Unveiling antibacterial and antioxidant activities of zinc phosphate-based nanosheets synthesized by Aspergillus fumigatus and its application in sustainable decolorization of textile wastewater

BACKGROUND

The development of an environment-friendly nanomaterial with promising antimicrobial and antioxidant properties is highly desirable. The decolorization potentiality of toxic dyes using nanoparticles is a progressively serious worldwide issue.

METHODS

The successful biosynthesis of zinc nanoparticles based on phosphates (ZnP-nps) was performed using the extracellular secretions of Aspergillus fumigatus. The antibacterial activity of the biosynthetic ZnP-nps was investigated against Gram-negative bacteria and Gram-positive bacteria using the agar diffusion assay method. The antioxidant property for the biosynthetic nanomaterial was evaluated by DPPH and H2O2 radical scavenging assay.

RESULTS

Remarkable antibacterial and antiradical scavenging activities of ZnP-nps were observed in a dose-dependent manner. The minimum inhibitory concentration (MIC) for Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli was 25 µg/ml, however, the MIC for Bacillus subtilis was 12.5 µg/ml. The maximum adsorptive performance of nanomaterial was respectively achieved at initial dye concentration of 200 mg/L and 150 mg/L using methylene blue (MB) and methyl orange (MO), where sorbent dosages were 0.5 g for MB and 0.75 g for MB; pH was 8.0 for MB and 4.0 for MO; temperature was 30 °C; contact time was 120 min. The experimental data was better obeyed with Langmuir's isotherm and pseudo-second-order kinetic model (R2 > 0.999). The maximum adsorption capacity (qmax) of MB and MO dyes on nanomaterial were 178.25 mg/g and 50.10 mg/g, respectively. The regenerated nanomaterial, respectively, persist > 90% and 60% for MB and MO after 6 successive cycles. The adsorption capacity of the prepared zinc phosphate nanosheets crystal toward MB and MO, in the present study, was comparable/superior with other previously engineered adsorbents.

CONCLUSIONS

Based on the above results, the biosynthesized ZnP-nanosheets are promising nanomaterial for their application in sustainable dye decolorization processes and they can be employed in controlling different pathogenic bacteria with a potential application as antiradical scavenging agent. Up to our knowledge, this is probably the first study conducted on the green synthesis of ZnP-nanosheets by filamentous fungus and its significant in sustainable dye decolorization.

Biochar applications for treating potentially toxic elements (PTEs) contaminated soils and water: a review

Environmental pollution with potentially toxic elements (PTEs) has become one of the critical and pressing issues worldwide. Although these pollutants occur naturally in the environment, their concentrations are continuously increasing, probably as a consequence of anthropic activities. They are very toxic even at very low concentrations and hence cause undesirable ecological impacts. Thus, the cleanup of polluted soils and water has become an obligation to ensure the safe handling of the available natural resources. Several remediation technologies can be followed to attain successful remediation, i.e., chemical, physical, and biological procedures; yet many of these techniques are expensive and/or may have negative impacts on the surroundings. Recycling agricultural wastes still represents the most promising economical, safe, and successful approach to achieving a healthy and sustainable environment. Briefly, biochar acts as an efficient biosorbent for many PTEs in soils and waters. Furthermore, biochar can considerably reduce concentrations of herbicides in solutions. This review article explains the main reasons for the increasing levels of potentially toxic elements in the environment and their negative impacts on the ecosystem. Moreover, it briefly describes the advantages and disadvantages of using conventional methods for soil and water remediation then clarifies the reasons for using biochar in the clean-up practice of polluted soils and waters, either solely or in combination with other methods such as phytoremediation and soil washing technologies to attain more efficient remediation protocols for the removal of some PTEs, e.g., Cr and As from soils and water.

