REVERSE OSMOSIS MEMBRANES UNDER DUTY-CYCLED OPERATION: COMPACTION, SCALING, BIOFILM REGROWTH AND PERMEATE TRANSIENTS IN PHOTOVOLTAIC-DRIVEN BRACKISH DESALINATION

Photovoltaic-driven reverse osmosis is the dominant architecture for decentralised brackish-water supply in arid regions, yet it violates the condition under which almost all membrane performance data are obtained: steady pressure, steady flux and continuous operation. This review assembles the evidence on how the polyamide membrane itself, considered as a mechanical and biological object, responds to duty cycling, and reconciles findings that disagree in sign rather than merely in magnitude. Primary studies published between 2006 and 2026 were coded against a purpose-built parameterisation of non-steady operation comprising duty cycle, stop duration, cycle count, ramp rate, fluctuation amplitude and frequency, minimum-flux floor, idle-state fluid, flush protocol and buffering. Four membrane-side consequences are examined: irreversible compaction and creep recovery across repeated pressurisation; scaling induction time relative to residence time at peak supersaturation; biological regrowth during idle intervals; and permeate-quality transients on restart. Reported outcomes span a permeability loss exceeding fifty per cent after seven days of cycling and no measurable degradation after 1,568 start-stop cycles. Three variables reconcile most of that disagreement: idle-state chemistry, spontaneous osmotic backwash on depressurisation, and the partition between reversible compaction of the active layer and irreversible compaction of the support. No located study varies shutdown duration as a controlled independent variable against a biological endpoint on a membrane, and an experimental design closing that gap is specified.

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