RESUMO
Highly colored azo dye-contaminated wastewater poses significant environmental threats and requires effective treatment before discharge. The anaerobic azo dye treatment method is a cost-effective and environmentally friendly solution, while its time-consuming and inefficient processes present substantial challenges for industrial scaling. Thus, the use of iron materials presents a promising alternative. Laboratory studies have demonstrated that systems coupled with iron materials enhance the decolorization efficiency and reduce the processing time. To fully realize the potential of iron materials for anaerobic azo dye treatment, a comprehensive synthesis and evaluation based on individual-related research studies, which have not been conducted to date, are necessary. This review provides, for the first time, an extensive and detailed overview of the utilization of iron materials for azo dye treatment, with a focus on decolorization. It assesses the treatment potential, analyzes the influencing factors and their impacts, and proposes metabolic pathways to enhance anaerobic dye treatment using iron materials. The physicochemical characteristics of iron materials are also discussed to elucidate the mechanisms behind the enhanced bioreduction of azo dyes. This study further addresses the current obstacles and outlines future prospects for industrial-scale application of iron-coupled treatment systems.
Assuntos
Compostos Azo , Corantes , Ferro , Águas Residuárias , Poluentes Químicos da Água , Compostos Azo/química , Corantes/química , Águas Residuárias/química , Poluentes Químicos da Água/química , Ferro/química , Eliminação de Resíduos Líquidos/métodos , Descoloração da Água/métodosRESUMO
In recirculating aquaculture systems (RAS), maintaining water quality in aquaculture tanks is a paramount factor for effective fish production. A down-flow hanging sponge (DHS) reactor, a trickling filter system used for water treatment of RAS that employs sponges to retain biomass, has high nitrification activity. However, nitrification in seawater RAS requires a long start-up time owing to the high salinity stress. Therefore, this study aimed to evaluate the nitrification characteristics and changes in the microbial community during the conversion of freshwater to seawater in a DHSreactor fed with ammonia-based artificial seawater. The total ammonia nitrogen concentration reached 1.0â¯mg-N·L-1 (initial concentration 10â¯mg-N·L-1) within 11 days of operation, and nitrate production was observed. The 16â¯S rRNA gene sequence of the DHS-retained sludge indicated that the detection rate of the ammonia-oxidizing archaeon Candidatus Nitrosocosmicus decreased from 23.9â¯% to 14.0â¯% and 25.8-17.6â¯% in the upper and lower parts of the DHS reactor, respectively, after the introduction of seawater. In contrast, the nitrite-oxidizing bacteria Nitrospira spp. increased from 0.1â¯% to 9.5â¯% and from 0.5â¯% to 10.5â¯%, respectively. The ammonia oxidation rates of 0.12 ± 0.064 and 0.051 ± 0.0043â¯mg-N·g-MLVSS-1·h-1 on the 37th day in the upper and bottom layers, respectively. Thus, nitrification in the DHS reactor performed well, even under high-salinity conditions with short operational days. This finding makes the transition from freshwater to saltwater fish in the RAS system simple and economical, and has the potential for early start-up of the RAS.
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Aerobic ammonia and nitrite oxidation reactions are fundamental biogeochemical reactions contributing to the global nitrogen cycle. Although aerobic nitrite oxidation yields 4.8-folds less Gibbs free energy (∆Gr ) than aerobic ammonia oxidation in the NH4 + -feeding marine recirculating trickling biofilter reactors operated in the present study, nitrite-oxidizing and not ammonia-oxidizing Nitrospira (sublineage IV) outnumbered ammonia-oxidizing Nitrosomonas (relative abundance; 53.8% and 7.59% respectively). CO2 assimilation efficiencies during ammonia or nitrite oxidation were 0.077 µmol-14 CO2 /µmol-NH3 and 0.053-0.054 µmol-14 CO2 /µmol-NO2 - respectively, and the difference between ammonia and nitrite oxidation was much smaller than the difference of ∆Gr . Free-energy efficiency of nitrite oxidation was higher than ammonia oxidation (31%-32% and 13% respectively), and high CO2 assimilation and free-energy efficiencies were a determinant for the dominance of Nitrospira over Nitrosomonas. Washout of Nitrospira and Nitrosomonas from the trickling biofilter reactors was also examined by quantitative PCR assay. Normalized copy numbers of Nitrosomonas amoA were 1.5- to 1.7-folds greater than Nitrospira nxrB and 16S rRNA gene in the reactor effluents. Nitrosomonas was more susceptible for washout than Nitrospira in the trickling biofilter reactors, which was another determinant for the dominance of Nitrospira in the trickling biofilter reactors.
