Modifying a Conventional UASB Reactor to an Integrated UASB-g

Digester System for Sewage Pre-Treatment in Mountain Areas at Low

Temperatures (15 °CTemperatures (15 °C

Nidal Mahmoud, Grietje Zeeman, Jules B. van Lier, Gatze LettingaInstitute of Environmental and Water Studies,Institute of Environmental and Water Studies,Institute of Environmental and Water Studies,Institute of Environmental and Water Studies,

BirzeitBirzeit UniversityUniversitynmahmoud@birzeit.edu

Ecological Sanitation Training CourseSWITCH PROJECT

IEWS, Birzeit University, 25-27 January 2011

Modifying a Conventional UASB Reactor to anModifying a Conventional UASB Reactor to an Integrated UASB-Digester System for Sewage

Pre-Treatment in Mountain Areas at Low T t (15 °C)Temperatures (15 °C)

Nid l M h d G i tj Z J l B Li G tNidal Mahmoud, Grietje Zeeman, Jules B. van Lier, Gatze Lettinga

Sub-Department of Environmental Technology W i U i it Th N th l dWageningen University, The Netherlands

Water studies Institute,Birzeit University, Palestine

1st IWA International Workshop Anaerobic Digestion in Mountain Area (& isolated

rural zones)

Wastewater f lfacilities in Palestine

Ramallah WWTP: primary clarifier + ponds

Open conveyance & drains Al-Bireh WWTP: Oxidation Ditch

Wastewater characteristics in PalestineWastewater characteristics in Palestine

Vulnerable society with very limited water resources andlimited water resources and virtually no treatment

Decentralised treatment willDecentralised treatment will play an important role in the Palestinian water sector

biogas use

Application of full scale Anaerobic WWTP in tropical areas biogas usep

influent effluentU A S B

Post treatment

screening grit chamber

U A S B

- polishing pond- Trickling filterg- RBC- activated sludge- etc.

sludge drying bedreusewater

l d sludge drying bedsludgebiogas

UASB Overall Results “Sewage treatment”

COD Removal:………………. 70 - 80% BOD Removal: ………………. 75 - 85%SS Removal: 70 80%

Average Results Latin America SS Removal: …………………. 70 - 80%

Pathogen Removal: - Coliforms: 70 - 90%

Latin America and India:(COD < 500/600 mg/l)

- Helminth eggs: “up to 100%”

14.000 m3/d UASB Mirzapur 12.000 m3/d UASB BucaramangaIndia Colombia

UASB: options for decentralised sewage treatmentUASB: options for decentralised sewage treatment

Campina Grande, Brasil Odemira, Portugal

Masterplan of Recife metropolitan area: decentralised approach(Florencio et al., 2001)

Overall project goal:Overall project goal: Assessment feasibility of anaerobic sewage treatment in the mountain areas of Palestinetreatment in the mountain areas of Palestine

Specific goalsA t l l h t i ti ( t k )• Assessment local sewage characteristics (not known)

• Validation of the technical feasibility of a UASB-digester systemdigester system

• Optimising the digester design

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

Parameters Ramallah Al-Bireh Al-Jalazoon

Bireh City and Al Jalazoon refugee camp

Highest altitude: 1000 m!COD Total 2180 1586 1489

Suspended 1096 919 725 Colloidal 323 274 327

Dissolved 761 393 438VFA as COD 187 160 123 SO4

2- as SO42- 975 138 213

TSS 729 736 630TSS 729 736 630VSS 584 617 480 pH 7.45 7.26 7.31 T Summer 30 9 25 8 23 4Tww 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

‘Multiplicate’ time interval composite samplesMultiplicate time-interval composite samples

Impact of Low Temperatures:

At low temperatures (< 15ºC) and/or strong temperature fluctuations between summer (25ºC) and winter (15ºC), the i l t UASB t d i d id tisingle step UASB reactor design needs reconsideration:

Limited HydrolysisLimited Hydrolysis

Accumulation of particulate

High SS

Accumulation of particulate organic matter Limited

hydrolysis

Deterioration of the reactor performanceLong retention

Low removal efficiency

gtime

Required SRT for Hydrolysis in Reactor

160

180

Required SRT for Hydrolysis in Reactor

120

140

160

e [d

ays] Conventional UASB:

HRT 22-24 hrs!!

