RESUMEN
Biofilm samples from a carbonaceous trickling filter (TF) were evaluated in bench scale reactors to determine their maximum potential denitrification rates. Intact, undisturbed biofilms were placed into 0.6 L bench-scale reactors filled with sterilized, primary clarifier effluent spiked with nitrate to a final concentration of 16-18 mg/L as N. Dissolved oxygen concentrations were maintained between 2 and 4 mg/L in the bulk aqueous phase. Nitrate loss from the reactors was monitored over a 5h period. Denitrification rates of 3.09-5.55 g-N/m(2)day were observed with no initial lag period. This suggests that the capacity for denitrification is inherent in the biofilm and that denitrification can take place even when oxygen is present in the bulk aqueous phase. There were no significant differences in denitrification rates per unit area of media (g-N/m(2)day) either between (a). experimental runs or (b). sampling locations over the trickling filter. This suggests that denitrification potentials are uniform over the entire volume of the full-scale TF. For wastewater treatment plants with TFs that currently nitrify downstream, this approach may be used to meet less stringent permitted discharge concentrations and may allow some facilities to postpone or eliminate construction of additional unit processes for denitrification.
Asunto(s)
Reactores Biológicos , Nitrógeno/aislamiento & purificación , Eliminación de Residuos Líquidos/métodos , Purificación del Agua/métodos , Biopelículas , Carbono/química , Filtración , Nitrógeno/químicaRESUMEN
The effect of alkalinity on nitrifying biofilm activity was determined by collecting 21-day-old biofilm samples from the top of a full-scale nitrifying trickling filter and evaluating bench-scale nitrate plus nitrite generation rates at (1) various initial carbonate alkalinity concentrations and (2) with four types of available alkalinity: carbonate only, phosphate only, phosphate plus hydroxide, and phosphate plus carbonate. Initial carbonate alkalinity concentrations were varied between 308 and 20 mg/L as calcium carbonate (CaCO3). Ammonia, nitrite, and nitrate concentrations were measured at time zero, 90 minutes, 180 minutes, and 270 minutes. Generation rates in grams of nitrogen per square meter per day were calculated for each time period and normalized against dry-weight biomass. Generation rates were impaired at initial carbonate alkalinity concentrations of 40 mg/L and lower (as CaCO3) and were unaffected at concentrations of 45 mg/L and greater. For reactor runs with different alkalinity types, ammonia, nitrite, and nitrate concentrations were measured at time zero and at 375 minutes. The type of alkalinity, carbonate versus phosphate, affected nitrification rates. When the carbonate alkalinity was less than 45 mg/L, nitrification rates were impaired regardless of the total alkalinity concentration. This effect seems to be independent of pH for the range of 6.92 to 7.99 evaluated here. This suggests that in addition to neutralizing the acid generated by the nitrification process, a minimum level of carbonate alkalinity is necessary to meet the ammonia-oxidizer's inorganic carbon requirement for cellular synthesis and growth.
Asunto(s)
Biopelículas , Nitrógeno/metabolismo , Reactores Biológicos , Concentración de Iones de Hidrógeno , Nitratos/análisis , Nitritos/análisis , Eliminación de Residuos LíquidosRESUMEN
Fluorescent in situ hybridization (FISH) was used to quantify the ammonia-oxidizing populations within intact biofilm samples collected from a full-scale nitrifying trickling filter (NTF). Ammonia, nitrite, and nitrate concentrations were measured for aqueous samples taken in conjunction with biofilm samples at multiple filter depths. The ammonia removal capability of collected biofilms was evaluated by transferring the biofilms to laboratory batch reactors. Nitrate plus nitrite generation rates were calculated for the full-scale NTF and for the bench-scale reactors. Correlation coefficients for individual sampling events, calculated by simple linear regression of FISH signal area and nitrate plus nitrite generation rates for the full-scale NTF, ranged from -0.882 to 0.984. Correlation coefficients obtained for FISH signal area and nitrate plus nitrite generation rates for the bench-scale reactors ranged from 0.853 to 0.994 when using probe Nso190 and from 0.919 to 0.986 when using probe Neu23a. Occasional differences between the number of ammonia-oxidizing bacteria quantified by the probe Nso190 versus the NEU23a probe with depth suggest that genera other than Nitrosomonas are present in the NTF.
Asunto(s)
Biopelículas , ADN Bacteriano/análisis , Hibridación Fluorescente in Situ , Nitrógeno/metabolismo , Amoníaco/química , Amoníaco/metabolismo , Bacterias/genética , Reactores Biológicos , Oxidación-ReducciónRESUMEN
The development of nitrifying biofilms collected from a full-scale nitrifying trickling filter was evaluated through the application of fluorescent in situ hybridization (FISH) and by quantification of nitrification rates in bench-scale reactors. Two sampling campaigns were conducted to evaluate the structure and function of biofilms between 14 and 70 days old. The structure, or number of ammonia-oxidizing bacteria, was quantified with Nso190. The function was quantified with bench-scale nitrification rates. The two assays were compared by calculating correlation coefficients by simple linear regression of the two data sets. The number of ammonia-oxidizing bacteria closely tracked activity data (linear correlation, r2 > 0.500). Changes in ammonia-oxidation capacity with time (7-day intervals) were mirrored by shifts in the percent of ammonia-oxidizing bacteria present. Nitrification rates did not correlate to the EUB338-probe stained area (r2 < 0.500), suggesting that nonnitrifying bacteria play a larger role in nitrifying biofilm ecology than previously thought. Dry-weight biomass accumulations did not correlate to either the EUB338-probe stained area or the bench-scale nitrification rates. This suggests that inert materials accumulate in the biofilms over time.