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Nanoparticles are inevitable byproducts of modern industry. However, the environmental impacts arising from industrial applications of nanoparticles are largely under-reported. This study evaluated the ecotoxicological effects of aluminum oxide nanoparticles (Al

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.

The anaerobic digestion (AD) has become an important part of the wastewater treatment plants that regulates the sustainable management of organic wastes with simultaneous production of bioenergy. AD at low temperatures using psychrophilic anaerobes with optimum growth temperatures

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%).

Textile dyes are xenobiotic contaminants which pose a potential risk on the ecosystem upon their disposal to the water bodies. This study evaluated the efficiencies of different immobilization matrices for its utilization in a reactor with continuous mode operation for decolorization of textile effluent. An effective consortium of bacteria (Brevibacillus laterosporus) and yeast (Galactomyces geotrichum) were immobilized in different support matrices including calcium alginate, polyvinyl alcohol, stainless steel sponge and polyurethane foam to investigate the decolorization of a model azo dye, Remazol red and textile industry effluent. The microbial consortia immobilized in stainless steel sponge and polyurethane foam exhibited 100% decolorization of 50 mg L−1 Remazol red in 11 and 15 h, respectively; however, calcium alginate and polyvinyl alcohol required considerably more time (20 and 24 h, respectively) for complete decolorization. Among all the matrices, The calcium alginate, stainless steel sponge and polyurethane foam showed >95% decolorization of textile industry effluent within 48 h. The calcium alginate and polyvinyl alcohol exhibited stable performance of decolorization with its repeated use for 5 cycles with >76% decolorization. An upflow fixed bed reactor (total volume- 215 mL) packed with the immobilized cells of consortium onto stainless steel sponge attained ∼90% decolorization of textile industry effluent in continuous operation at 10 mL h−1. The decolorization efficiency of the reactor was well maintained (>90%) when the reactor was used repeatedly for three cycles. The overall results indicated that immobilized mixed consortium cells can be considered as an effective tool for its potential application in removal of xenobiotic textile dyes from the textile industry wastewater with >90% of decolorization efficiency.

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.

A novel metal-biochar (Biochar/AMDS) composite were fabricated by co-pyrolysis of spent coffee waste (SCW)/acid mine drainage sludge (AMDS), and their effective application in adsorptive removal of air pollutants such as formaldehyde in indoor environments was evaluated. The physicochemical characteristics of Biochar/AMDS were analyzed using SEM/EDS, XRF, XRD, BET, and FTIR. The characterization results illustrated that Biochar/AMDS had the highly porous structure, carbonaceous layers, and heterogeneous Fe phases (hematite, metallic Fe, and magnetite). The fixed-bed column test showed that the removal of formaldehyde by Biochar/AMDS was 18.4-fold higher than that by metal-free biochar (i.e., SCW-derived biochar). Changing the ratio of AMDS from 1:6 to 1:1 significantly increased the adsorption capacity for formaldehyde from 1008 to 1811 mg/g. In addition, thermal treatment of used adsorbent at 100 °C effectively restored the adsorptive function exhausted during the column test. These results provide new insights into the fabrication of practical, low-cost and ecofriendly sorbent for formaldehyde.

Lipidic-waste such as fat, oil, and grease (FOG) are promising substrates for achieving higher bioenergy yields. An inadequate presence of an effective microbiome in the anaerobic digesters is the bottleneck for the proper utilization of FOG. Gradual introduction of FOG (0.2%, 1.2%, and 2.4% as volatile solids) in acidogenic fermentation showed a significant improvement in hydrogen yield (72%), compared to the control, after 2.4% FOG loading. Volatile solid (VS) reduction reached up to 65% in high FOG reactors with complete removal of major unsaturated fatty acids. Removal of saturated fatty acids increased to 90%. Improvement in hydrogen productivity (46 mL d−1) occurred during step-wise loading of 2.4% FOG to the acclimatized microbiome. The metabolic shift toward carboxylic chain elongation produced C4 and C6 fatty acids at concentrations of 1.61 mM and 0.90 mM, respectively in the acidogenic reactors. High-throughput sequencing of 16S rRNA amplicons revealed that the acclimatization process enriched the phylum Firmicutes (90%), followed by Bacteroidetes (12%) and Cloacimonetes (11%). The abundance of these phyla and their respective genera confirmed their preeminent role in hydrolysis, hydrogenogenic acidogenesis, and carboxylic chain elongation to produce hydrogen and C4–C7 fatty acids. Thus, we suggest that the improvement of hydrogen production using a microbiome acclimatized to FOG, and simultaneous production of high value organics (C4–C7 fatty acids), could facilitate the greater efficacy of the acidogenic fermentation.

