A Novel Approach to Explore New Means of Depletion of Potable Water Crisis by Phytoremediation of Abandoned Coalmine Pitlake and Generate Alternate Livelihood: A Case Study of Raniganj Coalfield, West Bengal, India

Abstract

Phytoremediation is using live plants to remove toxins and contaminants from land, water, or the air. Hydrocarbons, radionucleotides, fertilizers, explosives, heavy metals, and other contaminants are all efficiently removed from wastewater by this approach. Aquatic plants can be classified as free-floating, emergent, or submerged. Studies have been done on the capacity of Pontederia crassipes Mart. to extract pollutants like dissolved solids, and heavy metals from wastewater. The pollution of chromium in Indian chromite mining sites has also been addressed it and following phytoremediation, the biomass may be utilized to produce vermicompost, biogas, and bioethanol. Surface mining is producing changes in land use, land cover, and climate in the RCF area of West Bengal, India. By using aquatic plants to phytoremediate pit lakes (PLs), fresh water can be produced and chances for sustainable livelihoods can be created. The population in former mining regions has grown significantly, leading to the relinquishment of agriculture and the development of illegal mining and coal theft. This study aims to examine the literature on aquatic plant phytoremediation of water, emphasizing the necessity of phytoremediation of PL water in RCF and the potential applications of Pontederia crassipes Mart. biomass for the generation of biogas, bioethanol, and vermicompost.

