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Cold environments are the most widespread extreme habitats in the world. However, the role of wastewater treatment plants (WWTPs) in the cryosphere as hotspots in antibiotic resistance dissemination has not been well established. Hence, a snapshot of the resistomes of WWTPs in cold environments, below 5 °C, was provided to elucidate their role in disseminating antibiotic resistance genes (ARGs) to the receiving waterbodies. The resistomes of two natural environments from the cold biosphere were also determined. Quantitative PCR analysis of the aadA, aadB, ampC, blaSHV, blaTEM, dfrA1, ermB, fosA, mecA, qnrS, and tetA(A) genes indicated strong prevalences of these genetic determinants in the selected environments, except for the mecA gene, which was not found in any of the samples. Notably, high abundances of the aadA, ermB, and tetA(A) genes were found in the influents and activated sludge, highlighting that WWTPs of the cryosphere are critical hotspots for disseminating ARGs, potentially worsening the resistance of bacteria to some of the most commonly prescribed antibiotics. Besides, the samples from non-disturbed cold environments had large quantities of ARGs, although their ARG profiles were highly dissimilar. Hence, the high prevalences of ARGs lend support to the fact that antibiotic resistance is a common issue worldwide, including environmentally fragile cold ecosystems.

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Stigmasterol is a phytosterol contained in kraft mill effluent that is able to increase over 100% after aerobic biological treatment. This compound can act as an endocrine disrupter as its structure is similar to that of cholesterol. Furthermore, stigmasterol contained in kraft mill effluent shows high toxicity (25-fold more than ß-sitosterol) to aquatic organisms such as Daphnia magna. However, the operation of the aerobic treatment and biomass adaptation could be affecting their removal. The performances of activated sludge (AS), aerated lagoon (AL), and moving bed biofilm reactors (MBBR) are compared to remove the stigmasterol contained in kraft mill effluent. The AL operates at a hydraulic retention time of 6 h and removes up to 90% of phytosterols. So, a 96% of stigmasterol is removed by AL when the sterol retention load is 0.6 mg/L · d. However, stigmasterol concentrations increase from 29% to 37% at a low stigmasterol load rate (0.2 mg/L · d). On the other hand, the stigmasterol is removed between 65% and 87% by an AS under a hydraulic retention time of 3 h. Moreover, a 100% of stigmasterol can be removed by the MBBR when the hydraulic retention time is 2 days.

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BACKGROUND: The phylum Chloroflexi is highly abundant in a wide variety of wastewater treatment bioreactors. It has been suggested that they play relevant roles in these ecosystems, particularly in degrading carbon compounds and on structuring flocs or granules. Nevertheless, their function is not yet well understood as most species have not been isolated in axenic cultures. Here we used a metagenomic approach to investigate Chloroflexi diversity and their metabolic potential in three environmentally different bioreactors: a methanogenic full-scale reactor, a full-scale activated sludge reactor and a lab scale anammox reactor. RESULTS: Differential coverage binning approach was used to assemble the genomes of 17 new Chloroflexi species, two of which are proposed as new Candidatus genus. In addition, we recovered the first representative genome belonging to the genus 'Ca. Villigracilis'. Even though samples analyzed were collected from bioreactors operating under different environmental conditions, the assembled genomes share several metabolic features: anaerobic metabolism, fermentative pathways and several genes coding for hydrolytic enzymes. Interestingly, genome analysis from the anammox reactor indicated a putative role of Chloroflexi in nitrogen conversion. Genes related to adhesiveness and exopolysaccharides production were also detected. Complementing sequencing analysis, filamentous morphology was detected by Fluorescent in situ hybridization. CONCLUSION: Our results suggest that Chloroflexi participate in organic matter degradation, nitrogen removal and biofilm aggregation, playing different roles according to the environmental conditions.

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Polycyclic aromatic hydrocarbons (PAHs) are one of the main pollutants generated by the refining and use of oil. To search bioremediation alternatives for these compounds, mainly in situ, considering the biotic and abiotic variables that affect the contaminated sites is determinant for the success of bioremediation techniques. In this study, bioremediation strategies were evaluated in situ, including biostimulation and bioaugmentation for 16 priority PAHs present in activated sludge farms. B. vietnamiensis G4 was used as a biodegradation agent for bioaugmentation tests. The analyses occurred for 12 months, and temperature and humidity were measured to verify the effects of these factors on the biodegradation. We used the technique GC-MS to evaluate and quantify the degradation of PAHs over the time of the experiment. Of the four treatments applied, bioaugmentation with quarterly application proved to be the best strategy, showing the degradation of compounds of high (34.4% annual average) and low (21.9% annual average) molecular weight. A high degradation rate for high molecular weight compounds demonstrates that this technique can be successfully applied in bioremediation of areas with compounds considered toxic and stable in nature, contributing to the mitigation of impacts generated by PAHs.

