Simultaneous Removal of Lindane, Lead and Cadmium from Soils by Rhamnolipids Combined with Citric Acid

Biosurfactant-mediated transport of tetracycline antibiotics in saturated porous media: Combined effects of the chemical properties of contaminants and solution chemistry conditions

The mobility of tetracycline antibiotics (TCs) in saturated aquifers is possibly affected by the presence of biosurfactants, which are widespread in the aquatic/soil environments. This study investigated the mobility characteristics of various tetracyclines-specifically tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC)-within quartz sand columns in the presence of rhamnolipid, a common biosurfactant. Exogenous rhamnolipid significantly inhibited the transport of the three TCs over the pH range of 5.0-9.0 (e.g., the mass of retained TC, OTC, and CTC increased from 32.6 %, 26.9 %, and 39.2 % (in the absence rhamnolipid) to 39.4 %, 38.9 %, and 51.7 % (in the presence of rhamnolipid), respectively). This observation could be attributed to the bridging effects of this biosurfactant. Specifically, the hydrophilic head of rhamnolipid molecules is likely associated with the surfaces of sand grains through surface complexation and/or hydrogen bonding interactions. Accordingly, the hydrophobic moieties of the deposited rhamnolipid molecules (i.e., the aliphatic chains) interact with the hydrophobic groups of TCs molecules via hydrophobic interactions. Interestingly, the extent of the inhibitory effect on CTC mobility was greater than that on OTC and TC, which was related to the different hydrophobic characteristics of the three antibiotics. Furthermore, the inhibitory effect of rhamnolipid on the transport of TCs diminished as the pH of the background solution increased. This observation was attributed to the weakened bridging effects, resulting from the reduced deposition of the biosurfactant on the sand surfaces. Additionally, the cation-bridging mechanism involved in the retention of TCs in the addition of rhamnolipid when the background electrolyte was Ca2+ (i.e., Ca2+ ions served as bridging agents between the deposited rhamnolipid molecules and TCs). The insightful findings enhance our understanding of the critical roles of biosurfactants in influencing the environmental dynamics and ultimate fate of conventional antibiotic pollutants within groundwater systems.

Microbe cultivation guidelines to optimize rhamnolipid applications

In the growing landscape of interest in natural surfactants, selecting the appropriate one for specific applications remains challenging. The extensive, yet often unsystematized, knowledge of microbial surfactants, predominantly represented by rhamnolipids (RLs), typically does not translate beyond the conditions presented in scientific publications. This limitation stems from the numerous variables and their interdependencies that characterize microbial surfactant production. We hypothesized that a computational recipe for biosynthesizing RLs with targeted applicational properties could be developed from existing literature and experimental data. We amassed literature data on RL biosynthesis and micellar solubilization and augmented it with our experimental results on the solubilization of triglycerides (TGs), a topic underrepresented in current literature. Utilizing this data, we constructed mathematical models that can predict RL characteristics and solubilization efficiency, represented as logPRL = f(carbon and nitrogen source, parameters of biosynthesis) and logMSR = f(solubilizate, rhamnolipid (e.g. logPRL), parameters of solubilization), respectively. The models, characterized by robust R2 values of respectively 0.581-0.997 and 0.804, enabled the ranking of descriptors based on their significance and impact-positive or negative-on the predicted values. These models have been translated into ready-to-use calculators, tools designed to streamline the selection process for identifying a biosurfactant optimally suited for intended applications.

A critical review of sustainable pesticide remediation in contaminated sites: Research challenges and mechanistic insights

Incidental pesticide application on farmlands can result in contamination of off-target biota, soil, groundwater, and surrounding ecosystems. To manage these pesticide contaminations sustainably, it is important to utilize advanced approaches to pesticide decontamination. This review assesses various innovative strategies applied for remediating pesticide-contaminated sites, including physical, chemical, biological, and nanoremediation. Integrated remediation approaches appear to be more effective than singular technologies. Bioremediation and chemical remediation are considered suitable and sustainable strategies for decontaminating contaminated soils. Furthermore, this study highlights key mechanisms underlying advanced pesticide remediation that have not been systematically studied. The transformation of applied pesticides into metabolites through various biotic and chemical triggering factors is well documented. Ex-situ and in-situ technologies are the two main categories employed for pesticide remediation. However, when selecting a remediation technique, it is important to consider factors such as application sites, cost-effectiveness, and specific purpose. In this review, the sustainability of existing pesticide remediation strategies is thoroughly analyzed as a pioneering effort. Additionally, the study summarizes research uncertainties and technical challenges associated with different remediation approaches. Lastly, specific recommendations and policy advocacy are suggested to enhance contemporary remediation approaches for cleaning up pesticide-contaminated sites.

