Monitoring Biofouling Potential Using ATP-Based Bacterial Growth Potential in SWRO Pre-Treatment of a Full-Scale Plant.

Delia Pastorelli,Said Goueli,Maria D Kennedy,Jan C Schippers,Moses Kapala,Subhanjan Mondal,Almotasembellah Abushaban,Sergio G Salinas-Rodriguez

doi:10.3390/membranes10110360

Abstract

Several potential growth methods have been developed to monitor biological/organic fouling potential in seawater reverse osmosis (SWRO), but to date the correlation between these methods and biofouling of SWRO has not been demonstrated. In this research, the relation between a new adenosine triphosphate (ATP)-based bacterial growth potential (BGP) test of SWRO feed water and SWRO membrane performance is investigated. For this purpose, the pre-treatment of a full-scale SWRO plant including dissolved air flotation (DAF) and two stage dual media filtration (DMF) was monitored for 5 months using BGP, orthophosphate, organic fractions by liquid chromatography coupled with organic carbon detection (LC-OCD), silt density index (SDI), and modified fouling index (MFI). Results showed that particulate fouling potential was well controlled through the SWRO pre-treatment as the measured SDI and MFI in the SWRO feed water were below the recommended values. DAF in combination with coagulation (1–5 mg-Fe3+/L) consistently achieved 70% removal of orthophosphate, 50% removal of BGP, 25% removal of biopolymers, and 10% removal of humic substances. Higher BGP (100–950 µg-C/L) in the SWRO feed water corresponded to a higher normalized pressure drop in the SWRO, suggesting the applicability of using BGP as a biofouling indicator in SWRO systems. However, to validate this conclusion, more SWRO plants with different pre-treatment systems need to be monitored for longer periods of time.

Highlights

Membrane fouling is the main challenge in the operation of seawater reverse osmosis (SWRO)systems [1,2]
(~2.9 nephelometric turbidity units (NTU)) in the seawater was measured in August, which was confirmed by the silt density index (SDI)-15
The measured turbidity after DMF2 and cartridge filtration (CF) were very low (

Summary

Introduction

Membrane fouling is the main challenge in the operation of seawater reverse osmosis (SWRO)systems [1,2]. Membrane fouling is the main challenge in the operation of seawater reverse osmosis (SWRO). Pre-treatment is commonly applied to improve water quality prior to reverse osmosis (RO), and to minimize/mitigate the fouling issue in SWRO systems [3,4]. Almost all SWRO desalination plants require pre-treatment and the type of pre-treatment depends on the fouling potential of the raw seawater. Particulate fouling potential is commonly monitored by measuring the silt density index (SDI) and modified fouling index (MFI). Both SDI and MFI-0.45 are American Society for Testing. It has been reported that the maximum SDI15 (SDI of 15 min) value for acceptable SWRO feed water is Membranes 2020, 10, 360 and Material (ASTM) methods [5,6], in which MFI takes into account the occurrence of cake filtration [7].

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Results

Conclusion