Nitrate increases the capacity of an aerobic moving-bed biofilm reactor (MBBR) for winery wastewater treatment.

We used bench-scale tests and mathematical modeling to explore chemical oxygen demand (COD) removal rates in a moving-bed biofilm reactor (MBBR) for winery wastewater treatment, using either urea or nitrate as a nitrogen source. With urea addition, the COD removal fluxes ranged from 34 to 45 gCOD/m2-d. However, when nitrate was added, fluxes increased up to 65 gCOD/m2-d, twice the amount reported for aerobic biofilms for winery wastewater treatment. A one-dimensional biofilm model, calibrated with data from respirometric tests, accurately captured the experimental results. Both experimental and modelling results suggest that nitrate significantly increased MBBR capacity by stimulating COD oxidation in the deeper, oxygen-limited regions of the biofilm. Our research suggests that the addition of nitrate, or other energetic and broadly used electron acceptors, may provide a cost-effective means of covering peak COD loads in biofilm processes for winery or another industrial wastewater treatment.

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.

Sustainable technology: potential of biomass (Bambusa tuldoides) for biological denitrification of wastewater generated in shrimp farming.

Wastewater from shrimp farming is rich in organic material, solids, and nutrients, which cause a series of environmental problems when released into the environment. Currently, for the removal of nitrogen compounds from wastewater, among the most studied methods is biological denitrification. The objective of this study was to evaluate the operational parameters for the development of a more sustainable technology for the removal of nitrogen compounds from shrimp farm wastewater, using Bambusa tuldoides (a species of bamboo) as a source of carbon and a material conducive to the development of selected denitrifying bacteria. To optimize the process, biological denitrification assays were performed varying the following parameters: bamboo length (cm), pH, temperature, and stoichiometric proportions of C and N. The operational stability of the process with the reuse of the bamboo biomass was also evaluated. Cronobacter sakazakii and Bacillus cereus were identified as denitrifying microorganisms present in reactor with bamboo biomass. The best operational conditions observed were pH 6 to 7 and temperature 30 to 35 °C, and the addition of an external carbon source was not necessary for the denitrification process to occur efficiently. Under these conditions, biological denitrification occurred with an average efficiency above 90% based on the removal of the nitrogen contaminants evaluated (NO3-N and NO2-N). Regarding operational stability, 8 cycles were performed using the same source of carbon without reducing the efficiency of the process.

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.

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.

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.

Biotransformation of 17ß-Estradiol through a Denitrifying Sludge.

17ß-estradiol (E2) is the natural estrogen with the most significant potential for endocrine disruption in the biota of aquatic ecosystems at trace concentrations. It is, therefore, essential to study treatments for water polluted with E2 that would guarantee its complete elimination and mineralization. Denitrification is a biological process shown to have the capacity to completely biodegrade drugs, such as ampicillin. This work is aimed to evaluate the biotransformation of 17ß-estradiol by employing a denitrifying sludge. The assays performed were: (I) abiotic with 3.5 mg E2-C L-1 and (II) denitrifying with 10 mg CH3COO--C L-1 as the reference, 10 mg E2-C L-1 as the sole electron donor, and a mixture of (mg L-1) 10 E2-C with 10 CH3COO--C at C N-1 of 1.1. The E2-C and NO3--N consumption efficiencies were greater than 99%, and HCO3--C and N2 production yields were close to 1 in all assays. The denitrifying sludge could biodegrade up to 10 mg E2-C L-1 as the sole electron donor and when mixed with 10 mg CH3COO--C L-1. No intermediate metabolites were generated from the process.

Enhanced nitrogen and carbon removal in natural seawater by electrochemical enrichment in a bioelectrochemical reactor.

