The primary goal
The removal and degradation of organic
matter under controlled condition
Three major steps
Primary treatment
Secondary treatment
Tertiary treatment
Primary treatment
A physical process that involves the separation of large debries, followed by sedimentation
Comprises grit tank and settling tank
Settling tank also known as sedimentation tank (sand and gravel)/clarifier
About half suspended organic solids settle to the bottom as sludge or biosolids (primary sludge)
Secondary treatment
Consist of biological degradation
(decomposed and the number of
pathogens is reduced)
The effluent from primary treatment may
be pumped into a tricklingfilter bed ( an
aeration tank/a sewage lagoon
Disinfection step is generally included at
the end of treatment
Large-scale wastewater
treatment
Trickling filter bed • Rocks provide a matrix supporting the growth
of a microbial biofilm that actively degrades the organic material under aerobic conditions
• Effluen from primary treatment is pumped into a tank and mixed with bacteria-rich known as activated sludge
• air and pure oxygen pumped through the mixture promotes bacterial growth and decomposition of the organic material
Then goes to a secondary
settling tank
Water siphon off the top of the tank
Sludge is removed from the bottom
Some of the sludge is used as an inoculum
for the incoming activated sludge
The sludge that is not return as secondary
sludge
Trickling filters
Gram negative bacteria : Zooglea,
Pseudomonas, Alcaligenes,
Achromobacter, Flavobacterium
Gram positive : Corynebacterium, etc
Fungi : Fusarium, Trisporon, Ascoidea
In secondary treatment
It contains a high level of the organic
nutrients phosphate and nitrate
Nitrosomonas : oxidize ammonia to nitrite
Nitrobacter : oxidize nitrite to nitrate
Secondary treatment
Aerobic digestion tank
Anaerobic digestion tank
Anaerobic digestion tank
The degradatif and fermentative process
divided into 2 stages : acid forming and
methane forming
Genera of Methane forming stage :
Methanobacterium, Methanosarcina,
Methanococcus (convert acetate,
hydrogen and CO2 to methane)
The major metabolic stages
Complex organic compounds
(polysaccharides, fats, protein)
Hydrolisis
Hydrolysis by extracellular bacterial enzymes
Monomeric compounds (sugar, fatty acids,
amino acids)
Higher organic acids Acidogenesis
Acetic acid, H2, CO2 Acetogenesis
CH4 methanogenesis
Types of Bioremediation
In situ bioremediation
Composting
Landfarming
Above-ground bioreactors
Activated sludge process
Activated sludge flocs
Note filamentous bacteria
Note Vorticella and other protozoa
Activated sludge model
L L0
L
L
L
L
Urban Water Systems
12 Sludge treatment
© PK, 2006 -
page 21 Composition of sludge
All non-degraded compounds extracted from wastewater are found in the
sludge
• Micro-organisms
• Viruses, pathogens, germs in general
• Organic particles, heavily bio-degradable
• Organic compounds, inert, adsorpted to sludge flocs
• Heavy metals
• Micro-pollutants, pharmaceuticals, endocrine disrupters
• Predominantly water
Activated sludge plants
Hyperion, Playa del Rey, CA)
Primary aeration tank
Tertiary treatment
Involve some type of physicochemical
treatment such as coagulation, filtration,
activated carbon adsorbtion of organics
and additional disinfectan
Urban Water Systems
12 Sludge treatment
© PK, 2006 -
page 25 Goals of sludge treatment
Volume reduction
Elimination of pathogenic
germs
Stabilisation of organic
substances
Recycling of substances
• Thickening
• Dewatering
• If used in agriculture as fertiliser or compost
• Gas production
• Reduction of dry content
• Improvement of dewatering
• Reduction of odour
• Nutrients, fertiliser
• Humus
• Biogas
Urban Water Systems
12 Sludge treatment
© PK, 2006 -
page 26 Overview
Thickening
Thickening
Hygienisation
Stabilisation
Dewatering
Drying
Incineration
Pro
cess w
ate
r
Biogas
Energy
Agriculture
Disposal site
Atmosphere
Wastewater treatment
Primary, secondary, tertiary sludge
Construction industry
Gujer (1999)
Oxygenated systems
Cryogenic air separation facility, Hyperion, Playa del Rey, CA)
Typical steps in modern wastewater
treatment
Urban Water Systems
12 Sludge treatment
© PK, 2006 -
page 29 Flotation unit
Examples of naturally
transmissible catabolic
plasmids
Primary
substrate
Plasmid Size
(kb)
Host
Toluene pWW0 (TOL) 117 Pseudomonas
putida mt-2
Alkylbenzene
sulfonate
ASL 91.5 Pseudomonas
testosroni
octane OCT ~500 P.oleovorans
Naphthalene Nah7 83 P. Putida PpG7
Pseudomonas putida mt-2
Chromosomal gene encode ortho
pathway : acetyl CoA and succinate
TOL plasmid encodes meta pathway :
acetaldehide and pyruvic acid
TOL (pWW0) plasmid
The genes encoding catabolic enzymes :
xyl genes
The Xyl genes : xyl ABC (upper) and xyl
XYZLEGFJKIH (lower/meta)
Xyl ABC
Encode degradation toluene and xylene
to benzoate and metylbenzoates
Xyl XYZLEGFJKIH
Encodes degradation of benzoate and
methylbenzoate to acetaldehyde and
pyruvat