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Plants serve as appropriate markers of worldwide pollution because they are present in almost every corner of the globe and bioaccumulate xenobiotic chemicals from their environment. The potential of a semi-aquatic plant, Ipomoea aquatica, to uptake and metabolize sulfamethoxazole (SMX) was investigated in this study. I. aquatica exhibited 100% removal of 0.05 mg L−1 SMX from synthetic media within 30 h. The I. aquatica achieved 93, 77 and 72% removal of SMX at 0.2, 0.5 and 1 mg L−1, respectively, after 48 h. This indicated that removal efficiency of I. aquatica was deteriorating at high concentrations of SMX. The chlorophyll and carotenoid content of I. aquatica was insignificantly influenced by SMX irrespective of its high concentration. Similarly, scanning electron microscopy (SEM) showed that exposure to SMX had an insignificant impact on morphology of the plant organelles. The mechanisms of removal by I. aquatica were explored by evaluating contributions of bioadsorption, bioaccumulation and biodegradation. There was negligible adsorption of SMX to plant roots. Accumulation of SMX within plant roots and stems was not observed; however, I. aquatica accumulated 17% of SMX in leaves. Thus, the major mechanism of elimination of SMX was biodegradation, which accounted for 82% removal of SMX. Gas chromatography-mass spectrometry (GC-MS) confirmed that I. aquatica biodegraded SMX into simpler compounds, and generated 4-aminophenol as its final product. A laboratory scale phytoreactor was used to investigate the application of I. aquatica in a simulated system, where it achieved 49% removal of SMX (0.2 mg L−1) in 10 d.

A comprehensive ecotoxicological evaluation of a sulfamethazine (SMZ) and sulfamethoxazole (SMX) mixture was conducted using an indicator microalga, Scenedesmus obliquus. The toxicological effects of this mixture were studied using microalgal growth patterns, biochemical characteristics (total chlorophyll, carotenoid, carbohydrate, fatty acid methyl ester), and elemental and Fourier-transform infrared spectroscopy analyses. The 96-h half maximal effective concentration (EC50) of the SMZ and SMX mixture was calculated to be 0.15 mg L−1 according to the dose-response curves obtained. The chlorophyll content decreased with elevated SMZ and SMX concentrations, while the carotenoid content initially increased and then decreased as concentration raised. The unsaturated fatty acid methyl esters (FAMEs) content was enhanced with higher SMZ and SMX concentrations, while that of saturated FAMEs simultaneously decreased due to SMZ and SMX stress. Elemental analyses showed an improved percentage of nitrogen and sulfur in the microalgal biomass as SMZ and SMX concentrations increased. The microalga S. obliquus was shown to biodegrade the chemicals tested and removed 31.4–62.3% of the 0.025–0.25 mg SMZ L−1 and 27.7–46.8% of the 0.025–0.25 mg SMX L−1 in the mixture after 12 days of cultivation. The greater biodegradation observed at higher SMZ and SMX concentrations indicates that microalgal degradation of SMZ and SMX could act as an efficient adaptive mechanism to antibiotics.

Microalgae represent a promising feedstock for biofuel production. However, the energy efficiency of microalgal pretreatment and conversion technologies needs to be improved to meet the economic viability. Herein, we introduce a novel integrated approach to achieve unprecedented energy conversion efficiency (46%) of microalgal biomass (Chlamydomonas mexicana). A successive high-throughput fermentation followed by transesterification were employed. This process provided a platform for maximum recovery of energy carriers from biomass utilization (89%). Serial fermentations were implemented for thorough utilization of the biomass constituents, starting with carbohydrate, followed by protein to derive ethanol (C2) and higher alcohols (C3–C5), respectively. Lipid was the dominant component after the previous fermentation, which was converted to biodiesel via transesterification process. Successive fermentations served as a bio-pretreatment to enhance the bioavailability of the leftover protein and lipid, which minimized the use of expensive and laborious methods for their extraction from the microalgal biomass. The proposed serial fermentation process would maximize the utilization of biomasses for biofuel production, with minimum leftover (11%).

Biofiltration (BF) facilitates the removal of organic and inorganic compounds through microbial reactions. Water is one of the most important elements in biotrickling filters that provides moisture and nutrients to microbial biofilms. The maintenance of proper trickle watering is very critical in biotrickling filtration because the flow rate of the trickling water significantly influences contaminant removal, and its optimal control is associated with various physicochemical and biological mechanisms. The lack of water leads to the drying of the media, creating several issues, including the restricted absorption of hydrophilic contaminants and the inhibition of microbial activities, which ultimately deteriorates the overall contaminant removal efficiency (RE). Conversely, an excess of water limits the mass transfer of oxygen or hydrophobic gases. In-depth analysis is required to elucidate the role of trickle water in the overall performance of biotrickling filters. The processes involved in the treatment of various polluted gases under specific water conditions have been summarized in this study. Recent microscopic studies on biofilms were reviewed to explain the process by which water stress influences the biological mechanisms involved in the treatment of hydrophobic contaminated gases. In order to maintain an effective mass transfer, hydrodynamic and biofilm conditions, a coherent understanding of water stress and the development of extracellular polymeric substances (EPS) in biofilms is necessary. Future studies on the realistic local distribution of hydrodynamic patterns (trickle flow, water film thickness, and wet efficiency), integrated with biofilm distributions, should be conducted with respect to EPS development.

Metal–organic frameworks (MOFs) have gained attention as promising materials for aqueous-phase sorptive removal of emerging contaminants (ECs). Attributes such as large adsorption capacity, high surface area, tunable porosity, hierarchical structure, and recyclability give MOFs an edge over conventional adsorbents. The poor stability of MOFs in water is a major challenge to their real-world environmental application. The performance of MOFs and their selectivity toward targeted pollutants for removal can be regulated by judicious selection of metal ion and organic linker. A range of water-stable MOFs (e.g., MIL-53, MIL-100, MIL-101, UiO-66, and MIL-125) and their composites with other materials have been reported to remove the ECs from water. The present review critically addressed the performance of MOFs for the adsorptive removal of different categories of ECs from water and the adsorption mechanisms involved. The performance of MOFs compared with other adsorbents has also been discussed. This body of rapidly developing research signifies the emerging importance of MOFs in environmental applications and provides a future direction for the development of treatment technology to effectively remove ECs from aqueous environments.

Fats, oil and grease (FOG) are energy-dense wastes that substantially increase biomethane recovery. Shifts in the microbial community during anaerobic co-digestion of FOG was assessed to understand relationships between substrate digestion and microbial adaptations. Excessive addition of FOG inhibited the methanogenic activity during initial phase; however, it enhanced the ultimate methane production by 217% compared to the control. The dominance of Proteobacteria was decreased with a simultaneous increase in Firmicutes, Bacteriodetes, Synergistetes and Euryarchaeota during the co-digestion. A significant increase in Syntrophomonas (0.18-11%), Sporanaerobacter (0.14-6%) and Propionispira (0.02-19%) was observed during co-digestion, which substantiated their importance in acetogenesis. Among methanogenic Archaea, the dominance of Methanosaeta (94%) at the beginning of co-digestion was gradually replaced by Methanosarcina (0.52-95%). The absence/relatively low abundance of syntrophic acetate oxidizers and hydrogenotrophic methanogens, and dominance of acetoclastic methanogens suggested that methane generation during co-digestion of FOG was predominantly conducted through acetoclastic pathway led by Methanosarcina.

