The performance of a demo nitrate analyser installed at Driefontein Wastewater Works, one of six hi-tech wastewater treatment facilities operated by Johannesburg Water, has resulted in Endress+Hauser winning a tender for six units. The water/wastewater industry has many defining characteristics, one of which is the long sales cycle that often requires instrument manufacturers to install demo units to prove the effectiveness of the instrument in the given process.
Endress+Hauser has been dedicated to investing time and expertise in finding optimum solutions for this industry for many years. At the beginning of 2003, the company installed a demo Stamosens sensor CNS 70 and transmitter CNM 750 - to form an analysis system for continuous nitrate measurement - at Driefontein Works. It was specially designed to monitor the denitrification process and the outlet of wastewater treatment plants. The nitrate content is determined using the multiple beam flash process. After 18 months of successful operation and consistent results that matched laboratory readings, Johannesburg Water sent out a tender for six nitrate analysers.
"We were awarded the tender in November 2003 and installation began in early 2004. The six units are installed in six different wastewater plants around Gauteng," says Endress+Hauser marketing manager, Grant Joyce.
Nitrate measurement is becoming more important as government requires nitrate levels in the outflow to not exceed 10 mg/l. At this stage the legislation is not official, but it is imminent. Besides monitoring the levels in the outflow, the nitrate analyser also enables the wastewater plant operator to optimise the denitrification process, with cost savings in the long term.
The measuring principle of the nitrate sensor is based on self-UV absorption by nitrate. The water or sludge sample is irradiated by light at a wavelength range of 190 nm to 2 mm. The transmission light is diverted by means of an optical system made up of mirrors and lenses, and guided to a photo-receiver.
Two sensitive photo-receivers are used for the measuring light (ML), which is being weakened in the presence of nitrate. Two other photo-receivers are used for the reference light (RL), which eliminates interference caused by suspended solids or organic substances. The in-field calibration feature helps the user adapt the measuring system to the wastewater requirements.
The picture shows Driefontein Wastewater Works, proving grounds for Endress+Hauser's Stamosens nitrate analysing technology, where nitrate measurement is becoming more important as government requires nitrate levels in the outflow to not exceed 10 mg/l.
For more information contact Grant Joyce, Endress+Hauser, 011 262 8000, [email protected], www.za.endress.com
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