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The denitrification rate of bacteria indigenous to aquifers with different nitrate concentrations was investigated. The objective was to test how high nitrate loads affect community composition and select for enhanced nitrate reduction rates among denitrifying strains. Groundwater bacteria were isolated from two aquifers with high in situ concentrations of nitrate (24.1 and 35.2 mg NO3−‐N 1−1) and one aquifer with a lower in situ concentration (6.3 mg NO3−‐N 1−1). The isolates were characterized with respect to 15 colony and cell morphological and 8 physiological features. The frequency of heterotrophic denitrifiers of all isolated strains was 45–50% in the nitrate contaminated aquifers compared to slightly more than 20% in the uncontaminated aquifer. Kinetics of nitrate reduction were measured by using progress curves ot nitrous oxide production. Bacterial respiration was measured to determine whether proposed differences in denitrification rates were due to differences in carbon utilization. Strains from the aquifers with enhanced nitrate concentrations showed shorter lag periods and higher growth rates than strains from the aquifer with low nitrate concentration. Denitrification rates for unamended incubations varied between 0.10 and 0.42 ml cells−1 day−1 and between 0.42 and 2.10 ml cells−1 day−1 for the glucose amended incubations. The average denitrification rate for the strains from the contaminated sites was 2‐fold higher than for the strains from the uncontaminated site, and glucose amendment increased the difference to 2.5‐fold. The differences in rates were not explained by differences in carbon utilization. The strains from the contaminated sites reduced more nitrate per unit of carbon dioxide produced than the strains from the uncontaminated aquifer. This suggests that strains in soils which have been heavily N‐fertilized may have developed denitrification reductases with optimum activities at high in situ concentrations of nitrate.

The potential occurrence of guaiacol producing Alicyclobacillus in sugar products and in the sugar production process was evaluated. Final product testing revealed that granulated sugar products showed random background contamination while liquid sugar products were free from guaiacol producing bacteria. Contamination tracing in the sugar factory process showed that beet soil is a primary contamination route to a sugar factory. The bacteria were completely eliminated in the juice purification at all evaluated factories. Random re-contamination was observed in wash syrups from the A-station. Environmental contamination from air and surfaces could not be observed while 20% of human test subjects showed skin contamination of guaiacol producing bacteria. A successful elimination of guaiacol producing bacteria from sugar products was concluded to be unfeasible due to random re-contamination events in the sugar production process. It is suggested that the goal must be to evaluate realistic technical solutions located at the last step of the supply chain. Thermal and non-thermal treatment techniques are available and among those UV-treatment appears to be a promising elimination technique for TAB (thermophilic acidophilic bacteria) and GP-TAB.

The investigations presented in this work were carried out in order to further deepen the knowledge about nitrite pathways in the area of sugar beet extraction. The article consists of two parts with different experimental set-up: the first part focuses on laboratory trials in which the fate of nitrate and nitrite was studied in a so-called mini-fermenter. These trials were carried out using juice from the hot part of the cossette mixer of an Agrana sugar factory in Austria. In the experiments, two common sugar factory disinfectants were used in order to study microbial as well as microbial-chemical effects on nitrite formation and degradation caused by bacteria present in the juice. The trials demonstrated that the direct microbial effect (denitrification) on nitrite degradation is more pronounced than the indirect microbial-chemical effect coming from pH value decrease by these bacteria and subsequent nitrite loss. The second part describes the findings from laboratory experiments and full scale factory trials using a mobile laboratory set-up based on insulated stainless steel containers and spectrophotometric detection of nitrite in various factory juices. The trials were made at two Nordzucker factories located in Finland (factory A) and Sweden (factory B). The inhibiting effect of the two common sugar factory disinfectants on nitrite formation was evaluated in laboratory trials, whereas the full scale trials focused on one disinfectant. Other trials to evaluate potential contamination sources of thermophilic nitrite producing bacteria to the extraction system, reactivation of nitrite producing bacteria in raw juice and the effect of a pH gradient on bacterial nitrite activity in cossette mixer juice are also reported.

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