The application of microalgal biomass for fermentation has been highlighted as a means of producing a range of value-added biofuels and chemicals. On the other hand, the microalgal residue from the fermentation process still contains as much as 50% organic contaminants, which can be a valuable substrate for further bioenergy recovery. In this study, a microbial fuel cell and automatic external load control by maximum power point tracking (MPPT) were implemented to harvest the electrical energy from waste fermented microalgal residue (FMR). The MFC with MPPT produced the highest amount of energy (1.82 kJ/L) compared to the other MFCs with fixed resistances: 0.98 (1000 Ω), 1.16 (500 Ω), and 1.17 kJ/L (300 Ω). The MFC with MPPT also showed the highest maximum power density (88.6 mW/m2) and COD removal efficiency (620.0 mg COD/L removal with 85% removal efficiency). The implementation of MPPT gained an approximate 12.9% energy yield compared to the previous fermentation stage. These results suggest that FMR can be an appropriate feedstock for electrical energy recovery using MFCs, and the combined fermentation and MFC system improves significantly the energy recovery and treatment efficiency from FMR.

A proper waste management practice such as anaerobic digestion for the waste generated by the agro-food industries could minimize the amount of material disposal to landfill. In our study, the improvement of methane production was elucidated through the pretreatment optimization of the mixed fruit wastes (FW). Dilute acetic acid pretreatment of FW was optimized in order to increase the bioavailability and microbial accessibility. A maximum sugar recovery of 95% was achieved from the pretreated FW under the optimized conditions (0.2 M acetic acid, 62.5 °C, and 30 min). Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric (TG) analyses verified the presence of cellulosic material in the pretreated FW. X-ray diffraction (XRD) analysis indicated that the crystallinity index was increased to 56% after the disruption of complex hemicellulosic structures during pretreatment. Increased porosity and surface roughness of pretreated FW for better microbial attachment were confirmed in scanning electron microscopy (SEM). Anaerobic digestion showed increased methanogenic activity (10.17 mL g−1 VSinitial d−1) in pretreated FW, during 86-day experimental period due to better microbial attachment and accessibility during the digestion process. Higher methane yield of 53.58 mL g−1 VSinitial was observed in pretreated FW. Thus, acetic acid pretreatment is an effective method to improve the utilization and conversion of FW to methane.

UV-C-mediated advanced oxidation processes (AOPs) for the enhanced degradation of ethyl paraben (EP) in the presence of oxidants such as persulfate (PS), hydrogen peroxide (H2O2) and peroxymonosulfate (PMS) were systematically investigated. The AOP treatments showed 98.1%, 97.0% and 81.3% degradation of EP with rates of 0.0373, 0.0339, and 0.0202 min−1 within 90 min for UV/PS, UV/H2O2 and UV/PMS, respectively. Degradation rates of EP increased with higher initial dosages of oxidant(s), while the opposite trend was observed in the case of increasing initial EP concentration. Maximum EP removal was achieved at pH 6.5 for UV/PS and UV/PMS and at pH 3 for UV/H2O2. Humic acid significantly retarded the degradation of EP. Chloride (Cl−) and carbonate (CO32−) suppressed reaction rates using UV/PS and UV/H2O2 systems, whereas they elevated the degradation rates with UV/PMS treatment. Degradation of EP in each of the UV-C based AOPs followed pseudo-first-order kinetics. The use of ethanol and t-butyl alcohol as scavengers revealed that HO and radicals were the major reactive radicals in UV/H2O2, UV/PS, and UV/PMS treatments. The efficiency (according to electrical energy per order and total cost per cubic meter) of the systems followed the order UV/PS > UV/H2O2 > UV/PMS. Thus, UV/PS process was more efficient and economical for EP degradation than the other processes examined in this study.

The commercial feasibility regarding conversion of the high-solid-loading microalgal suspensions for high-titer biofuels production is questionable owing to incomplete utilization and high processing costs. In this study, the production of multiple highly concentrated biofuels (bioethanol, higher alcohols, and biodiesel) was achieved through cost-effective integrated approach (pretreatment, serial fermentation of carbohydrate/protein, and transesterification of lipid) from highly concentrated (100 g/L) microalgal suspensions (Chlamydomonas mexicana and Chlamydomonas pitschmannii). This integrated approach attained unprecedented total conversion efficiency (48–63%) and maximum total biomass utilization (77–86%) for both the microalgal strains with high yields of bioethanol (0.48 g-ethanol/g-carbohydrate), higher alcohols (0.44 g-higher alcohols/g-protein), and biodiesel (0.82–0.89 g-biodiesel/g-lipid) at suspensions of 100 g/L. Transmission electron microscopy was employed to visualize the changes in the intercellular morphologies before and after serial fermentations. Thus, this study demonstrates a cost-effective and energy-saving integrated approach for the holistic conversion of high-solid-loading microalgal biomass to produce high-density biofuels with minimum waste generation.

Different inoculum to slaughterhouse waste (SHW) ratios (Ino/SHW) influences the digester performance, substrate utilization, and methane yield through microbial shift and their metabolic syntrophy. Acetoclastic Methanosarcina (68–87%) was dominant in the exponential phase, overpowering the initial abundance of Methanosaeta (86% of methanogens) in the SHW digesters. Positive interactions among acetogenic and acetate-oxidizing species of Clostridium (11%) with Methanosarcina (84% of methanogens) improved the methanogenic activity (292 mL g−1 VSinitial d−1) and final VS utilization (90%) at the highest Ino/SHW loading. In contrast, significant improvement of methane yield (152% higher than the control) at the lowest Ino/SHW loading was attributed to strong syntrophy among Methanosaeta (24% of methanogens) and its exoelectrogenic partners, Bythopirellula (0.52%) and Mariniphaga (0.08%) and the acetogenic Cloacimonas (0.16%) and Longilinea (0.32%). These syntrophic interactions among the core microbiota induced major metabolic activities, including butanoate, glycine, serine and threonine, methane, propanoate, and pyruvate metabolism, and quorum sensing.

Enhancement of microalgal growth and fatty acid production is essential for development of a microalgae-based biodiesel production platform. Three different microalgal species (Scenedesmus obliquus GU732418, Ourococcus multisporus GU732424 and Chlorella vulgaris FR751187) were individually cultivated in media containing both indole-3-acetic acid (IAA) and diethyl aminoethyl hexanoate (DAH) at concentrations of 10−8−10−4 M. Combined phytohormones (10−8 to 10−5 M) increased the growth of all three species compared to growth in media without phytohormones. IAA and DAH supported the maximum growth of S. obliquusi (38.12 × 106 cells mL−1) at 10−8 M, O. multisporus (85.89 × 106 cells mL−1) at 10−6 M, and C. vulgaris (4.09 × 106 cells mL−1) at 10−5 M. Addition of 10−7 M IAA and DAH also assisted the removal of Zn2+ (97%), K+ (88%) and Mg2+ (99%) from the media by S. obliquus. The highest removal of Zn2+, K+, and Mg2+ by C. vulgaris was achieved at 10−5 M IAA and DAH. Under all experimental conditions (10−8−10−4 M IAA and DAH) the amounts of poly-unsaturated fatty acids were significantly increased. Palmitic acid, linoleic acid and γ-linolenic acid were the major fatty acids, accounting for 11.75–21.55%, 2.55–6.73%, and 52.93–75.89% of the total fatty acid content, respectively. The fatty acids that accumulated in O. multisporus and C. vulgaris were found to be suitable for production of high quality biodiesel with characteristics equivalent to crop seed oil-derived biodiesel.

Methyl paraben (MP), a widely used preservative, exhibits endocrine-disrupting properties with estrogenic activities. The aqueous phase degradation of MP, using UV-activated persulfate method, was investigated in the present study. The combination of UV irradiation and persulfate anion successfully degraded MP showing 98.9% removal within 90 min. A quenching experiment using ethanol (EtOH) and tert -butyl alcohol (TBA) showed the presence of both radicals (OH and SO 4 – ) in the system; near neutral pH SO 4 – radical was the major species. The influence of various factors such as persulfate dose, initial MP concentration, solution pH, and water matrix components on the degradation kinetics was examined in view of the practical applications of the developed process. The degradation rate of MP was considerably increased as the amount of persulfate increased. The degradation of MP in the UV/persulfate system was pH dependent and more promising near neutral pH (6.5) conditions. The presence of anions such as Cl − , HPO 4 2− and HCO 3 − showed inhibitory effect towards MP degradation. The presence of humic acid also suppressed the degradation efficiency of MP. The reaction rate followed pseudo-first-order kinetics for all of the degradations. The degradation of MP by UV/persulfate treatment led to the production of seven transformation byproducts, which were identified using ultra-high-performance liquid chromatography-mass spectrometry (UPLC-MS). A degradation pathway for MP degradation was also proposed. The results of the present study reveal that the UV/persulfate process could be an effective approach to remove MP from aqueous solutions.

Levofloxacin (LEV), a fluoroquinolone antibiotic has been frequently observed in water resources imposing ecotoxicological effects on aquatic microbiota. The biodegradation and metabolic fate of LEV via a microalga, Scenedesmus obliquus in synthetic saline wastewater were investigated in this study. LEV removal (1 mg L− 1) by S. obliquus was relatively low in the synthetic wastewater without the addition of sodium chloride (NaCl); however, its removal increased significantly from 4.5 to 93.4% with increasing of its salinity from 0 to 171 mM NaCl. Kinetic studies showed that the removal rate constant (k) increased from 0.005 to 0.289 d− 1 and degradation half-life decreased from 272 to 5 d in the presence of NaCl (0–856 mM). The removal mechanism analysis showed that the major mechanism of NaCl mediated enhancement of LEV removal was the bioaccumulation and subsequent intracellular biodegradation of LEV in microalgal cells. Six metabolites were identified via gas chromatography–mass spectrometry analysis after biodegradation of LEV. A metabolic pathway was postulated with regard to various cellular biocatalytic reactions in S. obliquus, including decarboxylation, demethylation, dehydroxylation, side chain breakdown, and ring cleavage.

The impact of bioreduction on the remobilization of adsorbed cadmium Cd(II) on minerals, including hematite, goethite, and two iron(III)-rich clay minerals nontronites (NAU-1 and NAU-2) under anoxic conditions was investigated. Langmuir isotherm equation better described the sorption of Cd(II) onto the all minerals. The maximum adsorption capacity was 6.2, 18.1, 3.6, and 4 mg g-1 for hematite, goethite, NAU-1 and NAU-2, respectively. The desorption of Cd(II) was due to the production of Fe(II) as a result of bioreduction of structural Fe(III) in the minerals by Shewanella putrefaciens. The bioreduction of Cd(II)-loaded Fe(III) minerals was negligible during the initial 5 days followed by a rapid increase up to 20 days. The amount of Cd(II) in solution phase at the end of 30 days increased up to 0.07 mmol L-1 for hematite, NAU-1, and NAU-2 and 0.02 mmol L-1 for goethite. The X-ray diffraction study showed negligible changes in bioreduced minerals phases.

The extensive contamination of levofloxacin (LEV) in aquatic ecosystems has attracted increasing attention because of the potential for development of bacterial resistance and its eco-toxicity to non-target organisms. Biodegradation of LEV was significantly improved upon the acclimation of a freshwater microalga, Chlorella vulgaris and in the presence of elevated salinity. Among the six wild species (Chlamydomonas mexicana, Chlamydomonas pitschmannii, Chlorella vulgaris, Ourococcus multisporus, Micractinium resseri, Tribonema aequale), C. vulgaris showed the highest removal capacity (12%) of LEV at 1 mg L−1. The acclimated C. vulgaris, which was pre-exposed to 200 mg L−1 of LEV for 11 days, exhibited enhanced removal of 1 mg LEV L−1 by 16% after 11 days of cultivation. The addition of 1% (w/v) sodium chloride into the microalgal media significantly improved LEV removal by >80% in the C. vulgaris culture. The bioaccumulation of LEV at day 11 in C. vulgaris cells without NaCl was 34 μg g−1, which was elevated to 101 μg g−1 LEV at 1% NaCl. The bioconcentration factor for LEV was 34 and 1004 in 0 and 1% NaCl, respectively. The mass balance analysis of LEV showed that more than 90% of LEV was biodegraded by C. vulgaris at day 11 with the addition of 1% NaCl. These results demonstrated that the enhanced removal of LEV by salinity was mainly through bioaccumulation and subsequent intracellular biodegradation by C. vulgaris cells.

We evaluated various agricultural lignocellulosic biomass and variety of fungi to produce cellulolytic enzymes cocktail to yield high amount of reducing sugars. Solid-state fermentation was performed using water hyacinth, paddy straw, corn straw, soybean husk/tops, wheat straw, and sugarcane bagasse using fungi like Nocardiopsis sp. KNU, Trichoderma reesei, Trichoderma viride, Aspergillus flavus, and Phanerochaete chrysosporium alone and in combination to produce cellulolytic enzymes. Water hyacinth produced (U ml−1) endoglucanase (51.13) and filter paperase (0.55), and corn straw produced (U ml−1) β-glucosidase (4.65), xylanase (113.32), and glucoamylase (41.27) after 7-day incubation using Nocardiopsis sp. KNU. Production of cellulolytic enzymes was altered due to addition of various nitrogen sources, metal ions, vitamins, and amino acids. The maximum cellulolytic enzymes were produced by P. chrysosporium (endoglucanase; 166.32 U ml−1 and exoglucanase; 12.20 U ml−1), and by T. viride (filter paperase; 1.57 U ml−1). Among all, co-culture of T. reesei, T. viride, A. flavus, and P. chrysosporium showed highest β-glucosidase (17.05 U ml−1). The highest xylanase (1129 U ml−1) was observed in T. viride + P. chrysosporium co-culture. This study revealed the dependency on substrate and microorganism to produce good quality enzyme cocktail to obtain maximum reducing sugars.

Environmental contamination by benzophenone-3 has gained attention because of its frequent occurrence and adverse environmental impact. Studies investigating the toxicity and removal mechanisms, along with its degradation pathway in microalgae are still rare. In this study, the ecotoxicity of benzophenone-3 on Scenedesmus obliquus was assessed through dose-response test, risk quotient evaluation, and changes of microalgal biochemical characteristics and gene expression. The calculated risk quotients of benzophenone-3 were >1, implying its high environmental risk. Expression of the ATPF0C and Tas genes encoding ATP-synthase and oxidoreductase was significantly increased in S. obliquus after exposure to benzophenone-3, while that of Lhcb1 and HydA genes was reduced. When exposed to 0.1−3 mg L−1 benzophenone-3, 23–29 % removal was achieved by S. obliquus, which was induced by abiotic removal, bioadsorption, bioaccumulation and biodegradation. Metabolic fate analyses showed that biodegradation of benzophenone-3 was induced by hydroxylation, and methylation, forming less toxic intermediates according to the toxicity assessment of the identified products. This study provides a better understanding of the toxicity and metabolic mechanisms of benzophenone-3 in microalgae, demonstrating the potential application of microalgae in the remediation of benzophenone-3 contaminated wastewater.

This work focused on the application of calcium (0.1–1% w/v) to overcome the inhibition caused by the high loadings (2% v/v) of fat, oil, and grease (FOG) in the context of biomethane production, organic removal, and microbial community shift. Addition of 0.5% calcium showed maximum biomethane production (6-fold increase); biomethane production decreased following the addition of calcium (>0.5%). The highest organic removal rates were 83 and 89% upon the addition of 0.3 and 0.5% calcium, respectively. Addition of calcium facilitated the growth of bacteria of phylum Firmicutes from the Clostridium, Syntrophomonas, and Sedimentibacter genera. The population of members from the genus Methanosaeta increased after the addition of 0.5% calcium, which is one of the factors responsible for high biomethane production. This study demonstrated that addition of calcium is an attractive strategy to avoid the inhibition of the growth of anaerobic microflora due to the presence of high FOG concentrations.

Pharmaceutical contamination in diverse water resources has been recognized as an emerging concern in environment because of its wide distribution and adverse effects on aquatic microorganisms and human health. Plant remediation with augmentation of microorganisms is a cost-effective and environmentally friendly approach toward an efficient treatment of pollutants, which can be easily applied in situ. (Bio)degradation of sulfamethazine (SMZ) by Iris pseudacorus, microalgal consortium, and plant-microalgal consortium was investigated. I. pseudacorus and microalgae could remove 63.5, and 25.8% of 1 mg SMZ L-1, respectively, whereas, the plant-microalgal consortium achieved 74% removal. The identified intermediates extracted after plant remediation indicated (bio)degradation of SMZ was through ring cleavage, hydroxylation, and dehydroxylation. Pigment content (total chlorophyll and carotenoid) of I. pseudacorus was significantly influenced by SMZ stress. A phytoreactor (20 L) constructed with I. pseudacorus achieved 30.0% and 71.3% removal of 1 mg SMZ L-1 from tap water and nutrient medium. This study has provided a better understanding of the metabolic mechanisms of SMZ in plants and showed the potential development of a plant-microalgal consortium as an advanced technology for treatment of these emerging contaminants. Graphical abstract.

Compositional variations in organic wastes influence microbial abundancy and syntrophy during anaerobic digestion (AD), impacting the normal performance of digesters for methanation. Investigation of the microbial dynamics during AD following augmentation with polysaccharidic wastes (PW) revealed the association of effective digester performance and methane yields with the microbial nexus. Dominance of the acidogenic saccharolytic genera, Prevotella, Eubacterium, and Lachnoclostridium, enhanced the utilization of carbohydrates (54%) in PW-augmented digesters. Spearman's rs correlation showed dynamic interspecies interactions among acetogenic syntrophs, and that of iron oxidizers/reducers with acetoclastic and hydrogenotrophic methanogens. Propionate oxidizers in Chloroflexi (i.e., Bellilinea, Levilinea, and Longilinea) exhibited positive associations with acetoclastic methanogens. Increase in the population of acetoclastic methanogens (Methanosaeta, 77% and Methanosarcina, 9%) accelerated the methanogenic activity of PW-augmented digesters by 7 times during the exponential phase, increasing the methane yield (75%) compared to the control. Thus, microbial syntrophy facilitated the effective methanation of PW during AD process.

This study determines the optimum food waste (FW) loading in an anaerobic digester for methane production. Interrelation between the degradation mechanism and microbial community composition was assessed through in-depth metabolic pathway analysis and gene quantification. Higher methane production and short lag phase were observed in the FW reactors with low substrate loadings (4% v/v) while extended lag phase and incomplete substrate utilization were observed in the reactors fed with higher substrates (6% v/v). The long-chain fatty acids (LCFAs) degradation was influenced by initial FW loading, and up to 99% LCFA degradation occurred at 4% FW reactor. The addition of 8 to 10% FW substrate inhibited methanogenesis due to the accumulation of volatile fatty acids (VFA) and low LCFA degradation. Under optimal conditions of substrate loading, Methanosaeta and Methanosarcina were abundant, indicating their role in methanogenesis and syntrophic acetogenesis, along with enhanced metabolic pathways specific for carbohydrate and lipid metabolism.

The industrial revolution in the production of pharmaceuticals and personal care products (PPCPs) has significantly improved public health in recent years. However, this development has also led to water pollution because of the unintentional disposal of these synthetic chemicals, creating unacceptable sanitary conditions. Conventional wastewater treatment systems can eliminate most of the contaminants, however these are not efficient in removing PPCPs. Plant-based remediation is a simple, yet very effective and eco-friendly approach that can complement existing wastewater treatment. Phytoremediation of emerging contaminants is relatively new, and various key concepts including the uptake and detoxification mechanisms remain relatively unexplored compared with microbial processes. This review comprehensively discusses the latest studies on the biochemistry and application of phytoremediation for the removal of PPCPs from wastewater, focusing on the mechanisms of uptake and detoxification through the enzymatic biotransformation of PPCPs and the latest field applications using innovative engineered systems. Future research recommendations are addressed, including the need of topics warranting investigation in PPCPs interactions with plant tissues, their metabolic transformation in plants, development of new predictive uptake models and futuristic advancements involving the cutting-edge methodologies in genetic engineering for the realization of advanced phytoremediation technologies. This review is an effort to gather the scattered information on research updates of phytoremediation in recent decade to present an outlook of the emerging, green biotechnology for the rehabilitation of the environment.

