Benzene, toluene, and xylene (BTX) are volatile aromatic compounds used in industries, however, they are hazardous when released into the environment. BTX degradation by Aspergillus niger cells ...combined with semiconducting zinc sulfide (ZnS) nanoparticles was explored in batch systems. Experiments were conducted individually for benzene, toluene, and xylene as well as in binary and trinary mixtures using A. niger cells-ZnS nanobiohybrids. The mechanism governing the removal of BTX by both A. niger cells and A. niger cells-ZnS nanobiohybrids were elucidated. Complete BTX degradation was achieved in 75 min and 60 min, respectively, by nanobiohybrids composed of chemical and biological ZnS nanoparticles in the presence of UV-A light at 1.83 * 1018 photons/second and 1.68 * 1018 photons/second, respectively. The removal efficiency was in the order of the molecular weight for A. niger cells, whereas for the light-driven A. niger-ZnS nanobiohybrids, the removal efficiency was according to the methyl group number. Further, the respiratory coefficient and volumetric mass transfer coefficient (Ka) values are higher for A. niger cells compared to the light-driven A. niger-ZnS nanobiohybrids.
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•Removal efficiency of BTX hydrocarbons enhanced in the presence of light driven Aspergillus niger ZnS nanobiohybrids.•100% efficiency achieved in 75 min and 60 min with chemical and biological ZnS nanobiohybrids, respectively.•Respiratory coefficient values were higher for Aspergillus niger ZnS nanobiohybrids in the presence of light.•Degradation mechanisms for benzene, toluene and p-xylene proposed
Biological reduction of selenium oxyanions is widely used for selenium removal from wastewater. The process is, however, limited by the availability of a suitable, efficient and low cost electron ...donor. In this study, selenite and selenate reduction by waste activated sludge using hydrogen as the electron donor was investigated. Both selenite and selenate (80 mg/L) were completely removed using H2 within 8 days of incubation. In the presence of sulfate in the medium, the Se removal efficiency decreased to 77.8–95.4% (for selenite) and 88.2–99.4% (for selenate) at different temperatures and initial sulfate concentrations. Thermophilic conditions (50 °C) were better suited for both selenite and selenate reduction using H2 as electron donor with a 0.8–13.5% increase in overall Se removal. Similarly, sulfate reduction also increased from 69.1– 88% at 30 °C to 72–94.6% at 50 °C. Most of the H2 utilized was diverted towards Se and sulfate reduction with minimal production of byproducts such as methane (<0.32 mM) or volatile fatty acids (<0.92 mg/L). The elemental Se produced from selenite and selenate reduction ranged between 33.9 and 52.1 mg/L. The elemental selenium nanoparticles produced as a result of selenite and selenate reduction were characterized using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and dynamic light scattering (DLS) spectroscopy. Furthermore, characterization of the biomass using Fourier-transform infrared spectroscopy (FTIR) and excitation emission matrix (EEM) spectra of the extracellular polymeric substances (EPS) produced by the waste activated sludge were performed to elucidate the mechanism of selenium oxyanion reduction to elemental selenium nanoparticles.
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•Selenium oxyanion reduction using hydrogen as electron donor was assessed.•Simultaneous Se and sulfate reduction could be achieved.•Presence of sulfate negatively affected Se reduction.•Thermophilic temperature (50 °C) was better for Se reduction.•Majority of Se(VI)/Se(IV) was converted to elemental Se nanoparticles.
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•Colloidal stability of Se(0) is linked to its nanosize and ζ-potential (−20±5mV).•High speed (4500rpm) centrifugation achieved 91% Se(0) removal.•Filtration through 0.45μm filters ...yields a Se(0) removal efficiency of 87%.•Aluminum sulfate (10−3M) can sediment up to 92% of colloidal elemental selenium.•Al–Se sediment shows better dewaterability than Fe–Se sediment.
Biogenic selenium, Se(0), has colloidal properties and thus poses solid–liquid separation problems, such as poor settling and membrane fouling. The separation of Se(0) from the bulk liquid was assessed by centrifugation, filtration, and coagulation–flocculation. Se(0) particles produced by an anaerobic granular sludge are normally distributed, ranging from 50nm to 250nm, with an average size of 166±29nm and a polydispersity index of 0.18. Due to its nanosize range and protein coating-associated negative zeta potential (−15mV to −23mV) between pH 2 and 12, biogenic Se(0) exhibits colloidal properties, hampering its removal from suspension. Centrifugation at different centrifugal speeds achieved 22±3% (1500rpm), 73±2% (3000rpm) and 91±2% (4500rpm) removal. Separation by filtration through 0.45μm filters resulted in 87±1% Se(0) removal. Ferric chloride and aluminum sulfate were used as coagulants in coagulation–flocculation experiments. Aluminum sulfate achieved the highest turbidity removal (92±2%) at a dose of 10−3M, whereas ferric chloride achieved a maximum turbidity removal efficiency of only 43±4% at 2.7×10−4M. Charge repression plays a minor role in particle neutralization. The sediment volume resulting from Al2(SO3)4 treatment is three times larger than that produced by FeCl3.
