Polyaromatic hydrocarbons (PAHs) are considered as hazardous organic priority pollutants. PAHs have immense public concern and critical environmental challenge around the globe due to their toxic, ...carcinogenic, and mutagenic properties, and their ubiquitous distribution, recalcitrance as well as persistence in environment. The knowledge about harmful effects of PAHs on ecosystem along with human health has resulted in an interest of researchers on degradation of these compounds. Whereas physico-chemical treatment of PAHs is cost and energy prohibitive, bioremediation i.e. degradation of PAHs using microbes is becoming an efficient and sustainable approach. Broad range of microbes including bacteria, fungi, and algae have been found to have capability to use PAHs as carbon and energy source under both aerobic and anaerobic conditions resulting in their transformation/degradation. Microbial genetic makeup containing genes encoding catabolic enzymes is responsible for PAH-degradation mechanism. The degradation capacity of microbes may be induced by exposing them to higher PAH-concentration, resulting in genetic adaptation or changes responsible for high efficiency towards removal/degradation. In last few decades, mechanism of PAH-biodegradation, catabolic gene system encoding catabolic enzymes, and genetic adaptation and regulation have been investigated in detail. This review is an attempt to overview current knowledge of microbial degradation mechanism of PAHs, its genetic regulation with application of genetic engineering to construct genetically engineered microorganisms, specific catabolic enzyme activity, and application of bioremediation for reclamation of PAH-contaminated sites. In addition, advanced molecular techniques i.e. genomic, proteomic, and metabolomic techniques are also discussed as powerful tools for elucidation of PAH-biodegradation/biotransformation mechanism in an environmental matrix.
PAHs are aromatic hydrocarbons with two or more fused benzene rings with natural as well as anthropogenic sources. They are widely distributed environmental contaminants that have detrimental ...biological effects, toxicity, mutagenecity and carcinogenicity. Due to their ubiquitous occurrence, recalcitrance, bioaccumulation potential and carcinogenic activity, the PAHs have gathered significant environmental concern. Although PAH may undergo adsorption, volatilization, photolysis, and chemical degradation, microbial degradation is the major degradation process. PAH degradation depends on the environmental conditions, number and type of the microorganisms, nature and chemical structure of the chemical compound being degraded. They are biodegraded/biotransformed into less complex metabolites, and through mineralization into inorganic minerals, H
2O, CO
2 (aerobic) or CH
4 (anaerobic) and rate of biodegradation depends on pH, temperature, oxygen, microbial population, degree of acclimation, accessibility of nutrients, chemical structure of the compound, cellular transport properties, and chemical partitioning in growth medium. A number of bacterial species are known to degrade PAHs and most of them are isolated from contaminated soil or sediments.
Pseudomonas aeruginosa,
Pseudomons fluoresens,
Mycobacterium spp.,
Haemophilus spp.,
Rhodococcus spp.,
Paenibacillus spp. are some of the commonly studied PAH-degrading bacteria. Lignolytic fungi too have the property of PAH degradation.
Phanerochaete chrysosporium,
Bjerkandera adusta, and
Pleurotus ostreatus are the common PAH-degrading fungi. Enzymes involved in the degradation of PAHs are oxygenase, dehydrogenase and lignolytic enzymes. Fungal lignolytic enzymes are lignin peroxidase, laccase, and manganese peroxidase. They are extracellular and catalyze radical formation by oxidation to destabilize bonds in a molecule. The biodegradation of PAHs has been observed under both aerobic and anaerobic conditions and the rate can be enhanced by physical/chemical pretreatment of contaminated soil. Addition of biosurfactant-producing bacteria and light oils can increase the bioavailability of PAHs and metabolic potential of the bacterial community. The supplementation of contaminated soils with compost materials can also enhance biodegradation without long-term accumulation of extractable polar and more available intermediates. Wetlands, too, have found an application in PAH removal from wastewater. The intensive biological activities in such an ecosystem lead to a high rate of autotrophic and heterotrophic processes. Aquatic weeds
Typha spp. and
Scirpus lacustris have been used in horizontal–vertical macrophyte based wetlands to treat PAHs. An integrated approach of physical, chemical, and biological degradation may be adopted to get synergistically enhanced removal rates and to treat/remediate the contaminated sites in an ecologically favorable process.