Reclamation of wastewater in wetlands using reed plants and biochar

To cope with water crisis, wastewater reuse has been introduced as a potential source for irrigation. On the other hand, irrigation with wastewater may negatively affect the surroundings. In this study, reed plant (Phragmits australis) and its biochar were tested as low-cost treatments to enhance the efficiency of wastewater reclamation in wetlands within only 72 h. The investigated water was of low irrigation quality and exhibited high contents of BOD₅ and fecal coliform. Moreover, this water contained high levels of soluble cations and anions; besides, being marginally contaminated with Cu, Mn and Cd. After 2 days in the sedimentation unit, wastewater was subjected to three reclamation treatments in parallel (each lasted for 24 h): (1) a "sand & gravel bed", (2) "reed plants grown on a sand & gravel bed" and (3) "biochar + a sand & gravel bed". The results showed that all treatments decreased BOD₅, fecal coliform, total cations and anions, with superiority for the second and third treatments. The levels of the potentially toxic elements also decreased to values within the permissible levels. Although the aforementioned wastewater treatment processes upgraded the quality of this water, it remained in the poor grade. Biochar or reed plants grown on sand and gravel beds significantly improved wastewater quality to the medium quality grade, with superiority for biochar treatment. In conclusion, investigated treatments are guaranteed in wetlands for wastewater reclamation; yet, further protocols should be followed to achieve safe handling of this water and attain the sustainable goals.

A Combined Use of Rhizobacteria and Moringa Leaf Extract Mitigates the Adverse Effects of Drought Stress in Wheat (Triticum aestivum L.)

Less nutrient availability and drought stress are some serious concerns of agriculture. Both biotic and abiotic stress factors have the potential to limit crop productivity. However, several organic extracts obtained from moringa leaves may induce immunity in plants under nutritional and drought stress for increasing their survival. Additionally, some rhizobacterial strains have the ability to enhance root growth for better nutrient and water uptake in stress conditions. To cover the knowledge gap on the interactive effects of beneficial rhizobacteria and moringa leaf extracts (MLEs), this study was conducted. The aim of this experimental study was to investigate the effectiveness of sole and combined use of rhizobacteria and MLEs against nutritional and drought stress in wheat. Nitrogen-fixing bacteria Pseudomonas aeruginosa (Pa) (108 CFU ml-1) was inoculated to wheat plants with and without foliar-applied MLEs at two different concentrations (MLE 1 = 1:15 v/v and MLE 2 = 1:30 v/v) twice at 25 and 35 days after seed sowing (50 ml per plant) after the establishment of drought stress. Results revealed that Pa + MLE 2 significantly increased fresh weight (FW), dry weight (DW), lengths of roots and shoot and photosynthetic contents of wheat. A significant enhancement in total soluble sugars, total soluble proteins, calcium, potassium, phosphate, and nitrate contents validated the efficacious effect of Pa + MLE 2 over control-treated plants. Significant decrease in sodium, proline, glycine betaine, electrolyte leakage, malondialdehyde, hydrogen peroxide, superoxide dismutase (SOD), and peroxide (POD) concentrations in wheat cultivated under drought stress conditions also represents the imperative role of Pa + MLE 2 over control. In conclusion, Pa + MLE 2 can alleviate nutritional stress and drought effects in wheat. More research in this field is required to proclaim Pa + MLE 2 as the most effective amendment against drought stress in distinct agroecological zones, different soil types, and contrasting wheat cultivars worldwide.

Co-composted biochar derived from rice straw and sugarcane bagasse improved soil properties, carbon balance, and zucchini growth in a sandy soil: A trial for enhancing the health of low fertile arid soils

Sustainable management of low fertile arid soils using carbon-rich organic amendments such as biochar and compost is of great concern from both agricultural and environmental points of view. The impact of pyrolysis, composting, and co-composting processes of different feedstocks on carbon loss and emissions, soil properties, and plant growth in arid soils with low organic matter content has not been sufficiently explored yet. Consequently, the aim of this work was to 1) investigate the effects of the pyrolysis, composting, and co-composting processes on the properties of the produced biochar, compost, and co-composted biochar from rice straw (RS) and sugarcane bagasse (SB), and 2) examine the impact of addition of RB biochar (RSB), SB biochar (SBB), RS compost (RSC), SB compost (SBC), co-composted RS biochar (RSCB), and co-composted SB biochar (SBCB) at an application dose of 10 ton/hectare on soil properties, carbon emission, and growth of zucchini (Cucurbita pepo) in a sandy arid soil. Carbon loss (kg C kg^-1 feedstock) was significantly (P < 0.05) lower during the preparation of the compost (90.36 in RSC, 220.00 in SBC) and co-composted-biochar (146.35 in RSCB, 125.20 in SBCB) than in biochar (176.5 in RSB, 305.6 in SBB). The C/N ratios of the compost and co-composted biochar (11-28.5) were narrower than the corresponding values of biochars (48-90). All amendments increased significantly soil organic carbon content (2.5 in RSC to 5.5 g kg^-1 in RSCB), as compared to the non-amended control (1.2 g kg^-1). All amendments, particularly RSCB, increased significantly (P < 0.05) the zucchini seed vigor index, dry weight, total chlorophyll content, and root and shoot length, as compared to the control. Moreover, RSCB was the only amendment that showed a positive soil carbon balance. The modified integrated two-way ecological model data also indicated that the co-composted biochar, particularly RSCB, is a promising amendment to improve soil quality and plant growth in sandy arid soils. However, those data should be verified under field conditions.

