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Anaerobic Reactors
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8th IWA Specialist Group Conference on Waste Stabilization Ponds
.
2nd Latin-American Conference on Waste Stabilization Ponds
Round TableIntegration of ponds with other systems
Belo Horizonte, April 2009
Carlos Augusto de Lemos ChernícharoDepartment of Sanitary and Environmental Engineering
Federal University of Minas Gerais – Belo Horizonte - Brazil
Brazilian and developing countries:
• Large pieces of flat land are not always available
• Enormous sanitation deficit
• Shortage of financial resources
• Lack of qualified operational personal
• Need of low cost, sustainable and simplified wastewater treatment systems
• Soil characteristics many times inappropriate for large natural systems, such as ponds and constructed wetlands
• Reuse still in early stages
Based on that scenario:
• Two process combinations have very interesting features:
• Quality of treated effluent is mainly regulated considering discharge and receiving body standards
• Compact anaerobic treatment systems can play a major role:
UASB + Polishing Ponds (PP)
UASB + Trickling Filters (TF)
UASB reactor is a very good alternative
Brief background on UASB reactors
Drawbacks and possible improvements
Examples of full-scale applications
Summary
Integration with Polishing Ponds
Integration with Trickling Filters
Final remarks
Brief background on UASB reactors
Main characteristics Advantages Applicability
Large urban areas
Small decentralized
systems
Small communities
No oxygen consumption
Low sludge production
Sludge is more concentrated and easy to dewater
Biogas production
Simple to operate
Lower O&M costs
Lower construction costs
Possibility of energy recovery
Anaerobic systems: general aspects
Brief background on UASB reactors
UASB Reactor
• The system is self-mixed by the upflow movement of biogas bubbles and by the liquid through the reactor, allowing the contact between the organic matter and the biomass. As a result, biogas is formed.
Brief background on UASB reactors
UASB Reactor
• The 3-phase separator is located in the upper part of the reactor, allowing the separation of gas, liquid and solids
Brief background on UASB reactors
UASB Reactor
• The settling zone allows the exit of the clarified effluent and the return of solids (biomass) to the digestion zone, in lower part of the reactor
Brief background on UASB reactors
UASB Reactor
• The UASB reactor functions, simultaneously, as a primary settler, as a biological reactor, as secondary clarifier and as sludge digester
Brief background on UASB reactors
UASB Reactor – Typical configurations
Brief background on UASB reactors
Examples of full-scale applications
• Location: Itabira – Brazil• Configuration: UASB reactors + TF
• Design population: 60,000 inhabitants• Design flowrate: 120 L/s (1st stage)
Itabira WWTP
Examples of full-scale applications
Itabira WWTP
Sludge withdrawal and sampling ports
Examples of full-scale applications
Itabira WWTP
Feed distribution system and 3-phase separator
Examples of full-scale applications
Itabira WWTP
Biogas flare and thermal sludge treatment device
Examples of full-scale applications
• Location: Belo Horizonte – Brazil• Configuration: UASB reactors + TF
• Design population: 1 million inhabitants• Design flowrate: 1.8 m3/s (1st stage)
Onça WWTP
Examples of full-scale applications
Aerial view
Onça WWTP
Examples of full-scale applications
Aerial view
Feed distribution system (top of the reactor)
Onça WWTP
Examples of full-scale applications
Feed distribution system (bottom of the reactor)
Onça WWTP
Examples of full-scale applications
3-phase separator
Onça WWTP
Examples of full-scale applications
Biogas system
Onça WWTP
Examples of full-scale applications
Drawbacks and possible improvements
Odour generation
Most of all are possible to control, with proper designs & adequate construction, operation and maintenance
Corrosion
Limited efficiency
Scum
Foam
Anaerobic systems: inherent limitations
Methane emission
Drawbacks and possible improvements
Proper materials
Proper lining
Turbulence minimization
Turbulence maximization
Corrosion
Inherent limitations: corrosion
Drawbacks and possible improvements
Liquid phase
Turbulence minimization
Aerobic post-treatment
Gaseous phase
Reactor cover
Gas collection
Gas treatment
Gas flare
Turbulence maximization
Odour
Inherent limitations: Odour
Drawbacks and possible improvements
Ongoing researches
Removal device
Treatment and final disposal
Minimize formation
The problem
Scum
Inherent limitations: Scum
Drawbacks and possible improvements
Control of household discharges
Turbulence minimization
Aerobic post-treatment
The problem
Foam
Inherent limitations: Foam
Drawbacks and possible improvements
Compliance with local guidelines ? (ex.: dilution, agricultural reuse etc.)
Post-treatment for the removal of carbonand pathogens (well established)
Improvement of anaerobic effluent quality(Ongoing research)
Post-treatment for the removal of N and P(research still needed)
Limited efficiency
Inherent limitations: Limited efficiency
Drawbacks and possible improvements
Micro-aeration inside the reactor?
Stripping outside the reactor?
Methane emission
Inherent limitations: Methane emission
Biological oxidation?
