Miljøprojekt, 1050 – Afprøvning af jernspånefilter til rensning af grundvand forurenet med klorerede opløsningsmidler

Afprøvning af jernspånefilter til rensning af grundvand forurenet med klorerede opløsningsmidler

Summary

At the address Østergade 14, Lyndby in the county of Roskilde, a pilot plant was established in 1999 for survey of the processes in connection with breakdown of chlorinated aliphates in water by means of reactive granular iron. The plant consists of 5 filters connected in series, each with 1 m³ granular iron as filter material.

The pilot plant was established in connection with an existing preventive plant cleaning pumped up, PCE-polluted ground water by the use of filtration through active carbon.

The total operating period was just under 2 years, divided in two operating phases. In both of these the following was observed:

Half-life for PCE quickly rose from the 1.5 hours expected from the literature to 10 hours – a substantial increase.
Increasing pressure-loss across the plant was observed. This was caused by crust formation at the top of the filters. This crust formation started in the first filter and spread to the subsequent filters in the line.

As a consequence of the high half-life, a granular iron filter with a total volume of 130 m³ is needed to replace the active carbon plant in Lyndby. The establishment of a plant this size is unrealistic for economical as well as for practical reasons.

The crust-formation - and the growing pressure-loss over the filters caused by it – resulted in a very short lifetime for the plant. The problem might have been solved by a regular opening of the filters followed by removal of crust. In a full-scale plant this would however mean very high maintenance costs.

Based on the active carbon plant and the granular iron plant in Lyndby, an economical and environmental comparative analysis was performed. In this analysis it was assumed that the problems with high half-time of PCE and crust-formation was solved. The calculations were thus based on 1.5 hours half-time for perchlorethylene and a 25 year lifetime for the plant.

In the light of the above, active carbon cleaning of the water seems to be the most advantageous, based on an economical as well as an environmental point of view.