Acidification during anaerobic digestion (AD) due to organic overloading is one of the major reasons for process failures and decreased methane productivity in anaerobic digesters. Process failures can cause the anaerobic digesters to stall completely, prolong the digester recovery period, and inflict an increased operational cost on wastewater treatment plants and adverse impacts on the environment. This study investigated the efficacy of bioaugmentation by using acclimatized microbial consortium (AC) in recovering anaerobic digesters stalled due to acidosis. Overloading of digesters with food waste leachate (FWL) led to the accumulation of volatile fatty acids (11.30 g L−1) and a drop in pH (4.67), which resulted in process failure and a 22-fold decline in cumulative methane production compared to that in the initial phase. In the failure phase, the syntrophic and methanogenic activities of the anaerobic digester microbiota were disrupted by a significant decrease in the abundance of syntrophic populations such as Syntrophomonas, Syntrophorhabdus, Sedimentibacter, and Levilinea, and the phylum Euryarchaeota. Bioaugmentation of the failed digesters by adding AC along with the adjustment of pH resulted in the prompt recovery of methane productivity with a 15.7-fold higher yield than that in unaugmented control. The abundance of syntrophic bacteria Syntrophomonas and phylum Euryarchaeota significantly increased by 29- and 17-fold in the recovered digesters, respectively, which showed significant positive correlations with methane productivity. Methanosarcina and acetoclastic Methanosaeta played a major role in the recovery of the digesters; they were later replaced by hydrogenotrophic Methanoculleus. The increase in the abundance of genes associated with biomethanation contributed to digester recovery, according to the functional annotation of 16S rDNA amplicon data. Thus, bioaugmentation with AC could be a viable solution to recover digesters experiencing process failure due to organic overloading.

Textile industry effluents contain a variety of dyes, which are normally resistant to biodegradation. A bacterial-yeast consortium ( Brevibacillus laterosporus and Galactomyces geotrichum ) was used for decolorization of two real textile effluents (RTE) and a simulated synthetic effluent (SSE). It showed enhanced decolorization compared to that of individual microorganisms with decolorization efficiency of 89, 60 and 69% for RTE-1, RTE-2 and SSE respectively, within 48 h. The cumulative action of oxido-reductive enzyme in the consortium was responsible for improved decolorization. Spectroscopic analysis suggested effective biodegradation of dyes present in the SSE by the consortium contrarily to the individual strains. The gradual biodegradation of each dye present in the SSE was monitored using high performance thin layer chromatography (HPTLC). The consortium biodegraded all of the dyes within 1 h as compared to that of partial biodegradation by the individual microorganisms. A novel, triple layered fixed bed reactor was designed for continuous decolorization of effluent. It showed >80% decolorization (at 100 mL h −1 flow-rate), for a period of 7 days, along with ∼78% reduction in COD. The reproducibility of the bioreactor could be maintained for three consecutive cycles (7 days each).

Diazinon is one of the most widely used organophosphorus insecticides for agricultural activities, and it is highly toxic to mammals and other non-target organisms. The present study demonstrated the effective removal of diazinon from the aqueous phase by a freshwater, green microalga, Chlorella vulgaris . Among the four screened species ( Scenedesmus obliquus , Chlamydomonas mexicana , Chlorella vulgaris and Chlamydomonas pitschmannii ), C. vulgaris showed the highest removal capacity (94%) of diazinon at 20 mg L − 1 . The growth of C. vulgaris was significantly affected above 40 mg L − 1 of diazinon, showing > 30% growth inhibition after 12 days of cultivation. Significant enhancement of the microalgal growth in the exponential growth phase suggested a less/non-toxic nature of the diazinon by-products. Biochemical properties, including carotenoid, chlorophyll a nd antioxidant enzymes of C. vulgaris were influenced by diazinon at relatively high concentrations. The degradation rate constant (k) and the half-life (T 1/2 ) of diazinon (0.5–100 mg L − 1 ) ranged between 0.2304–0.049 d − 1 and 3.01–14.06 d, respectively. Gas chromatography mass spectroscopic (GC–MS) study suggested the formation of a less toxic by-product, 2-isopropyl-6-methyl-4-pyrimidinol (IMP) as a result of microalgal metabolism of diazinon. This study demonstrated that C. vulgaris is highly tolerant of diazinon, which could be voluntarily involved in the removal of traces of diazinon from contaminated wastewater and has potential application in the removal of such artificial toxins using algae.

Maximizing the bioavailability of fermentable biomass components is a key challenge in biomass pretreatment due to the loss of sugars during conventional pretreatment approaches. Pretreatment of fruit peels and wastes (FPWs) with dilute acetic acid assisted in maximizing sugar recovery. Optimized conditions (0.2 M acetic acid, 100 °C, 1 h) at 10% substrate loading resulted in enhanced sugar recovery from banana peels (99.9%), pineapple wastes (99.1%), grape pomace (98.8%), and orange peels (97.9%). These high sugar recoveries retained the high C/N ratios (41–47) suitable for effective bioenergy production through the fermentation of these pretreated biomasses. Scanning electron microscopy (SEM) indicated considerable disruption of biomass structural integrity during acetic acid treatment, enhancing the surface area available for better microbial attachment. Fourier transform infrared spectroscopy (FTIR) showed that the acetic acid pretreatment yielded only minor changes to the functional groups in the biomasses, strongly suggesting minimal loss of fermentable sugars. Thus, acetic acid pretreatment aids in enhancing the bioavailability of fermentable sugars from these FPWs biomass, enabling improvements in bioenergy production.

Biogenic flocculant produced by Acidithiobacillus ferrooxidans was used for sludge conditioning to improve the dewaterability of anaerobically-digested sludge, and its efficiency was compared with commercial cationic polyacrylamide (PAM). Biogenic flocculant rapidly reduced the pH and increased the oxidation-reduction potential of sludge. Capillary suction time (CST) and specific resistant to filtration (SRF) of sludge was decreased by 74% and 89%, respectively, compared with control; and the reductions were 58% CST and 67% SRF higher when compared with commercial polymer. Biogenic treatment improved the sludge calorific value by 13%, and also reduced the unpleasant odor. The small-scale mechanical filter press study showed that the biogenic flocculant can reduce the moisture content of sludge to 70%, and improve the clarity of the filtrate in terms of removal of total suspended solids and total dissolved solids when compared with synthetic polymer treatment.

Mining industry has been using cyanide for more than ten decades to recover precious metals such as gold and silver. The presence of cyanide in the environment has long been a matter of concern due...

This study investigated the improvement in dewaterability of activated sludge (ACS) and anaerobically digested sludge (ADS) through bioacidification approach using iron-oxidizing bacterium, Acidithiobacillus ferrooxidans. ACS and ADS were treated with A. ferrooxidans culture with addition of different concentrations of energy substrate, in terms of Fe(2+):sludge solids ratio (0:1, 0.01:1, 0.05:1 and 0.1:1), and the dewaterability was assessed by determining the capillary suction time (CST), time to filter (TTF) and specific resistance to filtration (SRF) of the sludge. The results revealed that the levels of Fe(2+) significantly influenced the sludge acidification (pH⩽3). The CST, TTF and SRF values rapidly decreased in treated sludge, indicating that dewaterability of the sludge was significantly (p

