Simultaneous nitrate and organic matter removal from salmon industry wastewater: the effect of C/N ratio, nitrate concentration and organic load rate on batch and continuous process.

Although simultaneous denitrification-anaerobic digestion has been studied extensively, the use of salmon effluents as organic matter source has received little attention. This study evaluated the effect of C/N ratio, nitrate concentration, and organic load rate (OLR) on simultaneous nitrate and organic matter removal using salmon effluents. The study was carried out in a batch reactor with suspended biomass at 37 °C and pH 7.5, and in continuous biofilm tubular reactors at 37 °C fed with a mixture of a synthetic substrate and a saline protein-rich salmon-plant effluent. The results of the batch and continuous experiments showed that nitrate abatement was greater than 95% at all the studied C/N ratios, without effect of the C/N ratio on NO(3)(-)-N transformation and ammonia production. An increase of nitrate concentration increased organic matter consumption as well as the hydrolytic rate. The organic matter reduction varied between 88% and 40% in the continuous process. For a continuous process, the increase of the OLR decreases the removal of organic matter.

The effect of sodium chloride on the denitrification of saline fishery wastewaters.

The effect of sodium chloride concentration (0.47-100 g l(-1)) on the rates of nitrate and nitrite reduction was studied at 37 degrees C and pH 7.5 in a batch reactor fed with a mixture (v/v) of salmon bloodwater and synthetic substrate and inoculated with biomass adapted to saline conditions (24 g NaCl per litre). NaCl inhibited the nitrate and nitrite reduction rates; the rates were increasingly inhibited at increasing NaCl concentrations in the studied concentration range. An empiric noncompetitive model adequately quantified the effect of NaCl on the rates of nitrate and nitrite reduction. The maximum reduction rate (R(D,max)) in a low salt medium and the inhibition constant (K(I)) were determined for each reductive step. The calculated kinetic parameters were R(D,max) = 25.5 +/- 0.74 mg N (g VSS h)(-1) and K(I)= 34.9 +/- 2.34 x 10(-3) g l(-1) for nitrate reduction and R(D,max) = 18.7 +/- 1.05 mg N (g VSS h)(-1) and K(I) = 62.5 +/- 3.32 x 10(-3) g l(-1) for nitrite reduction. NaCl has a greater effect on nitrite reduction rate than on the nitrate reduction rate.

Organic and nitrogenous matter effects on the denitrification of saline and protein-rich effluents.

The separate effect of protein concentration, nitrate concentration and carbon/nitrogen (C/N) ratio on the rate and efficiency of nitrate reduction was studied in batch reactors fed with a mixture of a synthetic substrate and a saline protein-rich salmon-plant effluent. At a constant nitrate concentration (40 mg L(-1)), the specific rate of nitrate removal decreased by 60% with increasing initial protein concentration (392 to 1900 mg L(-1)) and ammonification prevailed under these conditions; meanwhile at a constant protein concentration (1104 mg L(-1)), the specific rate of nitrate removal increased 58 times with increasing nitrate concentrations (0.5 to 78 mg L(-1)) and denitrification was the main route for nitrate reduction. The C/N ratio had an inverse effect on the specific rate of denitrification; the latter ranged from 227 to 563 [mg NO3(-)-N (g VSS d)(-1)] for a C/N ratio of 163 to 16 [mg TOC (total organic carbon) (mg NO3(-)-N)(-1)], respectively. On the other hand, the ammonia production rate was proportional up to a C/N ratio of 150.

The effect of volatile fatty acids on the nitrification of a saline effluent.

Anaerobically produced volatile fatty acids (VFA) may affect the nitrification yield. The effect of the type of VFA (acetic, propionic and butyric acid) on nitrification of a saline (24 g NaCl l(-1)) medium was studied. Nitritation (40 mg N-NH4+ l(-1)) and nitratation (100 mg N-NO2- l(-1) were assessed in batch cultures fed with different VFA (32 mg TOC l(-1)). The effect of increasing VFA concentrations on nitrification was studied in batch reactors fed with an initial concentration of 40 mg N-NH4+ l(-1) and C/N ratios of 0, 2, 4, 8 and 16 as well as in a continuous mixed flow reactor operated at 30 degrees C and pH 7.5 and fed with 500 mg N-NH4+ l(-1) and 500, 1000, 2000, and 4000 mg TOC l(-1). Nitritation and nitratation rates were decreased by organic matter; inhibition increased with the VFA size. A non-competitive inhibition model fitted the experimental data on nitrification rate reduction at increasing acetic add concentrations; inhibition constants were 685 mg acetic acid l(-1) for ammonia oxidation and 74.3 mg acetic acid l(-1) for nitrite oxidation. The continuous reactor's nitrifying ability decreased from 82% to 40% at C/N ratios 1 and 4, respectively. Loss of nitrification, but a 50% ammonia removal was found at a C/N of 8. It was concluded that the nitrification rate reduction is proportional to the VFA molecular weight and that an increase in VFA concentration diminishes the nitrifying ability due to kinetic limitations.