80

100

ed s

ludg

e

40

60

r st

abili

ze

0

20

SRT

for

10 15 20 25 30 35 40 45

Temperature [°C]

Amended process designs for low temperature sewage treatment

Stable reactor performance by separating: 1 R l d di ti f d d lid

low temperature sewage treatment

1. Removal and digestion of suspended solids 2. Conversion (bio-methanation) of colloidal and soluble COD

Various set-ups has been proposed:

1. HUSB reactor followed by UASB2. HUSB reactor followed by EGSB3. AF followed by AH system3. AF followed by AH system4. Two-stage UASB system

1 7AF reactor AH reactorTarek Elmitwalli (2001)

UASB - Digester system

Gas metersGas holder

Effluent

UASBDigester Nidal Mahmoud

(PhD thesis 2002)

g W

ater

(PhD thesis, 2002)

Hea

ting

InfluentExcess sludge

II Digester optimisationII. Digester optimisationSubstrate: primary sludge diluted to 20 g TS/l

2 x 8 CSTRs (duplicate):SRT: 10, 15, 20, and 30 daysTemp.: 25 and 35 ºC20 g TS/l.

outlet

Temp.: 25 and 35 C

T = 25°C Expressed as percentage of influent COD inletT = 25°C Expressed as percentage of influent COD

SRT in days: 0 10 15 20 30

Hydrolysis 10 24 41 41 42

gas bag

y y

Acidogenesis 6 22 39 41 42

Methanogenesis 0 11 39 41 42

T = 35°C Expressed as percentage of influent COD

CSTR digesterSRT in days: 0 10 15 20 30

Hydrolysis 10 41 45 47 49

A id i 6 41 45 47 49Acidogenesis 6 41 45 47 49

Methanogenesis 0 41 45 47 49

II Digester optimisationII. Digester optimisation

Overall Results:Al l di i f i b h d outlet

inlet

Almost complete digestion of proteins, carbohydrates and lipids within 15 and 10 days at 25 and 35 °C, respectively.

gasHydrolysis constant (kh), fraction hydrolyzed (fh)

gas bag

CSTR digesterCSTR digester

III. The UASB reactor and UASB-Digester system

HRT: 20 d

HRT: 6hrs HRT: 6hrsTemp : 15ºC

HRT: 20 dTemp.: 35ºCMix.: 8 rpm

Temp.: 15ºC Temp.: 15ºC

Single stage UASB pilot plant (140 l)

UASB-Digester pilot plant (140 l + 106 l)

Period 1: 81 days operation

( )

Period 2: 83 days operation

Substrate: dilute sewage from Bennekom village, The Netherlands,COD: 500 – 750 mg/l

Results UASB - Digester systemUASB t t 15 ºC !!

Effluent concentrations

UASB reactor temp.: 15 ºC !!

Effluent concentration (mg/L)Reactor CODt CODss CODcol CODdis VFA-CODUASB 390 100 128 162 80

(62) (36) (19) (47) (40)UASB-Digester 151 32 68 50 3

(34) (24) (17) (10) (3)

Removal efficienciesRemoval efficiency (%)Reactor CODt CODss CODcol CODdis VFA-COD

UASB 44 73 3 5 -8(9) (14) (46) (17) (42)(9) (14) (46) (17) (42)

UASB-Digester 66 87 44 30 95(6) (5) (15) (36) (8)

COD Removal efficiency in comparison with UASB’s applied in tropical countries

UASB-Digester

Sao Paulo -Brazil

Bucaramanga -Columbia

Kanpur - India(Draaijer et alDigester

(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 - 30Temp ( C) 15 21 25 23 27 20 30COD (%) 66 (6) 70 66 62 - 70

Th UASB Di t tThe UASB-Digester system: 3.5 times less sludge than a parallel operating UASB reactor !!UASB: 0.77 g sludge-COD/g CODrem., 0.09 Nm3 CH4/Kg CODrem.g g g rem., 4 g rem.UASB-Digester: 0.21 g sludge-COD/g CODrem., 0.17 Nm3 CH4/Kg CODrem.