Assuntos
Nitritos , Nitrosomonas , Amônia , Bactérias/genética , Dióxido de Carbono , Nitrosomonas/genética , Oxirredução , RNA Ribossômico 16S/genéticaRESUMO
Conventional activated sludge (AS) systems are widely used to treat domestic sewage worldwide. However, the removal of nitrogen in the AS system is limited, and its concentration in the effluent exceeds the recommended values in the discharge standards. In this study, a pilot experiment was conducted to improve nitrogen removal during municipal sewage treatment by operating AS and anaerobic-aerobic (AO) systems under low dissolved oxygen (DO) conditions of less than 0.5 mg L-1 and by adding denitrifying granular sludge. The low DO operation of the AS and AO systems led to the sludge washout and increased the organic content and ammonia and nitrate concentration of the effluent. In contrast, the nitrate concentrations of the effluents produced by the AS and AO systems were 9.4 ± 3.6 and 8.4 ± 0.7 mg-N L-1, respectively, indicated that denitrifying granular sludge addition enhanced denitrification during sewage treatment. The total nitrogen (TN) removal efficiency increased by 13% and 9% for the AS and AO systems despite a decrease in the temperature of 6 °C for the water in the aeration tank. Thus, adding denitrifying granular sludge to the aeration tank is a simple and effective approach to improve organic and nitrogen removal during wastewater treatment.
Assuntos
Esgotos , Eliminação de Resíduos Líquidos , Amônia , Anaerobiose , Reatores Biológicos , Desnitrificação , Nitratos , Nitrificação , Nitrogênio , Oxigênio , Águas Residuárias , ÁguaRESUMO
In the production of natural rubber, formate or acetate is added to the latex solution to coagulate the rubber; therefore, the wastewater contains high concentrations of organic acids, requiring the application of anaerobic treatment technology. In this study, a two-phase continuous flow experiment using a laboratory-scale upflow anaerobic sludge blanket (UASB) was conducted to investigate the influence of formate inflow on the microbial and physical characteristics of the retained granular sludge. In phase 1, acetate-based wastewater was used as feed, while in phase 2, formate-based wastewater was used as feed. In phase 1, the UASB exhibited high COD removal efficiency (97.2%); in addition, the retained sludge showed increased methane production from acetate and proliferation of acetate-utilizing Methanosaeta species. In phase 2, the UASB performed as well as phase 1, with 98.2% COD removal efficiency. Microbial community structure analysis confirmed that relatives of Methanobacterium formicicum present in the retained sludge were responsible for the degradation of formate in phase 2. However, decreased diameter and slight deterioration of granular sludge settleability were observed. In conclusion, formate inflow has low risk of interference with the process performance of the UASB, but it has negative effects on the physical properties of the granular sludge.
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Esgotos , Águas Residuárias , Anaerobiose , Reatores Biológicos/microbiologia , Formiatos , Metano/metabolismo , Esgotos/microbiologia , Eliminação de Resíduos Líquidos , Águas Residuárias/químicaRESUMO
Biofilm development on the membrane surface is one of the main reasons for membrane fouling in membrane bioreactors (MBRs) and it is a big problem for their stable operation. Precise information on the microbial community composition of the biofilm is needed for a better understanding of biofilm development. However, there have been limited investigations of the relationship between the biofilm formation process and the microbial community of activated sludge and biofilm in MBRs treating real sewage. In this study, relationships between the microbial community structure of biofilm and activated sludge at each biofilm formation stage were investigated and biofilm growth was elucidated by nondestructive observations. Two anoxic/oxic MBRs were operated and membrane fouling was induced. Permeability rapidly decreased in both reactors and live cell microcolonies were formed on dead cell conditioning film on the membrane surface. Principal component analysis based on 16S rRNA gene sequences showed that the biofilm microbial community changed significantly from middle stage to mature biofilm when compared with that of activated sludge. The abundance of specific bacteria, such as unclassified Neisseriaceae, increased in middle-stage biofilm and the diversity indexes of middle-stage biofilm were lower than those of mature biofilm and activated sludge. These results suggested that the presence of specific bacteria with colonization ability played a crucial role in biofilm formation. Strategies are needed to target membrane fouling mitigation during early- and middle-stage biofilm formation to reduce MBR membrane fouling. KEY POINTS: ⢠Microbial community of mature biofilm was approached to that of activated sludge. ⢠In the middle-stage biofilm, live cells colonized on a dead-cell-conditioning-film. ⢠Microbial diversity was lower in live cell colonizing stage than in activated sludge.
