CRUISE LINER TECHNOLOGY
The Scanship bio-sludge drying process comprises a contact dryer with hot-air scrubber, plus an air dryer with filter.
handling room, where it is sorted manually into: burnable waste, glass (which is crushed), steel and aluminium tins (compressed for recycling), and cardboard, paper, plastics, and general waste. From here, burnable waste passes to a hopper, where it is shredded to reduce the volume and improve the burnable value, and then to a silo, which feeds the incinerator. The Scanship incinerator, with its multi-secondary chambers for decomposing dust and toxic materials, is fully automatic and approved by IMO and MARPOL. A special enclosed line using vacuum transport technology handles food waste fully automatically. Up to 20 feeding stations (operated by press-button) can be incorporated, and two separate lines are normally fitted; these can be linked via a cross-over line in the case of an equipment emergency. All waste ends up in two main collection tanks, which act as buffer zones and can separate out cutlery which may have accidentally been dropped into the chutes. Before proceeding to the bio-sludge treatment plant, waste is dewatered in a screw press and mixed with waste from the separate advanced waste-water purification (AWP) line handling food-waste liquid, black, and grey water.
This comprises
mechanical separation, aerobic biological respiration, chemical precipitation with dissolved air flotation, tertiary micro- filtration, and finally ultra-violet sterilisation. Solids (as sludge) are separated from the liquid, dewatered, and dried for final incineration or shore disposal.
After this
treatment, most of the resulting water can be pumped directly overboard in compliance with regulations, but a small quantity collected as solid sludge can be further processed further for incineration or bagging. Official liquid sampling has shown that Scanship average results are well below the Murkowski standard, eg, <10mg/litre for total suspended solids and biological oxygen demand, compared with Murkowski's <30mg/litre requirements for each. Faecal coliform bacteria and total chlorine figures were below the detectable limit for Scanship's waste water. These figures mean that waste water can be discharged continuously. As an added bonus, effluent has US Coast Guard approval for use as ballast water if necessary. Scanship has also supplied larger-size ultra-violet sterilisation units for secondary treatment of ballast water during de-ballasting.
The Scanship dried bio-sludge silo, with its bagging unit in the foreground.
52 THE NAVALARCHITECT FEBRUARY 2006
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