Dr. Bajnóczy GáborTonkó Csilla

HIGH OXYGEN DEMANDING NON-TOXIC WASTEWATERS

BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS

DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL PROCESS ENGINEERING

FACULTY OF CHEMICAL AND BIOCHEMICAL ENGINEERING

The pictures and drawings of this presentation can be used only for

education !

Any commercial use is prohibited !

HIGH OXYGEN DEMANDING NON-TOXIC WASTEWATERS

Contain significant amount of biodegradable organic matter,non-hazardous to aquatic life.

Main sources:

municipal wastewater

livestock

liquid manurefood industry

EFFECT OF HIGH OXYGEN DEMANDING, NON-TOXIC WASTES ON NATURAL WATER

high oxygen demandingwastewater flowsInto natural water

Dead organic matter in natural water (leaf, dead corpus, etc.) is decayed by bacteria using dissolved oxygen. The process is named mineralization and the final products carbon dioxide and water.

Number of aquatic bacteria is limited by the available organic matter

Increase of nutrientsfor the bacteria

number of decomposing

organisms increases significantly

oxygen consumption increases

↓dissolved oxygen in water

decreases

natural water:aerobic anaerobic

The process induced by non toxic organic materials in natural waters

PRODUCTS OF BIOLOGICAL DEGRADATION,AEROBIC AND ANAEROBIC CONDITIONS

Independently of water condition – aerobic or anaerobic – life is always present, only the living forms and the final product of organic metabolism differ (aerobic or anaerobic bacteria).

Aerobic conditions Anaerobic conditions

carbon

nitrogen

sulfur

phosphorus

carbon

nitrogen

sulfur

phosphorus

CO2

NH3 HNO3

H2SO4

H3PO4

CH4

NH3 amines

H2S

PH3 other phosphorus compounds

Flame in marsh.phosphorus hydrogen + air exothermic oxidation

The heat evolved ignites the methane

aerobic: oxygen is available ; anaerobic: lack of oxygen; anoxic: oxygen available only in form of eg.: nitrate, sulfate

BIOLOGICAL DEGRADATION OF ORGANIC COMPOUNDS

1. terminal oxidation of the carbon chain cytochrom-P450 (iron-containing enzyme) + oxygen in molecule

R – CH2 – CH2 – CH3 R – CH2 – CH2 – C - OH R – CH2 – CH2 – COOH

Simplified mechanism of the terminal oxidation and the formation of carboxyl group at the end of chain

2. step: β – oxidation enzymes playing significant roles in the process:

koenzyme – A : CoASH (reactive center: –SH thiol group)

hydrogen transfer enzymes: oxidized form reduced form

FAD FADH2

NAD+ NADH

O

R – CH2 – CH2 – C - OH

O

R – CH2 – CH2 – C - SCoACoASH

- H2O

O

R – CH = CH – C - SCoA

NAD+ NADH

OH O

R – CH – CH2 – C - SCoAH2O

water addition (Markovnyikov rule)

FAD FADH2

O O

R – C – CH2 – C - SCoA

O

R – C - OH

O

CH3 – C - SCoA+

instable compound in water decays immediately

H2O

acetil-koenzyme A

carbon chain is built backwards by the program of microorganism using this unit

In case of energy demand: citric acid cycle carbon

dioxide and water

BIOLOGICAL DEGRADATION OF ORGANIC COMPOUNDS

1. Long chain carbon compounds (number of carbon atoms > ≈ 32): poorly decomposable or remains intact.

This form is not favored by energetically This form has lower energy

?

?

microorganismdoesn’t find the end of

chain

Some bacteria have exocellular chain splittingenzymes. Short-term gains, the chain terminal

disappears in ball.

plastic degradation is very slow in nature

2. Branched carbon chain compounds: no or slow degradation

O

R – CH – CH2 – C – OH

CH3

O

R – CH – CH2 – C – SCoA

CH3

CoASH

- H2O

OH O

R – C – CH2 – C – SCoA

CH3

H2O

water addition (Markovnyikov rule)

FAD FADH2

O

R – C = CH2 – C – SCoA

CH3

O O

R – C – CH2 – C – SCoA

CH3

Motor oils contain mainly branched hydrocarbons, so the effect on environment is long-term.

