Nitrification and Denitrification Urea is promptly hydrolyzed in - PowerPoint PPT Presentation

SOURCES OF AMMONIA in Wastewaters 1. Urea a main component of urines is abundant in domestic sewage. Urea is a nitrogen organic compound with two amino groups: H 2 NCONH 2 Nitrification and Denitrification Urea is promptly hydrolyzed in sewers by an enzyme ‘urease’ found in many organotrophs associated with fecal Susete Martins Dias waste University of Lisbon, IST, DBE NH 2 CONH 2 + H 2 O + Citrobacter 2 NH 3 + CO 2 ( High kinetics reaction rate) 3 SOURCES OF AMMONIA Nitrogenous compounds At the sewer system pH, ammonia is quickly converted to Nitrogen cycle (Students are advised to review) o ammonium ions Ammonia used in chemical NH 3 + H + NH 4 + , f (T) o synthesis and associated Urea can also be found by products release in fertilizers and stockyard wastes Ammonium-Nitrogen quantification ü TAN (Total ammonium nitrogen is the sum up of the unionized and ionized forms) http://mattson.creighton.edu/ InorganicChemWeb/InorganicWorksheets/ Day_15_Main_Group_Pt_2.pdf 2 4

OTHER SOURCES OF ORGANIC NITROGEN in WW AMMONIA REMOVAL MECHANISMS PROTEINS are mostly in colloidal form and thus are not easily biodegradable ABIOTIC o in the activated sludge process. Colloidal matter is mostly removed adsorbed Physico-chemical processes (solubilization, n to the floc. precipitation, etc.) BIOTIC o However some proteins suffer HYDROLYSIS and DEAMINATION of aminoacids, Microbial transformation into nitrogen oxidized or n which is responsible for the release of the amino group (-NH 2 ) in the sewer reduced species, assimilation as energy and nitrogen or the more complex may be degraded in the activated sludge tank reactor source (ASTR) releasing ammonium ions . Ammonification Nitrification RCH(NH 2 )COOH +H 2 O NH 2 +2 RCO 2 NH 2 + 2 H + NH 4 + * ⇒ RNH 2 ⇒ NH 3 ( g ) ⇔ NH 4 + ⇒ NH 2 OH ⇔ NO 2 − ⇒ NO 3 − N 2 Due to the presence of hydrogen ions in wastewaters the amino group is quickly converted to the ammonium ion. Soluble forms Deniitrification 5 7 * N 2 fixation WHY NITRIFICATION /DENITRIFICATION ARE OTHER SOURCES OF ORGANIC NITROGEN NEEDED? Ammonia (NH 3 ) discharge affects receiving water bodies in several INDUSTRIAL SOURCES (Chemical, ² POLYELECTROLYTES AND agrochemical, livestock breeding) ways: it is toxic for fishes ( 0.2 to 22.8 mg/L) and promotes CHLOROAMINES (DBP): dissolved oxygen depletion. Fertilizers -Urea ;NH 4 NO 3 added to potable water Soluble nitrogenous species removal from discharges to receiving Acrylonitrile -Synthetic acrylic ² ² fibers u s e d t o o p t i m i z e fl o c ² water bodies enables eutrophication control. sedimentation and desinfection of Aniline- Polyurethanes chain (Students should review the water body eutrophication process) treated wastewater whenever Nitrobenzene- p-aminophenol something goes wrong and treated (pharmaceuticals) Nitrogen content control is also needed for water reuse including ² effluent has to be recirculated Dyes -Fabric and paper dyeing groundwater recharge. within the WWTP. Milk processing industries ; Piggery wastewaters Nitrate causes infant disease metahemoglobineamia; NO 3 distort DBP-desinfection by products ² Abbatoirs etc. hemoglobin affinity to oxygen; Fe2+ (ferrous) ions are oxidized to Detergents (NH 4 + ), slide 2, etc. Fe3+(ferric) which are no longer able to bind oxygen 6 8

FATE OF NITRATE IONS IN THE ACTIVATED FATE OF AMMONIUM IONS IN THE ACTIVATED SLUDGE PROCESS SLUDGE PROCESS Ammonia can be assimilated by microorganisms as N source for ü In the absence of ammonium ions nitrate may be used as ü growth and reproduction. Thus, MLVSS content increase in the nitrogen source (nitrate assimilation) ASTR or biosolids N content is noticed. Otherwise it will be discharged to secondary clarifier where it ü At pH > 9.4 (T= 20ºC) ammonium ions are easily converted ü may be denitrified. into ammonia (g) and can be released into the atmosphere NH 4 + NH 3 + H + Denitrification can occur in the secondary clarifier whenever ü soluble BOD is available with release of molecular nitrogen ( to Acid ionization constant: Ka = [NH 3 ][H + ] / [NH 4 + ] = 5.62 x be avoided ). 10 -10 NH 3 lost to the atmosphere (%) = 100 / (1+[H + ]/Ka) 9 11 MICROBES INVOLVED IN NITRIFICATION FATE OF AMMONIUM IONS IN THE ACTIVATED PROCESSES SLUDGE PROCESS 1. 90% of the reduced form of nitrogen is present as ammonium ion Biological removal of biodegradable organic matter is carried out mostly by ü due to organothrophs present in wastewater and excreta. 7 < pH < 8.5 and 10 < T < 20°C (see graph slide 4) NITRIFYING ORGANISMS Abundant in soil below the upper layer (UV radiation from § 2. Ammonium ions under the right conditions can also be converted sunlight kill them). to nitrite by Nitrosomas sp. Not naturally found in wastewaters but sewer inflow and § 3. Ammonium ions may also leave the aeration tank and enter the infiltration from soil acts as inocula. secondary clarifier. NITRIFYING BACTERIA 4. Nitrite can be converted into Nitrate by Nitrobacter sp. Possess special enzymes and cellular structures that permit them to achieve nitrification rates 1000 to 10 000 times higher than other organisms. 10 12

