Experimental data (
Abstract
In view of risks associated with the discharge of pharmaceuticals in the aquatic environment, the objective of this work was to assess the removal of paracetamol, salicylic acid and diclofenac from water by a microalgae‐based treatment. For a comparison purpose, the growth and kinetic parameters for the removal of drugs were determined for three different microalgae strains, namely Chlorella sorokiniana, Chlorella vulgaris and Scenedesmus obliquus. It was found that the drugs removal efficiency by these strains was related to their growth. Comparing the three pharmaceuticals, the salicylic acid was the most efficiently removed, especially by S. obliquus (>93% batch culture, >99% semicontinuous culture) and C. sorokiniana (>73% batch culture, >93% semicontinuous culture). Contrarily, paracetamol was the most poorly removed, the maximum efficiencies being those attained by C. sorokiniana (>67% batch culture, >41% semicontinuous culture). On the other hand, diclofenac was efficiently removed only by S. obliquus (>98% batch culture, >79% semicontinuous culture). For the three considered drugs, C. vulgaris was the strain showing the lowest removal capacity. The large differences here revealed between microalgae strains regarding their removal capacity of pharmaceuticals, pointed to the strain selection as a key issue for a successful application in wastewater treatment.
Keywords
- emerging contaminants
- wastewater treatment
- phytoremediation
- paracetamol
- salicylic acid
- diclofenac
1. Introduction
Emerging contaminants (ECs) include a wide range of compounds and may be defined as naturally occurring, manufactured or man‐made chemicals or materials that have been found or are suspected to be present in various environmental compartments and whose toxicity or persistence are likely to significantly alter the metabolism of a living being [1]. Among them, pharmaceuticals have received considerable attention with respect to their environmental fate and toxicological properties over the last decade [2]. Pharmaceuticals represent an especially worrying class since they were designed to cause a physiological response and their presence in the environment may affect non‐target individuals and species [3]. This concern on pharmaceuticals presence in the aquatic environment has led to the recent consideration by European regulations within the Water Framework Directive (2000/60/EC) (WFD). The Commission proposal of 31 January 2012 foresaw the inclusion of three pharmaceuticals, namely diclofenac, 17‐beta‐estradiol (E2) and 17‐alpha‐ethinylestradiol (EE2) in the list of priority substances. Instead, by the EU Decision 2015/495, these compounds together with another estrogen (E1) and three antibiotics (azithromycin, clarithromycin and erythromycin) were finally included in the first watch list of substances to be monitored in all member states to support future reviews of the priority substances list [4].
Pharmaceuticals in domestic sewage or from hospital or industrial discharges end in municipal sewage treatment plants (STPs), but conventional wastewater treatments have been reported to be ineffective in the removal of such pollutants, with efficiency values of <5 to 40% [5]. In fact, STPs were not originally designed for the removal of pharmaceuticals due to the non‐existence of limiting regulations on their discharge [6, 7]. Consequently, STPs are important sources of such pollutants in the aquatic environment [8, 9]. In this regard, Verlicchi et al. [10], who reviewed the occurrence of 118 pharmaceuticals in the influent and effluent of 244 STPs, found that the occurrence of some of them in the effluent discharged into surface water bodies may pose a medium‐high (acute) risk to aquatic life. Among the studied pharmaceuticals, diclofenac was shown to have the highest average mass load (240 mg/1000 inhabitant) in the effluents of municipal STPs [10]. The removal efficiencies of diclofenac in conventional STPs have been reported to be about 17% [11], which translates into relative high concentrations in the corresponding effluents [12].
In the recent years, phytoremediation of waters by using photoautotrophic aquatic organisms such as algae has gained attention for the removal of both organic and inorganic pollutants [13–15]. Microalgae are characterized by high photosynthetic efficiency, high growth rates, wide adaptability and high potential to remove inorganic nutrients from the wastewater. The principal mechanism of algal nutrient removal is their uptake into the cell biomass [16]. The main advantages of using microalgae for nutrients removal during the tertiary treatment of wastewaters are the possibility of recycling the assimilated nitrogen and phosphorus into algal biomass as a fertilizer, as a source of products (e.g. paraffin, olefin, glycerol, protein, anti‐oxidant, pigment, plastic, etc.), or as biofuel, and also the generation of an oxygenated high‐quality effluent [17]. However, although the capability of microalgae wastewater treatments systems to remove organic matter and nutrients has been deeply studied, little is known about the removal of ECs, such as pharmaceuticals, by algae. In fact, it has already been claimed the necessity of further studies on the removal of this sort of pollutants by algal systems [18].