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.

Anaerobic digestion (AD) of wastewater sludge is an effective approach to produce biomethane and subsequently reduce the amount of sludge disposal to landfill generated from wastewater treatment plants (WWTPs). Recently, anaerobic co-digestion (ACD) of lipidic-waste such as fat, oil, and grease (FOG) has received much attention for the enhancement of biomethanation in WWTPs. However, there are several major challenges associated with ACD of FOG which includes inhibition by long chain fatty acids, sludge floatation and washout, and scum formation. This review summarizes the scientific and engineering aspects of the FOG supplementation as a co-substrate in AD as well provides appropriate solutions for challenges encountered during the anaerobic operation. The discussion on the existing pretreatment approaches (including mechanical, thermo-chemical, and biological) for rapid degradation of FOG was also highlighted. Metagenomic analysis elucidates the microbial community and the interspecies interactions which are responsible for the degradation of FOG and its biomethanation during ACD. Addition of FOG to AD was found be economically feasible in municipal WWTPs.

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.

Microalgal biomass has received much attention as feedstock for biofuel production due to its capacity to accumulate a substantial amount of biocomponents (including lipid, carbohydrate, and protein), high growth rate, and environmental benefit. However, commercial realization of microalgal biofuel is a challenge due to its low biomass production and insufficient technology for complete utilization of biomass. Recently, advanced strategies have been explored to overcome the challenges of conventional approaches and to achieve maximum possible outcomes in terms of growth. These strategies include a combination of stress factors; co-culturing with other microorganisms; and addition of salts, flue gases, and phytohormones. This review summarizes the recent progress in the application of single and combined abiotic stress conditions to stimulate microalgal growth and its biocomponents. An innovative schematic model is presented of the biomass-energy conversion pathway that proposes the transformation of all potential biocomponents of microalgae into biofuels.

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 of energy-efficient conversion of highly concentrated microalgal suspensions to produce high-titer biofuels is a major bottleneck due to high energy consumption. Herein, high-titer biofuels (bioethanol, higher-alcohols, and biodiesel) were generated from carbohydrate-rich Chlamydomonas mexicana and lipid-rich Chlamydomonas pitschmannii biomass through energy-saving microwave pretreatment, successive fermentation, and transesterification. Microwave pretreatment needed low specific energy (4.2 MJ/kg) for 100 g/L of microalgal suspension. Proposed sustainable integrated pretreatments method achieved unprecedented total conversion efficiency (67%) and highest biomass utilization (87%) of C. pitschmannii (100 g/L) with high yields of bioethanol (0.48 g-ethanol/g-carbohydrates), higher-alcohols (0.44 g-higher-alcohols/g-proteins), and biodiesel (0.90 g-biodiesel/g-lipids). Transmission electron microscopy showed the changes in the microalgal cellular integrity before and after sequential fermentations. Energy-efficient integrated pretreatments enhanced the extraction efficiency and whole utilization of high-concentration microalgae to generate high-titer biofuels with minimum waste production.

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.

