Potential cause of aerobic granular sludge breakdown at high organic loading rates

Aerobic sludge granules are compact, strong microbial aggregates that have excellent settling ability and capability to efficiently treat high-strength and toxic wastewaters. Aerobic granules disintegrate under high organic loading rates (OLR). This study cultivated aerobic granules using acetate as the sole carbon and energy source in three identical sequencing batch reactors operated under OLR of 9–21.3 kg chemical oxygen demand (COD) m⁻³ day⁻¹. The cultivated granules removed 94–96% of fed COD at OLR up to 9–19.5 kg COD m⁻³ day⁻¹, and disintegrated at OLR of 21.3 kg COD m⁻³ day⁻¹. Most tested isolates did not grow in the medium at >3,000 mg COD l⁻¹; additionally, these strains lost capability for auto-aggregation and protein or polysaccharide productivity. This critical COD regime correlates strongly with the OLR range in which granules started disintegrating. Reduced protein quantity secreted by isolates was associated with the noted poor granule integrity under high OLR. This work identified a potential cause of biological nature for aerobic granules breakdown.     

Biological nitrification–denitrification with alternating oxic and anoxic operations using aerobic granules

Efficient nitrification and denitrification of wastewater containing 1,700 mgl⁻¹ of ammonium-nitrogen was achieved using aerobic granular sludge cultivated at medium-to-high organic loading rates. The cultivated granules were tested in a sequencing batch reactor (SBR) fed with 6.4 or 10.2 kg NH₄⁺-N m⁻³ day⁻¹, a loading significantly higher than that reported in literature. With alternating 2 h oxic and 2 h anoxic operation (OA) modes, removal rate was 45.5 mg NH₄⁺-N g⁻¹ volatile suspended solids⁻¹ h⁻¹ at 6.4 kg NH₄⁺-N m⁻³ day⁻¹ loading and 41.3 ± 2.0 at 10.2 kg NH₄⁺-N m⁻³ day⁻¹ loading. Following the 60 days SBR test, granules were intact. The fluorescence in situ hybridization and confocal laser scanning microscopy results indicate that the SBR-OA granules have a distribution with nitrifers outside and heterotrophs outside that can effectively expose functional strains to surrounding substrates at high concentrations with minimal mass transfer limit. This microbial alignment combined with the smooth granule surface achieved nitrification–denitrification of wastewaters containing high-strength ammonium using aerobic granules. Conversely, the SBR continuous aeration mode yielded a distribution with nitrifers outside and heterotrophs inside with an unsatisfactory denitrification rate and floating granules as gas likely accumulated deep in the granules.     

Nitrogen retention in the hyporheic zone of a glacial river in interior Alaska

We examined the hydrologic controls on nitrogen biogeochemistry in the hyporheic zone of the Tanana River, a glacially-fed river, in interior Alaska. We measured hyporheic solute concentrations, gas partial pressures, water table height, and flow rates along subsurface flowpaths on two islands for three summers. Denitrification was quantified using an in situ ¹⁵NO₃⁻ push–pull technique. Hyporheic water level responded rapidly to change in river stage, with the sites flooding periodically in mid−July to early−August. Nitrate concentration was nearly 3-fold greater in river (ca. 100 μg NO₃⁻–N l⁻¹) than hyporheic water (ca. 38 μg NO₃⁻–N l⁻¹), but approximately 60–80% of river nitrate was removed during the first 50 m of hyporheic flowpath. Denitrification during high river stage ranged from 1.9 to 29.4 mg N kg sediment⁻¹ day⁻¹. Hotspots of methane partial pressure, averaging 50,000 ppmv, occurred in densely vegetated sites in conjunction with mean oxygen concentration below 0.5 mgO₂ l⁻¹. Hyporheic flow was an important mechanism of nitrogen supply to microbes and plant roots, transporting on average 0.41 gNO₃⁻–N m⁻² day⁻¹, 0.22 g NH₄⁺–N m⁻² day⁻¹, and 3.6 g DON m⁻² day⁻¹ through surface sediment (top 2 m). Our results suggest that denitrification can be a major sink for river nitrate in boreal forest floodplain soils, particularly at the river-sediment interface. The stability of the river hydrograph and the resulting duration of soil saturation are key factors regulating the redox environment and anaerobic metabolism in the hyporheic zone.     