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Membrane Bioreactors (MBR) combine traditional biological treatments such as Activated Sludge (AS) with a membrane-based filtration process to extract suspended and organic solids. MBR operation involves high shear rates near the membrane surface due to the high crossflow velocity, which complicates any simulation process from a hydrodynamic point of view. In this regard, the viscosity as a function of total suspended solids (TSS) plays an essential role in characterizing and modeling the behavior of activated sludge (AS). However, AS has an intransparency property that prevents experimental measurements (i.e., velocity profiles) commonly associated with optical techniques from being peformed. In light of this limitation, two polymeric compounds, carboxymethyl cellulose (CMC) and xanthan gum (XG), are considered here in order to explore the possibility of mimicking the rheological behavior of AS. These compounds are commonly used in the food industry as food thickeners, and their rheological behavior is supposedly well defined in the literature. In this work, we reviewed the viscosity behavior of these compounds through their reported flow behavior and consistency indexes. It was found that the rheological properties of these two polymers differ depending on the chemical manufacturer, rheometers, and measurement protocols involved. Different curves (shear rate vs. viscosity/shear stress) are obtained, as each device and procedure seem to modify the polymer structure. Therefore, a statistical analysis was performed based on the flow and consistency indexes using different concentrations and temperatures reported in experimental data. Several insights regarding CMC, XG, and AS performance were obtained, including a better relationship with concentration than with temperature or certain exponential-based performances, which can support further MBR design and operational decision-making.

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This study aimed to evaluate an activated sludge system as a post-treatment step of anaerobic effluents from the co-digestion of sugarcane vinasse and hemicelluloses hydrolysate. The system consisted, initially, of a two-stage anaerobic system followed by a continuously fed activated sludge, all in bench scale. After adaptation of aerobic microorganisms to effluent conditions, the anaerobic digestion was conducted in a single-stage anaerobic reactor, increasing the influent organic loading rate (OLR) of activated sludge from 0.73 to an average of 2.36 gCOD/L·day. Under optimal conditions (12-h hydraulic retention time [HRT]), a 62 ± 9% efficiency was observed on the aerobic post-treatment, resulting in effluent chemical oxygen demand (COD) of 414.3 ± 95 mg/L. Overall efficiency of the combined system (anaerobic + aerobic) averaged 88 ± 3%. Influent and effluent characteristics were then analyzed by Folin-Ciocalteau method, UV-Vis spectrophotometry, and gas chromatography-mass spectrometry (GC-MS) for identification of potentially toxic and recalcitrant compounds. Compounds that absorb light within the visible spectra were well removed by the combined treatment system. Most compounds identified by GC-MS in the influent were completely removed by aerobic microorganisms. Saturated fatty acids such as adipic acid, hexadecanoic acid, and octadecanoic acid were observed in the final effluent, as well as other potentially toxic compounds such as stigmasterol, di-isobutyl phthalate, and benzene. Activated sludge proved to be an efficient post-treatment for anaerobic co-digestion, able to cope with changes of anaerobic effluent quality and providing a final effluent of stable organic load. However, phenol removal was not efficient and further studies could be performed to optimize its degradation. PRACTITIONER POINTS: Conventional activated sludge with a 12-h HRT was capable of handling significant OLR variation, providing a final effluent with lower and stable COD concentration. Glucose addition for carbon supplementation was necessary during the start-up of activated sludge. Compounds that absorb light within the visible spectra were mostly removed by the combined (anaerobic-aerobic) treatment system. Most potentially toxic compounds were well removed in the post-treatment system. Saturated fatty acids, VFA, phenols, and low molecular weight aromatic compounds remained in the final effluent.