Natural surfactant mediated bioremediation approaches for contaminated soil

The treatment of environmental pollution by employing microorganisms is a promising technology, termed bioremediation, which has several advantages over the other established conventional remediation techniques. Consequently, there is an urgent inevitability to develop pragmatic techniques for bioremediation, accompanied by the potency of detoxifying soil environments completely. The bioremediation of contaminated soils has been shown to be an alternative that could be an economically viable way to restore polluted soil. The soil environments have long been extremely polluted by a number of contaminants, like agrochemicals, polyaromatic hydrocarbons, heavy metals, emerging pollutants, etc. In order to achieve a quick remediation overcoming several difficulties the utility of biosurfactants became an excellent advancement and that is why, nowadays, the biosurfactant mediated recovery of soil is a focus of interest to the researcher of the environmental science field specifically. This review provides an outline of the present scenario of soil bioremediation by employing a microbial biosurfactant. In addition to this, a brief account of the pollutants is highlighted along with how they contaminate the soil. Finally, we address the future outlook for bioremediation technologies that can be executed with a superior efficiency to restore a polluted area, even though its practical applicability has been cultivated tremendously over the few decades.

Biosurfactant-affected mobility of oxytetracycline and its variations with surface chemical heterogeneity in saturated porous media

Herein, the influences of rhamnolipid (a typical biosurfactant) on oxytetracycline (OTC) transport in the porous media and their variations with the surface heterogeneities of the media (uncoated sand, goethite (Goe)-, and humic acid (HA)-coated sands) were explored. Compared to uncoated sand, goethite and HA coatings suppressed OTC mobility by increasing deposition sites. Interestingly, rhamnolipid-affected OTC transport strongly depended on the chemical heterogeneities of aquifers and biosurfactant concentrations. Concretely, adding rhamnolipid (1-3 mg/L) inhibited OTC mobility through sand columns because of the bridging effect of biosurfactant between sand and OTC. Unexpectedly, rhamnolipid of 10 mg/L did not further improve the inhibition of OTC transport owing to the fact that the deposition capacity of rhamnolipid reached its maximum. OTC mobility in Goe-coated sand columns was inhibited by 1 mg/L rhamnolipid. However, the inhibitory effect decreased with the increasing rhamnolipid concentration (3 mg/L) and exhibited a promoted effect at 10 mg/L rhamnolipid. This surprising observation was that the increased rhamnolipid molecules gradually occupied the favorable deposition sites (i.e., the positively charged sites). In comparison, rhamnolipid facilitated OTC transport in the HA-coated sand column. The promotion effects positively correlated with rhamnolipid concentrations because of the high electrostatic repulsion and deposition site competition induced by the deposited rhamnolipid. Another interesting phenomenon was that rhamnolipid's enhanced or inhibitory effects on OTC transport declined with the increasing solution pH because of the decreased rhamnolipid deposition on porous media surfaces. These findings benefit our understanding of the environmental behaviors of antibiotics in complex soil-water systems containing biosurfactants.

Permeable reactive composite approaching cathode enhanced Cr removal in soil using the byproduct of electrokinetic technology: emphasized energy utilization efficiency

Cost-effective techniques with significant removal rates and low energy consumption are urgently required for in-situ Cr-contaminated soil remediation to reduce potential environmental toxicity to the ecosystem and human bodies. Electrokinetic technology is a valuable and promising soil remediation technology; however, the acidic and alkaline fronts evolution induced by the electrokinetic byproducts (H+, OH-) has significant hindering characteristics for ion removal. To effectively utilize the byproducts for enhancing Cr elimination, this paper proposed the permeable reactive composite approaching cathode with rhamnolipid-modified biochar as reactive material. Power utilization efficiency (η) was presented to comprehensively evaluate the target species elimination effect, considering removal rate and energy consumption. Results suggested that biosurfactant rhamnolipid stimulated Cr removal in acid and base fronts. Acid front induced rhamnolipid protonation reducing anolyte Cr(VI) to Cr(III), and base front induced rhamnolipid deprotonation complexing with Cr(III) and expediting Cr(VI) dissolution by electrostatic repulsion. Permeable reactive composite approaching cathode induced the maximum removal rate of Cr(VI) and Cr(III) in each section by impelling the alkaline front. Approaching cathode caused increased resistance and energy consumption in the near-anode regions, ultimately decreasing energy utilization efficiency. Optimized moving frequency and applied potential magnitude could adjust power consumption distribution in a single soil layer to obtain better electrokinetic removal performance of contaminates. This work provided essential scientific and practical importance for in-situ electrokinetic remediation of Cr(VI) and Cr(III), considering elimination efficiency and energy consumption in the future.