Rice straw application with different water regimes stimulate enzymes activity and improve aggregates and their organic carbon contents in a paddy soil

Soil organic carbon plays considerable roles in binding soil particles together forming aggregates. Carbon (C) incorporated within these aggregates is thought to be microbially processed; thus, investigating changes in microbial activities i.e. dehydrogenase, urease, catalase and phosphatase enzymes may explain, to some extent, the dynamics and probably mechanisms responsible of formation of these aggregates. Since, soil water content (SWC) may take part in stimulating/lessening activities of organic matter decomposers; thus, this study aimed at investigating the effects of rice straw as a source of organic C in combination with variable SWC on bioaccumulation of C within different soil aggregate size fractions (2000-250, 250-53 and < 53 μm) and hence formation of these aggregates. To achieve these objectives, a pot experiment was conducted for 90 days, including five water levels i.e. maintaining a water head 1 cm above the soil surface (W1), 100% of the saturation percentage, SP (W2), 80% of SP (W3), 65% of SP (W4) and 50% of SP (W5), beside of two rates of applied rice straw i.e. 0 and 15 g kg^-1 (w/w). Results revealed that application of rice straw at a rate of 15 g kg^-1 increased the activities of dehydrogenase, urease, neutral phosphatase and catalase enzymes within the first 60 days after application; thereafter, activities of the first three enzymes decreased considerably. Likewise, formation of soil macro- (2000-250 μm) and micro-aggregates (250-53 μm) increased by the end of the experimental period. The highest concentrations of soil carbon were incorporated within soil macro-aggregate, whereas the least C content was found within the "silt + clay" fraction. Increasing SWC resulted in significant reductions in activities of the aforementioned enzymes and consequent reductions occurred in soil aggregation. Carbon content within aggregates sized <250 μm were significantly correlated with the percentage of these aggregates in soil. Thus, soil aggregation is thought to be the byproduct of an aerobic biosynthetic microbial process in which more stable hydrophobic organic C existed mainly in macropores. This process probably occurred within the first 60 days after RS application.

Application of soil biofertilizers to a clayey soil contaminated with Sclerotium rolfsii can promote production, protection and nutritive status of Phaseolus vulgaris

Sclerotium rolfsii is a soil-borne fungus that causes big losses in productivity of various plant species including Phaseolus vulgaris L. The objectives of this study were to (1) evaluate the impacts of Sclerotium rolfsii on growth and production of common bean plants, (2) determine the effects of Sclerotium rolfsii on nutritive contents of beans, and (3) test the efficacy of bio-inoculants on suppressing plant infection with Sclerotium rolfsii. To fulfill these objectives, we used a coupled pot and field experimental approaches during two growing seasons. Common beans were inoculated with either arbuscular mycorrhizal fungi (Claroideoglomus etunicatum), Saccharomyces cerevisiae, or Trichoderma viride solely or in different combinations. Non-inoculated plants and fungicide treated ones were considered as reference treatments. Throughout these experiments, minimal amounts of rock phosphate were added during soil preparation for bio-inoculated treatments, while the non-inoculated reference treatments received a full dose of P as calcium superphosphate. Results revealed that all tested bioinoculants significantly raised the activities of plant defense enzymes i.e. chitinase, peroxidase and polyphenoloxidase as compared to non-inoculated control. Likewise, pre-, post- and plant survival percentages significantly increased due to these bio-inoculations. Increased survival percentages were attributed to the concurrent increases in uptake of N, P and Zn nutrients by plants treated with bioinoculants. In this concern, plant nutrients uptake was higher in combined than single bio-inoculant treatments. Moreover, the uptake values of plant nutrients owing to the combined bio-inoculants were higher than the corresponding ones achieved due to fungicide treatment. In conclusion, application of the tested bio-inoculants, especially the combined ones can be considered an eco-friendly approach that not only enhances plants resistance against infection with Sclerotium rolfsii but also improves plant nutritive status.

