Anaerobic wastewater treatmentAnaerobic wastewater treatment

Nidal MahmoudInstitute of Environmental and Water Studies,Institute of Environmental and Water Studies,,,

Birzeit UniversityBirzeit Universitynmahmoud@birzeit.edu

Ecological Sanitation Training CourseSWITCH PROJECT

IEWS, Birzeit University, 25-27 January 2011

Outline

1. Effect of Low Temperature on the bio-chemical and physical properties of wastewater and its effect onphysical properties of wastewater and its effect on anaerobic treatment

Anaerobic bio-chemical processesp Physical and chemical properties of wastewater

2 A bi T h l i f L T t S2. Anaerobic Technologies for Low Temperature Sewage Treatment

Difficulties of anaerobic (low temperature) sewage treatment Difficulties of anaerobic (low temperature) sewage treatment Technical perspectives for anaerobic sewage Treatment

Effect of Low Temperature on the bio-chemical and physical properties of wastewater and its effect on anaerobic treatmenton anaerobic treatment

Effect of Low Temperature on the bio-chemical and physical properties of wastewater and its effect on anaerobic treatment

Anaerobic bio-chemical processes:Mic oo ganisms t pe and g o th ateMic oo ganisms t pe and g o th ate

on anaerobic treatment

––Microorganisms type and growth rate Microorganisms type and growth rate –– Substrate utilization rateSubstrate utilization rate

Physical and chemical properties of wastewater–– Solubility of gaseous compoundsSolubility of gaseous compounds–– Viscosity of liquidsViscosity of liquids

Anaerobic biological conversion

Microorganisms type and growth rate

Relative growth rate of pshchrophilic, mesophilic and th hili ththermophilic methanogens

S b t t tili ti tS b t t tili ti tSubstrate utilization rateSubstrate utilization rate

Anaerobic conversion of organic matterAnaerobic conversion of organic matterAnaerobic conversion of organic matterAnaerobic conversion of organic matter

Hydrolysisy y

A id iAcidogenesis

Acetogenesis

M th iMethanogenesis

Hydrolysis Step

dF Arrhenius equation

xFkdtdF

hRTEAek /dt

h Aek

WithWith:

F:concentration of biodegradable solid substrate (g/L)

With:

T: the absolute temperature (ºK);

R: the ideal gas constant (J molesolid substrate (g/L)

Kh: hydrolysis constant (d-1)

t: time (d)

R: the ideal gas constant (J.mole -1.ºK-1);

A: the pre-exponential factor (d-1); t: time (d)E: activation energy (kJ.mole-1)

MethanogenesisMethanogenesis StepStep

temp Activitperatur ties at

re / act abscistivity a sa

t 35 ° C

Temperature dependency of the methane production rate ofTemperature dependency of the methane production rate of

C

Temperature (°C)Temperature dependency of the methane production rate of Temperature dependency of the methane production rate of

mesophilicmesophilic anaerobic processanaerobic process

Physical and chemical properties of wastewater

Solubility of gaseousSolubility of gaseousSolubility of gaseous Solubility of gaseous compoundscompounds

Solubility of gases increases below 20 °C

P

Henry’s law

At low temperatureg

Tg P

HPx

At low temperature HWith:

High dissolved gases in the effluent, i.e

Xg: mole fraction of gas in water;

H: Henry’s law constant; ,

methane and hydrogen sulfide

PT: total pressure;

Pg : mole fraction of gas in air

Viscosity of liquidsViscosity of liquids

Low waterLow water temperature

Viscosity of water Low biogas increases production

rate

Poor mixing; higher energy is required

f i ifor mixing

Degree of Water Mixing in the Reactor

Relation between temperature andRelation between temperature and

V*pG

μ Temperature Viscosity %

Relation between temperature and Relation between temperature and turbulence in the reactorturbulence in the reactor

Vμ

G l it di t ( 1)

() of water in the reactor

Increase of G from 15 ºCG: velocity gradient (s-1)

P: power input (W)