Drawbacks and possible improvements
The problem
UASB technology: summary
• Consolidated technology in many warm-climate regions
• Great advantages and broad application, but operational limitations still exist
• Further expansion and wider application can be significantly hindered if design and operationaldrawbacks are not solved
Drawbacks and possible improvements
Integration with Polishing Ponds
UASB reactor + Polishing Ponds: typical flowsheet
Integration with Polishing Ponds
• Location: Centre for Research and Training on Sanitation UFMG/COPASA• Design population: 250 inhabitants• Design flowrate: 1.6 m3/h
UASB reactor + Polishing Ponds: Experimental Units
Integration with Polishing Ponds
180 mg/L
60 mg/L
COD
TSS
Integration with Polishing Ponds
Performance regarding organic matter and solids
Operational conditions:
- HRT: 10 to 13 days
- H: 0.60 to 0.80 m
20 mg/L
Operational conditions:
- HRT: 10 to 13 days
- H: 0.60 to 0.80 m
103 MPN/100 mL
NH3
E. coli
Performance regarding ammonia and E. coli
Integration with Polishing Ponds
UASB + PP system: summary
• Area required is large: 2 – 3 m2/inhabitant
• Total HRT is lower than in most natural treatment systems
• UASB reactor: main unit responsible for organic matter removal
• Ponds: responsible for excellent coliform and good ammonia removals
• Coarse filter: decreases algal concentration, thus leading to complementary BOD and SS removal
Integration with Polishing Ponds
Integration with Trickling Filters
UASB reactor + Trickling Filter: typical flowsheet
Integration with Trickling Filters
• Location: Centre for Research and Training on Sanitation UFMG/COPASA• Design population: 500 inhabitants• Design flowrate: 3.2 m3/h
Compact UASB + Trickling Filter System: Experimental Units
Integration with Trickling Filters
Integration with Trickling Filters
Compact UASB + Trickling Filter System: Experimental Units
Individualized compartments
• Location: Centre for Research and Training on Sanitation UFMG/COPASA• Design population: 400 inhabitants• Design flowrate: 2.6 m3/h
Trickling Filter with different types of packing media
Integration with Trickling Filters
Full-scale UASB + TF system: Itabira – Minas Gerais
Integration with Trickling Filters
Concentrações de DBO total (mg/L) - efluente UASB e decantadores FBP
UASB Escória anel DHS Conduíte0
10
20
30
40
50
60
70
80
90
Concentrações de SST (mg/L) - efluentes UASB e decantadores FBPs
UASB Escória anel DHS Conduíte0
20406080
100120140160180200220240260
Concentrações de DQO total (mg/L) - efluente UASB e decantadores
UASB Escória Anel DHS Conduíte0
50
100
150
200
250
300
350
400
450
60 mg/L
180 mg/L
60 mg/L
BOD COD
TSS
Integration with Trickling Filters
Performance regarding organic matter and solids
Operational conditions:• Average temperature: 250C• HLR: 20 m³.m-2.d• OLR 0.43 kgBOD.m-3.d-1
20 mg/L
Operational conditions:• Average temperature: 230C• HLR: 10 m³.m-2.d-1
• OLR 0.38 kgBOD.m-3.d-1
NH3
Integration with Trickling Filters
Performance regarding ammonia removal
20 mg/L
Operational conditions:• Average temperature: 250C• HLR: 10 m³.m-2.d• OLR 0.24 kgBOD.m-3.d-1
NH3
2 mg/L
Operational conditions:• Average temperature: 230C• HLR: 20 m³.m-2.d-1
• OLR 0.43 kgBOD.m-3.d-1
LAS
Integration with Trickling Filters
Performance regarding anionic surfactants
2 mg/L
Operational conditions:• Average temperature: 250C• HLR: 10 m³.m-2.d• OLR 0.24 kgBOD.m-3.d-1
LAS
UASB + TF system: summary
• Very compact system: ~ 0.1 m2/inhabitant
Drawbacks and possible improvements
• UASB reactor: main unit responsible for organic matter removal
• TF: complementary BOD and SS removal
• TF: poor coliform removal
• TF: good ammonia removal can be accomplished, but surface area and depth should be increased
Final remarks
Critical and important aspects in the selection of alternatives for wastewater treatment in developed and developing regions
Selection criteria for developed and developing countries
Developed countries Developing countriesEfficiencyReliabilitySludge disposalLand requirementsEnvironmental impactsOperational costsConstruction costsSustainabilitySimplicity
critical Important Important criticaladapted from von Sperling, 1996
Relative comparison of UASB/PP and UASB/TF treatment methods
Treatment system
EconomySustainability
Simplicity in O&M
Removal efficiencyReli-ability
Lower possibility of environmental problems
Requirements CostsBOD Nutrients Coliforms Bad
odours Noise Aerosol Insects wormsLand Energy Constr. O & M
UASB + PP + +++++ ++/++++ ++++ +++++ ++++ ++++ +++ +++++ ++++ +++ +++++ +++++ ++
UASB + TF ++++ ++++ +++ +++ ++++ +++ +++++ ++/+++ ++ ++++ ++ ++++ ++++ +++
+++++: most favourable +: least favourable ++++, +++, ++: intermediate grades, in decreasing order + / +++++: variable with land and soil characteristics
Both alternatives are very attractive for treating domestic wastewater in developing countries
Thanks for your attention
Scum accumulation on settling compartment
Scum accumulation inside the 3-phase separator
Waste gas
Biogas
FunBi
ogas
: micr
o-ae
ratio
n Biogas treatent
Heat
Electricity
Cogeneration of heat and electricity
Biofiltro
H2S and CH4 control in large WWTP
Biofilter
COD balance in UASB reactors treating domestic wastewater
Best situation
Conversion to CH4 and
recovery as biogas64%
Conversion to CH4 and loss with the liquid
phase8%
Losses with the gaseous
phase5%
Used for sulfate
reduction4%
Conversion to biomass
21%
Conversion to CH4 and
recovery as biogas23%
Conversion to CH4 and loss with the liquid
phase36%
Losses with the gaseous
phase5%
Used for sulfate
reduction16%
Conversion to biomass
21%
COD balance in UASB reactors treating domestic wastewater
Worst situation
Biofiltro
Biogas FlareWaste gas
Degasified effluent
Biogas
Efflu
ent s
atura
ted w
ith C
H 4
Was
te ga
s fro
m pr
elimi
nary
treatm
ent
Fun
H2S and CH4 control in small WWTP
Biofilter