Fermentation processes have been shown to be a good approach to food waste (FW) management. Among the commodities that can be bioproduced by using FW as an organic substrate and exploiting its ...biodegradability, there is lactic acid (LA). LA has gained the interest of research because of its role in the production of polylactic acid plastics. In this study, the influence of the HRT (2-5 days) used during the fermentation of the liquid fraction (∼12-13 g COD/L) of FW on LA yield and concentration was investigated. Moreover, the changes in the chemical composition (in terms of carbohydrates and organic metabolites concentration) of the influent occurring in the feeding tank were monitored and its influence on the downstream fermentation process was examined. High instability characterized the reactor run with the optimal production yield obtained on day 129 at an HRT 2 days with 0.81 g COD/g COD. This study shows the importance of the fluctuating composition of FW, a very heterogeneous and biologically active substrate, for the LA fermentation process. The non-steady state fermentation process was directly impacted by the unstable influent and shows that a good FW storage strategy has to be planned to achieve high and constant LA production.
Light-driven algal-bacterial granular sludge (ABGS) is an innovative low-carbon technology with significant merits in treating municipal wastewater, but how to shorten the photogranulation process, ...especially under low aeration conditions, is largely unknown. Herein, two strategies were proposed to accelerate the start-up of the ABGS system in photo-sequencing batch reactors (PSBRs) with a low superficial gas velocity of 0.5 cm/s. Compared to directly dosing mycelial pellets (MPs), applying MPs to flocculate algae and using the formed algal-mycelial pellets (AMPs) as carriers enhanced the establishment of the algal-bacterial symbiosis. The ABGS system developed rapidly within 20 days, with a large particle diameter (mean diameter of 321 μm) and excellent settleability (SVI30 of 55.4 mL/g). More importantly, this system could be stably operated for at least 100 days, mainly attributed to the reinforced secretion of protein with unique secondary structure and elevated hydrophobic functional groups. As for the reactor performance, the average removal efficiencies of the ABGS system were 97.8% for organic matter, 80.0% for total nitrogen, and 84.4% for phosphorus. The enrichment of functional bacteria and algae, and the up-regulation of functional genes and enzymes involved in electron production and transport processes likely drove the transformation of the pollutants, underlining the inherent mechanism for the excellent nutrient removal performance. This study provides a promising approach to solve the problem of a long ABGS start-up period and unstable granular structure under low aeration conditions, which is significant for achieving effective wastewater treatment without energy intensive aeration.
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•Compared to dosing MPs, applying AMPs as carriers facilitated the photogranulation.•ABGS was developed within 20 d under low aeration conditions (SGV of 0.5 cm/s).•AMPs enhanced the secretion of protein with unique structure and high hydrophobicity.•AMPs enriched the functional bacteria related to nutrient removal and aggregation.•AMPs upregulated the genes involved in electron production and transport processes.
Efficient anaerobic digestion requires the syntrophic cooperation among diverse microorganisms with various metabolic pathways. In this study, two operational modes, i.e., the sequencing batch ...reactor (SBR) and the continuous-flow reactor (CFR), were adopted in ethanol-fed systems with or without the supplement of powdered activated carbon (PAC) to examine their effects on ethanol metabolic pathways. Notably, the operational mode of SBR and the presence of CO
facilitated ethanol metabolism towards propionate production. This was further evidenced by the dominance of Desulfobulbus, and the increased relative abundances of enzymes (EC: 1.2.7.1 and 1.2.7.11) involved in CO
metabolism in SBRs. Moreover, SBRs exhibited superior biomass-based rates of ethanol degradation and methanogenesis, surpassing those in CFRs by 53.1% and 22.3%, respectively. Remarkably, CFRs with the extended solids retention time enriched high relative abundances of Geobacter of 71.7% and 70.4% under conditions with and without the addition of PAC, respectively. Although both long-term and short-term PAC additions led to the increased sludge conductivity and a reduced methanogenic lag phase, only the long-term PAC addition resulted in enhanced rates of ethanol degradation and propionate production/degradation. The strategies by adjusting operational mode and PAC addition could be adopted for modulating the anaerobic ethanol metabolic pathway and enriching Geobacter.