Development of a low-cost harvesting technology could be an effective approach for making microalgal biofuel commercially feasible. The use of acid mine drainage (AMD) to coagulate/flocculate biomass is a cost-effective strategy for addressing this challenge. Here, settling kinetics, flocculation efficiency (FE), and concentration factor (CF) of two morphologically different microalgae species, Scenedesmus obliquus and Chlorella vulgaris, were investigated with respect to AMD dosage (5% and 10%) and medium pH (7 and 9). AMD was collected from two different sites, AMD (1) and AMD (2), and increasing its dosage to 10% improved the settling rate, FE, and CF of the floc. At 10% AMD (1) dosage and pH 9, the highest rate constants (k2) for the second order equations were 6.65 × 10−2 and 40 × 10−2 L mg−1⋅min−1 for S. obliquus and C. vulgaris, respectively; at 10% AMD (2), k2 values were 4.22 × 10−2 and 4.76 × 10−2 L mg−1 min−1, respectively. Similarly, FE/CF values were 89%/25 for S. obliquus and 93%/29 for C. vulgaris with 10% AMD (1); and 81%/17 and 79%/17, respectively, with 10% AMD (2). AMD effectively removed 99.80% of Fe3+, 99.99% of Al3+, 94% of Ca2+, 84% of Mg2+ and all of Na+ and K+ ions from the supernatant. The results of kinetics, EF, and CF measurements indicate that AMDs, naturally rich in iron and aluminum ions, could provide a feasible option for the harvesting of microalgal biomass for biofuel generation.

Microalgae, Chlorella vulgaris and Scenedesmus obliquus were cultivated in a small scale vertical flat-plate photobioreactor (PBR) supplemented with municipal wastewater in order to achieve simultaneous wastewater treatment and biomass production for biofuel generation. Microalgal growth and nutrient removal including total nitrogen (TN), total phosphorus (TP), total inorganic carbon (TIC) and trace elements (Ca2+, Na+, Mg2+ and Zn2+) were monitored during microalgae cultivation. C. vulgaris and S. obliquus showed optimal specific growth rates (μopt) of 1.39 and 1.41 day−1, respectively, and the TN and TP were completely removed (>99%) from the wastewater within 8 days. Microalgal biomass in the PBR was harvested using a natural flocculant produced from Moringa oleifera seeds. The harvesting efficiency of M. oleifera was 81% for C. vulgaris and 92% for S. obliquus. The amounts of saturated, mono-unsaturated, and poly-unsaturated fatty acids in the harvested biomass accounted for 18.66%, 71.61% and 9.75% for C. vulgaris and 28.67%, 57.14% and 11.15% for S. obliquus, respectively. The accumulated fatty acids were suitable to produce high quality biodiesel with characteristics equivalent to crop seeds oil-derived biodiesel. This study demonstrates the potential of microalgae-based biodiesel production through the coupling of advanced wastewater treatment with microalgae cultivation for low-cost biomass production in a PBR.

Bioremediation is one of the milestones achieved by the biotechnological innovations. It is generating superior results in waste management such as removal of textile dyes, which are considered xenobiotic compounds and recalcitrant to biodegradation. In the present bioremedial approach, Brevibacillus laterosporus was used as an effective microbial tool to decolorize disperse dye Disperse Red 54 (DR54). Under optimized conditions (pH 7, 40°C), B. laterosporus led to 100% decolorization of DR54 (at 50 mg L(-1)) within 48 h. Yeast extract and peptone, supplemented in medium enhanced the decolorization efficiency of the bacterium. During the decolorization process, activities of enzymes responsible for decolorization, such as tyrosinase, veratryl alcohol oxidase and NADH--DCIP reductase were induced by 1.32-, 1.51- and 4.37-fold, respectively. The completely different chromatographic/spectroscopic spectrum of metabolites obtained after decolorization confirmed the biodegradation of DR54 as showed by High pressure liquid chromatography, High pressure thin layer chromatography and Fourier transform infrared spectroscopy. Gas chromatography-Mass spectroscopy studies suggested the parent dye was biodegraded into simple final product, N-(1λ(3)-chlorinin-2-yl)acetamide. Phytotoxicity study suggested that the metabolites obtained after biodegradation of DR54 were non-toxic as compared to the untreated dye signifying the detoxification of the DR54 by B. laterosporus.

This study evaluated the toxicity and cellular stresses of carbamazepine (CBZ) on Chlamydomonas mexicana and Scenedesmus obliquus, and its biodegradation by both microalgal species. The growth of both microalgal species decreased with increase of CBZ concentration. The growth of S. obliquus was significantly inhibited (97%) at 200 mg CBZ L(-1), as compared to the control after 10days; whereas, C. mexicana showed 30% inhibition at the same experimental conditions. Biochemical characteristics including total chlorophyll, carotenoid contents and enzyme activities (SOD and CAT) for both species were affected by CBZ at relatively high concentration. C. mexicana and S. obliquus could achieve a maximum of 35% and 28% biodegradation of CBZ, respectively. Two metabolites (10,11-dihydro-10,11-expoxycarbamazepine and n-hydroxy-CBZ) were identified by UPLC-MS, as a result of CBZ biodegradation by C. mexicana. This study demonstrated that C. mexicana was more tolerant to CBZ and could be used for treatment of CBZ contaminated wastewater.

Pharmaceutical contaminants in environment induce unexpected effects on ecological systems and human; thus, development of efficient technologies for their removal is immensely necessary. In this study, biodegradation and metabolic fate of a frequently found pharmaceutical contaminant, doxylamine by Typha angustifolia and Ipomoea aquatica was investigated. Microbial community of the plant rhizosphere has been identified to understand the important roles of the functional microbes. The plants reduced 48-80.5 % of doxylamine through hydrolysis/dehydroxylation and carbonylation/decarbonylation. A constructed phytobed co-planted with T. angustifolia and I. aquatica removed 77.3 %, 100 %, 83.67 %, and 61.13 % of chemical oxygen demand, total nitrogen, total phosphorus, and doxylamine respectively from real wastewater. High-throughput sequencing of soil and rhizosphere indicated that the phyla Proteobacteria, Bacteroidetes, Firmicutes, Planctomycetes, Actinobacteria, and Cyanobacteria dominated the microbial communities of the phytobed. Current study has demonstrated the applicability of the developed phytobeds for the treatment of doxylamine from municipal wastewater and provide a comprehensive understanding of its metabolism through plant and its rhizospheric microbial communities.

The physiological properties, including biochemical composition and cell wall thickness, of microalgal species have a remarkable effect on the pretreatment of biomass and its further conversion to biofuels. In the present study, multiple biofuels (bioethanol, higher alcohols (C3–C5), and biodiesel) were produced using energy-efficient microwave pretreatment, successive carbohydrate/protein fermentation, and lipid transesterification from three microalgal strains (Pseudochlorella sp., Chlamydomonas mexicana, and Chlamydomonas pitschmannii). The microwave pretreatment method required the lowest specific energy (5 MJ/kg) compared to ultrasound pretreatment. The proposed integrated approach achieved high conversion efficiency (46%) and maximum biomass utilization (93%) of C. mexicana with improved yields of bioethanol (0.46 g-ethanol/g-carbohydrates), higher alcohols (0.44 g-higher alcohols/g-proteins), and biodiesel (0.74 g-biodiesel/g-lipids). This study suggests that the application of an appropriate pretreatment method for microalgal strains having different physiological properties is essential for improving the extraction efficiency and conversion of biomass to biofuels with less waste production.

