Decrease in pollutant compound concentration and some chemical parameter values in landfill leachate cultures (100% leachate) of three native microalgae strains from the Peruvian Amazon.
Abstract
Environmental pollution is a severe and common problem in all the countries worldwide. Various physicochemical technologies and organisms (e.g., plants, microorganisms, etc.) are used to address these environmental issues, but low-cost, practical, efficient, and effective approaches have not been available yet. Microalgae offer an attractive, novel, and little-explored bioremediation alternative because these photosynthetic organisms can eliminate pathogenic microorganisms and remove heavy metals and toxic organic compounds through processes still under study. Our research team has conducted some experiments to determine the bioremediation potential of native microalgae on some pollutant sources (i.e., leachate and wastewater) and its ability to remove hazardous chemical compounds. Therefore, in this chapter, we provide the results of our research and updated information about this exciting topic. Experiments were conducted under controlled culture conditions using several native microalgae species, variable time periods, different pollutant sources, and hazardous chemicals such as ethidium bromide. The results indicated that native microalgae can remove pollutants (i.e., phosphorus, ammonia, etc.) of wastewater, leachate, and some hazardous chemical compounds such as ethidium bromide. In conclusion, native microalgae have an excellent potential for removing several pollutants and, consequently, could be used to develop bioremediation technologies based on native microalgae from the Peruvian Amazon.
Keywords
- bioremediation
- native microalgae
- leachate
- pollutants
- wastewater
1. Introduction
Microalgae have aroused the scientific community’s interest by their biotechnological potential and increased commercial demand because these microorganisms are an excellent source of a wide range of chemicals with biomedical interest (e.g., carotenoids, essential fatty acids, polyphenols, polysaccharides, etc.) [1, 2, 3]. In addition, they are helpful for bioremediation applications in wastewater treatment and other decontamination applications [4, 5]. Some advantages of this biological system are that bioremediation reinforces biogeochemical processes, toxic chemicals are degraded and not simply physically separated from the environment, and the process requires less energy than other technologies and uses less manual supervision. Furthermore, the bioaccumulation of heavy metals by microalgae cells may represent a feasible method for the treatment of leachates and wastewater containing bioavailable heavy metals [6, 7, 8, 9, 10].
Additionally, microalgae could be cultivated in wastewater lagoons with small nutrient requirements for their maintenance and development. This component usually constitutes the final step to completing the decontamination process in many wastewater treatment systems [11, 12, 13]. Therefore, massive cultivation of microalgae using wastewater as a source of nutrients is a cost-effective approach due to the simplicity of the technology allowing both pollutants (i.e., biological and chemical) remotion and the obtention of a valuable microalgae biomass rich in proteins, lipids, pigments, bioactive chemicals, etc. [14, 15, 16, 17].
In this context, this chapter aims to provide updated information based on the results of investigations conducted by our research team using some strains from the freshwater microalgae collection culture native from the Peruvian Amazon.
2. Use of native microalgae for pollutants removal
2.1 Leachate treatment from an open-air garbage dump
Solid waste production in Iquitos city and other cities worldwide has been increased in direct relation to the demographic explosion. Commonly, cities such as Iquitos and other main cities of the Peruvian Amazon have an inefficient garbage collection system, and their main streets and popular markets are often full of garbage (Figure 1). In addition, these cities do not have a proper garbage disposal approach, and landfill sites are missing; consequently, the solid wastes are directly deposited in open-air garbage dumps (Figure 1).
In these open-air garbage dumps, the solid wastes can be dispersed and degraded by abiotic and biotic factors, producing a gamma of solid, gaseous, and liquid products; the latter is known as leachate. This wastewater flows out from a landfill or an open-air garbage dump sites due to precipitation, ground-water intrusion, moisture content of waste, and rate of evaporation [18]. The volume and pollutant composition of this leachate wastewater fluctuate over time; therefore, in the early acid phase, there exists a high concentration of the four groups of pollutants (dissolved organic matter, heavy metals, inorganic macrocomponents, and xenobiotic organic compounds); finally, in the long methanogenic phase, the leachate liquid has a lower concentration of the four groups of pollutants and is characterized by its very low concentration of heavy metals and biochemical oxygen demand/chemical oxygen demand (BOD/COD) ratio [19, 20, 21]. In addition, leachate liquid has a great diversity and composition of bacterial and archaeal populations of the members
According to these necessities, our research team evaluated the potential use of native microalgae of the Peruvian Amazon for leachate treatment generated in an open-air garbage dump. To do these experiments, leachate liquid samples (3 L) were collected from leachate pools generated from an open-air garbage dump of Nauta city, Loreto, Peru. After, leachate liquid samples were subsequently filtered through 0.45- and 0.25-μm filter membranes to remove particulate matter and microorganisms.