3. Aromatic compounds: aromatic ring slowly, but biologically degradable

OOH

OH

COOH

COOH

CH3 – COOH

O O HO – C – C – CH2 - COOH

+

cytochrom

P-450

COOH

OH

cytochrom

P-450

4. Highly condensed aromatic ring: not degradable

Carcinogenic compounds containing highly condensed aromatic rings decay a few hours in atmosphere (sunshine), but toxic effect takes a long time in water and soil.

ORGANIC MATTER CONTENT OF WATER,BOD AND COD

BOD (Biological Oxygen Demand)

The oxygen quantity in a unit of water, necessary for the biological oxidation of organic matter during 5 or 20 days, at 20 °C

Unit of BOD5 or BOD20 [mg oxygen/dm3]

BOD5 necessary oxygen quantity for the biological oxidation of organic carbon compounds

BOD20 necessary oxygen quantity for biological oxidation of organic carbon and nitrogen compounds

degradation of nitrogen compoundsstarts later

organic nitrogen-containing compounds

desamination

NH4+ + 1,5 O2 H2O + 2 H+ + NO2

-

NO2- + 0,5 O2 NO3

-

NH3

Nitrosomonas

Nitrobacter

In aqueous medium

slow

fastday

BOI

ORGANIC MATTER DEGRADATION IN NATURAL WATERS approximated by first-order reaction

BOD t = BOD0 *(1 – e -kt)BOD t: residual oxygen demand at the t time, BOD 0: total biological oxygen demand at the beginning t=0k : air supply constant at a given temperature

Air supply constant

water type k [day-1] 20°C

Little lakes, dead branches 0,1 – 0,23Slow flow 0,23 – 0,35Large, slow water flow 0,35 – 0,46Large, normal water flow 0,46 – 0,69Fast flow 0,69 – 1,15

Conversion to other temperature: k(T) = k(20°C)*1,024T-20

COD (Chemical Oxygen Demand)

The oxygen quantity in a unit of water, necessary for the chemical oxidation of all dissolved or suspended organic matter by a strong oxidizer (potassium dichromate or

potassium permanganate). The final product of the oxidation : CO2 and H2O.

Unit of COD [mg oxygen/dm3]

Relationship between BOD and COD

BOD < COD General relationship, the chemical oxidizer disintegrates all organic compounds, but the microorganisms are choosy.

BOD = COD Water sample contains only biologically degradable organic compounds.

BOD << COD Water sample may contain toxic compounds or only small amount of biologically degradable organic matter.

SIMPLIFIED AEROB BIOLOGICAL WASTEWATER TREATMENT

Accelerated biological degradation of organic matters by activated sludge in continuous aerobic fermenting tanks.

anoxic basin: a.) pre-degradation of organic matters b.) ammonification (organic nitrogen → ammonia) c.) denitrification of recycled purificated wastewater (nitrate → nitrogen)

aerobic basin: a.) air supply b.) oxidation of organic carbon c.) ammonia (formed in anoxic basin) oxidation to nitrate d.) increase of sludge mass

AEROB BIOLOGICAL WASTEWATER TREATMENT

SIMPLIFIED ANAEROB BIOLOGICAL WASTEWATER TREATMENT

Accelerated biological degradation of organic matters by activated sludge in continuous anaerob fermenting tanks.

COMPARISON OF WASTEWATER TREATMENT TECHNOLOGIES

organic matter content of waste water (100%)

carbon contentIn form of

carbon dioxide (~50%)

carbon contentof sludge

~50%

carbon content of drain water

~ 1%

organic matter content of waste water (100%)

carbon content of biogas 90-95 %methane : carbon dioxide ~ 50-50 %

carbon content of drain water

~ 1-5%

carbon content of sludge~1-5%

AEROB ANAEROB

- well known technology - lesser-known technology- aeration: energy intensive - large body of water –> warming problem- sludge disposal problem (heavy metals) - less sludge formation- sludge fermentation → biogas - fuel gas formation- sludge incineration - sensitive to toxic matter (ash content: < 60%) - COD > 2000 mg/dm3

(organic matter: > 25%) - higher capacity (water content: < 50 %) - 1 kg organic matter ~ 1 m3 biogas