Dynamics of soil organic carbon in Typic Torripsamment soils irrigated with raw effluent sewage water

The current research aimed at collecting detailed information about the consequences of cropping history on the accumulation of soil organic carbon (SOC) within different soil depths, i.e., 0-10, 10-20, 20-30 and 30-60 cm. The study site is located at El Gabal El Asfar area (Egypt) whose soils were irrigated with raw sewage effluent as a sole source of irrigation for different periods extended up to 80 years. SOC increased progressively with increasing cropping time, and on the other hand, decreased noticeably with increasing soil depth. The increases significantly correlated with both of the silt and clay contents in soils which increased with time. Soil bulk density and the hydraulic conductivity significantly and negatively correlated with SOC, respectively. Fractions of SOC, i.e., water soluble C, hot water C and soil biomass C in the surface soil layer (0-10 cm), increased progressively with increasing time of land use. Such pools significantly correlated with SOC on one hand and with each other on the other hand. Active (labile) organic carbon fraction increased with time. This fraction also significantly correlated with the different C pools. In conclusion, the hypothesis that SOC is physically protected against soil microbes within the soil requires more investigations to clarify such results obtained herein because this study highlighted the presence of a dynamic equilibrium among the different fractions or pools of the SOC.

Arbuscular mycorrhiza and environmentally biochemicals enhance the nutritional status of Helianthus tuberosus and induce its resistance against Sclerotium rolfsii

Chemical fungicides are effective tools in controlling plant pathogens; however, these chemicals can, on the other hand, distress the ecosystem. Accordingly, the current research investigates the potentiality of substituting traditional chemical fungicides by inducing plant resistance against infection with soil-born pathogens i.e. Sclerotium rolfsii in the presence of mycorrhizae (AMF) as plant inoculants and one of the following amendments: humic acid, sulphex (a mixture of canola oil and diluted sulphuric acid) and paclobutrazol (ABZ). To attain the abovementioned objective, a field (mildly infected with S. rolfsii) was cultivated with Helianthus tuberosus (a perennial plant belongs to the Asteraceae family) for two successive seasons (2014 and 2015) and the above-mentioned treatments were tested for their feasibilities in controlling S. rolfsii infection against the chemical fungicide "Vitavax-200" either solely or in combinations in a complete randomized block design. Inoculating plants with AMF or amending soils with either humic acid, Sulphex or ABZ solely increased significantly the activities of plant defense enzymes by approximately 1.5-2.1 folds higher than the control treatment. These treatments also improved NPK availability in soil and; hence, increased their contents within plant tubers. Consequently, these treatments decreased the disease incidence and severity caused by S. rolfsii while improved shoot biomass and tuber yield. In spite of that, these results stood below the prospective of the fungicide treatment. The integrated treatments i.e. "humic acid + AMF", "Sulphex + AMF" and "ABZ + AMF" caused further significant improvements in both NPK availabilities in soil and plant areal bio-masses. This probably induced further plant resistance against the investigated soil-borne pathogen while recorded insignificant variations in disease incidence and severity when compared with the fungicide treatment. Moreover, the integrated treatments increased the tuber yields beyond those attained for the fungicide treatment. Accordingly, such integrated strategies can completely substitute the chemical fungicides; thus, minimize their negative impacts on the ecosystem.