In this context, the aim of this study was to determine and compare the potential of green microalgae
2. Materials and methods
2.1. Microorganisms and culture conditions
The microalgae strains used in this study were
The inoculum of each strain was cultivated in 250‐ml Erlenmeyer flasks in the standard culture medium Mann and Myers [20], which is composed of (per litre of distilled water): 1.2 g MgSO4.7H2O, 1.0 g NaNO3, 0.3 CaCl2, 0.1 g K2HPO4, 3.0 x 10−2 g Na2EDTA, 6.0 x 10−3 g H3BO3, 2.0 x 10−3 g FeSO4.7H2O, 1.4 x 10−3 g MnCl2, 3.3 x 10−4 g ZnSO4.7H2O, 7.0 x 10−6 g Co(NO3)2.6H2O, 2.0 x 10−6 g CuSO4.5H2O. The inoculum was kept inside a vegetal culture chamber, where growth occurred under controlled temperature (25 ± 1°C), irradiance in the range of photosynthetically active radiation (175 µE m−2 s−1), photoperiod (12:12) and shaking (250 rpm).
Bubbling column photobioreactors (PBRs) with spherical bases (40 mm diameter and 300 mm height with 300 ml capacity) were used for the experimental setup, keeping an operating volume of 250 ml. In each PBR, the Mann and Myers culture medium was inoculated with the required volume of the corresponding pre‐cultured microalgae in order to have an initial concentration of about 3 × 106 cells ml−1.
During the experimental phase, the culture was aerated with filtered air (0.22‐µm sterile air‐venting filter, MillexFG50‐Millipore), at a rate of 0.3 v/v/min, enriched with CO2 at 7% v/v, which was injected on demand to keep a constant pH (pH = 7.5 ± 0.5), as controlled by a pH sensor. The irradiance supplied during this phase was 370 µE m−2 s−1, which was provided by eight fluorescent lamps (58 W, 2150 lumen, Philips, France). The photoperiod was maintained in 12:12 h light/dark and the temperature in 25 ± 1°C.
2.2. Experimental setup
PBRs were operated in batch mode until the end of the exponential growth phase and then under semicontinuous mode till the growth parameters remained constant at the steady state. During the batch culture, an aliquot of 5 ml was daily taken from each PBR for the analytical determinations, this volume being replaced with distilled water to keep the operation volume. During the semicontinuous culture, 30% of the culture volume was daily harvested and used for analysis, this volume being replaced with fresh medium.
For each strain of microalgae used in this work (
Throughout the experiments, the growth of the culture was daily monitored by the determination of biomass concentration and cell density. The removal of pharmaceuticals was daily determined by the analysis of the remaining concentration of this drug in the culture medium. All analyses were conducted in triplicate.
2.3. Analytical methods
Biomass concentration (Cb) was determined by optical density at 680 nm (OD680) by spectrophotometric (UV/visible spectrophotometer BECKMAN DU640) and verified by dry weight. Preliminary studies were conducted to determinate the relationship between dry weight and OD680 for each strain; as shown in Eq. (1) for
Dry weight measurements were performed by filtering 10 ml of culture through a 0.45 µm Whatman filter, which was then washed with 20 ml HCl (0.5 M) to dissolve precipitated salts. Then, the filtrate was dried in an oven at 80°C for 24 h. Additionally, the growth of the culture was measured as cell density (Nc) by cell counting with a Neubauer chamber.
