Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 175
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Environ Sci Technol ; 54(17): 10904-10915, 2020 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-32867479

RESUMO

A novel zerovalent iron (ZVI) technique to simultaneously improve the production of medium-chain fatty acids (MCFAs) from waste activated sludge (WAS) and enhance WAS degradation during anaerobic WAS fermentation was proposed in this study. Experimental results showed that the production and selectivity of MCFAs were effectively promoted when ZVI was added at 1-20 g/L. The maximum MCFAs production of 15.4 g COD (Chemical Oxygen Demand)/L and MCFAs selectivity of 71.7% were both achieved at 20 g/L ZVI, being 5.3 and 4.8 times that without ZVI (2.9 g COD/L and 14.9%). Additionally, ZVI also promoted WAS degradation, which increased from 0.61 to 0.96 g COD/g VS when ZVI increased from 0 to 20 g/L. The microbial community analysis revealed that the ZVI increased the populations of key anaerobes related to hydrolysis, acidification, and chain elongation. Correspondingly, the solubilization, hydrolysis, and acidification processes of WAS were revealed to be improved by ZVI, thereby providing more substrates (short-chain fatty acids (SCFAs)) for producing MCFAs. The mechanism studies showed that ZVI declined the oxidation-reduction potential (ORP), creating a more favorable environment for the anaerobic biological processes. More importantly, ZVI with strong conductivity could act as an electron shuttle, contributing to increasing electron transfer efficiency from electron donor to acceptor. This strategy provides a new paradigm of transforming waste sludge into assets by a low-cost waste to bring significant economic benefits to sludge disposal and wastewater treatment.

2.
Water Res ; 186: 116381, 2020 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-32916621

RESUMO

Traditional bioenergy recovery in the form of short chain fatty acids (SCFAs) from waste activated sludge (WAS) is generally limited by economic unattractiveness and complexity of products separation. Herein, a novel biotechnology process of two-stage anaerobic fermentation for converting the WAS into high energy density, easy-separated medium chain fatty acids (MCFAs) and long-chain alcohols (LCAs) was evaluated. In this process, the WAS was first converted to WAS alkaline fermentation liquid (WASAFL), serving as electron acceptors (EAs) and inoculum, then adding ethanol as electron donor (ED) for chain elongation (CE). The co-production of MCFAs and LCAs during CE were studied under three different ED to EA ratios, i.e., 3:1, 4:1 and 5:1. Experimental results demonstrated that when the ratio of ED to EA increased from 3:1 to 5:1, the production of MCFA and LCAs respectively increased from 5.57 ±â€¯0.17 and 2.58 ±â€¯0.18 to7.67 ±â€¯0.48 and 4.21 ±â€¯0.19 g COD/L. A similar observation was made in the total product electron efficiency, increasing from 59.9% to 72.1%. However, the highest total product selectivity (i.e., 68.0%) and highest products production yield (i.e., 59.77%) were not achieved at the ED to EA ratio of 5:1 due to toxicity caused by higher accumulation of n-caproate. The kinetic analysis further confirmed that high ratio of ED to EA induced improvement in product maximum yield, production rate for both MCFAs and LCAs. Microbial community analysis indicated that Clostridium, Caproiciproducens, Acinetobacter, Exilispira, and Oscillibacter were clearly enriched in the CE reactor and had positive correlation with MCFAs and LCAs production.