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Wastewater treatment plants (WWTPs) have been widely investigated in Europe, Asia and North America regarding the occurrence and fate of antibiotic resistance (AR) elements, such as antibiotic resistance genes (ARGs), mobile genetic elements (MGEs) and antibiotic resistant bacteria and pathogens. However, monitoring data about AR elements in municipal WWTPs in Brazil are scarce. This study investigated the abundance of intI1, five ARGs (sul1, tetA, blaTEM, ermB and qnrB) and 16S rRNA in raw and treated wastewater of three WWTPs, using different sewage treatments named CAS (Conventional activated sludge), UASB/BTF (UASB followed by biological trickling filter) and MAS/UV (modified activated sludge with UV disinfection stage). Bacterial diversity and the presence of potentially pathogenic groups were also evaluated, and associations between genetic markers and the bacterial populations were presented. All WWTPs decreased the loads of genetic markers finally discharged to receiving water bodies and showed no evidence of being hotspots for antimicrobial resistance amplification in wastewater, since the abundances of intI1 and ARGs within the bacterial population were not increased in the treated effluents. UASB/BTF showed a similar performance to that of the CAS and MAS/UV, reinforcing the sanitary and environmental advantages of this biological treatment, widely applied for wastewater treatment in warm climate regions. Bacterial diversity and richness increased after treatments, and bacterial communities in wastewater samples differed due to catchment areas and treatment typologies. Potential pathogenic population underwent considerable decrease after the treatments; however, strong significant correlations with intI1 and ARGs revealed potential multidrug-resistant pathogenic bacteria (Aeromonas, Arcobacter, Enterobacter, Escherichia-Shigella, Stenotrophomonas and Streptococcus) in the treated effluents, although in reduced relative abundances. These are contributive results for understanding the fate of ARGs, MGEs and potential pathogenic bacteria after wastewater treatments, which might support actions to mitigate their release into Brazilian aquatic environments in the near future.

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Lignin, a biological resource with great potential, can be as high as ∼16% of the total organics in the waste activated sludge (WAS). This work therefore aims to fill the knowledge gap about the effect of lignin on short-chain fatty acids (SCFAs) production from anaerobic fermentation of sludge. Experimental results showed that lignin promoted rather than inhibited SCFAs production. Specifically, the presence of 15% lignin promoted the SCFAs production from 129.1 ± 6.5 to 223.14 ± 7.8 mg COD/g VSS compared with the control, and the proportion of acetic increased by 61.8%, while that of propionic decreased by 44.9%. Mechanism exploration revealed that lignin improved the solubilization of biodegradable substrates due to its hydrophobic characteristics. In addition, lignin enhanced the acidogenesis process, possibly by perfecting the electron transfer chain in the fermentation system, and the quinone structure in lignin may compete electrons with methanogens to inhibit the consumption of SCFAs. Microbiological analysis showed that the abundance of microorganisms related to acidogenesi, especially the acetogenesis, including Proteiniclasticum sp., Acetoanaerobium sp., in the fermenter with lignin increased, which caused the community to shift towards specialized and diverse SCFAs production.

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The technology of anaerobic co-digestion to treat the excess biological sludge discharged from activated sludge systems in oil refineries was evaluated in bench scale experiments. Mixing food waste rich in fruits and vegetables with this sludge increased the reduction of volatile solids and biogas yield. An experimental design indicated that the best co-digestion condition was the use of waste activated sludge without previous dewatering (3.5% total solids) and food waste in an 80:20 ratio (% v/v), without the addition of inoculum. After 45 days at 35 °C, this condition resulted in volatile solid (VS) removal of 52% and biogas yield of 80.7 mL biogas/g VSadded, against only 19% and 38.5 mL biogas/g VSadded in mono-digestion of sludge alone. Anaerobic co-digestion demonstrates promising results and the potential for a simple and effective treatment method for excess biological sludge generated at refineries.

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RESUMO Neste artigo, apresenta-se uma abordagem conceitual sobre propostas de alternativas para a concepção de sistemas com reator anaeróbio de manta de lodo. Em essência, propõem-se: i) a eliminação dos separadores de gás, líquido e sólido que constam em reatores upflow anaerobic sludge blanket reactors e sua substituição por unidade de sedimentação de alta taxa em setor incluso ou externo ao volume do reator biológico; ii) a recirculação de parcela do lodo retido no sedimentador, transformando o conjunto em um sistema semelhante ao de lodo ativado, porém preservando a manta de lodo no reator anaeróbio (activated anaerobic sludge blanket system) e, assim, viabilizando melhor controle do tempo de retenção celular; e iii) a simplificação (menor número de entradas) do sistema de distribuição do afluente junto ao fundo da zona de reação, mediante duas alternativas: agitação mecânica ou agitação hidráulica com jatos — em ambos os casos, intermitentes. As propostas, conforme apresentadas, constituem resumo de pesquisa baseada em reatores de bancada sucedida pela operação e testes em duas unidades-piloto paralelas (volume total: 20,8 m3, incluindo volumes de reação e de sedimentação). Constatou-se que é possível remover sólidos suspensos do efluente da região de reação sem a necessidade do separador trifásico e, também, que é possível manter-se a manta de lodo mesmo com a agitação na região de reação. Foram obtidos bons resultados na remoção de sólidos suspensos totais, demanda bioquímica de oxigênio e demanda química de oxigênio nos sedimentadores com valores de taxa de aplicação superficial de 34,0 até 81,6 m3m-2dia. Constatou-se, também, que valores bastante baixos de gradiente de velocidade (G £ 20s-1) são suficientes para promover a manutenção da manta de lodo e que a intermitência na agitação é favorável ao processo biológico. Os resultados relacionados com a remoção de demanda química de oxigênio, demanda bioquímica de oxigênio e sólidos suspensos totais foram comparados com os de outros estudos sobre reatores upflow anaerobic sludge blanket reactors convencionais. Contudo, aqueles relacionados com o tempo de reação celulat foram os mais significativos para as conclusões desta pesquisa. Quando o reator foi operado com tempo de detenção hidráulica de 8,2 h e velocidade ascensional no reator biológico de 0,69 mh-1, o tempo de reação celular do sistema resultou em 175 dias. Com velocidade ascensional menores, os valores de tempo de reação nuclear foram ainda maiores (por exemplo: velocidade ascensional = 0,39 mh-1; tempo de reação celular = 363 dias). Os resultados deste trabalho abrem perspectivas para novas pesquisas e novos horizontes para projeto de sistemas com reatores anaeróbios de manta de lodo e decantadores de alta taxa.

