Hamworthy has supplied Queen Victoria with two types of water systems: membrane bioreactor (MBR) treatment plant for black and grey water, and desalination plant comprising ‘multi-stage flash’ (MSF) evaporators.
"The MBR project was unusual because of the ship construction schedule" said Allan Bentley, managing director, Hamworthy Water Systems. When Fincantieri received the newbuilding order, the shipyard had a slot available to build one module, which was then ‘mothballed’ for a year until work started on the rest of the ship. “Half of the MBR’s main process tank is located in that module,” Mr Bentley said. “About two years elapsed between delivering the first part of the plant and commissioning the complete system once the other half had been installed in the adjacent ship section. These equipment modules required simple interconnecting pipework and cabling to complete the installation, which demonstrates the flexibility that the Hamworthy modular system offers”.
Queen Victoria’s wastewater is handled by two MBR320 Type III units, each capable of processing up to 320 m3/day of black and grey water. Hamworthy MBRs utilise a combination of biological treatment and side stream crossflow membrane technology to treat wastewater to below the stringent standards that cruise ships must meet to be certified by the USCG for continuous discharge in Alaskan waters.
The bioreactors operate at typical mixed liquor suspended solids (MLSS) levels of 15,000 mg/l to 20,000 mg/l. These high solids levels allow the reactor volume – and hence equipment footprint – to be smaller than other technologies, and increase the biomass resistance to hydraulic, organic and toxicity fluctuations.
Each MBR has four banks of 2m-long membrane modules on the side of the bioreactor tank. The ultrafiltration membrane material has an average pore size of 0.040 micron, preventing solids from passing through. A typical bacteria is 1 micron across, so the membrane is also a barrier to all bacteria and most viruses.
To eliminate blockage and to keep the membrane surface clean for good permeate production, a 3 m/s crossflow is maintained. Side stream crossflow membrane technology offers many advantages over other advanced wastewater treatment systems, including:
- The Hamworthy system uses no chemicals for the main process
- The membrane modules are readily accessible and may be easily and quickly cleaned inplace
- Side-stream, low pressure, tubular membranes can achieve much higher flux rates than submerged membrane systems, resulting in a smaller membrane area and allowing independent location of the membranes from the process tank
Fresh water generation
Three Hamworthy Serck Como MSF evaporators produce fresh water: two with a capacity of 650 m3/day and the other 400 m3/day. Hamworthy expanded its fluid handling portfolio last year by acquiring Serck Como GmbH – a market leader in desalination plant for cruise ships.
Hamworthy Serck Como’s cruise ship desalination plant comprises one or more ‘multi-stage flash’ (MSF) evaporators. “The well proven MSF principle is the most reliable thermal seawater desalination process in the world,” said Arno Haase-Camper, Hamworthy Serck Como’s head of projects and sales.
Steam, engine jacket water or a combination of these can be used for heating. Capacities of these tailor-made MSF evaporators range from 100 tonnes/day to 1,000 tonnes/day – or even higher if the engine room arrangement allows, with steady production at sea water temperatures between 2°C and 32°C.
The MSF evaporation process has been proven for several decades, and is the only evaporation principle where heat transfer and evaporation are strictly separated. Seawater is first pumped through a cascade of condensers (for heat recovery) and then a heat exchanger (for supply of heat from engine jacket water and steam). After heating to a specific temperature (typically 80°C), all energy required for evaporation is stored in this stream of hot seawater. Once this has been injected into stage one, evaporation takes place through stepped pressure and temperature drops in the flash evaporation stages, without further heat transfer.
“The risks and problems found in other multi-effect evaporators do not arise with flash evaporators,” Mr Haase-Camper said. “We are convinced that our MSF technology on cruise ships is superior to any other evaporation process”.
