UV- Photometry used in Water Treatment Applications

MONITORING OF DISSOLVED ORGANICS IN WATER

The amount and character of dissolved organic carbon is a very important factor in the majority of the water treatment processes. This parameter is relevant for cost, effectiveness and quality of water treatment.
Our advanced inline UV-Colour photometer allow for reliable and accurate in-line detection of the dissolved organics and coloured species. The instruments contribute to determine the chlorine demand and the disinfection requirement to prevent by-product formation. The real time monitoring of dissolved organics will reduce costs through improved coagulation control, disinfection by chlorination or UV irradiation.

The UV photometer are used in the areas of:

• Wastewater

• Drinking water

• Surface water

• Chemical/industrial process water

• Spring- and well water

Dissolved organic substances in water are normally derived from biological substances and processes. These organic substances can reduce the efficiency of water treatment processes and lead to new toxic substances. A high load of these organic substances:

• Require removal with coagulation, flocculation and sedimentation

• Contribute to colour and taste issues

• Reduce the effectiveness of UV disinfection processes

• Form chlorinated disinfection by-products such as THMs (trihalomethanes) or haloacetic acids

IMPROVED MONITORING OF DISSOLVED ORGANICS

Our instrument design incorporates the following features:

• Real time monitoring of the sample with or without compensation for turbidity

• Low maintenance, high long-term reproducibility and stability.

• Extreme long life time of the Hg- UV- lamp

• Automated cleaning of the flowcell (optional)

• Dual wavelength option

254NM MONITORING OF ORGANICS AN ALTERNATIVE FOR TOC DETERMINATION

In response to the increasing use of UV measurement for dissolved organic substances in water and wastewater, The Standard Methods Organization, authors of Standard Methods for the Examination of Water and Wastewater, adopted Method 5910 in 2000. This method describes the measurement of dissolved organics using absorbance of UV light at 254 nm.

Figure 1. Correlation between TOC and UV absorbance.

There have been numerous studies that have characterized the relationship between total organic carbon or dissolved organic carbon and UV absorbance at 254 nm. TOC and UV₂₅₄ are complete different methods but fortunately there is a general correlation between the two measurements. Figure 1 shows the correlation between TOC and UV absorbance for water from the Alberta river system.

APPLICATIONS

UV- photometer can be used on the clean water side to improve control of UV irradiation or to predict THM formation due to chlorine addition. The monitoring of the raw water provides information about dissolved organics in the water. The degree that the dissolved organics are removed during the water treatment process depends on the nature of these organics and the treatment process itself. Treatments such as enhanced coagulation and the addition of activated carbon may be required for some surface waters.

Figure 1. Correlation between UV absorbance and cagulant dosage

The coagulation levels are typically controlled to achieve certain settled and filterable turbidity levels. Turbidimeters do not show a good correlation between chemical addition and turbidity. The correlation of the UV- absorbing organics compared to the required coagulant dose is shown in Figure 2. In this figure it is clear that the coagulant dose trends very closely to the UV absorbance. The correlation between UV-Absorption and coagulant dose is much better than the correlation between the raw turbidity values and coagulant dose.

Numerous studies have shown that UV absorbing species are more reactive to chemicals used for adsorption, coagulation, and disinfection. Normally dissolved UV absorbing substances may dominate the water purification chemistry even though these substances are not the target substances. For these reasons UV absorbance is excellent for measurement of dissolved organics in control or addition of the following water treatment chemicals: