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Taxonomic classi fi cation of DNA sequences from the microbial community of soil samples at genus and phylum levels. Relative
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Soil acidification has been a threat to sustainable agricultural development as a global environmental problem. The bioelectrochemistry system (BES) is an eco-friendly and low-cost technique for ameliorating acidic soil when compared with traditional technologies. Here, operational parameters from soil load and external resistance were investigated...
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Context 1
... P ameliorated denotes the changed unit a er BES- amelioration; P closed and P open denote the soil pHs under closed circuit and open circuit, respectively; and m denotes the mass of soil load. While a gradual downtrend could be observed in the soil pHs within the range tested, the index P ameliorated increased rst and then reached a plateau with the increase of soil loads ( Fig. 2B). To analyze the role of electrochemical e ff ects, the performances of soil MFCs were investigated under a series of external resistances ranging from 10 to 10 000 U . As shown in Fig. 2C, the soil pHs a er amelioration correlated in the opposite direction with the external resistance gradient, suggesting that the lower external resistance of MFCs showed the better amelioration for the acidic soil. The current densities of MFCs loaded with 10 000, 1000 and 100 U reached 41.16 Æ 7.63, 117.35 Æ 8.60 and 123.72 Æ 18.98 mA m À 2 , respectively, except that the current density of 10 U -MFC uctuated irregularly. The result suggests that a lower external resistance is more conducive to enhance the electrochemical force for the soil pH increase. Al toxicity in acidic soil is the main cause of inhibiting growth of plants and microorganisms. 22 The aluminum minerals mainly exist in the forms of layer aluminosilicate minerals, noncrystalline aluminosilicate, and gibbsite. In this study, the soil pH was obviously increased with the decrease of the external resistance as described above. Similarly, with the decrease of the external resistance, the exchangeable Al 3+ concentration in the ameliorated soil signi cantly reduced, and the removal rate of exchangeable Al 3+ showed an exponential correlation with the soil pH (Fig. 3). When the external resistance was 10 U , the removal rate of Al 3+ reached 39% a er 3 days of running. The microbial communities of acidic soils were investigated before and a er BES-amelioration. Six libraries were constructed from the soil samples. A total of 101653 e ff ective sequences with an average length of 271.9 bp were obtained from 16S rRNA gene V3 – V4 region amplicons of these samples. Overall sequencing information about six samples was listed in Table S1. † To fairly compare the di ff erent samples at the same sequencing depth, 13 056 sequences were extracted from each sample randomly. Although the rarefaction curves had not yet reached a plateau at 13 056 sequences, the Good's coverage was up to 75.55 Æ 2.93%, suggesting that the 13 056 sequences were enough to re ect the pro le of the microbial communities. As shown in Fig. 4, the size of red dots was bigger than that of the blue ones, indicating that microbial communities of acidic soils a er BES-amelioration were more diverse than those without BES-amelioration. The a -diversity indexes, that is observed species, Chao1 index and Shannon index (Fig. S4 † ), were consistent with the phylogenetic diversity. The weighted principal coordinate analysis showed that there was a relatively long distance between the acidic soil samples before (blue) and a er (red) BES-amelioration (Fig. 5), suggesting the shi s of microbial communities of the acidic soils when ameliorated by BES. This result indicated that BES technology changed the structure of the microbial community in the acidic soil with respect to a -diversity and b -diversity. To estimate the e ff ect of BES on phylogenetic distribution at the genus level, 353 classi ed genera were identi ed. As illustrated in Fig. 5, the samples a er BES-amelioration exhibited similar community composition and weakened the genus of Sinomonas , Methylobacterium and Burkholderia . Sinomonas belongs to Actinobacteria with high GC content, which is suitable for extreme environments. 23 Methylobacterium is known as methane-oxidizing bacteria. 24 Notably, Burkholderia consists of human, animal and plant pathogens, such as Burkholderia mallei , 25 Burkholderia pseudomallei 26 and Burkholderia cepacia . 27 The decrease of pathogens contributes to reducing the health and environmental risks. Geobacter , as common electrochemically active bacteria, 28 were obviously detected in our samples. Those electrochemically active microbes built a biological foundation for the use of BES technologies. The ux of proton into the cathodic chamber during the amelioration of acidic soil could be driven by the interaction of di ff usion and electromigration, which accords with Nernst – Planck equation. 29 Under open circuited condition, the di ff usion of proton, which is a concentration-driven process, plays a primary role. 30 As shown in Fig. 2, there was no signi cant increase in the soil pH under 3 day open circuit. At the same time, the exchangeable Al 3+ removal in the soil was not observed (Fig. 3). Indeed, the pH of the acidic soil showed a very slow increase through concentration-driven di ff usion only. For example, the soil pH only had a slight increase initially depending on the di ff usion of proton under open circuit until day 6 (Fig. 2A). The dilemma was signi cantly reversed by BES under closed circuit condition. The electrical eld promoted the electromigration of protons from soil to cathode, which was in uenced by the concentration of various ions, the di ff usion coe ffi cient of ionic species and the strength of electrical eld. 30 It is also worth mentioning that the consumption of soil protons caused by oxygen reduction reaction should accelerate the ow of protons from soil to cathode surface, thereby increasing soil pH. This process only consumes the soil H + by using the oxygen from the air, and does not add other substances into soil, suggesting that BES is an environmental- friendly way for acidic soil amelioration. External resistance is considered as an important factor a ff ecting BES performance by controlling the electron ow from the anode to the cathode, and further in uencing the reduction reaction on the cathode surface. 31 In the present study, a lower external resistance meant a higher current density, except for the irregular uctuation of the current density of 10 U -MFC. The gradually enhanced current density strengthened the electrochemical action of BES, resulting in the increase of the electron and proton ow into the cathode from anode and soil, respectively. This further explains why the BES with a lower external resistance shows a better amelioration. The negative correlation between the increased pH and the soil load suggested that the optimization of BES unit numbers and soil load was necessary in practical projects. Microbial community diversity is an important biological indicator of changes in soil quality, and a higher community diversity in soil generally implies a better soil quality. 32 A er BES-amelioration, the advantageous shi of a -diversity, b diversity and phylogenetic distribution in acidic soil e ff ectively demonstrated the superiority of the biological e ff ect of the BES approach, and the abundant microbial community would facilitate the gradual restoration of the fertility of the acidic soil. In addition, BES-amelioration also a ff ected the function of the microbial community in the acidic soil. For example, Cyanobacteria can produce toxins which are dangerous to humans as well as other animals. 33 The disappearance of Cyanobacteria in the acidic soil a er BES-amelioration may be a good indication of reduction of some hazardous components (Fig. S5 † ). Comparing the correlations between each pair of six factors, including external resistance, soil pH, anodic water pH, Al 3+ removal rate, phylogenetic diversity and Chao1, relatively high association could be observed except for the anodic water pH with others (Fig. 6). There was a strong link between soil pH and external resistance, because soil pH was mainly a ff ected by the levels of electrochemical function through di ff erent external resistances. The changed soil pH then led to the shi s of Al toxicity and the microbial community structure, and this result was supported by that the soil pH had high relevance with Al 3+ removal rate, phylogenetic diversity and Chao1 (Fig. 6). De nitely, the e ff ects among soil pH, Al toxicity and microbial community are mutual and bidirectional, rather than one completely decided another. The soil pH, Al toxicity and microbial community are regarded as an associated and inseparable system. In this study, an approach for ameliorating acidic soil was proposed on the ...
Context 2
... P ameliorated denotes the changed unit a er BES- amelioration; P closed and P open denote the soil pHs under closed circuit and open circuit, respectively; and m denotes the mass of soil load. While a gradual downtrend could be observed in the soil pHs within the range tested, the index P ameliorated increased rst and then reached a plateau with the increase of soil loads ( Fig. 2B). To analyze the role of electrochemical e ff ects, the performances of soil MFCs were investigated under a series of external resistances ranging from 10 to 10 000 U . As shown in Fig. 2C, the soil pHs a er amelioration correlated in the opposite direction with the external resistance gradient, suggesting that the lower external resistance of MFCs showed the better amelioration for the acidic soil. The current densities of MFCs loaded with 10 000, 1000 and 100 U reached 41.16 Æ 7.63, 117.35 Æ 8.60 and 123.72 Æ 18.98 mA m À 2 , respectively, except that the current density of 10 U -MFC uctuated irregularly. The result suggests that a lower external resistance is more conducive to enhance the electrochemical force for the soil pH increase. Al toxicity in acidic soil is the main cause of inhibiting growth of plants and microorganisms. 22 The aluminum minerals mainly exist in the forms of layer aluminosilicate minerals, noncrystalline aluminosilicate, and gibbsite. In this study, the soil pH was obviously increased with the decrease of the external resistance as described above. Similarly, with the decrease of the external resistance, the exchangeable Al 3+ concentration in the ameliorated soil signi cantly reduced, and the removal rate of exchangeable Al 3+ showed an exponential correlation with the soil pH (Fig. 3). When the external resistance was 10 U , the removal rate of Al 3+ reached 39% a er 3 days of running. The microbial communities of acidic soils were investigated before and a er BES-amelioration. Six libraries were constructed from the soil samples. A total of 101653 e ff ective sequences with an average length of 271.9 bp were obtained from 16S rRNA gene V3 – V4 region amplicons of these samples. Overall sequencing information about six samples was listed in Table S1. † To fairly compare the di ff erent samples at the same sequencing depth, 13 056 sequences were extracted from each sample randomly. Although the rarefaction curves had not yet reached a plateau at 13 056 sequences, the Good's coverage was up to 75.55 Æ 2.93%, suggesting that the 13 056 sequences were enough to re ect the pro le of the microbial communities. As shown in Fig. 4, the size of red dots was bigger than that of the blue ones, indicating that microbial communities of acidic soils a er BES-amelioration were more diverse than those without BES-amelioration. The a -diversity indexes, that is observed species, Chao1 index and Shannon index (Fig. S4 † ), were consistent with the phylogenetic diversity. The weighted principal coordinate analysis showed that there was a relatively long distance between the acidic soil samples before (blue) and a er (red) BES-amelioration (Fig. 5), suggesting the shi s of microbial communities of the acidic soils when ameliorated by BES. This result indicated that BES technology changed the structure of the microbial community in the acidic soil with respect to a -diversity and b -diversity. To estimate the e ff ect of BES on phylogenetic distribution at the genus level, 353 classi ed genera were identi ed. As illustrated in Fig. 5, the samples a er BES-amelioration exhibited similar community composition and weakened the genus of Sinomonas , Methylobacterium and Burkholderia . Sinomonas belongs to Actinobacteria with high GC content, which is suitable for extreme environments. 23 Methylobacterium is known as methane-oxidizing bacteria. 24 Notably, Burkholderia consists of human, animal and plant pathogens, such as Burkholderia mallei , 25 Burkholderia pseudomallei 26 and Burkholderia cepacia . 27 The decrease of pathogens contributes to reducing the health and environmental risks. Geobacter , as common electrochemically active bacteria, 28 were obviously detected in our samples. Those electrochemically active microbes built a biological foundation for the use of BES technologies. The ux of proton into the cathodic chamber during the amelioration of acidic soil could be driven by the interaction of di ff usion and electromigration, which accords with Nernst – Planck equation. 29 Under open circuited condition, the di ff usion of proton, which is a concentration-driven process, plays a primary role. 30 As shown in Fig. 2, there was no signi cant increase in the soil pH under 3 day open circuit. At the same time, the exchangeable Al 3+ removal in the soil was not observed (Fig. 3). Indeed, the pH of the acidic soil showed a very slow increase through concentration-driven di ff usion only. For example, the soil pH only had a slight increase initially depending on the di ff usion of proton under open circuit until day 6 (Fig. 2A). The dilemma was signi cantly reversed by BES under closed circuit condition. The electrical eld promoted the electromigration of protons from soil to cathode, which was in uenced by the concentration of various ions, the di ff usion coe ffi cient of ionic species and the strength of electrical eld. 30 It is also worth mentioning that the consumption of soil protons caused by oxygen reduction reaction should accelerate the ow of protons from soil to cathode surface, thereby increasing soil pH. This process only consumes the soil H + by using the oxygen from the air, and does not add other substances into soil, suggesting that BES is an environmental- friendly way for acidic soil amelioration. External resistance is considered as an important factor a ff ecting BES performance by controlling the electron ow from the anode to the cathode, and further in uencing the reduction reaction on the cathode surface. 