Nitrous Oxide Emissions from Nitritation Reactors under Hypersaline Conditions.

This study focuses on nitrous oxide (N2O) emissions during hypersaline (4 % salinity) nitritation in continuously fed and mixed fixed bed reactors. In the presence of high concentrations of nitrite and ammonium, the percent yield of N2O emissions from ammonium removed decreased with increasing dissolved oxygen (DO). However, N2O production continued even at a high DO of 15 mg/L. Bulk ammonium concentration (not ammonia) was found to be the main controlling factor for N2O emissions under high and low DO during both nitritation and nitrification. Reducing bulk ammonium concentrations below 1 mg N/L in the nitritation reactor under both high and low DO conditions resulted in a reduction of N2O emissions of approximately 90 %. Under full nitrification and low DO, reducing nitrite concentrations below 0.3 mg N/L resulted in a 60 % reduction in N2O emissions. Similar results were observed in a low salinity reactor.

Nanoparticles in induced sputum - a window to airway inflammation among active smokers.

Aims: To evaluate the role of nanoparticles (NP) in sputum samples of active smokers as markers of inflammation and disease. Materials & methods: 29 active smokers were included (14 with chronic obstructive pulmonary disease [COPD]) and underwent clinical assessment, pulmonary function tests, sputum induction (with NP analysis) and blood sampling. Results: Higher particle and NP concentrations and smaller mean size directly correlated with clinical parameters such as the COPD Assessment Test score and impulse oscillometry results. Similar correlations were found between NPs and increased sputum IL-1ß, IL-6 and TNF-α. Among COPD patients, higher IL-8 and lower IL-10 serum levels also correlated with NP concentrations. Conclusion: This proof-of-concept study shows the potential of sputum NPs as markers of airway inflammation and disease.

What is this article about? Identifying markers of lung inflammation and diseases could offer early diagnosis and treatment. In this study, we questioned whether nanoparticles in the sputum of active smokers correlate with lung inflammation and disease. What were the results? We found that higher nanoparticle concentration in the sputum and lower mean nanoparticle size correlated with different clinical parameters and inflammatory markers. What do the results mean? This proof-of-concept study suggests that nanoparticle analysis in the sputum of active smokers has potential as a marker that correlates with lung inflammation and disease. Our results should encourage additional research in this field to better understand the role of nanoparticles in the diagnosis, prognosis and treatment of active smokers.

Preparation, performances and mechanisms of magnetic Saccharomyces cerevisiae bionanocomposites for atrazine removal.

Saccharomyces cerevisiae and nanoparticles of iron oxide (Fe3O4) which were linked with chitosan (CS) through epichlorohydrin (ECH) were encapsulated in calcium alginate to prepare a novel type of bionanocomposites. Characterization results showed that the Fe3O4-ECH-CS nanoparticles were quasi-spherical with an average diameter of 30 nm to which chitosan was successfully attached through epichlorohydrin. The saturation magnetization value of the nanoparticles was 21.88 emu/g, and ferrous and ferric irons were simultaneously observed in the magnetic nanoparticles. Data of atrazine removal by yeasts showed that both inactivated and live yeasts could decrease the concentration of atrazine effectively. The inactivated yeasts achieved 20% removal rate, which indicated that adsorption by the yeasts also played a role in the removal. Removal efficiency of atrazine was maximized at 88% under 25 °C, pH of 7 and an initial atrazine concentration of 2 mg/L. When the magnetic bionanocomposite was recycled and reused twice, only 12% and 20% drop in removal efficiency was observed at the first time and the second time severally. So, atrazine could be used by the yeasts as the sole carbon source for growth and multiplication, and both adsorption and biodegradation by the bionanocomposite contributed to atrazine removal.

Pressurized hydrogenotrophic denitrification reactor for small water systems.