Electron transfer between microorganisms and an electrode — even across long distances — enables the former to live by coupling to an electronic circuit. Such a system integrates biological ...metabolism with artificial electronics; studying these systems adds to our knowledge of charge transport in the chemical species involved, as well as, perhaps most importantly, to our knowledge of charge transport and chemistry at the cell–electrode interfaces. This understanding may lead to microbial electrochemical systems finding widespread application, particularly in the energy sector. Bioelectrochemical systems have already shown promise for electricity generation, as well as for the production of biochemical and chemical feedstocks, and with improvement are likely to give rise to viable applications.Electrodes colonized by microbial electrocatalysts can serve as useful components in the electrosynthesis of valuable chemical products. This Review outlines the mechanisms by which electrons are transferred between microorganisms and electrodes, and describes the challenges involved in designing robust and efficient systems.
Upflow anaerobic sludge bed (UASB) bioreactors are commonly used for anaerobic wastewater treatment. Trace metals need to be dosed to these bioreactors to maintain microbial metabolism and growth. ...The dosing needs to balance the supply of a minimum amount of micronutrients to support a desired microbial activity or growth rate with a maximum level of micronutrient supply above which the trace metals become inhibitory or toxic. In studies on granular sludge reactors, the required micronutrients are undefined and different metal formulations with differences in composition, concentration and species are used. Moreover, an appropriate quantification of the required nutrient dosing and suitable ranges during the entire operational period has been given little attention. This review summarizes the state-of-the-art knowledge of the interactions between trace metals and cells growing in anaerobic granules, which is the main type of biomass retention in anaerobic wastewater treatment reactors. The impact of trace metal limitation as well as overdosing (toxicity) on the biomass is overviewed and the consequences for reactor performance are detailed. Special attention is given to the influence of metal speciation in the liquid and solid phase on bioavailability. The currently used methods for trace metal dosing into wastewater treatment reactors are overviewed and ways of optimization are suggested.
Certain types of anaerobic granular sludge, which consists of microbial aggregates, can reduce selenium oxyanions. To envisage strategies for removing those oxyanions from wastewater and recovering ...the produced elemental selenium (Se(0)), insights into the microbial community structure and synthesis of Se(0) within these microbial aggregates are required. High-throughput sequencing showed that Veillonellaceae (c.a. 20%) and Pseudomonadaceae (c.a.10%) were the most abundant microbial phylotypes in selenite reducing microbial aggregates. The majority of the Pseudomonadaceae sequences were affiliated to the genus Pseudomonas. A distinct outer layer (∼200 μm) of selenium deposits indicated that bioreduction occurred in the outer zone of the microbial aggregates. In that outer layer, SEM analysis showed abundant intracellular and extracellular Se(0) (nano)spheres, with some cells having high numbers of intracellular Se(0) spheres. Electron tomography showed that microbial cells can harbor a single large intracellular sphere that stretches the cell body. The Se(0) spheres produced by the microorganisms were capped with organic material. X-ray photoelectron spectroscopy (XPS) analysis of extracted Se(0) spheres, combined with a mathematical approach to analyzing XPS spectra from biological origin, indicated that proteins and lipids were components of the capping material associated to the Se(0) spheres. The most abundant proteins associated to the spheres were identified by proteomic analysis. Most of the proteins or peptide sequences capping the Se(0) spheres were identified as periplasmic outer membrane porins and as the cytoplasmic elongation factor Tu protein, suggesting an intracellular formation of the Se(0) spheres. In view of these and previous findings, a schematic model for the synthesis of Se(0) spheres by the microorganisms inhabiting the granular sludge is proposed.
Microbial reduction of selenium (Se) oxyanions to elemental Se is a promising technology for bioremediation and treatment of Se wastewaters. But a fraction of biogenic nano-Selenium (nano-Se
b
) ...formed in bioreactors remains suspended in the treated waters, thus entering the aquatic environment. The present study investigated the toxicity of nano-Se
b
formed by anaerobic granular sludge biofilms on zebrafish embryos in comparison with selenite and chemogenic nano-Se (nano-Se
c
). The nano-Se
b
formed by granular sludge biofilms showed a LC
50
value of 1.77 mg/L, which was 3.2-fold less toxic to zebrafish embryos than selenite (LC
50
=
0.55 mg/L) and 10-fold less toxic than bovine serum albumin stabilized nano-Se
c
(LC
50
=
0.16 mg/L). Smaller (nano-Se
cs
; particle diameter range: 25-80 nm) and larger (nano-Se
cl
; particle diameter range: 50-250 nm) sized chemically synthesized nano-Se
c
particles showed comparable toxicity on zebrafish embryos. The lower toxicity of nano-Se
b
in comparison with nano-Se
c
was analyzed in terms of the stabilizing organic layer. The results confirmed that the organic layer extracted from the nano-Se
b
consisted of components of the extracellular polymeric substances (EPS) matrix, which govern the physiochemical stability and surface properties like ζ-potential of nano-Se
b
. Based on the data, it is contented that the presence of humic acid like substances of EPS on the surface of nano-Se
b
plays a major role in lowering the bioavailability (uptake) and toxicity of nano-Se
b
by decreasing the interactions between nanoparticles and embryos.
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