Nanoparticles have been commercially used worldwide; however, there is a lack of information of their environmental impacts and ecotoxicity. In this study, the effect of cerium oxide nanoparticle (CeO2NP) on a green microalga Scenedesmus obliquus, and microalgal biodegradation of four sulfonamides (sulfamethazine, sulfamethoxazole, sulfadiazine, and sulfamethoxazole) was investigated. There is insignificant inhibition of microalgal growth induced by CeO2NP; however, it substantially influenced the expression of genes involved in key cellular metabolic activities of S. obliquus. For example, genes involved in photosynthetic activity (psbA) and energy production (ATPF0C) were downregulated with exposure to CeO2NP. The low concentrations of CeO2NP improved microalgal degradation of sulfonamides. This may be because of the upregulated genes encoding hydrogenase and oxidoreductase. The exploration of this study has provided a new understanding of the environmental impacts of CeO2NP on microalgae-based biotechnologies for treatment of wastewater containing emerging organic contaminants.

Biodegradation of phenolic compounds in wastewater can be effectively carried out in packed bed reactors (PBRs) employing immobilized microorganisms. A low-cost, reusable immobilization matrix in PBR can provide economic advantages in large scale removal of high concentration phenol. In this study, we evaluated the efficiency and reusability of sugarcane bagasse (SCB) as a low-cost immobilization support for high strength phenol removal in recirculating upflow PBR. An isolated yeast Candida tropicalis PHB5 was immobilized onto the SCB support and packed into the reactor to assess phenol biodegradation at various influent flow rates. Scanning electron microscopy exhibited substantial cell attachment within the pith and onto the fibrous strand surface of the SCB support. The PBR showed 97% removal efficiency at the initial phenol concentration of 2400 mg L−1 and 4 mL min−1 flow rate within 54 h. Biodegradation kinetic studies revealed that the phenol biodegradation rate and biodegradation rate constant were dependent on the influent flow rate. A relatively higher rate of biodegradation (64.20 mg g−1 h−1) was found at a flow rate of 8 mL min−1, indicating rapid phenol removal in the PBR. Up to six successive batches (phenol removal >94%) were successfully applied in the PBR using an initial phenol concentration of 400–2400 mg L−1 at a flow rate of 4 mL min−1 indicating the reusability of the PBR system. The SCB-immobilized C. tropicalis could be employed as a cost-effective packing material for removal of high strength phenolic compounds in real scale PBR.

A combination of photocatalysis and biodegradation is a promising approach for the removal of xenobiotic organic compounds from wastewater, since photocatalysis cleaves the molecules into simpler intermediates that are later mineralized by microorganisms. Sequential photocatalytic and biological treatment (SPABT) consisting of ZnO as a photocatalyst and a microbial consortium (Galactomyces geotrichum and Brevibaccilus laterosporus) enhanced the degradation of a model textile dye, methyl red (MR). SPABT completely decolorized 500 mg MR/L within 4 h. Biotreatment alone required 6 h for 100% decolorization. A maximum of 70% decolorization was achieved with the photocatalytic treatment but reductions in COD and toxicity were not adequate. Significant elevated activities of enzymes, including azo reductase, laccase and veratryl alcohol oxidase, were observed in the microbial consortium after exposure of MR. The degradation pathway and products of MR varied with treatment applied. The persistent azo bond was cleaved by following photocatalytic treatment with the microbial biotreatment. Tests with Sorghum vulgare and Phaseolus mungo indicated the products obtained by SPABT were non-phytotoxic.

Densitometric high performance thin layer chromatography (HPTLC) quantification method was developed to validate the decolorization/biotransformation of Disperse Orange ERL and dye mixture by lichen Parmelia sp. which release several colored compounds during decolorization process, hence unable to use colorimetric estimation. Percent decolorization of Disperse Orange ERL and dye mixture by lichen Parmelia sp. was observed when estimated using developed HPTLC method. Limit of detection and limit of quantification for both dyes in mixture were obtained as 0.3 and 1 μg/μl, respectively. Area of peak of control Disperse Orange ERL was reduced by 43% after 12 h, 71% after 48 h and upto 82% after 72 h of incubation. Precision and repeatability of data elucidated the % relative standard deviation less than 3 for all the values thus indicating statistically acceptable. Biodegradation of dye and mixture was confirmed with Fourier transform infrared spectroscopy analysis, i.e., altered fingerprinting spectral pattern.

In situ phytoremediation of dyes from textile wastewater was carried out in a high rate transpiration system ridges (91.4 m × 1.0 m) cultivated independently with Tagetes patula, Aster amellus, Portulaca grandiflora and Gaillardia grandiflora which reduced American Dye Manufacturers Institute color value by 59, 50, 46 and 73%, respectively within 30 d compared to dye accumulated in unplanted ridges. Significant increase in microbial count and electric conductivity of soil was observed during phytoremediation. Reduction in the contents of macro (N, P, K and C), micro (B, Cu, Fe and Mn) elements and heavy metals (Cd, As, Pb and Cr) was observed in the soil from planted ridges due to phyto-treatment. Root tissues of these plants showed significant increase in the specific activities of oxido-reductive enzymes such as lignin peroxidase, laccase, veratryl alcohol oxidase, tyrosinase and azo reductase during decolorization of textile dyes from soil. Anatomical studies of plants roots revealed the occurrence of textile dyes in tissues and subsequent degradation. A minor decrease in plant growth was also observed. Overall surveillance suggests that the use of garden ornamental plants on the ridges of constructed wetland for the treatment of dyes from wastewater along with the consortia of soil microbial flora is a wise and aesthetically pleasant strategy.

This study investigated the environmental effects of two common emerging contaminants, sulfamethazine (SMZ) and sulfamethoxazole (SMX), and their mixture using a green microalga, Scenedesmus obliquus. The calculated EC50 values of SMZ, SMX, and their mixture (11:1 wt/wt) after 96 h were 1.23, 0.12, and 0.89 mg L-1, respectively. The toxicity of the mixture could be better predicted using a concentration addition model than an independent action model. The risk quotients of SMZ, SMX, and their mixture were >1 during the experiment, indicating their high potential risks on aquatic microorganisms. Despite their toxicity, S. obliquus exhibited 17.3% and 29.3% removal of 0.1 mg L-1 and 0.2 mg L-1 after 11 days of cultivation. The changes of SMZ and SMX removal were observed when combined, which showed a significantly improved removal of SMZ (up to 3.4 folds) with addition of SMX (0.2 mg L-1). The metabolic pathways of SMZ and SMX were proposed according to mass spectroscopic analysis, which showed six metabolites of SMX and seven intermediates of SMZ, formed as a result of ring cleavage, hydroxylation, methylation, nitrosation, and deamination.

Bioleaching using an iron-oxidizing bacterium, Acidithiobacillus ferrooxidans, and its biogenic flocculants was evaluated to improve the dewaterability of chemically enhanced primary treatment (CEPT) sewage sludge. CEPT sludge in flasks was inoculated with A. ferrooxidans culture, medium-free cells and the cell-free culture filtrate with and without the energy substance Fe2+, and periodically the sludge samples were analysed for the dewaterability. This investigation proves that bioleaching effectively improved the sludge dewaterability as evidenced from drastic reduction in capillary suction time (≤20 seconds) and specific resistance to filtration (≥90%); however, it requires an adaptability period of 1–2 days. On the other hand, the biogenic flocculant produced by A. ferrooxidans greatly decreased the time-to-filtration and facilitated the dewaterability within 4 h. Results indicate that rapid dewatering of CEPT sludge by biogenic flocculants provides an opportunity to replace the synthetic organic polymer for dewatering.