Chlorophenols represent one of the most abundant families of toxic pollutants emerging from various industrial manufacturing units. The toxicity of these chloroderivatives is proportional to the ...number and position of chlorine atoms on the benzene ring. In the aquatic environment, these pollutants accumulate in the tissues of living organisms, primarily in fishes, inducing mortality at an early embryonic stage. Contemplating the behaviour of such xenobiotics and their prevalence in different environmental components, it is crucial to understand the methods used to remove/degrade the chlorophenol from contaminated environment. The current review describes the different treatment methods and their mechanism towards the degradation of these pollutants. Both abiotic and biotic methods are investigated for the removal of chlorophenols. Chlorophenols are either degraded through photochemical reactions in the natural environment, or microbes, the most diverse communities on earth, perform various metabolic functions to detoxify the environment. Biological treatment is a slow process because of the more complex and stable structure of pollutants. Advanced Oxidation Processes are effective in degrading such organics with enhanced rate and efficiency. Based on their ability to generate hydroxyl radicals, source of energy, catalyst type, etc., different processes such as sonication, ozonation, photocatalysis, and Fenton's process are discussed for the treatment or remediation efficiency towards the degradation of chlorophenols. The review entails both advantages and limitations of treatment methods. The study also focuses on reclamation of chlorophenol-contaminated sites. Different remediation methods are discussed to restore the degraded ecosystem back in its natural condition.
•Chlorophenols are the ubiquitous compounds widely distributed in almost all the components of ecosystem.•The toxicity of CPs causes multiple organs and endocrine systems to malfunction and reduced reproductive rates.•The review evaluates the different treatment methods and their mechanism towards the degradation of these pollutants.•The study also focuses on reclamation of chlorophenol-contaminated sites and restoring the degraded ecosystem .
Groundwater has become increasingly vulnerable to quality degradation. An elaborate understanding of its flow, draft, recharge and pollutant transport processes needs to be developed to understand ...its risk to contamination. This paper has discussed different tools and methods that are used to map groundwater vulnerability around the world. To maintain the quality and impact of the study, rigorous search for relevant literature published in high impact scientific journals has been done, and the comprehensive information on groundwater vulnerability assessment methods being used, has been compiled. The GIS based overlay and index-based methods like DRASTIC, GALDIT, GOD, COP and PI takes into consideration various thematic layers, overlays them to calculate weighted index and identifies vulnerability classes. They have been criticised for the lack of numerical basis in their formulation. Therefore, over the years, many of the proposed indices have been modified to provide quantitative estimates of groundwater potential to degrade and deplete. However, where the data and software are not a constraint, the use of numerical based simulation models can be done for more elaborate and numerical based quantification of the vulnerability. These numerical models typically require extensive data and are exceedingly becoming more sophisticated with the introduction of new parameters. This study concludes that integrating the GIS with numerical models offers the advantage of data management and assists to spatially analyse the datasets. The difficulties that are associated with the differences between GIS and numerical model's data structures should be thoroughly understood, prior to coupling, to develop uniform conversion software.
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•GIS based overlay and Index methods have been modified to include quantitative estimates of aquifer vulnerability.•Different set of indices have been developed for karst aquifers.•Numerical models simulate the aquifer conditions for flow and solute transport.•GIS based methods and numerical models can be coupled through loose, tight and embedded coupling.