31 In the present study, a lower external resistance meant a higher current density, except for the irregular uctuation of the current density of 10 U -MFC. The gradually enhanced current density strengthened the electrochemical action of BES, resulting in the increase of the electron and proton ow into the cathode from anode and soil, respectively. This further explains why the BES with a lower external resistance shows a better amelioration. The negative correlation between the increased pH and the soil load suggested that the optimization of BES unit numbers and soil load was necessary in practical projects. Microbial community diversity is an important biological indicator of changes in soil quality, and a higher community diversity in soil generally implies a better soil quality. 32 A er BES-amelioration, the advantageous shi of a -diversity, b diversity and phylogenetic distribution in acidic soil e ff ectively demonstrated the superiority of the biological e ff ect of the BES approach, and the abundant microbial community would facilitate the gradual restoration of the fertility of the acidic soil. In addition, BES-amelioration also a ff ected the function of the microbial community in the acidic soil. For example, Cyanobacteria can produce toxins which are dangerous to humans as well as other animals. 33 The disappearance of Cyanobacteria in the acidic soil a er BES-amelioration may be a good indication of reduction of some hazardous components (Fig. S5 † ). Comparing the correlations between each pair of six factors, including external resistance, soil pH, anodic water pH, Al 3+ removal rate, phylogenetic diversity and Chao1, relatively high association could be observed except for the anodic water pH with others (Fig. 6). There was a strong link between soil pH and external resistance, because soil pH was mainly a ff ected by the levels of electrochemical function through di ff erent external resistances. The changed soil pH then led to the shi s of Al toxicity and the microbial community structure, and this result was supported by that the soil pH had high relevance ...
Citations
... Unlike organic pollutants, heavy metals can only be converted into less toxic forms or immobilized to reduce their bioavailability (Fig. 1). In SMES, the removal of heavy metals is mainly Soil acidification -- (Zheng et al., 2014) accomplished by receiving the electrons generated through the oxidation of substrates by microorganisms. The way and area of receiving the electrons may be different. ...
Remediation of contaminated soil and sediments has been drawing our attention, efficient and eco-friendly technologies are urgently needed for the removal of pollutants in soil and sediments. Although conventional remediation technologies have been in application for decades and have achieved great performance, the significant drawbacks limit their application (e.g., complicated operation and secondary pollution). Microbial electrochemical system (MES) has been intensively studied as a promising technology for soil/sediment remediation. Compared with other technologies, soil/sediment MES (SMES) exhibited many potential benefits, such as adequate electron acceptors, self-sustained operation, and facile control. However, due to the diversity of soil/sediment contamination and the significant difference in the remediation performance of conventional SMES, it is imperative to develop strategies for enhancing the remediation performance of SMES. In this review, we briefly introduce the removal mechanisms of different pollutants, including the mechanisms of electron releasing, transportation, and receiving. Afterward, we comprehensively present a detailed discussion of the recent progress in the enhancement of soil/sediment remediation in terms of reactor configurations, electrode arrangements, and electrode materials. Moreover, different materials used to amend soil/sediments and their corresponding enhancement principles are summarized in detail. Finally, we discuss the current emerging limitations of SMES and the future research endeavors to improve the performance and promote the practical application. Therefore, this review can fill the gaps in SMES development and guide the practical application in contaminated soil/sediments.
... Various studies has been conducted to report the employment of MES for bioremediation of soil because soil has electrochemical characteristics Wang, Yi, Cao, Fang, & Li, 2017). Various methods have been designed for the utilization of MES in remediation of soil as (1) oxidation process holds at the anode as products like petroleum behave as source of electron donors and degradation occurs during oxidationÀreduction reactions ; (2) anodic reduction: synthetic products behave as electron acceptors in reducing atmosphere and get degraded ; (3) sorption process: products absorption upon electrodes or on electrode existing biofilm; (4) electrokinetic energy: in electric field influence, particles of soil go hydrological and physicochemical variations (Wang, Song et al., 2016); (5) cathode alkalization: utilization of protons at cathode where pH enhances during O 2 reduction (Zheng et al., 2014); and (6) cathode reduction: azo compounds, metals, halogen-based organics attain electrons that were anode produced (Wang, Deng, & Zhao, 2016;Wang, Song et al., 2016). A bioelectrochemical system has been designed and this system has been known as bioelectric well, and this can be used in polluted groundwater sources or wells for applications (Palma, Daghio, Franzetti, Petrangeli Papini, & Aulenta, 2018). ...
