New technology of mechanical treatment of dredged material from Hamburg Harbour

Harbours and water ways can only fulfil their commercial task if there is always sufficient water depth for navigation. Environmental problems have started to influence dredging methods in recent decades. As a logical consequence of a policy giving high priority to environmental protection, Hamburg built the METHA plant (Mechanical Treatment of Harbour Sediments). METHA produces a clean sand product (grain size > 63 mu m) which is reused and a contaminated silt fraction (grain size < 150 mu m) which is disposed presently. Previous investigations showed that the content of heavy metals and organic contaminants are primarily governed by the grain size. In 1995 Strom- und Hafenbau started a new investigation to produce a further fraction from the METHA silt which can be reused. The result of laboratory- and pilot-scale research showed the possibility of a further separation at 20 mu m grain size. The best result was reached through a two-step separation made by hydrocyclons and spirals. The produced fraction (20-150 mu m) is mainly quartz material with a low level of contamination. In February 1996 Strom- und Hafenbau decided to built a test plant in a technical scale. The capacity of the test-plant is 50 t/h based on dry substance The technical concept is integrated into the METHA concept. All aspects of technical feasibility, economy, environment and product reuse will be investigated in the test plant. The results of the early test phase will be presented. (C) 1998 IAWQ. Published by Elsevier Science Ltd.