Influence of COD/N ratio and carbon source on nitrogen removal in a structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA)

Partial nitrification and simultaneous denitrification in sequential anaerobic and aerobic reactors: performance and microbial community dynamics

ABSTRACTThe removal of organic matter and nitrogen from domestic sewage was evaluated using a system composed of two sequential reactors: an anaerobic reactor (ANR) with suspended sludge and an aerobic (AER) reactor with suspended and adhered sludge to polyurethane foams. Nitrogen removal consisted of AER operating at low dissolved oxygen (DO) concentrations; this favoured the simultaneous nitrification and denitrification (SND) process. The concentration of COD and N were 440 mgO2.L-1 and 37 mgTN.L-1, respectively. The operation was divided into three phases (P), lasting 51, 53, and 46 days, respectively. The initial DO concentrations applied in the AER were: 3.0 (PI) and 1.5 mg.L-1 (PII and PIII). In PIII, the AER effluent was recirculated to the ANR at a ratio of 0.25. Kinetic assays were performed to determine the nitrification and denitrification rates of the biomasses (ANR and AER in PIII). Changes in the microbial community were evaluated throughout phases PI to PIII by massive sequencing. In PIII, the best results obtained for chemical oxygen demand (COD) and total nitrogen (TN-N) removal efficiencies, were close to 94% and 65%, respectively. Under these conditions, system effluent concentrations below 30 mg COD.L-1 and 15 mg TN-N.L-1 were verified. The nitritation and nitration rates were 10.5 and 6.5 mg N.g VSS-1.h-1, while the denitrification via nitrite and nitrate were 6.8 and 5.8 mg N.g VSS-1.h-1, respectively. A mixotrophic community was prevalent, with Rhodococcus, Nitrosomonas, Pseudomnas, and Porphyromonas being dominant or co-dominant in most of the samples, confirming the SND process in the AER sludge.

Assessing the phytotoxicity of wastewater from the structured-bed hybrid baffled reactor (SBHBR) for agricultural reuse during the germination phase

This study investigated the quality of anaerobic (AnE) and oxic/anoxic (O/A) effluents from a continuous-feed structured-bed hybrid baffled reactor (SBHBR) treating dairy wastewater impacts on lettuce and cucumber germination. While sustainable technologies like SBHBR have successfully removed organic matter and total nitrogen from dairy wastewater, residual concentrations may still represent a risk to water resources. Therefore, phytotoxicity bioassays were conducted with lettuce and cucumber seeds in contact with effluent during early stages to evaluate the potential implications of dairy wastewater reuse in agriculture. The study also explored the potential of SBHBR technology in promoting water resource preservation and creating a sustainable energy and nutrient cycling system. The physicochemical parameters of both effluents were characterized, and the phytotoxicity was evaluated by measuring the germination index (GI), root length (RL), the number of germinated seeds (SG), and epicotyl elongation (EE) for both lettuce and cucumber. The study revealed that the O/A effluent demonstrated lower phytotoxicity than the AnE effluent. The mean results indicate that the O/A zone wastewater was more conducive to cucumber germination than the AnE zone. Moreover, a positive influence of organic matter in the effluent on root growth and epicotyl elongation in cucumber, as well as the presence of nitrogen on the germination index, in both plant species. These findings emphasize the importance of considering effluent characteristics for suitable irrigation, highlighting SBHBR's potential as an effective solution for treating and reusing dairy wastewater in agriculture. This approach helps conserve water resources and promote a sustainable energy and nutrient cycling system.

A pilot-scale study of a novel system for simultaneous nitrogen and carbon removal: technological advancement of a structured bed reactor with intermittent aeration (SBRIA) in real domestic sewage treatment

