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.     

An upflow microaerobic sludge blanket reactor operating at high organic loading and low dissolved oxygen levels

The activated sludge process (ASP) has high operational costs due to the need for aeration at dissolved O₂ (DO) levels of ≥2 mg l⁻¹ and high capital costs to construct large reactors due to a low organic loading [typically 1 kg chemical oxygen demand (COD) m⁻³ day⁻¹]. A novel method for improving the energy use and treatment efficiency of the ASP via limited oxygenation (0.4 mg DO l⁻¹) and high organic loading (6.2 kg COD m⁻³ day⁻¹) is proposed based on a laboratory-scale ASP for ammonia-rich industrial wastewaters. The sludge blanket phenomenon and granulation occurred simultaneously in the upflow microaerobic reactor.     

Improvement of biodegradation in compact co-current biotrickling filter by high recycle liquid flow rate: Performance and biodegradation kinetics of ammonia removal

As a microbial-environmental-control-type deodorizing system, we have developed a compact biotrickling filter system for small-scale livestock farms. The performance of the compact co-current biotrickling filter operated at high recycle liquid flow rates was systematically examined. In particular, we studied improvements in the nitrification ability of the system due to the resultant enhancement of absorption and dissolution of NH₃ and absorption of O₂ with the high flow rates of recycle liquid flowing downward co-currently with gas flow. At the empty bed residence time of 50 s, almost complete removal of NH₃ was obtained with recycle liquid flow rates of 103 and 205 L m⁻³ day⁻¹ for 20 days while the inlet NH₃ concentration was increased from 200 to 500 ppm. With a recycle liquid flow rate of 411 L m⁻³ day⁻¹ the removal efficiency remained above 95% for 57 days while the inlet NH₃ concentration was increased from 200 to 700 ppm. The biodegradation kinetics for NH₃ removal was successfully analyzed using the Haldane substrate inhibition kinetics. The present data and kinetic analyses showed that the substrate inhibition was suppressed and the biodegradation of ammonia in the compact biotrickling filter could be improved by the high recycle liquid flow rate.     

Two ways to achieve an anammox influent from real reject water treatment at lab-scale: Partial SBR nitrification and SHARON process

A comparative study to produce the correct influent for Anammox process from anaerobic sludge reject water (700–800 mg NH₄⁺-N L⁻¹) was considered here. The influent for the Anammox process must be composed of NH₄⁺-N and NO₂⁻-N in a ratio 1:1 and therefore only a partial nitrification of ammonium to nitrite is required. The modifications of parameters (temperature, ammonium concentration, pH and solid retention time) allows to achieve this partial nitrification with a final effluent only composed by NH₄⁺-N and NO₂⁻-N at the right stoichiometric ratio. The equal ratio of HCO₃⁻/NH₄⁺ in reject water results in a natural pH decrease when approximately 50% of NH₄⁺ is oxidised. A Sequencing batch reactor (SBR) and a chemostat type of reactor (single-reactor high activity ammonia removal over nitrite (SHARON) process) were studied to obtain the required Anammox influent. At steady state conditions, both systems had a specific conversion rate around 40 mg NH₄⁺-N g⁻¹ volatile suspended solids (VSS) h⁻¹, but in terms of absolute nitrogen removal the SBR conversion was 1.1 kg N day⁻¹ m⁻³, whereas in the SHARON chemostat was 0.35 kg N day⁻¹ m⁻³ due to the different hydraulic retention time (HRT) used. Both systems are compared from operational (including starvation experiments) and kinetic point of view and their advantages/disadvantages are discussed.     

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.     

Responses of community structure of amoA‐encoding archaea and ammonia‐oxidizing bacteria in ammonia biofilter with rockwool mixtures to the gradual increases in ammonium and nitrate

Aims

To investigate community shifts of amoA‐encoding archaea (AEA) and ammonia‐oxidizing bacteria (AOB) in biofilter under nitrogen accumulation process.

