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

Nitrification and Denitrification

Susete Martins Dias University of Lisbon, IST, DBE Nitrogenous compounds

• Nitrogen cycle (Students are advised to review)
• Ammonia used in chemical

synthesis and associated by products release

2

http://mattson.creighton.edu/ InorganicChemWeb/InorganicWorksheets/ Day_15_Main_Group_Pt_2.pdf

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: H2NCONH2 Urea is promptly hydrolyzed in sewers by an enzyme ‘urease’ found in many organotrophs associated with fecal waste NH2CONH2 + H2O + Citrobacter 2 NH3 + CO2

( High kinetics reaction rate)

3

SOURCES OF AMMONIA

At the sewer system pH, ammonia is quickly converted to ammonium ions NH3 + H+ NH4

+ , f (T)

Urea can also be found in fertilizers and stockyard wastes ü TAN (Total ammonium nitrogen is the sum up of the unionized and ionized forms) Ammonium-Nitrogen quantification

4

PROTEINS are mostly in colloidal form and thus are not easily biodegradable

in the activated sludge process. Colloidal matter is mostly removed adsorbed to the floc. However some proteins suffer HYDROLYSIS and DEAMINATION of aminoacids, which is responsible for the release of the amino group (-NH2) in the sewer

• r the more complex may be degraded in the activated sludge tank reactor

(ASTR) releasing ammonium ions.

RCH(NH2)COOH +H2O NH2 +2 RCO2 NH2 + 2 H+ NH4

+

Due to the presence of hydrogen ions in wastewaters the amino group is quickly converted to the ammonium ion.

OTHER SOURCES OF ORGANIC NITROGEN in WW

5

POLYELECTROLYTES AND CHLOROAMINES (DBP): ² added to potable water ² u s e d t o o p t i m i z e fl o c sedimentation and desinfection of treated wastewater whenever something goes wrong and treated effluent has to be recirculated within the WWTP. ² DBP-desinfection by products

INDUSTRIAL SOURCES (Chemical,

agrochemical, livestock breeding)

Fertilizers -Urea ;NH4NO3

Acrylonitrile -Synthetic acrylic fibers Aniline- Polyurethanes chain Nitrobenzene- p-aminophenol (pharmaceuticals) Dyes -Fabric and paper dyeing Milk processing industries ; Piggery wastewaters Abbatoirs etc. Detergents (NH4

+), slide 2, etc.

OTHER SOURCES OF ORGANIC NITROGEN

6

AMMONIA REMOVAL MECHANISMS

• ABIOTIC

n Physico-chemical processes (solubilization, precipitation, etc.)

• BIOTIC

n Microbial transformation into nitrogen oxidized or reduced species, assimilation as energy and nitrogen source

N2

* ⇒ RNH2 ⇒ NH3(g)⇔ NH4 + ⇒ NH2OH ⇔ NO2 − ⇒ NO3 −

7

Soluble forms Ammonification Nitrification Deniitrification

* N2 fixation

WHY NITRIFICATION /DENITRIFICATION ARE NEEDED?

² Ammonia (NH3) discharge affects receiving water bodies in several ways: it is toxic for fishes (0.2 to 22.8 mg/L) and promotes dissolved oxygen depletion. ² Soluble nitrogenous species removal from discharges to receiving water bodies enables eutrophication control.

(Students should review the water body eutrophication process)

² Nitrogen content control is also needed for water reuse including groundwater recharge.

