aerobic bacterial cultures

For the purpose of this section, aerobic bacterial cultures must be understood as all those processes that use reactions that are primarily aerobic, combined with, if required, anoxic periods (see denitrification) or anaerobic-anoxic (see biological phosphorus removal).

For a long time, water treatment plants using the anaerobic digestion system have been dimensioned empirically, using "golden numbers":150 to 200 litres of aeration tank or 100 litres of trickling filter per population equivalent…

A conventional approximation to designing and dimensioning these plants is now feasible thanks to the development of many studies on the degradation kinetics based on operating parameters which, starting with the elements emphasized in the general section of this chapter, now allow the following to be undertaken:

• calculation of the equilibrium achieved by any culture under established conditions (contact time, substrates, biomass...);

• and even simulating changes in discharge parameters over time when contact time (flow rate) and variations in supply concentrations have been defined over time (dynamic simulation or modelling).

These options are provided by a range of softwares. However, these softwares assume that we can:

• accurately characterise the biological reactor from a hydraulics viewpoint (an ideal combination of elements) (see bioreactors), and its clarifier (sedimentation and thickening function);

• clearly establishing the appropriate typology (see wastewater typology), and fluctuations in effluent concentration over time, in the knowledge that the more meticulous the description, the better the forecast.

Although the same biological mechanisms apply during sludge aerobic stabilisation, the relevant processes will only be described in the liquid sludge stabilisation.