Micropollutants are the pollutant fragments less than 5 mm in diameter. They enter the ecosystem from different resources such as clothing, cosmetics, packaging products, and various industrial processes. The utilization of clothing, packaging, personal care, and pharmaceutical products is associated with the improved quality of life; however, their resulting wastes are widely contaminating ecosystem. For the removal of such environmental pollutants, different remediation techniques have been reported for the removal of environmental micropollutants including nanoremediation, photocatalysis, bioremediation, and sonochemical catalysis techniques. Few of these techniques require the usage of high energy excessive amount of chemicals resulting the formation of toxic byproducts. Several microorganisms have been reported for efficient biodegradation of variety of different organic, inorganic, and other environmental pollutants. Microbial engineering has introduced opportunities to develop efficient microbes for pollution remediation processes. This chapter provides details of various techniques employed to remove micropollutants from the environment under various conditions. Recent advances in bioremediation technologies, their advantages, drawback, applications, and future perspectives have also been comprehensively discussed on different biotechnological methods.
... The methods employed for the application of MES in soil remediation are as follows: (1) oxidization at the anode: SPs such as petroleum hydrocarbons act as electron donors and are thus degraded during redox reactions ; (2) anodic reduction: SPs can also act as electron acceptors in reducing environments and thus can also be degraded (Wang et al., 2017c); (3) sorption: absorption of SPs onto the electrodes or onto a biofilm present on the electrodes ; (4) electrokinetic energy: under the influence of an electric field, soil particles undergo physicochemical and hydrological changes, thus affecting the chemical speciation and dissemination of SPs (Wang et al., 2016b); (5) cathodic alkalization: proton consumption at the cathode during oxygen reduction increases the pH (Zheng et al., 2014b); and (6) cathodic reduction: halogenated organics, azo dyes, high-valent metals, and nitroaromatics acquire electrons produced at the anode (Mu et al., 2009;Wang et al., 2011Wang et al., , 2016a. Palma et al. (2017) reported a bio-electrochemical system design, the "bioelectric well," that can be established in contaminated groundwater bodies or in wells for in situ applications. ...
The environment is contaminated by synthetic contaminants owing to their extensive applications globally. Hence, the removal of synthetic pollutants (SPs) from the environment has received widespread attention. Different remediation technologies have been investigated for their abilities to eliminate SPs from the ecosystem; these include photocatalysis, sonochemical techniques, nanoremediation, and bioremediation. SPs, which can be organic or inorganic, can be degraded by microbial metabolism at contaminated sites. Owing to their diverse metabolisms, microbes can adapt to a wide variety of environments. Several microbial strains have been reported for their bioremediation potential concerning synthetic chemical compounds. The selection of potential strains for large-scale removal of organic pollutants is an important research priority. Additionally, novel microbial consortia have been found to be capable of efficient degradation owing to their combined and co-metabolic activities. Microbial engineering is one of the most prominent and promising techniques for providing new opportunities to develop proficient microorganisms for various biological processes; here, we have targeted the SP-degrading mechanisms of microorganisms. This review provides an in-depth discussion of microbial engineering techniques that are used to enhance the removal of both organic and inorganic pollutants from different contaminated environments and under different conditions. The degradation of these pollutants is investigated using abiotic and biotic approaches; interestingly, biotic approaches based on microbial methods are preferable owing to their high potential for pollutant removal and cost-effectiveness.
