BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS
FACULTY OF CHEMICAL AND
BIOCHEMICAL ENGINEERING
DEPARTMENT OF CHEMICAL AND
ENVIRONMENTAL PROCESS
ENGINEERING
HIGH OXYGEN DEMANDING
NON-TOXIC WASTEWATERS
Dr. Bajnóczy Gábor
Tonkó Csilla
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:
livestock
food industry
liquid manure
municipal wastewater
EFFECT OF HIGH OXYGEN DEMANDING,
NON-TOXIC WASTES ON 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
high oxygen demanding
wastewater flows
Into natural water
number of
decomposing
organisms increases
significantly
oxygen consumption increases
↓
dissolved oxygen in water
decreases
Increase of nutrients
for the bacteria
natural water:
aerobic  anaerobic
The process induced by non toxic organic materials in natural waters
PRODUCTS OF BIOLOGICAL DEGRADATION,
AEROBIC AND ANAEROBIC CONDITIONS
aerobic: oxygen is available ;
anaerobic: lack of oxygen;
anoxic: oxygen available only in form of eg.: nitrate, sulfate
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
CO2
carbon
CH4
nitrogen
NH3 HNO3
nitrogen
NH3 amines
sulfur
H2SO4
sulfur
H2S
phosphorus
H3PO4
phosphorus
PH3 other phosphorus
compounds
Flame in marsh.
phosphorus hydrogen + air  exothermic oxidation
The heat evolved ignites the methane
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
CoASH
R – CH2 – CH2 – C - SCoA
- H2O
FAD
OH
O
R – CH – CH2 – C - SCoA
O
H2O
water addition
(Markovnyikov rule)
NAD+
O
FADH2
R – CH = CH – C - SCoA
NADH
O
R – C – CH2 – C - SCoA
H2O
O
R – C - OH
instable compound in water
decays immediately
O
+
CH3 – C - SCoA
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
?
microorganism
doesn’t find the end of
chain
?
Some bacteria have exocellular chain splitting
enzymes. 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
CoASH
- H2O
O
R – CH – CH2 – C – SCoA
CH3
FAD
OH
O
R – C – CH2 – C – SCoA
water addition
(Markovnyikov rule)
CH3
O
O
R – C = CH2 – C – SCoA
CH3
O
R – C – CH2 – C – SCoA
CH3
H2O
FADH2
Motor oils contain mainly branched
hydrocarbons, so the effect on environment
is long-term.
3. Aromatic compounds: aromatic ring slowly, but biologically degradable
cytochrom
OH
COOH
OH
COOH
O
P-450
O
COOH
O
HO – C – C – CH2 - COOH
cytochrom
P-450
OH
+
CH3 – COOH
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 compounds
starts later
BOI
organic nitrogen-containing compounds
day
desamination
NH3
NH4+ + 1,5 O2
Nitrosomonas
NO2- + 0,5 O2
slow
In aqueous medium
H2O + 2 H+ + NO2-
Nitrobacter
fast
NO3-
ORGANIC MATTER DEGRADATION IN NATURAL WATERS
approximated by first-order reaction
BOD t: residual oxygen demand at the t time,
BOD 0: total biological oxygen demand at the beginning t=0
k : air supply constant at a given temperature
BOD t = BOD0 *(1 – e -kt)
Air supply constant
water type
Little lakes, dead branches
Slow flow
Large, slow water flow
Large, normal water flow
Fast flow
k [day-1] 20°C
0,1 – 0,23
0,23 – 0,35
0,35 – 0,46
0,46 – 0,69
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
AEROB
ANAEROB
carbon content
In form of
carbon dioxide
(~50%)
organic
matter content of
waste water (100%)
carbon content
of sludge
~50%
carbon content of biogas 90-95 %
methane : carbon dioxide ~ 50-50 %
organic matter content
of waste water (100%)
carbon content of
drain water
~ 1%
- well known technology
- aeration: energy intensive
- sludge disposal problem (heavy metals)
- sludge fermentation → biogas
- sludge incineration
(ash content: < 60%)
(organic matter: > 25%)
(water content: < 50 %)
carbon content of
sludge
~1-5%
carbon content of drain
water
~ 1-5%
- lesser-known technology
- large body of water –> warming problem
- less sludge formation
- fuel gas formation
- sensitive to toxic matter
- COD > 2000 mg/dm3
- higher capacity
- 1 kg organic matter ~ 1 m3 biogas