PES Process Description of a Conventional Activated Sludge System (CAS)
SCREENING CHAMBER
Raw sewage shall pass through the bar screen, wherein large solids are trapped on it and disposed offsite as solid waste.
EQUALIZATION
Raw wastewater is allowed to flow by gravity to the equalization, wherein varying concentration of pollutants and flowrate is homogenized or equalized. Homogenization is achieved through the introduction of air into the tank to create turbulence. This action likewise results in partial BOD removal of the waste stream by resident microorganisms.
COAGULATION (Optional)
Incoming wastes from equalization shall be diverted to the Coagulation Tank. Coagulation is the first step in breaking up the oil emulsion of the waste stream and promote the clustering of the solids and grease. Acidic coagulant chemicals such as Aluminum Sulfate or Polyaluminum Chloride (PAC) shall be dosed into the Coagulation Tank and mixed rapidly with the incoming wastes. This initiates the coagulation process, which chemically breaks down the oil emulsion and agglomerates the grease into loose clusters or lumps.
FLOCCULATION (Optional)
From the Coagulation Tank, the wastes shall flow into the Flocculation Tank. The next treatment step consists of dosing a flocculant chemical, usually an anionic polymer, to further enlarge the clusters and lumps formed earlier in the coagulation process. As the umps become bigger, it increases its settleability – in the case of the grease and other suspended solids, or floatability. Slow mixing is performed to avoid destroying the flocs being formed out of the coagulated lumps
The pH shall likewise be adjusted to a level suitable for discharge into the Sewage Treatment Plant (STP). A chemical metering pump shall dose caustic soda to neutralize the pH. A pH controller shall be installed to control the operation of the chemical metering pump and avoid overdosing of caustic soda. After pH adjustment, the wastewater containing metal precipitates are dosed with a coagulant such as aluminum sulfate or polyaluminum chloride (PAC). The coagulant enables the precipitates to agglomerate together forming microflocs. Suspended solids and oils likewise attached to these clusters. Air mixing is provided by an air blower.
INDUCED AIR FLOTATION
Induced Air Flotation (IAF) is a highly efficient process for removal of oils, greases and suspended solids, which is further enhanced by chemical flocculation. The IAF disc features a diffuser that incorporates fine holes near it perimeter for ultra-fine bubble diffusion into the liquid. The motor spins the unique diffuser disc, creating a low-pressure zone at disc’s diffuser ports. The disc draws air above the liquid surface, which then precedes down trough the draft tube, into the disc and out of the submerged diffuser ports. As each bubble exits trough a hole in the end of the diffuser disc, the spinning disc shears it into microscopic air bubble fragments measuring form 10-100 microns in diameter. These air bubbles adhere to minute solids such as oil and grease. The bubbles slowly rise to the surface around the unit, bringing the solids to the surface. The floated solids are then skimmed off by the scum skimmer, while the clear effluent flows under a weir towards the Aeration tank. The Induced Air Flotation System is expected to remove most of the oils and suspended solids, while having a significant impact on BOD reduction as well.
AERATION TANK
From the Induced Air Flotation, the treated effluent flows into the Aeration Tank in parallel operation, wherein aerobic and facultative bacterial culture is maintained in complete suspension. The activated-sludge process involves the production of an active mass of microorganisms capable of degrading organic
wastes in the presence of oxygen. The Aeration tanks are equipped with air blowers and fine bubble diffusers to provide the required oxygen for sustained bacterial growth and activity. Bacterial cells and inorganic matter formed during this activity shall form bioflocs that will settle in the Settling Tank.
A minimum mixed liquor suspended solids (MLSS) concentration shall be maintained to ensure the complete biodegradation of the estimated Biological Oxygen Demand (BOD) load. This is achieved by returning a portion of the sludge from the Settling Tank to the Aeration Tank. The purpose of the Return Activated Sludge (RAS) is to maintain a sufficient level of biomass in the Aeration Tank so that the required degree of treatment can be obtained in that time interval desired. The sludge recirculation rate may be increased or decreased depending on the influent BOD level, thus lending flexibility to the treatment in various field conditions.
SETTLING TANK
From the Aeration Tank, the mixed liquor overflows to the Settling Tanks in parallel operation for the separation of bioflocs from the supernatant. Efficient removal of these bioflocs from the wastewater shall result in a well-clarified stable effluent, which is in low BOD and suspended solids. A certain mean-cell residence time is maintained to enable the MLSS to form settleable bioflocs at the bottom hopper of the Settling Tank. A portion of the settled sludge at the hopper is recycled back to the Aeration Tank as seed biomass in order to maintain the required MLSS concentration. Less sludge volume is generated in this process, resulting in reduced sludge pumps out. Treated effluent shall be suitable for discharge to Class C waters.
AEROBIC SLUDGE DIGESTION
Excess sludge from the Induced Air Flotation and Settling Tank is further treated in the Sludge Digestion Tank where the endogenous phase of the microorganism occurs. In the Endogenous phase, the microorganisms are forced to metabolize their own protoplasm in the absence of sufficient nutrients. This results in a substantial reduction of the sludge volume as the surviving cells “digest” each other for sustenance.
CHLORINE CONTACT CHAMBER
Biologically-treated effluent shall then flow into the Chlorine Contact Chamber, wherein liquid chlorine is dosed inline to destroy pathogens in the effluent prior to discharge or reuse. The disinfected effluent maybe recycled as gray water for non-potable uses such as landscape irrigation and toilet flushing after installing a simple tertiary filtration system.