The initial and remaining pharmaceuticals concentration in the culture medium was quantified by a Waters HPLC 600 equipped with a 2487 Dual λ Absorbance Detector. A Phenomenex Gemini‐NX C18 column (5 µm, 250 mm × 4.6 mm) was used for the separation. The wavelengths of detection were 246 nm for paracetamol, 236 nm for salicylic acid and 276 nm for diclofenac. The mobile phase consisted of a mixture of acetonitrile to water (30:70, v/v) for the analysis of paracetamol and a mixture of acetonitrile to water to orthophosphoric acid (70:30:0.1, v/v/v) for salicylic acid and diclofenac. HPLC quality acetonitrile (CH3CN) and orthophosphoric acid (H3PO4) from Prolabo Chemicals and ultrapure water obtained by a Millipore System were used for the preparation of the mobile phase. Before use, each mixture was passed through a Millipore 0.45‐µm pore‐size filter and degasified in an ultrasound bath for 30 min. Before analysis, all the samples were centrifuged twice at 7500 rpm for 10 min (SIGMA 2‐16P centrifuge). For the chromatographic analysis, the mobile phase flow rate was 1 ml min‐1 and the injection volume was 100 μl.
2.4. Data analysis
Growth kinetics were resolved in OriginPro 8 using the classic model originally described by Verhulst [21] called logistic model, which has been proved to fit the growth of microalgae [22]. The logistic model fits to a sigmoidal curve that describes the relationship between microorganisms’ growth and density in limited environmental conditions (Eq. (4)).
Where
Furthermore, the kinetic curves for the removal of pharmaceuticals were fitted to the logistic model. In each case, the parameter
Finally, differences among the strains with respect to the kinetic parameters of growth and removal of pharmaceuticals were compared by a non‐parametric test using IBM SPPS Statistics 21. The comparison of means was performed by means of the U Mann‐Whitney test. Significance was defined at
For the removal of pharmaceuticals, the volumetric efficiency for each target compound was calculated as the difference between its average concentration in the influent (
The specific efficiency of the removed pharmaceuticals was calculated as the ratio between the volumetric efficiency and the biomass concentration (Cb) (Eq. (6)). Likewise, during the batch culture these efficiencies were cumulatively expressed as milligram per gram per biomass and as milligram per gram day during the steady state of the semicontinuous culture:
3. Results
3.1. Growth of the culture
The growth curves of
3.1.1. Growth of the culture under paracetamol addition
The microalgae growth curves of
CCS+ | PCS | CCV+ | PCV | CSO+ | PSO | |
---|---|---|---|---|---|---|
0.04 | 0.04 | 0.11 | 0.11 | 0.08 | 0.08 | |
3.20 × 106 | 3.20 × 106 | 1.21 × 106 | 1.21 × 106 | 8.35 × 105 | 8.35 × 105 | |
1.41 ± 0.29 | 2.05 ± 0.03 | 2.48 ± 0.11 | 3.35 ± 0.08 | 3.33 ± 0.06 | 3.09 ± 0.20 | |
2.12 × 108 ± 0.49 × 108 | 4.20 × 108 ± 0.22 × 108 | 1.18 × 108 ± 0.09 × 108 | 2.17 × 108 ± 0.20 × 108 | 4.77 × 107 ± 0.01 × 107 | 4.62 × 107 ± 0.20 × 107 | |
3.77 ± 0.01 | 4.33 ± 0.21 | 4.47 ± 0.25 | 5.58 ± 0.03 | 5.45 ± 0.43 | 4.97 ± 0.31 | |
1.40 ± 0.29 | 2.09 ± 0.02 | 2.60 ± 0.15 | 3.42 ± 0.15 | 3.46 ± 0.08 | 3.27 ± 0.15 | |
0.94 ± 0.06 | 0.96 ± 0.07 | 0.84 ± 0.06 | 1.08 ± 0.04 | 1.16 ± 0.07 | 1.12 ± 0.03 | |
0.9935 | 0.9939 | 0.9971 | 0.9968 | 0.9874 | 0.9886 |
