24 Water/Wastewater
Final Effluent Monitors Protect Wastewater Treatment Efficiency
Southern Water operates 370 wastewater treatment plants (WWTP), many of which are unmanned for most of the time and most have numeric environmental permits, so a network of online monitors has been established to improve treatment and protect discharge compliance. This has involved the installation of final effluent monitors at over 300 sites in a programme that has lasted for more than ten years.
The project has been very successful because we have established the skills, tools and spares to ensure that every installation is conducted quickly and efficiently and the quality of the HACH LANGE instruments ensures reliability and accuracy.
The online monitors are comprised of a HACH LANGE turbidity probe with sensors for temperature and level (to show when the turbidity probe is out of the water) and mounted on a plastic ‘spade’ which holds the sensors in position at the final effluent monitoring point.
Using turbidity to estimate BOD and TSS
As a measure of clarity, turbidity provides extremely useful data; a cloudy final effluent suggests poor treatment and possible discharge permit failure.
In 1993 Southern Water conducted an extensive research project to demonstrate that effluent clarity, as measured by turbidity, can be related on a site by site basis to permitted BOD (Biological Oxidation Demand) and TSS (Total Suspended Solids).
The constituents of final effluent are such that biological slimes and algae are prone to develop on optical surfaces, and the trials therefore concentrated on the most efficient method of probe cleaning. Probes with no automatic cleaning were therefore eliminated. The technically preferred monitor was the HACH LANGE Solitax turbidity probe, which incorporates a silicon rubber wiper, which sweeps over both optical surfaces at a programmable frequency. Southern Water also found that the cleaning efficiency was improved by the addition of an air purge which blows away the loosened solids.
MCERTS certification on 1st November 2012. MCERTS is the Environment Agency’s monitoring certification scheme and currently only a small number of analytical instruments have achieved this award. However, an MCERTS certificate demonstrates that equipment has met or exceeded the stringent performance requirements of the scheme.
The monitor control unit is mounted in a separate cabinet which also houses the air compressor. When the plc calls for a clean, the wiper operates followed by two air purges which release the algae/biofilm. A further wipe then removes any remaining material.
Cleaning is initiated every hour and, when a clean is called for, the last recorded turbidity reading is held in the monitor for 5 minutes, to avoid recording the false turbidity generated by the loosened material.
Design and Installation
Linton Electrical Contractors (Kent) Limited has a longstanding relationship with Southern Water and was responsible for the final design and installation of the final effluent monitoring systems. Subject to prior approval by Southern Water, the installations incorporate the latest HACH LANGE instrumentation as it becomes available.
D Ballinger
R Reeves Author Details:
D Ballinger & R Reeves, Southern Water
Contact Details: Sarah Blayds
HACH LANGE LTD Pacific Way, Salford, Manchester. M50 1DL
Tel:+44(0)161 872 1487 Fax: +44(0)161 848 7324 Email:
info@hach-lange.co.uk Web:
www.hach-lange.co.uk
The Solitax probes use a single LED light source with three detectors, one for light intensity and two for light scatter. HACH LANGE’s Clive Murren says “This provides reliable colour-independent readings with a low maintenance requirement. However, we have a contract to routinely visit each site to service and calibrate the turbidity sensors.”
HACH LANGE has confirmed that the SC200 and SC1000 HACH LANGE controllers and the SOLITAX sc turbidity probe were awarded
IET Annual Buyers’ Guide 2013
www.envirotech-online.com
Linton Electrical is now installing as standard the 110V MKV SC200 controller and occasionally the MKVI SC1000. Each system is complete with conductivity sensor, level sensor, temperature probe and air cleaning system; all of which is mounted on a PVC spade.
Linton’s Mark Pendry says “The project has been very successful
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