1. Introduction

Phytoremediation is characterized as the utilization of green plants and their corresponding microbes, soil enhancements, and the application of agronomic techniques to eliminate, contain, or render harmless environmental toxins [1, 2]. The three main categories of water pollutants are inorganic (such as metals or synthetic and manure-based fertilizers containing excess levels of N, and P), biological (such as pathogens and algal toxins), and organic pollutants including hydrocarbons, pesticides, and algal toxins [3]. Various aquatic plants have been evaluated for their phytoremediating ability explained by different authors globally. PLs are generated when dugouts made during surface-cut mining operations fill with water after the mining operations have been completed by groundwater recharge, surface water diversion, and monsoon precipitation over the years. PLs differ from natural lakes in that they have significantly higher relative depths. Today when the world is moving towards a water crisis, the abandoned PLs might act as an alternative supply of water because they contain enormous amounts of water. Regarding the phytoremediation of water in mining sites, numerous studies have been carried out in India and elsewhere in the world. The aquatic, and wetlands plant species are very effective at removing a wide range of organic, and inorganic pollutants from wastewater, including potentially toxic elements (PTE), fertilizers, explosives, radionucleotides, and hydrocarbons [4]. In this regard, it is worth mentioning that there are three categories into which aquatic plants can be divided free-floating, emergent, and submerged which can be used for effective phytoremediation [5]. After being purified, the water can be used sustainably for a variety of tasks, including hydroponics, irrigation, horticulture, aquaculture, etc. The phytoremediating ability of Spirodela polyrhiza (L.) Schleid. in the phytofiltration of As, and the mechanism of As uptake by the plant was studied in Dhaka, Bangladesh. For this, the plants were collected from a rice field in Manikgonj, Dhaka, Bangladesh, and were stock-cultured in a greenhouse using standard MS (Murashige and Skoog) media solution for 2 weeks [6]. The adsorption properties of a cationic dye (methylene blue, MB) on Pontederia crassipes Mart. in Egypt [7]. Likewise the effectiveness of Pontederia crassipes Mart. in removing Zn (II) and Cd (II) as well as their admixtures was assessed [8]. The effectiveness of Pontederia crassipes Mart. as a phytoremediation agent in the removal of metals from contaminated coastal areas of Nigeria. The evaluation was based on the presence of 10 metals in the water, including As, Cd, Cu, Cr, Fe, Mn, Ni, Pb, and Zn were evaluated from Ondo State in Nigeria’s coastal region [9]. A Research was conducted on the ability of duckweed (Lemna minor L.) to break down the azo dye C.I. Acid Blue 92 (AB92) [10]. The removal of two harmful and cancer-causing contaminants, As and Cd, from water in Japan using an aquatic plant as Micranthemum umbrosum (J.F. Gmel.) S.F. Blake was investigated [11]. Whereas, in Chile, it was investigated how the aquatic plant Oenothera picensis Phil. extracted copper using compost and a biodegradable chelate called methylglycinediacetic acid [12]. Scirpus grossus L.f. is an aquatic plant, and it was investigated if this plant may assist Sago mill effluent (SME) in having reduced levels of TSS, COD, and BOD [13]. To determine the phytoremediating effectiveness of Pistia stratiotes L., the plant was exposed the plant to the physiological effects of artificial acid mine drainage (AMD) [14]. Looking at various research on the phytoremediation of aquatic weeds in India, the potential for uranium buildup, and subsequent biochemical reactions in Hydrilla verticillata (L.f.) Royle. was investigated [15]. A study showed that Pontederia crassipes Mart. is effective at removing dissolved solids, and heavy metals like Cr and Cu from wastewater, and investigated how the pH of wastewater changed as the grew in wastewater [16]. In the flying ash ponds of NTPC Unchahar, which is located in Uttar Pradesh, India, the potential of Azolla caroliniana Willd. as a heavy metal accumulator was investigated [17]. The effectiveness of Pontederia crassipes Mart. in the phytoremediation of Amravati River bank polluted dye industrial water was also studied [18]. Azolla pinnata R. Br. and Lemna minor L., two aquatic plants, were used in a study at the coal mines of Singrauli, Madhya Pradesh, India, to investigate the phytoremediation process for the detoxification of coal mine effluents [19]. A study was conducted in order to create a viable phytoremediation system for the efficient removal of hazardous hexavalent Cr from wastewater of the chromite mining sites in Sukinda, Orissa, India [20]. The aquatic species in that study to address the issue of Cr contamination in chromite mine wastewater was the Pontederia crassipes Mart [20]. After some biological processing, the biomass can be used for the manufacture of bioethanol, biogas, and vermicompost [21, 22]. In the RCF, West Bengal in India, surface mining, and its activities are the main force behind changes in land use, land cover, and climate. Since it opened 246 years ago, RCF, India the oldest coal mine, has been producing non-coking coal of the highest grade. The mining authority favors opencast mining over underground mining in order to lower the cost per unit of coal output [23]. PL clusters make up a significant percentage of RCF in West Bengal. Around 260 hectares of RCF, there are around 78 historic opencast coal pits [24, 25]. Over the years, the population has grown significantly in mining areas. Such townships are located above around 4400 million tons of significant coal reserves, which will have an impact on current and upcoming mining operations [26]. According to Guha [27], the extremely low rainfall and poor soil fertility have led to the abandonment of agriculture. Along with social ties, and organizational structures, human behavior has altered substantially. The locals no longer have any alternative means of support due to illegal mining and coal theft. They are unable to rely on fishing, agriculture, etc. [28]. They are compelled to work in the illegal industry as a quick method to get paid and as an alternative to subsistence farming. Nowadays it is happening so blatantly that there are often processions of misfit guys seen driving little vehicles and riding bicycles while hauling heavy loads of coal through the highways of Raniganj [28, 29].Thus the phytoremediation of PLs by aquatic plants not only generates fresh water but also creates scopes for alternate livelihood through sustainable uses of PL water. The authors of this article are presently working on the phytoremediation of PLs in RCF by Pontederia crassipes Mart. and other aquatic plants, and using the biomass of the harvested aquatic plants in the production of biogas, bioethanol, and vermicompost with the noble approach of generating entrepreneuric scopes in the tribal-based regions.

The aim of the present study is to review various studies on the phytoremediation of water by aquatic plants, highlighting the need for phytoremediation of PL water in RCF, and using the phytoremediating biomass of Pontederia crassipes Mart. in the production of biogas, bioethanol, and vermicompost.

2. Methodology

2.1 Study site

The Asansol and Durgapur subdivisions of Paschim Bardhaman district in West Bengal, India are where the RCF is mostly encompassed with 23°37′44″N 87°06′54″ (Figure 1). According to Chattopadhyay [30], it extends to the Jharkhand districts of Dhanbad and its districts of Birbhum, Bankura, and Purulia in West Bengal, India. In RCF, coal mining initially got underway when coal was explored in 1774 by British East India Company employees John Sumner, and Suetonius Grant Heatly close to Ethora. Early exploration and mining operations were conducted in an indiscriminate way [30]. Alexander, and Co., a brokerage, spearheaded the beginnings of regular mining in 1820. With the purchase of the collieries by Prince Dwarkanath Tagore in 1835, Carr, Tagore, and Company dominated the industry. RCF served as the country’s primary coal producer during the entirety of the 19th century and a significant portion of the 20th century [30]. The Coal Mines Authority of India was granted authority over all non-coking coal mines in 1973. Coal India Limited established Eastern Coalfields Limited in 1975 as a subsidiary. In RCF, it absorbed all of the preceding private collieries. The RCF has a total area of 443.50 km² and 49.17 billion tons of coal reserves in West Bengal and Jharkhand respectively [31]. In terms of reserves, the coalfield is the second-largest in the nation, 30.61 billion tons of the total reserve are in West Bengal, and 18.56 billion tons are in Jharkhand (Figure 2) [32].

