Wastewater Treatment

Wastewater Treatment

Oxygen Demand

·  stabilization/decomposition of organic matter in wastes accomplished biologically

·  oxygen depletion in natural waters due to wastes is undesirable – dissolved oxygen reduction poses a threat to aquatic life

·  anything that can be oxidized (metabolized by microorganisms) in a receiving water (river, lake, estuary, ocean) is an oxygen demanding material; these include biodegradable organic matter and certain inorganic compounds

Theoretical Oxygen Demand (ThOD): amount of oxygen required to completely oxidize a substance to carbon dioxide and water as calculated by stoichiometry if chemical composition is known

Chemical Oxygen Demand (COD): based on the amount of strong oxidizing agent required to oxidize a substance

Biochemical Oxygen Demand (BOD): amount of oxygen used by acclimated microorganisms to metabolize a substance

·  BOD < ThOD and COD (usually)

·  determined by measuring DO over time in a sample inoculated with bacteria that use oxygen

·  not all organic matter is biodegradable and test procedures lack precision, but still one of the most widely used measures of waste strength

·  ultimate BOD is the maximum amount of oxygen used – does not indicate how fast oxygen will be used, but is directly proportional to the concentration of organic matter in the waste

·  BOD5 is the amount of oxygen used in 5 days – standard value used for treatment design and regulatory purposes, but ultimate BOD a better indicator of total waste strength

Nitrogen Oxidation: in addition to carbon, nitrogen is oxidized with oxygen consumption, but mechanisms are different

·  CBOD – carbonaceous BOD

·  NBOD – nitrogenous BOD

Population Dynamics

Requirements for Growth

·  terminal electron acceptor

·  macronutrients

·  micronutrients

·  environment

Monod Equation: use biomass as an indicator of number of organisms

Wastewater Characteristics

Domestic/Municipal

·  physical

·  chemical

Industrial

·  conventional pollutants

·  non-conventional pollutants

·  priority pollutants

Municipal Wastewater Treatment Plants (WWTP)

·  pre and primary treatment

·  secondary treatment

·  tertiary treatment

Secondary Treatment: bio-oxidation of waste

·  trickling filters

·  rotating biological contactors

·  oxidation ponds

·  activated sludge*

Activated Sludge (AS)

·  mixture of wastewater and biological sludge that is agitated and aerated – microorganisms grow and clump together into active masses

·  mixture of activated sludge and wastewater called mixed liquor

Ø  MLSS: mixed liquor TOTAL suspended solids.

Ø  MLVSS: mixed liquor VOLATILE suspended solids – indicator of active microorganisms

~ more to follow… ~