3.
Environ Sci Technol ; 54(17): 10964-10973, 2020 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-32786580

RESUMO

As a promising technology for sustainable nitrogen removal from wastewater, the membrane-aerated biofilm reactors (MABRs) performing autotrophic deammonification are faced with the problem of unwanted production of nitrous oxide (N2O, a potent greenhouse gas). As a common tool to study N2O production from such an MABR, the traditional one-dimensional modeling approach fails to simulate the existence of longitudinal gradients in the reactor and therefore might render N2O production significantly deviated from reality. To this end, this work aims to study the influences of key longitudinal gradients (i.e., in oxygen, liquid-phase components, and biofilm thickness) on the N2O production from a typical MABR performing autotrophic deammonification by applying a modified version of a newly developed compartmental model. Through comparing the modeling results of different reactor configurations, this work reveals that the single impact of the longitudinal gradients studied on the N2O production from the MABR follows the order: oxygen (significant) > liquid-phase components (slight) > biofilm thickness (almost none). When multiple longitudinal gradients are present, they become correlated and would jointly influence the N2O production and nitrogen removal of the MABR. The results also show the need for multispot measurements to get an accurate representation of spatial biofilm features of the MABR configuration with the membrane lumen designed/operated as a plug flow reactor. While the traditional modeling approach is acceptable to evaluate the nitrogen removal in most cases, it might overestimate or underestimate the N2O production from the MABR with at least one of the longitudinal gradients in oxygen and liquid-phase components. For such an MABR, the longitudinal heterogeneity in biofilm thickness and the number of biofilm thickness classes to be included in the model would also make a difference to the simulation results, especially the N2O production. The work also proposes that under the studied conditions, proper design/operation of the MABR in consideration of longitudinal heterogeneity has the theoretical potential of reducing the N2O production by 77% without significantly compromising the nitrogen removal.

4.
Water Res ; 185: 116196, 2020 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-32738601

RESUMO

Mitigation of nitrous oxide (N2O) emissions is of primary importance to meet the targets of reducing carbon footprints of wastewater treatment plants (WWTPs). Despite of a large amount of N2O mitigation studies conducted in laboratories, full-scale implementation of N2O mitigation is scarce, mainly due to uncertainties of mitigation effectiveness, validation of N2O mathematical model, risks to nutrient removal performance and additional costs. This study aims to address the uncertainties by investigating the quantification, development and implementation of N2O mitigation strategies at a full-scale sequencing batch reactor (SBR). To achieve this, N2O emission dynamics, nutrient removal performance and operation of the SBR were monitored to quantify N2O emissions, and identify the N2O generation mechanisms. N2O mitigation strategies centered on reducing dissolved oxygen (DO) levels were consequently proposed and evaluated using a multi-pathway N2O production mathematical model before implementation. The implemented mitigation strategy resulted in a 35% reduction in N2O emissions (from the emission factor of 0.89 ± 0.05 to 0.58 ± 0.06%), which was equivalent to annual reduction of 2.35 tonne of N2O from the studied WWTP. This could be mainly attributed to reductions in N2O generated via the NH2OH oxidation pathway due to the lowering of DO level. As the first reported mitigation strategy permanently implemented at a full scale WWTP, it showcased that the mitigation of N2O emissions at full-scale is feasible and that widely accepted N2O mitigation strategies developed in laboratory studies are also likely effective in full-scale plants. Furthermore, the close agreement between the validated and predicted N2O emission factors (0.58% vs 0.55%, respectively), showed that the N2O mathematical model is a useful tool to evaluate N2O mitigation strategies at full-scale. Importantly this work demonstrated that N2O mitigation does not necessarily require additional operational cost to meet reduction targets. In contrast, the N2O mitigation applied here reduced energy requirements for aeration by 20%. Equally important, long-term monitoring identified that N2O mitigation did not affect the nutrient removal performance of the plant. Finally, with the knowledge acquired in this study, a standard approach for mitigating N2O emissions from full-scale treatment plants was proposed.