Effect of ice melting on bacterial carbon fluxes channelled by viruses and protists in the Arctic Ocean

During the last few years, extensive sea ice melting in the Arctic due to climate change has been detected, which could potentially modify the organic carbon fluxes in these waters. In this study, the effect of sea ice melting on bacterial carbon channelling by phages and protists has been evaluated in the northern Greenland Sea and Arctic Ocean. Grazing on bacteria by protists was evaluated using the FLB disappearance method. Lysis of bacteria due to viral infections was measured using the virus reduction approach. Losses of bacterial production caused by protists (PMM_BP) dominated losses caused by viruses (VMM_BP) throughout the study. Lysogenic viral production was detected in 7 out of 21 measurements and constituted from 33.9 to 100.0% of the total viral production. Significantly higher PMM_BP and lower VMM_BP were detected in waters affected by ice melting compared with unaffected waters. Consequently, significantly more bacterial carbon was channelled to the higher trophic levels in affected waters (13.05 ± 5.98 μgC l⁻¹ day⁻¹) than in unaffected waters (8.91 ± 8.33 μgC l⁻¹ day⁻¹). Viruses channelled 2.63 ± 2.45 μgC l⁻¹ day⁻¹ in affected waters and 4.27 ± 5.54 μgC l⁻¹ day⁻¹ in unaffected waters. We conclude that sea ice melting in the Arctic could modify the carbon flow through the microbial food web. This process may be especially important in the case of massive sea ice melting due to climate change.     

Impact of dissolved oxygen and loading rate on NH3 oxidation and N2 production mechanisms in activated sludge treatment of sewage

Microaerobic activated sludge (MAS) is a one-stage process operated at 0.5–1.0 mg l⁻¹ dissolved oxygen (DO) aiming at simultaneous nitrification and denitrification. We used molecular techniques and a comprehensive nitrogen (N)-transformation activity test to investigate the dominant NH₃-oxidizing and N₂-producing mechanism as well as the dominant ammonia-oxidizing bacteria (AOB) species in sludge samples individually collected from an MAS system and a conventional anoxic/oxic (A/O) system; both systems were operated at a normal loading rate (i.e. 1.0 kg chemical oxygen demand (COD) m⁻³ day⁻¹ and 0.1 kg NH₄⁺-N m⁻³ day⁻¹) in our previous studies. The DO levels in both systems (aerobic: conventional A/O system; microaerobic: MAS system) did not affect the dominant NH₃-oxidizing mechanism or the dominant AOB species. This study further demonstrated the feasibility of a higher loading rate (i.e. 2.30 kg COD m⁻³ day⁻¹ and 0.34 kg NH₄⁺-N m⁻³ day⁻¹) with the MAS process during sewage treatment, which achieved a 40% reduction in aeration energy consumption than that obtained in the conventional A/O system. The increase in loading rates in the MAS system did not affect the dominant NH₃-oxidizing mechanism but did impact the dominant AOB species. Besides, N₂ was predominantly produced by microaerobic denitrification in the MAS system at the two loading rates.     

Biodegradation and kinetics of aerobic granules under high organic loading rates in sequencing batch reactor

Biodegradation, kinetics, and microbial diversity of aerobic granules were investigated under a high range of organic loading rate 6.0 to 12.0 kg chemical oxygen demand (COD) m⁻³ day⁻¹ in a sequencing batch reactor. The selection and enriching of different bacterial species under different organic loading rates had an important effect on the characteristics and performance of the mature aerobic granules and caused the difference on granular biodegradation and kinetic behaviors. Good granular characteristics and performance were presented at steady state under various organic loading rates. Larger and denser aerobic granules were developed and stabilized at relatively higher organic loading rates with decreased bioactivity in terms of specific oxygen utilization rate and specific growth rate (μ _overall) or solid retention time. The decrease of bioactivity was helpful to maintain granule stability under high organic loading rates and improve reactor operation. The corresponding biokinetic coefficients of endogenous decay rate (k _d), observed yield (Y _obs), and theoretical yield (Y) were measured and calculated in this study. As the increase of organic loading rate, a decreased net sludge production (Y _obs) is associated with an increased solid retention time, while k _d and Y changed insignificantly and can be regarded as constants under different organic loading rates.     

