ORC assisted ballast water treatment under the EU ETS: Comparative assessment of UV, electrochlorination, and thermal options

Ballast water treatment (BWT) is mandatory, and its lifecycle cost increasingly depends on carbon pricing. This study quantifies the energy and cost trade‑offs of three options for a BDELTA‑type handymax bulk carrier (ballast pump 1,600 m3 h-1; 34 operations yr-1): filtration + UV with double pass, filtration + electrochlorination (EC) at 10 mg L-1 TRO, and an exploratory thermal pasteurization case (55 oC) using waste‑heat plus a fired boiler. A 100 kW Organic Rankine Cycle (ORC) recovers main‑engine waste heat and supplies BWT electricity; surplus generation is credited to hotel loads. Costs include fuel and EU ETS allowances (80 USD tCO2, 70% coverage in 2025) and are annualized with a 7% discount rate over 20 years. A deterministic model is complemented with a ±10% Monte Carlo analysis of key parameters. ORC output exceeds the electrical demand of UV and EC, leaving substantial surplus. The resulting net annualized costs are 20 kUSD yr-1 for UV+ORC and about -2.9 kUSD yr-1 (a small net saving) for EC+ORC, while thermal pasteurization remains prohibitive at 1.96 MUSD yr-1 because the boiler must supply most of the heat. The ranking is robust in the Monte Carlo results; variations in fuel and ETS price move totals but do not change the preference for UV/EC over thermal. The thermal pathway is presented as a feasibility case rather than a type‑approved solution. Overall, coupling UV or EC with a modest ORC module yields low net operating cost for treatment electricity while reducing ETS exposure through avoided auxiliary‑generator use. Thermal pasteurization is only economically plausible if near‑free, high‑grade heat and effective heat recovery are available, and the approach can be validated under current IMO/USCG protocols. Thermal treatment may be economically plausible only when continuous waste‑heat recirculation (multi‑pass) is used with well‑insulated tanks. In practice, it is unlikely to be viable for short trials.