5.
Water Res ; 185: 116273, 2020 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-32805664

RESUMO

The widespread of antibiotic resistance genes (ARGs) in the environment can pose severe threats to public health. The wastewater treatment plant (WWTP) is regarded as an important hotspot of ARGs in the urban environment, but the removal of ARGs through conventional treatment techniques has been proven not sufficient. In this study, ferrate (Fe(VI)) was applied for the first time to remove intracellular ARGs from the secondary effluent of the WWTP. The results showed that Fe(VI) treatment could effectively remove 15 ARGs covering eight different types as well as intI1, the most common integron important to ARGs horizontal transfer. The removal efficiencies of tested genes could reach 1.10-4.37 log at the Fe(VI) dosage of 10 mg-Fe/L, which is significantly higher than those achieved through traditional disinfection methods. The DNA gel electrophoresis suggested that Fe(VI) could induce microbial DNA damage and consequently resulted in ARGs elimination. The presence of ARGs in settled residues indicated that coagulation initiated by Fe(VI) reduction products also contributed to ARGs removal from wastewater. In addition, the viability and relative abundances of potential ARGs hosts in the wastewater were decreased after Fe(VI) treatment. This study suggested a promising prospect for applying Fe(VI) to efficiently remove ARGs from wastewater, and consequently to control their proliferation and transfer in the environment.

6.
Bioresour Technol ; 316: 123947, 2020 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-32769002

RESUMO

Deterioration of anaerobic fermentation can occur with the presence of grease in food waste, but little information on eliminating this deterioration is currently available. In this study, it was found that the presence of 10 g/L grease decreased SCFAs production from 16.97 to 13.32 g COD/L and prolonged the optimal fermentation time to 7 days, but could be respectively recovered to 39.10 g COD/L and 4 days with 0.02 mg/g VS (volatile solids) calcium peroxide addition. Mechanism investigations indicated that calcium peroxide facilitated biodegradable organics release and improved grease degradation, thereby providing enough nutrients and better growth environments to microbes for SCFAs-producing, which could be further supported by the elevated enzymes activities responding to hydrolysis and acidification process. Further investigations revealed that among the main derivates of calcium peroxide, OH- and Ca2+ played vital role in SCFAs production promotion, O2- and OH radicals were the main contributors to grease degradation.

7.
Water Res ; 186: 116311, 2020 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-32836148

RESUMO

Perfluorochemicals (PFCs) are a set of chemicals containing C-F bonds, which are concerned due to their bioaccumulation property, persistent and toxicological properties. Photocatalytic approaches have been widely studied for the effective removal of PFCs due to the mild operation conditions. This review aims to provide a comprehensive and up-to-date summary on the homogenous and heterogeneous photocatalytic processes for PFCs removal. Specifically, the homogenous photocatalytic methods for remediating PFCs are firstly discussed, including generation of hydrated electrons (eaq‒) and its performance and mechanisms for photo-reductive destruction of PFCs, the active species responsible for photo-oxidative degradation of PFCs and the corresponding mechanisms, and metal-ion-mediated (Fe(III) mainly used) processes for the remediation of PFCs. The influences of molecular structures of PFCs and water matrix, such as dissolved oxygen, humic acid, nitrate, chloride on the homogenous photocatalytic degradation of PFCs are also discussed. For heterogeneous photocatalytic processes, various semiconductor photocatalysts used for the decomposition of perfluorooctanoic acid (PFOA) are then discussed in terms of their specific properties benefiting photocatalytic performances. The preparation methods for optimizing the performance of photocatalysts are also overviewed. Moreover, the photo-oxidative and photo-reductive pathways are summarized for remediating PFOA in the presences of different semiconductor photocatalysts, including active species responsible for the degradation. We finally put forward several key perspectives for the photocatalytic removal of PFCs to promote its practical application in PFCs-containing wastewater treatment, including the treatment of PFCs degradation products such as fluoride ion, and the development of noble-metal free photocatalysts that could efficiently remove PFCs under solar light irradiation.

8.
Neural Plast ; 2020: 7839536, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32684923

RESUMO

AD is a common chronic progressive neurodegenerative disorder. However, the understanding of the dynamic longitudinal change of the brain in the progression of AD is still rough and sometimes conflicting. This paper analyzed the brain networks of healthy people and patients at different stages (EMCI, LMCI, and AD). The results showed that in global network properties, most differences only existed between healthy people and patients, and few were discovered between patients at different stages. However, nearly all subnetwork properties showed significant differences between patients at different stages. Moreover, the most interesting result was that we found two different functional evolving patterns of cortical networks in progression of AD, named 'temperature inversion' and "monotonous decline," but not the same monotonous decline trend as the external functional assessment observed in the course of disease progression. We suppose that those subnetworks, showing the same functional evolving pattern in AD progression, may have something the same in work mechanism in nature. And the subnetworks with 'temperature inversion' evolving pattern may play a special role in the development of AD.