The addition of paracetamol increased the lag phase of the strains of the genus
At the end of the batch culture, the biomass concentration was increased above 49% by the presence of paracetamol in the
Respect to microalgae growth rate (
3.1.2. Growth of the culture under salicylic acid addition
The microalgae growth curves of
CCS+ | SCS | CCV+ | SCV | CSO+ | SSO | |
---|---|---|---|---|---|---|
Cb0 (g l-1) | 0.04 | 0.04 | 0.11 | 0.11 | 0.08 | 0.08 |
Nc0 (cell ml-1) | 3.20 ×106 | 3.20 ×106 | 1.21×106 | 1.21×106 | 8.35×105 | 8.35×105 |
Cbm (g l-1) | 1.41 ± 0.29 | 2.05 ± 0.15 | 2.48 ± 0.11 | 3.02 ± 0.27 | 3.33 ± 0.06 | 4.33 ± 0.30 |
Ncm (cell ml-1) | 2.12 × 108 ± 0.49 × 108 | 3.15 × 108 ±0 0.08 × 108 | 1.18 × 108 ± 0.09 × 108 | 1.76 × 108 ± 0.49 × 108 | 4.77 × 107 ± 0.01 × 107 | 6.97 × 107 ± 0.20 × 107 |
3.77 ± 0.01 | 4.16 ± 0.48 | 4.47 ± 0.25 | 7.99 ± 0.41 | 5.45 ± 0.43 | 4.20 ± 0.09 | |
1.40 ± 0.29 | 2.14 ± 0.13 | 2.60 ± 0.15 | 3.09 ± 0.23 | 3.46 ± 0.08 | 4.71 ± 0.30 | |
0.94 ± 0.06 | 0.77 ± 0.12 | 0.84 ± 0.06 | 1.69 ± 0.13 | 1.16 ± 0.07 | 0.72 ± 0.01 | |
R2 | 0.9935 | 0.9912 | 0.9971 | 0.9929 | 0.9874 | 0.9883 |
Regarding the parameter
As it can be seen in Figure 2, the maximum algal density reached at the end of the batch culture was significantly higher in the treatments with salicylic acid for all strains here considered as compared with the positive controls. The
The
3.1.3. Growth of the culture under diclofenac addition
The microalgae growth curves of
CCS+ | DCS | CCV+ | DCV | CSO+ | DSO | |
---|---|---|---|---|---|---|
Cb0 (g l−1) | 0.04 | 0.04 | 0.23 | 0.23 | 0.14 | 0.14 |
Nc0 (cell ml−1) | 3.39×106 | 3.39×106 | 3.53×106 | 3.53×106 | 3.40×106 | 3.40×106 |
Cbm (g l−1) | 1.53 ± 0.11 | 2.28 ± 0.03 | 1.69 ± 0.06 | 2.51 ± 0.13 | 1.27 ± 0.04 | 1.40 ± 0.05 |
2.49 × 108 ± 0.22 × 108 | 4.19 × 108 ± 0.04 × 108 | 7.91 × 107 ± 0.19 × 107 | 1.73 × 108 ± 0.22 × 108 | 5.15 × 107 ± 0.38 × 107 | 6.33 × 107 ± 0.32 × 107 | |
3.31 ± 0.16 | 4.24 ± 0.00 | 2.60 ± 0.05 | 3.57 ± 0.12 | 3.30 ± 0.24 | 3.76 ± 0.37 | |
1.58 ± 0.11 | 2.30 ± 0.03 | 1.96 ± 0.13 | 2.65 ± 0.10 | 1.34 ± 0.03 | 1.49 ± 0.05 | |
0.72 ± 0.04 | 0.96 ± 0.01 | 0.56 ± 0.00 | 0.74 ± 0.01 | 0.79 ± 0.03 | 0.81 ± 0.09 | |
0.9907 | 0.9988 | 0.9804 | 0.9915 | 0.9890 | 0.9860 |
There were significant differences respect the parameter
As it can be seen in Figure 2, the treatments with diclofenac achieved significantly higher biomass concentration than their respective positive controls. At the end of the batch culture, the
With respect to microalgae growth rate, there were significant differences between the positive control and the corresponding treatment for the two strains of the genus
3.2. Removal of pharmaceuticals
The pharmaceutical concentration in each reactor was daily monitored and compared with the concentration of each pharmaceutical in the corresponding negative control. The concentration of the pharmaceuticals here studied decreased over the time in the treatments with microalgae, either with
3.2.1. Removal of paracetamol
The removal curves of paracetamol by each strain of microalgae and the corresponding fittings to the logistic kinetic model during the batch mode are displayed in Figure 4(a). In addition, differences among the treatments were analysed according to removal kinetic parameters, as shown in Table 4.