Nitrate causes infant disease metahemoglobineamia; NO3 distort hemoglobin affinity to oxygen; Fe2+ (ferrous) ions are oxidized to Fe3+(ferric) which are no longer able to bind oxygen

8

FATE OF AMMONIUM IONS IN THE ACTIVATED SLUDGE PROCESS

ü Ammonia can be assimilated by microorganisms as N source for growth and reproduction. Thus, MLVSS content increase in the ASTR or biosolids N content is noticed. ü At pH > 9.4 (T= 20ºC) ammonium ions are easily converted into ammonia (g) and can be released into the atmosphere NH4

+ NH3 + H+

Acid ionization constant: Ka = [NH3][H+] / [NH4

+] = 5.62 x

10-10 NH3 lost to the atmosphere (%) = 100 / (1+[H+]/Ka)

9

• 1. 90% of the reduced form of nitrogen is present as ammonium ion

due to 7 < pH < 8.5 and 10 < T < 20°C (see graph slide 4)

• 2. Ammonium ions under the right conditions can also be converted

to nitrite by Nitrosomas sp. 3. Ammonium ions may also leave the aeration tank and enter the secondary clarifier.

• 4. Nitrite can be converted into Nitrate by Nitrobacter sp.

10

FATE OF AMMONIUM IONS IN THE ACTIVATED SLUDGE PROCESS

ü In the absence of ammonium ions nitrate may be used as nitrogen source (nitrate assimilation) ü Otherwise it will be discharged to secondary clarifier where it may be denitrified. ü Denitrification can occur in the secondary clarifier whenever soluble BOD is available with release of molecular nitrogen (to be avoided).

11

FATE OF NITRATE IONS IN THE ACTIVATED SLUDGE PROCESS MICROBES INVOLVED IN NITRIFICATION PROCESSES

ü Biological removal of biodegradable organic matter is carried out mostly by

• rganothrophs present in wastewater and excreta.

NITRIFYING ORGANISMS

§ Abundant in soil below the upper layer (UV radiation from sunlight kill them). § Not naturally found in wastewaters but sewer inflow and infiltration from soil acts as inocula.

NITRIFYING BACTERIA

Possess special enzymes and cellular structures that permit them to achieve nitrification rates 1000 to 10 000 times higher than other

• rganisms.

12

TABLE 6.1 Organisms in the Aeration Tank That Are Capable of Nitrification Organism Genus Actinomycetes Myocbacterim Nocardia Streptomyces Algae Chlorella Bacteria Arthrobacter Bacillus Nitrobacter Nitrosomonas Proteus Pseudomonas Vibrio Fungi Aspergillus Protozoa Epistylis Vorticella

13 14

MICROBES INVOLVED IN NITRIFICATION PROCESSES

ü Use carbon dioxide (CO2) or other inorganic carbon (bicarbonate or carbonate) as their carbon source for the synthesis of cellular material. § Carbon dioxide is assimilated to a 5 carbon sugar, ribulose di- phosphate, to produce a 6 carbon sugar, glucose. ü Promotes Nitrification in a two step biochemical reaction that takes place inside the cell.

§ Needs free molecular oxygen.

ü Nitrification can be inhibited by simple organic compounds (alcohols and short chain organic acids) that can easily enter the cell and inactivate their enzyme array.

§ These organic compounds should be removed by organotrophs before nitrification in the aerobic tank.

15

BACTERIA genus INVOLVED IN NITRIFICATION NITROSOMONAS sp. and NITROBACTER sp. NITRIFICATION BIOCHEMICAL REACTIONS

ü Nitrosomonas sp. @ pH 7 (1) NH4

+ +1.5 O2= NO2

• + 2H++ H2O+ 272 kJ 3.43gO2/gNH3-N

ü Nitrobacter sp. @ pH 7 (2) NO2

• + 0.5 O2 =NO3
• + 76 kJ 1.14 g O2/gNO2-N

actual consumption 4.3 g O2/g NH3-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

16

NITRIFICATION BIOCHEMICAL REACTIONS

The energy needed to assimilate 1 molecule of CO2 is 30 x E (1) =100 x E (2) thus, nitrifying bacteria have a very low growth rate (td ≈ 10 to 12h) YX/S (1+2) = 0.17g(dw)cells/g NH3-Nconsumed dw- dry weight

