Analyzing organic fouling and biofouling on zwitterionic modified reverse osmosis membrane

Our planet has abundant amount of water recourses which exceeds up to 1,386 million cubic kilometers of water, that only 3.5 % of this high amount of water recourses is fresh which only one third of this occurs in glaciers, ground waters, rivers and lakes; location and bad accessibility is an obstacle to allocate most of this resources for beneficial uses specially for drinking purposes. Consequently, the difficulty in meeting the increasing demand for new freshwater resources has motivated many municipalities and water utilities to explore the desalination of seawater, brackish waters, and reclaimed water as alternative water supplies. In the desalination process salt and minerals can be removed within a couple of actions. Unlike traditional method, desalination doesn't use fresh water; so, by considering problems which is stated, desalination can be assumed as a good solution, especially for coastal areas. Two general types of technologies are thermal based process which can be done by multi-stage flash distillation (MSF), multi-effect distillation (MED), vapor compression distillation (VCD) that mostly are used in Caribbean, Red sea, and Persian Gulf regions which have concentrations of up to 39,000 and 41,000 mg/L and cheap fossil energy, and membrane based process, which use membrane for water purification; reverse osmosis (RO), nanofiltration (NF), electrodialysis reversal (EDR), electrodialysis (ED) are practiced as membrane based desalination in other regions than were stated. Fouling is one of the major ubiquitous challenges of the membrane in water treatment processes. Fouling can be categorized into inorganic fouling, organic fouling, colloidal fouling, and biofouling which are interrelated to each other. The fouling layer cause pressure drop in the feed channel that leads to reduction in the permeability and more energy consumption. To tackle this, different approaches have been practiced such as pretreatment of feed water, modification of the operating condition, and membrane surface moddification. Feed water pretreatment is an effective way but not well enough because of pre-existed bacteria in the system . Limited amout of bacteria in water after pretreatmnet can also cause very drastice fouling on the membrane by colonizing on the surface of the membrane. What makes biofouling problmatic is the extracellular polymeric substances (EPS) that excreted from the microorganisms on the membrane and this EPS layer is composed from the polysaccharides and protein which are considered as organic matters. Organic fouling also is another type of fouling which humic substances and polysaccharides, carohydrates, lipids, and amino acids are responsible for organic fouling. In order to cope with the fouling problem the mechanisms for fouling should be elucidated and proper step for banishing to that routh should be taken. Unfortunately, in research papers, the key word of "Antifouling" membrane has been utilized by testing only one mechanisms of fouling. However, applying such word needs to inverstigate all of the aspect of the fouling to make sure about the characteristics of the modified membranes. In this study, some issues which are practiced usually in research about the fouling phenomena are challenged. The membranes which were used in this study are zwitterionic coated RO TFC membranes. Firstly, organic fouling was investigated by applying xanthane gum and bovine serum albomin (BSA), and the cationic surfactant DTAB. Then the biofoulant marine bacteria was isolated and the biofouling tests were performed on the membranes to analyse the mechanisms and relating the organic fouling and biofouling to each other. The key point in the biofouling is utilizing the marine biofoulant bacteria instead of the "Escherichia coli" as a steriotype baceria for biofouling in the reseraches