Assuntos
Reatores Biológicos , Esgotos , Biofilmes , Membranas Artificiais , RNA Ribossômico 16S/genética , Eliminação de Resíduos LíquidosRESUMO
OBJECTIVE: Heterotrophic manganese (Mn)-oxidizing microorganisms responsible for biogenic manganese oxide (Bio-MnOx) production are fastidious. Their enrichment is not easily accomplished by merely adding a soluble organic substrate to non-sterile mixed cultures. The objective of this study was to evaluate polycaprolactone (PCL), an aliphatic polyester, as an effective solid organic substrate for the enrichment of marine Mn-oxidizing microorganisms. RESULTS: We successfully obtained marine microbial enrichment with the capacity for dissolved Mn removal and MnOx production using PCL as a solid organic substrate. The removal of dissolved Mn by the Mn-oxidizing enrichment culture followed first-order kinetics with a rate constant of 0.014 h-1. 16S rRNA gene amplicon sequencing analysis revealed that the Mn-oxidizing enrichment culture was highly dominated by operational taxonomic units related to the bacterial phyla Cyanobacteria, Planctomycetes, and Proteobacteria. CONCLUSIONS: Our data demonstrate that PCL can serve as a potential substrate to enrich Mn-oxidizing microorganisms with the ability to produce MnOx under marine conditions.
Assuntos
Bactérias/classificação , Manganês/química , Poliésteres/química , Análise de Sequência de DNA/métodos , Bactérias/genética , Bactérias/crescimento & desenvolvimento , Bactérias/isolamento & purificação , Biodegradação Ambiental , DNA Bacteriano/genética , DNA Ribossômico/genética , Oxirredução , Filogenia , RNA Ribossômico 16S/genética , Microbiologia da ÁguaRESUMO
Given the toxicity and widespread occurrence of hexavalent chromium [Cr(VI)] in aquatic environments, we investigated the feasibility of a down-flow hanging sponge (DHS) biofilm reactor for the enrichment of microbial communities capable of Cr(VI) removal. In the present study, a laboratory-scale DHS reactor fed with a molasses-based medium containing Cr(VI) was operated for 112 days for the investigation. The enrichment of Cr(VI)-removing microbial communities was evaluated based on water quality and prokaryotic community analyses. Once the DHS reactor began to operate, high average volumetric Cr(VI) removal rates of 1.21-1.45 mg L-sponge-1 h-1 were confirmed under varying influent Cr(VI) concentrations (approximately 20-40 mg L-1). 16S rRNA gene amplicon sequencing analysis suggested the presence of phylogenetically diverse prokaryotic lineages, including phyla that contain well-known Cr(VI)-reducing bacteria (e.g., Bacteroidetes, Firmicutes, and Proteobacteria) in the polyurethane sponge media of the DHS reactor. Therefore, our findings indicate that DHS reactors have great potential for the enrichment of Cr(VI)-removing microbial communities.
Assuntos
Biofilmes/crescimento & desenvolvimento , Reatores Biológicos/microbiologia , Cromo/análise , Microbiota/efeitos dos fármacos , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Bacteroidetes/efeitos dos fármacos , Firmicutes/efeitos dos fármacos , Poliuretanos/química , Proteobactérias/efeitos dos fármacos , RNA Ribossômico 16S/genéticaRESUMO
This study evaluates the process performance of a real-scale anaerobic baffled reactor (ABR) coupled with swim bed tank (SBT) as an aerobic post-treatment process in treating fishmeal wastewater discharged from an actual fishmeal processing factory in Bali, Indonesia. The industrial wastewater released from the aforementioned factory contains high concentrations of organic COD (more than 10 g COD·L-1) and ammonia (100 to 200 mg-N·L-1). During the study period, ABR demonstrated a high organic removal of 95.7 ± 2.9%, with an organic loading rate of 2.1 ± 1.3 kg COD·m-3·day-1. Furthermore, the average total COD influent and effluent of the proposed system were 37,800 ± 15,000 mg COD·L-1 and 435 ± 113 mg COD·L-1, respectively, during the entire experimental period. Based on the determination of volatile fatty acids (VFAs) and microbial community analysis of the ABR-retained sludge, the first and second columns of the ABR were utilized as hydrolysis zones and the third column functioned as an acidification zone. The remaining columns were used for methane production and as final removal zones. The results concluded that this system has the potential to treat fishmeal wastewater under onsite industrial conditions.
