobile: clive@partech.co.uk Tel: +44 (0)