Michael J. Bazin

Dynamics of nitrification in a continuous flow system

Abstract Ammonium sulphate was added at constant rates to a column containing a mixture of glass beads and marble chips inoculated with the nitrifying bacteria, Nitrosomonas europaea and Nitrobacter agilis . Changing the rate of NH 4 + addition caused nitrite and nitrate concentrations in the outflow to stabilize at characteristic steady state values after brief transition periods. The steady state concentrations were inversely related to the flow rate. The transition phases were characterized by overshoots in the concentrations of nitrite and nitrate when the flow was reduced and a smooth monotonic change to the new steady state values when it was increased. Three mathematical models were developed based on several simplifying assumptions and tested with the data. The best fit was obtained when it was assumed that growth of the organisms could be described by a modification of the Verhulst-Pearl logistic equation.

Distribution of bacteria in a continuous-flow nitrification column

Nutrient solution containing (NH4)2SO4 was supplied at a constant rate to Nitrosomonas europaea and Nitrobacter agilis growing in a column packed with glass beads. Conversion of NH4+ to NO2− and NO3− was incomplete indicating that growth of the bacteria was not nutrient limited. After 7 months the column was dismantled and the arrangement of the bacteria on the beads examined using a scanning electron microscope. Nitrifying bacteria were found only in the upper regions of the column. They occurred most commonly in monolayers, less commonly in layers of about 20 cells and rarely in piles of about 100 cells in depth. Further down the column the glass beads were covered in a layer of slime and no bacteria were seen. This suggests that growth of the nitrifiers was neither controlled by diffusion of metabolites through a microbial film nor limited by competition between the bacteria for space on the surface of the glass beads.

Nitrification in a column reactor: Limitations, transient behaviour and effect of growth on a solid substrate

Abstract Metabolic inhibition, insufficient O 2 , CO 2 and trace metals, pH and bacterial wash-out were investigated as potential causes of incomplete nitrification of ammonium supplied to column reactors containing Nitrosomonas europaea and Nitrobacter agilis . Of these only the last two factors offered a partial explanation of the phenomenon. The transient behaviour of the columns after flow rate and nutrient perturbations could be classified as either short term ( 20h). The major properties conferred by adhesion of the nitrifiers to a solid substrate in a nitrification column were the ability to respond rapidly to environmental changes, asymmetric transient responses and increased likelihood of multiple steady states.

Behaviour of Dictyostelium discoideum amoebae and Escherichia coli grown together in chemostat culture.

When Dictyostelium discoideum amoebae and Escherichia coli were grown together in chemostat culture damped oscillations in the popullation densities of the organisms occurred followed by a sudden increase in bacterial numbers and a concommitant decrease in the number of amoebae. After the system had come to equilibrium altering the dilution rate resulted in a monotonic change in the experimental variables to new steady state levels. A square wave increase in the concentration of limiting nutrient in the feed medium during the oscillatory phase of culture produced a sinusoidal response indistinguishable from that prior to the perturbation. The results are more complicated than those predicted by simple models of microbial predator-prey dynamics although they correspond most nearly to models which incorporate saturation kinetics.

Nonsteady state studies of nitrification in soil: Theoretical considerations

Abstract Equations are derived for the reactions NH 4 + → NO 2 − → NO 3 − in a column of inert particulate material containing Nitrosomonas and Nitrobacter and through which a solution is flowing with constant flow rate. The equations are solved analytically for two different assumptions about the growth rates of the nitrifying organisms. The effects of factors such as diffusion, ion exchange and fixation of nutrients by nitrifiers are neglected. The work generalizes a paper of McLaren and corrects a second by the same author.

Cellulose degradation in a structured ecosystem which is analogous to soil

Trichoderma reesei was grown in a vertical glass column filled with a mixture of glass beads and cellulose. A nutrient solution was supplied to the column at a constant flow rate and the effluent solution was collected in a refrigerated fraction collector. Cellulase and β-glucosidase activities were first detected in the effluent about 50 h after inoculation and were still present in the effluent collected 300 h later.

Growth of Trichoderma reesei and the production of cellulolytic enzymes in a continuous-flow column

Trichoderma reesei (Q.M. 9414) was grown in a vertical glass column filled with a mixture of glass beads and cellulose. The column was aerated and maintained at 25° C. A carbon-free nutrient solution, or nutrient solution plus glucose, was passed down the column at a constant flow rate for several 100 h. The effluent solution was collected in a refrigerated fraction collector and assayed for carboxymethylcellulase activity, β-glucosidase activity, extracellular protein and reducing sugar. The pH of the effluent solution and the CO2 content of the effluent gas were also, measured. At the end of one experiment the column was dismantled and the fungus, glass beads and residual cellulose examined by scanning electron microscopy.A mathematical model was formulated by assuming that the column could be approximated to a series of wellmixed flow-through compartments. The model was used to simulate the dynamics of the system and the results generated gave a reasonable qualitative description of some of the experimental results.