The experiments were conducted for 5 days with three native microalgae strains (
We evaluated the microalgae capabilities for chemical pollutant removal in leachates by quantifying these pollutants in the culture medium at the beginning and on the 5th day of the experiments, using standardized methods with the multiparameter LaMotte 3633-04 Fresh Water Aquaculture Test Kit. In addition, phosphate was quantified using a spectrophotometric method [26].
The results showed that the three microalgae strains were able to eliminate chemical pollutants in leachate (Table 1). Ammonium was efficiently removed from 90% (
Pollutant compound/chemical parameter | Microalgae strain | Concentration at the beginning of the experiments (mg/L) | Concentration on the 5th day of the experiments (mg/L) | Percentage decrease |
---|---|---|---|---|
Ammonium | 0.20 ± 0.01 | 0.00 ± 0.000 | 100 ± 0.00 | |
0.20 ± 0.03 | 0.02 ± 0.001 | 90 ± 0.95 | ||
0.20 ± 0.01 | 0.01 ± 0.000 | 95 ± 0.22 | ||
Nitrite | 0.50 ± 0.05 | 0.05 ± 0.002 | 90 ± 0.72 | |
0.50 ± 0.01 | 0.04 ± 0.001 | 92 ± 0.16 | ||
0.50 ± 0.06 | 0.03 ± 0.002 | 94 ± 0.33 | ||
Chloride | 24 ± 1.00 | 2 ± 0.10 | 91.7 ± 0.68 | |
24 ± 1.15 | 2 ± 0.21 | 91.7 ± 0.49 | ||
24 ± 0.58 | 2 ± 0.10 | 91.7 ± 0.33 | ||
Phosphate | 100 ± 5.03 | 10 ± 0.26 | 90 ± 0.39 | |
100 ± 3.61 | 10 ± 0.17 | 90 ± 0.21 | ||
100 ± 1.00 | 10 ± 0.20 | 90 ± 0.30 | ||
Carbon dioxide | 37 ± 1.00 | 0.0 ± 0.0 | 100 ± 0.0 | |
37 ± 1.73 | 0.0 ± 0.0 | 100 ± 0.0 | ||
37 ± 0.58 | 0.0 ± 0.0 | 100 ± 0.0 | ||
Calcium and magnesium salts (hardness) | 160 ± 1.53 | 28 ± 0.50 | 82.5 ± 0.24 | |
160 ± 0.58 | 28 ± 0.92 | 82.5 ± 0.59 | ||
160 ± 1.53 | 48 ± 1.00 | 70.0 ± 0.90 | ||
Carbonate and bicarbonate salts (alkalinity) | 180 ± 0.58 | 76 ± 1.00 | 57.8 ± 0.44 | |
180 ± 1.00 | 96 ± 0.50 | 46.7 ± 0.29 | ||
180 ± 1.15 | 96 ± 1.00 | 46.7 ± 0.31 | ||
pH | 9 ± 0.50 | 9 ± 0.50 | 0.0 ± 0.0 | |
9 ± 0.51 | 9 ± 0.50 | 0.0 ± 0.0 | ||
9 ± 0.50 | 9 ± 0.00 | 0.0 ± 0.0 |
2.2 Wastewater treatment
The generation of great volumes of wastewater in the main cities of the Peruvian Amazon is increasing notably in the past 20 years. This environmental issue is associated with the intense migration of people from rural to urban areas with the hope to get better opportunities to improve their life qualities. This unplanned migration is generating unorganized human settlements in the marginal areas of the big cities, which lack basic services, such as electric fluid, potable water, and sewage system (Figure 2). In addition, none of these cities have wastewater treatment plants; then, wastewater is directly disposed into the main rivers of the Amazon basin, causing significant pollution of the aquatic ecosystems and affecting the aquatic flora, fauna, microbiota, and, of course, the human settlements located along the main rivers.
