Techno-Economic Analysis of ElectroSAnMBR for Commercial Vessels

Commercial shipping remains one of the most demanding sectors for onboard wastewater engineering. Bilge water accumulates in the lowest compartments of every vessel, carrying lubricating oils, hydraulic fluids, fuel residues, and a cocktail of dissolved organics that conventional oil-water separators struggle to break down. Fleet managers typically pay for slops to be pumped ashore, which means per-call reception charges, vessel downtime in harbours like Fremantle or Port Botany, and exposure to penalties whenever oily discharges exceed regulatory thresholds. As ship owners look to modernise, they want technology that treats the waste onboard, occupies a small footprint, and ideally produces something valuable in the process.

A techno-economic analysis weighs those engineering promises against the bottom-line reality of running a ship. For the submerged anaerobic electrochemical membrane bioreactor developed by the ElectroSAnMBR team, the calculation depends on how electrolysis, anaerobic digestion, and membrane separation interact under real marine loads. The three unit operations share a single reactor volume, but the financial case still needs to be drawn from performance data, electricity tariffs in port, and the avoided cost of offloading waste.

Why commercial shipping needs better bilge water solutions

International Maritime Organization rules under MARPOL Annex I already cap bilge water oil content at 15 parts per million, but enforcement has tightened at coastal sites where states want stricter safeguards. Australia's Marine Order 91 and the Great Barrier Reef Marine Park Authority have pushed discharge controls beyond the international baseline, and vessels calling at Cairns or Gladstone routinely carry extra holding capacity to avoid fines. Operators who run older mechanical separators often face the practical problem of emulsified oil droplets too small for gravity separation, which drags removal efficiency below the threshold inspectors care about.

Conventional flow-through treatment plants on merchant ships also struggle with variable salinity and the presence of detergents from tank cleaning. The result is often a two-step approach: a coalescing unit to catch free oil, followed by transfer to a slop tank and eventual pumping ashore at premium rates. This is a logistics cost as much as a treatment cost, because each pump-out holds the vessel alongside while bunkers and provisions are loaded. Ship owners in Western Australia's offshore sector have told researchers that a single avoided pump-out can justify several thousand dollars in retained schedule flexibility.

ElectroSAnMBR changes the equation because electrochemistry destabilises the emulsion while anaerobic digestion breaks down dissolved organics, all in one submerged reactor with an attached membrane module. The membrane holds back biomass and any remaining oil, which removes the need for a separate polishing stage. The combination is light enough for retrofit on a harbour tug in Sydney Harbour, yet robust enough for the oily bilge water a chemical tanker produces in heavy weather. Several European regional authorities have piloted organic waste sorting in public institutions, including an organic school meals programme in a provincial Italian institute, demonstrating how source-level separation unlocks downstream processing value.

Breaking down capital and operating costs

The headline capital cost of an ElectroSAnMBR unit scales with hydraulic throughput, electrode surface area, and membrane area. For a mid-sized offshore support vessel with daily flows around 10 to 15 cubic metres, indicative installed costs land in the same order of magnitude as a high-end oily-water separator plus an extended slop tank arrangement. The electrode stack and power supply add a premium, but this is partly offset by the smaller tankage the vessel no longer needs to allocate to waste holding.

Operating expenditure looks different from a legacy system. Electricity drawn for electrolysis replaces the consumables, filter cartridges, and centrifuge maintenance that drain budgets on existing separators. Membrane fouling still demands periodic chemical or relaxation cleaning, but the anaerobic conditions lower fouling rates compared to aerobic membrane bioreactors on similar loads. Sludge yield is lower than in conventional activated-sludge systems, so off-vessel disposal costs shrink alongside the volume needing transport.

The most sensitive variable in any techno-economic model is the tariff applied to grid power or auxiliary generation. Vessels berthed in Hamburg, Genoa, or Brisbane plug into shore power at rates that differ by a factor of three or more. When the same equipment runs on auxiliary diesel at sea, the fuel cost dominates and the analysis tilts toward designs that recover energy. ElectroSAnMBR's hydrogen side-product, discussed below, is what the model needs to soften that line item.