Municipal and industrial wastewater discharges in coastal and marine environments are of major concern due to their high carbon and nitrogen loads and the resulted phenomenon of eutrophication. Bioelectrochemical reactors (BERs) for simultaneous nitrogen and carbon removal have gained attention owing to their cost efficiency and versatility, as well as the possibility of electrochemical enrich specific groups. This study presented a scalable two-chamber BERs using graphite granules as electrode material. BERs were inoculated and operated for 37 days using natural seawater with high concentrations of ammonium and acetate. The BERs demonstrated a maximum current density of 0.9 A m-3 and removal rates of 7.5 mg NH4+-N L-1 d-1 and 99.5 mg L-1 d-1 for total organic carbon (TOC). Removals observed for NH4+-N and TOC were 96.2% and 68.7%, respectively. The results of nutrient removal (i.e., ammonium, nitrate, nitrite and TOC) and microbial characterization (i.e., next-generation sequencing of the 16S rRNA gene and fluorescence in situ hybridization) showed that BERs operated with a poised cathode at -260 mV (vs. Ag/AgCl) significantly enriched nitrifying microorganisms in the anode and denitrifying microorganisms and planctomycetes in the cathode. Interestingly, the electrochemical enrichment did not increase the total number of microorganisms in the formed biofilms but controlled their composition. Thus, this work shows the first successful attempt to electrochemically enrich marine nitrifying and denitrifying microorganisms and presents a technique to accelerate the start-up process of BERs to remove dissolved inorganic nitrogen and total organic carbon from seawater.

Performance of an anaerobic-oxic-anoxic (AOA) system in the simultaneous removal of nutrients and triclosan and bacterial community.

The constant presence of triclosan (TCS) in surface water and wastewater has been verified due to its application in several pharmaceutical and personal care products. Thus, removing this emerging contaminant is essential to minimize the contamination of water bodies. The anaerobic-aerobic-anoxic (AOA) system is an innovative alternative that combines the removal of nutrients and triclosan. This study focuses on the simultaneous removal of carbonaceous matter, nitrogen, phosphorus, and triclosan in a continuous pilot-scale AOA system from synthetic wastewater. The upflow system, in series, was operated at hydraulic retention time (HRT) of 8 h and a flowrate of 2.40 L h-1. Glucose (190 mg L-1) was added to the anoxic reactor as the external carbon source. Besides that, bacterial community structure was investigated using 16S rRNA sequencing in each reactor. The system achieved average removal efficiencies of 96% (14.03 g d-1) for Chemical Oxygen Demand (COD), 85% (2.64 g d-1) for Total Kjeldahl Nitrogen (TKN), 88% (1.40 g d-1) for Total Ammonia Nitrogen (TAN), 20% (0.12 g d-1) for Total Phosphorus (TP), and 93% (1.87 µg d-1) for Triclosan (TCS). The phyla Proteobacteria, Firmicutes, Bacteroidetes, and Chloroflexi were found in greater abundance. The main genera identified were Anaeromusa, Aeromonas, Azospira, Clostridium, and Lactococcus. The organisms related to phylum and genus corroborate the involved processes and the removal performance achieved. In addition, Lactococcus, Thermomonas, Ferruginibacter, and Dechloromonas were involved in triclosan biodegradation. The anaerobic-oxic-anoxic system successfully removed carbonaceous, nitrogenous matter, and triclosan, with glucose increasing the denitrifying activity.

Ubiquity and Diversity of Cold Adapted Denitrifying Bacteria Isolated From Diverse Antarctic Ecosystems.

Nitrogen cycle has been poorly investigated in Antarctic ecosystems. In particular, how extreme conditions of low temperature, dryness, and high radiation select the microorganisms involved in the cycle is not yet understood. Denitrification is an important step in the nitrogen cycle in which nitrate is reduced stepwise to the gases NO, N2O, and N2. Denitrification is carried out by a wide group of microorganisms spread in the phylogenetic tree. The aim of this work was to isolate and characterize denitrifying bacteria present in different cold environments from Antarctica. Bacterial isolates were obtained from lake, meltwater, sea, glacier ice, ornithogenic soil, and penguin feces samples from King George Island, Fildes peninsula in the Antarctic. Samples were taken during the deicing season in five sampling campaigns. From all the samples we were able to isolate denitrifying strains. A total of 199 bacterial isolates with the capacity to grow in anaerobic mineral media reducing nitrate at 4°C were obtained. The characterization of the isolates by 16S rRNA gene sequence analysis showed a high predominance of the genus Pseudomonas, followed by Janthinobacterium, Flavobacterium, Psychrobacter, and Yersinia. Other minor genera detected were Cryobacterium, Iodobacter, Kaistella, and Carnobacterium. The capacity to denitrify was not previously described for most of the bacteria related to our isolates and in many of them denitrifying genes were not present suggesting the presence of new genes in this extreme environment. Our work demonstrates the ubiquity of denitrification in the Maritime Antarctica and gives important information linking denitrification at cold temperature with taxa in an unequivocal way.

