The common features of the conventional sequential activated sludge (SBR) and ICEA system are the following:

• Wastewater continuously flowing in the aeration tank

• Wastewater treatment is carried out in a continuous mode

• The treatment is carried out in several steps

• Sludge sedimentation is carried out in the biological reactor

Wasted sludge and return activated sludge streams have a different:

• Soluble BOD concentration

• Nitrate concentration

• MLSS concentration

• Flowrate value

For an activated sludge process, when F/M ratio increases:

• The BOD removal decreases

• The volume of the aeration tank necessary to carry out the process increases

• The extent of endogenous decay is decreased

• The sludge retention time (SLR) increases

The net biomass production rate in the biological treatment of wastewater is dependent on:

• The temperature of wastewater

• The phosphate concentration

• BOD concentration and endogenous decay

• The concentration of microorganisms

The removal of the carbonaceous BOD of WW by means of biological treatment:

• Can be performed by aerobic chemoheterotrophic bacteria

• Is usually performed by means of algae

• May be carried out using anaerobic processes

• Is the result of the autotrophic bacteria metabolism

Regarding the biological removal of BOD from WW, it is true that:

• The microorganisms are more effective at lower temperatures

• The rate of substrate utilization increases as microbial growth rate increases

• Nitrate can be used as electron acceptor

• The presence of nitrogen and phosphorus in the wastewater is required

The rate of microbial growth:

• Increases sharply as the concentration of substrate increases

• Increases with temperature

• Is higher in the anaerobic processes than in the aerobic

• Increases with the concentration of substrate until it reaches a maximum value

In activated sludge process, the sludge retention time (SLR):

• Is equivalent to the average retention time of the microorganisms in the system formed by the aeration tank and the secondary clarifier

• Is equal to the hydraulic retention time of the microorganisms in the secondary clarifier

• Is the average time that microorganisms remain in the aeration tank

• Can be increased by increasing the flowrate of wasted sludge

Regarding the sludge treatment in WW treatment facilities, it is true that:

• It includes the composting of the sludge

• Sludge coming from any type of biological treatment operation needs to be further stabilized

• Sludge coming from any type of biological treatment operation needs to be further treated

• Its main objective is the recycling of sludge in the own plant

Regarding the combination of attached growth and activated sludge processes, it is true that:

• The combined processes require more energy than the activated sludge processes

• The combined processes allow to reach treated WW with similar or lower pollution level than that of the activated sludge processes

• The combined processes generate a sludge more difficult to settle than that of the activated sludge processes

• The combined processes are more resistant than activated sludge processes to shock organic loads