9.
Environ Sci Technol ; 54(15): 9175-9190, 2020 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-32657581

RESUMO

The continuous increase of nitrous oxide (N2O) in the atmosphere has become a global concern because of its property as a potent greenhouse gas. Given the important role of ammonia-oxidizing archaea (AOA) in ammonia oxidation and their involvement in N2O production, a clear understanding of the knowledge on archaeal N2O production is necessary for global N2O mitigation. Compared to bacterial N2O production by ammonia-oxidizing bacteria (AOB), AOA-driven N2O production pathways are less-well elucidated. In this Critical Review, we synthesized the currently proposed AOA-driven N2O production pathways in combination with enzymology distinction, analyzed the role of AOA species involved in N2O production pathways, discussed the relative contribution of AOA to N2O production in both natural and anthropogenic environments, summarized the factors affecting archaeal N2O yield, and compared the distinctions among approaches used to differentiate ammonia oxidizer-associated N2O production. We, then, put forward perspectives for archaeal N2O production and future challenges to further improve our understanding of the production pathways, putative enzymes involved and potential approaches for identification in order to potentially achieve effective N2O mitigations.

10.
Environ Sci Technol ; 54(15): 9662-9671, 2020 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-32658461

RESUMO

Polyvinyl chloride microplastics (PVC-MPs) are emerging contaminants affecting biological wastewater treatment processes. However, most of the previous studies mainly focused on their short-term impacts on floc sludge, with little work being conducted to explore their potential effects on more complex anaerobic granular sludge (AGS), which has been widely used for high-strength organic wastewater treatment. In this paper, the long-term effects of PVC-MPs on AGS were investigated via continuous feeding tests that are representative of real wastewater treatment processes. The results of a continuous 264 days test showed that the prolonged exposure of PVC-MPs at 15-150 MPs·L-1 significantly (p = 7.86 × 10-37, 3.44 × 10-43, and 5.29 × 10-46) inhibited the COD removal efficiency of AGS by 13.2%-35.5%, accompanied by a 11.0%-32.3% decreased production of methane and 40.3%-272.7% increased accumulation of short-chain fatty acids (SCFAs). In addition, the PVC-MPs exposure suppressed the secretion of extracellular polymeric substances (EPS), causing AGS and the inside microorganisms to lose the protection of EPS, thereby resulting in granule breakage and decreased cells viability. Aligning with the deteriorated performance, the long-term exposure of PVC-MPs reduced the total microbial populations and the relative abundances of key methanogens and acidogens. A toxicity mechanism assessment revealed that the negative impacts induced by PVC-MPs are mainly attributed to the toxic leachate and excess oxidative stress.

11.
J Hazard Mater ; 398: 122897, 2020 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-32516728

RESUMO

Natural sponge is an ancient marine organism with a single lamellar structure, on which there are abundant porous channels to compose full-fledged spatial veins. Illumined by the natural spongy system, herein, the Cl doped surface defective graphite carbon nitride (g-C3N4-xClx) was constructed through microwave etching. In this process, microwave with HCl was employed to produce surface defects and peel bulk g-C3N4 to form natural spongy structured g-C3N4-xClx with three-dimensional networks. The spongy structure of the photocatalyst could provide abundant and unobstructed pathways for the transfer and separation of electron-hole pairs, and it was beneficial for photocatalytic reaction. The spongy defective g-C3N4-xClx achieved excellent degradation of diclofenac sodium (100%), bisphenol A (88.2%), phenol (85.7%) and methylene blue (97%) solution under simulated solar irradiation, respectively. The chlorine atoms were introduced into the g-C3N4 skeleton in microwave field with HCl, forming C-Cl bonds and surface polarization field, which could significantly accelerate the separation of photogenerated electrons and holes. As an efficient and universal approach, microwave etching can be generally used to create surface defects for most photocatalysts, which may have potential applications in environmental purification, energy conversion and photodynamic therapy.

