Raw water intake monitoring - Case study


The Situation
Hydrocarbons in municipal water supplies, including fresh water and desalination systems, are commonly limited to less than 1 part per million. Surface water from rivers, lakes, or the sea with marine traffic, nearby pipelines, or regular flooding can be contaminated by hydrocarbons. Freshwater treatment systems can be damaged by hydrocarbons or allow them to pass through undetected. Desalination systems using reverse osmosis (RO) membranes can be irreversibly damaged by the presence of hydrocarbons. Continuous monitoring of water source intakes can prevent system contamination and subsequent damage. Accurate, low maintenance monitoring systems such as the TD-4100 XD and XDC have been protecting water intakes worldwide for over 20 years.

Naturally occurring organics in raw water are typically removed with chemicals. Total Organic Carbon (TOC) analyzers in the water treatment system can alert technicians when generic organic material is present but cannot differentiate between natural organics, such as algae or decomposed plant matter, and hydrocarbons. Using UV fluorescence technology, a properly configured TD-4100XD can alert operators to upsets caused by hydrocarbons such as gasoline, diesel, fuel oil, and crude oil. Desalination systems using reverse osmosis membranes can be irreversibly fouled and damaged by hydrocarbons. When fouled, the differential pressure across the membranes increases, as does the pumping energy needed to maintain the same flux rate through the membrane. Membrane cleaning and restoration to 100% is nearly impossible.

A fluorescence monitor can be configured for sensitivity to hydrocarbons, with reduced response to other organics. The TD-4100XDC has the highest sensitivity to hydrocarbons in raw water, has a low cost of ownership, and can be modified with Teflon, Monel, and other corrosion resistant materials for sea water environments. For raw water intakes, the TD-4100XDC can measure diesel from the limit of detection, other fuels, polycyclic aromatic hydrocarbons (PAH), and is sensitive to benzene, toluene, ethylbenzene, and xylenes (BTEX).

The fluorescence measurement is instant, continuous, and direct with no chemicals, reagents, or sample conditioning. Local technicians can perform all regular maintenance and calibrations.

The flexible optical arrangement of the TD-4100XDC reduces the response to naturally occurring organics in the water, usually without sacrificing hydrocarbon sensitivity. In Graph 1, you can see the measurement of a raw water intake system using a TOC analyzer (in green) and a fluorescence monitor (in red). The TOC analyzer is responding to both natural organics and hydrocarbons. The fluorescence monitor is responding to only the hydrocarbons present in the water.

In the 'Contamination Warning Systems' chapter of Security and Emerfiencv PlanninR for Water and Waste Water Utilities, the American Water Works Association has recognized the TD-4100 series monitors as a method for detecting BTEX and dissolved fuels in drinking water intake.

The TD-4100XDC includes some important features for reducing the cost of ownership, such as field replaceable components. Unlike other fluorescence monitors, the TD-4100 series of monitors can be fully maintained in the field, including field calibration. Further, a unique 'cell condition monitor' verifies that the optical system is clean, and alerts the operator if cleaning is needed. Monitoring history is displayed on the monitor screen, and all diagnostic data, including calibration values, can be accessed through the USB port or the Ethernet connection for quick, remote troubleshooting.

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