Difference between attached growth and suspended growth systems
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In a well-maintained aeration tank, the bacteria are concentrated in the flocculent material of the activated sludge, although some always occur free in the wastewater. The flocs are formed from aggregates of non-living organic polymers
that are probably secreted by bacteria. They have an open porous structure, and are sufficiently robust to withstand the shear forces created by water movement, during aeration of the tanks. They vary in size from less than 10 µm up to 1mm (1000 µm). The bacteria are adsorbed on to the internal and external surfaces of the floc, and a medium sized floc may harbour several million bacteria. Immediately after the wastewater enters the aeration tank, the fine particulates, colloidal particles and large molecules, become entangled with, and adsorbed to, the floc material. The bacteria of disaggregated flocs may continue to grow when the oxygen concentration of the mixed liquor is only 0.6 mg O2/l, whereas to ensure this concentration on the inside of a large floc, a mixed liquor oxygen concentration of 1.2 – 2.0 mg O2/l may be required. In a well-operated plant, most of the bacterial biomass is associated with the activated sludge floc. By filtering and drying a sample of the suspended solids, and then weighing the dried residue, a measure of the biomass may be obtained. It is referred to as the Mixed Liquor Suspended Solids.
Suspended growth processes:
The microorganisms responsible for treatment are maintained suspension
by appropriate mixing methods.
Attached – growth processes :
The microorganisms are attached to some inert medium, such as rock, slag or specially designed ceramic or plastic materials.
Both processes have its own adv and disadv. Like suspended gr. it requires larger area, no small equipments involved, monitoring is tough etc. whereas in attached system small equipments r involved, no larger area necessary, maintainence is easier but labour intensive, cleaning systems available r mutiple n so on....Pretreatment processes, Type of filter media, Recirculation rate , Hydraulic and organic loadings applied to the filter, Underdrainage and ventilation systems play an imp role here....
that are probably secreted by bacteria. They have an open porous structure, and are sufficiently robust to withstand the shear forces created by water movement, during aeration of the tanks. They vary in size from less than 10 µm up to 1mm (1000 µm). The bacteria are adsorbed on to the internal and external surfaces of the floc, and a medium sized floc may harbour several million bacteria. Immediately after the wastewater enters the aeration tank, the fine particulates, colloidal particles and large molecules, become entangled with, and adsorbed to, the floc material. The bacteria of disaggregated flocs may continue to grow when the oxygen concentration of the mixed liquor is only 0.6 mg O2/l, whereas to ensure this concentration on the inside of a large floc, a mixed liquor oxygen concentration of 1.2 – 2.0 mg O2/l may be required. In a well-operated plant, most of the bacterial biomass is associated with the activated sludge floc. By filtering and drying a sample of the suspended solids, and then weighing the dried residue, a measure of the biomass may be obtained. It is referred to as the Mixed Liquor Suspended Solids.
Suspended growth processes:
The microorganisms responsible for treatment are maintained suspension
by appropriate mixing methods.
Attached – growth processes :
The microorganisms are attached to some inert medium, such as rock, slag or specially designed ceramic or plastic materials.
Both processes have its own adv and disadv. Like suspended gr. it requires larger area, no small equipments involved, monitoring is tough etc. whereas in attached system small equipments r involved, no larger area necessary, maintainence is easier but labour intensive, cleaning systems available r mutiple n so on....Pretreatment processes, Type of filter media, Recirculation rate , Hydraulic and organic loadings applied to the filter, Underdrainage and ventilation systems play an imp role here....
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