Methods and Results

A laboratory‐scale rockwool biofilter with an irrigated water circulation system was operated for 436 days with ammonia loading rates of 49–63 NH₃ g m^?3 day^?1. The AEA and AOB communities were investigated by denaturing gradient gel electrophoresis, sequencing and real‐time PCR analysis based on amoA genes. The results indicated that changes in abundance and community compositions occurred in a different manner between archaeal and bacterial amoA during the operation. However, both microbial community structures mainly varied when free ammonia (FA) concentrations in circulation water were increasing, which caused a temporal decline in reactor performance. Dominant amoA sequences after this transition were related to Thaumarchaeotal Group I.1b, Nitrosomonas europaea lineages and one subcluster within Nitrosospira sp. cluster 3, for archaea and bacteria, respectively.

Conclusions

The specific FA in circulation water seems to be the important factor, which relates to the AOB and AEA community shifts in the biofilter besides ammonium and pH.

Significance and Impact of the Study

One of the key factors for regulating AEA and AOB communities was proposed that is useful for optimizing biofiltration technology.     

Wastewater treatment efficiency of a multi-media biological aerated filter (MBAF) containing clinoptilolite and bioceramsite in a brick-wall embedded design

A multi-media biological aerated filter (MBAF) with clinoptilolite media was used to treat synthetic wastewater. Coal ash bioceramsite with supplemental metallic iron was added to the clinoptilolite media of MBAFs in a brick-wall embedded design. Performance parameters, such as hydraulic, organic, N and P loading capacity and microbial community composition were studied for different quantity of supplemental metallic iron contained in three MBAFs. The MBAFs with more metallic iron were found to have superior hydraulic and organic loading, and higher N and P capacities. COD, NH₃-N and TP removal dropped by 7-10%, 6-7% and 4-5%, respectively, with when hydraulic loading was raised from 2.8 to 7.5 m³ m⁻² d⁻¹. NH₃-N removal also decreased 8-9% when ammonia loading was elevated from 0.078 to 0.156 kg NH₃-N m⁻³ d⁻¹. Real-time PCR revealed a relatively stable bacterial community composed primarily of eubacteria that formed after an initial 120 d operational period. Doubling the amount of metallic iron in the bioceramsite media resulted in a twofold increase of eubacteria in the MBAF, but a decrease in the ratio of anaerobic ammonia-oxidizing bacteria to total bacteria.     

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).     

Impact of loads,season, and plant species on the performance of a tropical constructed wetland polishing effluent from sugar factory stabilization ponds

The effects of wastewater loading rates and two macrophyte species on treatment of sugar factory stabilization pond effluent were investigated in a pilot-scale free water surface constructed wetland (FWS CW) system in western Kenya. For 12 months, four CWs were operated at a hydraulic loading rate of 75 mm day⁻¹ and four at 225 mm day⁻¹. Half the CWs were planted with Cyperus papyrus and half with Echinochloa pyramidalis. Water samples were taken at the inlets and outlets and analyzed for TP, TDP, NH₄-N, and TSS. Mass removal rates of the selected water quality parameters were compared during three periods designated the short rain (period 1), dry (period 2), and long rain (period 3) seasons. There was a significant linear relationship between the mass removal rate of TP, NH₄-N, and TSS and the mass load, and season had a significant effect on the mass removal rate of TSS, NH₄-N, and TDP. Mass loading rates for TDP were about 78% of those for TP, whereas TDP comprised 78–99% of TP mass outflow rates, indicating a release of dissolved P within the CWs. The only significant difference between the two macrophyte species was associated with mass removal of NH₄-N, with more efficient removal in CWs planted with C. papyrus than those with E. pyramidalis. TP mass removal rates were 50–80% higher when a mean water loss for CWs 6–8 during periods 1 and 2 was assumed to represent evapotranspiration for all CWs in period 3 instead of pan evaporation data. This illustrated the importance of accurate estimations of evapotranspiration for pollutant mass removal rates in CWs in tropical climates.     