17

ALKALINITY AND BIOMASS PRODUCTION

Nitrification of ammonia to nitrate consumes 7.1g of alkalinity (as CaCO3) for each nitrified g of ammonia nitrogen, as two moles of H+ are released per each mole of ammonia nitrogen consumed:

NH4

+ + 2 HCO3

• + 2 O2 = NO3
• + 2 CO2 + 3 H2O (3)

Biomass synthesis reaction promoted by energy release (3)

4CO2 + HCO3

• + NH4

+ + H2O = C5H7NO2 + 5 O2

Overall equation

NH4

++1.83O2+1.98 HCO3

• = 0.021C5H7NO2+1.04H20+0.98NO3
• +

+1.88 H2CO3

18

ALTERNATIVE AMMONIA REMOVAL MECHANISMS

ü The oxidation of ammonia to nitrite in natural systems is suggested to comprise two steps, not one (Bothe et al., 2000), catalyzed by Nitrosomonas enzymes:

(1a) NH3 +O2+2 H++ 2e - + 16 kJ/mole NH2OH + H2O Ammonia Monooxygenase (1b) NH2OH + H2O NO2- + 5H+ + 4e- + 228 kJ/mole Hydroxylamine oxidoredutase

These reactions suggest that hydroxylamine is an intermediate in the process, which presents alternate nitrogen processing possibilities. Further, one of the oxygen atoms in nitrite derives from O2, the other from water.

19

ALTERNATIVE AMMONIA REMOVAL MECHANISMS

Reaction (1b) is exothermic favouring Nitrite formation Nitrobacter sp. NO2

• + 0.5 O2 = NO3
• + 76 kJ

(pH 7)

ü Nitrobacter sp. have several double layer membranes envolving the interior of the cell equipped with a complex enzymatic array and thus nitrite entering the cell is oxidized within these membranes and can not penetrate into the interior of the cell where it might have toxic effect.

20

ANAEROBIC AMMONIUM OXIDATION (ANAMMOX PROCESS)

Discovery: E. Broda, Austria, 1977 Process implementation:Delft Univ Technol, Holland, 1986

Bacteria belonging to at least three genera: Brocadia, Kuenenia found in WWTP Scalindua ( in marine systems) Anammox bacteria grow very slowly (td≈2 weeks) and are strictly anaerobes and autotrophs 1st step – Partial nitritation: 2nd step _ Anammox NH4

+ + 1.32 NO2

• + 0.066 HCO3
• + 0.13 H+

1.02 N2 + 0.26 NO3

• + 0.066 CH2O0.5N0.15 + 2.03 H2O

ANAEROBIC AMMONIUM OXIDATION MECHANISMS

Under oxygen limitation (<0.5% air saturation), a co- culture of Aerobic (Nitrosomonas) and anaerobic ammonium oxidizers (Brocadia) can be

• btained. This co-

culture can grow in the form of biofilm or granules.

ANAEROBIC AMMONIUM OXIDATION MECHANISMS

Compared to conventional nitrification/denitrification, this method saves 100% of the required C source and 50% of the required oxygen. This leads to a reduction of operational costs of 90%, a decrease in CO2 emissions of more than 100% (the process actually consumes CO2),

a decrease in energy demand.

Wastewaters that are very suitable for treatment with anammox :

• sludge reject waters ("sludge liquor")
• industrial wastewaters
• gases

ANAEROBIC AMMONIUM OXIDATION ADVANTAGES

The first full scale Anammox reactor, Rotterdam, The Netherlands (2002) Capacity 500 kg N/day.

http://www.hindawi.com/journals/bmri/2013/134914/

ANAEROBIC AMMONIUM OXIDATION Reactors and granules

25

ü Ammonium is first partially oxidized to nitrite in the presence of air. ü In the second reactor (anaerobic) the Anammox bacteria oxidize the remaining ammonium to nitrogen gas with nitrite as the electron acceptor. Almost complete nitrogen removal from wastewater containing high ammonia concentrations (1-2 g/L), in two stages :

SHARON-ANAMMOX PROCESS