Municipal wastewater treated by reverse osmosis (RO) membranes is an attractive source for unrestricted irrigation, industrial process water, or potable uses after aquifer recharge.
During the RO filtration process, microbial biofilm growth on the membranes is a major impediment decreasing permeate flux, and in most cases, decreasing the rejection of salts and small organic molecules.
Taxonomic distributions of bacterial phylum, subphylum, order and family of the RO membrane biofilm after one and five cycles of cleaning and without cleaning, the numbers indicate the percentage of the total sequences.
In this project, the critical need for a sustainable process during RO filtration that will minimize RO membrane biofouling will be addressed. In particular, (i) biofouling propensities of RO membranes and polyamide model surfaces that are similar to the RO membrane's active layer will be characterized under various aquatic conditions; (ii) effectiveness of variety of commercial biocides will be tested for their sustainable use to eliminate biofouling.
Fast screening methods of different biocides for biofouling reduction will be developed as well as wise biocide selection; (iii) in a similar manner, cleaning efficiencies of biofouled RO membranes and model surfaces will be assessed using fast screening developed protocols and most effective cleaning agents will be tailored to the fouling layer characteristics; (iv) microbial community analysis of biofouling layers of RO versus those of ultra-filtration (UF) membranes will be delineated.
In addition, the effect of different biocides on microbial communities developed on RO membranes will complement the critical need for the advanced knowledge of RO biofouling. RO biofouling layers will be characterized using attenuated total reflection – Fourier transform infrared (ATR-FTIR) spectroscopy, laser scanning confocal microscopy (LSCM), and scanning electron microscopy coupled with energy dispersive X-ray detection (SEM/EDX).
Fouling experiments of RO membranes with UF permeate will be carried out and will be compared to the propensity of the model polyamide surfaces to adsorb potential foulants (including microorganisms, organic matter, colloids, and inorganic precipitates).
Adherence properties of biofilms and their extracted extra cellular polymeric substances (EPS) will be delineated using atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D). Selection of best cleaning agents will be carried out based on mechanistic approach in which QCM-D and AFM will be used. Well controlled QCM-D and AFM experiments will be compared to the recovery of the RO membrane performance after cleaning.
The proposed research approach offers a novel and fast screening protocols for biocides and cleaning agents as well as actual recommendations for cleaning agents and biocides tailored to the fouling layer developed and characterized on the RO membrane.
Our long term aim is to prolong the RO membranes operation period and decrease operation and maintenance costs. More specifically, the goal of this project is to define and address the key factors in fouling of RO membranes used for salt and small organics removal in the reclamation process of tertiary wastewater effluents originated from the UF pretreatment stage.
Specific Technical Objectives:
- RO fouling layers are often composed of organics, colloids, inorganic precipitates, and microbial biofilms. We will characterize the fouling layer components and physico-chemical interactions under different operational conditions including cross-flow velocity and permeate flux. We will meet this objective by using laser scanning confocal microscope (LSCM), scanning electron microscopy coupled with energy dispersive X-ray detection (SEM/EDX), and ATR-FTIR spectroscopy. In RO membranes, we will address the detection of inorganic precipitates (scaling) in the fouling layer but we will not aim our study on optimization of antiscalants use.
- We will find the main adsorbants/foulants which tertiary wastewaters contain by controlled adsorption experiments using QCM-D.
- We will characterize the adherence of the fouling layers and then we will relate the adherence properties to membrane performance.
- Optimizing cleaning procedures.
- Analysis of the microbial composition on RO membrane biofouling layers.
Sweity, A., Ying, W., Ali-Shtayeh, M.S., Yang, F., Bick, A., Oron, G., Herzberg, M. Relation between EPS adherence, viscoelastic properties, and MBR operation: Biofouling study with QCM-D. Water Research 45, 6430-6440. doi: 10.1016/j.watres.2011.09.038