V: volume of water in the reactor (m3)

reactor 15 CºC Pa.s % 15 1.14x10-03 -

03V: volume of water in the reactor (m3)

: dynamic viscosity (Pa.s)20 1.00x10-03 725 8.90x10-04 13 30 7.98x10-04 1940 6.53x10-04 32

Anaerobic Technologies for Low TemperatureAnaerobic Technologies for Low Temperature Sewage Treatment

Anaerobic Technologies for Low Temperature Sewage Anaerobic Technologies for Low Temperature Sewage TreatmentTreatmentTreatmentTreatment

Difficulties of anaerobic (low temperature) sewage treatment

Technical perspectives for anaerobic sewage Treatment– Anaerobic High Rate Wastewater Treatment Systems– Digestion Limiting Step– Technology Innovation

Difficulties of anaerobic (low temperature) sewage treatmenttreatment

Sewage belongs to the ‘complex’ wastewater category because:category because:

It contains a higher fraction particulate COD

The biodegradability of the various COD fractions is moderate

It is a low strength wastewater with varying concentrations

Its temperature is relatively low

COD fractions

Raw sewageRaw sewage

Suspended COD (CODss)

4 4 m paper-filtered sewage

Suspended COD (CODss)

4.4 m paper-filtered sewage

Colloidal COD (COD l)

0.45 m membrane filtered

Colloidal COD (CODcol)

Dissolved COD (CODdi )sewage

Dissolved COD (CODdis)

Wastewater Characteristics of Ramallah City,

Parameters Ramallah Al-Bireh Al-Jalazoon

Wastewater Characteristics of Ramallah City, Al - Bireh City and Al-Jalazoon refugee camp

COD Total 2180 1586 1489

Suspended 1096 919 725Suspended 1096 919 725Colloidal 323 274 327

Dissolved 761 393 438 VFA as COD 187 160 123VFA as COD 187 160 123SO4

2- as SO42- 975 138 213

TSS 729 736 630 VSS 584 617 480pH 7.45 7.26 7.31 Tww Summer 30.9 25.8 23.4

Winter 13 Tamb. Summer 27

Winter 13.8 Winter 13.8Colour Reddish to black Medium brown Light brown

Technical Perspectives for Anaerobic Sewage TreatmentTreatment

Anaerobic High Rate Wastewater Treatment SystemsAnaerobic High Rate Wastewater Treatment Systems

Advantages of High-rate anaerobic systemsAdvantages of High-rate anaerobic systemsLow construction, operation and maintenance costs,Small-land requirement,q ,Low excess-sludge production,Production of biogas (source of energy).

Anaerobic biotechnology

Anaerobic biotechnologyUASB for sewage treatment has been applied successfully in several countries of hot climates, e.g. India, Colombia, Brazil, and GhanaGhana

Digestion Limiting Step

Under low temperature conditions (< 15ºC) and/or strong temperature fluctuations between summer (25ºC) and winter (15ºC), the

g g p

fluctuations between summer (25 C) and winter (15 C), the conventional UASB design needs reconsideration:

Limited Hydrolysis High SS

Accumulation of particulate organic matter

High SS

Deterioration of the reactor performance Limited hydrolysis p

Low removal efficiency

y y

Long retention time

Technology InnovationTechnology Innovation

Sewage treatment under low temperature conditions (<

gygy

g p (15ºC) and/or temperature fluctuations:

One stage:One stage:1. UASB reactor

Two Stage1. HUSB reactor followed by UASB2 HUSB t f ll d b EGSB2. HUSB reactor followed by EGSB3. AF followed by AH system4 Two-stage UASB system4. Two stage UASB system

UASB-Digester1. UASB-Digester system

Wang (1994) treated domestic sewage in a two-step system: UASB/EGSB reactor at 12oC

Removal (%)Parameter

UASB+EGSBTotal COD* 51Suspended COD 67Colloidal COD 42Dissolved COD 41

* measure for organic matter measure for organic matter

Elmitwalli (2000) improved the particulate matter removal during ( ) p p gthe anaerobic treatment of domestic sewage at low temperature using two stage AF-AH system

5 5

10

9

10

46

9

1 2 827

AF reactor AH reactor

Packing material: AF and AH reactors

The packing material consists of vertical sheet ofKnob thicknessBase thickness

The packing material consists of vertical sheet of reticulated poly-urethane foam (RPF) with knobs .