Shifts of lipid metabolites help decode immobilization of soil cadmium under reductive soil disinfestation

Cadmium (Cd) contamination in soil can cause serious environmental problems and threaten human health. Previous studies have shown that the reductive soil disinfestation (RSD) is regarded as an effective soil disinfection technology, which will affect the bioavailability of Cd. However, the influence of soil microorganisms and their metabolites on the morphologies of Cd during RSD treatment are still poorly understood. Here, a laboratory incubation experiment that composed of untreated soil (CK), two RSD treatments with flooded soil (FL) and added 2% bean dregs soil (BD) was conducted. After the treatment, the content of different morphologies of Cd in the soil and the molecular characteristics (the composition of the microbial community, functional enzymes and metabolites) of the soil were measured. The study found that, compared to CK treatment, the dominant phyla, such as Acidobacteria, Bacteroidetes, Firmicutes, etc., were significantly increased in BD treatment, and enzymes related to metabolism also showed noticeable enhancement. The differential accumulated metabolite (DAM) analysis revealed that the abound of lipids and lipid-like molecules involved with fatty acyls, steroids and steroid derivatives, glycerophospholipids, fatty acids and conjugates, glycerolipids, and sphingolipids were significant different among treatments. The correlation analysis showed the exchangeable fraction cadmium contents (EX-Cd) were negatively correlated with the content of glycerophospholipids and sphingolipids, and positively correlated with glycerolipids content. However, the relationship between the residual cadmium (RS-Cd) and these three metabolites was just the opposite. Compared with another two treatments, the BD treatment significantly reduced EX-Cd contents. Biological interaction network analysis indicated that the phyla Gemmatimonadetes and Proteobacteria assumed the primary responsibility for the morphological transformation of Cd through their corresponding functional enzymes. Overall, this study provided a new perspective on RSD-mediated soil Cd immobilization, and the findings should be beneficial to further applications of RSD technology on the remediation of Cd-polluted soils.

Integrated soil washing and bioreactor systems for the treatment of hexachlorocyclohexane contaminated soil: A review on enhanced degradation mechanisms, and factors affecting soil washing and bioreactor performances

Investigations about the remediation of Hexachlorocyclohexane (HCH), a persistent organic pollutant of global concern, have been extensively reported to treat the HCH contaminated soil. The difficulty arising due to desorption and long ageing procedures of this hydrophobic organic compound in the soil, make it necessary to exploit techniques like soil washing or addition of surfactants, for enhancing the mass transfer rate of hydrophobic compounds. However, this technique gives rise to the generation of a large quantity of waste solution containing the pollutant and various other toxic substances. Moreover, it is challenging to deal with the complex soil washing solution, and thus a follow-up treatment of such washing solution is essentially required before its discharge. This follow-up treatment could be the bioreactor system to efficiently treat the pollutant in the wash solution, thereby reducing the amount of contaminated soil that has to be treated. Among many suggested remediation methods and treatment technologies, integrated soil washing and post-treatment with the bioreactor system could be an environmentally viable method for the remediation of HCH contaminated sites. This review focuses on the soil washing procedures applied so far for the HCH contaminated soil and various factors affecting the efficiency of separation of the target pollutant. Furthermore, the environmental and reactor design-related factors are also discussed for degradation of HCH in the reactor system. Finally, advantages and environmental feasibility of this proposed combined technology and the challenges that need to be encountered are envisaged.