Contamination of fluoroquinolones (FQs) are of emerging concerns because of their adverse effects on environment and humans. This study investigated the ecotoxicological effects, biodegradation, and multiple metabolic pathways of a frequently found FQ, enrofloxacin (ENR) by ryegrass (Lolium perenne L.). Key metabolic genes for driving the metabolism of ENR have been identified using transcriptome profiling of L. perenne and gene network analysis. Toxicity of ENR on ryegrass has been evaluated according to the morphological changes, lipid peroxidation content, and antioxidant enzymatic activities. Moreover, there was 94.33%, 71.58%, 57.22%, and 55.23% removal of 1, 10, 50 and 100 mg L−1 ENR, respectively, which was mainly achieved by biodegradation according to the mass balance. A biodegradation pathway has been proposed by incorporating mass spectrums of extracted ENR intermediates with their formation dynamics. Analysis of differentially expressed genes (DEGs) and their network unraveled that the genes encoding monooxygenase, oxidative carboxylase, methyltransferase, lyase, hydroxylase, dehydrogenase, and peroxidase were the key functional genes. These enzymes can induce di/hydroxylation, decarboxylation, methylation, and bond and ring cleavage of ENR for its effective degradation. This study demonstrated that ryegrass can be used for efficient treatment of ENR polluted water and extended the understanding of the molecular mechanism of antibiotics’ biodegradation in plants.

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.

Microalgae are a potential source of sustainable biomass feedstock for biofuel generation, and can proliferate under versatile environmental conditions. Mass cultivation of microalgae is the most overpriced and technically challenging step in microalgal biofuel generation. Wastewater is an available source of the water plus nutrients necessary for algae cultivation. Microalgae provide a cost-effective and sustainable means of advanced (waste)water treatment with the simultaneous production of commercially valuable products. Microalgae show higher efficiency in nutrient removal than other microorganisms because the nutrients (ammonia, nitrate, phosphate, urea and trace elements) present in various wastewaters are essential for microalgal growth. Potential progress in the area of microalgal cultivation coupled with wastewater treatment in open and closed systems has led to an improvement in algal biomass production. However, significant efforts are still required for the development and optimization of a coupled system to simultaneously generate biomass and treat wastewater. In this review, the systematic description of the technologies required for the successful integration of wastewater treatment and cultivation of microalgae for biomass production toward biofuel generation was discussed. It deeply reviews the microalgae-mediated treatment of different wastewaters (including municipal, piggery/swine, industrial, and anaerobic wastewater), and highlight the wastewater characteristics suitable for microalgae cultivation. Various pretreatment methods (such as filtration, autoclaving, UV application, and dilution) needed for wastewater prior to its use for microalgae cultivation have been discussed. The selection of potential microalgae species that can grow in wastewater and generate a large amount of biomass has been considered. Discussion on microalgal cultivation systems (including raceways, photobioreactors, turf scrubbers, and hybrid systems) that use wastewater, evaluating the capital expenditures (CAPEX) and operational expenditures (OPEX) of each system was reported. In view of the limitations of recent studies, the future directions for integrated wastewater treatment and microalgae biomass production for industrial applications were suggested.

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.

Methanation was improved during the dual-stage pulse-feed anaerobic co-digestion of extracted lipid (EL) from food waste leachate using acclimatized consortia by gradually increasing the organic loading rates (OLRs) in the subsequent phases. The utilization of major saturated and unsaturated long chain fatty acids (LCFAs) reached 78% and 98% in the acidogenic fermenters with consecutive organic loading, respectively. The acclimatized consortium induced the LCFA degradation and interconversion of short-medium chain fatty acids (SCFA–MCFAs) in the fermenters, even under highest OLR values. The highest methane yield (0.46 g g−1 VSinitial) was achieved in the third phase (61% EL loading of total injected volatile solid) with the complete utilization of LCFAs and SCFA–MCFAs in the digester. The assessment of the microbial community revealed that acidogenic Intestinimonas and Megasphaera, and acetogenic Levilinea were predominant in the fermenters due to their preeminent activities. The predominance of acetogenic Syntrophomonas (26%) indicated that it played a major role in β-oxidation, and its syntrophy with mixotrophic methanogens, such as Methanosarcina (93%), facilitated methanation through the complete degradation of EL in the digesters. The use of pulse-feed operation in dual-stage anaerobic co-digestion improved the methanation through complete utilization of EL under varied OLRs mediated by the acclimatized consortia.

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.