ABSTRACT This paper presented a conceptual approach toward alternatives for the design of anaerobic sludge blanket reactors. In essence, it is proposed: i) the elimination of gas-liquid-solid separators that integrate the upflow anaerobic sludge blanket reactors and their replacement by a high rate settlers placed inside or outside the volume of biological reactor; ii) the recirculation of a fraction of the of the sludge retained in the settler, converting the process into a solution that resembles the activated sludge system, however, preserving the sludge blanket (Activated Anaerobic Sludge Blanket System), and thus ensuring better control of the cell retention time; and iii) the simplification (lower inlet points) of the influent distribution system placed over the bottom of the reaction zone, upon the implementation of two alternatives: mechanical mixing or hydraulic agitation with jet discharges, intermittent, in both cases. The proposals, as presented, are a summary of researches based on bench scale tests succeeded by the operation and tests in two parallel pilot units (total volume: 20.8 m3, including reaction zone and settler). It was found that it is possible to remove suspended solids from the effluent of the reaction zone without the need for a three-phase separator, and also, that it is possible to maintain the sludge blanket even with mixing in the reaction zone. Good results regarding total suspended solids, biochemical oxygen demand and chemical oxygen demand removal in the settlers were obtained, with applied hydraulic loading rate from 34.0 to 81.6 m3m-2 day. It was also found that very low velocity gradient values (G £ 20 s-1) are required to promote the maintenance of the sludge blanket, and the intermittency in the agitation is favorable to the biological process. The results concerning, , and TSS removal were compared with those of other studies on conventional upflow anaerobic sludge blanket reactors. However, those related to sludge age were the most significant to the conclusions of this research. When the reactor was operated with a hydraulic retention time of 8.2 h and a upflow velocity upflow velocity of 0.69 mh-1 in the biological reactor, the average sludge age reached 175 days. When applying smaller values of upflow velocity, the sludge age values reached greater values (Example: upflow velocity = 0.39 mh-1; sludge age = 363 days). The results and conclusions of this research open new perspectives for future research and new horizons for designing systems consisting of anaerobic sludge blanket and high-rate settlers.

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RESUMO A melhoria da qualidade dos efluentes das estações de tratamento de esgotos Brasília Norte e Sul tornou-se premente após o corpo receptor dos seus efluentes, o lago Paranoá, passar a ser utilizado como manancial de abastecimento. Este trabalho apresenta estudo comparativo entre o tratamento terciário por ultrafiltração precedido por coagulação em escala piloto e a flotação por ar dissolvido existente na estação de tratamento de esgotos Brasília Norte. A instalação piloto de ultrafiltração e a flotação por ar dissolvido foram alimentadas pela mesma matriz, o efluente da etapa de lodos ativados das estações de tratamento de esgotos Brasília Norte, após coagulação. Foram avaliadas sete condições operacionais da instalação piloto de ultrafiltração variando-se a vazão, o tempo de operação entre limpezas e a duração da limpeza física. O comportamento operacional e a qualidade do efluente produzido foram monitorados. O aumento do fluxo do permeado (de 40,2 para 50,6 e 61,0 L.m−2.h−1) e do tempo de operação entre as limpezas (de 25 para 38 e 50 min), bem como a redução da duração da retrolavagem (de 80 para 60 e 30 s) resultaram em evolução mais intensa da pressão transmembrana. A ultrafiltração foi mais eficiente do que a flotação por ar dissolvido na remoção de turbidez, sólidos suspensos totais, demanda química de oxigênio e fósforo total, com ganho médio de remoção de 9,4, 13,0, 8,5 e 12,8%, respectivamente. Destaca-se a remoção de coliformes na ultrafiltração, 3,4 log superior à da flotação por ar dissolvido. A utilização da ultrafiltração como alternativa à flotação por ar dissolvido apresenta a vantagem de produzir efluente de melhor qualidade, particularmente no aspecto microbiológico, com menor flutuação da qualidade, porém o tratamento e a destinação do lodo produzido pela ultrafiltração devem ser equacionados.