... The methods employed for the application of MES in soil remediation are as follows: (1) oxidization at the anode: SPs such as petroleum hydrocarbons act as electron donors and are thus degraded during redox reactions ; (2) anodic reduction: SPs can also act as electron acceptors in reducing environments and thus can also be degraded (Wang et al., 2017c); (3) sorption: absorption of SPs onto the electrodes or onto a biofilm present on the electrodes ; (4) electrokinetic energy: under the influence of an electric field, soil particles undergo physicochemical and hydrological changes, thus affecting the chemical speciation and dissemination of SPs (Wang et al., 2016b); (5) cathodic alkalization: proton consumption at the cathode during oxygen reduction increases the pH (Zheng et al., 2014b); and (6) cathodic reduction: halogenated organics, azo dyes, high-valent metals, and nitroaromatics acquire electrons produced at the anode (Mu et al., 2009;Wang et al., 2011Wang et al., , 2016a. Palma et al. (2017) reported a bio-electrochemical system design, the "bioelectric well," that can be established in contaminated groundwater bodies or in wells for in situ applications. ...
The environment is contaminated by synthetic contaminants owing to their extensive applications globally. Hence, the removal of synthetic pollutants (SPs) from the environment has received widespread attention. Different remediation technologies have been investigated for their abilities to eliminate SPs from the ecosystem; these include photocatalysis, sonochemical techniques, nanoremediation, and bioremediation. SPs, which can be organic or inorganic, can be degraded by microbial metabolism at contaminated sites. Owing to their diverse metabolisms, microbes can adapt to a wide variety of environments. Several microbial strains have been reported for their bioremediation potential concerning synthetic chemical compounds. The selection of potential strains for large-scale removal of organic pollutants is an important research priority. Additionally, novel microbial consortia have been found to be capable of efficient degradation owing to their combined and co-metabolic activities. Microbial engineering is one of the most prominent and promising techniques for providing new opportunities to develop proficient microorganisms for various biological processes; here, we have targeted the SP-degrading mechanisms of microorganisms. This review provides an in-depth discussion of microbial engineering techniques that are used to enhance the removal of both organic and inorganic pollutants from different contaminated environments and under different conditions. The degradation of these pollutants is investigated using abiotic and biotic approaches; interestingly, biotic approaches based on microbial methods are preferable owing to their high potential for pollutant removal and cost-effectiveness.
... Importantly, the soil BERS was verified to be an effective treatment method for 27 low-polluted sediments/soils, whether by ML or by its degradates. The quantitative 28 degradates of ML showed that the first step was dechlorination based on the 29 bioelectrochemical degradation pathway. The biocurrent selectively enriched special 30 species, e.g., Geobacter and Thermincola for bioelectricity generation and Ralstonia, ...
... with the ML 356 degradation in the soil BERS of this study, which was supported by the significantly 357 negative correlation (-0.523* − -0.665**, Table 1) between pH and ML content, and 358 consistent with the previous studies [19,28,29]. That was why a higher pH was 359 observed in the top soil layer of the BERS than in other layers between 14 and 66 360 days. ...
Herbicide-polluted soils have posed a threat to the crop growth and agro-product quality and safety. Even worse, the low-content of residue is still appreciable for a long time in subsurface soils. The soil bioelectrochemical remediation system (BERS) provides an inexhaustible electron acceptor to cause in situ indigenous microorganisms to generate biocurrent and accelerate the removal of metolachlor (ML). As a result of carbon fiber amendment, the highest current density (637 ± 19 mA/m2) to date has been generated in a soil BERS. The ML half-life and complete removal time decreased from 21 to 3 d and from 245 to 109 d, respectively. Importantly, the soil BERS was verified to be an effective treatment method for low-polluted sediments/soils, whether by ML or by its degradates. The quantitative degradates of ML showed that the first step was dechlorination based on the bioelectrochemical degradation pathway. The biocurrent selectively enriched special species, e.g., Geobacter and Thermincola for bioelectricity generation and Ralstonia, Phyllobacterium and Stenotrophomonas for degradation in soils. Meanwhile, Flavisolibacter and Gemmatimonas occupied the core niche in strengthening interspecific relationships by the biocurrent. This study firstly revealed the explicit abundance of Geobacter in agricultural soils and laid a foundation for the function design of mixed bacteria in the sediment/soil BERS.