Depthprofile distribution of Cs and its toxicity for canola plants grown on arid rainfed soils as affected by increasing K-inputs

Radioactive cesium (Cs) is more likely to be trans-located via rainfall into surrounding environments. Upon Cs-contaminated water reaching soil, Cs is retained on soil components, mainly organic matter and clay fraction. This study aims are i) comparing the relative ability of five arid soils, differing in their textural and chemical properties, to accumulate Cs when subjected to Cs-artificially contaminated rain droplets and ii) testing whether K fertilizer can decrease the uptake of Cs and its translocation within plants or not. A lab experiment was then conducted to simulate artificial rain droplets contaminated with 1000 becquerel (Bq) of ¹³⁴Cs L^-1 precipitated on soil columns each of 10.5 cm inner diameter at a rate of 1.15 mL cm^-2 over a period of 2-months. At least 89% of ¹³⁴Cs accumulated within the uppermost 5-cm layer of these soils. Another greenhouse experiment was set to test the hypothesis which indicates that Cs uptake increases unexpectedly by supplying plants with K-fertilizers. In this experiment, canola (Brassica napus L.) seeds were cultivated into three K-deficient soils (Typic Haplotorrent, Typic Haplocalcid, and Typic Torripsamment) which were contaminated with 100 mg Cs kg^-1 soil (stable-Cs was used instead of radioactive-Cs to designate its behavior on the long run). Canola plants were fertilized with 0, 80 and 120 mg K₂SO₄ kg^-1 soil. Results carried on Typic Haplotorrent soil confirmed the aforementioned assumption as K-addition increased Cd-uptake up to 40.1%. Contradictory results were achieved in the other two soils where Cs-uptake decreased by 21.5 and 15.3% in Typic Haplocalcid and Typic Torripsamment soils, respectively due to the application of the aforementioned dose of K. In the K non-amended soils, Cs shoot-root translocation factor was >1; yet, it was <1 in response to K addition, regardless of its application rate.

Feasibility of using natural mineral ores for removing Cs and Sr from contaminated water

Proper and economical treatments of wastewater are among the important and potential solutions to increase the water budget. Although mineral ores are barriers of potentially toxic metal contaminants; however to what extent, can these ores stand successfully for decontaminating waters polluted with Cs or Sr is the question of the current study. Therefore a trial was carried out on some of these ores i.e. kaolinite, montmorillonite, and illite, to investigate their effects as decontaminants for waters polluted with either 50 μg Cs L^-1 or 50 μg Sr L^-1. Results showed that sorption of Cs and Sr increased with decreasing the ratio of the applied sorbents to the quantities of contaminated waters. Such a finding was more obvious when the rate of the sorbent: water was only 1 g L^-1. The highest sorption was attained by montmorillonite followed by kaolinite, then Illite. Thus, montmorillonite was selected to complete the sorption studies at a rate of 1 g L^-1. Sorption of both Cs and Sr and consequently their removal efficiencies increased with increasing the pH of the sorbents-contaminated waters suspensions up to 7 beyond which significant reductions occurred. Also, increasing the temperature of the suspension resulted in significant increases in the removal efficiencies of the investigated sorbents. Only 120 min were enough to attain the highest removal efficiency. Moreover, Ca-salts could successfully substitute sorbed Cs and Sr on surfaces of the montmorillonite used previously for decontamination of these elements from waters. Accordingly, this mineral ore can be reused successively for further decontamination processes.

Use of plant growth promoting Rhizobacteria (PGPR) and mycorrhizae to improve the growth and nutrient utilization of common bean in a soil infected with white rot fungi

Extensive use of fertilizers and pesticides led to dangerous ecological effects and therefore the biological approaches have been widely recommended to prevent further deterioration for the environment. The current study was conducted to explore the potentiality of using single or combined inoculations by mycorrhizae, Bacillus subtilis and Pseudomonas fluorescence for controlling the infection of common bean plants with Sclerotium rolfsii on one hand and as bio-fertilizers for improving plants nutritional status on the other hand. The soil of study was mildly infected with S. rolfsii and contained high total-P content. Thus, minimal P inputs were added to the inoculated soil in the form of rock phosphate. Activities of plant defense enzymes i.e. chitinase, peroxidase and polyphenol oxidase were determined under the greenhouse conditions and the results obtained herein indicated that activities of such enzymes increased significantly owing to bio-agent inoculations. In this concern, combined treatments resulted in further significant increases over the single ones. A field study was then conducted for two successive years and the results reveal that single inoculations increased straw and green pod yields as well as the uptake of P and Fe by plants as compared with the non-inoculated treatment. Combined inoculants recorded further significant increases in these parameters even when compared with the fungicide treated plants. Generally, straw and pod yields obtained from the second growing season were significantly higher than those attained in the first growing one. Our study confirms the success of the used bio-treatments in minimizing soil pollution through fertilizer and/or pesticide inputs.