Formation and stability of aerobic granular sludge in a sequential batch reactor for the simultaneous removal of organic matter and nutrients from low-strength domestic wastewater.

Simultaneous removal of organic matter, nitrogen, and phosphorus, via simultaneous nitrification and denitrification (SND) and enhanced biological phosphorus removal processes, was evaluated in a pilot-scale sequential batch reactor. The focus was on granule's morphology, stability, microbiological composition, and reactor performance while treating diluted domestic wastewater with total chemical oxygen demand (CODt) of ≈ 200 mg.L-1. The applied organic loading rate was 0.9 ± 0.3 kg CODt.m-3.d-1 in the experiment. Aerobic granular sludge developed gradually. After 87-day operation, granules (diameter ≥ 0.2 mm) were ≥ 50 % of the biomass, and after 168 days, complete granulation was obtained (≥ 80 % of biomass). In the third period (days 168-247, complete granulation), mixed liquor biomass reached a volatile suspended solids (VSS) concentration of 1.2 ± 0.3 g VSS.L-1, with the granules remaining stable until the experimental end. In this period, low effluent concentrations of COD, nitrogen (NH4+-N, NO2--N and NO3--N) and phosphate (PO43-P) were obtained (mg.L-1): 36 ± 11; 4 ± 5; 3 ± 3, 4 ± 5; and 0.9 ± 0.4, respectively. COD, NH4+-N, and PO43--P removal efficiencies (%) were 80 ± 11; 83 ± 20; and 55 ± 24, respectively. Heterotrophic nitrification and SND were observed, resulting in a process efficiency of 31 % even with dissolved oxygen applied to saturation. The phosphate removal was mainly attributed to denitrifying phosphorus accumulating organisms. Pseudomonas, the dominant genus found, acted in nitrogen and phosphorus removal. Pseudoxanthomonas also assisted in phosphorus removal. Bacterial communities in the flocs (≈ 20 % of biomass) during the last period were similar to those in the granules; therefore, they constituted the basis for granule formation, directly contributed to the simultaneous good removal of organic matter and nutrients.

Microbial Electrochemical Technologies for Sustainable Nitrogen Removal in Marine and Coastal Environments.

For many years, the world's coastal marine ecosystems have received industrial waste with high nitrogen concentrations, generating the eutrophication of these ecosystems. Different physicochemical-biological technologies have been developed to remove the nitrogen present in wastewater. However, conventional technologies have high operating costs and excessive production of brines or sludge which compromise the sustainability of the treatment. Microbial electrochemical technologies (METs) have begun to gain attention due to their cost-efficiency in removing nitrogen and organic matter using the metabolic capacity of microorganisms. This article combines a critical review of the environmental problems associated with the discharge of the excess nitrogen and the biological processes involved in its biogeochemical cycle; with a comparative analysis of conventional treatment technologies and METs especially designed for nitrogen removal. Finally, current METs limitations and perspectives as a sustainable nitrogen treatment alternative and efficient microbial enrichment techniques are included.

Nitrogen removal from poultry slaughterhouse wastewater in anaerobic-anoxic-aerobic combined reactor: Integrated effect of recirculation rate and hydraulic retention time.

