An innovative Water Treatment Solution for Heavy Metals
Challenge:
In the Summer of 2011 HMVT was asked to provide a practical solution for the treatment of 600 m³ polluted water in an old cellar in Zwolle, The Netherlands. On this project old buildings were being demolished and also a soil remediation was carried out. The location was severely polluted with Chromium3, Chromium6 and Nickel. As a result of the very wet Summer the old and still to demolish concrete cellar stood full of polluted water with Chromium6 concentrations of 400.000 µg/l. A temporary water treatment plant based on ion-exchange was having a lot of problems due to clogging and was not capable of treating the water to meet the discharge levels.
Solution:
Our solution was based on precipitation of the heavy metals to the bottom of the cellar and additionally discharging the cleaned water to the local sewage system. The residual
polluted sediments could then be removed together with the demolishing of the cellar and the soil excavations and for treatment transported from the site. Before executing this plan, we first collected water from the location and tested this water in our lab facility. The aim was to find a recipe of needed chemicals which could meet the local water discharge levels (<100 µg/l). The lab results were then translated to the full scale situation.
Results:
The First lab results showed that the water contained mainly Crhomium6. The concentrations showed to be much lower than earlier levels: 25-36.000 µg/l. We found out that a three-staged treatment with chemicals was needed to get the best results. Phase 1 was a pH correction. Then the Chromium was precipitated with iron3chloride and the last step was to ad a polymer for optimal settlement of the created sediments. In the lab we could reduce the water concentrations below 100 µg/l. Also visible results where good: a good defined sedimentation with on top a brightened water. The lab results where then translated to the full scale application. In the field the water in the old cellar is been treated with the same recipe by spraying the different chemicals over the water surface. Due to the wet autumn the total amount of water was raised from 600 to 1.500 m³ and in the end we had to treat the water several times. Each treatment lasted 1-2 days. But the results were very good: like in the lab we were able to reduce the Chromium6 concentrations below 100 µg/l.
Beside the on-site water treatment we also took care of the discharging of the water in the cellar. Discharging this water without the sediments was done by floating pumps. To be sure, we also installed a small water treatment unit to prevent any sediments from discharging to the local sewer (sand filtration).
