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•The addition of fats, oil and grease enhanced ultimate methane production by 217%.•Firmicutes, Bacteriodetes, Synergistetes and Euryarchaeota were greatly increased.•Dominance of ...Methanosaeta was replaced by Methanosarcina at the end of digestion.•Methane was predominantly generated through acetoclastic pathway by Methanosarcina.
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.
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•Chlorella vulgaris was tolerant to levofloxacin, and could withstand its high doses.•96h EC50 of levofloxacin for C. vulgaris was 58.6mgL−1.•The acclimation of C. vulgaris enhanced ...the removal of levofloxacin.•Sodium chloride stimulated the biodegradation of levofloxacin up to 91%.•NaCl (1%w/v) increased the degradation rate constant (k) of LEV from 0.011 to 0.257d−1.
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 1mgL−1. The acclimated C. vulgaris, which was pre-exposed to 200mgL−1 of LEV for 11days, exhibited enhanced removal of 1mgLEVL−1 by 16% after 11days 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 34μgg−1, which was elevated to 101μgg−1LEV 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.
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.
Water contamination with numerous pharmaceutical contaminants (PCs) has been one of the most important emerging environmental problems facing humanity due to their ecotoxicities and health issues.
Culturing microalgae in wastewater can create a ‘zero-waste concept’ and stimulate an effective and sustainable practice for the microalgae biofuel industry.
Constructing microbial consortia, acclimating microorganisms, and cometabolic approaches can improve the engineering feasibility of microalgae-based biotechnologies.
Some innovative concepts, such as integrated processes (algae-based technologies with advanced oxidation processes, constructed wetlands, and microbial fuel cells) and genetic modifications, can help to realize algae-based bioremediation technologies.
•Methane productivity of unacclimatized and acclimatized sludge were investigated.•Biogas produced in ASS showed higher methane content (65–76%) than in USS (26–73%).•The ASS exhibited greater ...degradation of LCFAs than in USS.•Firmicutes, Bacteroidetes, Synergistetes and Euryarchaeota were highly increased.•Abundance of Syntrophomonas and Methanosarcina in ASS improved methane generation.
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.
•Challenges in biomethane production from anaerobic co-digestion of FOG.•Pretreatment of FOG for improved anaerobic co-digestion.•Metagenomics of population dynamics and interspecies ...interactions.•Process optimization for FOG co-digestion.•Operation of commercial plants and economic feasibility of FOG co-digestion.
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.
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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.
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•Toxicity of enrofloxacin on pure microalgae and microalgae consortium was studied.•Enrofloxacin influenced the biochemical characteristics of microalgae cells.•96 h EC50 of enrofloxacin ranged from 9.6 to 15.0 mg L-1 for microalgae.•Microalgae consortium showed highest sensitivity to enrofloxacin.•Enrofloxacin removal by the consortium was comparable to that of the individual microalgal species.
Detailed studies on the ecotoxicological effects of one emerging contaminant, enrofloxacin and its remediation by microalgae were investigated.
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 < 20 °C has gained significant attention for improvement of biogas productivity in cold regions. The present review discusses the detailed characteristics of psychrophilic anaerobes, and how the properties of those particular psychrophiles can be utilized towards the cost-effective production of methane at cold environment. The different challenges for AD at low temperature have been described thoroughly. The various strategies such as (a) adaptation of microbial community, (b) optimization of operational parameters, (c) utilization of specialized biodigester design, and (d) modification of downstream process to improve the AD and biomethane production in cold environments have also been summarized. The present review proposes the future technological developments which should be aimed at effective performance of anaerobic digesters to improve biomethanation in cold regions.
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•Psychrophilic AD is an energy efficient process for biomethanation in cold regions.•Alterations of cellular physiology increases the adaptive response in psychrophiles.•Cold adaptation of inoculum and process optimization could improve psychrophilic AD.
•Addition of calcium improved the co-digestion of fat, oil, and grease (FOG).•Calcium (0.3–0.5% w/v) enhanced the biomethane production and COD removal.•Higher calcium concentrations (0.7–1% w/v) ...affected the anaerobic co-digestion.•Calcium supported the growth of un-acclimated microbes by lowering FOG toxicity.
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.
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•Toxicological effects of ciprofloxacin on C. mexicana was studied.•96h EC50 of ciprofloxacin for C. mexicana was 65mgL−1.•Ciprofloxacin influenced the biochemical characteristics of ...microalgal cells.•MDA and SOD of C. mexicana were significantly increased by ciprofloxacin.•Sodium acetate acts as an electron donor and enhanced ciprofloxacin removal.
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.
A composite adsorbent to remove arsenite As(III), arsenate As(V), and copper Cu(II) from aqueous phase was synthesized by immobilizing zirconium oxide on alginate beads (ZOAB). The composition (wt%) ...of ZOAB (Zr-34.0; O-32.7; C-21.3; Ca-1.0) was confirmed by energy dispersive X-ray (EDX) analysis. Sorption studies were conducted on single and binary sorbate systems, and the effects of contact time, initial adsorbate concentration, and pH on the adsorption performance of ZOAB (pHPZC = 4.3) were monitored. The sorption process for As(III)/As(V) and Cu(II) reached an equilibrium state within 240 h and 24 h, respectively, with maximum sorption capacities of 32.3, 28.5, and 69.9 mg g−1, respectively. The addition of Cu(II) was favorable for As(V) sorption in contrast to As(III). In the presence of 48.6 mg L−1 Cu(II), the sorption capacity of As(V) increased from 1.5 to 3.8 mg g−1 after 240 h. The sorption data for As(III)/As(V) and Cu(II) conformed the Freundlich and Langmuir isotherm models, respectively. The adsorption of As(III), As(V), and Cu(II) followed pseudo second order kinetics. The effect of arsenic species on Cu(II) sorption was insignificant. The results of present study demonstrated that the synthesized sorbent could be useful for the simultaneous removal of both anionic and cationic contaminants from wastewaters.
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•Hydrous zirconium oxide-immobilized alginate beads (ZOAB) were synthesized.•ZOAB successfully removed arsenite, arsenate and copper ion from aqueous phase.•Addition of Cu2+ was favorable for arsenate sorption.•Maximum sorption capacities (qmax) of ZOAB for AsO33−, AsO43− and Cu2+ were 32.3, 28.5 and 69.9 mg g−1.•Sorption followed pseudo-second order kinetics.