Simultaneous biological removal of sulfur, nitrogen and carbon using EGSB reactor

High-rate biological conversion of sulfide and nitrate in synthetic wastewater to, respectively, elemental sulfur (S⁰) and nitrogen-containing gas (such as N₂) was achieved in an expanded granular sludge bed (EGSB) reactor. A novel strategy was adopted to first cultivate mature granules using anaerobic sludge as seed sludge in sulfate-laden medium. The cultivated granules were then incubated in sulfide-laden medium to acclimate autotrophic denitrifiers. The incubated granules converted sulfide, nitrate, and acetate simultaneously in the same EGSB reactor to S⁰, N-containing gases and CO₂ at loading rates of 3.0 kg S m⁻³ d⁻¹, 1.45 kg N m⁻³ d⁻¹, and 2.77 kg Ac m⁻¹ d⁻¹, respectively, and was not inhibited by sulfide concentrations up to 800 mg l⁻¹. Effects of the C/N ratio on granule performance were identified. The granules cultivated in the sulfide-laden medium have Pseudomonas spp. and Azoarcus sp. presenting the heterotrophs and autotrophs that co-work in the high-rate EGSB-SDD (simultaneous desulfurization and denitrification) reactor.     

Biotreatment of phenol-contaminated wastewater in a spiral packed-bed bioreactor

A spiral packed-bed bioreactor inoculated with microorganisms obtained from activated sludge was used to conduct a feasibility study for phenol removal. The reactor was operated continuously at various phenol loadings ranging from 53 to 201.4 g m⁻³ h⁻¹, and at different hydraulic retention times (HRT) in the range of 20–180 min to estimate the performance of the device. The results indicated that phenol removal efficiency ranging from 82.9 to 100% can be reached when the reactor is operated at an HRT of 1 h and a phenol loading of less than 111.9 g m⁻³ h⁻¹. At an influent phenol concentration of 201.4 g m⁻³, the removal efficiency increased from 18.6 to 76.9% with an increase in the HRT (20–120 min). For treatment of phenol in the reactor, the maximum biodegradation rate (V _m) was 1.82 mg l⁻¹ min⁻¹; the half-saturation constant (K _s), 34.95 mg l⁻¹.     

Simultaneous nutrients and carbon removal during pretreated swine slurry degradation in a tubular biofilm photobioreactor

The biodegradation potential of an innovative enclosed tubular biofilm photobioreactor inoculated with a Chlorella sorokiniana strain and an acclimated activated sludge consortium was evaluated under continuous illumination and increasing pretreated (centrifuged) swine slurry loading rates. This photobioreactor configuration provided simultaneous and efficient carbon, nitrogen, and phosphorous treatment in a single-stage process at sustained nitrogen and phosphorous removals efficiencies ranging from 94% to 100% and 70–90%, respectively. Maximum total organic carbon (TOC), NH₄ ⁺, and PO₄ ³⁻ removal rates of 80 ± 5 g C m_r ⁻³ day⁻¹, 89 ± 5 g N m_r ⁻³ day⁻¹, and 13 ± 3 g P m_r ⁻³ day⁻¹, respectively, were recorded at the highest swine slurry loadings (TOC of 1,247 ± 62 mg L⁻¹, N–NH₄ ⁺ of 656 ± 37 mg L⁻¹, P–PO₄ ³⁺ of 117 ± 19 mg L⁻¹, and 7 days of hydraulic retention time). The unusual substrates diffusional pathways established within the phototrophic biofilm (photosynthetic O₂ and TOC/NH₄ ⁺ diffusing from opposite sides of the biofilm) allowed both the occurrence of a simultaneous denitrification/nitrification process at the highest swine slurry loading rate and the protection of microalgae from any potential inhibitory effect mediated by the combination of high pH and high NH₃ concentrations. In addition, this biofilm-based photobioreactor supported efficient biomass retention (>92% of the biomass generated during the pretreated swine slurry biodegradation).     

