On-Line Nitrification Monitoring in Activated Sludge with a Titrimetric Sensor

Abstract

Nitrification is an important part of activated sludge wastewater treatment processes in view of the severe effluent discharge standards for nitrogen (N) that are nowadays imposed by legislation. Several on-line analyzers have been developed to achieve better monitoring and control of biological N removal processes. In this paper, the results of on-line experiments on a pilot-scale activated sludge plant with a recently developed titrimetric sensor are described. Based on a titration of an activated sludge sample, it was possible to estimate the ammonium N (NH4 +-N) concentration in the activated sludge, without the need for any sample pretreatment. The NH4 +-N concentrations obtained with the titration method were consistent with the NH4 +-N concentrations measured with an on-line analyzer, which was operated on the effluent of the pilot plant. Contrary to chemical on-line NH4 +-N analyzers, the titration method provides data about the nitrification rate of the activated sludge.

New Insights into Methyl Bromide Cooxidation by Nitrosomonas europaea Obtained by Experimenting with Moderately Low Density Cell Suspensions

“…In the presence of 0.44 mM MeBr, the initial rate of MeBr oxidation responded to most incremental changes in the NH 4 ϩ concentration and decreased at NH 4 ϩ concentrations between 5 and 2.5 mM and between 2.5 and 1 mM. When we examined the ratio of amount of MeBr oxidized to amount of NO 2 Ϫ produced (M/N ratio), we found that the maximum initial rates of MeBr oxidation occurred at almost identical M/N ratios (the M/N ratios were 0.24, 0.21, and 0.21 for MeBr concentrations of 0.44, 0.22, and 0.11 mM, respectively) regardless of the MeBr and NH 4 ϩ concentrations. We also observed another trend: M/N ratios of Ն0.30 and Ͻ0.1 were associated with suboptimal initial rates of MeBr oxidation.…”

“…Previously described studies of cooxidation of halogenated hydrocarbons by NH 3 -oxidizing bacteria have focused primarily on determining the range of compounds cooxidized by N. europaea (6,7,13,(16)(17)(18) and, to a lesser degree, on kinetic parameters (12). The majority of these studies were conducted by using short incubation periods (Յ1 h), high-density cell suspensions (10 9 to 10 11 cells ml Ϫ1 ) exhibiting high rates of NO 2 Ϫ production (ϳ3 mol ml Ϫ1 h Ϫ1 ), and pH values considered to be optimal for NH 3 oxidation (pH 7.8 to 8.0). Comprehensive studies have not been performed yet with lowerdensity cell suspensions (Ͻ10 8 cells ml Ϫ1 ) that exhibit NH 3 oxidation rates more typical of environments like nitrifying bioreactors (ϳ0.1 mol of NH 4 ϩ ml Ϫ1 h Ϫ1 ) (1,2), in which cooxidation may occur (15,23).…”

“…The majority of these studies were conducted by using short incubation periods (Յ1 h), high-density cell suspensions (10 9 to 10 11 cells ml Ϫ1 ) exhibiting high rates of NO 2 Ϫ production (ϳ3 mol ml Ϫ1 h Ϫ1 ), and pH values considered to be optimal for NH 3 oxidation (pH 7.8 to 8.0). Comprehensive studies have not been performed yet with lowerdensity cell suspensions (Ͻ10 8 cells ml Ϫ1 ) that exhibit NH 3 oxidation rates more typical of environments like nitrifying bioreactors (ϳ0.1 mol of NH 4 ϩ ml Ϫ1 h Ϫ1 ) (1,2), in which cooxidation may occur (15,23). Furthermore, the sustainability of cooxidation and the relationship of cooxidation to NO 2 Ϫ production could not be examined adequately in our previous studies because total ammonium (NH 4 ϩ plus NH 3 ) became limiting very quickly because of high rates of consumption and because a decrease in pH reduced NH 3 availability.…”

“…Thus, the fate of MeBr has some applied significance, and this compound also is an excellent model compound for examining cooxidation by N. europaea because the end products of MeBr cooxidation (formaldehyde and HBr) have been identified (11,12,17). The objective of this study was to examine cooxidation of MeBr by a moderately low-density suspension of N. europaea cells (ϳ6 ϫ 10 7 cells ml Ϫ1 ) that oxidized NH 3 at a rate similar to the rates measured in nitrifying bioreactors (1,2).…”

“…The reactions were started by adding 1-ml aliquots of cells suspended in phosphate buffer (pH 7.0), and MeBr disappearance and NO 2 Ϫ production were monitored as described above. (iv) Influence of inhibition of protein synthesis on NO 2 ؊ production during MeBr cooxidation. Either chloramphenicol (final concentration, 200 or 400 g/ ml) or kanamycin (10 to 50 g/ml) was dissolved in 50 mM phosphate buffer (pH, 7.2).…”