Conventional water treatment systems have been shown to provide inadequate treatment of pollutants of emergent concern (CEC) [1]. The increasing worldwide contamination of freshwater with a manifold of pharmaceutical residues threatens aquatic organisms and human health. The environmental effects of pharmaceuticals, antibiotics, and disinfectants are of increasing concern [2]. The CEC has posed raising concerns recently. They are increasingly discharged in water and wastewater at worryingly high levels and being treated ineffectively in water and wastewater treatment systems. The CEC can be classified as pharmaceuticals, personal care products, pesticides and industrial chemicals [3]. Due to the inevitable environmental release, antibiotics have been detected in global water which brings challenges to not only targeted bacteria but also to the health of non-target species such as fishes, plants, and algae [4]. Wastewater from animal husbandry, aquaculture, and the pharmaceutical industry is the major source of antibiotics in the environment [5]. Pharmaceutical residues are responsible for a number of harmful pollutants, such as antibiotics [6].
Antibiotics are often found in various environments and can be extremely dangerous for both human health and ecosystems [7]. Pollutants not subject to regulation are increasingly found in wastewater discharges, due to modern consumption patterns. These compounds are generally referred to be contaminants of emergent concern (CEC) due to the potential effects of their existence in the world's water systems. Pharmaceuticals, personal care products, industrial additives, insecticides, and a variety of chemical compounds have all been detected in wastewater [3, 8]. Antibiotics, including ciprofloxacin (CIP), are used to mitigate or cure microbial infections and illnesses in veterinary, human, and aquatic systems by targeting specific bacteria. These antibiotics continually enter the aquatic environment by multiple pathways, such as hospital wastewater and pharmaceutical wastewater, veterinary, human excretions, and sewers, reaching treatment facilities in amounts ranging from ng/L to µg/L [9]. The occurrence of CIP in the surface water could achieved 5.02 mg/ L [10]. The emergence of antibiotic-resistant genes (ARGs) and bacteria (ARBs), which cause 700,000 annual fatalities, is the main issue connected to antibiotic-polluted water [11]. Due to their resistance to the specific antibiotics suggested for their therapy, ARBs are extremely difficult to treat [12].
Ciprofloxacin (CIP) is a significant pharmaceutical drug belonging to the fluoroquinolone (FQ) class that targets both Gram-positive and Gram-negative bacteria to treat serious illnesses. Its global emissions are primarily found in surface water, which accounts for 25% of the total emission, and municipal wastewater, which accounts for 58% of the total emission [13]. This family of antibiotics is extremely mobile in the aquatic environment due to its hydrophilic characteristics. fluoroquinolone antibiotic ciprofloxacin is found in a variety of sources, including drinking water and WWTP effluents, due to its significant usage in both human and veterinary medicine [14]. Like other antibiotics, CIP can stack up in the cells of an organism and pose a major risk to human health. The successful removal of CIP is therefore feasible given adequate consideration to their high levels in a variety of wastewaters, stability, resistance to decomposition, and possible ecotoxicity [15]. Antibiotic removal has been accomplished by a variety of methods, including coagulation, membrane separation, advanced oxidation, adsorption, photocatalysis, electrolysis, and biological degradation. These methods have several drawbacks, including high energy and material costs and secondary contamination from the addition of other chemicals. Adsorption, on the other hand, is the most adaptable and extensively utilized of these because of its great removal capacity, high efficiency, straightforward design, and simplicity of usage. In this regard, biosorption which relies on the ability of various types of live and inactive dead biomasses (heat, dried, chemically treated) to bind and concentrate contaminants from water-based solutions has emerged as an environmentally friendly, practical, and financially viable method for the removal of antibiotics [16]. An ecologically benign method with great promise for antibiotic elimination is microalgae-based wastewater treatment. The precise antibiotics and microalgae species used, however, determine how well CIP is removed by microalgae [7, 17].
Microalgae are photosynthetic eukaryotic or prokaryotic organisms that can grow single, in chains or colonies, or filamentous forms. They can be found in a variety of ecosystems, including airborne, aquatic, and terrestrial habitats [18]. Microalgae serve a significant role in the oxygen production in aquatic ecosystems, as well as an important element of the food chain. Microalgae have attracted interest in the bioremediation research community for their capacity for acclimation and eliminating the antibiotics themselves from contaminated water, yielding important biomass [11]. The antibiotic removal effectiveness of the adsorption technique is strongly reliant on the adsorbent, which is often costly. Accelerated oxidation and photocatalysis may be usually successful, but they require expensive chemical agents or catalysts, as well as the potential generation of secondary pollutants. In contrast, microalgae wastewater treatment is a biological process that requires minimal chemical agents and may be tailored to successfully remove new pollutants such as antibiotics [19]. The biosorption efficiency depends on the sorbent properties (Microalgae) and pollutant structures [20]. In microalgae, the cell walls include polymer assemblages and functional groups that can facilitate biosorption [16].
Factors affecting antibiotic removal performance by microalgae are (1) algal species, (2) antibiotic classes and concentration, (3) algal growth conditions [19]. Some literature comparing different algal species on ciprofloxacin removal is presented in Table 1. This study aimed to determine the biosorption capability of Synechocystis sp. and C. vulgaris for antibiotic ciprofloxacin at different concentrations and investigated in comparison with the control medium. The selected microalgae species are Synechocystis sp. and Chlorella vulgaris without modification in powder form at a constant concentration in the removal of CIP as CEC. A thorough investigation is conducted on process optimization by the adjustment of process parameters, such as time, pH, dosage, and starting concentration, in addition to the isotherm of adsorption and kinetic investigations.
Table 1
Illustrate removal of ciprofloxacin by different Microalgae species and removal mechanisms.
Microalgae | Initial antibiotic concentration and removal rate, hydraulic retention time | removal mechanisms. | WW Category | Ref. |
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Chlamydomonas mexicana | 2 mg/L and 13%, 11d | Biodegradation, accumulation, and adsorption | Bold’s Basal medium | [21] |
Nannochloris sp. | 57 ng/L and 100%, 7d | Direct photolysis | Water from Las Vegas wash | [22] |
Chlamydomonas pitschmannii | 2 mg/L and 1.6%, 11d | Biodegradation, accumulation, and adsorption | Bold’s Basal medium | [21] |
Ourococcus multisporus | 2 mg/L and 2%, 11d | Biodegradation, accumulation, and adsorption | Bold’s Basal medium | [21] |
Chlorella Vulgaris | 2 mg/L and 0%, 11d | Biodegradation, accumulation, and adsorption | Bold’s Basal medium | [21] |
Chlamydomonas Mexicana | 2 mg/L and 56%, 11d | Biodegradation, accumulation, and adsorption | Bold’s Basal medium + sodium acetate (4g/L) | [21] |
The mixture of algae-bacteria consortia in pilot high-rate algae pond (HRAP) | 1.31 mg/L and 20.1%, 24h (8 h sunlight/16h dark) | Photodegradation during daytime, and adsorption during nighttime | Real domestic wastewater | [23] |