BACTERIA genus INVOLVED IN NITRIFICATION TABLE 6.1 Organisms in the Aeration Tank That NITROSOMONAS sp . and NITROBACTER sp . Are Capable of Nitrification Organism Genus Use carbon dioxide (CO 2 ) or other inorganic carbon (bicarbonate or ü Actinomycetes Myocbacterim carbonate) as their carbon source for the synthesis of cellular Nocardia material. Streptomyces Carbon dioxide is assimilated to a 5 carbon sugar, ribulose di- § Algae Chlorella phosphate, to produce a 6 carbon sugar, glucose. Bacteria Arthrobacter Bacillus Promotes Nitrification in a two step biochemical reaction that takes ü Nitrobacter place inside the cell. Nitrosomonas Needs free molecular oxygen. Proteus § Pseudomonas Nitrification can be inhibited by simple organic compounds (alcohols ü Vibrio and short chain organic acids) that can easily enter the cell and Fungi Aspergillus inactivate their enzyme array. Protozoa Epistylis These organic compounds should be removed by organotrophs before nitrification in § Vorticella the aerobic tank. 13 15 MICROBES INVOLVED IN NITRIFICATION PROCESSES NITRIFICATION BIOCHEMICAL REACTIONS Nitrosomonas sp. @ pH 7 ü (1) NH 4 + +1.5 O 2 = NO 2 - + 2H + + H 2 O+ 272 kJ 3.43gO 2 /gNH 3 -N Nitrobacter sp. @ pH 7 ü (2) NO 2 - + 0.5 O 2 =NO 3 - + 76 kJ 1.14 g O 2 /gNO 2 -N actual consumption 4.3 g O 2 /g NH 3 -N* * In addition to oxidaton consumption, oxygen is obtained from fixation of carbon dioxide and nitrogen into cell mass. (see next slide) Energy (1) >> Energy (2) and it is released inside the cell 14 16

NITRIFICATION BIOCHEMICAL REACTIONS ALTERNATIVE AMMONIA REMOVAL MECHANISMS The oxidation of ammonia to nitrite in natural systems is suggested ü The energy needed to assimilate 1 molecule of CO 2 is to comprise two steps, not one (Bothe et al ., 2000), catalyzed by Nitrosomonas enzymes: 30 x E (1) =100 x E (2) (1a) NH 3 +O 2 +2 H + + 2e - + 16 kJ/mole � NH 2 OH + H 2 O Ammonia Monooxygenase thus, (1b) NH 2 OH + H 2 O � NO 2 - + 5H + + 4e - + 228 kJ/mole nitrifying bacteria have a very low growth rate ( td ≈ 10 to 12h ) Hydroxylamine oxidoredutase These reactions suggest that hydroxylamine is an intermediate in the Y X/S (1+2) = 0.17g(dw)cells/g NH 3 -Nconsum ed process, which presents alternate nitrogen processing possibilities. Further, one of the oxygen atoms in nitrite derives from O 2 , the other dw- dry weight from water. 17 19 ALKALINITY AND BIOMASS PRODUCTION ALTERNATIVE AMMONIA REMOVAL MECHANISMS Nitrification of ammonia to nitrate consumes 7.1g of alkalinity (as Reaction (1b) is exothermic favouring Nitrite formation CaCO 3 ) for each nitrified g of ammonia nitrogen, as two moles of H + are released per each mole of ammonia nitrogen consumed: Nitrobacter sp . NO 2 - + 0.5 O 2 = NO 3 - + 76 kJ - + 2 CO 2 + 3 H 2 O (3) NH 4 + + 2 HCO 3 - + 2 O 2 = NO 3 (pH 7) Biomass synthesis reaction promoted by energy release (3) Nitrobacter sp . have several double layer membranes envolving the ü 4CO 2 + HCO 3 - + NH 4 + + H 2 O = C 5 H 7 NO 2 + 5 O 2 interior of the cell equipped with a complex enzymatic array and thus nitrite entering the cell is oxidized within these membranes and can not Overall equation penetrate into the interior of the cell where it might have toxic effect. NH 4 + +1.83O 2 +1.98 HCO 3 - = 0.021C 5 H 7 NO 2 +1.04H 2 0+0.98NO 3 - + +1.88 H 2 CO 3 18 20