Aerobic Treatment Processes Principles and Dimensioning Eduardo Cleto Pires

Wastewater Treatment Processes  Physical-Chemical Physical separation processes: usually used for pre-treatment and conditioning Chemical coagulation-flocculation followed by physical separation  Biological Anaerobic processes: no oxygen Aerobic processes: oxygen

Principles of Aerobic Processes  Higher efficiency than anaerobic  Resistance to chock loads, low temperatures and temperature variations  Great amount of data and sources of information on design and operation

Principles of Aerobic Processes  Depending on the configuration it is possible to apply fine adjustments simple: aerated ponds – limited control complex: activated sludge – extensive control  Adequate for low strength (concentration) wastewaters

Principles of Aerobic Processes  Main disadvantage: High energy consumption  Aeration!!

Principles of Aerobic Processes  Combined processes: anaerobic + aerobic may result in better removal of recalcitrant compounds (anaerobic) lower energy consumption  substantial fraction of pollutants are removed at the anaerobic reactor lower biological sludge generation  resulting from the decreased load at the aerobic reactor

Main Aerobic Systems  Trickling filters  Stabilization ponds (facultative and aerated)  Activated sludge

Aerobic Carbonaceous Matter Removal  Organic matter soluble  greatest fraction of soluble matter from sanitary sewage is easily degradable suspended  slow biodegradation adsorbed by the biomass and converted into soluble matter by means of hydrolysis

Aerobic Carbonaceous Matter Removal  Two phases removal: oxidation and microorganism synthesis endogenous respiration (microorganism decay) Metcalf & Eddy. Wastewater Engineering. 4 ed. p.609

Aerobic Carbonaceous Matter Removal  Auto ionization of ammonia in aqueous solution:

Nitrogen Removal nitrification: two steps conversion of ammonia into nitrate:  oxidation of ammonia into nitrite (NO 2 − )  oxidation of nitrite into nitrate (NO 3 − )

Nitrogen Removal nitrification: two steps conversion of ammonia into nitrate: total oxidation reaction oxygen consumption → nitrogen demand

Nitrogen Removal  Denitrification occurs under anoxic environment (absence of oxygen but presence of nitrates – NO 3 − )  reduction reaction of nitrates to gaseous nitrogen

Biological Phosphorous Removal  A not well controlled complex process.  Usually occurs by means of absorption and use of phosphorous as a nutrient for microorganism synthesis.

Reference  Tchobanoglous, G.; Burton, F.L. and Stensel, H.D. Wastewater Engineering Treatement and Reuse (Metcalf & Eddy). McGraw Hill, 4 th. ed., 2003 (Chap. 7)