Assuntos
Reatores Biológicos/microbiologia , Indústria Alimentícia , Águas Residuárias/química , Poluentes Químicos da Água/análise , Purificação da Água/métodos , Amônia/análise , Anaerobiose , Análise da Demanda Biológica de Oxigênio , Ácidos Graxos Voláteis/análise , Produtos Pesqueiros/análise , Indonésia , Esgotos/química , Esgotos/microbiologia , Resíduos/análiseRESUMO
Conventional aerated tank technology is widely applied for post treatment of natural rubber processing wastewater in Southeast Asia; however, a long hydraulic retention time (HRT) is required and the effluent standards are exceeded. In this study, a downflow hanging sponge (DHS) reactor was installed as post treatment of anaerobic tank effluent in a natural rubber factory in South Vietnam and the process performance was evaluated. The DHS reactor demonstrated removal efficiencies of 64.2 ± 7.5% and 55.3 ± 19.2% for total chemical oxygen demand (COD) and total nitrogen, respectively, with an organic loading rate of 0.97 ± 0.03 kg-COD m-3 day-1 and a nitrogen loading rate of 0.57 ± 0.21 kg-N m-3 day-1. 16S rRNA gene sequencing analysis of the sludge retained in the DHS also corresponded to the result of reactor performance, and both nitrifying and denitrifying bacteria were detected in the sponge carrier. In addition, anammox bacteria was found in the retained sludge. The DHS reactor reduced the HRT of 30 days to 4.8 h compared with the existing algal tank. This result indicates that the DHS reactor could be an appropriate post treatment for the existing anaerobic tank for natural rubber processing wastewater treatment.
Assuntos
Reatores Biológicos/microbiologia , Resíduos Industriais/análise , Borracha/química , Águas Residuárias , Anaerobiose , Bactérias/genética , Bactérias/metabolismo , Nitrificação , Nitrogênio/análise , RNA Ribossômico 16S , Esgotos/microbiologia , Eliminação de Resíduos LíquidosRESUMO
In this study, granular sludge formation was carried out using an aluminum chloride supplement in an upflow anaerobic sludge blanket (UASB) reactor treating natural rubber processing wastewater. Results show that during the first 75 days after the start-up of the UASB reactor with an organic loading rate (OLR) of 2.65 kg-COD·m(-3)·day(-1), it performed stably with a removal of 90% of the total chemical oxygen demand (COD) and sludge still remained in small dispersed flocs. However, after aluminum chloride was added at a concentration of 300 mg·L(-1) and the OLR range was increased up to 5.32 kg-COD·m(-3)·day(-1), the total COD removal efficiency rose to 96.5 ± 2.6%, with a methane recovery rate of 84.9 ± 13.4%, and the flocs began to form granules. Massively parallel 16S rRNA gene sequencing of the sludge retained in the UASB reactor showed that total sequence reads of Methanosaeta sp. and Methanosarcina sp., reported to be the key organisms for granulation, increased after 311 days of operation. This indicates that the microbial community structure of the retained sludge in the UASB reactor at the end of the experiment gave a good account of itself in not only COD removal, but also granule formation.