The implementation of hydrogenotrophic denitrification is limited due to safety concerns, poor H2 utilization and low solubility of H2 gas with the resulting low transfer rate. The current paper presents the main research work conducted on a pressurized hydrogenotrophic reactor for denitrification that was recently developed. The reactor is based on a new concept suggesting that a gas-liquid equilibrium is achieved in the closed headspace of denitrifying reactor, further produced N2 gas is carried out by the effluent and gas purging is not required. The feasibility of the proposed reactor was shown for two effluent concentrations of 10 and 1 mg NO3--N/L. Hydrogen gas utilization efficiencies of 92.8% and 96.9% were measured for the two effluent concentrations, respectively. Reactor modeling predicted high denitrification rates above 4 g NO3--N/(Lreactor·d) at reasonable operational conditions. Hydrogen utilization efficiency was improved up to almost 100% by combining the pressurized reactor with a following open-to-atmosphere polishing unit. Also, the potential of the reactor to remove ClO4- was shown.

Submerged bed versus unsaturated flow reactor: A pressurized hydrogenotrophic denitrification reactor as a case study.

The paper compares the main features of a submerged bed reactor (SuBR) with bubbling and recirculation of gas to those of an unsaturated flow reactor (uSFR) with liquid recirculation. A novel pressurized closed-headspace hydrogenotrophic denitrification system characterized by safe and economic utilization of H2 gas was used for the comparison. Under similar conditions, denitrification rates were lower in the SuBR as a result of a lower effective biofilm surface area and overall gas-liquid mass transfer coefficient kLa. Similar values of effluent DOC were achieved for both reactors, although effluent suspended solids concentration of the SuBR were substantially higher. On the other hand, the required cleaning frequency in the SuBR was 2.5 times lower. Moreover, the SuBR is expected to reduce the recirculation energy consumption by 0.35 kWh/m(3) treated.

Effect of high electron donor supply on dissimilatory nitrate reduction pathways in a bioreactor for nitrate removal.

The possible shift of a bioreactor for NO3(-) removal from predominantly denitrification (DEN) to dissimilatory nitrate reduction to ammonium (DNRA) by elevated electron donor supply was investigated. By increasing the C/NO3(-) ratio in one of two initially identical reactors, the production of high sulfide concentrations was induced. The response of the dissimilatory NO3(-) reduction processes to the increased availability of organic carbon and sulfide was monitored in a batch incubation system. The expected shift from a DEN- towards a DNRA-dominated bioreactor was not observed, also not under conditions where DNRA would be thermodynamically favorable. Remarkably, the microbial community exposed to a high C/NO3(-) ratio and sulfide concentration did not use the most energy-gaining process.

Storage-based denitrification with municipal wastewater: influence of the denitrification stage duration.

Microbial polyhydroxyalkenoates (PHAs) degradation is the rate limiting step for denitrification which is based on microbial carbon storage. The influence ofdenitrification stage duration (3, 2 and 1.5 h) on PHA degradation kinetics and denitrification efficiency during PHA-based denitrification ofmunicipal wastewater and acetate-based synthetic wastewater was investigated. PHA degradation kinetics showed a good fit to first-order reaction, with higher rates at higher PHA concentrations. Decreasing the denitrification stage duration from 3 to 2 h resulted in an increase in biomass PHA content with the corresponding higher specific denitrification rate. Moreover, the daily denitrification rates increased by about 30% in both the acetate fed reactor and the wastewater fed reactor. Further decreasing the denitrification stage duration to 1.5 h resulted in a decrease in sludge PHA content in both reactors. The amount of filtered chemical oxygen demand removed by storage and PHA stored, remained similar regardless of the denitrification stage duration.

The contribution of suspended solids to municipal wastewater PHA-based denitrification.

