The removal of the carbonaceous BOD of wastewater by means of biological treatment Can be performed by aerobic chemoheterotrophic bacteria May be carried out anaerobic processes Is usually performed by means of algae Is the result of the autotrophic bacteria metabolism.
The phosphorous removed by biological treatment needs BOD availability in the wastewater A high concentration of nitrate in the wastewater The combination of aerobic and anaerobic steps A secondary clarifier.
Common features of activated sludge processes and lagoon processes are Microorganism are suspending in the wastewater The biological treatment is mainly conducted in aerobic conditions Aeration of the wastewater is achieved by natural means Recirculation of the sludge is continuously carried out.
The rate of microbial growth: Is higher in the anaerobic processes than in the aerobic Increases with the concentration of substrate until it reaches a maximum value Increases with temperature Increases sharply as the concentration of substrate increases.
In general, biodegradability of organic compounds increases As the complexity of the molecule decreases As the number of double bonds in the molecule increases As the number of carbon atoms in the molecule increases With the presence of halogen elements (Cl, Br, …).
The extended aeration activated sludge processes Show high values of MLSS concentration in the aeration tank Allow the sludge stabilization by means of recirculating it to the primary clarifier Let to reduce the energy requirements of the biological reactor Generate higher amounts of sludge per kg of BOD removed than the medium loading processes.
The saturation oxygen concentration in wastewater Is always lower than in clean water Depends on the value of KLa transfer coefficient Depends only on the MLVSS concentration in the bioreactor Decreases the greater is the altitude at which the WWTP is located .
In the fraction of COD in wastewater rbCOD refers to particle biodegradable organic pollutants bCOD is usually lower than BOD sbCOD is the soluble and biodegradable COD nbCOD is the COD that cannot be degraded by the microorganism.
An activated sludge process uses a F/M value of 0.07 kg BOD/kg MLSS. Day and a SRT of 5 days; so, it can be
said: It is a low loading process It is a high loading process It is probably that the BOD concentration of the influent is low It is a medium loading process.
For an activated sludge process, when F/M ratio increases The volume eof the aeration tank necessary to carried out the process increases The sludge retention time (SLR) increases The BOD removal decreases The extent of endogenous decay is decreased .
In the design of secondary clarifiers Overflow rate is usually calculated tanking into account the sludge recycle flowrate Suspended solids are more difficult to sttle than those of the primary clarification Concentration of the MLSS in the aeration tank must be taken into account Solid loading is usually calculated taking into account the sludge recycle flowrate.
In a plug flow aeration tank used in an activated sludge process The oxygen needs are higher in the first part of the tank The microorganism concentration is the same in any point of the tank The BOD concentration decreases as the wastewater flows throughout the tank The BOD concentration is the same in any point of the tank.
In the activated sludge processes, higher flowrates of sludge recycle Decreases the oxygen requirements of the biological reactor Increase the F/M ratio of the process Improve the efficiency of the secondary clarification Decrease the amount of wasted sludge .
n an activated sludge process, the sludge retention time (SLR): Is equal to hydraulic retention time of the microorganisms in the secondary clarifier Can be increased by increasing the flowrate of wasted sludge Is the average time that microorganisms remain in the aeration tank Is equivalent to the average retention time of the microorganisms in the system formed by the
aeration tank and the secondary clarifier.
Biological treatment in oxidation ditchs May be used medium loading processes Is mainly used for low loading processes Is characterized because the substrate concentration, biomass and oxygen is the same at any
point in the reactor Can easily combine anoxic and aerobic areas .
The microorganisms involved biological treatment of a wastewater treatment plant: Only grow under aerobic conditions May belong to different species Form an ecosystem which does not change over time Grow spontaneously in the bioreactor .
Nitrifying bacteria Use organic material as carbon source Use redox reactions as energy source Grow faster then the chemoheterotrophic bacteria Are chemoautotrophs organisms .
In the activated sludge processes, sludge recycle is necessary in order to Have an adequate concentration of microorganisms in the aeration tank Have an enough flow of water in the secondary clarifier Get an adequate value for the sludge retention time (SLR) Have an adequate BOD concentration in the bioreactor.
The suspended solids existing in the aaeration tank Are only microorganisms May be inorganic ions such as nitrate Are mainly microorganisms Are only alive microorganisms.
Wasted sludge and return activated sludge streams have a different Soluble BOD concentration MLSS concentration Flowrate value Nitrate concentration.
Sequential activated sludge (SBR) systems Requiere less control than concentional activated sludge systems Are characterized because BOD and microorganism concentrations change throughout the time of
treatment Are specially recommended to treat discontinuos flows with large variation in pollutant
concentrations Work in non-steady-state .
Membrane bioreactor processes (MBR) Are cheaper than conventional activated sludge processes Allow to obtain very high quality effluent Are mainly used for water reclamation applications Need secondary settling.
Between the objectives of the wastewater biological treatment may be the following: to remove the biodegradable organic solid pollutants to reduce the concentration of nonbiodegradable pollutants of the wastewater to decrease the COD of the wastewater to reduce the pH of the wastewate.
Regarding the microbial metabolism is true that: wastewater treatment may be conducted using only photoautotrophic organisms there are heterotrophic bacteria with aerobic metabolism and others with anaerobic metabolism photoautotrophic organisms uses light as energy source and inorganic carbon to generate new
cells chemoheterotrophic organisms uses light as energy source and organic carbon to generate new
cells.
An activated sludge process uses a F/M value of 0.07 kg BOD/kg MLSS.day and a SRT of 5 days; so, it can be
said: it is a high loading process it is a low loading process it is probably that the BOD concentration of the influent is low it is a medium loading process.
The common features of the conventional sequential activated sludge (SBR) and ICEA system are the
following: the treatment is carried out in several steps wastewater treatment is carried out in a continuous mode sludge sedimentation is carried out in the biological reactor wastewater is continuously flowing in the aeration tank.
In the aeration of the biological reactor: A higher temperature increases the concentration of dissolved oxygen in the wastewater The selection of the aeration device depends on the depth of the aeration tank SO TR values of the aeration systems are always higher than aotr values A higher agitation of the wastewater decreases the aeration efficiency.
O xygen transfer on the aeration tank depends on: The concentration of pollutants in the wastewater The type of microorganism that work in the biological treatment The surface to volume ratio of the air bubbles The temperature of the wastewater .
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