[By Wei Chen, Oliver Jost, Niclas Karlsson, Markus Joswig and Mark Beavis]
This short paper reviews food waste and food waste reject water (FWRW) from ships and how FWRW has been caught up in non-compliant practices across much of the passenger ship sector.
Food waste and its characteristics
A ship’s food waste is regulated under the IMO’s MARPOL Annex V Convention. When food waste is offloaded from an international ship to ports, it is also regulated under the national biosecurity regulations in force in countries such as the EU Member States, the UK, the US, Canada, Australia and New Zealand, among others.
Studies showed that there are significant variations in the food waste characteristics and generation rate, depending on the system designs, operational practices, passenger behaviours, food services, and voyage itineraries. Each study has its own unique circumstances. Taking representative food waste samples and having them suitably prepared for analysis is not without challenges. To simplify and rationalise a broad spectrum of findings, a cruise ship generates approximately 1 kg/person/day at 25 percent dry solids (DS), as collected in the bins, which has an organic content of about 1,200 g COD/kg DS or 600 g BOD/kg DS.
Food waste reject water (FWRW) and its characteristics
Many merchant ships dispose food waste from the bin to the sea. This is simple, compliant, and sustainable. To take food waste bins up and down a cruise ship is prohibitive due to hygiene and resource constraints. Instead, food waste is sorted at the pulper station to remove bones, plastics, and occasionally cutlery. It is then macerated and transferred from the pulper station to a holding tank by pumping or vacuum. Fresh water is added to aid the transfer and cleaning. This results in a food waste slurry of about 10 percent DS in the holding tank, accumulating at a rate of about 2.5 kg/person/day. 30~50 percent of the organics can be soluble, with most particles being less than 2 mm.
Not many facilities on land can receive this slurry. It causes odour, is too thick to flow freely in the sewers and too wet to be incinerated. It carries the risks of disease or pests, which may prevent it from being anaerobically digested under biosecurity rules. Traditionally, this slurry has been discharged into the sea 3 or 12 nm from the nearest land, which is simple and compliant.
In order to achieve zero-discharge and to ‘go beyond the rules’, the food waste slurry is dewatered to a paste of 20~25 percent DS, then dried to a powder of 70~90 percent DS for incinerating on board. This is done at great expense in terms of capital costs, space, fuel, chemicals, and man-hours.
The waste management hierarchy governing the waste policies of our society would suggest that food waste incineration is a worse option than compliant discharge at sea. The absence of effective heat recovery during drying and incineration blurs the line between ‘waste to energy’ and wasting energy.
There are also mixed messages on system availability. But when they are operating, it is evident that only half of the food waste is converted into incineration emissions and ashes. The other half is in the so-called food waste reject water (FWRW) which is produced during dewatering of the food waste slurry.
Grey water or FWRW?
Setting aside the issue of efficiencies, the industry’s zeal for ‘zero-discharge’ can be well intended and compliant. The problem starts when the FWRW is wrongly considered as being grey water.
Is FWRW grey water? No, being a food waste derivative and carrying half of the food waste, FWRW is clearly not grey water. Grey water is generated from showers, wash basins, laundries and kitchen sinks, and is unregulated by the IMO rules. The definition of grey water does not include food waste or food waste derivatives. When FWRW goes into a spider web of piping diagrams and reappears as grey water, it renders compliant entries to the Garbage Record Book impossible. The practice does not comply with the IMO’s MARPOL Annex IV Convention. When this ‘grey water’ is connected to the sewage treatment plant onboard, it also causes non-compliance with the MARPOL Annex IV convention.
But the implications do not stop here.
Some insist the FWRW is grey water because ‘it looks better than grey water’. But its clarity or concentration are never the criteria when it comes to the risks of diseases and pests under the national biosecurity rules. Foreign food waste must be kept separately in tightly covered containers and transported to the approved facilities ashore for safe disposal. It is not permitted to change the physical structure of such food waste. These national rules are recognized and respected by the IMO’s Guidelines. To consider food waste derivatives as grey water and to allow it into the coastal waters and local sewers flouts the biosecurity rules.
However, such non-compliant designs and practices were often approved by the approval authorities serving some of the flag states at the expense of the agricultural interests of some of the port states.
Such approvals make any corrective actions difficult if not impossible. There is safety in numbers. But the issues will not go away. They serve as a long-lasting reminder to maritime and biosecurity professionals about the status of some of the marine rules.
The industry is innovative by nature. The regulations are often playing catch-up. But when we crave to be green, to achieve zero discharge, to ‘go beyond the rules’, can we do so without breaking the rules?
Dr Wei Chen, Future Program Development Manager, Wartsila UK Ltd, UK
Oliver Jost, Maritime Environmental Affairs, Wasserschutzpolizei (Water Police) Hamburg, Germany
Niclas Karlsson, Managing Director, Clean Ship Scandinavia AB, Sweden
Markus Joswig, Head of Marine Department, PIA GmbH, Germany
Mark Beavis, IEng IMarEng FIMarEST, Sales & Special Projects Director, ACO Marine s.r.o., Czech Republic, ACO Marine Systems GmbH, Germany
Benny Carlson, Chairman and owner, Marinfloc, Sweden
Ed White, Environmental Consultant, former Alaska DEC cruise ship compliance manager
Felix von Bredow, Board of Hamman AG, Hamman AG, Germany
Antony Chan, Engineering Manager, Victor Marine Ltd., UK
Helge Østby, Senior Technical Advisor, Jets Vacuum AS, Norway