The role of wastewater suspended solids in denitrification based on intracellular carbon storage was investigated in a biofilm sequencing batch reactor performing alternately anaerobic carbon storage and denitrification. Municipal wastewater as the feeding was compared with filtered wastewater and with acetate. The results show that the amount of PHA (polyhydroxyalkanoates) stored during a cycle was quite similar, irrespective of the substrate type used as feeding (acetate, real wastewater and real wastewater after filtration). PHA storage was limited even under excess chemical oxygen demand (COD) conditions, with a reducing power capacity enough for denitrification of only 25-26 mg/L N. However, when non-filtered wastewater was used, the denitrification capacity was about 50% higher (38 mg/L N) due to the contribution of entrapped suspended solids as the electron donor. In addition, the involvement of the hydrolyzed wastewater suspended solids resulted in a different PHA composition containing a much higher poly-3-hydroxyvalerate content.

PHA based denitrification: municipal wastewater vs. acetate.

Denitrification of municipal wastewater based on bacterial storage polymers-Polyhydroxyalkanoates (PHA) - was investigated in biofilm sequencing batch reactors, as a part of a two sludge system for wastewater treatment and in comparison to acetate based synthetic wastewater. The results show that PHA based denitrification (PBD) of real wastewater can be a viable alternative, especially for wastewater with low COD/N ratio, without the need for external carbon source addition. High nitrate removal capacity of about 40-50 mg N/L with a low COD/N requirement of about 4-5, were observed. It was found that entrapped particulate organic matter contributed additional reducing power, on top of the storage materials, thus allowing for the high nitrate reduction capacity. Daily removal rates were similar to those of extensive treatment systems (0.24-0.31 gr N/L reactor*d). Large differences in storage yield and composition between biomass grown on synthetic and municipal wastewater were observed.

Characterization of denitrifying granular sludge with and without the addition of external carbon source.

In this study granular sludge taken from a denitrifying upflow sludge reactor was characterized. Denitrification rates were determined in batch tests with and without external carbon source addition and pH microprofiles of the granules were studied. The microbial community structure was also determined. The results showed that denitrification without carbon source addition occurs; however, the process rate was lower than with external carbon source. This suggests that bacteria use dead biomass and extracellular material in the granular sludge as a carbon source when readily available substrate has been exhausted and nitrate is still present. Microprofiles showed a slight pH decrease for denitrification without external carbon source addition, and an increase in pH when using nitrite as the electron acceptor. Microprofiles using acetate as the carbon source for denitrification showed a significant increase in pH. Clone sequences obtained were close to the species Vitellibacter sp., Denitromonas indolicum str. and Denitromonas aromaticaus sp.

Encapsulation of Pseudomonas sp. ADP cells in electrospun microtubes for atrazine bioremediation.

Electrospun hollow polymeric microfibers (microtubes) were evaluated as an encapsulation method for the atrazine degrading bacterium Pseudomonas sp. ADP. Pseudomonas sp. ADP cells were successfully incorporated in a formulation containing a core solution of polyethylene oxide dissolved in water and spun with an outer shell solution made of polycaprolactone and polyethylene glycol dissolved in a chloroform and dimethylformamide. The resulting microtubes, collected as mats, were partially collapsed with a ribbon-like structure. Following encapsulation, the atrazine degradation rate was low (0.03 ± 0.01 mg atrazine/h/g fiber) indicating that the electrospinning process negatively affected cell activity. Atrazine degradation was restored to 0.5 ± 0.1 mg atrazine/h/g fiber by subjecting the microtubes to a period of growth. After 3 and 7 days growth periods, encapsulated cells were able to remove 20.6 ± 3 and 47.6 ± 5.9 mg atrazine/g mat, respectively, in successive batches under non-growth conditions (with no additional electron donor) until atrazine was detected in the medium. The loss of atrazine degrading capacity was regained following an additional cell-growth period.

An integrated UASB-sludge digester system for raw domestic wastewater treatment in temperate climates.