Influences of different nitrogen sources on nitrogen- and water-use efficiency, and carbon isotope discrimination, in C3 Triticum aestivum L. and C4 Zea mays L. plants

The impacts of various nitrogen sources, i.e. NO⁻ ₃, NH₄ ⁺ or NH₄NO₃ in combination with gaseous NH₃, on nitrogen-, carbon- and water-use efficiency and ¹³C discrimination (δ¹³C) by plants of the C₃ species Triticum aestivum L. (wheat) and the C₄ species Zea mays L. (maize) were studied. Triticum aestivum and Z. mays were hydroponically grown with 2 mol · m⁻³ of N supplied as NO⁻ ₃, NH₄ ⁺ or NH₄NO₃ for 21 and 18 d, respectively, and thereafter exposed to gaseous NH₃ at 320 μg · m⁻³ or to ambient air for 7 d. In T. aestivum and Z. mays over a 7-d growth period, nitrogen-use efficiency (NUE) values were influenced by N-sources in the decreasing order NH₄NO₃-N > NO⁻ ₃-N > NH₄ ⁺-N and NO⁻ ₃-N > NH₄NO₃-N > NH₄ ⁺-N, respectively. Fumigation with NH₃ decreased the NUE values of plants grown with any of the N-forms. During 28- and 7-d growth periods, N-sources affected water-use efficiency (WUE) values in the decreasing order of NH₄ ⁺-N > NO⁻ ₃-N≈NH₄NO₃-N in non-fumigated T. aestivum, while fumigation with NH₃ increased the WUE of NO⁻ ₃-grown plants. There were insignificant effects of N-sources on WUE values of Z. mays over 25- and 7-d growth periods. Furthermore, δ¹³C values in plant tissues (leaves, stubble and roots) were higher (less negative) in NH₄ ⁺-grown plants of T. aestivum and Z. mays than in those supplied with NH₄NO₃ or NO⁻ ₃. Regardless of the N-form supplied to the roots of the plant species, exposure to NH₃ caused more-positive δ¹³C values in the plant tissues. These results indicate that the variations in N-source were associated with small but significant variations in δ¹³C values in plants of T. aestivum and Z. mays. These differences in δ¹³C values are in the direction expected from differences in WUE values over long or short growth periods and with differences in the extent of non-Rubisco (ribulose-1,5-bisphosphate carboxylase-oxygenase, EC 4.1.1.39) carboxylate contribution to net C acquisition, as a function of N-source. Received: 12 September 1997 / Accepted: 13 January 1998     

Use of Aliphatic n-Alkynes To Discriminate Soil Nitrification Activities of Ammonia-Oxidizing Thaumarchaea and Bacteria

Ammonia (NH₃)-oxidizing bacteria (AOB) and thaumarchaea (AOA) co-occupy most soils, yet no short-term growth-independent method exists to determine their relative contributions to nitrification in situ. Microbial monooxygenases differ in their vulnerability to inactivation by aliphatic n-alkynes, and we found that NH₃ oxidation by the marine thaumarchaeon Nitrosopumilus maritimus was unaffected during a 24-h exposure to ≤20 μM concentrations of 1-alkynes C₈ and C₉. In contrast, NH₃ oxidation by two AOB (Nitrosomonas europaea and Nitrosospira multiformis) was quickly and irreversibly inactivated by 1 μM C₈ (octyne). Evidence that nitrification carried out by soilborne AOA was also insensitive to octyne was obtained. In incubations (21 or 28 days) of two different whole soils, both acetylene and octyne effectively prevented NH₄⁺-stimulated increases in AOB population densities, but octyne did not prevent increases in AOA population densities that were prevented by acetylene. Furthermore, octyne-resistant, NH₄⁺-stimulated net nitrification rates of 2 and 7 μg N/g soil/day persisted throughout the incubation of the two soils. Other evidence that octyne-resistant nitrification was due to AOA included (i) a positive correlation of octyne-resistant nitrification in soil slurries of cropped and noncropped soils with allylthiourea-resistant activity (100 μM) and (ii) the finding that the fraction of octyne-resistant nitrification in soil slurries correlated with the fraction of nitrification that recovered from irreversible acetylene inactivation in the presence of bacterial protein synthesis inhibitors and with the octyne-resistant fraction of NH₄⁺-saturated net nitrification measured in whole soils. Octyne can be useful in short-term assays to discriminate AOA and AOB contributions to soil nitrification.     