ABSTRACT Improvement in the effluent quality of the Brasília Norte and Brasília Sul wastewater treatment plants became necessary after their effluent receiving body, Paranoá Lake, started being used as source of drinking water for the population of Brasília (Federal District, Brazil). This is a comparative study between the tertiary treatment with ultrafiltration membrane (pilot scale) and the existing dissolved air flotation of Brasília Norte wastewater treatment plant. Both ultrafiltration pilot plant and dissolved air flotation were fed with the same matrix, the effluent of the activated sludge stage of Brasília Norte wastewater treatment plants, after coagulation. Seven operational conditions were evaluated at ultrafiltration pilot plant, with variations in flow rate, time of operation between cleaning processes, and the duration of backwashing. The operational behavior and the quality of the produced effluent were monitored. The increase in permeate flux (from 40.2 to 50.6 and 61.0 L.m−2.h−1) and in the time of operation between cleaning processes (from 25 to 38 and 50 min), as well as the reduction of backwashing duration (from 80 to 60 and 30s), resulted in a more intense evolution of transmembrane pressure. Ultrafiltration was more efficient than dissolved air flotation in the removal of turbidity, total suspended solids, chemical oxygen demand, and total phosphorous, with average gain in removal of 9.4, 13.0, 8.5, and 12.8%, respectively. It is worth mentioning the removal of coliforms by ultrafiltration, which was, on average, 3.4 log higher than that by dissolved air flotation. The use of ultrafiltration as an alternative to dissolved air flotation has the advantage of producing better quality effluent, particularly regarding microbiological aspects, providing lower quality fluctuation; however, treatment and destination of the ultrafiltration waste must be considered.

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RESUMO A remoção de matéria orgânica e de nitrogênio em esgoto doméstico diluído foi avaliada em dois reatores híbridos, um anaeróbio (RHAN) e outro aeróbio (RHAE). O RHAN era formado por uma câmara tipo upflow anaerobic sludge blanket sobreposta por outra de filtro anaeróbio, enquanto o RHAE tinha uma câmara de lodo ativado sobreposta por outra de biofilme aerado submerso. A operação do sistema foi dividida em duas fases, FI e FII, com razões de recirculação de 50 e 75% e duração de 94 e 110 dias, respectivamente. Para a remoção de nitrogênio, o RHAE foi operado com oxigênio dissolvido de 3,0 mg.L-1. A técnica da reação em cadeia da polimerase foi empregada tanto para o lodo suspenso das câmaras inferiores, como para o biofilme aderido nas câmaras superiores, para identificar a presença de micro-organismos desnitrificantes e nitrificantes. As maiores eficiências de remoção em termos de demanda química de oxigênio e nitrogênio total foram obtidas em FII, sendo 91% e ~50%, respectivamente; as concentrações no efluente foram ~40 mg O2.L-1 e ~15 mg N-NT.L-1. A presença de três grupos de bactérias, as desnitrificantes, as oxidantes de amônia e as oxidantes de nitrito, foi confirmada no biofilme aderido do RHAE, indicando uma biomassa mixotrófica e sugerindo a possibilidade do processo de nitrificação e desnitrificação simultânea.

ABSTRACT The removal of organic matter and nitrogen in diluted domestic sewage was evaluated in two hybrid reactors, one anaerobic (ANHR) and another aerobic (AEHR). ANHR was formed by a upflow anaerobic sludge blanket (UASB)-type chamber overlaid by an anaerobic filter, while AEHR had an activated sludge chamber overlaid by a submerged aerated biofilm chamber. The experimental period was divided into two phases, FI and FII, with recirculation ratios of 50 and 75%, and duration of 94 and 110 days, respectively. For nitrogen removal, AEHR was operated with a 3.0-mg.L-1 dissolved oxygen. Polymerase chain reaction technique was used for both suspended sludge in the down-chambers and attached biofilm in the upper-chambers, to identify the presence of denitrifying and nitrifying microorganisms. The highest removal efficiencies in terms of chemical oxygen demand and total nitrogen were obtained in FII, being 91 and ~50%, respectively; effluent concentrations were ~40 mg O2.L-1 and ~15 mg N-TN.L-1. The presence of three groups of bacteria, the denitrifiers, the ammonia oxidants and the nitrite oxidants, was confirmed in the attached biofilm of the RHAE, indicating a mixotrophic biomass and suggesting the possibility of simultaneous nitrification and denitrification process.