This study outlines the development of an effective pilot-scale simultaneous denitrification and nitrification (SDN) system using intermittent aeration for the removal of carbon and nitrogen from real domestic sewage. Given the limited research in this area, the main objective was to evaluate the overall performance of the SBRIA system on a pilot scale and show its benefits in domestic wastewater treatment. The structured bed reactor with intermittent aeration (SBRIA) notably achieved 57% efficiency in removing total nitrogen without requiring external carbon sources. It also demonstrated impressive removal rates of 56% for total chemical oxygen demand (CODT) and 82% for biochemical oxygen demand (BOD5), indicating its effectiveness in degrading organic matter. In addition, the SBRIA showed high pH control and managed the consumption of alkalinity without the need for an alkalizer, maintaining consistent mean values of 7.7 ± 0.8 for pH and 166.8 ± 79.8 mg·L-1 for alkalinity. The system also proved resilient against toxic shocks caused by significant variations in influent characteristics. This study offers valuable insights and compelling results into a cost-effective and efficient treatment approach using an innovative technology not previously applied at the pilot scale. Its potential to remediate polluted water is substantial.

Unique biofilm structure and mass transfer mechanisms in the foam aerated biofilm reactor (FABR)

The foam-aerated biofilm reactor (FABR) is a novel biofilm process that can simultaneously remove carbon and nitrogen from wastewater. A porous polyurethane foam sheet forms an interface between wastewater and aerated water, making it a counter-diffusional biofilm process similar to the membrane-aerated biofilm reactor (MABR). However, it is not clear how biofilm develops the foam interior, and how this impacts mass transfer and performance. This research explored biofilm development within the foam sheet and determined whether advective transport within the sheet played a significant role. Foam sheets with 2-, 4.5- and 9-mm thicknesses were explored. Oxygen, nitrate, nitrite and ammonia profiles in the sheet were measured using microsensors, and biofilm imaging studies were carried out using optical coherence tomography (OCT). On the foam's aerated side, a dense nitrifying biofilm formed. Beyond the aerobic zone, much less biomass was observed, with a high porosity foam-biofilm layer. The higher effective diffusivity within the foam for the 4- and 9-mm sheets suggested advective transport within the foam channel structures. Using an effective diffusivity factor in conventional 1-D biofilm models reproduced the measured substrate concentration profiles within the foam. Four different practical conditions were modelled. The maximum TN removal efficiency was about 70% and a nitrogen removal flux of 1.25 gN.m-2.d-1. We conclude that mass transfer resistance occurred primarily in the dense, nitrifying layer near the aerated side. The rest of the foam sheet was porous, allowing the advective mass transfer.

Removal of organic matter and nitrogen from dairy effluents in a structured bed reactor operated with intermittent aeration

The objective of this research was to evaluate the performance of a structured bed reactor (SBRIA), carried out with intermittent aeration (IA), in the removal of organic matter and nitrogen from dairy effluent, when run with different organic loading rates (OLR). The SBRIA was operated for 227 days, with 2:1 AI cycles (2 h with aeration on and 1 h off) and Hydraulic Retention Time (HRT) of 16 h. Three phases, with different OLR, were evaluated: phases A (1000 gCOD m-3 day-1 - 63 days), B (1400 gCOD m-3 day-1 - 94 days), and C (1800 gCOD m-3 day-1 - 70 days). The percentage of COD, NH4+-N removal, and nitrogen removal, respectively, were above 85 ± 7%, 73 ± 27%, and 83 ± 5, in all phases. There was no accumulation of the oxidized forms of nitrogen in the reactor. The kinetic test, performed to evaluate the nitrification and denitrification in the system, indicated that even in dissolved oxygen concentrations of 4.5 mg L-1, it was possible to obtain the denitrification process in the system. The results demonstrate that the reactor under study has positive characteristics to be used as an alternative for removing the removal of organic material and nitrogen in the biological treatment of dairy effluents.

Evaluating the potential of a new reactor configuration to enhance simultaneous organic matter and nitrogen removal in dairy wastewater treatment

