Phosphorus Concentration in Water Affects the Biofilm Community and the Produced Amount of Extracellular Polymeric Substances in Reverse Osmosis Membrane Systems

Abstract

Biofouling is a problem that hinders sustainable membrane-based desalination and the stratification of bacterial populations over the biofilm’s height is suggested to compromise the efficiency of cleaning strategies. Some studies reported a base biofilm layer attached to the membrane that is harder to remove. Previous research suggested limiting the concentration of phosphorus in the feed water as a biofouling control strategy. However, the existence of bacterial communities growing under phosphorus-limiting conditions and communities remaining after cleaning is unknown. This study analyzes the bacterial communities developed in biofilms grown in membrane fouling simulators (MFSs) supplied with water with three dosed phosphorus conditions at a constant biodegradable carbon concentration. After biofilm development, biofilm was removed using forward flushing (an easy-to-implement and environmentally friendly method) by increasing the crossflow velocity for one hour. We demonstrate that small changes in phosphorus concentration in the feed water led to (i) different microbial compositions and (ii) different bacterial-cells-to-EPS ratios, while (iii) similar bacterial biofilm populations remained after forward flushing, suggesting a homogenous bacterial community composition along the biofilm height. This study represents an exciting advance towards greener desalination by applying non-expensive physical cleaning methods while manipulating feed water nutrient conditions to prolong membrane system performance and enhance membrane cleanability.

Permeation Increases Biofilm Development in Nanofiltration Membranes Operated with Varying Feed Water Phosphorous Concentrations

“…For the 0 μg P·L −1 under permeation conditions, the higher effect on pressure drop increase is explained by a higher EPS ratio per bacterial cell, which translated into “expanded” EPS in the flow channel ( Figure 5 ) following Javier et al (2020) [ 20 ] results. Previous studies [ 37 ] found that the dominant bacterial families for biofilms grown under 0 μg P·L −1 were Sphingomonadaceae , which are related to extracellular polymeric substances production [ 57 , 58 , 59 ]. This study’s results agree with Jin and Marshall’s model [ 56 ], where OCT images confirmed that a compact biofilm formed around the spacer ( Figure 5 ) at higher dosed phosphorus concentration (low EPS to bacterial cell ratio).…”

“…Residual chlorine was removed by passing the tap water through an activated carbon filter as in previous studies [ 37 ]. The dechlorinated tap water then flowed through two cartridge filters (pore size 4 µm) to remove any possible particles from the activated carbon filter.…”

“…The image analysis was done as follows: (i) Automatically defining the membrane and (ii) determining the biofilm by performing automatic thresholding for pixels above 20 dB. The 20 dB threshold was defined based on measurements done on more than 200 images, as described in our previous studies [ 18 , 19 , 20 , 37 ]. An area of 5.00 mm × 0.61 mm from the bottom of the glass to below the spacer was taken to quantify the number of pixels in each OCT intensity interval.…”

“…Total bacterial cell counts (TCC) in the biofilm were measured by retrieving coupons of 4 × 2 cm of the biofouled membrane and spacer from the MFS’s inlet and outlet positions and using a flow cytometer, following the protocol reported by [ 46 ]. Adenosine triphosphate (ATP) measurements were done by retrieving membrane and feed spacer coupons of 4 × 4 cm from the MFS inlet and outlet positions, as described by [ 18 , 19 , 20 , 37 ] to obtain a homogenous liquid sample solution. The biofilm ATP concentrations were determined with a luminometer (Celsis Advance, Charles River Laboratories, Inc., Wilmington, MA, USA).…”

Effect of Aeration Intensity on Performance of Lab-Scale Quorum-Quenching Membrane Bioreactor

“…It causes a rise of transmembrane pressure (TMP) until it reaches a point where the filtration slows down or even stops in some cases [ 5 ]. This stage is called membrane biofouling [ 6 ]. At this point, the membrane modules are fouled and need to be cleaned by stronger methods or replaced with new ones.…”