Biological Treatment: Susp. Growth Process

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Activated Sludge

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A mixture of sludge particles (floc.), bacteria, fungi, protozoa, & rotifers maintained in suspension by aeration and mixing.

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Aerobic (oxic) [O2]

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A condition in which free and dissolved oxygen (DO) is available in an aqueous environment.

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Anaerobic [0]

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A condition in which free, dissolved, and combined oxygen is unavailable in an aqueous environment.

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Aonxic [NO2, NO3, SO4]

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A condition in which oxygen is only available in a combined form such as nitrite (NO3), nitrite (NO2), or sulfate (SO4) in an aqueous environment.

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Dentrification

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A biological process where bacteria convert nitrate (NO3) and nitrite (NO2) to nitrogen gas (N2) under anoxic conditions.

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Floc

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Is clusters of microorganisms and solid particles that form in the activated sludge process and settle in the final clarifier.

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Food to microorganism ratio (F:M or F/M)

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The amount of food (biochemical oxygen demand (BOD) provided to the microorganisms (mixed liquor volatile suspended solids (MLVSS) or mixed liquor suspend solids (MLSS) in the aeration basins.

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How to determine F:M or F/M

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Dividing the pounds of influent BOD by the pounds of MLVSS or MLSS under aeration.

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Hydraulic retention time (HRT)

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The period of time that wastewater remains in a tank. This is important because treatment processes require sufficient time for the wastewater to be treated. This is important because treatment processes require sufficient time for the wastewater to be treated.

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Marbling

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The variegated, stone like appearance on a quiescent part of an aeration basin as a result of good floc (solids) and water separation.

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Marbling

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Indicative of good sludge age.

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Mixed Liquor Suspended Solids (MLSS)

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The amount of suspended solids in an aeration tank, expressed in milligrams per liter (mg/l). MLSS consists of microorganisms and non-biodegradable suspended matter.

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MLSS Calculation

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Total pounds in an aeration tank: multiply the concentration of MLSS (mg/L)in the aeration tank (X) tank volume (MG), (X) 8.34.

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Mixed Liquor Volatile Suspended Solids (MLVSS)

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The amount of organic or volatile suspended solids in an aeration tank, expressed in m/L. This volatile portion is used as a measure of the microorganisms present in the aeration tank.

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MLVSS Calculation

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Multiply concentration MLVSS aeration tank(X) Aeration tank volume (X) 8.34. equals ____.

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Nitrification

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A biological process where nitrifying bacteria convert nitrogen in the form of ammonia (NH3) into nitrite (NO2) and nitrate (NO3) under aerobic conditions.

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Organic Loading

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The amount of biodegradable material that exerts and oxygen demand on the biological treatment process

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BOD in mg/L

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The organic strength of the wastewater is usually measured by ______.

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Organic Overload

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An event which significantly increases the organic loading (BOD) to the aeration basin above normal influent organic loading conditions.

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Protozoa

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Single celled microscopic organisms that require oxygen & food (bacteria) for growth & reproduction.

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Protozoa

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Amoeba, flagellates & ciliates.

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Return Activated sludge (RAS)

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The settled activated sludge (biomass) that is collected in a final clarifier & returned to the secondary treatment process to mix with incoming wastewater.

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RAS

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This returns a concentrated population of microorganisms back into the aeration basin.

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Secondary Treatment

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Describes the biological treatment of wastewater. Activated sludge is a type of secondary treatment.

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Secondary Treatment Provides:

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A high level of removal of biodegradable organic pollutants to protect receiving water quality that clarification alone cannot provide.

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Sludge Age

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The theoretical length of time a particle of activated sludge stays in the treatment plant & is measured in days.

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Sludge Age Calculation

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#MLSS divided by #suspended solids (or #excess cell mass withdrawn from (WAS) Waste Activated Sludge).

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Sludge Blanket

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The layer of solids on the bottom of the clarifier.

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Sludge Volume Index (SVI)

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A numerical expression of the settling characteristics of activated sludge in the final clarifier. SVI is expressed as the ratio of volume

in milliliters of activated sludge settled from a 1000 mL sample in 30 minutes.

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SVI Calculation

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Sledge settles from a 1,000 mL sample in 30 minutes divided by the concentration of mixed liquor in milligrams per liter multiplied by 1,000.

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Good Settling Sludge Value

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Textbook value is 100, but can commonly be 80 to 150.

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Treatment Facility Overflow (TFO)`

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A release of wastewater, other than permitted outfalls into a water of the state or land surface.

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TFO's Must be reported to:

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_____ within __ hours of the occurance.

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Waste Activated Sludge(WAS)

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The excess biomass or cell mas removed from the secondary treatment process. For most treatment plants, this will be a portion of the RAS flow stream.