18 WATER / WASTEWATER
Plug-‘n-play de-chlorination analyser measures near zero chlorine levels with repeatable accuracy
Municipal water system and industrial process engineers in search of an analyser that accurately measures near zero levels of chlorine will want to learn more about the plug-n-play, long-life DC80 De-Chlorination Analyser from Electro-Chemical Devices (ECD), which utilises a zero- shift methodology to ensure stable and reliable chlorine measurement prior to effluent discharge.
When measuring near zero amounts of chlorine, conventional amperometric chlorine sensors are unstable, and this leads to inaccurate or inconsistent readings. In comparison, the DC80 De-Chlorination Analyser utilises a “zero-shift” methodology to provide accurate measurement and to protect total chlorine sensors from damage, which occurs when the water samples measured contains near zero or zero levels of chlorine.
In wastewater treatment systems, for example, when monitoring for chlorine just before outfall, there can be no chlorine present and yet measurement is still necessary.
When there is no chlorine present then the electrode becomes unstable and finally unresponsive. For this reason, the process of measuring de- chlorination itself becomes problematic. When all of the chlorine is removed then the sensor will provide an inaccurate reading after a few hours and fail after a few days still reporting zero chlorine
Problem solved with the DC80 De-Chlorination Analyser: This next-gen total chlorine analyser uses “zero shifts” technology to monitor near zero amounts of total chlorine. Using this method, some chlorine is actually metered into the sample shifting the zero from a near zero chlorine concentration to a measurable value. The analyser’s offset feature allows the metered value to be subtracted from the measurement.
The presence of chlorine in wastewater treatment effluent, both municipal and industrial, is a potentially harmful contaminant that affects plants and other aquatic life forms.
The DC-80 De-Chlorination Analyser monitors chlorine in drinking water, wastewater, cooling water and other de-chlorination applications from 0.05 – 20 ppm. Its mounted system includes built-in flow control, which eliminates the need for complicated plug-and-play design installs quickly right out of the box.
The DC80 features advanced panel pressure regulators and rotameters. Built-in automatic pH compensation for samples between 4 and 12 pH also eliminates the need for expensive reagents to reduce maintenance and life-cycle costs.
The analyser’s total chlorine sensor is a three electrode amperometric sensor with a gold cathode, silver halide anode and 304 stainless steel counter electrode. The counter electrode provides a stable base potential that minimises drift for superior accuracy. The total chlorine sensor has a micro-porous membrane that allows ions to diffuse in and out of the sensor.
The analyser’s pH sensor provides accurate compensation for samples between 4 and 12 pH, which eliminates the need for a sample conditioning system. The total chlorine sensor graphically displays both the total chlorine and pH levels for easy trend analysis.
The DC80 Analyser is available with either 110-240 VAC or 24 VDC power. The standard configuration features dual measurements, two 4-20 mA outputs and three alarm relays. The user friendly DC80 also is available with an auto clean option that includes a solenoid actuated spray cleaner using either 30 psi process water or air. An easily adjusted timer controls the period and duration of the cleaning cycle.
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Responding to global demand for improved monitoring of nitrate in freshwater, OTT Hydromet has launched an optical nitrate sensor, the OTT ecoN, specifically for use in environmental surface and groundwater applications. “This is fantastic news for scientists, catchment managers, water companies, regulators and environmental consultants,” says Peter Schaeffeler, Product Lifeycle Manager at OTT HydroMet. “In the past, customers have been caught between low-cost/limited-performance sensors and high-end technologies, for which purchase costs prevent large scale deployment. The OTT ecoN neatly fills that gap; as a continuous nitrate monitor, with minimal maintenance requirements, it can be left to monitor in remote locations, and an optional wiper makes it suitable for extended deployments.”
In addition to a low purchase cost, the OTT ecoN also lowers the cost of ownership because it is factory calibrated for life. With automatic drift compensation, zero baseline checks with ultrapure water are quick and easy to perform and are only required as an occasional test of instrument function.
The OTT ecoN measures nitrate by the absorption of UV light at 212 nm and removes the possible effects of organics and turbidity by similar measurements at 254 nm and 360 nm respectively. As an optical sensor, the OTT ecoN provides high accuracy and low resolution without the drift and interferences of ion-selective electrodes, or the ongoing reagent and maintenance costs of wet-chemistry analysers.
The OTT ecoN can transmit data via an SDI-12 interface due to the new OTT ecoN Modbus to SDI- 12 Converter. The converter translates the Modbus protocol for the OTT ecoN nitrate sensor to allow for easy and continuous remote data access. Remote configuration can be achieved as well, to export data and configure the OTT ecoN via a web interface.
No specialised software is necessary to communicate with the OTT ecoN – a simple, intuitive browser- based user interface is accessed by connecting a small interface unit to the sensor.
Measurements can be stored internally within the sensor, but as a specialist in sensing, datalogging and telemetry, OTT HydroMet can supply the most appropriate monitoring system for every application. This includes the choice of sensor, because the OTT ecoN is available with different cell pathlengths to ensure optimum performance across all measurement ranges. However, OTT HydroMet is also able to conduct a retrospective change of optical path length when customers need to change application, such as moving it from very turbid surface water to groundwater for example.
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Summarising, Schaeffeler says: “Nitrate is an extremely important contaminant of fresh surface and groundwater; causing health issues in humans and playing a major role in eutrophication and the proliferation of algae. It is therefore essential that the role of nutrients is fully understood and that water professionals are able to access accurate, reliable data on nutrient sources and loading, as well as being provided with alarms when pollution events take place.
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“The OTT ecoN has proven extremely accurate and reliable in the field, and has been priced for extensive deployment, so we are very excited with the prospects for this technology.”
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IET JANUARY / FEBRUARY 2021
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Low maintenance UV nitrate sensor
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