How electrolysis generates revenue and reduces load

Electrolysis of the bilge water produces hydrogen gas at the cathode while oxidising organic contaminants at the anode. That hydrogen is not a curiosity; it is a working reagent inside the same reactor. The project team has documented how hydrogen supports digestion, and the practical effect is faster breakdown of volatile fatty acids and more stable digester operation under shock loads.

From an accounting perspective, the in-reactor use of hydrogen offsets the electrical draw by lowering the energy that would otherwise be needed to mix or heat the anaerobic digester. Some operators will eventually see a stronger return by capturing excess hydrogen for low-grade auxiliary uses such as burner feed or inerting, although the safety case for on-board storage still needs careful review. The more reliable revenue line is the avoided cost of shore reception, which can climb above 200 Australian dollars per cubic metre at remote Australian terminals.

Reduced waste volume carries a second financial effect. Less sludge means fewer port calls, fewer harbour moves, and a smaller carbon footprint per voyage under emerging emissions accounting frameworks. The same logic of treating organics as a resource, validated in municipal waste programmes across Europe, applies at sea: capturing the organic fraction on board turns a disposal line item into a treatment opportunity.

Australian maritime realities and regulatory drivers

Australian waters shape the techno-economic case in ways that European or Asian operators do not face. The Great Barrier Reef no-anchor zones and the Torres Strait sensitive areas mean that any spill event within those boundaries attracts heavy regulatory scrutiny and remediation orders. Vessels serving the offshore gas fields off Dampier or the Browse Basin operate far from convenient reception facilities, so the cost of pumping slops ashore includes helicopter transfers or extended deviations to a service port.

Sydney Harbour and the commuter corridors of the Parramatta River host harbour ferries and cruise tenders whose tight turnaround windows punish any system needing hours of settling. A unit that treats bilge water continuously, with minimal operator attention, slots directly into those schedules. Smaller passenger vessels operating between Circular Quay and the eastern suburbs have an additional incentive: Sydney's noise and emission restrictions for harbour craft push designers toward quieter, electrically driven systems, and ElectroSAnMBR's electrochemical core fits that direction better than a centrifuge with its high-speed rotating parts.

The Australian Maritime Safety Authority has tightened its expectations on discharge monitoring since 2022, and port state control inspections in Melbourne and Brisbane now routinely test oil content sensors against laboratory samples. Operators who install a treatment train with reliable online readings enjoy shorter inspections and fewer detentions. The economic value of that compliance certainty rarely shows up in a CAPEX line, but it is real and recurring.

Techno-economic indicators worth tracking

When evaluating an ElectroSAnMBR installation, the analysis usually converges on a handful of indicators that drive the financial decision.

• Payback period against avoided pump-out costs, measured in years per vessel class
• Net present value over a 10-year operating horizon, discounted at the operator's weighted average cost of capital
• Levelised cost of treatment per cubic metre of bilge water processed
• Energy intensity in kilowatt-hours per cubic metre, compared with legacy separators
• Avoided CO2-equivalent emissions from reduced sludge transport and shore reception

A second set of indicators covers the operational and regulatory side of the case.

• Percentage of operating hours meeting the 15 ppm discharge limit without manual intervention
• Membrane replacement interval in months, given typical feed variability
• Reduction in slop tank volume required, freeing capacity for cargo or ballast
• Number of port state control detentions avoided per year on the route
• Operator hours saved per month compared with running a conventional separator and centrifuge

Fleet operators considering a transition to onboard treatment can begin with the data sheets published by the project consortium and the project's technical overview, then model the treatment costs against the specific tariff they pay at their home port. For Australian owners, the most useful exercise is a side-by-side comparison of current pump-out bills at Fremantle, Sydney, and Brisbane against a forecast of operating costs once the membrane bioreactor is running on shore power. Reach out to the project team through the website to request pilot data, scale-up references, or a tailored cost worksheet for a particular vessel class.