Advantages obtained through the elimination of chemical products in the pre-treatment process of large desalination plants for the control of fouling, biofouling and scaling in reverse osmosis membranes

Manuscript for: Journal of Environmental Chemical Engineering New insights into the influence of ultrafiltration pretreatment on reverse osmosis membrane fouling during urban sewage reclamation: Interaction between extracellular polymeric substances and inorganic foulants

Performance of different pretreatment methods on alleviating reverse osmosis membrane fouling caused by soluble microbial products

Protein (BSA) fouling of reverse osmosis membranes: Implications for wastewater reclamation

Colloidal interactions and fouling of NF and RO membranes: A review

Pretreatment for alleviation of RO membrane fouling in dyeing wastewater reclamation

Landfill leachate from some sites contains a high concentration of Mn2+, which may cause reverse osmosis (RO) membrane fouling during RO treatment. In this study, the effect of Mn2+ on RO membrane fouling caused by typical organic pollutants (humic acid (HA), protein (BSA), and sodium alginate (SA)) was systematically investigated, and it was found that Mn2+ exacerbates RO membrane fouling caused by HA, SA, and HBS (mixture of HA + BSA + SA). When the Mn2+ concentration was 0.5 mM and 0.05 mM separately, the membrane fouling caused by HA and SA began to become significant. On the other hand, with for HBS fouling only, the water flux decreased significantly by about 21.7% and further decreased with an increasing Mn2+ concentration. However, Mn2+ has no direct effect on BSA. The effect degrees to which Mn2+ affected RO membrane fouling can be expressed as follows: HBS > SA > HA > BSA. The density functional theory (DFT) calculations also gave the same results. In modeling the reaction of the complexation of Mn2+ with the carboxyl group in these four types of organic matter, BSA has the highest energy (-55.7 kJ/mol), which predicts that BSA binding to Mn2+ is the most unstable compared to other organic matter. The BSA carboxylate group also has the largest bond length (2.538-2.574 Å) with Mn2+ and the weakest interaction force, which provides a theoretical basis for controlling RO membrane fouling exacerbated by Mn2+.

Reverse osmosis (RO) membranes have been widely applied in membrane filtration processes for water purification, since the high selective RO membranes are designed to reject all materials with particle diameter larger than 10 angstrom (A) [1]. However, this optimal selectivity leads to fouling that can greatly affect the performance and productivity of RO membranes. Biofouling remains as one of the major operational problems in RO processes and is caused by unwanted deposit and growth of microorganisms on the membrane. Numerous biofouling control strategies have been developed to restore the performance of RO membranes, but none of them are able to prevent or remove biofouling completely. A novel cleaning technique using a weak and monobasic acid (pKa=3.34, 25℃)named free nitrous acid (FNA) in combined with hydrogen dioxide (H2O2) was proposed. The effects of FNA with or without H2O2 on biofouling of RO membranes were investigated in Chapter 4, five RO membranes with different degree of biofouling were cleaned using FNA solutions (10, 35 and 47 mg HNO2-N/L) at pH 2.0, 3.0 and 4.0 under cross-flow conditions for 24 hours. The cleaning efficiency of FNA solutions was compared with conventional cleaning solution sodium hydroxide (NaOH, pH 11). The cleaning tests demonstrated that FNA cleaning solutions were more efficient than NaOH at biomass removal and inactivation. At the optimum cleaning conditions (35 mg HNO2-N/L at pH 3.0),FNA has achieved higher biomass removal than NaOH for both heavily fouled (86-96% versus 41-83%) and moderately fouled (92-95% against 89-92%) membranes, respectively.In accordance to the biomass removal, 6-32% of viable cells remained on the moderately fouled RO membranes under the impact of FNA cleaning (pH 3), whereas 38-58% of viable cells stayed on the heavily fouled RO membranes. These results revealed that FNA cleaning is more effective for moderately fouled membranes, implying that early cleaning for biofouling is preferable. Although applying FNA alone, or combining it with H2O2 have shown better efficiency at biofouling removal than NaOH, the cleaning efficiency has not been significantly improved (<1% of enhancement) by adding H2O2 to FNA cleaning solutions. The effects of FNA on scaling of RO membranes were also studied using the same cleaning protocol developed for biofouling control. The results showed that FNA solutions at pH 2.0 and 3.0 were as efficient as conventional cleaning acids (hydrochloric acid and citric acid). The scaling layers which contain 32.4±1.7 g/cm2 of calcium were completely removed by all acidic cleaning solutions. Based on the results, FNA is shown to be a promising cleaning agent for RO membrane biofouling and scaling removal. Further investigation focused on the effectiveness of FNA for biofouling prevention in RO processes (Chapter 5). The results showed that weekly FNA cleanings were unable to prevent fouling in the RO filtration systems, as the hydraulic performances (permeability and salt rejection) of RO membranes have gradually declined over two to three weeks filtration period. Although FNA cleaning was able to restore the permeability of RO membranes for one to two days, continuing declined permeability implied that the fouling rate was greater than the inhibition rate of FNA. The results of prevention tests also showed that FNA was more efficient at biomass inactivation and removal. The biomass contents and viable cells of the fouling layers formed in the experiment filtration unit (with FNA weekly cleaning) were less than half of that in the control filtration unit (without FNA weekly cleaning). Moreover, the results of live/dead cell staining revealed the abundance of viable cells in the control unit(57±5%) was four times higher than that in the experiment unit (13±2%). However, there was no significant difference in the concentration of macromolecules such as proteins and polysaccharides between control and experiment filtration units.