Assuntos
Compostos de Alumínio/análise , Cloretos/análise , Resíduos Industriais/análise , Microbiota , Esgotos/microbiologia , Eliminação de Resíduos Líquidos/métodos , Poluição Química da Água/análise , Cloreto de Alumínio , Anaerobiose , Bactérias/genética , Bactérias/metabolismo , Reatores Biológicos , Microbiota/efeitos dos fármacos , RNA Bacteriano/genética , RNA Bacteriano/metabolismo , RNA Ribossômico 16S/genética , RNA Ribossômico 16S/metabolismo , Borracha , Eliminação de Resíduos Líquidos/instrumentaçãoRESUMO
A novel bio-carrier, PVA/Fe/starch gel bead, was fabricated and developed to enhance the anaerobic treatment performance of synthetic azo dye-containing wastewater. PVA-gel beads with 5 % magnetite and 0.5 % starch were optimal for physical strength and treatment performance. A pair of 2 L-up-flow anaerobic sludge blankets (UASB), one with the bead (UB) and another without (U) as a controller, operated continuously at 30 °C and an HRT of 11-24 h for 302 days. UB showed better performance than U in most phases, especially with influent dye of 200 mg·L-1, suggesting a greater tolerance to dye toxicity of UB than U. Microbial analysis revealed that the PVA/Fe/starch gel beads successfully captured the dye degrader Clostridium. Diversity indices indicated that PVA/Fe/Starch gel beads effectively support microbial diversity and resilience under varying dye concentrations. Overall, these findings demonstrate the potential of PVA/Fe/Starch gel beads to improve the stability and efficiency of the dye treatment system.
Assuntos
Compostos Azo , Reatores Biológicos , Corantes , Álcool de Polivinil , Amido , Amido/química , Corantes/química , Álcool de Polivinil/química , Compostos Azo/química , Anaerobiose , Géis/química , Ferro/química , Purificação da Água/métodos , Esgotos/microbiologia , Biodegradação AmbientalRESUMO
A down-flow hanging sponge (DHS) reactor is a trickling filter system used for wastewater treatment, which employs sponges to retain biomass. This study assessed the process performance of a compact DHS combined with a sedimentation tank with seven phases at varying hydraulic retention times (HRT) over 500 days. The BOD of the DHS effluent was maintained at 4.0 ± 0.5 mg·L-1 for the shortest HRT 0.3 ± 0.1 h. The nitrification efficiency was considerably impacted by the reduced HRT, with NH4+-N and NO3--N concentrations of 9.0 ± 1.2 mgN·L-1 and 2.2 ± 0.5 mgN·L-1, respectively. Nevertheless, the effluent complied with effluent discharge standards throughout the trial period. The number of comammox 16S rRNA gene copies ranged from 5.58 to 13.2 × 107 copies·mL-1, indicating that sponges biomass retained carrier can provide favorable conditions for comammox growth and could contribute to nitrification in the high-rate DHS reactor.
Assuntos
Reatores Biológicos , Nitrificação , Águas Residuárias , Purificação da Água , Reatores Biológicos/microbiologia , Águas Residuárias/química , Purificação da Água/métodos , RNA Ribossômico 16S/genética , Biomassa , Análise da Demanda Biológica de Oxigênio , Eliminação de Resíduos Líquidos/métodos , NitrogênioRESUMO
An anaerobic baffled reactor (ABR) is one of the useful wastewater treatment technologies, but the knowledge about its treatment performance for actual wastewater with load fluctuation is limited. The organic removal performance of an ABR for treating supermarket wastewater was evaluated. The ABR, which consisted of eight columns, was examined under four hydraulic retention time (HRT) conditions of 19.4, 12.9, 8.0, and 4.4â h. As a result, the unfiltered chemical oxygen demand (COD) removal efficiency was 80 (±8) % at an HRT of 19.4â h. When the HRT was shortened to 12.9â h, the average unfiltered COD removal efficiency decreased to 58 (±15) %. However, it showed buffering effect against high load inflow in the first column, indicating that it is useful as a pretreatment system under this condition. At an HRT of 4.4â h, the unfiltered COD removal efficiency decreased to 9%, indicating the system failed. The results of the microbial community structure analysis showed that the detection frequency of acidogenic bacteria decreased in proportion to the extension of residence time in the reactor. These results indicate that the ABR is useful for the treatment of supermarket wastewater with load fluctuations as a main treatment system at a HRT of 19.4â h and as a pretreatment system at a HRT of 12.9â h.