... Agricultural soils are vulnerable to different kinds of contamination, including acidification [140], petroleum hydrocarbon (mainly from on-farm vehicles) [141], metals [142], and transgenic toxins [143], etc. In order to reuse the contaminated soils for agricultural activities, in-situ remediation is required. ...
... However, with appropriate methods to increase soil porosity and decrease Ohmic resistance, BES-based in-situ soil remediation can be a potent cost-effective tool in the near future. For example, using a two-chamber soil-MFC inoculated with activated sludge, Zheng et al. were able to ameliorate acidic soils from pH value of around 5 to nearly 6, while recovering electric current as high as 123.72 mA/m 2 [140]. Another research group succeeded in degrading 82.1-89.7% of petroleum hydrocarbon (originally 12.25 g/kg dry soil) within 120 days in a pilot study of column-type BESs that could be directly installed on site for in-situ soil remediation [141]. ...
Background: Bioelectrochemical systems (BESs) are emerging energy-effective and environment-friendly technologies. Different applications of BESs are able to effectively minimize wastes and treat wastewater while simultaneously recovering electricity, biohydrogen and other value-added chemicals via specific redox reactions. Although there are many studies that have greatly advanced the performance of BESs over the last decade, research and reviews on agriculture-relevant applications of BESs are very limited. Considering the increasing demand for food, energy and water due to human population expansion, novel technologies are urgently needed to promote productivity and sustainability in agriculture. Methodology: This review study is based on an extensive literature search regarding agriculture-related BES studies mainly in the last decades (i.e., 2009-2018). The databases used in this review study include Scopus, Google Scholar and Web of Science. The current and future applications of bioelectrochemical technologies in agriculture have been discussed. Findings/Conclusions: BESs have the potential to recover considerable amounts of electric power and energy chemicals from agricultural wastes and wastewater. The recovered energy can be used to reduce the energy input into agricultural systems. Other resources and value-added chemicals such as biofuels, plant nutrients and irrigation water can also be produced in BESs. In addition, BESs may replace unsustainable batteries to power remote sensors or be designed as biosensors for agricultural monitoring. The possible applications to produce food without sunlight and remediate contaminated soils using BESs have also been discussed. At the same time, agricultural wastes can also be processed into construction materials or biochar electrodes/electrocatalysts for reducing the high costs of current BESs. Future studies should evaluate the long-term performance and stability of on-farm BES applications.
... After 3 days of operation, the microbial samples harvested from the bioleaching solutions were washed with 50 mM phosphate buffer (pH = 2.0 or 7.0) three times and centrifuged at 6000 ×g to collect the cells. After the total DNA was extracted using FastDNA SPIN Kit for Soil (MP, USA), the raw DNA was amplified with the PCR reaction condition (Deng et al., 2014;Zheng et al., 2014). Then, a Universal DNA Purification Kit (TIANGEN, China) was used to purify the PCR products. ...
Solid wastes are currently produced in large amounts. Although bioleaching of metals from solid wastes is an economical and sustainable technology, it has seldom been used to recycle metals from abandoned catalyst. In this study, the bioleaching of vanadium from V2O5-WO3/TiO2 catalyst were comprehensively investigated through five methods: Oligotrophic way, Eutrophic way, S-mediated way, Fe-mediated way and Mixed way of S-mediated and Fe-mediated. The observed vanadium bioleaching effectiveness of the assayed methods was follows: S-mediated > Mixed > Oligotrophic > Eutrophic > Fe-mediated, which yielded the maximum bioleaching efficiencies of approximately 90%, 35%, 33%, 20% and 7%, respectively. The microbial community analysis suggested that the predominant genera Acidithiobacillus and Sulfobacillus from the S-mediated bioleaching way effectively catalyzed the vanadium leaching, which could have occurred through the indirect mechanism from the microbial oxidation of S0. In addition, the direct mechanism, involving direct electron transfer between the catalyst and the microorganisms that attached to the catalyst surface, should also help the vanadium to be leached more effectively. Therefore, this work provides guidance for future research and practical application on the treatment of waste V2O5-WO3/TiO2 catalyst.