The dairy industry is a very productive sector worldwide and known for producing great volumes of wastewater that is rich in organic matter and nutrients. Apart from fat, the organic matter in such effluents is easily degradable, demanding an external carbon source for conventional denitrification. In this manner, new configurations of reactors promoting a suitable environment for more sustainable nitrogen removal are beyond required-they are paramount. Therefore, the performance of a structured-bed hybrid baffled reactor (SBHBR) with anaerobic and oxic/anoxic chambers was designed and assessed for treating different dairy wastewaters. A combination of baffled and biofilm-structured systems under intermittent aeration was the solution proposed to obtain a new method for nitrogen removal under low COD/TN ratios. The COD/TN ratios tested were 2.1 ± 0.6, 0.84 ± 0.5, and 0.35 ± 0.1 in the inlet of the O/A chambers for operational stages I, II, and III, respectively. The SBHBR provided COD removal efficiencies above 90% in all experimental stages. During stage III, the process had nitrification and denitrification efficiencies of 85.9 ± 17% and 85.2 ± 9%, respectively, resulting in a TN removal efficiency of 74.6 ± 14.7%. Stoichiometric calculations were used to corroborate the activity of bacteria that could perform the anammox pathways as their main mechanisms.

Heterotrophic nitrification-aerobic denitrification performance of a novel strain, Pseudomonas sp. B-1, isolated from membrane aerated biofilm reactor

A heterotrophic nitrification-aerobic denitrification (HN-AD) strain isolated from membrane aerated biofilm reactor (MABR) was identified as Pseudomonas sp. B-1, which could effectively utilize multiple nitrogen sources and preferentially consume NH₄-N. The maximum degradation efficiencies of NO₃-N, NO₂-N and NH₄-N were 98.04%, 94.84% and 95.74%, respectively. The optimal incubation time, shaking speed, carbon source, pH, temperature and C/N ratio were 60 h, 180 rpm, sodium succinate, 8, 30 °C and 25, respectively. The strain preferred salinity of 1.5% and resisted heavy metals in the order of Mn²⁺ > Co²⁺ > Zn²⁺ > Cu²⁺. It can be preliminarily speculated from the results of enzyme assay that the strain removed nitrogen via full nitrification-denitrification pathway. The addition of strain into the conventional MABR significantly intensified the HN-AD performance of the reactor. The relative abundance of the functional bacteria including Flavobacterium, Pseudomonas, Paracoccus, Azoarcus and Thauera was obviously increased after the bioaugmentation. Besides, the expression of the HN-AD related genes in the biofilm was also strengthened. Thus, strain B-1 had great application potential in nitrogen removal process.

Biofilm stratification and autotrophic-heterotrophic interactions in a structured bed reactor (SBRIA) for carbon and nitrogen removal

The structured-bed reactor with intermittent aeration (SBRIA) is a promising technology for simultaneous carbon and nitrogen removal from wastewater. An in depth understanding of the microbiological in the reactor is crucial for its optimization. In this research, biofilm samples from the aerobic and anoxic zones of an SBRIA were analyzed through 16S rRNA sequencing to evaluate the bacterial community shift with variations in the airflow and aeration time. The control of the airflow and aeration time were essential to guarantee reactor performances to nitrogen removal close to 80%, as it interfered in nitrifying and denitrifying communities. The aeration time of 1.75 h led to establishment of different nitrogen removal pathways by syntrophic relationships between nitrifier, denitrifier and anammox species. Additionally, the predominance of these different species in the internal and external parts of the biofilm varied according to the airflow.

Enhanced biological nitrogen and phosphorus removal from sewage driven by fermented glycerol: comparative assessment between sequencing batch- and continuously fed-structured fixed bed reactor

The nutrient biological removal from sewage, especially from anaerobic reactor effluents, still represents a major challenge in conventional sewage treatment plants. In this work, the nitrogen and phosphorus removal from anaerobic pre-treated domestic sewage in an up-flow anaerobic sludge blanket (UASB) reactor was assessed in a structured fixed bed reactor (SFBR) operated in a continuous and in a batch mode using polyurethane foam as material support for biomass and fermented glycerol as the exogenous carbon source. The SFBR was operated as a sequencing batch reactor with cycles of 90, 120, and 150 min under anaerobic, oxic, and anoxic conditions, respectively, reaching average efficiencies for total nitrogen and phosphorus removal of 88% and 56%, respectively. Fermented glycerol was added during the non-aerated periods. Under continuous feeding, the SFBR was operated with aeration/non-aeration periods of 2/1 (h) and 3/1 (h), hydraulic retention time of 12 h, and a recirculation ratio of 3. Without fermented glycerol addition, the maximum removal of total nitrogen (TN) reached 42%, while adding glycerol in the non-aerated period improved TN removal to 64.9% (2/1 h) and 69.5% (3/1 h). During continuous operation, no phosphorus removal was observed, which was released during the non-aerated period, remaining in the effluent. Optical microscopy analyses confirmed the presence of polyphosphate granules and of the phosphorus accumulating organisms in the reactor biofilm. It was concluded that the batch feeding method was determinant for phosphorus removal. The structured fixed bed reactor with polyurethane foam proved to be feasible in the removal of organic matter and nutrients remaining in the UASB reactor effluent.