Considering the prevalence of eutrophication of water bodies, sustainable treatment technologies like constructed wetlands (CWs) have come up as a promising alternate for nutrient removal and ...wastewater treatment. The present study was undertaken to investigate the potential of Brachiaria-based constructed wetland for removal of phosphorus and nitrogen in different seasons of a sub-tropical region. The CW cell could efficiently remove phosphate and nitrogen under varying influent concentrations across different seasons. Average removal of total phosphate increased from 55.2% (winter) to 78.5% (spring), 80.7% (autumn), and 85.6% (summer), and maximum removal rate was 384.4 mg/m2-day during the summer season. The soluble/available phosphate was removed on priority owing to its easy bio-availability. The removal efficiency of Brachiaria increased with increasing influent phosphate concentration (5–20 mg/l), if supplemented with nitrogen maintaining the N:P ratio of 5:1. This highlighted the characteristic of Brachiaria to absorb chemical shocks w.r.t. phosphate. The neutral pH (6.2–8.3) and oxidising conditions in rhizosphere ruled out possibility of binding of phosphate with cations (Ca, Fe, and Al) in sediments. Ambient temperature and sunshine hours regulated evapotranspiration and hence nutrient removal. Simultaneous removal of nitrogen (75.6–84.6%) by Brachiaria indicated that it can serve dual purpose of nutrient removal and fodder-production for livestock, thus serving as a sustainable prototype for rural communities in sub-tropical regions.
•Brachiaria mutica efficiently removes phosphate and nitrogen under varying influent concentrations.•Phosphorus removal is enhanced if nitrogen is amended with.•Ambient temperature and sunshine hours regulated nutrient removal.
This study characterises the quality of groundwater for the Ludhiana district of Punjab, India by analysing water samples collected from 152 locations spread across 3767 km
2
. The samples were ...analysed for 18 parameters consisting of pH, EC, TDS, TA, TH, major anions and cations. The parameter values have been used to calculate the drinking water quality index of the study area which suggests that 2.6, 57.9, 32.9, 4 and 2.6% of the samples fall under the excellent, good, poor, very poor and unsuitable categories, respectively. The sequence of abundance for ions (in meq/l) as revealed from the laboratory tests is Na
+
(37.1%) > Ca
2+
(30.8%) > Mg
2+
(29.1%) > K
+
(2.8%) for cations and HCO
3
−
(80%) > Cl
¯
(8.9%) > CO
3
2−
(6.5%) > SO
4
2−
(3.9%) > NO
3
−
, F
−
, PO
4
3−
(< 1%) for anions. The spatial variability of these parameters has been depicted through the use of interpolation maps. Evaluation of different ionic ratios indicates that carbonate weathering and silicate weathering are both significantly affecting the groundwater chemistry with a slight dominance of carbonate weathering. Also, the ion exchange process is taking place in the area as confirmed by CAI index values. In terms of saturation index, the groundwater is undersaturated with respect to halite, fluorite and sylvite, whereas it is supersaturated for calcite, dolomite and aragonite minerals. The principal components in PCA explained 75.4% of the total variance with 29.1 and 28.3% contributions from PC1 and PC2. Both of these components indicate towards the geogenic and anthropogenic influence on groundwater mineralization of the area. The analysis suggests that groundwater for the study area is suitable for drinking in most of the region expect in a few places. Such a study could be used to understand the current status of groundwater quality in the area, the results of which can be used to prevent further contamination and sustain the resource for the future.
Soil contamination by heavy metals has become a serious environmental issue considering its effects on health and the environment. Several techniques are being used for the treatment of contaminated ...soil, but these methods have limitations on account of cost, chemical/energy efficiency, and application in the field. On the other hand, phytoremediation is a cost-effective, solar energy-driven, and eco-friendly method for heavy metal removal. The present study discusses hyperaccumulating ornamental plants that can remove metal contaminants from the soil without any visible phytotoxic symptoms. Besides the uptake and translocation, the specific metal accumulation potential of ornamental plants, the mechanism involved in the removal, and the growth response of hyperaccumulators towards metal exposure have also been discussed. The essential indices- bioconcentration factor and translocation factor to determine the suitability of plants towards phytoextraction, the role of different plant parts in translocation and biochemical mechanisms for detoxification of metals have been presented as a highlight of this study. For optimum removal and efficient management of a phytoremediation design, the role of controlling factors such as soil characteristics, type of metal, plant species, organic amendments, phytochelators, bio-inoculants, etc. is very important. Considering the advent of biotechnology, the use of genetically modified plants is also recommended for significantly improved efficiency. It is expected that the present study will provide a guiding path for future researchers in exploring the scope of phytoremediation using ornamental plants.