Efficient Inorganic/Organic Acid Leaching for the Remediation of Protogenetic Lead-Contaminated Soil

In this study, inorganic acid and organic acid were used to leach and remediate superheavy, lead-contaminated protogenetic soil with a lead pollution level of 8043 mg∙kg−1. Among the compounds studied, HCl and citric acid (CA) presented the best effects, respectively. Under the optimal experimental conditions, the remediation efficiency of 0.05 mol∙L−1 CA reached 53.6%, while that of 0.2 mol∙L−1 HCl was 70.3%. According to the lead morphology analysis, CA and HCl have certain removal ability to different fractions of lead. Among them, the removal rates of acid-soluble lead in soil by HCl and CA are 93% and 83%, and the soil mobility factor (MF) value decreased from 34.4% to 7.74 % and 12.3%, respectively, indicating that the harm of lead in soil was greatly reduced. Meanwhile, the leaching mechanisms of CA and HCl were studied. The pH values of the soil after leaching with HCl and CA were 3.88 and 6.97, respectively, showing that HCl leaching has caused serious acidification of the soil, while the process of CA leaching is more mild. CA has a relatively high remediation efficiency at such a low concentration, especially for the highly active acid-soluble fraction lead when maintaining the neutrality of the leached soil. Hence, CA is more suitable for the remediation of lead-contaminated soil.

Characteristic properties of spray-drying Bifidobacterium adolescentis microcapsules with biosurfactant

The surfactants used for emulsion is one of the best techniques for microencapsulation of lactic acid bacteria (LAB) since it is economical. The biosurfactants have many advantages such as lower toxicity, higher biodegradability. In this study, microcapsules were prepared via spray drying using Bifidobacterium adolescentis species cultured in soy milk extract with biosurfactant prepared using Alcaligenes piechaudii CC-ESB2 to improve their powder properties. The soy milk was used to increase the health benefits instead of the milk. The optimum bacterial strain viability, water activity, and moisture content of the microcapsules were achieved at a spray dryer inlet/outlet temperature of 120/60°C. The composition of the carrier affects the particle size of the microcapsules. Using 90% maltodextrin (MD), 5% isomalto-oligosaccharide syrup (IMOS) and 5% biosurfactant as a carrier increased the viability of the LAB. Scanning electron microscope observations showed that the LAB microcapsules were able to effectively retain their completeness. Furthermore, microcapsules added with a biosurfactant prepared using A. piechaudii CC-ESB2 displayed significantly better flow properties than those without the surfactant and biosurfactant, which indicates that the biosurfactant assists in enhancing the powder properties of the microcapsules. It also has sufficient biological activity as a LAB product because the probiotics exceed 10⁶ CFU/mL The spray-dried abandoned supernatant with biosurfactant exhibited superior bacteriostasis, which suggests that the supernatant of B. adolescentis during microencapsulation not only retains its bacteriostatic effect under high spray drying temperatures, but also provides additional antibacterial effects for the microcapsules.

Biosurfactant is a powerful tool for the bioremediation of heavy metals from contaminated soils

Heavy metal toxicity has become a pressing ecological problem that affects the ecosystems through bioaccumulation, representing a serious public health hazard. Many conventional strategies have been developed and applied to decontaminate and restore metal-contaminated areas. However, these conventional approaches are not very suitable and environmentally safe for heavy metal remediation because of their high operational costs, high energy requirements, post-waste disposal problems, and secondary pollutant generation. Thus, biosurfactant-based bioremediation of heavy metals is a sustainable and promising approach because of its biodegradation capability, economic effectiveness, and ecofriendly nature. Pseudomonas sp., Bacillus sp., Citrobacter freundii, and Candida tropicalis have been isolated as potential sources of biosurfactants and produce compounds such as surfactin, rhamnolipids, and sophorolipids. Owing to the severity of heavy metal pollution in certain parts of the environment, biosurfactants have garnered great interest and attention as an emerging multi-functional technology of the new century for successful removal of heavy metal pollutants. The present study describes the role of biosurfactants in the bioremediation of heavy metals from contaminated environments. Moreover, the interaction mechanism underlying biosurfactant-metal complexation and metal remediation are discussed. Based on the review of the literature, further research is warranted to elucidate the mechanistic roles and explore the structural characterization and gene regulation of biosurfactants to improve their productivity and expand their applicability in bioremediation.

