Mobile dewatering of dredged sediments: a case study from Belfast.
Type:
Presented during:
WODCON XVII: "Dredging in a Sensitive Environment" - 2004, Hamburg, Germany
Authors:
S. Pensaert
Abstract: One of the major problems associated with small local maintenance dredging works is the handling of the sediments. Often treatment centers are not available in the neighbourhood or even not available at all resulting in large transport distances for the sediments by barge or by road. After treatment, which is mostly limited to dewatering, extra transport is required to bring the dewatered sediments to a disposal site.
Due to the local and small nature of the dredging works (i.e. order of 1000 to 10,000 m³) an investment in a nearby dewatering center cannot be justified. A solution however is the deployment of a mobile mechanical dewatering plant.
DEC designed a mobile mechanical dewatering plant, of which the basis is a compact filter press of 2.8 m³ cake volume. The combination of the robust piston-membrane pump, parallel feeding of the filter press chambers, and wear resistant filter cloth allows sand and fine gravel particles up to 10 mm and reach productions of up to 6 tons an hour of dry solids. The high tolerance with respect to grain size reduces the need for pretreatment to a simple screening and sieving, and prevents dilution of the sludge with water which would only decrease the production drastically. The sludge cakes contain around 65 % of dry solids.
Moreover, as this filter press concept requires lime to improve dewatering, two extra beneficial effects are proven.
First of all, the lime increases the later geotechnical behaviour of the cakes being beneficial for disposal or when reuse is possible. Secondly, part of the organic pollutants and most of the heavy metals are immobilized, creating a new reuse potential for lightly polluted sludge.
Since October 2003 the mobile plant has been in action along the River Lagan in Belfast, where about 10000 m³ of PCB polluted sediment is being dredged. The paper and presentation will present the mobile dewatering plant and discusses its production efficiencies, costs, etc.
Keywords: dewatering, filter press, sediment treatment, dredging.