Biological breakdown of denitrifying sulfide removal process in high-rate expanded granular bed reactor

This work conducted a denitrifying sulfide removal (DSR) test in an expanded granular sludge bed (EGSB) reactor at sustainable loadings of 6.09 kg m⁻³ day⁻¹ for sulfide, 3.11 kg m⁻³ day⁻¹ for nitrate–nitrogen, and 3.27 kg m⁻¹ day⁻¹ for acetate–carbon with >93% efficiency, which is significantly higher than those reported in literature. Strains Pseudomonas sp., Nitrincola sp., and Azoarcus sp. very likely yield heterotrophs. Strains Thermothrix sp. and Sulfurovum sp. are the autotrophs required for the proposed high-rate EGSB-DSR system. The EGSB-DSR reactor experienced two biological breakdowns, one at loadings of 4.87, 2.13, and 1.82 kg m⁻³ day⁻¹; reactor function was restored by increasing nitrate and acetate loadings. Another breakdown occurred at loadings of up to 8.00, 4.08, and 4.50 kg m⁻¹ day⁻¹; the heterotrophic denitrification pathway declined faster than the autotrophic pathway. The mechanism of DSR breakdown is as follows. High sulfide concentration inhibits heterotrophic denitrifiers, and the system therefore accumulates nitrite. Autotrophic denitrifiers are then inhibited by the accumulated nitrite, thereby leading to breakdown of the DSR process.     

Reclamation of an activated-sludge microbial consortium by selective biostimulation

Our previous study showed that an activated-sludge process broke down at the phenol-loading rate of 1.5 g l⁻¹ day⁻¹, when non-flocculating bacteria (called R6T and R10) overgrew the sludge, resulting in a sludge washout. In this study, we attempted to circumvent this breakdown problem by reclaiming the consortium structure. Activated sludge was fed phenol, and the phenol-loading rate was increased stepwise from 0.5 g l⁻¹ day⁻¹ to 1.0 g l⁻¹ day⁻¹ and then to 1.5 g l⁻¹ day⁻¹. Either galactose or glucose (at 0.5 g l⁻¹ day⁻¹) was also supplied to the activated sludge from the phenol-loading rate of 1.0 g l⁻¹ day⁻¹. Pure culture experiments have suggested galactose to be a preferential substrate for a floc-forming bacterium (R6F) that predominantly degrades phenol under low phenol-loading conditions. Supplying galactose allowed sustainment of the R6F population and suppression of the overgrowth of R6T and R10 at the phenol-loading rate of 1.5 g l⁻¹ day⁻¹. This measure allowed the activated-sludge process to treat phenol at a phenol-loading rate up to 1.5 g l⁻¹ day⁻¹, although it broke down at 2.0 g l⁻¹ day⁻¹. In contrast, supplying glucose reduced the R6F population and allowed the activated-sludge process to break down at the phenol-loading rate of 1.0 g l⁻¹ day⁻¹. This study demonstrated that reclamation of the activated-sludge consortium by selective biostimulation of the floc-forming population improved the phenol-treating ability of the process. Received: 13 January 2000 / Received revision: 10 March 2000 / Accepted: 7 April 2000     