To improve the performance of an upflow anaerobic sludge blanket (UASB) reactor treating raw domestic wastewater under temperate climates conditions, the addition of a sludge digester to the process was investigated. With the decrease in temperature, the COD removal decreased from 78% at 28 °C to 42% at 10 °C for the UASB reactor operating alone at a hydraulic retention time of 6 h. The decrease was attributed to low hydrolytic activity at lower temperatures that reduced suspended matter degradation and resulted in solids accumulation in the top of the sludge blanket. Solids removed from the upper part of the UASB sludge were treated in an anaerobic digester. Based on sludge degradation kinetics at 30 °C, a digester of 0.66 l per liter of UASB reactor was design operating at a 3.20 days retention time. Methane produced by the sludge digester is sufficient to maintain the temperature at 30 °C.

Anaerobic degradation pathway and kinetics of domestic wastewater at low temperatures.

The effect of temperatures below 20 degrees C (20, 15 and 10 degrees C) on the anaerobic degradation pathway and kinetics of domestic wastewater fractionated at different sizes was studied in a fluidized-bed batch reactor. The overall degradation pathway was characterized by a soluble fraction degrading according to zero-order kinetics and a colloidal fraction (between 0.45 and 4.5 microm) that first disintegrates into a particulate fraction smaller than 0.45 microm before finally degrading. The colloidal degradation processes follow a first-order kinetic. In contrast, suspended solids (bigger than 4.5 microm) degrade to soluble and colloidal fractions according to first-order kinetics. The colloidal fraction originating from suspended solids further degrades into soluble fraction. These soluble fractions have the same degradation kinetics as the original soluble fraction. The suspended solids degradation was highly affected by temperature, whereas the soluble fraction slightly affected and the colloidal fraction was not affected at all. On the other hand, the colloidal non-degradable fraction increased significantly with the decrease in temperature while the suspended solids slowly increased. The soluble non-degradable fraction was little affected by temperatures changes.

Visualization of active biomass distribution in a BGAC fluidized bed reactor using GFP tagged Pseudomonas putida F1.

A favorable microenvironment for biofilm growth on GAC particles was shown using green fluorescent protein (GFP) as a marker for a phenol degrading bacterium, Pseudomonas putida F1. The dispersion of P. putida F1 in a biofilm covering granulated activated carbon (GAC) particles was monitored and compared to a biofilm on non-activated granular carbon particles. Laser scanning confocal microscopy (LSCM) micrographs of the biofilms taken from two fluidized bed reactors operating under identical conditions, showed higher fluorescent green areas in the GAC biofilm, especially close to the GAC surface. Quantitative analysis of the biofilm by COMSTAT, a three-dimensional biofilm structure analysis program, showed higher biomass concentration and higher viability in the GAC covered biofilm vs. the non-activated carbon biofilm. In addition, better effluent quality was measured for the BGAC reactor, which strongly suggests a significantly larger biofilm surface area available to the substrate, as opposed to that of the non-activated carbon carrier reactor.

Nitrification in a biofilm at low pH values: role of in situ microenvironments and acid tolerance.

The sensitivity of nitrifying bacteria to acidic conditions is a well-known phenomenon and generally attributed to the lack and/or toxicity of substrates (NH3 and HNO2) with decreasing pHs. In contrast, we observed strong nitrification at a pH around 4 in biofilms grown on chalk particles and investigated the following hypotheses: the presence of less acidic microenvironments and/or the existence of acid-tolerant nitrifiers. Microelectrode measurements (in situ and under various experimental conditions) showed no evidence of a neutral microenvironment, either within the highly active biofilm colonizing the chalk surface or within a control biofilm grown on a nonbuffering (i.e., sintered glass) surface under acidic pH. A 16S rRNA approach (clone libraries and fluorescence in situ hybridizations) did not reveal uncommon nitrifying (potentially acid-tolerant) strains. Instead, we found a strongly acidic microenvironment, evidence for a clear adaptation to the low pH in situ, and the presence of nitrifying populations related to subgroups with low Km s for ammonia (Nitrosopira spp., Nitrosomonas oligotropha, and Nitrospira spp.). Acid-consuming (chalk dissolution) and acid-producing (ammonia oxidation) processes are equilibrated on a low-pH steady state that is controlled by mass transfer limitation through the biofilm. Strong affinity to ammonia and possibly the expression of additional functions, e.g., ammonium transporters, are adaptations that allow nitrifiers to cope with acidic conditions in biofilms and other habitats.

