Background
In accordance with the German Drinking Water Ordinance (2001), the 1 NTU turbidity limit at the outlet of the waterworks must be adhered to and any sudden or continuous increase must be immediately reported to the responsible authority. To guarantee this, online measurement technology which continuously measures turbidity and then transfers the values to a control system is used in most cases nowadays. The compulsory measuring technique in Europe, as per ISO 7027, is the 90° scattered light method using an NIR light source with a wavelength of 860 nm (+/-30nm). Because mineral deposits and other contaminants can negatively affect the optical measuring system, the accuracy of the system must be regularly checked and corrected if necessary. Calibration is performed to so-called liquid secondary standards which are traceable to Formazin. These calibration liquids are extremely expensive. With conventional systems, the liquids must be filled directly into the device and then disposed following calibration. Multiple use is not possible due to the possibility of cross-contamination. In addition, the contaminated optics must be regularly cleaned. Accordingly, the calibration and maintenance of the turbidity systems is extremely time-consuming and expensive. A reduction in the amount of maintenance as well as the possibility of multiple usage of the calibration standard is thus desirable.
• Continuous turbidity measurement in accordance with ISO 7027
• Easy to calibrate thanks to cuvette technology
• Minimal maintenance thanks to ultrasonic cleaning
Measurement requirements
In addition to measuring the turbidity at the outlet of the waterworks in order to monitor limits, additional turbidity measurement points are often located at the inlet and outlet of the sand filter to monitor the filter and initiate back-flush processes. It is important to ensure that this measuring point operates automatically and as continuously as possible with minimal maintenance.
Customer benefits
The KROHNE OPTIMASS flowmeters considerably reduced the filling time of the mixers. In addition, the filling of the mixers now stops automatically. Precise adherence to the mixing ratios of the chemicals increases the quality of the colour and paint additives. The long-term stability and excellent reproducibility of the OPTIMASS meters also contributes to this.
The increased in accuracy when filling the mixers with the various chemicals increases product quality. Self-drainage and the lack of need for maintenance also lower operating costs.
Solution
The OPTISENS TUR 1050 turbidity measurement system is used to monitor turbidity values before and after the sand filter and during the process. The measurement is to be done as a bypass measurement with an open outlet. The system features automatic ultrasonic cleaning of the measuring cuvettes and is calibrated using reusable calibration cuvettes which contain a traceable secondary standard.
Products Used
OPTISYS TUR 1050 turbidity measuring system
• Turbidity measurement using a 90° scattered light technique
(ISO 7027 / EPA 180.1)
• Measuring range 0…100 NTU/FNU
• Compact device with 1x 4..20 mA current output,
RS485 interface and 2 alarm relays
• Cuvette technology makes it easy to calibrate and isolates the
optical measuring system from the