Foam aerated biofilm reactor: a novel counter-diffusional process for COD and nitrogen removal from low COD/N effluents

Counter-diffusional biofilms are efficient in the removal of nitrogen from low strength wastewaters. Although counter-diffusion is usually established using expensive gas-permeable membranes, a polyurethane sheet is used to separate the aerobic and anoxic environments in the novel foam aerated biofilm reactor (FABR). Foam sheets with thicknesses of 10, 5 and 2 mm and synthetic wastewater with COD/N ratios of 5 and 2.5 were evaluated. The 2 mm thick foam reactor did not show good biomass adherence and, therefore, did not show N removal efficiency. The 5 and 10 mm reactors, in both COD/N ratios, showed similar total nitrogen and COD removal performance, up to 60% and 80%, respectively. The denitrification efficiency was close to 100% throughout the experimental period. Nitrification efficiency decreased with microbial growth, which was recovered after removal of excessive biomass. Lower values of polyurethane foam thickness and COD/N ratio did not provide a higher nitrification rate, as expected. The increase in resistance to mass transfer was associated with the growth of biomass attached to the foam rather than to its thickness and resulted in specialization of the microbial communities as revealed by 16S amplicon sequencing. FABR reveals as a promising alternative for simultaneous removal of nitrogen and COD from low COD/N ratio wastewaters.

Aeration and non-aeration cycles (AE/NA) time: influence in combined organic matter and nitrogen removal and features of biofilm

This research aimed the performance evaluation of a structured bed reactor with different cycles of Intermittent Aeration (IA)(SBRRIA) in the municipal sewage treatment and the verification of the effect of IA cycles on the total nitrogen (TN) removal and organic matter (COD). Three IA cycles were evaluated: phase I (4 h AE (aeration on) - 2 h NA (aeration off)); II (2 h AE-1 h NA) and III (2 h AE-2 h NA), with Hydraulic Retention Time of 16 h. The best nitrogen removal was obtained during phase II, with the lowest non-aeration time: efficiency of nitrification, denitrification, TN and COD removal of 80 ± 15%, 82 ± 12%, 67 ± 6% and 94 ± 7%, respectively. The mean cell residence time was 19, 26 and 33 d in phases I, II and III, respectively. The statistical analysis applied to the AE/NA profiles showed that the time of AE and NA in the cycles did not influence nitrogen and organic matter removal. Thus, this indicates the recirculation and the gradient formed in the support material facilitate the process of Simultaneous Nitrification and Denitrification. The lowest concentration of nitrifying and denitrifying microorganisms was obtained in effluent and sludge at the end of phase III. From the TP (Total Proteins)/TPS (Total Polysaccharides) ratio obtained (0.8 ± 0.1, 1.3 ± 0.1 e 1.5 ± 0.1 in phases I, II and III), it was possible to conclude that the biofilm in phase I was more porous, with a thin layer if compared to that in phase II and III.

Optimization of airflow and aeration cycles in a new structured bed reactor configuration for carbon and nitrogen removal

