Reverse osmosis for water treatment can be maximized at lower energy consumption by powering it with solar PV, according to a recent study by researchers at Mohammed V University in Rabat, Morocco.
Compared to thermal processes, reverse osmosis can be used to eliminate almost all contaminants and pollutants in water treatment at lower capital costs, as well as overall costs. However, its high energy requirements have thus far limited the spread of this technology for such applications. Reverse osmosis high-pressure pumps commonly require energy consumption of between 4 kWh/m3 and 19 kWh/m3, depending on the size of the industrial units.
The Moroccan group claims that the combination of reverse osmosis with PV power generation can help to improve the rejection of chlorophenols in the water treatment process. Chlorophenols are toxic, colorless, and weakly acidic organic compounds that are ubiquitous contaminants in the environment.
The academics demonstrated a reverse osmosis unit with a tubular module containing a spiral wound polyamide thin-film composite membrane and a high-pressure pump. Polycrystalline modules and lithium-ion storage were also included in the modeling.
They used an artificial neural network (ANN) method to analyze the operating parameters of reverse osmosis on chlorophenol rejection and energy consumption. These include the feed flow rate, the initial concentration of chlorophenol, the temperature, the initial pressure, and the water recovery rate.
“Wastewater strongly loaded with chlorophenol requires a low feed pressure and a high water recovery rate, to avoid or reduce the phenomenon of clogging membranes,” the researchers said.
The reliability of the ANN model was performed using a set of tests based on two statistical quantities. One of them was the correlation coefficient, which is a statistical measure of the strength of the relationship between the relative movements of two variables. The other was the mean squared error (MSE), which is a model evaluation metric that is often used with regression models.
Using this model, the scientists calculated the quantity of water produced, the chlorophenol rejection, and PV power consumption.
“The results showed that the optimal values obtained, relating to feed pressure of 9.713 atm, water recovery rate of 40%, operating flow rate of 10−4 m3/s and temperature of 40 C could remove 91% of chlorophenol with an energy consumption of 0.8 kWh/m3,” the scientists stated. “This consumption allowed us to deduce that photovoltaic solar panel with a peak power of 280 Wp and a battery capacity of 9.22 kWh is sufficient to produce 1 m3/day.”
All of these values are considered optimal by the group, which claims that reverse osmosis for water treatment powered by solar has strong potential, especially in sunny countries such as Morocco.
In their next step, the scientists plan to conduct a techno-economic analysis to assess the investment and operating costs of the reverse-osmosis system. They presented their findings in “Parametric study to enhance performance of wastewater treatment process, by reverse osmosis-photovoltaic system,” which was recently published in Applied Water Science.
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