General Cleanup Technology

Optimisation of vacuum stripping technologies for groundwater decontamination

In this project, vacuum stripping techniques were tested and optimised for the treatment of VOC contaminated groundwater. The use of a vacuum stripping process allows the mass transfer of pollutants from the liquid to the solid phase without the precipitation of other dissolved matter as a result of contact with air.

Summary

Air stripping processes are generally used for the cleaning of water contaminated with VOCs (volatile hydrocarbons such as chlorinated hydrocarbons and BTEX aromatics), during which the VOCs pass through the gaseous phase.  Yet such air contact often also prompts the precipitation of other dissolved matter, such as iron and manganese. 

The aim of this project was therefore to further develop two milieu stable (constant pH value, O2 concentration) anoxic vacuum stripping technologies (atomization and thin film spraying), which negate the need to use complicated pretreatments of water to avoid precipitation processes. First the Henry coefficients of the contaminated water were determined, which provide information regarding the distribution of pollutants in the liquid and gaseous phases. The packing material for the wastewater facility consists of a quartz pebble mixture (grain diameter 3.2 – 5.6 mm). The two systems developed were tested at two locations, SAFIRA Bitterfeld and Zeitz. 

Results:

  • The efficiency of the stripping procedure increases as the system pressure decreases. The Henry coefficients changed with a variation in the range of 10kPa < P < 100 kPa, which was not significant.
  • Beyond its critical micelle concentration, the biosurfactant sophorolipid leads to a stark reduction of the Henry coefficient.
  • In terms of atomisation, parallel gas carrier ducts are more efficient than ducts aligned in a row.
  • Water circulation within the atomisation system increases efficiency. The limit of quantitation of contaminants is nearly reached through the use of atomisation, meaning that it can be used as a fine purification stage.
  • The use of auxiliary gases (nitrogen, carbon dioxide) does not increase the mass transfer. However, they can serve to control the environment, as measures of the control parameters and precautionary concentrations show milieu stability during use of both pilot systems.
  • For monochlorobenzene (MCB), atomisation yielded an efficiency of 80 % (with continuous operation) and 98 % (interval operation). Stripping MCBs through irrigation results in an efficiency of > 98 %.
  • Both systems achieved a sanitation effect without pre-treatment, at a level sufficient for the re-infiltration of the water.

Project Participants

Implementing Institution

Dresden Groundwater Research Centre (DGFZ e.V.)

More Project Informations

Project title:  Verbundprojekt: Erforschung, Entwicklung und Erprobung der Möglichkeiten zur Aufbereitung von HKW-kontaminiertem Grundwasser durch Vakuum-Strippen mit Konditionierung (VSK)

Project number:  02WT0504

Project period:  2005 - 2008

Project region:  Germany (Saxony)

Project contact:

Herr Dr.-Ing. Giese

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Source: German National Library of Science and Technology Hannover (TIB)