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The coexistence of different foulant compositions in the feed water of reverse osmosis (RO) systems causes serious complications in the fouling process of the membranes. Hence, in this technical research, the phenomenon of combined inorganic (gypsum)-colloidal (silica particles) fouling (inorganic-colloidal fouling) of brackish water RO (BWRO) process was studied in the lab-scale experiments. Moreover, the effect of the presence of air micro–nano bubbles (AMNBs) in the feed water; as a new practical method for control of membrane fouling, was investigated on this phenomenon. For this purpose, a suspension with the potential of inorganic scaling [calcium sulfate, Saturation index (SI)=0.96 ] and colloidal fouling (colloidal silica, 50 mg/L) was used to form the inorganic and colloidal foulings (simultaneously) on the membrane surface during the inorganic-colloidal fouling process. All experiments were performed twice, once in the absence and once in the presence of AMNBs. Finally, the results of this research were compared with the results of the inorganic and colloidal fouling studies. Based on the results, the inorganic-colloidal fouling formed a dense and compact fouling layer on the membrane surface, which severely reduced the permeate flux (76.3%) and salt rejection (4%). The amount of decrease of these two parameters in inorganic-colloidal fouling was much higher than each of individual inorganic and colloidal foulings. In the presence of AMNBs, both types of inorganic and colloidal foulings greatly reduced and the major portion of inorganic-colloidal fouling was related to the colloidal fouling. Thus, a significant decline was observed in adverse effects of inorganic-colloidal fouling on the membrane performance and the permeate flux and salt rejection decreased by 18.5% and about 1%, respectively. The results of this study could introduce the micro–nano bubbles (MNBs) technology as an effective method to inhibit the inorganic-colloidal fouling in RO systems. Practical Applications: Today, reverse osmosis processes are known as efficient technologies for supplying drinking water from brackish and sea water resources due to their high ability to remove various compounds. The separated compounds from the water accumulate near the membrane surface and consequently deposit on it and/or inside its pores. This phenomenon is called membrane fouling and has adverse effects on the performance of reverse osmosis processes. Water resources usually have different types of pollutants that simultaneous presence of them can intensify the membrane fouling process. Gypsum scaling and colloidal silica fouling are two major common types of reverse osmosis membrane fouling. Therefore, in this research, the effects of the inorganic-colloidal fouling were studied on the performance of a commercial brackish water reverse osmosis membrane, in presence and absence of air micro–nano bubbles. The results showed that the combined fouling formed a complex fouling layer on the membrane surface in absence of air micro–nano bubbles. In real-scale reverse osmosis process, this layer can severely reduce the membrane permeate flux and salt rejection which result to increase in the operational and maintenance costs. Alternatively, the presence of air micro–nano bubbles in the reverse osmosis feed flow could limit both inorganic and colloidal foulings and their synergetic effects on each other. [ABSTRACT FROM AUTHOR]

Colloidal fouling on a brackish water reverse osmosis (BWRO) membrane was simulated by a lab-scale plate-and-frame module in the presence and absence of air micro-nano bubbles (AMNBs). Synthetic feed water samples with the same physical and chemical properties, but various concentrations of colloidal silica (50, 100, 200, and 300 mg/L), were used for experiments. The results illustrate that colloidal fouling caused a severe decrease in permeate flux (24%–56%) and salt rejection (1.25% to 4.18%) in the absence of AMNBs. This reduction in membrane performance was attributed to the high hydraulic resistance and the cake-enhanced osmotic pressure (CEOP) of a fouled gel layer that were intensified with increase in the colloidal concentration. On the other hand, presence of AMNBs decreased the deposition rate of colloidal particles significantly and increased the porosity of fouling layer. Thus, an improvement in the membrane permeate flux (21%–40%) and salt rejection (1.2%–2.6%) were seen in the different concentrations of colloidal particles. The SEM images also confirmed the formation of loose fouling layers which were easily removed from the membrane surface by a clean-in-place (CIP) process. This research introduces AMNBs technology as an effective in-line method to control the adverse effects of colloidal fouling in reverse osmosis (RO) systems. RO is a well-known process in the field of water and wastewater treatment. RO membranes have the ability to remove all pollutants, undesirable ions, and micro-organisms from the liquid phase that leads to their accumulation on the membrane surface. This phenomenon is called membrane fouling. Colloidal particles are one of the major fouling agents that are found in all water resources which has a direct adverse effect on the efficiency of RO systems. Various technics (based on the filtration process) are used to remove the colloidal particles in pretreatment stage of RO systems. In this research, the micro-nano bubbles (MNBs) technology was used to control the colloidal fouling in RO process. The results showed the presence of MNBs in feed water of RO could decrease the fouling of the membrane surface and improve the quality and quantity of produced water. Also, the energy consumption of this technology can be restored easily by the improvement in the quantity of the produced water. Thus, the MNBs technology could control the colloidal fouling of RO membranes with no adverse environmental effects. [ABSTRACT FROM AUTHOR]

The present study investigated the effects of air micro–nanobubbles (AMNBs) on calcium sulfate dehydrate (gypsum) scaling over a reverse-osmosis (RO) membrane in a lab-scale plate-and-frame module processing brackish water. Membrane performance for the treatment of a synthetic solution sample with high gypsum scaling potential was evaluated by measuring permeate flux and salt rejection and high-resolution scanning of fouled membrane surface in the presence and absence of AMNBs. The results show that AMNBs significantly reduce gypsum scaling on the membrane surface due to enhanced dispersion effect in flow and decrease the effect of concentration polarization (CP), especially in central areas and the outlet of the channel flow. In the absence of AMNBs, after 20 h of scaling, the membrane permeate flux and salt rejection reduced to 70% and 96.4%, respectively. However, the presence of AMNBs in the solution improved these values notably in the same conditions (flux-83% and rejection-98%). The results indicate that the application of AMNBs is able to play an effective role in the control of gypsum scaling and improvement of membrane performance in the RO desalination process. [ABSTRACT FROM AUTHOR]

Mining residues, in general and metal ores, in particular, contain heavy metals within the rock. These heavy metals, including copper (Cu) for which there is an increasing demand around the world, are very harmful to humans and, as such, are a serious problem for the environment. In this study, a rhamnolipid biosurfactant was used to extract copper from an oxide residue with 8,950 mg copper per kg ore. To optimize the conditions for maximum extraction, several batch tests were performed on washed ore samples at 25°C. The best ore particle size for optimal extraction was determined to be between 0.15 and 0.3 mm while the optimal pH of the washing solution was 6. A minimum volume of 10 mL rhamnolipid of 2% concentration for 1 g of ore was required to extract about 28% of copper from the ore. Adding 1% NaOH to the biosurfactant solution dramatically improved the copper extraction from the residue up to 42% in 6 days. Unwashed samples of mixed size particles were tested under the optimized conditions and 24% of copper was extracted. A sequential extraction procedure on the residues was performed to determine the forms of copper in the ore. Although the oxide and hydroxide, residual, and carbonates are the main forms, copper was extracted mainly by the biosurfactant from the oxide and hydroxide portions. [ABSTRACT FROM AUTHOR]