12.
Water Res ; 182: 116041, 2020 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-32574821

RESUMO

Wastewater has been identified as an important carrier for nanoplastics, which could elicit unintended impacts on critical microbial processes. However, the long-term impacts of nanoplastics on anaerobic granular sludge (AGS) for methane recovery from wastewater and the mechanisms involved remains unclear. In this study, we investigated the long term exposure-response relationship between polystyrene nanoplastics (Nano-PS) and AGS. In continuous test over 120 days with 86 days' Nano-PS exposure, feeding wastewater with 10 µg/L of Nano-PS had no significant impacts on the AGS performance. In comparison, higher levels (i.e., 20 and 50 µg/L) of Nano-PS decreased methane production and chemical oxygen demand (COD) removal by 19.0-28.6% and 19.3-30.0%, respectively, along with volatile fatty acids (VFA) accumulation. More extracellular polymeric substance (EPS) was induced by 10 µg/L of Nano-PS as a response to protect microbes, but higher levels (i.e., 20 and 50 µg/L) of Nano-PS decreased EPS generation, causing a decline in granule size and cell viability. Fluorescence tagging found that a large number of Nano-PS agglomerated/accumulated on the outer layer of AGS and even transferred into deeper layers of AGS over exposure time, producing toxic effects to adherent microorganisms, e.g., Longilinea sp., Paludibacter sp. and Methanosaeta sp.. The oxidative stress induced by Nano-PS was revealed to be a key factor for reshaping the AGS, reflected by the increased reactive oxygen species (ROS) generation and lactate dehydrogenase (LDH) release. The sodium dodecyl sulfate (SDS) leached from Nano-PS was also demonstrated to restrain the activities of antioxidant enzymes, thereby further lessening resistance to oxidative stress induced by Nano-PS. This work improves our ability to predict the risks associated with this ubiquitous contaminant in the environment.


Assuntos
Esgotos , Águas Residuárias , Anaerobiose , Reatores Biológicos , Matriz Extracelular de Substâncias Poliméricas , Metano , Microplásticos , Poliestirenos , Eliminação de Resíduos Líquidos
13.
J Phys Chem Lett ; : 4990-4997, 2020 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-32498513

RESUMO

Polar surfaces of ionic crystals are of growing technological importance, with implications for the efficiency of photocatalysts, gas sensors, and electronic devices. The creation of ionic nanocrystals with high percentages of polar surfaces is an option for improving their efficiency in the aforementioned applications but is hard to accomplish because they are less thermodynamically stable and prone to vanish during the growth process. Herein, we develop a strategy that is capable of producing polar surface-dominated II-VI semiconductor nanocrystals, including ZnS and CdS, from copper sulfide hexagonal nanoplates through cation exchange reactions. The obtained wurtzite ZnS hexagonal nanoplates have dominant {002} polar surfaces, occupying up to 97.8% of all surfaces. Density functional theory calculations reveal the polar surfaces can be stabilized by a charge transfer of 0.25 eV/formula from the anion-terminated surface to the cation-terminated surface, which also explains the presence of polar surfaces in the initial Cu1.75S hexagonal nanoplates with cation deficiency prior to cation exchange reactions. Experimental results showed that the HER activity could be boosted by the surface polarization of polar surface-dominated ZnS hexagonal nanoplates. We anticipate this strategy is general and could be used with other systems to prepare nanocrystals with dominant polar surfaces. Furthermore, the availability of colloidal semiconductor nanocrystals with dominant polar surfaces produced through this strategy opens a new avenue for improving their efficiency in catalysis, photocatalysis, gas sensing, and other applications.