Why RPF?

has a high specific surface area (500 m2/m3), K b

g p ( / ),has a high porosity of 97%, RPF enables the retention of 15 gVS/l in attached

Knob

All biomass is attached, as the accumulated sludge

form.

, gon the bottom of the reactor is wasted weekly. Therefore clogging of the AF reactor is avoided.

COD removal efficiency (%) in the AF+AH at HRT of 4+8 h at y ( )13 oC

Removal(%)

Maximumremoval (%)*

Total COD 71**Suspended COD 91Colloidal COD 60 72Colloidal COD 60 72Dissolved COD 55 55

* from Last and Lettinga (1992) from Last and Lettinga (1992)** similar to that achieved in tropical countries

Two – stage UASBFirst stage inlet

Second stage inlet Maha Hallalsheh, 2002

Results two-stage pilot trials Middle

COD Removal: up to 80% BOD Removal: up to 85%SS Removal: up to 80%pilot trials Middle

East (Jordan):SS Removal: up to 80%Pathogen Removal: insufficient Potential CH4 production in Amman(at 170 000 m3 sewage/day): 17 500 m3/day !(at 170.000 m3 sewage/day): 17,500 m3/day !

2 – 2.5 MW

UASB - Digester system

Effluent

Gas metersGas holder

UASB Digester

Wat

erat

ing

WH

eaInfluentExcess sludge

Nidal Mahmoud, 2002

HRT: 6 hrs

HRT: 6 HRT: 20 d

T: 35 °CT: 15 °C

hrs

T: 15 °C

T: 35 C

C

Schematic diagram of Schematic diagram ofSchematic diagram of the UASB-Digester

pilot plant

Schematic diagram of the one stage UASB

pilot plantp p

SRT: 10, 15, 20 and 30 days

Process temperature: 25 and 35 outletinlet

p°C

The most substantial portion of the di ti f t i b h d t d

inlet

digestion of proteins, carbohydrates and lipids occurs within the first 15 and 10 days at Process temperatures of 25 and

gas bag

y p35 °C

Schematic diagram of a

CSTR digesterCSTR digester

Results UASB - Digester system, Mahmoud (2002)

Effluent concentrationsEffluent concentration (mg/L)Reactor CODt CODss CODcol CODdis VFA-COD

UASB 390 100 128 162 80(62) (36) (19) (47) (40)

UASB-Digester 151 32 68 50 3(34) (24) (17) (10) (3)

R l ffi i (%)Removal efficiencies

Removal efficiency (%)Reactor CODt CODss CODcol CODdis VFA-CODUASB 44 73 3 5 -8

(9) (14) (46) (17) (42)UASB Digester 66 87 44 30 95UASB-Digester 66 87 44 30 95

(6) (5) (15) (36) (8)

Results UASB - Digester system, Mahmoud (2002)

Removal efficiency of total COD in the UASB-Digester i i h d f UASB’system in comparison to those reported for UASB’s

applied in tropical countriesUASB-Di

Sao Paulo -B il

Bucaramanga -C l bi

Kanpur - India(D ij lDigester

(This study)Brazil(Vieira, 1988)

Columbia(Schellinkhout et al., 1988)

(Draaijer et al.,1992)

HRT (hr) 6 4.7 - 9 5 6Temp (C) 15 21 - 25 23 - 27 20 - 30CO (%) 66 (6) 0 66 62 0COD (%) 66 (6) 70 66 62 - 70

The UASB-Digester system produced 3 5 times lessThe UASB-Digester system produced 3.5 times less sludge than a parallel operating UASB reactor