Figure 1.

Geographical location of RCF.

Figure 2.

Total coal reserve of RCF in West Bengal and Jharkhand [32].

2.2 Materials and methods

Drawing up the review employed a specific keyword-based hunt methodology. The keywords included phytoremediation by aquatic weeds, heavy metals, potable water crisis, freshwater status, coalmine pit lake, Raniganj Coalfield, etc. The chosen portals included Research Gate, Science Direct, PubMed, NCBI, and Google Scholar, among others. Results from the most recent three decades that is from 2001 to 2023 were approved for the custom search strategy.

3. Results and discussion

Azolla caroliniana Willd. and Hydrilla verticillata (L.f.) Royle, for their effectiveness in removing fly ash, and uranium, respectively, are the aquatic plants that have been mentioned as effective phytoremediation agents [15, 17]. Rahman et al. [6] reported on the efficiency of another species of duckweed, Spirodela polyrhiza (L.) Schleid, in removing As absorption through the phosphate uptake pathway. According to research on phytoremediation by Khataee et al. [10], duckweed plays a key role in the conversion of pollutants into intermediate molecules, and the elimination of dyes like Acid blue. Oenothera picensis Phil. and Micranthemum umbrosum (J.F. Gmel.) S.F. Blake are examples of aquatic plants that are effective at removing As, and Cd, respectively, according to recent studies by Gonzalez et al. [12] and Islam et al. [11]. According to Bharti et al. [19], both the plants, Azolla pinnata R. Br. and Lemna minor L., are suitable for phytoremediation of mine effluents at contaminated locations. It was also claimed that due to the high level of pollutants in these phytoremediated plants, it is necessary to pay attention to developing disposal plans [19]. Novita et al. [14] showed that Pistia stratiotes L. can change the artificial AMD’s pH level from 4 to 7.3 in just 14 days. With initial concentrations of 5.3 mg/l and 7.5 mg/l, respectively, this plant can also reduce the copper content by up to 92.45% and 88.00% in 14 days, with the highest removal occurring on day 3. It is clear that Pistia stratiotes L. has the power to lower copper levels and neutralize pH in artificial AMD. It was claimed that the SS batch system outperforms the FS batch system for the survival of the plant Scirpus grossus L.f. Additionally, the plant has the ability to reduce TSS, COD, and BOD by 98.88, and 93%, respectively [13]. We can therefore draw the conclusion that this plant has extraordinary potential for removing contaminants during the phytoremediation of SME. According to Chandra and Yadav [33], Typha angustifolia L. has the ability to control Cd, Cr, Cu, Fe, Mn, Ni, and Pb levels in water. The phytoremediation process in abandoned mines in Korea is currently under evaluation. In this context, Lee et al. [34] discussed the difficulties with this phytoremediation approach and asserted that additional study is necessary to comprehend the interactions between plant roots, microbes, the soil, and contaminants, that make up the rhizosphere, in order to make advances in the field of phytoremediation of Korea.

Khaiary et al. [7] discussed the widespread usage of Pontederia crassipes Mart. for phytoremediation of dye-contaminated water. According to Hasan et al. [8], Pontederia crassipes Mart. is capable of effectively absorbing Zn (II) and Cd (II) from aqueous solutions up to concentrations of 6, and 2.5 mg/L, respectively. The effectiveness of the plant in phytoremediating water contaminated by PTEs like Cd, As, Pb, Cr, microbial toxins, and suspended particles has been documented. The plant was also able to remove 99.5% of the hexavalent Cr from the wastewater. Additionally, this purifying system is both economically, and environmentally sound and does not need much expert opinion [9, 16, 18, 20].