Paracetamol | PCS | PCV | PSO |
---|---|---|---|
4.49 ± 0.24 | 3.84 ± 0.01 | 3.19 ± 0.58 | |
17.62 ± 0.91 | 6.23 ± 0.02 | 10.41 ± 1.58 | |
1.01 ± 0.06 | 0.77 ± 0.01 | 0.86 ± 0.21 | |
0.9941 | 0.9827 | 0.9766 | |
Volumetric efficiency (mg l−1 d−1) | 3.13 ± 0.22 | 0.95 ± 0.05 | 0.72 ± 0.07 |
Specific efficiency (mg g biomass−1 d−1) | 2.68 ± 0.26 | 0.32 ± 0.02 | 0.37 ± 0.03 |
10.20 ± 3.16 | 4.09 ± 0.87 | 4.11 ± 0.16 | |
17.68 ± 0.96 | 6.44 ± 0.63 | 24.67 ± 0.32 | |
4.07 ± 1.21 | 0.84 ± 0.17 | 0.76 ± 0.03 | |
0.9919 | 0.9947 | 0.9973 | |
Volumetric efficiency (mg l−1 d−1) | 6.98 ± 0.31 | 1.72 ± 0.15 | 7.55 ± 0.01 |
Specific efficiency (mg g biomass−1 d−1) | 8.34 ± 1.21 | 0.67 ± 0.06 | 1.85 ± 0.02 |
3.88 ± 0.62 | 3.23 ± 0.02 | 3.01 ± 0.38 | |
14.55 ± 0.73 | 15.52 ± 0.26 | 22.43 ± 0.20 | |
2.03 ± 0.33 | 1.44 ± 0.05 | 1.25 ± 0.19 | |
0.9626 | 0.9755 | 0.9690 | |
Volumetric efficiency (mg l−1 d−1) | 2.18 ± 0.39 | 1.53 ± 0.32 | 5.66 ± 0.39 |
Specific efficiency (mg g biomass−1 d−1) | 1.73 ± 0.38 | 0.97 ± 0.19 | 5.21 ± 0.18 |
Regarding the parameter
The parameter
As a consequence of the different responses obtained for the removal parameters between the strains, at the end of the batch culture, efficiencies in the removal of paracetamol above 67% for
The average volumetric efficiencies on the paracetamol removal by each strain at the steady stage of the semicontinuous culture are depicted as percentages in Figure 4(b). The paracetamol volumetric efficiency reached values above 41% for
3.2.2. Removal of salicylic acid
The removal curves of salicylic acid by each strain of microalgae and the corresponding fittings to the logistic kinetic model during the batch mode are displayed in Figure 5(a). In addition, differences among the treatments were analysed according to removal kinetic parameters, as shown in Table 4.
In the case of
The results obtained for the maximum removal capacity (
The average salicylic acid volumetric efficiencies by each strain at the steady stage of the semicontinuous culture are depicted as percentages in Figure 5(b). The paracetamol volumetric efficiency did not showed significant differences between the strains
3.2.3. Removal of diclofenac
The removal curves of diclofenac by each strain of microalgae and the corresponding fittings to the logistic kinetic model during the batch mode are displayed in Figure 6(a). In addition, differences among the treatments were analysed according to removal kinetic parameters, as shown in Table 4.
The
Concerning the removal rate, the obtained results revealed significant differences among the treatments. The quickest removal rate was attained by
The average volumetric efficiencies for the diclofenac removal in the steady stage of the semicontinuous culture are showed in Figure 6(b). The volumetric efficiency for
4. Discussion
In view of the obtained results, it may be inferred that the presence of paracetamol, salicylic acid and diclofenac modified the growth parameters of the strains here studied. In most of the treatments, the addition of the pharmaceutical increased the biomass concentration, which may be explained by the fact that these pharmaceuticals were an additional source of organic carbon. It is well known that the genus
The fact that removal curves displayed a similar trend than growth curves points to the association between the microalgae growth and the removal efficiency of pharmaceuticals.