Hexachlorocyclohexane toxicity in water bodies of Pakistan: challenges and possible reclamation technologies

Pakistan is an agro-economy country where hexachlorocyclohexane (HCH) pesticides are being used to improve crop productivity, as a result the risk of contamination of soil and sediment has been increased. HCH exhibits all the characteristics of persistent organic pollutants (POP), and was therefore added to the list of 'new POPs' in 2009. This review report revealed that the major rivers of Pakistan such as the Indus Basin, River Ravi, River Chenab and their tributaries all are contaminated with HCH and the highest residual concentration (4,090 ng/g) was detected in a pesticide burial ground in Hyderabad city. Major sources of HCH contamination were identified as agricultural runoff, discharge of untreated industrial effluents and surface runoff. In order to manage HCH pollution, various ex-situ and in-situ remediation techniques along with their merits and demerits are thoroughly reviewed. Among these, microbial bioremediation is a low cost, environment friendly, effective in-situ remediation technique for remediation of HCH. Overall, the information provided in this manuscript will provide a future reference to the scientific community and bridge the knowledge gap between HCH release in the environment and their mitigation through proper treatment methods.

Sustainable Remediation of Contaminated Soil Using Biosurfactants

Selection of the most appropriate remediation technology must coincide with the environmental characteristics of the site. The risk to human health and the environment at the site must be reduced, and not be transferred to another site. Biosurfactants have the potential as remediation agents due to their biodegradability, low toxicity, and effectiveness. Selection of biosurfactants should be based on pollutant characteristics and properties, treatment capacity, costs, regulatory requirements, and time constraints. Moreover, understanding of the mechanisms of interaction between biosurfactants and contaminants can assist in selection of the appropriate biosurfactants for sustainable remediation. Enhanced sustainability of the remediation process by biosurfactants can be achieved through the use of renewable or waste substrates, in situ production of biosurfactants, and greener production and recovery processes for biosurfactants. Future research needs are identified.

Towards Rational Biosurfactant Design-Predicting Solubilization in Rhamnolipid Solutions

The efficiency of micellar solubilization is dictated inter alia by the properties of the solubilizate, the type of surfactant, and environmental conditions of the process. We, therefore, hypothesized that using the descriptors of the aforementioned features we can predict the solubilization efficiency, expressed as molar solubilization ratio (MSR). In other words, we aimed at creating a model to find the optimal surfactant and environmental conditions in order to solubilize the substance of interest (oil, drug, etc.). We focused specifically on the solubilization in biosurfactant solutions. We collected data from literature covering the last 38 years and supplemented them with our experimental data for different biosurfactant preparations. Evolutionary algorithm (EA) and kernel support vector machines (KSVM) were used to create predictive relationships. The descriptors of biosurfactant (logP_BS, measure of purity), solubilizate (logP_sol, molecular volume), and descriptors of conditions of the measurement (T and pH) were used for modelling. We have shown that the MSR can be successfully predicted using EAs, with a mean R² _val of 0.773 ± 0.052. The parameters influencing the solubilization efficiency were ranked upon their significance. This represents the first attempt in literature to predict the MSR with the MSR calculator delivered as a result of our research.

Comparing straw, compost, and biochar regarding their suitability as agricultural soil amendments to affect soil structure, nutrient leaching, microbial communities, and the fate of pesticides

The emission of nutrients and pesticides from agricultural soils endangers natural habitats. Here, we review to which extent carbon-rich organic amendments help to retain nutrients and pesticides in agricultural soils and to reduce the contamination of surrounding areas and groundwater. We compare straw, compost, and biochar to see whether biochar outperforms the other two more traditional and cheaper materials. We present a list of criteria to evaluate the suitability of organic materials to be used as soil amendments and discuss differences in elemental compositions of straw, compost, and biochar to understand, how soil microorganisms utilize those materials. We review their effects on physical and chemical soil characteristics, soil microbial communities, as well as effects on the transformation and retention of nutrients and pesticides in detail. It becomes clear that for all three amendments their effects can vary greatly depending on numerous aspects, such as the type of soil, application rate, and production procedure of the organic material. Biochar is most effective in increasing the sorption capacity of soils but does not outperform straw and compost with regards to the other aspects investigated. Nevertheless, the possibility to design biochar properties makes it a very promising material. Finally, we provide critical comments about how to make studies about organic amendments more comparable (comprehensive provision of material properties), how to improve concepts of future work (meta-analysis, long-term field studies, use of deep-insight microbial DNA sequencing), and what needs to be further investigated (the link between structural and functional microbial parameters, the impact of biochar on pesticide efficiency).