The aim of this work was to assess the nitrogen removal from slaughterhouse wastewater in an anaerobic-anoxic-aerobic combined reactor, evaluating the integrated effect of recirculation rate and hydraulic retention time. The recirculation of the liquid phase from the aerobic zone to the anoxic zone was applied to promote the denitrification through the use of endogenous electron donors. Three recirculation rates (R: 0.5, 1 and 2) and three hydraulic retention times (14, 11 and 8 h) were applied. The operation of the reactor was divided into 3 steps (I, II, and III) according to the factors evaluated (recirculation rate and HRT), to achieve operational conditions that would allow satisfactory performance in the different compartments of the reactor. During the experiment the reactor was fed with average total nitrogen (TN) and chemical oxygen demand (COD) of 65 mg L-1 and 580 mg L-1, respectively. The denitrification efficiency (theoretical) and kinetics parameters for COD decay were calculated. The highest performance was verified in the Step III (R = 2) and HRT of 11 h with NH4+ and TN removals of 84% and 65%, respectively. The TN removal efficiency (65%) was considered satisfactory, since the theoretical denitrification efficiency expected for this condition (R = 2) is 67%, without addition of an external carbon source. The lowest nitrification efficiency values were obtained in HRT of 8 h in the Step I and II (R = 0.5 and 1, respectively), indicating that the nitrification time (3 h - aerobic phase) may be the limiting factor in this HRT. The COD removal efficiency was high in all assays (>95%). The values of the kinetic degradation constants of organic matter were close for all recirculation rates, and the highest values were recorded for the HRT of 8 h and R = 1 and R = 2 (-0.48 and -0.43, respectively).

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.

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.

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.

In situ differences in nitrogen cycling related to presence of submerged aquatic vegetation in a Gulf of Mexico estuary.

Estuaries provide a suite of ecosystem services to people but are also under heavy stress from human development including excess nutrient loading and alterations in benthic habitat that affect nutrient cycling. Here we examine the interaction of two important and common ecosystem management priorities in estuaries: limiting eutrophication and restoration of submerged aquatic vegetation (SAV). Rates of benthic nitrogen processing can vary by habitat type and there is need for more complete data on the contribution of SAV to overall nitrogen cycling in estuaries, as well as a need to examine nitrogen cycling in situ to better characterize the role of SAV areal coverage in mediating estuarine eutrophication. We compare nitrogen cycling between two common and adjacent habitat types (SAV and adjacent bare sediment [BS]) in an index coastal estuary using an in situ chamber-based approach to better capture realized habitat differences. We also examined genomic community structure of sediment bacteria and archaea to identify biological indicators of nitrogen exchange. Both mean sediment-water exchange of dissolved N2 and microbial functional community structure differed between SAV and BS. Habitat differences were more consistent with lower variability at locations with low salinity and when sediment organic content was highest, which aligns with findings in other studies. Habitat types differed significantly in microbial composition, including functional groups and genes, like nifH, that may contribute to observed differences in nitrogen cycling. Overall, habitat type appeared most important to nitrogen cycling near the river mouth where sediment nitrogen was higher, and this information has implications for integrated management of habitat restoration/conservation and nutrient loading.

Sulfur-based mixotrophic denitrification with the stoichiometric S0/N ratio and methanol supplementation: effect of the C/N ratio on the process.

The impact of the organic carbon to nitrate ratio (C/N ratio) on mixotrophic denitrification rate has been scarcely studied. Thus, this work aims to investigate the effect of the C/N ratio on the mixotrophic denitrification when methanol is used as a source of organic matter and elemental sulfur as an electron donor for autotrophic denitrification. For this, two initial concentrations of NO3--N (50 and 25 mg/L) at a stoichiometric ratio of S0/N, and four initial C/N ratios (0, 0.6, 1.2, and 1.9 mg CH3OH/mg NO3- -N) were used at 25 (±2) °C. The results showed that when using a C/N ratio of 0.6, the highest total nitrogen removal was obtained and the accumulation of nitrites was reduced, compared to an autotrophic system. The most significant contribution to nitrate consumption was through autotrophic denitrification (AuDeN) for a C/N ratio of 0.6 and 1.2, while for C/N = 1.9 the most significant contribution of nitrate consumption was through heterotrophic denitrification (HD). Finally, organic supplementation (methanol) served to increase the specific nitrate removal rate at high and low initial concentrations of substrate. Therefore, the best C/N ratio was 0.6 since it allowed for increasing the removal efficiency and the denitrification rate.