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The effluent from the textile industry is a complex mixture of recalcitrant molecules that can harm the environment and human health. Biological treatments are usually applied for this wastewater, particularly activated sludge, due to its high efficiency, and low implementation and operation costs. However, the activated sludge microbiome is rarely well-known. In general, activated sludges are composed of Acidobacteria, Bacillus, Clostridium, Pseudomonas, Proteobacteria, and Streptococcus, in which Bacillus and Pseudomonas are highlighted for bacterial dye degradation. Consequently, the process is not carried out under optimum conditions (treatment yield). Therefore, this review aims to contextualize the potential environmental impacts of azo dye-containing wastewater from the textile industry, including toxicity, activated sludge microbiome identification, in particular using the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) as a novel, rapid and accurate strategy for the identification of activated sludge microbiome (potential to enhance treatment yield).

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BACKGROUND: Most of the organic content of waste activated sludge (WAS) comprises microbial cells hard to degrade, which must be pre-treated for energy recovery by anaerobic digestion (AD). Electrooxidation pre-treatment (EOP) with boron-doped diamond (BDD) electrode have been considered a promising novel technology that increase hydrolysis rate, by the disintegrating cell walls from WAS. Although electrochemical oxidation could efficiently solubilize organic substances of macromolecules, limited reports are available on EOP of WAS for improving AD. In this endeavour, the mathematical optimization study and the energy analysis of the effects of initial total solids concentrations [TS] of WAS and current density (CD) during EOP on the methane production and removal of chemical oxygen demand (COD) and volatile solids (VS) were investigated. Because limited reports are available on EOP of WAS for improving biogas production, it is not well understood; however, it has started to attract interest of scientists and engineers. RESULTS: In the present work, the energy recovery as biogas and WAS conversion were comprehensively affected by CD and [TS], in an integrated EOP and AD system. When working with WAS at 3% of [TS] pre-treated at current density of 24.1 mA/cm2, the highest COD and VS removal were achieved, making it possible to obtain the maximum methane (CH4) production of 305 N-L/kg VS and a positive energy balance of 1.67 kWh/kg VS. Therefore, the current densities used in BDD electrode are adequate to produce the strong oxidant (hydroxyl radical, ·OH) on the electrode surface, allow the oxidation of organic compounds that favours the solubilization of particulate matter and VS from WAS. CONCLUSIONS: The improvement of VS removal and COD solubilization were due to the effects of pre-treatments, which help to break down the microbial cells for faster subsequent degradation; this allows a decomposition reaction that leads to biodegrade more compounds during AD. The balance was positive, suggesting that even without any optimization the energy used as electricity could be recovered from the increased methane production. It is worth noting that this kind of analysis have not been sufficiently studied so far. It is therefore important to understand how operational parameters can influence the pre-treatment and AD performances. The current study highlights that the mathematical optimization and energy analysis can make the whole process more convenient and feasible.

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Hexavalent chromium becomes in one of the tops internationally concern environmental issues due to its wide usage in several industrial activities. There are two stable oxidation states of chromium in the environment which differ significantly on its toxicity; Cr(III) has lower solubility, mobility and lesser biological toxicity in comparison with Cr(VI). While Cr(VI) is a well-known carcinogen, Cr(III) is an essential dietary element. For this reason, most technologies focus attention on the reduction of Cr(VI) to Cr(III). On this context, the ability of microorganisms to reduce Cr(VI) to Cr(III) has gained attention. The objectives of the present work were to analyze the effect of Cr(VI) on the activated sludge community in a continuous reactor, and to evaluate the differences on the metabolic activity of native (NAS) and Cr(VI)-acclimated activated sludge (CrAAS) using a respirometric method. Results showed that the activated sludge community had the capability to acclimate to the presence of Cr(VI). On the other hand, the increase of the initial Cr(VI) concentration from 0 to 100 mgCr/L leads to a decrease in the specific exogenous respiration rate (qEx ) values, but this reduction was more noticeably in the case of NAS in comparison with CrAAS. The respirometric curves were well described by the proposed mathematical model. It was concluded that the CrAAS tolerated a Cr(VI) concentration about one order of magnitude higher than NAS, which was positively reflected in the respiration rate first-order decay constant (kd ), the specific maximum exogenous respiration rate (qExm ), and the observed oxidation coefficient (YO/S ) values.

