A comprehensive review on contaminants removal from pharmaceutical wastewater by electrocoagulation process

Highlights

• Pharmaceuticals contaminants in the aquatic environment cause eco-toxicity.

• The conventional process is not so useful in removing pharmaceutical contaminants.

• The review offers deep insight of the EC in removing the pharmaceutical contaminant.

• EC process is quick coagulation by the assistance of electricity application.

• EC endure lack of scale-up systems and the developments techniques are reviewed.

Abstract

The pharmaceuticals are emergent contaminants, which can create potential threats for human health and the environment. All the pharmaceutical contaminants are becoming enormous in the environment as conventional wastewater treatment cannot be effectively implemented due to toxic and intractable action of pharmaceuticals. For this reason, the existence of pharmaceutical contaminants has brought great awareness, causing significant concern on their transformation, occurrence, risk, and fate in the environments. Electrocoagulation (EC) treatment process is effectively applied for the removal of contaminants, radionuclides, pesticides, and also harmful microorganisms. During the EC process, an electric current is employed directly, and both electrodes are dissoluted partially in the reactor under the special conditions. This electrode dissolution produces the increased concentration of cation, which is finally precipitated as hydroxides and oxides. Different anode materials usage like aluminum, stainless steel, iron, etc. are found more effective in EC operation for efficient removal of pharmaceutical contaminants. Due to the simple procedure and less costly material, EC method is extensively recognized for pharmaceutical wastewater treatment over further conventional treatment methods. The EC process has more usefulness to destabilize the pharmaceutical contaminants with the neutralization of charge and after that coagulating those contaminants to produce flocs. Thus, the review places particular emphasis on the application of EC process to remove pharmaceutical contaminants. First, the operational parameters influencing EC efficiency with the electroanalysis techniques are described. Second, in this review emerging challenges, current developments and techno-economic concerns of EC are highlighted. Finally, future recommendations and prospective on EC are envisioned.

Introduction

Pharmaceuticals drugs play a vital role in improving life expectancy and quality of life for peoples. Vast amounts of pharmaceutical are used in every year for human as well as a veterinary medicine for the treatment of fever, infections, mental and physical stress, pregnancy prevention and also stimulating the agricultural growth (Sofowora et al., 2013). There are so many pharmaceuticals which are especially using for medical issues and problems and found as a higher concentration of these compounds in wastewater which are now becoming emerging contaminants of concern (Liu et al., 2015). It is mentionable to remark that the pharmaceutical manufacturing industry and hospitals are the most significant sources of pharmaceutically polluted wastewater. These pharmaceutical compounds are usually generated in different operation by the pharmaceutical industry, where the abundant volume of waters are needed for washing and extraction of solid cake or equipment used (Gadipelly et al., 2014). The highly strength contaminated wastewater produced from the different manufacturing process of pharmaceuticals contain a large variety of toxic compounds leading to water plants and detrimental to seeds, new-borns, children, and the grown person (Verlicchi et al., 2012). The possible pharmaceutical compounds existence in humans water consumption has two sources; (a) production process of pharmaceutical manufacturing industry and (b) common usage of pharmaceuticals which results in their presence in urban and agricultural wastewater. These frequently detected toxic compounds in different water bodies and drinking water has got extensive attention for efficient treatment to water reuse because of their non-biodegradable character which may persist and remain contaminated leading to potential health and environmental risks (Kanakaraju et al., 2018). This may also establish a possible hazard for the aqueous ecosystem as well as affects the life of the animal and human beings exist in the long run (Klavarioti et al., 2009).

Recently, researchers are noticing high amounts of pharmaceutical compounds in different types of wastewater, i.e., surface and ground waters, and also to drinking water sources (Yang et al., 2014). So, the environmental effects and human health risks can be affected by these types of wastewater, and thus, researchers around the world are giving much attention. Generally, pharmaceuticals compounds enter the natural water sources by the overflow of different non-point water sources like agronomic action or static water sources like municipal and hospital wastewater treatment plant (Yang et al., 2016). Most of the pharmaceuticals are unregulated contaminants which are needed to bring under standard discharge regulations because of their existence in the ecological media and possible health injury. In view of mitigating water resources scarcity around the world, it is essential to comprehend and create advancement in waste management for treating pharmaceutical wastewater (Gadipelly et al., 2014). Fig. 1 shows different paths and its recycling how the pharmaceutical wastewater is released from the manufacturing industry to the ecosystem. The numerous wastewater sources coming from the active pharmaceutical industry, unpackaged medicines and related pharmaceuticals which are normally using huge amounts of water need to be identified, and the finest technologies need to be evaluated for removing them to improve environmental health and water resources.