The fuel crisis is a major issue that the globe is currently experiencing. Moreover, air pollution is a result of the burning of fuels. The use of ethanol, a green energy, as a fuel substitute in this scenario has been studied by various authors which also limits air pollution. However, ethanol production is economically challenging so bioethanol must be considered in this regard. The phytoremediated biomass of water hyacinth is a rich source of lignocellulose which can be further reused to produce bioethanol. Pretreatment, hydrolysis, and fermentation are the three steps in the synthesis of bioethanol (Figure 3) [35]. Upon pretreatment, the lignocellulosic biomass produces lignin, and fermentable carbohydrates [36, 37, 38]. By making more cellulose, and hemicellulose accessible for the hydrolysis stage, this process removes lignin and modifies the structure of cellulose and hemicellulose [39].

Figure 3.

Flowchart showing bioethanol preparation [35].

According to Lin et al. [40], there are numerous approaches to pretreating lignocellulosic biomass, including mechanical pretreatment, alkali or acid pretreatment, and steam explosion. The use of biological agents like fungi as part of other pretreatment techniques is known as biological pretreatment. Commonly utilized as biological pretreatment agents include white-rot fungi, brown-rot fungi, and soft-rot fungi [21, 22, 41]. After pretreatment, cellulose, and hemicellulose are hydrolyzed to yield straightforward fermentable sugars. It is more difficult to hydrolyze cellulose than hemicellulose because of its crystalline structure. Because of this, cellulose hydrolysis is always performed with the aid of an acid or specialist enzyme (cellulase). The breakdown of cellulose is referred to as biochemical hydrolysis or saccharification, whereas the hydrolysis of hemicelluloses is referred to as chemical or enzymatic hydrolysis [42]. Following hydrolysis, the biological process of fermentation takes place. Which eventually reduces simple carbohydrates to smaller molecules like acids, and alcohols. For this stage, microorganisms are required. To catalyze chemical reactions during fermentation, these bacteria produce enzymes. Despite the fact that these sugars are essential for the metabolism, and reproduction of all living things, a number of bacteria and yeasts are capable of fermenting them. The two most popular species employed to produce ethanol from hexose sugars on a big scale are Saccharomyces cerevisiae and Zymomonas mobilis. Saccharomyces cerevisiae is the species that produces bioethanol most frequently. The durability, and suitability of this strain of yeast for the fermentation of glucose from lignocellulosic biomass are its main advantages. The gram-negative, facultatively anaerobic species of bacterium Zymomonas mobilis, on the other hand, is less frequently employed for the fermentation process due to its lower yield and more active metabolism, which makes it more prone to contamination [43, 44, 45]. The anaerobic digestion of Pontederia crassipes Mart. to produce biogas is a practical alternative strategy for the provision of environmentally friendly energy and aquatic weed management. The presence of firmly bound refractory lignin, crystalline cellulose, and hemicellulose polymers slows anaerobic digestion and restricts the production of biogas [46]. If collected biomass is valuable for use in converting biomass or other product preparation, aquatic restoration might move along more swiftly. It serves as a substrate for the breakdown of organic matter or the production of biogas, which can yield fertilizer-making byproducts from digestion. According to past research on this subject by Priya et al. [47], Pontederia crassipes Mart. can contain a lot of nitrogen, up to 3.2% of its dry mass, and have a C/N ratio of about 15. The inoculant sludge was made using the wastewater from a biogas system that processed cow manure. The ratio of water to Pontederia crassipes Mart. used to make the slurry was 1:10 (w/w). The slurry underwent H₂SO₄ pretreatment. The slurry’s volatile solid content was increased by the addition of water until it reached 4% g/g Total Mass of Slurry (TMS). Using NaOH, the pH of the slurry was kept between 6 and 8. The active sludge was applied using an inoculum ratio of slurry: sludge of 75:25 with a total volume of 600 ml. Pretreating slurry with H₂SO₄ at a concentration of 5% v/v for 60 minutes produced the highest methane content (64.38%) and the maximum amount of total biogas (424.30 ml) (Figure 4) [48]. NPK concentration in vermicompost is higher than in the original feed supply. The vermicompost C/N ratio rose as a result of earthworm activity. Earthworm activity increased bacteria, fungi, and actinomycetes in the microflora. Additionally, they deliver the nutrients required for the growth of the microbes. In vermicompost, which has higher enzyme activity than typical compost earthworms and an aerobic heterotrophic microbial community drive the breakdown process (Figure 5) [37, 49].

Figure 4.

Preparation of biogas [48].