In this context, with a view to alleviate this pollution problem, we need to investigate eco-friendly, efficient, and low-cost options to treat wastewater. In this sense, we did experiments to determine whether native microalgae are useful to decontaminate wastewater generated in Iquitos city because there are several successful experiences around the world using these microorganisms [4, 5, 11, 27].
Therefore, to do the experiments, wastewater samples (5 L) were collected from the two main wastewater drainage systems of Iquitos city (Moronacocha and Huequito), Loreto, Peru. Furthermore, particulate matter and microorganisms were removed from the wastewater samples using the same previously described filtration approach (item 2.1) and were sterilized by autoclaving at 121°C for 30 min.
The experiments were conducted for 15 days with two native microalgae strains (
We evaluated the microalgae capabilities for chemical pollutants removal in wastewater by quantifying these pollutants in the culture medium at the beginning and on the 15th day of the experiments, using standardized methods with the multiparameter LaMotte 3633-04 Fresh Water Aquaculture Test Kit. In addition, phosphate was quantified using a spectrophotometric method [26].
The results showed that the two microalgae strains were capable to remove chemical pollutants from the two wastewater samples (Tables 2 and 3). However, there are marker differences; for example, ammonium was efficiently removed from wastewater of the Huequito wastewater drainage system (from 97.2% to 100%); in contrast, this pollutant was poorly removed from wastewater of the Moronacocha wastewater drainage system (only 20% with both microalgae strains).
Pollutant compound/chemical parameter | Microalgae strain | Concentration at the beginning of the experiments (mg/L) | Concentration on the 15th day of the experiments (mg/L) | Percentage decrease |
---|---|---|---|---|
Ammonium | 50 ± 1.00 | 40 ± 1.00 | 20 ± 0.40 | |
50 ± 1.50 | 40 ± 2.00 | 20 ± 3.47 | ||
Chloride | 24 ± 0.76 | 2 ± 0.10 | 91.7 ± 0.57 | |
24 ± 0.76 | 2 ± 0.26 | 91.7 ± 1.29 | ||
Phosphate | 2 ± 0.10 | 1.10 ± 0.20 | 45.0 ± 0.83 | |
2 ± 015 | 1.05 ± 0.07 | 47.5 ± 0.72 | ||
Carbon dioxide | 40 ± 1.53 | 8.5 ± 0.57 | 78.8 ± 2.08 | |
40 ± 1.53 | 5.0 ± 0.55 | 87.5 ± 1.33 | ||
Calcium and magnesium salts (hardness) | 65 ± 0.70 | 60 ± 1.73 | 7.7 ± 1.86 | |
65 ± 1.76 | 52 ± 2.29 | 20.0 ± 4.63 |
Pollutant compound/chemical parameter | Microalgae strain | Concentration at the beginning of the experiments (mg/L) | Concentration on the 15th day of the experiments (mg/L) | Percentage decrease |
---|---|---|---|---|
Ammonium | 36 ± 1.00 | 0.0 ± 0.00 | 100 ± 0.00 | |
36 ± 1.73 | 1.0 ± 0.10 | 97.2 ± 0.39 | ||
Chloride | 38 ± 1.00 | 36 ± 2.00 | 5.3 ± 0.06 | |
38 ± 2.00 | 28 ± 1.05 | 26.3 ± 3.28 | ||
Phosphate | 1.9 ± 0.10 | 1.5 ± 0.10 | 21.1 ± 4.94 | |
1.9 ± 0.20 | 1.2 ± 0.10 | 36.8 ± 1.25 | ||
Carbon dioxide | 50 ± 3.46 | 14 ± 1.59 | 72 ± 1.30 | |
50 ± 1.73 | 4 ± 0.15 | 92 ± 0.54 | ||
Calcium and magnesium salts (hardness) | 60 ± 1.73 | 38 ± 1.01 | 36.7 ± 3.28 | |
60 ± 2.00 | 32 ± 2.00 | 46.7 ± 1.56 |
2.3 Ammonium removal using an immobilized microalgae
Ornamental fish export is an important economic activity in Iquitos city, they provide benefits to several families dedicated to this area. A frequent problem during the process of ornamental fish transportation is high mortality rate, which could be attributable to decrease in water quality during transportation. These changes are due to the accumulation of toxic and metabolites of the fish catabolic process, such as ammonium [28], which, in turn, alkalinizes the pH and decreases the dissolved oxygen concentration in the aqueous medium [29]. Oxygen deficiency, toxin accumulation, and an increase in total ammonium concentration in the water are believed to be the main cause of fish mortality during transportation [30].