Epipelic and pelagic primary production in Alaskan Arctic lakes of varying depth

We compared on eight dates during the ice-free period physicochemical properties and rates of phytoplankton and epipelic primary production in six arctic lakes dominated by soft bottom substrate. Lakes were classified as shallow ( < 2.5 m), intermediate in depth (2.5 m <  < 4.5 m), and deep ( > 4.5 m), with each depth category represented by two lakes. Although shallow lakes circulated freely and intermediate and deep lakes stratified thermally for the entire summer, dissolved oxygen concentrations were always >70% of saturation values. Soluble reactive phosphorus and dissolved inorganic nitrogen (DIN = NO₃ ⁻–N + NH₄ ⁺–N) were consistently below the detection limit (0.05 μmol l⁻¹) in five lakes. However, one lake shallow lake (GTH 99) periodically showed elevated values of DIN (17 μmol l⁻¹), total-P (0.29 μmol l⁻¹), and total-N (33 μmol l⁻¹), suggesting wind-generated sediment resuspension. Due to increased nutrient availability or entrainment of microphytobenthos, GTH 99 showed the highest average volume-based values of phytoplankton chlorophyll a (chl a) and primary production, which for the six lakes ranged from 1.0 to 2.9 μg l⁻¹ and 0.7–3.8 μmol C l⁻¹ day⁻¹. Overall, however, increased resulted in increased area-based values of phytoplankton chl a and primary production, with mean values for the three lake classes ranging from 3.6 to 6.1 mg chl a m⁻² and 3.2–5.8 mmol C m⁻² day⁻¹. Average values of epipelic chl a ranged from 131 to 549 mg m⁻² for the three depth classes, but levels were not significantly different due to high spatial variability. However, average epipelic primary production was significantly higher in shallow lakes (12.2 mmol C m⁻² day⁻¹) than in intermediate and deep lakes (3.4 and 2.4 mmol C m⁻² day⁻¹). Total primary production (6.7–15.4 mmol C m⁻² day⁻¹) and percent contribution of the epipelon (31–66%) were inversely related to mean depth, such that values for both variables were significantly higher in shallow lakes than in intermediate or deep lakes. Handling editor: L. Naselli-Flores     

Start-up and inhibition analysis of the Anammox process seeded with anaerobic granular sludge

The longer start-up period of the Anammox process is due to the very low cellular yield and growth rates of Anammox bacteria. Nitrite inhibition is considered to be the key factor in the instability of the Anammox process during the operation. However, little attention was paid to the inhibitory effect of pH and free ammonia. This paper presents start-up and inhibition analysis of an Anammox biofilm reactor seeded with anaerobic granular sludge. Results showed that the start-up period could be divided into the sludge lysis phase, lag phase, propagation phase, stationary phase and inhibition phase. Optimization control could be implemented correspondingly to accelerate the start-up of Anammox bioreactors. Effluent pH increased to 8.7–9.1 when the nitrogen removal rate was higher than 1,200 mg l⁻¹ day⁻¹. The free ammonia concentration was accompanied with a higher level of 64–73 mg l⁻¹. Inhibitory effects of high pH and free ammonia on Anammox bacteria contributed to the destabilization of the Anammox bioreactor during the first 125 days with influent KHCO₃ of 0.5 g l⁻¹. Increasing the suffering capacity in the inlet by dosing 1.25 g KHCO₃ l⁻¹ effectively reduced the pH variation, and the nitrogen removal performance of the reactor was further developed.     

Denitrification of a landfill leachate with high nitrate concentration in an anoxic rotating biological contactor

The denitrification performance of a lab-scale anoxic rotating biological contactor (RBC) using landfill leachate with high nitrate concentration was evaluated. Under a carbon to nitrogen ratio (C/N) of 2, the reactor achieved N-NO₃ ⁻ removal efficiencies above 95% for concentrations up to 100 mg N-NO₃ ⁻ l⁻¹. The highest observed denitrification rate was 55 mg N-NO₃ ⁻ l⁻¹ h⁻¹ (15 g N-NO₃ ⁻ m⁻² d⁻¹) at a nitrate concentration of 560 mg N-NO₃ ⁻ l⁻¹. Although the reactor has revealed a very good performance in terms of denitrification, effluent chemical oxygen demand (COD) concentrations were still high for direct discharge. The results obtained in a subsequent experiment at constant nitrate concentration (220 mg N-NO₃ ⁻ l⁻¹) and lower C/N ratios (1.2 and 1.5) evidenced that the organic matter present in the leachate was non-biodegradable. A phosphorus concentration of 10 mg P-PO₄ ³⁻ l⁻¹ promoted autotrophic denitrification, revealing the importance of phosphorus concentration on biological denitrification processes.     