The Structured Bed Reactor with Recirculation and Intermittent Aeration (SBRRIA) is a reactor configuration that presents high efficiency of organic matter and nitrogen removal, besides low sludge production. However, operational parameters, as the recirculation rate, aeration time, and airflow, are not fully established. A bench-scale structured bed reactor with intermittent aeration was fed with synthetic effluent simulating the characteristics of sanitary sewage. The reactor was operated for 280 days with an operational hydraulic retention time (HRT) of 10 h. The reactor was operated without effluent recirculation for the first time since this approach was not yet reported, and was named Structured Bed Reactor with Intermittent Aeration (SBRIA). The COD removal was higher than 81% for all operational conditions, and the total nitrogen removal ranged from 10 to 80%. The highest efficiencies were obtained with an aeration time of 1 h 45 min (total cycle of 3 h) and an airflow rate of 4.5 L.min^-1. Different nitrification and denitrification behaviours were observed, resulting in nitrification efficiencies over 90% when the reactor was submitted to higher aeration times and denitrification efficiencies above 90% when the reactor was submitted to low aeration times. The airflow ranges tested in this study affected the nitrification and the total nitrogen efficiencies. Even without effluent recirculation, the temporal profile showed that there were no peaks in the concentration of the nitrogen forms in the reactor effluent, saving electrical energy up to 75% due to pumping.

Tetrabromobisphenol A (TBBPA) anaerobic biodegradation occurs during acidogenesis

This is the first study to bring evidence on the anaerobic biodegradation of TBBPA occurring during acidogenesis in domestic sewage at environmentally relevant concentrations by complex microbial communities. This was accomplished by continuously operating two anaerobic structured bed reactors (ASTBR) for over 100 days under acidogenic (Acidogenic Reactor, AR) and multistep methanogenic (Methanogenic Reactor, MR) conditions. In the AR, the temporal carbohydrates consumption and the acetic acid production were strongly correlated with TBBPA removal by the Pearson's test. The spatial concentration of TBBPA and carbohydrates along the MR and the kinetic degradation profiles corroborate the AR results. It is hypothesized that TBBPA biodegradation in the studied conditions occurs during acidogenesis via the cometabolism supported by non-specific enzymes and the metabolism (dehalorespiration) established by electrons donors such as H₂, which are both produced during the macrocomponents breakdown in the early stages of the anaerobic digestion. The TBBPA mass balance showed that approximately 86.8 ± 0.05% and 97 ± 0.01% of the removed TBBPA was biodegraded in the AR and MR, respectively. Furthermore, TBBPA biodegradation went further than reductive debromination as total phenols were detected in the reactors' effluent.

Two-stage partial nitrification-Anammox process for nitrogen removal from slaughterhouse wastewater: Evaluation of the nitrogen loading rate and microbial community analysis

The production of inputs for animal feed using slaughterhouse byproducts is a predominant waste valorization route of the meat industry. This practice generates complex effluents containing high concentrations of organic matter and nutrients. The partial nitrification process followed by the Anammox process (PN/A) has been shown to be a viable technology for nitrogen removal from wastewaters with high concentrations of ammonia and low COD/N ratios, as found in Upflow Anaerobic Sludge Blanket (UASB) effluent from animal feed inputs industries. However, its application has not been assessed for slaughterhouse byproducts processing wastewaters. This work aimed at evaluating the influence of the nitrogen loading rate (NLR) on the removal of total nitrogen (TN) of a PN/A process treating real animal feed industry wastewater. The NLR in the Anammox reactor varied from 1.3 to 6.3 g N L^-1.d^-1, with a constant COD/N ratio of 0.5 ± 0.1 mg COD.mg N^-1. An average removal efficiency of TN of 84.2 ± 9.8% was observed throughout 440 days of operation. Microbiological analyses of the granular Anammox sludge performed before and after the operation revealed an increase in the population of heterotrophic denitrifying bacteria, while the relative abundance of Anammox species decreased. It was demonstrated that although both microbial groups can coexist synergistically, the presence of organic matter contributed to the growth of heterotrophic denitrifying species and impaired the growth of Anammox bacteria, without affecting system performance.