SCREENING CHAMBER
Raw sewage shall pass through the bar screen, wherein large solids are trapped on it and disposed offsite as solid waste.
EQUALIZATION
Raw wastewater is allowed to flow by gravity to the equalization, wherein varying concentration of pollutants and flowrate is homogenized or equalized. Homogenization is achieved through the introduction of air into the tank to create turbulence. This action likewise results in partial BOD removal of the waste stream by resident microorganisms.
COAGULATION (Optional)
Incoming wastes from equalization shall be diverted to the Coagulation Tank. Coagulation is the first step in breaking up the oil emulsion of the waste stream and promote the clustering of the solids and grease. Acidic coagulant chemicals such as Aluminum Sulfate or Polyaluminum Chloride (PAC) shall be dosed into the Coagulation Tank and mixed rapidly with the incoming wastes. This initiates the coagulation process, which chemically breaks down the oil emulsion and agglomerates the grease into loose clusters or lumps.
FLOCCULATION (Optional)
From the Coagulation Tank, the wastes shall flow into the Flocculation Tank. The next treatment step consists of dosing a flocculant chemical, usually an anionic polymer, to further enlarge the clusters and lumps formed earlier in the coagulation process. As the umps become bigger, it increases its settleability – in the case of the grease and other suspended solids, or floatability. Slow mixing is performed to avoid destroying the flocs being formed out of the coagulated lumps
The pH shall likewise be adjusted to a level suitable for discharge into the Sewage Treatment Plant (STP). A chemical metering pump shall dose caustic soda to neutralize the pH. A pH controller shall be installed to control the operation of the chemical metering pump and avoid overdosing of caustic soda. After pH adjustment, the wastewater containing metal precipitates are dosed with a coagulant such as aluminum sulfate or polyaluminum chloride (PAC). The coagulant enables the precipitates to agglomerate together forming microflocs. Suspended solids and oils likewise attached to these clusters. Air mixing is provided by an air blower.
INDUCED AIR FLOTATION
Induced Air Flotation (IAF) is a highly efficient process for removal of oils, greases and suspended solids, which is further enhanced by chemical flocculation. The IAF disc features a diffuser that incorporates fine holes near it perimeter for ultra-fine bubble diffusion into the liquid. The motor spins the unique diffuser disc, creating a low-pressure zone at disc’s diffuser ports. The disc draws air above the liquid surface, which then precedes down trough the draft tube, into the disc and out of the submerged diffuser ports. As each bubble exits trough a hole in the end of the diffuser disc, the spinning disc shears it into microscopic air bubble fragments measuring form 10-100 microns in diameter. These air bubbles adhere to minute solids such as oil and grease. The bubbles slowly rise to the surface around the unit, bringing the solids to the surface. The floated solids are then skimmed off by the scum skimmer, while the clear effluent flows under a weir towards the Aeration tank. The Induced Air Flotation System is expected to remove most of the oils and suspended solids, while having a significant impact on BOD reduction as well.
AERATION TANK
From the Induced Air Flotation, the treated effluent flows into the Aeration Tank in parallel operation, wherein aerobic and facultative bacterial culture is maintained in complete suspension. The activated-sludge process involves the production of an active mass of microorganisms capable of degrading organic
wastes in the presence of oxygen. The Aeration tanks are equipped with air blowers and fine bubble diffusers to provide the required oxygen for sustained bacterial growth and activity. Bacterial cells and inorganic matter formed during this activity shall form bioflocs that will settle in the Settling Tank.
A minimum mixed liquor suspended solids (MLSS) concentration shall be maintained to ensure the complete biodegradation of the estimated Biological Oxygen Demand (BOD) load. This is achieved by returning a portion of the sludge from the Settling Tank to the Aeration Tank. The purpose of the Return Activated Sludge (RAS) is to maintain a sufficient level of biomass in the Aeration Tank so that the required degree of treatment can be obtained in that time interval desired. The sludge recirculation rate may be increased or decreased depending on the influent BOD level, thus lending flexibility to the treatment in various field conditions.
SETTLING TANK
From the Aeration Tank, the mixed liquor overflows to the Settling Tanks in parallel operation for the separation of bioflocs from the supernatant. Efficient removal of these bioflocs from the wastewater shall result in a well-clarified stable effluent, which is in low BOD and suspended solids. A certain mean-cell residence time is maintained to enable the MLSS to form settleable bioflocs at the bottom hopper of the Settling Tank. A portion of the settled sludge at the hopper is recycled back to the Aeration Tank as seed biomass in order to maintain the required MLSS concentration. Less sludge volume is generated in this process, resulting in reduced sludge pumps out. Treated effluent shall be suitable for discharge to Class C waters.
AEROBIC SLUDGE DIGESTION
Excess sludge from the Induced Air Flotation and Settling Tank is further treated in the Sludge Digestion Tank where the endogenous phase of the microorganism occurs. In the Endogenous phase, the microorganisms are forced to metabolize their own protoplasm in the absence of sufficient nutrients. This results in a substantial reduction of the sludge volume as the surviving cells “digest” each other for sustenance.
CHLORINE CONTACT CHAMBER
Biologically-treated effluent shall then flow into the Chlorine Contact Chamber, wherein liquid chlorine is dosed inline to destroy pathogens in the effluent prior to discharge or reuse. The disinfected effluent maybe recycled as gray water for non-potable uses such as landscape irrigation and toilet flushing after installing a simple tertiary filtration system.
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