Biogeochemistry of inter-reef sediments on the northern and central Great Barrier Reef

The deposition and cycling of carbon and nitrogen in carbonate sediments located between coral reefs on the northern and central sections of the Great Barrier Reef were examined. Rates of mass sediment accumulation ranged from 1.9 kg m⁻² year⁻¹ (inshore reefs) to 2.1–4.9 kg m⁻² year⁻¹ (between mid-shelf reefs); sedimentation was minimal off outer-shelf reefs. Rates of total organic carbon decomposition ranged from 1.7 to 11.4 mol C m⁻² year⁻¹ and total nitrogen mineralization ranged from 77 to 438 mmol N m⁻² year⁻¹, declining significantly with distance from land. Sediment organic matter was highly reactive, with mineralization efficiencies ranging from 81 to 99% for organic carbon and 64–100% for nitrogen, with little C and N burial. There was no evidence of carbonate dissolution/precipitation in short-term incubation experiments. Rates of sulfate reduction (range 0–3.4 mmol S m⁻² day⁻¹) and methane release (range 0–12.8 μmol CH₄ m⁻² day⁻¹) were minor or modest pathways of carbon decomposition. Aerobic respiration, estimated by difference between total O₂ consumption and the sum of the other pathways, accounted for 55–98% of total carbon mineralization. Rates of ammonification ranged from 150 to 1,725 μmol NH₄ m⁻² day⁻¹, sufficient to support high rates of denitrification (range 30–2,235 μmol N₂ m⁻² day⁻¹). N₂O release was not detected and rates of NH₄ ⁺ and NO₂ ⁻ + NO₃ ⁻ efflux were low, indicating that most mineralized N was denitrified. The percentage of total N input removed via denitrification averaged ≈75% (range 28–100%) with little regenerated N available for primary producers. Inter-reef environments are therefore significant sites of energy and nutrient flow, especially in spatially complex reef matrices such as the Great Barrier Reef.     

Nitrifying granules cultivation in a sequencing batch reactor at a low organics-to-total nitrogen ratio in wastewater

It is possible to cultivate aerobic granular sludge at a low organic loading rate and organics-to-total nitrogen (COD/N) ratio in wastewater in the reactor with typical geometry (height/diameter = 2.1, superficial air velocity = 6 mm/s). The noted nitrification efficiency was very high (99%). At the highest applied ammonia load (0.3 ± 0.002 mg NH₄⁺–N g total suspended solids (TSS)⁻¹ day⁻¹, COD/N = 1), the dominating oxidized form of nitrogen was nitrite. Despite a constant aeration in the reactor, denitrification occurred in the structure of granules. Applied molecular techniques allowed the changes in the ammonia-oxidizing bacteria (AOB) community in granular sludge to be tracked. The major factor influencing AOB number and species composition was ammonia load. At the ammonia load of 0.3 ± 0.002 mg NH₄⁺–N g TSS⁻¹ day⁻¹, a highly diverse AOB community covering bacteria belonging to both the Nitrosospira and Nitrosomonas genera accounted for ca. 40% of the total bacteria in the biomass.     

Mechanical shear contributes to granule formation resulting in quick start-up and stability of a hybrid anammox reactor

It appears that if suspended biomass washout can be reduced effectively, granule formation will be fastened in fluidized bed. Quicker reactor start-up can be anticipated especially for those system keeping slow growth bacteria such as anammox. A hybrid reactor combined fixed-bed with nonwoven fabrics as biomass carrier and fluidized bed with slow speed mechanical stirring was therefore developed, and its nitrogen removal performances was evaluated experimentally. Only in 38 days, the total nitrogen removal rate (NRR) reached to 1.9 kg(N) m⁻³ day⁻¹ and then doubled within 17 days, with total nitrogen removal efficiency kept above 70%. After 180 days reactor operating, the NRR reached a maximum value of 6.6 kg(N) m⁻³ day⁻¹ and the specific anammox activity was gradually constant in 0.32 kg(N) kg(VSS)⁻¹ day⁻¹. Biomass attached on nonwoven fabrics could additionally improve reactor nitrogen removal by 8%. The dominant size of granular sludge reached to 0.78 mm with stirring speed adjusted from 30 to 80 rpm and the hydraulic retention time (HRT) from 8 to 1.5 h during the whole operating time. Scanning electron microscope observation showed especially compact structure of granular sludge. A 70% of anammox bacteria percentage was identified by fluorescence in situ hybridization analysis.     