In view of the obtained results, it may be concluded that paracetamol was more efficiently removed by
On the other hand,
Regarding diclofenac, despite
Comparing the three pharmaceuticals, the salicylic acid was more efficiently removed, with
As in this work, published results on the removal of ECs by microalgae have revealed different efficiencies depending on the pollutant and on the microalgae strain. For example, Gattullo et al. [23] demonstrated that
5. Conclusions
Among the here considered strains,
Acknowledgments
Authors thank University of León for funding given to MICROTRAT (project UXXI2016/00128). Carla Escapa and Sergio Paniagua acknowledge the Spanish Ministry of Educations, Culture and Sports for their PhD fellowships (FPU12/03073 and FPU14/05846, respectively). Marta Otero acknowledges University of León for the extension of her RYC‐2010‐05634 contract.
References
- 1.
Sauvé S, Desrosiers M: A review of what is an emerging contaminant. Chemistry Central Journal. 2014; 8 :15. DOI: 10.1186/1752‐153X‐8‐15 - 2.
Evgenidou E, Konstantinou I, Lambropoulou D: Occurrence and removal of transformation products of PPCPs and illicit drugs in wastewaters: A review. Science of the Total Environment. 2015; 505 :905–926. DOI: 10.1016/j.scitotenv.2014.10.021 - 3.
Santos L, Araújo A, Fachini A, Pena A, Delerue‐Matos C, Montenegro M: Ecotoxicological aspects related to the presence of pharmaceuticals in the aquatic environment. Journal of Hazardous Materials. 2010; 175 :45–95. DOI: 10.1016/j.jhazmat.2009.10.100 - 4.
Barbosa M, Moreira N, Ribeiro A, Pereira M, Silva A: Occurrence and removal of organic micropollutants: An overview of the watch list of EU Decision 2015/495. Water Research. 2016; 94 :257–279. DOI: 10.1016/j.watres.2016.02.047 - 5.
Rigobello E, Dantas A, Di Bernardo L, Vieira E: Removal of diclofenac by conventional drinking water treatment processes and granular activated carbon filtration. Chemosphere. 2013; 93 :184–191. DOI: 10.1016/j.chemosphere.2013.03.010 - 6.
Barceló D, Petrovic M: Reducing the environmental risk from emerging pollutants. In: Trac‐Trends in Analytical Chemistry, editor. 1st EMCO workshop “Analysis and removal of contaminants from wastewater for the implementation of the Water Framework Directive (WFD)”; 20‐21 October 2005; Dubrovnik, Croatia. 2006. p. 191–193. DOI: 10.1016/j.trac.2005.11.003 - 7.
Bolong N, Ismail A, Salim M, Matsuura T: A review of the effects of emerging contaminants in wastewater and options for their removal. Desalination. 2009; 239 :229–246. DOI: 10.1016/j.desal.2008.03.020 - 8.
Farré M, Pérez L, Kantiani L, Barceló D: Fate and toxicity of emerging pollutants, their metabolites and transformation products in the aquatic environment. Trac‐Trends in Analytical Chemistry. 2008; 27 :991–1007. DOI: 10.1016/j.trac.2008.09.010 - 9.
Pal A, He Y, Jekel M, Reinhard M, Gin K: Emerging contaminants of public health significance as water quality indicator compounds in the urban water cycle. Environment International. 2014; 71 :46–62. DOI: 10.1016/j.envint.2014.05.025 - 10.
Verlicchi P, Aukidy M, Zambello E: Occurrence of pharmaceutical compounds in urban wastewater: Removal, mass load and environmental risk after a secondary treatment‐A review. Science of the Total Environment. 2012; 429 :123–155. DOI: 10.1016/j.scitotenv.2012.04.028 - 11.
Heberer T, Reddersen K, Mechlinski A: From municipal sewage to drinking water: Fate and removal of pharmaceutical residues in the aquatic environment in urban areas. Water Science and Technology. 2002; 46 :81–88. - 12.
Ashton D, Hilton M, Thomas K: Investigating the environmental transport of human pharmaceuticals to streams in the United Kingdom. Science of the Total Environment. 2004; 333 :167–184. DOI: 10.1016/j.scitotenv.2004.04.062 - 13.