... For the cathode, precipitations were formed by certain increasing cations, for example, Ca (119%), Mg (84%), and Fe (155%), due to the production of hydroxyl ions on the air cathode oxidation reaction . Actually, these formed precipitations may directly result in the reduction of OH − and cations and thus the downdrift of soil pH and electrical conductivity (Fig. S4, Electronic Supplementary Material) (Zheng et al. 2014). For the anode, the accumulated Fe may be directly related with bioelectricity generation since the ferric reducing microorganisms are the typical electricigens (Renslow et al. 2013). ...
Purpose: The electrode aging in soil microbial fuel cells (MFCs) disturbed the removal of pollutants and sensitivity of electrophysiological signal. Therefore, surveying the causes of aging electrodes could assist to take the prevention measures for remediation and biosensor application of soil MFCs. Materials and methods: The surface morphology, element accumulation on the surface of electrodes, and element migration in soils between electrodes were investigated by scanning electronic microscopy, energy-dispersive spectrometry, and X-ray photoelectron spectroscopy in a constructed soil MFC. Results and discussion: The rust was observed on the anode, and the soil gypsification was noted on the cathode after a long-term (300-day) contribution of soil MFCs. The major elements (At%) Na and Ca in soils on two electrodes increased by 338–562 and 100–119%, respectively. Beside, Al and Fe of increment (24 and 21%) in the anode and Mg and Fe of augmenter (84 and 155%) in the cathode were detected. Conclusions: The stacking of Ca and Fe besides Na in soils adjacent to electrodes probably led to the electrode corrosion and soil gypsification on the surface of electrodes. Thus, the electrode aging of soil MFCs should be paid more attention in further applications.
... For Illumina Hiseq 2500 sequencing, the barcoded-primers 341F and 806R targeting microbial 16S rDNA fragment were selected (Yang et al., 2016). Filtration of sequencing data was performed as previously described by Zheng et al. (2014). Complete sequences data were submitted to NCBI with the accession number SUB2118508. ...
... Statistical analysis, including relative abundance, Good's coverage, rarefaction curves, alpha diversity of microbial community were calculated using Mothur (www.Mothur.org/) (Zheng et al., 2014). Correlation map was built with Pearson indexes (r > 0.8 and P-value <0.05) for phylotypes using microbial abundance data in SPSS (v. ...
... Clean sequences were annotated into operational taxonomic units (OTUs) from phyla to genus level to estimate the phylotype richness and diversity, using a 97% sequence similarly cut-off value. Alpha-diversity of microbial community indexes were calculated to compare inter-species diversity in each sample (Table 4) (Zheng et al., 2014). The highest Shannon-Wiener index (9.42 ...
... After 6 days of running, the samples taken from the leaching solutions were flushed gently with 50 mM phosphate buffer (pH 2.0 and pH 7.0) and centrifuged at 6000 × g to collect the bacteria. A FastDNA SPIN Kit for Soil (MP, USA) was used to extract the total DNA, and then the DNA was amplified with the PCR reaction system as previously described [22]. The PCR products were purified with the Universal DNA Purification Kit (TIANGEN, China) according to the previous report [23]. ...
Electronic wastes (E-wastes) contain a huge amount of valuable metals that are worth recovering. Bioleaching has attracted widespread attention as an environment-friendly and low-cost technology for the recycling of E-wastes. To avoid the disadvantages of being time-consuming or having a relatively low efficiency, biochar with redox activity was used to enhance bioleaching efficiency of metals from a basic E-waste (i.e., printed circuit boards in this study). The role of biochar was examined through three basic processes: Carbon-mediated, Sulfur-mediated and Iron-mediated bioleaching pathways. Although no obvious enhancement of bioleaching performance was observed in the C-mediated and S-mediated systems, Fe-mediated bioleaching was significantly promoted by the participation of biochar, and its leaching time was decreased by one-third compared with that of a biochar-free system. By mapping the dynamic concentration of Fe(II) and Cu(II), biochar was proved to facilitate the redox action between Fe(II) to Fe(III), which resulted in effective leaching of Cu. Two dominant functional species consisting of Alicyclobacillus spp. and Sulfobacillus spp. may cooperate in the Fe-mediated bioleaching system, and the ratio of these two species was regulated by biochar for enhancing the efficiency of bioleaching. Hence, this work provides a method to improve bioleaching efficiency with low-cost solid redox media.