High-rate nitrification at low pH in suspended- and attached-biomass reactors.

This article reports on high-rate nitrification at low pH in biofilm and suspended-biomass reactors by known chemolithotrophic bacteria. In the biofilm reactor, at low pH (4.3 +/- 0.1) and low bulk ammonium concentrations (9.3 +/- 3.3 mg.liter(-1)), a very high nitrification rate of 5.6 g of N oxidized.liter(-1).day(-1) was achieved. The specific nitrification rate (0.55 g of N.g of biomass(-1).day(-1)) was similar to values reported for nitrifying reactors at optimal pH. In the suspended-biomass reactor, the average pH was significantly lower than that in the biofilm reactor (pH 3.8 +/- 0.3), and values as low as pH 3.2 were found. In addition, measurements in the suspended-biomass reactor, using isotope-labeled ammonium (15N), showed that in spite of the very low pH, biomass growth occurred with a yield of 0.1 g of biomass.g of N oxidized(-1). Fluorescence in situ hybridization using existing rRNA-targeted oligonucleotide probes showed that the nitrifying bacteria were from the monophyletic genus Nitrosomonas, suggesting that autotrophic nitrification at low pH is more widespread than previously thought. The results presented in this paper clearly show that autotrophic nitrifying bacteria have the ability to nitrify at a high rate at low pH and in the presence of only a negligible free ammonia concentration, suggesting the presence of an efficient ammonium uptake system and the means to cope with low pH.

Patchy biofilm coverage can explain the potential advantage of BGAC reactors.

An adsorbing biofilm carrier, like granular activated carbon (GAC), can be the source of an extra flux of pollutant to the biofilm in addition to the bulk liquid. This double flux can improve the performance of a biological GAC (BGAC) reactor as compared to a nonabsorbing carrier reactor but only under conditions of pollutant partial penetration in the biofilm. Pollutant partial penetration in a biofilm often occurs in treatment processes where very low effluent concentrations are required. However, under these conditions, adsorption in BGAC reactors is questionable and requires the existence of biofilm free areas on the GAC carrier. The purpose of this investigation is to prove that under normal BGAC fluidized bed reactor operational conditions patchy biofilm coverage with exposed areas of GAC develops. Adsorption and desorption through these exposed areas can explain the widely debated advantage of BGAC reactors regarding higher biofilm activity. The patchy-like nature of the biofilm coverage on the GAC particles was verified using experimental and modeling tools. Comparison between a nonadsorbing granular carbon carrier and a GAC carrier with an atrazine degrading biofilm (Pseudomonas ADP) under conditions of atrazine partial penetration in the biofilm showed higher biodegradation and lower effluent atrazine concentrations in the BGAC reactor.

The effect of CO2 concentration on a nitrifying chalk reactor.

The effect of CO2 concentration on nitrification rate was studied in a fluidized bed reactor using chalk (solid calcium carbonate) as the biomass carrier and buffering agent. Using one chalk type and uniform particle size, carbon dioxide was found to limit the nitrification rate in the reactor at concentrations up to 0.3 mmol l(-1). At this concentration the nitrification rate was about 2.5-2.7g NH4+-Nl reactor(-1) d(-1). The pH established in the reactor varied between 4.5 and 5.5, remarkably with lower pH obtained remarked at higher nitrification rates. Kinetic parameters for nitrification rate with CO2 as the rate limiting substrate were determined: a Michaelis-Menten constant, Km, of 0.013 mmol l(-1) CO2 and a maximum ammonium oxidation rate of 2.33g NH4+-Nl reactor(-1) d(-1).