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Wastewater reuse has been widely discussed as an essential strategy to minimize the consumption of drinking water for less noble purposes. During biological wastewater treatment, organic matter is converted into a complex matrix containing a variety of soluble organic compounds. The objective of the present study was to evaluate the removal efficiency of the residual organic load in the final effluent from wastewater treatment plant with a conventional activated sludge process by different coagulants and parameters of coagulation-flocculation process, using dissolved organic carbon (DOC) concentration, molecular weight (MW) size distribution by size exclusion chromatography (SEC) coupled to mass spectrometry (MS), and zeta potential (ZP) analyses. The results showed a DOC removal efficiency up to 45% with iron chloride, and of 38% for aluminum sulfate and 31% for PAC coagulants. ZP was also measured during the procedures and authors conclude that the ZP also does not have a determining role in these removals. SEC and MS assessment was able to detect changes on secondary effluent molecular weight distribution profile after effluent coagulation-flocculation, this technique might be a promising tool to understand the composition of effluent organic matter and be helpful to estimate and optimize the performance of wastewater effluents treatment processes.

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In this study, mixed culture (microalgae:activated sludge) of a photobioreactor (PBR) were investigated at different inoculation ratios (1:0, 9:1, 3:1, 1:1, 0:1 wt/wt). This work was not only to determine the optimal ratio for pollutant remediation and biomass production but also to explore the role of microorganisms in the co-culture system. The results showed high total biomass concentrations were obtained from 1:0 and 3:1 ratio being values of 1.06, 1.12 g L-1, respectively. Microalgae played a dominant role in nitrogen removal via biological assimilation while activated sludge was responsible for improving COD removal. Compared with the single culture of microalgae, the symbiosis between microalgae and bacteria occurred at 3:1 and 1:1 ratio facilitated a higher COD removal by 37.5-45.7 %. In general, combined assessment based on treatment performance and biomass productivity facilitated to select an optimal ratio of 3:1 for the operation of the co-culture PBR.

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Effective wastewater management is crucial to ensure the safety of water reuse projects and effluent discharge into surface waters. Multiple studies have demonstrated that municipal wastewater treatment with conventional activated sludge processes is inefficient for the removal of a wide spectrum of viruses in sewage. In this study, a well-accepted statistical approach was used to investigate the relationship between viral indicators and human enteric viruses during wastewater treatment in a resource-limited region. Influent and effluent samples from five urban wastewater treatment plants (WWTPs) in Costa Rica were analyzed for somatic coliphage and human enterovirus, hepatitis A virus, norovirus genotypes I and II, and rotavirus. All WWTPs provide primary treatment followed by conventional activated sludge treatment prior to discharge into surface waters that are indirectly used for agricultural irrigation. The results revealed a statistically significant relationship between the detection of at least one of the five human enteric viruses and somatic coliphage. Multiple logistic regression and receiver operating characteristic curve analysis identified a threshold of 3.0 × 103 (3.5 log10) somatic coliphage PFU per 100 ml, which corresponded to an increased likelihood of encountering enteric viruses above the limit of detection (>1.83 × 102 virus targets/100 ml). Additionally, quantitative microbial risk assessment was executed for farmers indirectly reusing WWTP effluent that met the proposed threshold. The resulting estimated median cumulative annual disease burden complied with World Health Organization recommendations. Future studies are needed to validate the proposed threshold for use in Costa Rica and other regions.IMPORTANCE Effective wastewater management is crucial to ensure safe direct and indirect water reuse; nevertheless, few countries have adopted the virus log reduction value management approach established by the World Health Organization. In this study, we investigated an alternative and/or complementary approach to the virus log reduction value framework for the indirect reuse of activated sludge-treated wastewater effluent. Specifically, we employed a well-accepted statistical approach to identify a statistically sound somatic coliphage threshold value which corresponded to an increased likelihood of human enteric virus detection. This study demonstrates an alternative approach to the virus log reduction value framework which can be applied to improve wastewater reuse practices and effluent management.

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RESUMO

RESUMO No presente trabalho, foi avaliado o desempenho de um sistema de lodo ativado em batelada, com módulo de filtração, proporcionado por uma manta geotêxtil, na remoção de matéria orgânica presente em esgoto sanitário. O reator em escala piloto tinha volume útil de 85 L e foi operado durante 182 dias, com tempo total de ciclo de 24 horas de duração e idade do lodo (θc) de 25 dias. O sistema foi composto de um reator convencional (SB1), utilizado como controle e operado nas mesmas condições que o SM1, o qual utilizou a filtração em manta geotêxtil. Para confecção dos três módulos de filtração, foi utilizada uma manta sintética não tecida combinada com três tipos de espaçadores: tela antiderrapante em poliéster com revestimento em PVC (etapa I) durante 56 dias, geomanta tridimensional de filamentos de polipropileno termosoldados (etapa II) durante 49 dias e manta acrílica 100% poliéster (etapa III) durante 76 dias. A concentração de oxigênio dissolvido (OD) manteve-se na faixa de 3 mgO2.L-1, a relação alimento (A)/microrganismo (M) variou de 0,2 a 0,1 gDBO5.gSSV-1.d-1, e a carga orgânica média aplicada mudou de 0,194 a 0,267 kgDQO.m-3.d.-1. A remoção da turbidez manteve-se na faixa de 97%, a de matéria orgânica em termos de demanda bioquímica de oxigênio (DBO5) foi de 93% e entre 87 e 93% para o parâmetro demanda química de oxigênio (DQO), com o reator SM1 apresentando valores de eficiência e estabilidade operacional superiores ao SB1.

