TL;DR: In this article, the authors compared the performance of two-pass nanofiltration and single-pass reverse osmosis (RO) membranes in seawater desalination, and found that both types of membranes contained similar amounts of deposited solids, while significantly fewer solids were found on second-pass NF membranes.
Abstract: A recent innovation in seawater desalination is the use of multi-stage and multi-pass combinations of nanofiltration (NF) and reverse osmosis (RO) membranes. One example of this approach is the “Long Beach method,” in which seawater passes through two different types of NF membranes to produce potable water. After several years of pilot studies comparing the performance of two-pass NF and single-pass RO systems, a number of membrane elements were sacrificed for autopsy analyses. The selected membranes represent different stages of operation including (1) new, (2) fouled, and (3) cleaned membranes. Used NF and RO spiral wound elements were removed from the first and last positions of the demonstration plant. Although operating data suggested no outward signs of membrane fouling – inorganic, organic, and bacterial accumulation were identified on all membranes. First pass RO and NF membranes contained similar amounts of deposited solids, while significantly fewer solids were found on second pass NF membranes. Viable, culturable marine bacteria were observed on all fouled and cleaned membranes, indicating that bacterial colonization of seawater NF/RO membranes was not (a) detected by plant performance monitoring devices, (b) prevented by microfiltration and chlorination, or (c) removed by chemical cleaning. Chemical cleaning recovered the measurable performance of both first pass RO and second pass NF membranes, but was relatively ineffective at removing deposited solids from first-pass NF membranes. Therefore, chemical-cleaning methods may need to be tailored and optimized more specifically for NF membranes used in seawater desalination.
TL;DR: In this paper , the authors present four case studies of RO membrane biofouling in seawater, municipal wastewater, brackish groundwater and industrial wastewater, and describe what is known about the causes and consequences of bacterial biofilm formation and growth through a process level RO-means model.
Abstract: Abstract Biofouling has been referred to as “the Achilles heel” of reverse osmosis (RO) membrane technology; the main cause being polyamide RO membranes lack of chlorine tolerance. Biofouling increases the operating cost of water treatment by increasing RO system feed pressure (i.e., energy demand) and increasing membrane cleaning frequency, which increases downtime and reduces membrane useful life. For waters with known high biofouling potential, plant designs also may require more extensive pretreatment, which increases capital and operating costs as well as the footprint of a desalination plant. It is known from the literature that the three keys to fending off biofouling in RO systems and/or recovering from biofouling once it takes root include (1) understanding site-specific processes governing biofilm formation, (2) implementing effective biofouling pretreatment ahead of RO membranes, and (3) monitoring biofouling to enable more proactive and effective RO membrane cleaning. Herein, we present four case studies of RO membrane biofouling in seawater, municipal wastewater, brackish groundwater and industrial wastewater. Next, we describe what is known about the causes and consequences of bacterial biofilm formation and growth through a process level RO membrane biofouling model. Finally, we review common biofouling control methods including pre-treatment, chemical cleaning and the most common strategies for monitoring biofouling in RO membrane systems.
25 Apr 2003
TL;DR: In this paper, a two-stage seawater desalination system is described, which utilizes a first stage to produce a first permeate accept fully pressurized feed seawater by the first stage of the pump (125), at least one high performance nanofiltration membrane (135) have.
Abstract: This invention utilizes a two-step seawater desalination system seawater is directed to methods and apparatus for desalination. (Figure 1) a first stage, to produce a first permeate accept fully pressurized feed seawater by the first stage of the pump (125), at least one high performance nanofiltration membrane (135) have. The second stage receives the first permeant pressurized to about 200psi~ about 300psi by a second-stage pump (150) to produce drinking water, at least one high performance nanofiltration membrane (160) have.
TL;DR: A review of the use of methods to visualize hydrodynamics and fouling in membrane filtration systems can be found in this article , where the authors highlight the recent trends in the usage of methods.
Abstract: ABSTRACT Membrane filtration is a key technology for producing freshwater sustainably. However, fouling is a major setback in this technology. Several studies have revealed that hydrodynamics significantly affects the fouling pattern. This review highlights the recent trends in the use of methods to visualize hydrodynamics and fouling in membrane filtration systems. These methods can be classified into invasive and non-invasive types. Invasive methods are predominantly used for root cause analysis of fouling and are more oriented towards industrial applications. The non-invasive methods such as computational fluid dynamics, biofouling simulation, and real-time fouling-monitoring are used to understand hydrodynamics in the membrane channel, the kinetics and mechanism of fouling deposition, etc., and aid substantially in laboratory-scale studies. These methods have shown great potential to predict membrane performance in real-scale applications. Since the non-invasive and invasive methods are “preventive” and “cure” types, respectively, the recent focus has shifted more towards non-invasive methods. This review paper comprehensively discusses these techniques along with an outline of the future scope of work.
TL;DR: In this article , an integrated analysis of the saline water quality and discarded reverse osmosis membranes was developed to understand the cause of the scale, and a spatula and sonication were used to remove scale.
Abstract: To understand the cause of the scale, an integrated analysis of the saline water quality and discarded reverse osmosis membranes was developed. Damaged areas on the membrane were excised and characterized by the Fujiwara test, infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. A spatula and sonication were used to remove scale. Thermodynamic modeling (PHREEQC) was used to predict scale formation at 75 bar, resulting in saturation index values for both mixed and pure compounds. Fujiwara's test revealed damage to the polyamide and organic fouling by polysaccharides, silica, and aromatics. Thermo-oxidative decomposition and residual masses of metal oxides and salts were observed. The microscopy detected incrustations in the membrane by analyzing compounds with silicon, oxygen, calcium, magnesium, aluminum, etc. The modeling indicated the low-solubility compounds of scale are aluminum silicates, clays, quartz, etc., identified experimentally. PHREEQC can model desalination to predict scale problems, allowing for early decision-making.