Figure 5.

Vermicompost production [49, 37].

Water is a necessary component for life to exist on Earth. Water is required for both life on Earth and nearly all other human endeavors. As a result, water is necessary for all life. Our planet is around 75% covered in water. The total volume of water on Earth is approximately 1.386 billion km³, of which 97.5% is salt water. Eakins et al. [50] estimated the total oceanic volume to be 1332 x 10⁶ km³. Therefore, freshwater (FW) makes up only 2.5% of water (Figure 6). Furthermore, just 0.3% of the total water supply is surface water, and the great majority of freshwater is deposited as glaciers [51, 52]. UNICEF estimates that nearly 4 billion people, or nearly 65% of the world’s population, experience extreme water scarcity for at least one month; nearly 2 billion people live in areas with inadequate water supplies; by 2025, nearly half of the world’s population will experience water scarcity; by 2030, 700 million people will have to relocate due to severe water constraints; and by 2040, 25% of children will have to live in areas with extreme water stress. The lack of freshwater resources worldwide is a significant barrier to advancing human progress and realizing sustainable development objectives [53]. More people are realizing that the FW shortage is a widespread structural issue on a worldwide scale [54]. Between 0.5 and 3.1 billion people will experience greater water scarcity by the year 2050 as a result of climate change, according to a study by Gosling et al. [55]. His study made use of climatic predictions based on numerous global climate models [55].

Figure 6.

Percentage of saltwater and freshwater according to Kundzewicz et al. [51]; Oki et al. [52].

With an average annual rainfall of 1150–1450 mm, the RCF area receives 80–90% of its rainfall during the monsoon season. The Damodar, Ajay, and Barakar rivers govern the drainage system.

According to several studies [56, 57, 58], the geological structure of the RCF region, where water table depths typically range from 3 to 15 meters below ground level, significantly affects the occurrence and storage of groundwater. In this scenario, PL water (Figure 7) can be an alternate source of FW following purification in accordance with the Jal Jeevan Mission and Swachh Bharat Mission of the Government of India.

Figure 7.

An abandoned PL in RCF.

The purified water can be used sustainably in agriculture. One of the most cutting-edge methods for utilizing abandoned PL sustainably is hydroponics, which succeeded in phytoremediation. In hydrophonic farming, instead of using soil to grow the plants, nutrient-based water solutions are used. According to Helmreich [59], Dhananjani, and Pakeerathan [60], this kind of farming needs some fundamental conditions, such as access to clean water, oxygen, nutrients, and light, as well as root support materials including peat moss, vermiculite, perlite, and coconut fiber. The area where plants have been grown can be supplied with nutrient-rich water via a pump. The pots must be chosen so that the roots may stay submerged in water. As the plants absorb the nutrients from the water, the nutrient-rich water is provided at regular intervals. It is emptied of the extra water. Moreover, other ways of sustainability may include horticulture, and pisciculture In order to produce bioethanol, biogas, and vermicompost, the Pontederia crassipes Mart. biomass after phytoremediation can be employed. As a result, multiple levels of entrepreneurship will be possible. Bioethanol manufacturing processes can employ the gathered biomass as a raw material. Additionally, a number of companies can be established at the cooperative and small-scale levels to market bioethanol, biogas, and vermicompost. The production of vermicompost can also support the development of agriculture in that region. Thus our approach also supports the Make in India initiative by the Government of India according to which opportunities for new sources of income can be created as alternate livelihoods for the parishioners, who are otherwise involved in illegal practices.

4. Conclusion

There are effective mine-closing procedures in wealthy nations. However, developing countries like India observe major challenges in the implementation of such programmes. In addition to revealing alternative means of subsistence in RCF regions, the authors attempt to propose sustainable mine closure plans for surface-cut mining. The initial part of the plan is to phytoremediate PL water, making PLs an alternate supply of fresh water. Additionally, the authors propose the commercialization of bioethanol, biogas, and vermicompost made from the harvested biomass of phytoremediated aquatic plants. Furthermore, in order to address the major challenges of the water crisis, food insecurity, and entrepreneurship, the authors are currently working on the development of pollutant-resistant crop varieties to encourage agriculture in polluted soil of the catchment basin area of coal mine PLs.

Acknowledgments

The authors are grateful to the head of the botany department at the University of Burdwan in West Bengal, India.

Conflict of interest

The authors declare that they have no conflict of interest.