Cow manure-loaded biochar changes Cd fractionation and phytotoxicity potential for wheat in a natural acidic contaminated soil

The current study aims to investigate the implications of amending a soil contaminated with Cd with peanut residues biochar (BP) solely or in combination with cow manure (CMPB) at different rates on phytotoxicity of Cd for wheat plants and its distribution in a mine contaminated soil. Soil pH and EC increased progressively in soils amended with either PB or CMPB. Exchangeable Cd was decreased while its non-exchangeable fractions were increased. Dry weights of wheat straw, roots and grains increased when soils amended with either PB or CMPB, especially at the higher application rate. Such increases were correlated significantly with the extractable soil-Cd. Concentrations of Cd in roots were higher than those in straw; whereas, the concentrations in grains seemed to be the lowest. Generally, values of bio-concentration and translocation factors did not exceed "1" and decreased with application of either PB or CMPB. In conclusion, enriching biochar with cow manure is a recommended strategy to reduce Cd uptake and translocation to straw and seeds. Moreover, Concentrations of Cd did not exceed the permissible levels in grains when soils amended with the highest rate of CMPB.

Feasibility of biochar manufactured from organic wastes on the stabilization of heavy metals in a metal smelter contaminated soil

The main objectives of the current study were to evaluate the potential effects of biochar derived from sugar cane bagasse (SC-BC) and orange peel (OP-BC) on improving the physicochemical properties of a metal smelter contaminated soil, and determining its potentiality for stabilizing Pb and As in soil. To achieve these goals, biochar was produced in a small-scale biochar producing plant, and an incubation experiment was conducted using a silt loam metal-contaminated soil treated with different application rates of biochar (0-10% w/w). The obtained results showed that, the addition of SC-BC and OP-BC increased significantly the soil aggregate stability, water-holding capacity, cation exchange capacity, organic matter and N-status in soil. SC-BC considerably decreased the solubility of Pb to values lower than the toxic regulatory level of the toxicity characteristics leaching procedure extraction (5 mg L(-1)). The rise in soil pH caused by biochar application, and the increase of soil organic matter transformed the labile Pb into less available fractions i.e. "Fe-Mn oxides" and "organic" bound fractions. On the other hand, As was desorbed from Fe-Mn oxides, which resulted in greater mobility of As in the treated soil. We concluded that SC-BC and OP-BC could be used successfully for remediating soils highly contaminated with Pb. However, considerable attention should be paid when using it in soil contaminated with As.

Role of EDTA in arsenic mobilization and its uptake by maize grown on an As-polluted soil

EDTA amendments are widely used for micronutrient fertilization in arid soils, besides their effectiveness in the remediation process of heavy metal from contaminated soils. However, the persistence of EDTA in arsenic contaminated soil may have further negative effects on the grown plants. To investigate the influences of EDTA on soil As, a pot experiment was conducted using a sandy clay loam As-polluted soil treated with gradual rates of EDTA (0, 1.0, 2.5 and 5 mmol kg(-1)) and planted with maize for two months. The key findings reveal that EDTA applications increased AB-DTPA extractable and water soluble As significantly. Such increases seemed to be the main reasons behind the increase in As uptake by maize plants as the addition of EDTA at the rates of 1.0, 2.5 and 5.0 mmol kg(-1) increased significantly As uptake by shoots 1.5, 2.4 and 3.0 folds, respectively compared to the untreated soil. On the other hand, As uptake by roots did not increase significantly except with the highest application rates of 2.5 and 5.0 mmol kg(-1). The results also show that arsenic translocation factor (TF) values were too low to attain successful phytoextraction. In conclusion, the bioavailable fraction of As is important to investigate the phytoextraction and phytotoxicity of As.