Partial nitritation at elevated loading rates: design curves and biofilm characteristics

There is a need to develop low operational intensity, cost-effective, and small-footprint systems to treat wastewater. Partial nitritation has been studied using a variety of control strategies, however, a gap in passive operation is evident. This research investigates the use of elevated loading rates as a strategy for achieving low operational intensity partial nitritation in a moving bed biofilm reactor (MBBR) system. The effects of loading rates on nitrification kinetics and biofilm characteristics were determined at elevated, steady dissolved oxygen concentrations between 5.5 and 7.0 mg O₂/L and ambient temperatures between 19 and 21 °C. Four elevated loading rates (3, 4, 5 and 6.5 g NH₄⁺-N/m² days) were tested with a distinct shift in kinetics being observed towards nitritation at elevated loadings. Complete partial nitritation (100% nitrite production) was achieved at 6.5 g NH₄⁺-N/m² days, likely due to thick biofilm (572 µm) and elevated NH₄⁺-N load, which resulted in suppression of nitrite oxidation.

     

Conversion of NaHCO3 to Na2CO3 with a growth of Arthrospira platensis cells in 660 m2 raceway ponds with a CO2 bicarbonation absorber

The weight ratio of Na₂CO₃/NaHCO₃ was investigated in order to improve microalgal productivity in large-scale industrial operations by converting NaHCO₃ to Na₂CO₃ with a growth of Arthrospira platensis cells in 660 m² raceway ponds. Two microalgal cultivation systems with a NaHCO₃ by-product (SPBP) and a CO₂ bicarbonation absorber (CBAP) were firstly thoroughly introduced. There was a 13.3% decrease in the initial weight ratio of Na₂CO₃/NaHCO₃ resulting in a 25.3% increase in the biomass growth rate with CBAP, compared to that of SPBP. Increased sunlight intensity, solution temperature and pH all resulted in both a higher absorbance and release, thereby increasing the weight ratio of Na₂CO₃/NaHCO₃ during the growth of A. platensis. The biomass growth rate was peaked at 39.9 g m⁻² day⁻¹ when the weight ratio of Na₂CO₃/NaHCO₃ was 3.7. Correspondingly, the cell pigments (chlorophyll a and carotenoid) and trichome size (helix pitch and trichome length) reached to a maximum state of 8.47 mg l⁻¹, 762 μg l⁻¹, 57 and 613 μm under the CBAP system.     

The role of loading rate, backwashing, water and air velocities in an up-flow nitrifying tertiary filter

The vertical distribution of nitrification performances in an up-flow biological aerated filter operated at tertiary nitrification stage is evaluated in this paper. Experimental data were collected from a semi-industrial pilot-plant under various operating conditions. The actual and the maximum nitrification rates were measured at different levels inside the up-flow biofilter. A nitrogen loading rate higher than 1.0 kg NH₄-N m⁻³_media d⁻¹ is necessary to obtain nitrification activity over all the height of the biofilter. The increase in water and air velocities from 6 to 10 m h⁻¹ and 10 to 20 m h⁻¹ has increased the nitrification rate by 80% and 20% respectively. Backwashing decreases the maximum nitrification rate in the media by only 3-14%. The nitrification rate measured at a level of 0.5 m above the bottom of the filter is four times higher than the applied daily average volumetric nitrogen loading rate up to 1.5 kg NH₄-N m⁻³_media d⁻¹. Finally, it is shown that 58% of the available nitrification activity is mobilized in steady-state conditions while up to 100% is used under inflow-rate increase.     

Biological denitrification by <Emphasis Type="Italic">Pseudomonas stutzeri</Emphasis> immobilized on microbial cellulose

This study demonstrated the feasibility of a biological denitrification process using immobilized Pseudomonas stutzeri. The microbial cellulose (MC) from Acetobacter xylinum was used as the support material for immobilization of the bacterium. Nitrate removal took place mainly in the anoxic system. The effects of various operating conditions such as the initial nitrate concentration, pH, and carbon source on biological denitrification were demonstrated experimentally. The system demonstrated a high capacity for reducing nitrate concentrations under optimum conditions. The denitrification rate increased up to a maximal value of 1.6 kg NO₃-N m⁻³ day⁻¹ with increasing nitrate loading rate. Because of its porosity and purity, MC may be considered as appropriate supports for adsorbed immobilized cells. The simplicity of immobilization and high efficiency in operation are the main advantages of such systems. To date, the immobilization of microorganisms onto MC has not been carried out. The results of this research shows that a pilot bioreactor containing P. stutzeri immobilized on MC exhibited efficient denitrification with a relatively low retention time.     