Assuntos
Águas Residuárias , Purificação da Água , Anaerobiose , Eliminação de Resíduos Líquidos/métodos , Supermercados , Reatores Biológicos/microbiologiaRESUMO
This study evaluated the effects of acetone on the anaerobic degradation of synthetic latex wastewater, which was simulated from the wastewater of the deproteinized natural rubber production process, including latex, acetate, propionate, and acetone as the main carbon sources, at a batch scale in 5 cycles of a total of 60 days. Fe3O4 was applied to accelerate the treatment performance from cycle 3. Acetone was added in concentration ranges of 0%, 0.05%, 0.1%, 0.15%-included latex, and 0.15%-free latex (w/v). In the Fe3O4-free cycles, for latex-added vials, soluble chemical oxygen demand (sCOD) was removed at 43.20%, 43.20%, and 12.65%, corresponding to the input acetone concentrations varying from 0.05% to 0.15%, indicating the interference of acetone for COD reduction. After adding Fe3O4, all flasks reported a significant increase in COD removal efficiency, especially for acetone-only and latex-only vials, from 36.9% to 14.30%-42.95% and 83.20%, respectively. Other highlighted results of COD balance showed that Fe3O4 involvement improved the degradation process of acetate, propionate, acetone, and the other COD parts, including the intermediate products of latex reduction. Besides, during the whole batch process, the order of reduction priority of the carbon sources in the synthetic wastewater was acetate, propionate and acetone. We also found that the acetate concentration appeared to be strongly related to reducing other carbon sources in natural rubber wastewater. Microbial community analysis revealed that protein-degrading bacteria Bacteroidetes vadinHA17 and Proteinniphilum and methylotrophic methanogens might play key roles in treating simulated deproteinized-natural-rubber wastewater.
Assuntos
Látex , Águas Residuárias , Látex/metabolismo , Óxido Ferroso-Férrico/metabolismo , Anaerobiose , Acetona , Borracha , Propionatos , Reatores Biológicos/microbiologia , Carbono , Acetatos , Eliminação de Resíduos Líquidos/métodosRESUMO
The cycle of life and death and Earth's carbon cycle(s) are intimately linked, yet how bacterial cells, one of the largest pools of biomass on Earth, are recycled back into the carbon cycle remains enigmatic. In particular, no bacteria capable of scavenging dead cells in oxygen-depleted environments have been reported thus far. In this study, we discover the first anaerobes that scavenge dead cells and the two isolated strains use distinct strategies. Based on live-cell imaging, transmission electron microscopy, and hydrolytic enzyme assays, one strain (designated CYCD) relied on cell-to-cell contact and cell invagination for degrading dead food bacteria where as the other strain (MGCD) degraded dead food bacteria via excretion of lytic extracellular enzymes. Both strains could degrade dead cells of differing taxonomy (bacteria and archaea) and differing extents of cell damage, including those without artificially inflicted physical damage. In addition, both depended on symbiotic metabolic interactions for maximizing cell degradation, representing the first cultured syntrophic Bacteroidota. We collectively revealed multiple symbiotic bacterial decomposition routes of dead prokaryotic cells, providing novel insight into the last step of the carbon cycle.
Assuntos
Bactérias Anaeróbias , Bactérias , Anaerobiose , Bactérias/genética , Bactérias/metabolismo , Archaea , Meio AmbienteRESUMO
Partial water exchange is one of the most common conventional methods used to maintain water quality and aesthetic beauty in recirculating aquarium systems (RASs). However, this method uses substantial amount of water. The ozone-down-flow hanging sponge-up-flow sludge blanket (ozone-DHS-USB) system attempts to be a more responsible method for aquarium maintenance. It eliminates the necessity for water exchange in aquarium by maintaining nitrogen concentrations at a safe level and by reducing yellow substances. Also, the impact of O3 on the DHS-USB system was investigated. The system was assayed using an on-site freshwater aquarium influenced by ambient temperature ranging from 23°C to 34°C. During ozonation Phases 1 and 3, the colour of the water in the aquarium was successfully maintained below 10 colour units. The 16S rRNA gene analysis of microorganisms in the DHS revealed that constant application of O3 has caused a decrease in nitrite-oxidizing bacteria (NOB). Nevertheless, NH3 and NO2- were maintained within 0.1â mg N L-1, and NO3- was maintained at 14.6 ± 9.20â mg N L-1 throughout the study. Carps survived for 425 days without any water exchange performed. Our study supports that the ozone-DHS-USB system has a high potential towards creating low-maintenance aquaria.