ABSTRACT This work evaluated the performance of a batch activated sludge system with a filtration module, provided by a geotextile blanket to remove organic matter present in sewage. The pilot-scale reactor had a useful volume of 85L, and it was operated for 182 days, with a total cycle time of 24 hours, and sludge age (θc) 25 days. The system was based on a conventional controller (SB1), used as a control and operated under the same conditions as the reactor (SM1) using geotextile blanket filtration. The preparation of the three filtration modules was applied to a non-woven synthetic blanket combined with three types of spacers: PVC-coated non-slip polyester mesh (Step I) for 56 days, three-dimensional geo-mat of thermosolded polypropylene filament (Step II) for 49 days, and 100% polyester acrylic blanket (Step III) for 76 days. The OD concentration remained in the range of 3 mgO2L-1, an F/M ratio ranging from 0.2 to 0.1 gBOD5. gVSS-1d-1 and the organic loading rate average applied ranged from 0.194 to 0.267 kg COD / m3.d.-1. Turbidity removal remained in the range of 97%, and the organic matter removal in terms of BOD5 was 93%, and from 87 to 93% in terms of COD, with SM1 reactor showing efficiency and stability values higher than SB1.

RESUMO

RESUMO Sistemas anaeróbios modernos de tratamento de esgoto doméstico, embora bastante eficientes na remoção de matéria orgânica e sólidos em suspensão, não produzem um efluente com qualidade compatível com os padrões legais para descarga em corpos d'água. Por essa razão, esses sistemas têm de ser associados a unidades de pós-tratamento. Este trabalho trata de uma investigação experimental sobre a viabilidade de aplicação do sistema de lodo ativado como uma alternativa do pós-tratamento, especificamente para o caso em que se prevê o efluente final para fertirrigação. Na investigação experimental, utilizou-se um reator de bateladas sequenciais (RBS), em escala laboratorial, como unidade de pós-tratamento. Os resultados experimentais mostraram que o comportamento do sistema RBS pode ser descrito como o modelo geral de lodo ativado da Associação Internacional da Água (IWA, na sigla em inglês), que resulta na definição dos aspectos fundamentais: qualidade do efluente final, consumo de oxigênio e produção de lodo. Na otimização do reator RBS, desenvolveu-se um modelo que permite estabelecer o tempo de permanência mínimo para o pós-tratamento em função de dois parâmetros básicos: a constante de utilização de material orgânico biodegradável pelas bactérias heterotróficas do lodo gerado no sistema de pós tratamento e a sedimentabilidade desse lodo. A constante de utilização de material orgânico foi determinada por testes respirométricos. O lodo gerado no sistema de pós-tratamento surpreendentemente mostrou ter uma sedimentabilidade bem superior àquela normalmente encontrada em sistemas de lodo ativado tratando esgoto bruto, o que constitui um argumento sólido para a aplicação do sistema RBS na prática de pós-tratamento do efluente do reator upflow anaerobic slugde blanket (UASB).

ABSTRACT Modern anaerobic systems for domestic sewage treatment, although very effective in removing organic matter and suspended solids, do not produce a quality effluent that complies with the legal standards for discharge into water bodies. Therefore, such systems have to be associated with post treatment units. This paper deals with an experimental investigation into the feasibility of applying the activated sludge system as an alternative post-treatment, specifically for the case where reuse of the final wastewater for fertigation is expected. In the experimental investigation, a pilot-scale sequencing batch reactor (SBR), in laboratory scale, was used as a post-treatment unit. The experimental results showed that the behavior of the RBS system can be described with the general IWA model for activated sludge, resulting in the definition of the fundamental aspects: quality of the final effluent, oxygen consumption, and sludge production. In the optimization of the RBS reactor, a model was developed to establish the minimum retention time for the post-treatment in terms of two basic parameters: the biodegradable organic material utilization constant by heterotrophic bacteria sludge of the post-treatment system and the sedimentability of this sludge. The organic material utilization constant was determined by respirometry testing. The sludge generated in the post-treatment system surprisingly been shown to have a much higher sedimentability than that normally found in activated sludge systems dealing with raw sewage, which is a sound argument for applying the RBS system in the practice of post-treatment reactor effluent UASB