A case of thermal pollution limited primary productivity in a southwestern U.S.A. Reservoir

North Lake, a small (330 ha. surface area) southwestern U.S.A. cooling water reservoir was found to contain less phytoplankton production (104.0 mg C m⁻³ day⁻¹), lower annual mean total organic carbon (3.7 mg l⁻¹) and phytoplankton standing crops (0.9 ml m⁻³) than other local area reservoirs. Concentrations of inorganic P and N were at or below test detection limits during the study year 1973–1974.In situ ¹⁴C non-filtration primary productivity techniques demonstrated significant (≃13 percent) stimulation of planktonic primary productivity due to power plant entrainment. Optical counts showed no destruction of entrained phytoplankters. Populations of Cyanophyta were never dominant, although they frequently bloom in most other local reservoirs. Thermal loading at North Lake is thought to ultimately depress phytoplankton primary production and standing crop by causing nutrient limitation.     

Treatment of phenol in an anaerobic fluidized bed reactor (AFBR): continuous and batch regime

Results of this study describe the feasibility of anaerobic treatment of highly concentrated phenol synthetic wastewater using an anaerobic fluidized bed reactor (AFBR) in both continuous and batch modes. Wastewater with a maximum load of 2,100 mg C·l⁻¹ was prepared using phenol (maximum concentration of 1,600 mg C·l⁻¹) as substrate and a mixture of acetic, propionic and butyric acids (500 mg C·l⁻¹) as co-substrate. AFBR reached total organic carbon (TOC) and phenol removal efficiency over 95% treating the highest organic loading rate (OLR) containing phenol studied for this kind of reactor (5.03 g C·l⁻¹·d⁻¹). The phenol loading rate rise caused volumetric biogas rate increase up to 4.4 l·l⁻¹·d⁻¹ (average yield of 0.28 l CH₄·g⁻¹ COD_removed) as well as variation in the biogas composition; the CO₂ percentage increased while the CH₄ percentage decreased. Morphological examination of the bioparticles at 4.10 g C·l⁻¹·d⁻¹, revealed significant differences in the biofilm structure, microbial colonization and bacterial morphological type development. The five batch assays showed that phenol degradation may be favoured by the presence of volatile fatty acids (VFAs) (co-metabolism), whereas VFAs degradation may be inhibited by phenol. AFBR reached initial phenol degradation velocity of 0.25 mg C·l⁻¹·min⁻¹.     

Denitrification activity and oxygen dynamics in Arctic sea ice

Denitrification and oxygen dynamics were investigated in the sea ice of Franklin Bay (70°N), Canada. These investigations were complemented with measurements of denitrification rates in sea ice from different parts of the Arctic (69°N–85°N). Potential for bacterial denitrification activity (5–194 μmol N m⁻² day⁻¹) and anammox activity (3–5 μmol N m⁻² day⁻¹) in melt water from both first-year and multi-year sea ice was found. These values correspond to 27 and 7%, respectively, of the benthic denitrification and anammox activities in Arctic sediments. Although we report only potential denitrification and anammox rates, we present several indications that active denitrification in sea ice may occur in Franklin Bay (and elsewhere): (1) despite sea ice-algal primary production in the lower sea ice layers, heterotrophic activity resulted in net oxygen consumption in the sea ice of 1–3 μmol l⁻¹ sea ice per day at in situ light conditions, suggesting that O₂ depletion may occur prior to the spring bloom. (2) The ample organic carbon (DOC) and NO₃ ⁻ present in sea ice may support an active denitrification population. (3) Measurements of O₂ conditions in melted sea ice cores showed very low bulk concentrations, and in some cases anoxic conditions prevailed. (4) Laboratory studies using planar optodes for measuring the high-resolution two-dimensional O₂ distributions in sea ice confirmed the very dynamic and heterogeneous O₂ distribution in sea ice, displaying a mosaic of microsites of high and low O₂ concentrations. Brine enclosures and channels were strongly O₂ depleted in actively melting sea ice, and anoxic conditions in parts of the brine system would favour anaerobic processes.