Assuntos
Ozônio , Reatores Biológicos , Água Doce , RNA Ribossômico 16S , EsgotosRESUMO
Microbial hexavalent chromium (Cr(VI)) reduction is a promising method for Cr(VI)-laden wastewater treatment. However, the soluble organic substrate required for heterotrophic microbial Cr(VI) reduction necessitates constant supervision, and an excessive supply of soluble organic substrate can result in deterioration of the quality of the effluent. In this study, we evaluated aspen wood, a low-cost lignocellulose biomass, as a solid organic substrate for heterotrophic Cr(VI) reduction. A laboratory-scale aspen wood-packed glass column reactor inoculated with activated sludge was operated for 148 days for evaluation. Following reactor operation, an effective average dissolved Cr(VI) removal rate of 0.75 mg L-1 h-1 was confirmed under an average dissolved Cr(VI) loading rate of 0.90 mg L-1 h-1. Subsequently, 16S ribosomal ribonucleic acid gene amplicon sequencing analysis revealed that the dominant prokaryotic operational taxonomic units detected in the reactor were associated with prokaryotic lineages with the capacity for lignocellulose biodegradation, Cr compound resistance, and Cr(VI) reduction. Proteobacteria and Chloroflexi were two major prokaryotic phyla in the reactor. Our data indicate that aspen wood is an effective solid organic substrate for the development of simplified, effective, and low-cost microbial Cr(VI)-removing reactors.
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Reatores Biológicos , Madeira , Reatores Biológicos/microbiologia , Cromo/metabolismo , Oxirredução , Esgotos/microbiologia , Madeira/metabolismoRESUMO
Biogenic manganese oxides (BioMnOx) have been receiving increasing attention for the removal of environmental contaminants and recovery of minor metals from water environments. However, the enrichment of heterotrophic Mn(II)-oxidizing microorganisms for BioMnOx production in the presence of fast-growing coexisting heterotrophs is challenging. In our previous work, we revealed that polycaprolactone (PCL), a biodegradable aliphatic polyester, can serve as an effective solid organic substrate to enrich Mn-oxidizing microbial communities under seawater conditions. However, marine BioMnOx-producing bioreactor systems utilizing PCL have not yet been established. Therefore, a laboratory-scale continuous-flow PCL-packed aerated biofilm (PAB) reactor was operated for 238 days to evaluate its feasibility for BioMnOx production under seawater conditions. After the start-up of the reactor, the average dissolved Mn removal rates of 0.4-2.3 mg/L/day, likely caused by Mn(II) oxidation, were confirmed under different influent dissolved Mn concentrations (2.5-14.0 mg/L on average) and theoretical hydraulic retention time (0.19-0.77 day) conditions. The 16S rRNA gene amplicon sequencing analysis suggested the presence of putative Mn(II)-oxidizing and PCL-degrading bacterial lineages in the reactor. Two highly dominant operational units (OTUs) in the packed PCL-associated biofilm were assigned to the genera Marinobacter and Pseudohoeflea, whereas the genus Lewinella and unclassified Alphaproteobacteria OTUs were highly dominant in the MnOx-containing black/dark brown precipitate-associated biofilm formed in the reactor. Excitation-emission matrix fluorescence spectroscopy analysis revealed the production of tyrosine- and tryptophane-like components, which may serve as soluble heterotrophic organic substrates in the reactor. Our findings indicate that PAB reactors are potentially applicable to BioMnOx production under seawater conditions.
RESUMO
The main objective of this study was to investigate the cause of gel fouling in membrane bioreactors (MBRs) treating real sewage in terms of soluble microbial products (SMPs) and microbial aspects. Two anoxic/oxic-MBRs were operated as the control reactor (S1) and the sludge loading rate increased reactor (S2). The reactors were operated under low-temperature around 11 °C conditions. Membrane permeability substantially decreased in S2, and gel layer biofilm was formed on membrane surface. In contrast, the permeability of S1 gradually decreased and cake layer formed. When gel fouling occurred, the protein and polysaccharide of SMP in S2 were 47 and 23 mg L-1, which were significantly lower than those recorded in S1 accounted for 118 and 68 mg L-1, respectively. Furthermore, the total organic carbon concentration of SMPs was 24 mg L-1, which was lower than the influent in S2, accounted for 62 mg L-1. Finally, Campylobacteraceae which exists in sewage and uncultured OD1, dominated the gel layer biofilm in S2, unlike the cake layer biofilm in S1. These results indicated that the gel layer biofilm might be composed of influent substances, demonstrating the importance of influent decomposition in MBR for gel fouling mitigation.