The effects of NH4+ and NO3− on growth,resource allocation and nitrogen uptake kinetics of Phragmites australis and Glyceria maxima

The effects of NH₄⁺ or NO₃⁻ on growth, resource allocation and nitrogen (N) uptake kinetics of two common helophytes Phragmites australis (Cav.) Trin. ex Steudel and Glyceria maxima (Hartm.) Holmb. were studied in semi steady-state hydroponic cultures. At a steady-state nitrogen availability of 34 μM the growth rate of Phragmites was not affected by the N form (mean RGR = 35.4 mg g⁻¹ d⁻¹), whereas the growth rate of Glyceria was 16% higher in NH₄⁺-N cultures than in NO₃⁻-N cultures (mean = 66.7 and 57.4 mg g⁻¹ d⁻¹ of NH₄⁺ and NO₃⁻ treated plants, respectively). Phragmites and Glyceria had higher S/R ratio in NH₄⁺ cultures than in NO₃⁻ cultures, 123.5 and 129.7%, respectively.Species differed in the nitrogen utilisation. In Glyceria, the relative tissue N content was higher than in Phragmites and was increased in NH₄⁺ treated plants by 16%. The tissue NH₄⁺ concentration (mean = 1.6 μmol g fresh wt⁻¹) was not affected by N treatment, whereas NO₃⁻ contents were higher in NO₃⁻ (mean = 1.5 μmol g fresh wt⁻¹) than in NH₄⁺ (mean = 0.4 μmol g fresh wt⁻¹) treated plants. In Phragmites, NH₄⁺ (mean = 1.6 μmol g fresh wt⁻¹) and NO₃⁻ (mean = 0.2 μmol g fresh wt⁻¹) contents were not affected by the N regime. Species did not differ in NH₄⁺ (mean = 56.5 μmol g⁻¹ root dry wt h⁻¹) and NO₃⁻ (mean = 34.5 μmol g⁻¹ root dry wt h⁻¹) maximum uptake rates (V_max), and V_max for NH₄⁺ uptake was not affected by N treatment. The uptake rate of NO₃⁻ was low in NH₄⁺ treated plants, and an induction phase for NO₃⁻ was observed in NH₄⁺ treated Phragmites but not in Glyceria. Phragmites had low K_m (mean = 4.5 μM) and high affinity (10.3 l g⁻¹ root dry wt h⁻¹) for both ions compared to Glyceria (K_m = 6.3 μM, affinity = 8.0 l g⁻¹ root dry wt h⁻¹). The results showed different plasticity of Phragmites and Glyceria toward N source. The positive response to NH₄⁺-N source may participates in the observed success of Glyceria at NH₄⁺ rich sites, although other factors have to be considered. Higher plasticity of Phragmites toward low nutrient availability may favour this species at oligotrophic sites.     

Seasonal nutrient fluxes variability of northern salt marshes: examples from the lower St. Lawrence Estuary