Molecular analysis of the community structure of nitrifying bacteria in a continuous-flow bioreactor.

We herein report the diversity and relative abundance of chemolithotrophic nitrifying bacteria in a continuous-flow bioreactor using 16S-ribosomal RNA quantitative dot-blot hybridizations. About 14.9% of the total bacterial population, determined by epifluorescence microscopy in the bioreactor suspended phase, was represented by nitrifying bacteria. Of this fraction, ammonia- and nitrite-oxidizing bacteria accounted for 10% and 90%, respectively, the latter group being mostly Nitrospira-like. On the other hand, the nitrifiers adhesion/colonization capacity on polyethylene surfaces as evaluated by scanning electron microscopy and hybridizations analyses was 12.6% of the total bacterial community adhered. Finally, in spite of the relatively small contribution of nitrifiers to the total bacterial abundance in the bioreactor, we determined a mean ammonia removal rate of 170.48 +/- 8.29 mg N l(-1) d(-1); thus, the low percentage of ammonia-oxidizing bacteria, was not limiting the bioreactor performance.

Ammonia inhibition in the anaerobic treatment of fishery effluents.

Inhibition of the organic matter consumption rate of a saline and rich proteic effluent by free ammonia was assessed in anaerobic filters at 37 degrees C. Inhibition of substrate (total organic carbon, TOC) consumption rate by ammonia was fitted by the Luong and noncompetitive models. Calculated kinetic parameters using the Luong model were maximum specific growth rate, micromax = 0.28 day(-1); average saturation constant, Ks = 568 mg TOC/L; Luong inhibition parameter, KNH3 = 1707mg ammonia-nitrogen (NH3-N)/L; and Luong exponent, gamma = 0.283 and the noncompetitive calculated parameters were umax= 0.26 day(-1), Ks = 703 mg TOC/L, and inhibition parameter, INH3 = 325 mg NH3-N/L. The Luong and noncompetitive models predicted 50% inhibition of the substrate consumption rate at ammonia concentrations of 147 and 325 mg NH3-N/L, respectively, suggesting biomass adaptation to the ammonia concentration (80 mg NH3-N/L as average) at which the anaerobic filters were previously operating. Ammonia formation by anaerobic digestion of fishing effluent would produce a maximum of 65.1 and 58.6% inhibition of the efficiency, predicted by the Luong and noncompetitive models, respectively. Ammonia influence on the digestion steps was determined by comparing fishing effluent with volatile fatty acids as substrates. The noncompetitive model predicted a 50% inhibition of methane production rate at ammonia concentrations of 196.6 and 188.6 mg NH3-N/L for fishing effluent and volatile fatty acids, respectively, suggesting that the methanogenic step is the one most affected by ammonia.

Growth of methylaminotrophic, acetotrophic and hydrogenotrophic methanogenic bacteria on artificial supports.

The efficiency of organic matter degradation in attached biomass reactors depends on the suitable selection of artificial support for the retention of bacterial communities. We have studied the growth on glass and clay beads of methylaminotrophic, acetotrophic and hydrogenotrophic methanogenic bacterial communities isolated from anaerobic reactors. Bacterial counts were performed by the standard MPN technique. Experiments were performed in 50 ml vials for 12 days at 35 degrees C. Increase in the counts of methylaminotrophic and hydrogenotrophic methanogens occurred on both glass and clay beads. The latter support material also stimulated the growth rate of methylaminotrophic methanogens.

Optimization of in vitro flux through hairless mouse skin of cidofovir, a potent nucleotide analog.

The in vitro flux (4-8 h) of cidofovir (1-[(S)-3-hydroxy-2-(phosphonomethoxy)propyl]cytosine) was measured across full-thickness hairless mouse skin to evaluate potential formulations for local treatment of herpes virus infections. The effects of propylene glycol, isopropyl alcohol, oleic acid, pH, and cidofovir concentration were examined. In addition, several prototype aqueous gel formulations were studied. Flux values (4-8 h) increased linearly with cidofovir concentration in both solution and gel formulations. Removal of the stratum comeum by tape stripping increased the flux by approximately 400-fold, whereas pH (4.5 versus 7) had little effect on flux. The presence of propylene glycol, isopropyl alcohol, or their combination did not significantly increase mean flux (p > or = 0.05). Pretreatment of the skin with oleic acid resulted in a significant enhancement of cidofovir flux (p < or = 0.01). From the measured flux values, the calculated concentration of cidofovir achievable in the viable epidemis from a 1% cidofovir gel formulation was approximately 14 micrograms/mL, which is comparable to the in vitro 50% inhibitory dose (ID50) values for herpes simplex viruses HSV-1 and HSV-2.