Harmful
non-indigenous microorganism invasion caused by ballast
water discharge poses severe threats to marine environments. In this
study, a conceptual in situ photo-Fenton system without
additional oxidants was first established for ballast water sterilization.
Pyromellitic acid diimine (PDI)-modified g-C3N4 was utilized as a photocatalyst to produce H2O2, which was in situ activated by Fe(II) to produce
•OH for deep oxidation. Marine bacterium Vibrio alginolyticus (7 log) in ballast seawater was totally inactivated within 35 min
of visible light irradiation. Simultaneous bacterial inactivation
and H2O2 production was monitored to confirm
the in situ coupling mechanism, and •OH instead
of H2O2 was determined to be the dominant reactive
species. The influence of seawater parameters, such as salinity, pH,
and dissolved oxygen, on the inactivation efficiency was revealed.
In addition, the bacterial inactivation mechanisms in terms of cell
membrane rupture, intracellular enzyme activity, and total protein
change were clarified. The organic matter release profile during bacterial
lysis was probed by fluorescence excitation–emission matrix
technology, which revealed minimal acute toxicity and impacts on the
marine environment. This work not only advances an external oxidant-free
system for on-board ballast water sterilization using sustainable
solar energy but also creates an avenue for exploring bacterial inactivation
mechanisms in seawater.