High-recovery inland desalination: Concentrate treatment by electrodialysis and batch reverse osmosis

Since fresh water resources are finite and stressed, it is of the utmost importance to develop alternative water resources. Efforts to recover and treat impaired water are happening in arid areas around the world, where water resources are already scarce. Such efforts are particularly focused on high-recovery treatment systems, accomplished by reducing the amount of liquid discharge with the intent to eventually reach zero liquid discharge. The goal of this research is to improve the feasibility of high-recovery inland desalination systems. Two types of high-recovery treatment systems were selected for study: (1) combined reverse osmosis (RO) and electrodialysis (ED) systems, such as the Zero Discharge Desalination (ZDD) process; and (2) reverse osmosis systems with concentrate recycling, such as the Concentrate Enhanced Recovery Reverse Osmosis® (CERRO) process. The objectives of this research were to investigate two challenges associated with electrodialysis (ED) used in high-recovery desalination processes, and to evaluate a reverse osmosis (RO) system with concentrate recycling for desalination and contaminant removal of recreational water. Experimental evaluation was performed with laboratory-scale-ED systems, to investigate the voltage loss associated with the electrodes and rinse solution. Large scale ED processes can be precisely simulated in laboratory-scale ED systems, but power calculations will be inaccurate if the electrode and electrode solution voltage losses are not properly considered. A mathematical model was developed using electrochemistry theory to effectively predict the voltage loss associated with the electrodes and rinse solutions by considering the membrane specifications, electrode compartment geometries, solution conductivity, and electrode material. The model was compared against experimental data and results demonstrated the prediction of voltage drop within 5% error. A second project was conducted to investigate a membrane-modification process to minimize the shunt currents in high-recovery ED applications. In high-recovery desalination systems, the ED process can produce a concentrate stream with a very high electrical conductivity, and this concentrate solution flowing through the manifold can become a significant short-circuiting path for the electrical current. (The electrical current passes through the electrolyte and then shunts into the manifold distribution system of the ED cell.) This short-circuiting in the compartments causes serious overheating to the membranes and spacer and may cause permanent damage to the system. This research project evaluates the use of chemicals to intentionally neutralize the ion-exchange capacity of the membrane surrounding the manifold and thereby increase the manifold resistance to minimize the shunt current. Results identified neutralizing chemicals that were able to reduce the membrane in-plane conductivity by 90% and decrease the ion exchange capacity more than 80%. Neutralized membranes were analyzed with Fourier-transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM), which revealed distinct changes in chemical moiety and surface morphology. Experimentation with neutralized membranes demonstrated stable long-term performance. A third investigation was performed to evaluate a batch reverse osmosis process with concentrate recycling (UTEP-patented process called CERRO ®) for desalination and contaminant removal from sun-exposed swimming pools. Cyanuric acid (CYA) is a stabilizer added to the pools to reduce chlorine photodegradation. However, as water evaporates from the pool, CYA and total dissolved solids (TDS) are concentrated. Subsequent chlorination is then primarily sequestered to the concentrated CYA, which may result in ineffective disinfection. Experimentation with the CERRO ® process was performed using nanofiltration (NF) and seawater reverse osmosis (SWRO) membranes, which demonstrated removal of more than 90% of CYA and TDS, achieving 70% and 85% recoveries using NF and SWRO, respectively of water that would otherwise be lost

Modeling and analysis of a manufacturing simulation process

The purpose of this thesis is to develop an integrated model of a highly complex manufacturing process. The simulation was carried out to implement a re-engineering design problem. The specific company in which the study took place is a medium size company dedicated to the printing solution Industry. The study required a deep analysis of its current manufacturing process to maximize throughput and productivity. The current production layout with cycle time of 42 hours was analyzed and simulated with a variance of 5% in order to propose a set of changes. Research was done to support the decision process concerning the implementation phase of the suggested changes. The mean production rate for the experiment A model was 49,620 units per week with a standard deviation of 1,193, for the experiment B model, the mean was 60,946 units/week with a standard deviation of 1,409. For the experiment C model, the mean was 67,844 units/week with a standard deviation of 4,706; the experiment D model gave a mean of 139,152 units/week with a standard deviation of 8,007. Similarly, twenty-five runs of the simulation model were performed, with a simulation length equal to 168 hours and a warm-up period of 10 hours, reporting a mean production rate of 55,283 units and a standard deviation of 1,301 for the first and a 103,498 mean and a standard deviation of 6,402 for the second experimentation. Based on the positive results obtained from this work, management will now use Arena® as a simulation tool for future investments and/or process modifications in order to avoid delays and economic loses

Hypochlorite Generation from a Water Softener Spent Brine

Industries that require water with low hardness consume large amounts of NaCl for water softening. In this work, water softener spent brines were recovered and used as raw material in an electrolysis cell with cationic exchange membrane (CEM) to yield both sodium hypochlorite and sodium hydroxide amounts, which are the most common disinfectants used to sanitize production areas. Spent brines contained mainly an average of 4.5% NaCl, 650 mg L−1 Ca2+, and 110 mg L−1 Mg2+, the last two cations adversely affect the CEM and must be treated prior to the electrolytic process. Two hardness removal methods were evaluated separately—lime-soda ash and sodium hydroxide-soda ash softening—the last one being the most effective as total hardness was decreased by 99.98%. This pretreated spent brine was then introduced into the electrolysis cell. Experimental design comprised five level variations for current intensity, % NaCl, and time. The best operation conditions yielded 2800 mg L−1 NaOCl for a 5% NaCl solution. By incorporating chlorine gas trap to increase OCl− concentration a maximum of 7400 mg L−1 NaOCl was achieved. Finally, biocidal activity was tested following sanitation protocols (NaOCl dilution level) on workbenches and a decrease in bacterial count of at least 5 logs under laboratory-controlled conditions