This study presents the tidal exchange of ammonium, nitrite + nitrate, phosphate and silicate between two salt marshes and adjacent estuarine waters. Marsh nutrient fluxes were evaluated for Pointe-au-Père and Pointe-aux-épinettes salt marshes, both located along the south shore of the lower St. Lawrence Estuary in Rimouski area (QC, Canada). Using nutrients field data, high precision bathymetric records and a hydrodynamic numerical model (MIKE21-NHD) forced with predicted tides, nutrients fluxes were estimated through salt marsh outlet cross-sections at four different periods of the year 2004 (March, May, July and November). Calculated marsh nutrient fluxes are discussed in relation with stream inputs, biotic and abiotic marsh processes and the incidence of sea ice cover. In both marshes, the results show the occurrence of year-round and seaward NH₄ ⁺ fluxes and landward NO₂ ⁻ + NO₃ ⁻ fluxes (ranging from 9.06 to 30.48 mg N day⁻¹ m⁻² and from −32.07 to −9.59 mg N day⁻¹ m⁻², respectively) as well as variable PO₄ ³⁻ and Si(OH)₄ fluxes (ranging from −3.73 to 6.34 mg P day⁻¹ m⁻² and from −29.19 to 21.91 mg Si day⁻¹ m⁻², respectively). These results suggest that NO₂ ⁻ + NO₃ ⁻ input to marshes can be a significant source of NH₄ ⁺ through dissimilatory nitrate reduction to ammonium (DNRA). This NH₄ ⁺, accumulating in marsh sediment rather than being removed through coupled nitrification–denitrification or biological assimilation, is exported toward estuarine waters. From average P and Si tidal fluxes analysis, both salt marshes act as a sink during high productivity period (May and July) and as a source, supplying estuarine water during low productivity period (November and March).     

Nitrogen and phosphorus removal by wetland mesocosms subjected to different hydroperiods

The effect of hydroperiod on nutrient removal efficiency from simulated wastewater was investigated in replicate wetland mesocosms (area, 2 m², planted with Scirpus californicus). Alternate draining and flooding of sediments (pulsed discharge) increased nutrient removal efficiency compared to the continuous-flow “control”. Average PO₄³⁻ removal efficiency was 20–30% higher in wetland mesocosms that drained twice daily compared to the control. Inorganic N removal efficiency was less affected than phosphate removal by hydroperiod variation. At the higher NH₄⁺ loading rate (1.83 g N m⁻² day⁻¹), inorganic N removal efficiency was consistently 5–20% higher in pulsed-discharge wetland mesocosms than in the control. At the lower NH₄⁺ loading rate (0.9 g N m ⁻² day ⁻¹), pulsed-discharge hydrology had no effect on inorganic N removal efficiency. Twice-daily drainage exhibited average inorganic N removal efficiencies of 96% (lower N loading rate) and 87% (higher N loading) and average phosphate removal efficiencies of 81% (lower P loading) and 90% (higher P loading). Mass balance data from the continuous-flow treatment revealed that the aquatic macrophyte Scirpus californicus was the most important nutrient sink, assimilating 50% of the NH₄⁺ and PO₄³⁻ supply. The high plant productivity in the mesocosms (15.6 kg m⁻² year⁻¹) occurred under conditions of high light (high edge per mesocosm area) and high root contact with nutrient-rich influent (shallow, sandy substrate) and may overestimate plant uptake in larger wetlands. The addition of a nitrification-inhibitor (N-Serve) indicated that 34% of the NH₄⁺ supply was transformed to NO₃⁻ by nitrifying bacteria.     

Ammonia biofiltration and community analysis of ammonia-oxidizing bacteria in biofilters

Biological removal of ammonia was investigated using compost and sludge as packing materials in laboratory-scale biofilters. The aim of this study is to characterize the composition of ammonia-oxidizing bacteria (AOB) in two biofilters designed to remove ammonia. Experimental tests and measurements included analysis of removal efficiency and metabolic products. The inlet concentration of ammonia applied was 20–100 mg m⁻³. Removal efficiencies of BFC and BFS were in the range of 97–99% and 95–99%, respectively. Periodic analysis of the biofilter packing materials showed ammonia was removed from air stream by nitrification and by the improved absorption of NH₃ in the resultant acidity. Nitrate was the dominant product of NH₃ transformation. Changes in the composition of AOB were examined by using nested PCR, denaturing gradient gel electrophoresis (DGGE) and sequencing of DGGE bands. DGGE analysis of biofilter samples revealed that shifts in the community structure of AOB were observed in the experiment; however, the idle phase did not cause the structural shift of AOB. Phylogenetic analysis revealed the population of AOB showed Nitrosospira sp. remains the predominant population in BFC, while Nitrosomonas sp. is the predominant population in BFS.     

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.