Methanotrophic denitrification in wastewater treatment: microbial aspects and engineering strategies

Anaerobic technologies are consolidated for sewage treatment and are the core processes for mining marketable products from waste streams. However, anaerobic effluents are supersaturated with methane, which represents a liability regarding greenhouse gas emissions. Meanwhile, anaerobic technologies are not capable of nitrogen removal, which is required to ensure environmental protection. Methane oxidation and denitrification processes can be combined to address both issues concurrently. Aerobic methane oxidizers can release intermediate organic compounds that can be used by conventional denitrifiers as electron donors. Alternatively, anoxic methanotrophic species combine methane oxidation with either nitrate or nitrite reduction in the same metabolism. Engineered systems need to overcome the long doubling times and low NO_x consumption rates of anoxic methanotrophic microorganisms. Another commonly reported bottleneck of methanotrophic denitrification relates to gas-liquid mass transfer limitations. Although anaerobic effluents are supersaturated with methane, experimental setups usually rely on methane supply in a gaseous mode. Hence, possibilities for the application of methane-oxidation coupled to denitrification in full scale might be overlooked. Moreover, syntrophic relationships among methane oxidizers, denitrifiers, nitrifiers, and other microorganisms (such as anammox) are not well understood. Integrating mixed populations with various metabolic abilities could allow for more robust methane-driven wastewater denitrification systems. This review presents an overview of the metabolic capabilities of methane oxidation and denitrification and discusses technological aspects that allow for the application of methanotrophic denitrification at larger scales.

Advances in Biological Nitrogen Removal of Landfill Leachate

With the development of economy and the improvement of people’s living standard, landfill leachate has been increasing year by year with the increase in municipal solid waste output. How to treat landfill leachate with high efficiency and low consumption has become a major problem, because of its high ammonia nitrogen and organic matter content, low carbon to nitrogen ratio and difficult degradation. In order to provide reference for future engineering application of landfill leachate treatment, this paper mainly reviews the biological treatment methods of landfill leachate, which focuses on the comparison of nitrogen removal processes combined with microorganisms, the biological nitrogen removal methods combined with ecology and the technology of direct application of microorganisms. In addition, the mechanism of biological nitrogen removal of landfill leachate and the factors affecting the microbial activity during the nitrogen removal process are also described. It is concluded that the treatment processes combined with microorganisms have higher nitrogen removal efficiency compared with the direct application of microorganisms. For example, the nitrogen removal efficiency of the combined process based on anaerobic ammonium oxidation (ANAMMOX) technology can reach more than 99%. Therefore, the treatment processes combined with microorganisms in the future engineering application of nitrogen removal in landfill leachate should be paid more attention to, and the efficiency of nitrogen removal should be improved from the aspects of microorganisms by considering factors affecting its activity.

Hacking biofilm developed in a structured-bed reactor (SBRRIA) with integrated processes of nitrogen and organic matter removal

Biomass samples from a structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA) were analyzed to investigate the bacterial community shift along with the changes in the C/N ratio. The C/N ratios tested were 7.6 ± 1.0 (LNC) and 2.9 ± 0.4 (HNC). The massive sequencing analyses revealed that the microbial community adjusted itself to different organic and nitrogenous applied loads, with no harm to reactor performance regarding COD and Total-N removal. Under LNC, conventional nitrification and heterotrophic denitrification steered the process, as indicated by the detection of microorganisms affiliated with Nitrosomonadaceae, Nitrospiraceae, and Rhodocyclaceae families. However, under HNC, the C/N ratio strongly affected the microbial community, resulting in the prevalence of members of Saprospiraceae, Chitinophagaceae, Xanthomonadaceae, Comamonadaceae, Bacillaceae, and Planctomycetaceae. These families include bacteria capable of using organic matter derived from cell lysis, ammonia-oxidizers under low DO, heterotrophic nitrifiers-aerobic denitrifiers, and non-isolated strains of Anammox. The DO profile confirmed that the stratification in aerobic, anoxic, and anaerobic zones enabled the establishment of different nitrogen degradation pathways, including the Anammox.

Application of Dispersive Liquid-Liquid Microextraction Followed by High-Performance Liquid Chromatography/Tandem Mass Spectrometry Analysis to Determine Tetrabromobisphenol A in Complex Matrices