Simultaneous ammonium and sulfate biotransformation driven by aeration: Nitrogen/sulfur metabolism and metagenome-based microbial ecology.

The present study aimed to clarify the effect of oxygen respiration on biotransformation of alternative electron acceptors (e.g., nitrate and sulfate) underlying the simultaneous removal of ammonium and sulfate in a single aerated sequencing batch reactor. Complete nitrification was achieved in feast condition, while denitrification was carried out in both feast and famine conditions when aeration intensity (AI) was higher than 0.22 L/(L·min). Reactors R1 [0.56 L/(L·min)], R2 [0.22 L/(L·min)], and R3 [0.08 L/(L·min)] achieved 72.39% sulfate removal efficiency in feast condition, but H2S release occurred in R3. Following exogenous substrate depletion, sulfate concentration increased again and exceeded the influent value in R1, indicating that sulfate transformation was affected by oxygen intrusion. Metagenomic analysis showed that a higher AI promoted sulfate reduction by switching from dissimilatory to assimilatory pathway. Lower AI-acclimated microorganisms (R3) produced H2S and ammonium, while higher AI-acclimated microorganisms (R1) accumulated nitrite, which confirmed that biotransformation of N and S was strongly regulated by redox imbalance driven by aeration. This implied that respiration control, a microbial self-regulation mechanism, was linked to the dynamic imbalance between electron donors and electron acceptors. Aerobic nitrate (sulfate) reduction, as one of the effects of respiration control, could be used as an alternative strategy to compensate for dynamic imbalance, when supported by efficient endogenous metabolism. Moderate aeration induced microorganisms to change their energy conservation and survival strategy through respiration control and inter-genus protection of respiratory activity among keystone taxa (including Azoarcus in R1, Thauera in R2, and Thiobacillus, Ottowia, and Geoalkalibacter in R3) to form an optimal niche in response to oxygen intrusion and achieve benign biotransformation of C, N, and S without toxic intermediate accumulation. This study clarified the biotransformation mechanism of ammonium and sulfate driven by aeration and provided theoretical guidance for optimizing existing aeration-based techniques.

Responses of Low-Cost Input Combinations on the Microbial Structure of the Maize Rhizosphere for Greenhouse Gas Mitigation and Plant Biomass Production.

The microbial composition of the rhizosphere and greenhouse gas (GHG) emissions under the most common input combinations in maize (Zea mays L.) cultivated in Brazil have not been characterized yet. In this study, we evaluated the influence of maize stover coverage (S), urea-topdressing fertilization (F), and the microbial inoculant Azospirillum brasilense (I) on soil GHG emissions and rhizosphere microbial communities during maize development. We conducted a greenhouse experiment and measured methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) fluxes from soil cultivated with maize plants under factorial combinations of the inputs and a control treatment (F, I, S, FI, FS, IS, FIS, and control). Plant biomass was evaluated, and rhizosphere soil samples were collected at V5 and V15 stages and DNA was extracted. The abundance of functional genes (mcrA, pmoA, nifH, and nosZ) was determined by quantitative PCR (qPCR) and the structure of the microbial community was assessed through 16S rRNA amplicon sequencing. Our results corroborate with previous studies which used fewer input combinations and revealed different responses for the following three inputs: F increased N2O emissions around 1 week after application; I tended to reduce CH4 and CO2 emissions, acting as a plant growth stimulator through phytohormones; S showed an increment for CO2 emissions by increasing carbon-use efficiency. IS and FIS treatments presented significant gains in biomass that could be related to Actinobacteria (19.0%) and Bacilli (10.0%) in IS, and Bacilli (9.7%) in FIS, which are the microbial taxa commonly associated with lignocellulose degradation. Comparing all factors, the IS (inoculant + maize stover) treatment was considered the best option for plant biomass production and GHG mitigation since FIS provides small gains toward the management effort of F application.