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Updated: Jan 27, 2026

Large Volume 20L+ Filtration of Coastal Seawater Samples
Published on: June 18, 2009
Slow sand filtration for biofouling reduction in seawater desalination by reverse osmosis
Fernando Freitas de Oliveira1, René Peter Schneider2
1Programa de Pósgraduação Interunidades em Biotecnologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, Avenida Prof. Lineu Prestes, 1374, Cidade Universitária, CEP 05508-900, São Paulo - SP, Brazil; CEBIMAR - Centro de Biologia Marinha da Universidade de São Paulo, Rodovia Manoel Hypólito do Rego, km. 131, CEP 11600-000, São Sebastião - SP, Brazil.
Abstract:
Control of the organic substrate pool that determines the microbial growth potential (MGP) of feedwater in seawater reverse osmosis (SWRO) is a challenge unresolved in conventional or advanced membrane pretreatment. Slow sand filtration (SSF) combines filtration with biodegradation, but its capability of reducing MGP, proteins and carbohydrates on seawater feeds is not known. Two SSF, one constructed with new media (newSSF) and one from a previous filtration run (oldSSF), reduced MGP as measured in a growth assay with the marine organism Pseudoalteromonas songiae by one order of magnitude after maturation periods of 76 and 61 days, respectively. The reduction of the amount of biopolymers deposited on the surfaces of SWRO membranes in laminar fluid flow cells was significant with filtrates from biologically non-acclimated SSF (proteins: 60% (oldSSF) and -66% (new SSF), carbohydrates: 75% (oldSSF) and -70% (newSSF)) and an even greater reduction was observed after filter maturation (proteins: 81% (oldSSF) and -76% (new SSF), carbohydrates: 88% (oldSSF) and -88% (newSSF). Turbidity was less than 0.3 nephelometric turbidity units (NTU) and silt density index (SDI) < 4 immediately after startup and during the 181 days operating period regardless of the oscillations of the raw sea water quality. Filtration and biological activity were restricted to the top 30 cm of the media column, with no significant further contribution of the deeper media layers to filtrate quality.
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