Citric acid from Aspergillus niger: a comprehensive overview

Microbial citric acid has high economic importance and widely used in beverage, food, detergents, cosmetics and pharmaceutical industries. The filamentous fungus Aspergillus niger is a work horse and important cell factory in industry for the production of citric acid. Although in-depth literatures and reviews have been published to explain the biochemistry, biotechnology and genetic engineering study of citric acid production by Aspergillus niger separately but the present review compiled, all the aspects with upto date brief summary of the subject describing microorganisms, substrates and their pre-treatment, screening, fermentation techniques, metabolic engineering, biochemistry, product recovery and numerous biotechnological application of citric acid for simple understanding of microbial citric acid production. The availability of genome sequence of this organism has facilitated numerous studies in gene function, gene regulation, primary and secondary metabolism. An attempt has been also made to address the molecular mechanisms and application of recent advanced techniques such as CRISPR/Cas9 systems in enhancement of citric acid production.

Removal of Lindane from Aqueous Solution Using Aluminum Hydroxide Nanoparticles with Surface Modification by Anionic Surfactant

In the present study, we investigated the removal of an emerging pesticide lindane from aqueous solution using synthesized aluminum hydroxide Al(OH)₃ (bayerite) nanomaterials with surface modification by an anionic surfactant sodium dodecyl sulfate (SDS). The Al(OH)₃ nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) and zeta potential. The lindane removal using SDS-modified nano-aluminum hydroxide nanoparticles (SMNAH) achieved removal of up to 93.68%, which was 3.3 times higher than that of nano-aluminum hydroxide nanoparticles. The adsorptive removal conditions were studied and found to have an adsorption time of 60 min, a pH of 6, an adsorbent dosage of 25 mg/mL and an ionic strength of 10 mM NaCl. After reusing four times, the removal efficiency of lindane using SMNAH still reached 75%. Two-step adsorption can fit adsorption isotherms of lindane onto SMNAH at two salt concentrations. On the basis of the change in zeta potential, surface functional groups and adsorption isotherms, we suggest that the formation of a bilayer micelle induced the removal of lindane.

Synergistic Effect of Rhamnolipid and Saponin Biosurfactants on Removal of Heavy Metals from Oil Contaminated Soils

In this study synergistic effect of the biosurfactants saponin and rhamnolipid on the removal of the heavy metals such as vanadium, nickel and chromium from contaminated soil was investigated. Washing solutions were prepared by using different concentrations of two biosurfactants. In this work, the optimum HLB value of the extraction process of about 10.5 was obtained for the mixture of 62.5 % rhamnolipid and 37.5 % saponin. According to our results, at the optimal HLB value, a maximum removal was obtained for Ni of 87 %, Cr of 71 % and Va of 70 %. Our results also showed that the efficiency of heavy metals decreased with increasing the pH value of system. The optimum pH value of heavy metals removal was 5. According to the results of this research saponin and rhamnolipid have the synergistic effect on the heavy metals removal and it seems to be a good alternative to chemical surfactants for environmental applications.

Advances in applications of rhamnolipids biosurfactant in environmental remediation: A review

The objective of this review is to provide a comprehensive overview of the advances in the applications of rhamnolipids biosurfactants in soil and ground water remediation for removal of petroleum hydrocarbon and heavy metal contaminants. The properties of rhamnolipids associated with the contaminant removal, that is, solubilization, emulsification, dispersion, foaming, wetting, complexation, and the ability to modify bacterial cell surface properties, were reviewed in the first place. Then current remediation technologies with integration of rhamnolipid were summarized, and the effects and mechanisms for rhamnolipid to facilitate contaminant removal for these technologies were discussed. Finally rhamnolipid-based methods for remediation of the sites co-contaminated by petroleum hydrocarbons and heavy metals were presented and discussed. The review is expected to enhance our understanding on environmental aspects of rhamnolipid and provide some important information to guide the extending use of this fascinating chemical in remediation applications.

Early Detection of Biofouling on Water Purification Membranes by Ambient Ionization Mass Spectrometry Imaging