An accurate and sensitive ultrasound-dispersive liquid-liquid microextraction technique followed by high-performance liquid chromatography separation coupled with electrospray ionization tandem mass spectrometry detection method to determine the presence of tetrabromobisphenol A (TBBPA) in complex environmental matrices is proposed. The miniaturized procedure was used to extract and quantify the analyte in domestic sewage, anaerobic sludge, and the aquatic test organism species Daphnia magna and Chironomus sancticaroli, which are standardized organisms for ecotoxicity bioassays. Limits of detection of 2 ng L^-1 (domestic sewage), 2 ng g^-1 (anaerobic sludge), 0.25 ng g^-1 (D. magna), and 5 ng g^-1 (C. tentans) were obtained. The presence of TBBPA was determined in domestic sewage and anaerobic sludge from an anaerobic batch bioreactor at a concentration of 0.2 ± 0.03 μg L^-1 and 507 ± 79 ng g^-1 , respectively. In D. magna and C. sancticaroli exposed to TBBPA in an acute toxicity bioassay, the micropollutant accumulated at 3.74 and 8.87 μg g^-1 , respectively. The proposed method is a simple and cost-effective tool to determine TBBPA environmental occurrence and biomagnification potential compared with conventional extraction methods. To the best of our knowledge, this is the first liquid-liquid miniaturized extraction method to be applied to D. magna and C. sancticaroli. Environ Toxicol Chem 2020;39:2147-2157. © 2020 SETAC.

Establishing simultaneous nitrification and denitrification under continuous aeration for the treatment of multi-electrolytes saline wastewater

Simultaneous nitrification and denitrification (SND) was established under continuous aeration (6 mgO₂ L^-1) aiming at achieving a feasible and simple operational strategy for treating multi-electrolyte saline wastewaters. Two Structured Fixed-Bed Reactors (SFBR) were used to assess SND performance with (Saline Reactor, SR) and without (Control Reactor, CR) salinity interference. Salinity was gradually increased (from 1.7 to 9 atm) based on the composition of water supplied in arid regions of Brazil. At 1.7 atm, N-NH₄⁺ oxidation and Total Nitrogen (TN) removal efficiencies of 95.9 ± 2.8 and 65.76 ± 7.5%, respectively, were obtained. At osmotic pressure (OP) of 9 atm, the system was severely affected by specific salt toxicity and OP. High chemical oxygen demand (COD) removal efficiency was achieved at all operational conditions (97.2 ± 1.6 to 78.5 ± 4.6%). Salinity did not affect microbial diversity, although it modified microbial structure. Halotolerant genera were identified (Prosthecobacter, Chlamydia, Microbacterium, and Paenibacillus).

Feasibility of anaerobic packed and structured-bed reactors for sulfamethoxazole and ciprofloxacin removal from domestic sewage

This study assessed the applicability of fixed bed bioreactors in two configurations - anaerobic structured bed reactor (ASBR) and anaerobic packed bed reactor (APBR) - in the removal of Sulfamethoxazole (SMX) and Ciprofloxacin (CIP), two antibiotics frequently detected in sanitary sewage. The problem of these pharmaceuticals as emerging contaminants in conventional sewage treatment systems is mainly because they encourage the development and spread of resistance genes in bacteria. Both reactors had similar performances, and the antibiotics were highly removed - APBR: 85 ± 10% for SMX and 81 ± 16% for CIP; ASBR: 83 ± 12% for SMX and 81 ± 15% for CIP. The ASBR showed to be potentially more feasible in operating and economic terms compared to the APBR, as the former presents a smaller amount of support material in the bed. SMX was completely biotransformed, while the influence of the sorption mechanism was observed for CIP, as its presence was detected sorbed onto biomass throughout the reaction bed of the reactors, with a partition coefficient (log K_D) of around 2.8 L·kg^-1TSS. The degradation kinetics of the pharmaceuticals were fitted using a first-order kinetic model, whereby the reactors behaved as plug flow ones, indicating the possibility of optimizing the operation for a hydraulic retention time of 6 h. The removal kinetics was more favorable for CIP (higher apparent constant kinetic - k_CIP^app > k_SMX^app), since its biodegradation is linked to the biomass, which is more concentrated in the bed bottom layer. The experimental results showed the potential of anaerobic fixed bed reactors in removing environmentally relevant concentrations of SMX and CIP found in sewage.