Wastewater generated from the pharmaceuticals industry has severe color, pungent odor, high COD, and low BOD (Farhadi et al., 2012). These properties exhibit challenges for anaerobic or aerobic treatment methods as the presence of their stubborn components may greatly inhibit the activity of the microbes (Gebhardt and Schröder, 2007). The application of activated sludge and trickling filter method are also done for the treatment of pharmaceutical wastewater which became unsuccessful and resulted in releasing the wastewater in eco-system and continuously contaminated soil, surface, and groundwater (Ahmadzadeh et al., 2017). Actually, for pharmaceutical wastewater treatment, the main treatment methods are physio-chemical and biological methods. Comparatively, biological treatment method is cost-effective but is not so operative in stubborn carbon-based wastewater (Farhadi et al., 2012). Then again, the results found from physio-chemical treatment are highly effective and is steady with high-strength wastewater, but installation and operating cost are comparatively high (Klavarioti et al., 2009). Actually, neither physio-chemical nor biological treatment method is suggested alone and the combined treatment system is often the most suitable procedures in this high-strength pharmaceutical contaminants treatment (Quintana et al., 2005). In fact, it is not so effective because of their complicated properties so the conventional wastewater treatment processes cannot fully remove active pharmaceutical compounds (Crouse et al., 2012). Table 1 shows the benefits and drawback of different treatment technologies for wastewater treatment.

Actually, electrocoagulation process was more effective in eliminating stubborn pharmaceutically active contaminants (Ensano et al., 2017b). Pharmaceuticals have much organically active compounds and presence of those in the water system causes serious apprehensions because of their antagonistic toxicological properties on active creatures as well as human health (Pan et al., 2008; Schwaiger et al., 2004; Vernouillet et al., 2010). These contaminants can persist and bioaccumulate in the environment (Mompelat et al., 2009). Additionally, typical wastewater treatment by biological methods are so scarce for removing refractory contaminants completely from pharmaceuticals wastewater (Inyang et al., 2016). In an EC process, the dissolute metal hydroxides ions are capable enough to eliminate solvable inorganic contaminants (Solak et al., 2009). The foremost reactions in the EC procedure are iron/aluminum dissolution from anode and hydroxyl ion production at cathode (Liu et al., 2015).

Several researchers have been studied the application of EC methods for different types of industrial and agricultural wastewaters (Holt et al., 2005; Kyzas et al., 2015b; Nanaki et al., 2015; Nasrullah et al., 2019; Terzopoulou et al., 2016). In EC process, electrodes are normally made of stainless steel (SS), aluminum (Al) and iron (Fe), and their primary function is as a dynamic coagulant precursor via dissolution in the anode and progressing hydrogen gas production on the cathode with gas bubble (Bhatnagar et al., 2013). In EC process, mostly three consecutive phases are involved which are coagulant species generation by the oxidized dissolution of the sacrificial metal anode, pollutants inconstancy, particulate deferral, emulsions breaking and lastly destabilized phase accumulation to form flocs (Kamaraj and Vasudevan, 2016). A search on science direct showed a noticeable increase in EC implementations in attempting the removal of pharmaceutical contaminants, representing an increase in research options in the field of pharmaceutical wastewater, as shown in Fig. 2.

The objective of this review was to regulate a systematic literature assessment on the removal of pharmaceutical contaminants in wastewater by the EC process. The maximum typical pharmaceutical contaminants found in a water body are designated, and water contamination problems are reviewed. The efficiency of the EC system is discussed in removing pharmaceuticals contaminants, which are affected by various operating parameters. Also, the techno-economic analysis was analyzed to get a clear view for future industrial application for pharmaceutical wastewater treatment. The necessity of the operational parameters affecting in effective implementation of the process along with the electrolysis techniques, EC treatment background and potentials, emerging challenges, and current developments are summarized. To conclude, the perspectives for future studies and recommendations of EC treatment for pharmaceutical wastewater has been deliberated along with their existing weaknesses in operational parameters and energy proficiency.