Arsenic contamination, effects and remediation techniques: A special look onto membrane separation processes

Abstract

In many countries, arsenic (As) concentrations above acceptable standards for drinking water have been found, which is bringing awareness and becoming a worldwide concern. As occurs in the environment naturally, but anthropogenic activities such as mining, fossil fuels burning, pesticide and herbicide application have been playing a major role in the As occurrence in groundwater and drinking water. The two inorganic arsenic ions As(III) and As(V) are ubiquitous in natural waters and pose significant health risks to humans even at low concentrations, for example, lung cancer, cirrhosis and myocardial infarction. Therefore, there is an increasingly search for technologies that have high removal efficiency, simplicity, cost-effectiveness, feasibility and lower chemical requirements. In this regard, this paper reviews the occurrence, exposure pathways, effects and removal technologies such as oxidation, flocculation, coagulation, adsorption, ion exchange and particularly membrane separation processes (MSP), with attention to the disadvantages and limitations of these technologies. Furthermore, integrated approaches between MSP and others are discussed. Lastly, emergent technologies in MSP such as forward osmosis, membrane distillation and electrodialysis were discussed and their efficiency and performance towards As retention was presented.

Introduction

Arsenic (As), the 20th most abundant element, has become a worldwide concern (Chai, 2019). As is mostly associated with igneous and sedimentary rocks, particularly sulfidic ores (Chai, 2019). Natural phenomena for instance weathering, biological and volcanic activity, along with anthropogenic activities (such as mining, fossil fuels burning, pesticide and herbicide application and crop desiccants) are responsible for the leakage of arsenic into the ecosphere. Arsenic exists mainly in four oxidation states: arsine (As³⁻), arsenic (As°), arsenite (As³⁺) and arsenate (As⁵⁺), besides the environmental forms including arsenious acids, arsenic acids, methylarsenic acid, dimethylarsinic acid, arsine, among others.

Arsenic has been detected in both inorganic and organic forms in groundwater, surface water and sediments (Borba et al., 2004; Dsikowitzky et al., 2013; Dummer et al., 2015; Klassen et al., 2009; Liang et al., 2016; Nickson et al., 2005). Furthermore, several studies have reported the presence of organoarsenic compounds in fish and other aquatic fauna and flora (Grotti et al., 2008; Jankong et al., 2007). In the environment, human arsenic exposure may occur through ingestion, inhalation, or absorption through the skin, however, ingestion is the predominant type of arsenic exposure. Various As effects were described due to short-term and long-term exposure, these include respiratory (Gerhardsson et al., 1988; Hopenhayn-Rich et al., 1998; Mazumder et al., 1997; Milton et al., 2001), hepatic (Guha Mazumder, 2001; Naqvi et al., 1994; Santra et al., 2000, 1999), neurological (Bansal et al., 1991; Chhuttani et al., 1967; Grantham and Jones, 1977; Wagner et al., 1979), renal (Gerhardt et al., 1978; Hopenhayn-Rich et al., 1998; Shiobara et al., 2001), reproductive (Léonard and Lauwerys, 1980; Squibb and Fowler, 1983), mutagenetic (Astolfi et al., 1981; Bencko et al., 1988) among others. Furthermore, emerging evidence suggests that cofactors such as genetics, diet, and other environmental exposures are important determinants of arsenic toxicity in moderately exposed populations (Watson, 2015). As a consequence of this widespread contamination and given the effects and toxicity, the World Health Organization (WHO) has set a guideline for 10 μg/L as the drinking water standard.

Because exposure to low levels of As can be fatal to human health, and given the increasingly strict legislation, treatment of contaminated water is critical. Removal of As is highly dependent on the polluted water's chemistry and composition. In most of the reported major incidences As occurs as As(III), therefore, an As(III) to As(V) oxidation stage is considered necessary in most cases in order to achieve the satisfactory results. It is important to notice that most drinking water treatment plants (DWTP) uses simple physical-chemical processes such as oxidation followed by coagulation-flocculation. This route for As treatment has several drawbacks such as low removal efficiency and the formation of by-products (for example, oxidation byproducts and arsenical sludge) can be a further potential source for secondary As pollution. In fact, DWTPs are not conventionally designed aiming for arsenic removal. Some of the most used technologies will be discussed in this review, such as, oxidation, coagulation-flocculation, adsorption, ion exchange and, in particular, membrane technologies.

A concise overview of the current knowledge of arsenic occurrence, effects and mostly the treatment options, focusing on membrane separation processes is presented. A systematic literature search was carried out in Web of Science comprising the Web of Science core database; Derwent innovations index; KCI-Korean journal database; Russian science citation index and SciELO citation index using combinations of keywords including arsenic, removal, occurrence, drinking water treatment plants (DWTP), ion exchange, membrane separation processes (MSP), reverse osmosis (RO), nanofiltration (NF), adsorbents, biosorption, oxidation, forward osmosis (FO), membrane distillation (MD), electrodialysis (ED), among others. The cited references were also checked to find more relevant studies. This combined databased resulted in 11,605 articles between 1945−2019. The areas that accounted for more than 80 % of the total articles were engineering, environmental sciences, chemistry, water resources, toxicology, and public environmental occupational health. In Fig. 1 the concern for this topic is highlighted by the exponential growth in publications containing the aforementioned keywords. Lastly, from this database, further selection was made based on article relevance, date and importance, these comprised to more than 200 studies that were consulted and cited in this work.