Enhanced performance of wastewater treatment process, by reverse osmosis-photovoltaic system

Enhanced performance of wastewater treatment process, by reverse osmosis-photovoltaic system

PV-powered reverse osmosis for wastewater treatment

Moroccan scientists have tested reverse osmosis paired with PV generation to maximize chlorophenol rejection in wastewater treatment. They said the tech combination can help to reduce energy consumption. 

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.

Abstract

The presence of certain toxic pollutants in water and wastewater such as chlorophenol must be eliminated, as they have negative effects on human health and the environment. Based on the state of the art, the reverse osmosis (RO) coupled with photovoltaic (PV) was chosen for wastewater treatment. The aim of this article is to evaluate the optimal operating conditions of RO-PV system that maximize chlorophenol rejection with minimal energy consumption. Two complementary approaches were followed combining physical models with statistical ones. The physical model used for the simulation is based on the equations of diffusion and matter balance. After demonstrating the reliability of this model, it was used for parametric sensitivity analysis, performing numerical experiments using a program developed under Python. The data obtained were used for operating parameters optimization, using artificial neural network method coupled with the desirability function. 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. 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.

Introduction

Water is a vital element for human regardless of its gaseous, liquid or solid-state. It is useful for economic and social development, as well as our environmental sustainability. Around the world, water needs are growing more and more (Fiorenza et al. 2003). Many people do not have access to drinking water, especially in dry areas. It is becoming a fundamental ecological concern due to water scarcity. This shortage derives from global warming, population growth and groundwater pollution from industrial effluents or agricultural treatment. There is no fresh water supply available in sufficient quality and quantity to permit excessive use. This growing shortage and the desalination of seawater or brackish water remains an alternative to drinking water. Wastewater treatment is also an economical solution that can be used in the agricultural and industrial sectors. The latter option was put in place by the Moroccan government in order to minimize water consumption, particularly in the agricultural sector, thus using 40% of treated wastewater in agriculture and reducing 60% of pollution by 2020 (National Council of the Environment 2007). Additionally, the use of wastewater is considered as an additional resource that contributes to the protection of our environment, but this wastewater must be treated before its use, as it contains polluting substances which have negative effects on human health and the environment (Ayoub et al. 2016; El Brahmi and Abderafi 2020). Depending on the nature of the process, the composition of industrial wastewater may vary from one process to another, but it usually contains large amounts of dissolved organic matter such as benzene, toluene, ethylbenzene, xylenes, phenols and organic acids. Suspended organic mattes such as oils and greases; dissolved inorganic materials such as heavy metals, sulfates, nitrites and nitrates; and dissolved salts such as chlorides and bromides (MDDEFP 2012; Shi and Qian 2000). In water, chlorine forms toxic chlorophenols with phenol (Bliefert and Perraud 2001). These toxic pollutants must be removed by wastewater treatment (Kusic et al. 2011; España-Gamboa et al. 2012). This treatment must make it possible to extract water of quality corresponding to the different uses.

A wide variety of treatment research is available for wastewater treatment. There are studies that have demonstrated the performance of the microfiltration (MF) process for the treatment of wastewater rich in oils and greases by testing synthetic water or wastewater (Kumar and Pal 2015; Abadikhah et al. 2018). The nanofiltration (NF) process has been tested and recommended for an oil–water emulsion and for micro-pollutants (Muppalla et al. 2015). The same mixture was pretreated by electrocoagulation and followed by reverse osmosis (Silva et al. 2015). This process has proven reliable for removing chemical oxygen demand (COD), total dissolved solids turbidity, electrolytic conductivity and aluminum ions. Hafez et al. (2007) use NF followed by RO membrane separation technology for the treatment of synthetic solutions. They found that the NF membrane removes about 30% of the divalent and trivalent ions, while the RO membrane allows the separation of 99% of sulfate ions, 96% iron, 93% bicarbonate, 90% sodium ions, magnesium and sulfide, 86% potassium, 73% phosphate and 25% calcium ions. Recently, the RO process has been used for a wastewater treatment plant and has eliminated various contaminants such as caffeine, theobromine, theophylline, amoxicillin and penicillin G (Lopera et al. 2019). Different studies have shown the use of the RO for the separation of chlorophenol from wastewater (Al-Obaidi and Mujtaba 2016; Al-Obaidi et al. 2018ab). Furthermore, this technology has been shown to be very promising for the removal of other hazardous industrial effluents, such as  N -nitrosamine compounds and especially  N -nitrosodimethylamine (Al-Obaidi et al. 2018ab). These various researches revealed to us that the reverse osmosis is being developed for the treatment of different types of wastewater and can be used to eliminate almost all contaminants and pollutants. In addition to its operational flexibility, the RO involves lower capital cost and overall cost compared to thermal processes (Nisana and Benzartib 2008). During the last 10 years, the cost of membranes has been reduced by almost half.

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