Insights into the coupling pre-ozonation with coagulation pre-treatment for mitigating biopolymer fouling of reverse osmosis membrane: Role of Ca2+

Fatty acid fouling of reverse osmosis membranes: Implications for wastewater reclamation

Sequential effects of cleaning protocols on desorption of reverse osmosis membrane foulants: Autopsy results from a full-scale desalination plant

Evaluating the impact of pretreatment processes on fouling of reverse osmosis membrane by secondary wastewater

The objective of the study was to evaluate the impact of anti-scalant on fouling of reverse osmosis (RO) membranes in reclamation of secondary effluent which was produced by a conventional activated sludge process at Kranji Water Reclamation Plant with the capacity of 151,000 m3/d. The study was carried out using a RO pilot plant with the capacity of 2.4 m3/h. The RO plant was in 2:1 configuration and was operated at 75% recovery and at membrane flux of 17 l m(-2) h(-1). Pilot trials were conducted with and without anti-scalant. Compositions of feed and concentrate streams were analyzed and the pilot data were normalized. The results of the study showed that the plant operation was stable during the first few days after stopping dosage of anti-scalant but after 3-6 days of operation the membranes were fouled. The time lag effect of anti-scalant without dosage was not reported previously and could be potentially beneficial to save chemicals. The membrane fouling was more serious at the second stage due to the formation of calcium phosphate scale when the pilot plant was operated without anti-scalant. The flux of fouled membranes could be completely recovered after clean-in-place (CIP) with citric acid, indicating that scaling dominated the fouling of the RO membranes. These findings in the study could be applied to select an appropriate anti-scalant for prevention from formation of calcium phosphate scale in the RO operation.

Membrane application in reverse osmosis (RO) membrane is getting more attention especially in producing drinking water. However, RO membrane faces challenges that reduces its performance such as its permeation flux, salt rejection, additional energy demand, lifetime decrease, extra pre-treatment process, cleaning and maintenance. The challenge is the formation of fouling. RO membrane fouling can happen inside or outside the membrane and the characteristics of membrane fouling differs from one type to other types, depending on the nature and location of membrane fouling. There are several types of RO fouling, which are Biofouling, Organic Fouling, Inorganic Fouling and Colloidal Fouling. The causes of RO membrane are different from one to another. The properties and materials of the solution entering RO membrane are important as it affects the type of fouling of RO membrane fouling. All of the RO membrane foulings need to be considered during membrane usage and demand solution to be controlled. In order to control the fouling in Reverse Osmosis membrane, there have been several control solutions discovered to the membrane fouling challenges. The control solutions are specified to each one of the fouling, in spite of wide applications for some of it. The control solutions are pre-treatment, which has many methods such as photo oxidation, coagulation, scale inhibitor, ion exchange resins, granular media and membrane treatment, membrane monitoring, membrane cleaning, surface modification, and material addition to membrane or novel membrane material. With various control solutions discovered, the RO membrane still faces fouling issue and is still demanding some more advanced applicable control solutions.

Different bacterial species and their extracellular polymeric substances (EPSs) significantly affected reverse osmosis (RO) membrane fouling potentials in wastewater reclamation

Fouling reduction using centrifugal membrane separation