Transcript Document 7223646

The following slides are provided by
Vincent O’Flaherty.
Dr.
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Anaerobic Industrial
Wastewater Treatment Ecology and Technology
A Short 4 Lecture Course
Dr. Vincent O’Flaherty
www.nuigalway.ie/microbiology/mel
Course Outline
• Anaerobic biological treatment of
industrial wastewaters
• The phenomenon of granulation of
anaerobic sludge - an example of cooperative interaction between different
trophic groups of microbes
• The anaerobic treatment of sulphatecontaining wastewaters - an example of
competitive interactions between different
groups of microbes
INDUSTRIAL WASTEWATERS
• Very different from sewage sludge,
animal manures, MSW, etc.
• Usually produced in large volume; low
content of suspended solids; BOD/COD
contributed mainly by dissolved
organics; varied chemical composition
• Generally readily biodegradable (with the
exception of some pharmaceutical/fine
chemical wastewaters)
• Very variable range with respect to the
organic matter content (BOD/COD), the
solids content, the chemical composition,
the biodegradability of the chemicals and
the C:N:P ratio
• e.g. from food processing (abattoirs, dairy,
cannery etc.), brewing, distillery,
pharmaceutical, fine chemical, tannery,
etc.
3 categories based on COD content:
1.
< 2000 mg/l COD
2.
2000 - 10000 mg/l COD
3.
10000 - 100000 mg/l COD
Raw domestic sewage has a COD of 400 - 600 mg/l
Characteristics of some wastewaters
from the food-processing industrial
sector
Industry
BOD
COD Suspended
(mg/l) (mg/l)
solids
(mg/l)
pH
Brewery
850
17,000
90
4 - 6
Citrus
Cannery
2,000
-
7,000
Acid
Dairy
600 1,000
2 4,000
200 - 400
Acid
Potato
processing
2,000
3,500
2,500
11 13
Sugar beet
450 2,000
600 3,000
1,500
2,500
50,000
4,000
6,000
70 80,000
Slaughterhouse
Silage
800 - 1,000 7 - 8
800
7
low
Acid
Options available for treatment
of IWW
• Principal components are soluble
pollutants
• The removal of soluble organic matter
from wastewaters is always a biological
process - the most widely applied
biotechnological process
• Essentially, the choice is between aerobic
and anaerobic processes
ADVANTAGES AND DISADVANTAGES OF
AEROBIC AND ANAEROBIC TREATMENT
• Aerobic
• generally achieves full BOD removal
• occurs at ambient temperature
• doesn't need enclosure
• produces large quantities of waste biomass
requiring safe disposal
• Requires high energy consumption for
aeration purposes
• Systems include activated sludge,
trickling filters - very commonly used for
both sewage treatment and IWW
• Not covered here - but important!
• Anaerobic
• Won’t achieve complete BOD removal
• Must be heated* and enclosed
• Achieves a high rate of pathogen kill and
reduces odours
• Produces much smaller amounts of
waste biomass
* Uses up to 30% of the biogas - latest work is
on use of low-temperature systems
Main Advantage
• Between 70-80% of the energy content
of the waste constituents is conserved
in the methane product - net production
of a usable fuel, renewable energy
Why Anaerobic Treatment for
IWW ?
•
Increasingly used for the treatment as:
•
It produces biogas. This energy source is
used by industries for heat and power
generation or steam production - net
producer of fuels whereas aerobic systems
are heavy fossil fuel-utilisers, net reduction
in CO2 emissions/greenhouse effect
•
It produces less waste sludge (biomass)
than aerobic systems, less to dispose of
(expensive)
•
Used as an alternative to or in
conjunction with aerobic treatment
systems - depending on the fate of the
treated effluent
• Used to remove COD/BOD prior to discharge to a
municipal sewer
• Used with aerobic plant - first stage anaerobic
followed by aerobic treatment to discharge
standard (also other treatments if required)
• AD is increasingly applied because high-rate
reactor designs overcame some problems
Historical Difficulties
• CSTR designs originally used, same as for
manuries and sewage sludge
• In these systems the hydraulic retention time
(HRT) is equal to the solids retention time (SRT) necessary to allow hydrolysis of solid organics
• BUT also required because of the very slow
growth rate of methanogens and syntrophs (5-9
day dt in some cases)
• Risk of washout of bacteria is HRT is less than 10
days
• CSTR initially used for IWW with high levels of
particulates - e.g. abbatoir, vegetable processing
etc.
• As a result of v. long HRT need a very large
digester volume - capital and running costs are
high, so not often feasible
Development of AD designs
specifically for IWW
Aim was to get benefits of AD, but reduce the
disadvantages - i.e. costs, digester volume
Logic is :
1. Reduce HRT
2. Consequent decrease in heating costs
3. Resultant increase in the net gain of biogas,
financial and environmental benefit
TWO MAIN STRATEGIES DEVELOPED
• 1. Biomass Recycle (Anaerobic Contact)
• Analogous to aerobic activated
sludge systems
• Biomass washed out of the system
is separated and returned to the
digester
• Separate SRT from HRT - biomass
retention time becomes longer
Schematic diagram of the
anaerobic contact digester design
• Allows operation at higher organic loading
rates - smaller digester volumes required
lower capital costs for construction
• Used mainly for the kinds of IWW treated
previously by CSTR
• Allows reduction of the HRT to 6-12 days
(1/2 to 1/4 of digester volume) - 60-95%
COD removal
• Used mainly for food processing
wastewaters with a significant content of
suspended solids:• Starch production; meat processing;
abbatoir; distillery; green vegetable
canning wastewaters, etc.