To help solve this problem, our research team evaluated the hypothesis that by using immobilized microalgae, the ammonium concentration decreased significantly. To test the formulated hypothesis, the experiments were conducted by triplicate for 2 weeks with one native microalgae strain (
The results showed that immobilized
Ammonium ions enter microalgae cells through ammonium transporters/ammonia permeases (AMTPs) embedded into the plasmatic membrane. These membrane-spanning proteins be made of 11 highly conserved transmembrane domains that fold into a channel across ammonia or ammonium translocates [40, 41]. According to X-ray crystallographic studies of some prokaryotic partners of these protein transporters, these are characterized as a compact trimer with 11 transmembrane helices per monomer and a narrow, mainly hydrophobic, channel for substrate conduction, located at the center of each monomer of the trimeric molecule. In addition, at the periplasmic side of the transporter protein, a binding site for NH4+ is observed [42, 43]. In the particular case of
According to Ahmad and Hellebust [47], the microalga
2.4 Ethidium bromide removal using microalgae
The release of untreated effluent from research laboratories in our country and worldwide into water bodies is a major threat to the environment and human health. Commonly, effluent from laboratories and other research facilities is rich in toxic organic compounds, such as dyes used in the nucleic acid analysis, especially ethidium bromide, which is considered a serious biohazard due to its mutagenic, carcinogenic, teratogenic, and very toxic potentials when inhaled, ingested, or absorbed through the skin, and can irritate the eyes, mouth, and upper respiratory tract [48, 49]. To overcome these pollution problems, ethidium bromide and other toxic compounds could be partially or completely degraded to nontoxic forms before disposal. Consequently, some research laboratories worldwide are testing the biodegradation of ethidium bromide using plants and various kinds of microorganisms, including bacteria and microalgae [50, 51, 52, 53], to develop, in the next future, modern, cost-effective, and eco-friendly bioremediation approaches.
In this context, our research team has evaluated the ability of a microalgae consortium for the removal of ethidium bromide from aqueous medium. For this experiment, three previously cultured native microalgae strains
The results showed that on the 7th day of starting the experiments, it was evidenced that the microalgal consortium was able to decrease the ethidium bromide concentration (directly related to fluorescence intensity) in the culture supernatant until 70.5% (Figure 6). These results corroborate the previous report of Cavalcante de Almeida et al. [52]. These authors also evaluated the capability of the microalgae
Probably, the phycoremediation process used for microalgae to remove ethidium bromide is similar to several detoxification strategies used against aromatic organic pollutants (e.g., polycyclic aromatic hydrocarbons, phenolic compounds, dyes, etc.), including biosorption, bioaccumulation, biotransformation, and biodegradation [54, 55]. The first one is a metabolically independent process, which is a physicochemical phenomenon, supported by a gamma of mechanisms comprising absorption, adsorption, surface complexation, ion exchange, and precipitation [56]. The second one consists in the selective transportation by the monovalent cation uptake transport system [57] and other unidentified transporters, followed for its accumulation into some organelles such as nucleus, mitochondria, and chloroplast, which can be intercalated with DNA molecules (Figure 7). Finally, biotransformation and biodegradation are dependent on the metabolic capabilities of the microalgae cells, which are determined for their genomic background that codes a repertory of required enzymes [54]. To date, however, none of the metabolic pathways for ethidium bromide biodegradation has been described.
3. Conclusions
Native microalgae isolated from the Peruvian Amazon have a potential biotechnological application in the remotion of diverse chemical pollutants. These microorganisms showed abilities to remove pollutants contained into leachate generated in an open-air garbage dump and from two wastewaters from Iquitos city. In addition, an immobilized version of the microalgae
Acknowledgments
This research was supported by the Peruvian funding agency Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica (CONCYTEC) through the Programa Nacional de Investigación Científica y Estudios Avanzados (PROCIENCIA), Funding Award Contract No. 018-2018-FONDECYT/BM-Improvement of Research Infrastructure (Scientific Equipment), the Scientific University of Peru and the Specialized Biotechnology Unit of the Natural Resources Research Center, National University of the Peruvian Amazon.
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