14.
Sci Total Environ ; 730: 139018, 2020 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-32413601

RESUMO

Certain levels of sludge flocs would always coexist in granule-based reactors due to the biomass detachment from granules. Such inevitable coexistence could affect both total nitrogen (TN) removal and nitrous oxide (N2O) production in autotrophic nitrogen removal systems. This work utilized a mathematical approach to systematically study the influence of the coexisting sludge flocs on TN removal and N2O production in a granular nitritation-anaerobic ammonium oxidation (Anammox) process for the first time, based on a 2-pathway N2O production model concept. The modelling results reveal that the highest TN removal efficiency decreases from ca. 87-88% to ca. 41-49% as the fraction of sludge flocs in the system increases from 10% to 40%, while the N2O production rate gradually increases with such increase. Meanwhile, both bulk dissolved oxygen (DO, 0.05-0.3 mg/L) and the size of granule (200-400 µm) could also influence the TN removal efficiency and N2O production. As the fraction of sludge flocs increases from 10% to 40%, the contribution of granular biomass to total N2O production is reduced due to increase of N2O-producing ammonia-oxidizing bacteria (AOB) in the sludge flocs, and the increase of granule size could intensify such decrease. In addition, the hydroxylamine oxidation pathway dominates the nitrifier denitrification pathway in both granules and sludge flocs under various testing conditions, whereas the increasing contribution of the latter would occur at a certain DO range, higher fraction of sludge flocs and smaller granule size. These results disclose an important influence of the coexisting sludge flocs on the performance of granular nitritation-Anammox systems.


Assuntos
Esgotos , Reatores Biológicos , Desnitrificação , Nitrogênio , Óxido Nitroso , Oxirredução
15.
Water Res ; 178: 115851, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32371287

RESUMO

Triclocarban (TCC) is a highly effective antibacterial agent, which is widely used in a variety of applications and present at significant levels (e.g., 760 µg/L) in wastewater worldwide. However, the interaction between TCC and nitrifiers, important microbial cultures in wastewater treatment plants, has not been documented. This work therefore aimed to evaluate the fate of TCC in a nitrifying culture and its impact on nitrifiers in four long-term nitrifiers-rich reactors, which received synthetic wastewater containing 0, 0.1, 1, or 5 mg/L TCC. Experimental results showed that 36.7%-50.7% of wastewater TCC was removed by nitrifying cultures in stable operation. Mass balance analysis revealed that the removal of TCC was mainly achieved through adsorption rather than biodegradation. Adsorption kinetic analysis indicated that inhomogeneous multilayer adsorption was responsible for the removal while fourier transform infrared spectroscopy indicated that several functional groups such as hydroxyl, amide and polysaccharide seemed to be the main adsorption sites. The adsorbed TCC significantly deteriorated settleability and performance of nitrifying cultures. With an increase of influent TCC from 0 to 5 mg/L, reactor volatile suspended solids and effluent nitrate decreased from 1200 ± 90 mg/L and 300.81 ± 7.52 mg/L to 880 ± 80 and 7.35 ± 4.62 mg/L while effluent ammonium and nitrite increased from 0.41 ± 0.03 and 0.45 ± 0.23 mg/L to104.65 ± 3.46 and 182.06 ± 7.54 mg/L, respectively. TCC increased the extracellular polymeric substances of nitrifying cultures, inhibited the specific activities of nitrifiers, and altered the abundance of nitrifiers especially Nitrospira sp.. In particular, TCC at environmentally relevant concentration (i.e., 0.1 mg/L) significantly inhibited NOB activity and reduced NOB population.


