Analysis and monitoring of wastewater

Today, more than ever, environmental cause is one of the main concerns of everyone, from politicians and scientist, to the general public. All organisations must recognize the importance of protecting our ecosystems, and prosecutions for polluting the environment can not only lead to expensive fines, but can also result in companies image devaluation.

Water utility companies, industries with their own waster water treatment plants, petrochemical industries are acknowledging the importance of controlling pollution and are investing in high detection technologies and monitoring equipment, not just for clean water intake, but also for waste water in order to make sure water quality is acceptable before releasing in the nature.

In some of these cases where hydrocarbons pollutants are involved, instruments capable of measuring VOC at an early stage can prevent and reduce the impact on the environment and the costs related to the cleaning processes. There are already in the market several VOC detection methods available and can be simply used, with very little maintenance and calibration. Most of VOC detection technology are designed for ambient air monitoring, but some high profile companies developed similar solutions for liquid analysis.

Analysis and monitoring of wastewater quality for refinery processes was imposed by new environmental directives which require industrial sites to monitor their wastewater before release. Now, they must adapt their surveillance systems with automatic instrumentations.

Historically specialized in gas chromatography, Chromatotec has launched an analytical system, from liquid chromatography which has already proved its worth: the airmoVOC WMS. This unique and efficient Mcerts certified gas chromatography solution measures and quantifies VOCs and BTEX (Benzene, Toluene, Ethylbenzene and Xylene) dissolved in liquid matrices.

This unique instrument is composed of several parts and the most important one is the purge and trap system. This analytical tool, developed internally following US EPA 502.2 method, consists of an automatic sparger to extract VOCs from liquid samples in 11 min. The loop is filled with 5 ml of the liquid sampled by a pump and then are injected inside this glass purging device. Dead volume must be less than 15 ml. An inert gas, such as nitrogen delivered with embedded gas generator, is used to purge the water sparger with bubbles of less than 3 mm of diameter at the origin of the frit as shown here above.

Other contaminants in the sample, such as solid contaminants or bacteria, must be previously removed by water preparation systems (filters, separators) to avoid matrix and carry-over problems that may interfere with the analysis and also contaminate the gas chromatographic system.

The gaseous sample extracted from the liquid matrix is then injected automatically and in continuous mode into the system with a flow rate of 40 ml.min-1, regulated by a critical orifice 76µm. The sample passes first through a dryer to remove the humidity and then hydrocarbons are pre-concentrated on a trap filled with a mixture of Carboxen and Carbopack. The pre-concentrated air sample is thermally desorbed at 380°C for 4 minutes and directly injected in a 30m MXT 624 column (0.53 mm ID, 3.0 µm dF) located inside the oven of the GC, temperature-regulated at a very stable temperature to obtain repeatable retention times. Within the first minute of the analytical procedure, the oven temperature rises from 32°C to 34°C. Afterwards a constant heating rate of 7°C.min-1 is applied until 100 °C and then 10°C.min-1 until 200°C. Then the temperature is kept at 200°C for 600s before cooling. Hydrocarbons are detected by FID at 170 °C.

The typical cycle time is 60 minutes. This includes the following steps: automatic rinse (once with deionized water and then once with the sample), sampling, liquid injection in the sparger, purge with nitrogen, injection into the system, thermo-desorption, emptying of the sparger, separation in the analytical column, detection, quantification and cleaning of the system during acquisition.

This all-in-one solution is composed of an airmoVOC analyzer, hydrogen generators, nitrogen generator and zero air catalyzer. In addition, an internal calibration system can be inserted in order to validate the results and certify them in real time. The integrated multiplexing system allows the analysis of unknown gaseous samples, reference cylinders, embedded calibration (permeation tubes) and samples from the purge and trap system. The instrument has been designed in a robust housing and can work for long periods of time without maintenance. The main goal is to improve process efficiency and control using automatic on-line continuous monitoring without any human operations.

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