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We describe the construction and testing of a home-built ultrafiltration (UF) system, based on commercially available hollow fiber polysulfone membranes, for isolation of suspended particulate organic matter (POM susp ) from large volumes (2000-10,000 L) of ocean water. The overall apparatus consists of two sequential UF steps: a main filtration system (100 L reservoir) driven by a stainless steel centrifugal pump, and a subsequent reduction/diafiltration system (2 L reservoir) driven by a peristaltic pump. The system can be readily assembled using off-the-shelf parts at a fraction of the cost of commercial UF systems. Our system functioned comparably to previously described commercial units. We conducted a series of tests using both surface (21 m) and mesopelagic (674 m) N. Pacific central seawater from ocean pipeline sources at the Natural Energy Laboratory Authority of Hawaii (NELHA), while simultaneously collecting GFF-POM samples. We evaluated flow rates, fouling behavior, carbon and nitrogen recoveries and compositions, and also bacteria and virus retention of ultrafiltered-POM (UPOM) using both 0.1 μm and 500 kilodalton pore size membranes. We also compared composition of UPOM versus GFF-POM, finding clear differences, which also varied between surface and mesopelagic waters. Finally, to evaluate the appeal of large-volume filtrations at NELHA to study central N. Pacific Gyre POM susp , we compared our data with offshore station ALOHA.

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