anaerobic reactors - chernicharo

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

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


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.


UASB Reactor

• The 3-phase separator is located in the upper part of the reactor, allowing the separation of gas, liquid and solids


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


UASB Reactor

• The UASB reactor functions, simultaneously, as a primary settler, as a biological reactor, as secondary clarifier and as sludge digester


UASB Reactor – Typical configurations


• Location: Itabira – Brazil• Configuration: UASB reactors + TF

• Design population: 60,000 inhabitants• Design flowrate: 120 L/s (1st stage)

Itabira WWTP


Itabira WWTP

Sludge withdrawal and sampling ports


Itabira WWTP

Feed distribution system and 3-phase separator


Itabira WWTP

Biogas flare and thermal sludge treatment device


• Location: Belo Horizonte – Brazil• Configuration: UASB reactors + TF

• Design population: 1 million inhabitants• Design flowrate: 1.8 m3/s (1st stage)

Onça WWTP


Aerial view

Onça WWTP


Aerial view

Feed distribution system (top of the reactor)

Onça WWTP


Feed distribution system (bottom of the reactor)

Onça WWTP


3-phase separator

Onça WWTP


Biogas system

Onça WWTP


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


Proper materials

Proper lining

Turbulence minimization

Turbulence maximization

Corrosion

Inherent limitations: corrosion


Liquid phase


Aerobic post-treatment

Gaseous phase

Reactor cover

Gas collection

Gas treatment

Gas flare

Turbulence maximization

Odour

Inherent limitations: Odour


Ongoing researches

Removal device

Treatment and final disposal

Minimize formation

The problem

Scum

Inherent limitations: Scum


Control of household discharges


Aerobic post-treatment

The problem

Foam

Inherent limitations: Foam


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


Micro-aeration inside the reactor?

Stripping outside the reactor?

Methane emission

Inherent limitations: Methane emission

Biological oxidation?


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


UASB reactor + Polishing Ponds: typical flowsheet


• 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


180 mg/L

60 mg/L

COD

TSS


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


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


UASB reactor + Trickling Filter: typical flowsheet



Compact UASB + Trickling Filter System: Experimental Units


Individualized compartments


Trickling Filter with different types of packing media


Full-scale UASB + TF system: Itabira – Minas Gerais


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


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


Performance regarding ammonia removal

20 mg/L


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


Performance regarding anionic surfactants

2 mg/L


LAS

UASB + TF system: summary

• Very compact system: ~ 0.1 m2/inhabitant


• 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

anaerobic reactors - chernicharo

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