Retention of the Biomass within the
Reactor Independent of the Wastewater
Flow
2. Retained Biomass Systems
• Second generation of IWW AD designs
• AC systems rarely operated below 6 day HRT because ww being treated usually contains
insoluble organic polymers -i.e. hydrolysis is the
rate limiting step
• But most IWW have very low ss content, BOD or
COD is contributed by soluble, low Mwt organics
that are readily biodegradable
• So…use of long HRT is not necessary and is
obviously very costly
• Alternative designs were developed that
allowed further reduction of the HRT’s and
these 2nd generation digesters are the most
important in terms of modern IWW treatment
• Idea is to retain biomass inside the digester
independent of the ww flow - allows HRT to be
much reduced
• HRT in these retained biomass
digesters can be reduced to as low as
several hours depending on the
wastewater and the digester design
and mode of operation.
• Significant reduction in reactor volume
achieved
2 Main Types of RetainedBiomass Digesters
• 1. Fixed-Film Systems
• 2. Granular Sludge-based Systems
Anaerobic filter/fixed film systems
• Strategy is to provide an inert surface for
bacterial adhesion - biofilm formation
• Supports include plastic, sand etc. - depending
on the physical arrangement of the support,
biomass may also be retained as flocs or
aggregates in the interstitial spaces
• Either fixed-bed or fluidised-bed designs
• Fixed-bed Systems are packed with support
media with large surface area for biofilm
development
Schematic diagram of an Anaerobic
Filter Reactor
Biogas
xxxxxxx
xxxxxxx
xxxxxxx
xxxxxxx
xxxxxxx
xxxxxxx
xxxxxxx
xxx
Effluent/Influent
Influent/
Effluent
Sludge Bed
• WW is passed over the biofilm - either in upflow
or down flow direction - biogas is collected at the
top of the digester
• Fluidised-bed Systems use very small particles
of sand or activated carbon
• Very fast upflow velocity is applied so that the
bed is fluidised - HRT is in hours not days, but
expensive to operate and not very stable
High-rate reactor designs
• Anaerobic digester
designs based on
biomass retention:
• (a) anaerobic filter/fixed
bed reactor;
•
(b) downflow stationary
fixed-film reactor;
• (c) expanded bed/fluidised
bed reactor;
• (d) upflow anaerobic
sludge blanket reactor;
Expanded granular Sludge
Bed
• (e) hybrid sludge bed/fixed
bed reactor
2. Granular Systems
• Biomass self-aggregates into dense wellsettling granules
• Thus it is retained within the digester even
during upflow operation (not washed out)
Granular Sludge Bed
(UASB/EGSB/Hybrid) systems
• e.g. UASB reactor, most commonly
applied worldwide
• Very high biomass density in the
reactor - allows very high organic
loading rates
• Optimal spatial organisation of different
trophic groups within the granules
Schematic diagram of an Upflow
Anaerobic Sludge Bed (UASB) reactor
Biogas
Effluent
Sludge Bed
Influent
EGSB (Expanded Granular Sludge
Bed)
Biogas
Effluent
Upflow velocity
of 10-15 m/h
Sludge Bed
RECYCLE LINE
Increased sludgewastewater contact
Influent
Hybrid Reactor Design
BIOGAS
xxxxxx
xxxxxx
xxxxxx
S
L
U
D
G
E
INFLUENT
EFFLUENT
R
E
C
Y
C
L
E
Matrix plastic etc.
Scanning electron micrograph of mesophilic sludge granule
at low magnification (Sekiguchi et al., 1999).
• Well-settling nature
of granules allows
them to be retained
in the reactor
USE OF ANAEROBIC DIGESTION FOR
INDUSTRIAL WASTEWATER
TREATMENT
• Installation of anaerobic digesters for
industrial wastewaters has grown very
rapidly over the past 15-20 years.
• UASB design is the most widely used,
EGSB becoming more common.
• Very high loading rates and biogas
productivity; HRT typically 1 day or
less.
• Up to 30 kg COD/m3/d - UASB; 100 kg COD/m3/d EGSB
• Up to 20 m3 biogas/m3/d
• Typically achieve 80-99% COD removal.
• A.D. treated wastewater is either discharged to the
municipal sewer for final treatment prior to
discharge or subjected to aerobic polishing, NPK
removal, etc. by the industry prior to discharge to
the receiving waterbody.
• Used mainly at full-scale for treatment
of wastewaters from the food and drinks
sector.
• Growing recent application for more
recalcitrant wastewaters.
EXAMPLE OF FULL-SCALE ANAEROBIC
DIGESTER FOR INDUSTRIAL WASTEWATER
TREATMENT
• ADM citric acid production plant in Co.
Cork, Ireland.
• Wastewater characteristics:7000 m3/day
12000 mg COD/l
4000 mg sulphate/l
• Digester specification:-
Upflow, fully-packed anaerobic
filter random-packed,
polypropylene cascade rings;
7300 m3 volume
Diameter of 36 m, height of 12.4
• Operational performance:HRT of approximately 1 day
52% COD removal
81% BOD removal
30 m3 biogas/day (66% CH4)
(corresponds to 18 l/min)
• Biogas is used for steam generation
and space heating
North Kerry Milk Processing Plant
in Co. Kerry, Ireland
• Wastewater characteristics:4000 m3/day
5000 mg COD/litre
• Digester specification:Downflow, random-packed anaerobic filter,
polypropylene rings
4500 m3 volume
• Operational performance
• HRT of approximately 1 day
• c. 90% COD/BOD removal
• Biogas used for electricity generation
(combined heat and power plant).
• Post treatment (activated sludge)
prior to discharge
• Operated on a seasonal basis
(March - October)