Carbon-nitrogen removal in a structured-bed reactor (SBRRIA) treating sewage: Operating conditions and metabolic perspectives

The present study evaluated the efficiency of a structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA) to promote nitrogen and carbon removal from domestic sewage. The intermittent aeration and the recycling rate of 3 keeps the desired mixing degree inside the SBRRIA. Four different operational conditions were tested by varying the hydraulic retention time (HRT) from 12 to 8 h and aerated and non-aerated periods (A/NA) from 2 h/1 h and 3 h/1 h. At the THD of 8 h and A/NA of 2 h/1 h there was a decrease in the nitrification process (77.5%) due to the increase of organic matter availability, affecting the total-N removal performance. However, by increasing the aerated period from 2 h to 3 h, the nitrification efficiency rose to 91.1%, reaching a total-N removal efficiency of 79%. The system reached a maximum total-N loading removed of 0.117 kgN.m^-3.d^-1 by applying an HRT of 8 h and an intermittent aeration cycle of 3 h, aerated and 1 h non-aerated. The simultaneous nitrification and denitrification (SND) process was related to a complex interplay among microorganisms affiliated mostly to Acidovorax sp., Comamonas sp., Dechloromonas sp., Hydrogenophaga sp., Mycobacterium sp., Rhodobacter sp., and Steroidobacter sp.

Effects of intermittent aeration periods on a structured-bed reactor continuously fed on the post-treatment of sewage anaerobic effluent

This study assessed the simultaneous nitrification and denitrification processes and remaining organic matter removal from anaerobic reactor effluent treating wastewater in a single reactor. A structured-bed reactor, with polyurethane foam as support media, was subjected to intermittent aeration and effluent recirculation. Aerated/non-aerated periods varied in the range of 2/1-1/3 h. The chemical oxygen demand (COD) in the effluent remained between 26 and 42 mg L^-1 throughout all the aeration conditions. Aeration periods of 1/2 h removed 80 and 26% of Total Kjeldahl Nitrogen and Total Nitrogen, respectively. A low solid production was observed during the 300 days of operation, resulting in a solid retention time of 139 days. The results indicate that the non-aerated periods generated alkalinity that favored nitrification, maintaining low COD concentrations in the effluent. The structured bed reactor presented a low solid production and effluent loss below 20 mgSSV L^-1, similar to concentrations obtained in secondary decanters.

Media arrangement impacts cell growth in anaerobic fixed-bed reactors treating sugarcane vinasse: Structured vs. randomic biomass immobilization

This study reports on the application of an innovative structured-bed reactor (FVR) as an alternative to conventional packed-bed reactors (PBRs) to treat high-strength solid-rich wastewaters. Using the FVR prevents solids from accumulating within the fixed-bed, while maintaining the advantages of the biomass immobilization. The long-term operation (330days) of a FVR and a PBR applied to sugarcane vinasse under increasing organic loads (2.4-18.0kgCODm^-3day^-1) was assessed, focusing on the impacts of the different media arrangements over the production and retention of biomass. Much higher organic matter degradation rates, as well as long-term operational stability and high conversion efficiencies (>80%) confirmed that the FVR performed better than the PBR. Despite the equivalent operating conditions, the biomass growth yield was different in both reactors, i.e., 0.095gVSSg^-1COD (FVR) and 0.066gVSSg^-1COD (PBR), indicating a clear control of the media arrangement over the biomass production in fixed-bed reactors.

Effects of iron and calcium carbonate on the variation and cycling of carbon source in integrated wastewater treatments

Iron and calcium carbonate were added in wastewater treatments as the adjusting agents to improve the contaminant removal performance and regulate the variation of carbon source in integrated treatments. At different temperatures, the addition of the adjusting agents obviously improved the nitrogen and phosphorous removals. TN and TP removals were respectively increased by 29.41% and 23.83% in AC-100 treatment under 1-day HRT. Carbon source from dead algae was supplied as green microbial carbon source and Fe²⁺ was supplied as carbon source surrogate. COD concentration was increased to 30mg/L and above, so the problem of the shortage of carbon source was solved. Dead algae and Fe²⁺ as carbon source supplement or surrogate played significant role, which was proved by microbial community analysis. According to the denitrification performance in the treatments, dead algae as green microbial carbon source combined with iron and calcium carbonate was the optimal supplement carbon source in wastewater treatment.