By direct analysis of water purification membranes using ambient ionization mass spectrometry, an attempt has been made to understand the molecular signatures of bacterial fouling. Membrane based purification methods are used extensively in water treatment, and a major challenge for them is biofouling. The buildup of microbes and their extracellular polymeric matrix clog the purification membranes and reduce their efficiency. To understand the early stages of bacterial fouling on water purification membranes, we have used desorption electrospray ionization mass spectrometry (DESI MS), where ion formation occurs in ambient conditions and the ionization event is surface sensitive. Biosurfactants at the air-water interface generated by microorganisms as a result of quorum sensing, influence the water-membrane interface and are important for the bacterial attachment. We show that these biosurfactants produced by bacteria can be indicator molecular species signifying initiation of biofilms on membrane surfaces, demonstrated by specific DESI MS signatures. In Pseudomonas aeruginosa, one of the best studied models for biofilm formation, this process is mediated by rhamnolipids forewarning bacterial fouling. Species dependent variation of such molecules can be used for the precise identification of the microorganisms, as revealed by studies on P. aeroginosa (ATCC 25619). The production of biosurfactants is tightly regulated at the transcriptional level by the quorum-sensing (QS) response. Thus, secretion of these extracellular molecules across the membrane surface allows rapid screening of the biofilm community. We show that, the ambient ionization mass spectrometry can detect certain toxic heavy metals present in water, using surfactant-metal complexes as analytes. We believe that such studies conducted on membranes in various input water streams will help design suitable membrane processes specific to the input streams.

Soy molasses as a fermentation substrate for the production of biosurfactant using Pseudomonas aeruginosa ATCC 10145

Soy molasses is a product co-generated during soybean processing that has high production and low commercial value. Its use has great potential in fermentative processes due to the high concentration of carbohydrates, lipids and proteins. This study investigated the use of Pseudomonas aeruginosa to produce biosurfactants in a soy molasses-based fermentation medium. A central composite design (CCD) was prepared with two variables and three replicates at the central point to optimize the production of biosurfactant. The concentration of soy molasses had values between 29.3 and 170.7 g/L and the initial concentration of microorganism varied between 0.2 and 5.8 g/L. All the experiments were performed in duplicate on a shaker table at 30.0 ± 1.0 °C and 120 rpm for 72 h with samples taken every 12 h. Thus, to validate the experiments, the values of 120 g/L for the initial concentration of soy molasses and 4 g/L for the initial concentration of microorganisms were used. In response, the following values were obtained at 48 h of fermentation: surface tension of 31.9 dyne/cm, emulsifying index of 97.4%, biomass concentration of 11.5 g/L, rhamnose concentration of 6.9 g/L and biosurfactant concentration of 11.70 g/L. Further analysis was carried out for critical micelle concentration (CMC) which was obtained at approximately 80 mg/L. The bands found in Fourier transform infrared spectroscopy analysis had characteristic glycolipids as reported in the literature. These values show a great potential for biosurfactant production using soy molasses as a substrate and bacteria of the species P. aeruginosa.

Heavy metal (Cu, Cd, Pb, Cr) washing from river sediment using biosurfactant rhamnolipid

Heavy metal-contaminated sediments posed a serious threat to both human beings and environment. A biosurfactant, rhamnolipid, was employed as the washing agent to remove heavy metals in river sediment. Batch experiments were conducted to test the removal capability. The effects of rhamnolipid concentration, washing time, solution pH, and liquid/solid ratio were investigated. The speciation of heavy metals before and after washing in sediment was also analyzed. Heavy metal washing was favored at high concentration, long washing time, and high pH. In addition, the efficiency of washing was closely related to the original speciation of heavy metals in sediment. Rhamnolipid mainly targeted metals in exchangeable, carbonate-bound or Fe-Mn oxide-bound fractions. Overall, rhamnolipid biosurfactant as a washing agent could effectively remove heavy metals from sediment.

Advanced technologies for the remediation of pesticide-contaminated soils

The occurrence of pesticides in soil has become a highly significant environmental problem, which has been increased by the vast use of pesticides worldwide and the absence of remediation technologies that have been tested at full-scale. The aim of this review is to give an overview on technologies really studied and/or developed during the last years for remediation of soils contaminated by pesticides. Depending on the nature of the decontamination process, these techniques have been included into three categories: containment-immobilization, separation or destruction. The review includes some considerations about the status of emerging technologies as well as their advantages, limitations, and pesticides treated. In most cases, emerging technologies, such as those based on oxidation-reduction or bioremediation, may be incorporated into existing technologies to improve their performance or overcome limitations. Research and development actions are still needed for emerging technologies to bring them for full-scale implementation.

Citric acid: emerging applications of key biotechnology industrial product

Owing to new biotechnological production units mostly located in China, global supply of citric acid in the course of the last two decades rose from less than 0.5 to more than 2 million tonnes becoming the single largest chemical obtained via biomass fermentation and the most widely employed organic acid. Critically reviewing selected research achievements and production trends, we identify the reasons for which this polycarboxylic acid will become a key chemical in the emerging bioeconomy.Graphical abstract