Assuntos
Carbanilidas , Esgotos , Reatores Biológicos , Cinética , Eliminação de Resíduos Líquidos , Águas Residuárias
16.
Water Res ; 179: 115898, 2020 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-32388051

RESUMO

The negative effects of ubiquitous microplastics on wastewater treatment have attracted increasing attention. However, the potential impacts of microplastics on anaerobic granular sludge (AGS) remain unknown. To fill this knowledge gap, this paper investigated the response of AGS to the exposure of model microplastics (polyethylene terephthalate (PET-MPs)) and provided insights into the mechanisms involved. The 84 days' long-term exposure experiments demonstrated that PET-MPs, at relatively low level (15 MP L-1) did not affect AGS performance during anaerobic wastewater treatment, while 75-300 MP L-1 of PET-MPs caused the decreases of COD removal efficiency and methane yields by 17.4-30.4% and 17.2-28.4%, accompanied with the 119.4-227.8% increase in short-chain fatty acid (SCFA) accumulation and particle breakage. Extracellular polymeric substances (EPS) analysis showed that dosage-dependent tolerance of AGS to PET-MPs was attributed to the induced EPS producing protection role, but PET-MPs at higher concentrations (75-300 MP L-1) suppressed EPS generation. Correspondingly, microbial community analysis revealed that the populations of key acidogens (e.g., Levilinea sp.) and methanogens (e.g., Methanosaeta sp.) decreased after long-term exposure to PET-MPs. Assessment of the toxicity of PET-MPs revealed that the leached di-n-butyl phthalate (DBP) and the induced reactive oxygen species (ROS) by PET-MPs were causing toxicity towards AGS, confirmed by the increases in cell mortality and lactate dehydrogenase (LDH) release. These results provide novel insights into the ecological risk assessment of microplastics in anaerobic wastewater treatment system.


Assuntos
Polietilenotereftalatos , Esgotos , Anaerobiose , Microplásticos , Plásticos , Eliminação de Resíduos Líquidos
17.
Environ Sci Technol ; 54(11): 6968-6977, 2020 Jun 02.
Artigo em Inglês | MEDLINE | ID: mdl-32348129

RESUMO

Denitrifying anaerobic methane oxidation (DAMO) coupled to anaerobic ammonium oxidation (anammox) is a promising technology for complete nitrogen removal with economic and environmental benefit. In this work, a model framework integrating DAMO and anammox process was constructed based on suspended-growth systems. The proposed model was calibrated and validated using experimental data from a sequencing batch reactor and a membrane aerated membrane bioreactor (MAMBR). The model managed to describe removal rates of ammonium (NH4+), nitrite (NO2-), and total nitrogen, as well as biomass changes of DAMO archaea, DAMO bacteria, and anaerobic ammonium oxidizing bacteria (AnAOB) in both reactors. The estimated parameter values revealed that DAMO archaea possessed properties of faster growth and higher biomass yield in suspended-growth systems compared to those in attached-growth systems (e.g., biofilm). Model simulation demonstrated that solid retention time (SRT) was effective in washing out DAMO bacteria, but retaining DAMO archaea and AnAOB in the MAMBR. The optimal SRT and nitritation efficiency (the ratio of the NO2- to the sum of NH4+ and NO2- in the MAMBR influent) were simulated so that 99% of total nitrogen was removed to meet the discharge standard. MAMBR further suggested to be operated with SRT between 15 and 30 days so that the optimal nitritation efficiency could be minimized to 49% for cost savings.

18.
Bioresour Technol ; 306: 123159, 2020 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-32182472

RESUMO

This study conducted batch and continuous tests to reveal the feasibility of corn stover biochar on improving anaerobic digestion of primary sludge (PS). Dosing biochar (1.82, 2.55 and 3.06 g/g Total Solids (TS)) in digester improved methane content increasing from 67.5% to 81.3-87.3% and enhanced methane production by 8.6-17.8%. Model analysis indicated that biochar accelerated PS hydrolysis and enhanced methane potential of PS. The mechanistic studies showed that biochar enhanced process stability provided by strong buffering capacity and alleviated NH3 inhibition. In continuous test over 116 days, the volatile solids (VS) destruction in the biochar-dosed digester increased by 14.9%, resulting in a 14% reduction in the volume of digestate for disposal. Biochar changed microbial community in an expected direction for anaerobic digestion. This work suggests that biochar technology would apply to co-digestion of WAS and PS to maximize the energy recovery and sludge reduction from the two sludge streams.