Combarros R, Rosas I, Lavin A, Rendueles M, Diaz M: Influence of biofilm on activated carbon on the adsorption and biodegradation of salicylic acid in wastewater. Water, Air, and Soil Pollution. 2014; 225 :1858. DOI: 10.1007/s11270‐013‐1858‐9 - 14.
de Wilt A, Butkovskyi A, Tuantet K, Leal L, Fernandes T, Langenhoff A, Zeeman G: Micropollutant removal in an algal treatment system fed with source separated wastewater streams. Journal of Hazardous Materials. 2016; 304 :84–92. DOI: 10.1016/j.jhazmat.2015.10.033 - 15.
Hom‐Díaz A, LLorca M, Rodríguez‐Mozaz S, Vicent T, Barceló D, Blanquez P: Microalgae cultivation on wastewater digestate: Beta‐estradiol and 17 alpha‐ethynylestradiol degradation and transformation products identification. Journal of Environmental Management. 2015; 155 :106–113. DOI: 10.1016/j.jenvman.2015.03.003 - 16.
Ritchmon A: Handbook of Microalgal Mass Culture. Boca Raton, Florida: CRC Press; 1986. 528 p. - 17.
Matamoros V, Uggetti E, García J, Bayona J: Assessment of the mechanisms involved in the removal of emerging contaminants by microalgae from wastewater: A laboratory scale study. Journal of Hazardous Materials. 2016; 301 :197–205. DOI: 10.1016/j.jhazmat.2015.08.050 - 18.
Petrie B, Barden R, Kasprzyk‐Hordern B: A review on emerging contaminants in wastewaters and the environment: Current knowledge, understudied areas and recommendations for future monitoring. Water Research. 2015; 72 :3–27. DOI: 10.1016/j.watres.2014.08.053 - 19.
Beuckels A, Smolders E, Muylaert K: Nitrogen availability influences phosphorus removal in microalgae‐based wastewater treatment. Water Research. 2015; 77 :98–106. DOI: 10.1016/j.watres.2015.03.018 - 20.
Mann J, Myers J: On Pigments Growth and Photosynthesis of Phaeodactylum tricornutum . Journal of Phycology. 1968;4 :349–355. DOI: 10.1111/j.1529‐8817.1968.tb04707.x - 21.
Verhulst P: Notice sur la loi que la population suit dans son accroissement (A note on the law of population growth). Correspondace Mathématique et Physique. 1938;10 :113–121. - 22.
Xin L, Hu H, Ke G, Sun Y: Effects of different nitrogen and phosphorus concentrations on the growth, nutrient uptake, and lipid accumulation of a freshwater microalga Scenedesmus sp. Bioresource technology. 2010;101 :5494–5500. DOI: 10.1016/j.biortech.2010.02.016 - 23.
Gattullo C, Baehrs H, Steinberg C, Loffredo E: Removal of bisphenol A by the freshwater green alga Monoraphidium braunii and the role of natural organic matter. Science of the Total Environment. 2012;416 :501–506. DOI: 10.1016/j.scitotenv.2011.11.033 - 24.
Wang L, Xue C, Wang L, Zhao Q, Wei W, Sun Y: Strain improvement of Chlorella sp for phenol biodegradation by adaptive laboratory evolution. Bioresource Technology. 2016;205 :264–268. DOI: 10.1016/j.biortech.2016.01.022 - 25.
Peng F, Ying G, Yang B, Liu S, Lai H, Liu Y, Chen Z, Zhou G: Biotransformation of progesterone and norgestrel by two freshwater microalgae ( Scenedesmus obliquus andChlorella pyrenoidosa ): Transformation kinetics and products identification. Chemosphere. 2014;95 :581–588. DOI: 10.1016/j.chemosphere.2013.10.013 - 26.
Matamoros V, Gutiérrez R, Ferrer I, García J, Bayona J: Capability of microalgae‐based wastewater treatment systems to remove emerging organic contaminants: A pilot‐scale study. Journal of hazardous materials. Journal of Hazardous Materials. 2015; 288 :34–42. DOI: 10.1016/j.jhazmat.2015.02.002