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants having health hazards. PAH-utilizing bacterial strains were isolated from petroleum-contaminated soil from siding area, Bijwasan ...supply location of BPCL, Delhi, India. Bacterial strains with different morphology were isolated and acclimatized to a mixture of low molecular weight PAH compounds in the concentration range of 50–10,000 mg/L. Two bacterial strains surviving at 10,000 mg/L PAH concentration were identified as
Kocuria flava
and
Rhodococcus pyridinivorans,
based on 16S rRNA gene sequencing and phylogenetic analysis over MEGA X, are reported for the first time for PAH degradation. The strain
K. flava
could degrade phenanthrene, anthracene, and fluorene with efficiency of 55.13%, 59.01%, and 63.46%, whereas
R. pyridinivorans
exhibited 62.03%, 64.99%, and 66.79% degradation for respective PAHs at initial PAH concentration of 10 mg/L. Slightly lower degradation of phenanthrene could be attributed to its more stable chemical structure. The consortium of both the strains degraded 61.32%, 64.72%, and 66.64%, of 10 mg/L of phenanthrene, anthracene, and fluorene, respectively, in 15 days of incubation period indicating no synergistic or antagonistic effect towards degradation. Catechol 2,3-dioxygenase (C23O), dehydrogenase and peroxidase enzyme activities during PAH degradation coincided with degradation of PAHs, thus highlighting the role of these enzymes in catabolising three-ring PAHs. This is the first investigation confirming the participation of C23O, dehydrogenase and peroxidases enzyme profiles throughout the period of degradation. The study concludes that these strains can play significant role in microbial remediation of PAH-contaminated environment.
The present study investigates the degradation of amoxicillin (AMX) using TiO2 photocatalysis and sono-photocatalysis in aqueous solution under UV-A (365 nm) and sunlight exposure. The ...photocatalysis, as well as sono-photocatalysis, were coupled with H2O2 as well to assess the improvement in the degradation of AMX. Response surface methodology (RSM) based on three-level and four variable Box–Behnken experiment design was used to analyse and validate the degradation of AMX. Upon comparison of observed values with predicted, the value of the coefficient of regression (R2) was 0.87 which indicate the good fit of the model. The optimum conditions for maximum degradation (80%) of AMX were AMX - 30mg/l, TiO2 dosage - 450mg/l, H2O2 concentration — 150 mg/l and pH — 7.0 under UV irradiation (672 W/m2). Significant improvement in rate kinetics of degradation was observed when photocatalysis was complemented with H2O2 and sonication (40 KHz) under optimized condition, but the maximal removal remained almost unaffected. The method proved efficient towards degradation of AMX in real pharmaceutical wastewater with reduced reaction time for targeted level treatment. It was concluded that photocatalysis is a potential method for degradation of AMX under the set optimized conditions, and it may be adopted in-silo since photocatalysis coupled with sonication becomes energy-prohibitive for degradation of AMX.
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The present study aims to investigate the degradation of amoxicillin (AMX) using the Fenton process and hybrid Fenton-like processes such as photo-Fenton, solar photo-Fenton, sono-Fenton, and ...sono-photo-Fenton. The effect of ferrous ions (Fe2+), hydrogen peroxide (H2O2), and pH was evaluated. Complete degradation was achieved within 12 min of reaction time under the optimized conditions of Fe2+- 30 mg/l, H2O2 – 375 mg/l, and pH – 3.0 during Fenton’s process. Efficiency towards degradation of AMX was enhanced when the Fenton’s process was coupled with UV- light illumination, solar light illumination, and UV light-Ultrasound treatment. Complete degradation was observed within 3.5 min and 9 min during the photo-Fenton and solar photo-Fenton process, respectively. The sono-Fenton process takes a longer time to degrade AMX than other processes while sono-photo-Fenton process degrades AMX within 6 min. The reason for a reduced rate of degradation of AMX in the sono-Fenton process may be attributed to the competition of ultrasound and Fenton for H2O2, which ultimately decreases Fenton reagent in the process. The study concluded that the Fenton process coupled with other UV/solar light is more efficient than the stand-alone Fenton process towards degradation of AMX.