19.
Water Res ; 173: 115592, 2020 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-32062227

RESUMO

Wastewater treatment plants (WWTPs) have been identified as one of the reservoirs of antibiotics. Although nitrifying bacteria have been reported to be capable of degrading various antibiotics, there are very few studies investigating long-term effects of antibiotics on kinetic and microbial responses of nitrifying bacteria. In this study, cephalexin (CFX) and sulfadiazine (SDZ) were selected to assess chronic impacts on nitrifying sludge with stepwise increasing concentrations in two independent bioreactors. The results showed that CFX and SDZ at an initial concentration of 100 µg/L could be efficiently removed by enriched nitrifying sludge, as evidenced by removal efficiencies of more than 88% and 85%, respectively. Ammonia-oxidizing bacteria (AOB) made a major contribution to the biodegradation of CFX and SDZ via cometabolism, compared to limited contributions from heterotrophic bacteria and nitrite-oxidizing bacteria. Chronic exposure to CFX (≥30 µg/L) could stimulate ammonium oxidation activity in terms of a significant enhancement of ammonium oxidation rate (p < 0.01). In contrast, the ammonium oxidation activity was inhibited due to exposure to 30 µg/L SDZ (p < 0.01), then it recovered after long-term adaption under exposure to 50 and 100 µg/L SDZ. In addition, 16S rRNA gene amplicon sequencing revealed that the relative abundance of AOB decreased distinctly from 23.8% to 28.8% in the control phase (without CFX or SDZ) to 14.2% and 10.8% under exposure to 100 µg/L CFX and SDZ, respectively. However, the expression level of amoA gene was up-regulated to overcome this adverse impact and maintain a stable and efficient removal of both ammonium and antibiotics. The findings in this study shed a light on chronic effects of antibiotic exposure on kinetic and microbial responses of enriched nitrifying sludge in WWTPs.


Assuntos
Cefalexina , Esgotos , Amônia , Reatores Biológicos , Nitrificação , Oxirredução , RNA Ribossômico 16S , Sulfadiazina
20.
Water Res ; 174: 115626, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32101786

RESUMO

In this work, Fe(II) catalyzing sodium percarbonate (Fe(II)/SPC) was managed to facilitate waste activated sludge (WAS) dewatering for the first time. The results showed that after WAS was treated by 20 mg/g total suspended solids (TSS) Fe(II) and 50 mg/g TSS SPC, the water content of sludge cake (WCSC) by press filtration and capillary suction time (CST) dropped from 90.8% ± 1.6% and 96.1 ± 4.0 s (the control) to 55.6% ± 1.4% and 30.1 ± 2.5 s, respectively. The mechanism investigations indicated that four intermediates or products (i.e., •OH, H2O2, Fe(II), and Fe(III)) generated in the Fe(II)/SPC process were responsible for the improved WAS dewaterability, and •OH and Fe(III) were the two major contributors. It was found that •OH collapsed and fragmented extracellular polymeric substances, damaged cell wall and permeabilized cytoplasmic membrane, and transformed conformation of the extracellular proteins secondary structure via both affecting the hydrogen bond maintaining α-helix and cracking disulfide bond in cysteine residues while Fe(III), the oxidization product of Fe(II), decreased the surface electronegativity and water-affinity surface areas of WAS flocs. As a result, the bound water release, flocculability, surface hydrophobicity, drain capability, and flowability of WAS flocs were strengthened whereas the compact surface structure, colloidal forces, network strength, gel-like structure, and apparent viscosity of WAS flocs were weakened. In addition, Fe(II)/SPC process also reduced the recalcitrant organics and fecal coliforms in sludge, which facilitated land application of dewatered sludge. The findings acquired in this work not only deepens our understanding of Fe(II)/SPC-involved WAS treatment process but also may guide engineers to develop both effective and promising strategies to better condition WAS for dewatering in the future.


Assuntos
Esgotos , Eliminação de Resíduos Líquidos , Carbonatos , Compostos Férricos , Compostos Ferrosos , Peróxido de Hidrogênio , Água
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA