Water pollution is a global problem threatening the entire biosphere and affecting the life of many millions of people around the world. Not only is water pollution one of the foremost global risk factors for illness, diseases and death, but it also contributes to the continuous reduction of the available drinkable water worldwide. Delivering valuable solutions, which are easy to implement and affordable, often remains a challenge. Here we review the current state-of-the-art of available technologies for water purification and discuss their field of application for heavy metal ion removal, as heavy metal ions are the most harmful and widespread contaminants. We consider each technology in the context of sustainability, a largely neglected key factor, which may actually play a pivotal role in the implementation of each technology in real applications, and we introduce a compact index, the Ranking Efficiency Product (REP), to evaluate the efficiency and ease of implementation of the various technologies in this broader perspective. Emerging technologies, for which a detailed quantitative analysis and assessment is not yet possible according to this methodology, either due to scarcity or inhomogeneity of data, are discussed in the final part of the manuscript.

Sustainable technologies for water purification from heavy metals: review and analysis

Effects of microplastics on wastewater and sewage sludge treatment and their removal: A review

Application of response surface methodology in physicochemical removal of dyes from wastewater: A critical review.

Removal of heavy metal ions from wastewater is of prime importance for a clean environment and human health. Different reported methods were devoted to heavy metal ions removal from various wastewater sources. These methods could be classified into adsorption-, membrane-, chemical-, electric-, and photocatalytic-based treatments. This paper comprehensively and critically reviews and discusses these methods in terms of used agents/adsorbents, removal efficiency, operating conditions, and the pros and cons of each method. Besides, the key findings of the previous studies reported in the literature are summarized. Generally, it is noticed that most of the recent studies have focused on adsorption techniques. The major obstacles of the adsorption methods are the ability to remove different ion types concurrently, high retention time, and cycling stability of adsorbents. Even though the chemical and membrane methods are practical, the large-volume sludge formation and post-treatment requirements are vital issues that need to be solved for chemical techniques. Fouling and scaling inhibition could lead to further improvement in membrane separation. However, pre-treatment and periodic cleaning of membranes incur additional costs. Electrical-based methods were also reported to be efficient; however, industrial-scale separation is needed in addition to tackling the issue of large-volume sludge formation. Electric- and photocatalytic-based methods are still less mature. More attention should be drawn to using real wastewaters rather than synthetic ones when investigating heavy metals removal. Future research studies should focus on eco-friendly, cost-effective, and sustainable materials and methods.

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Removal of heavy metal ions from wastewater: a comprehensive and critical review

Fluoride contamination, health problems and remediation methods in Asian groundwater: A comprehensive review.

A comprehensive review of electrocoagulation for water treatment: Potentials and challenges.

Produced water refers to the water that is generated when oil and gas are extracted from the ground, and it usually includes the natural water layer within the reservoir (formation water) as well as the injected water. The generation of these large amounts of produced water represents a major environmental and economic challenge to the Oil and Gas Industry. Although many studies have attempted addressing this challenge, there has not been any significant development in the treatment of produced water, and most of these studies have achieved limited success. This work introduces a novel electrocoagulation cell for the treatment of produced water, with the aim of reducing electrode passivation, which has always been considered as a bottleneck in the electrochemical treatment of contaminated water. The main goal of the study is to develop an effective perforated electrode design that can reduce cathode passivation and consequently reduce energy consumption. The novel cell design has been tested and optimized for the treatment of produced water to reduce the concentration of the major organic contaminants in the water. The contaminants reduction efficiency of the proposed design was evaluated and benchmarked with multiple cell configurations. The perforated electrode was superior to other configurations and effective in mitigating passivation, reducing the energy consumption by about 70 % compared to the typical plate electrode. The cell performance was optimized, using response surface methodology, and then operated continuously to evaluate the electrocoagulation efficiency. The new cell design achieved a steadystate reduction of the organic contaminants in the produced water by up to 97 %, 98 % and 95 % for TOC, TPH and O&G, respectively.

Dina T. Moussa

Papers

A comprehensive review of electrocoagulation for water treatment: Potentials and challenges.

A perforated electrode design for passivation reduction during the electrochemical treatment of produced water