The increase in worldwide water contamination with numerous pharmaceutical contaminants (PCs) has become an emerging environmental concern due to their considerable ecotoxicities and associated health issues. Microalgae-mediated bioremediation of PCs has recently gained scientific attention, as microalgal bioremediation is a solar-power driven, ecologically comprehensive, and sustainable reclamation strategy. In this review, we comprehensively describe the current research on the possible roles and applications of microalgae for removing PCs from aqueous media. We summarize several novel approaches including constructing microbial consortia, acclimation, and cometabolism for enhanced removal of PCs by microalgae, which would improve practical feasibility of these technologies. Some novel concepts for degrading PCs using integrated processes and genetic modifications to realize algal-based bioremediation technologies are also recommended.

The methane productivity and long chain fatty acids (LCFAs) degradation capability of unacclimatized seed sludge (USS) and acclimatized seed sludge (ASS) at different substrate ratios of fats oil and grease (FOG) and mixed sewage sludge were investigated in this study. Biogas produced in ASS in initial phase of anaerobic digestion had higher methane content (65–76%) than that in USS (26–73%). The degradation of major LCFAs in the ASS was 22–80%, 33–191%, and 7–64% higher for the substrate ratios of 100:10, 100:20, and 100:30, respectively, as compared to the LCFAs’ degradation in USS. Microbial acclimatization increased the population of Firmicutes (40%), Bacteroidetes (32%), Synergistetes (10%), and Euryarchaeota (8%) in ASS, which supported the faster rate of LCFAs degradation for its later conversion to methane. The significant abundance of Syntrophomonas and Methanosarcina genera in ASS supported faster generation rate of methane in an obligatory syntrophic relationship.

Textile dye contamination is a serious concern that reduces soil productivity by destabilizing microbial community structures. Here, we investigated the influence of bioaugmentation on the degradation of a mixture of dyes (MOD) and textile industry effluent (TIE) in soil microcosms using eight different dye-degrading bacteria. The biodegradation potential improved in bioaugmented microcosms, especially in the initial phase. The bioaugmented MOD and TIE microcosms exhibited 98.33% and 94.19% decolorization, and 96.92% and 95% reduction in chemical oxygen demand, respectively, within 30 days. Activities of azoreductase, veratryl alcohol oxidase, lignin peroxidase, and tyrosinase were induced by >three-fold in bioaugmented microcosms. Changes in alpha diversity indicated significant alterations in microbial dynamics due to MOD and TIE feeding. The Rheinheimera, Kocuria, Ruminococcaceae UCG-010, Ralstonia and Pseudomonas assemblages were predominant after exposure to MOD and TIE, indicating their key role in dye degradation. The bacteria used for augmentation, namely, Staphylococcus, Bacillus, Arthrobacter and Pseudomonas dominantly survived in soil microcosms. Xenobiotic pathways including benzoate, aminobenzoate, chloroalkane and chloroalkene degradation contributed in dye’s detoxification as per illustration of functional annotation of metagenomes. This study indicates a mutualistic-symbiotic relationship between augmented bacteria and soil microflora with enhanced detoxification of xenobiotics leading to a sustainable approach for restoration of contaminated lands.

Enrofloxacin (ENR), a fluoroquinolone antibiotic, has gained big scientific concern due to its ecotoxicity on aquatic microbiota. The ecotoxicity and removal of ENR by five individual microalgae species and their consortium were studied to correlate the behavior and interaction of ENR in natural systems. The individual microalgal species (Scenedesmus obliquus, Chlamydomonas mexicana, Chlorella vulgaris, Ourococcus multisporus, Micractinium resseri) and their consortium could withstand high doses of ENR (≤1 mg L-1). Growth inhibition (68-81%) of the individual microalgae species and their consortium was observed in ENR (100 mg L-1) compared to control after 11 days of cultivation. The calculated 96 h EC50 of ENR for individual microalgae species and microalgae consortium was 9.6-15.0 mg ENR L-1. All the microalgae could recover from the toxicity of high concentrations of ENR during cultivation. The biochemical characteristics (total chlorophyll, carotenoid, and malondialdehyde) were significantly influenced by ENR (1-100 mg L-1) stress. The individual microalgae species and microalgae consortium removed 18-26% ENR at day 11. Although the microalgae consortium showed a higher sensitivity (with lower EC50) toward ENR than the individual microalgae species, the removal efficiency of ENR by the constructed microalgae consortium was comparable to that of the most effective microalgal species.

Separate hydrolysis fermentation (SHF) and simultaneous saccharification fermentation (SSF) processes were studied for bioethanol production from microalgal biomass. SSF was selected as an efficient process to enhance the bioethanol yield through repeated-batches using immobilized yeast cells. Combined sonication and enzymatic hydrolysis of Chlamydomonas mexicana generated 10.5 and 8.48 g/L of ethanol in SSF and SHF, respectively. Yeast utilized maximum portion of total reducing sugar (TRS) reaching a consumption efficiency of 91–98%. A bioethanol yield of 0.5 g/g (88.2% of theoretical yield) and volumetric productivity of 0.22 g/L/h was obtained after 48 h of SSF. Immobilized yeast cells enabled repetitive production of ethanol for 7 cycles displaying a fermentation efficiency up to 79% for five consecutive cycles. The maximum ethanol production was 9.7 g/L in 2nd–4th cycles. A total energy recovery of 85.81% was achieved from microalgal biomass in the form of bioethanol. Repeated-batch SSF demonstrated the possibility of cost-effective bioethanol production.

This study evaluated the toxicity and cellular stresses of ciprofloxacin (CIP) and its co-metabolic removal in a freshwater microalga Chlamydomonas mexicana. The toxicological effects of CIP on C. mexicana were assessed by studying the growth and biochemical characteristics of the microalga including total chlorophyll, carotenoid content, malondialdehyde (MDA) and superoxide dismutase (SOD) activity. The calculated effective concentration (EC50) of CIP on C. mexicana was 65±4mgL-1 at 96h. The growth of C. mexicana was significantly inhibited at increased concentrations of CIP, showing 36±1, 75±3. and 88±3% inhibition at 40, 60 and 100mgL-1 CIP, respectively, compared to the control after 11days of cultivation. The total chlorophyll, carotenoid, MDA and SOD activity were significantly increased as a result of relatively high concentrations of CIP stress. C. mexicana showed 13±1% removal of CIP (2mgL-1) after 11days of cultivation; however, the addition of an electron donor (sodium acetate, 4gL-1) highly enhanced the removal of CIP (2mgL-1) by>3-fold after 11days. Kinetic studies showed that removal of CIP followed a first-order model (R2 0.94-0.97) with the apparent rate constants (k) ranging from 0.0121 to 0.079 d-1.