Pressure drop increase by biofilm accumulation in spiral wound RO and NF membrane systems: role of substrate concentration, flow velocity, substrate load and flow direction

Abstract

In an earlier study, it was shown that biofouling predominantly is a feed spacer channel problem. In this article, pressure drop development and biofilm accumulation in membrane fouling simulators have been studied without permeate production as a function of the process parameters substrate concentration, linear flow velocity, substrate load and flow direction. At the applied substrate concentration range, 100-400 microg l(-1) as acetate carbon, a higher concentration caused a faster and greater pressure drop increase and a greater accumulation of biomass. Within the range of linear flow velocities as applied in practice, a higher linear flow velocity resulted in a higher initial pressure drop in addition to a more rapid and greater pressure drop increase and biomass accumulation. Reduction of the linear flow velocity resulted in an instantaneous reduction of the pressure drop caused by the accumulated biomass, without changing the biofilm concentration. A higher substrate load (product of substrate concentration and flow velocity) was related to biomass accumulation. The effect of the same amount of accumulated biomass on the pressure drop increase was related to the linear flow velocity. A decrease of substrate load caused a gradual decline in time of both biomass concentration and pressure drop increase. It was concluded that the pressure drop increase over spiral wound reverse osmosis (RO) and nanofiltration (NF) membrane systems can be reduced by lowering both substrate load and linear flow velocity. There is a need for RO and NF systems with a low pressure drop increase irrespective of the biomass formation. Current efforts to control biofouling of spiral wound membranes focus in addition to pretreatment on membrane improvement. According to these authors, adaptation of the hydrodynamics, spacers and pressure vessel configuration offer promising alternatives. Additional approaches may be replacing heavily biofouled elements and flow direction reversal.

Technical review and evaluation of the economics of water desalination: Current and future challenges for better water supply sustainability

“…The total desalination capacity worldwide using RO technology is continuously increasing, even in the Arabian Gulf region where energy is cheap and raw water quality is less suitable for RO technology, requiring an advanced pretreatment scheme to protect RO membranes mainly from fouling and biofouling [17]. The total global capacity (sea and brackish waters) of RO is the highest compared to any other process ( Figure 1).…”

A new high-pressure optical membrane module for direct observation of seawater RO membrane fouling and cleaning

“…This device appears an effective early warning sensor of biological fouling by monitoring increased tangential pressure drop through the system. Through a series of systematic studies the authors suggest that fouling is a "spacer problem" and that permeate flux has no impact on biological fouling during NF/RO membrane treatment (of non-chlorinated surface waters containing ample nutrients to promote biogrowth), which makes the pressure limitation of the MFS device appear a minor practical limitation [22][23][24][25][26].…”

New insights into sodium alginate fouling of ceramic hollow fiber membranes by NMR imaging

“…[10][11][12] Recent examples for the application of magnetic resonance imaging (MRI) in membrane filtration research are for example the investigation of the fouling behavior of spiral wound modules and the influence of feed spacers on velocity distribution and biofouling of these modules. [13][14][15][16][17] NMR imaging was also applied to visualize flow, concentration polarization and cake layer formation in hollow fiber geometries. 10,[18][19][20][21] For this purpose, typically colloidal particle suspensions 18,22,23 or oil-water emulsions 20,24 were used as model substances.…”