30

40

rati

on TS (UASB-Digester) VS (UASB-Digester)

10

20ds

con

cent

r(g

/L)

010 29 39 49 63 69 79 90 100

Sl d b d h i ht (%)

Soli

d

Sludge bed height (%)

UASB-Digester70

%)

60

65

VS/

TS (%

5510 29 39 49 63 69 79 90 100

sludge bed height (%)

Sludge profile in UASB-unit of UASB-Digester system as VS and TS (a) and VS/TS ratio (b) along the sludge bed height expressed as percentagesand VS/TS ratio (b) along the sludge bed height expressed as percentages of the total bed height. 0% = reactor bottom; 100% = 1.90 m.

Full scale calculations for Palestine:O ti i i l UASB CSTR itOptimising volumes UASB + CSTR unit

Model calculations using:g- obtained kinetic constants- Palestinian sewage characteristics

UASB: 0.25 m3/m3 sewageCSTR: 0.107 m3/m3 sewage

(40-45% of UASB reactor volume)

Based on:Based on:- UASB: 6 hrs HRT- CSTR-temp.: 35°C

SRT (CSTR) 15 d- SRT (CSTR): 15 days- Sludge recycling from bottom of UASB: 22 g VS/l

Conclusions 1

Sewage in Palestine is of high strength (COD: 1500-2200 mg/l, TSS: 650-750 mg/l) and low temperatures (15 ºC) during winter time

Conventional single stage UASB reactors in Palestine require HRTs approaching 1 day (3 x the value of tropical applications) pp g y ( p pp )

E t i t bili ti f i l d i th l d CSTRExtensive stabilisation of primary sludge in the coupled CSTRs occurs within the first 15 and 10 days SRT at 25 and 35 ºC, respectivelyp y

Conclusions 2

The enhancement of methanogenic conditions in UASB reactor, g ,improves both physical removal and hydrolysis of solids

The UASB-Digester system is a technically feasible alternative for h h h ( ) d hhigh-strength sewage (pre) treatment at 15 ºC, reducing the required HRT to 8 hrs (similar to tropical applications)

160017001800

35

40stage 2 stage 3stage 1

1200130014001500

30

900100011001200

(mg/

L)

20

25

atur

e (°

C)

600700800900

CO

Dto

t

15

20

Tem

pera

300400500600

10Influent COD totalEffl t UASB t

0100200

0

5Effluent UASB reactorTemperature

0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510

time (days)

Influent, effluent and air temperature during the anaerobic treatment of domestic sewage from Al Bireh City/Palestine in a one stage UASB reactor (Stage 1) and a modified UASB reactor to a UASB-Digester system through sludge re-circulation from the digester to the UASB reactor (Stage 2 and 3)

0 50 100 150 200 250 300 350 400 450 500

time (days)

90.000

100.000

30

350 50 100 150 200 250 300 350 400 450 500

stage 1 stage 2 stage 3

70.000

80.000

25

30

C)

50.000

60.000

TS

(g/L

)

15

20

erat

ure

(°CTS tap 1

TS tap 2TS tap 3T

30.000

40.000T

10

15

Tem

pTemp

0 000

10.000

20.000

0

5

0.0000 21 32 62 93 130 193 266 289 352 377 396 424 446 462 483

time (days)

0

Sludge profile of a one stage UASB reactor (Stage 1) and a UASB reactor of a UASB-Digester system (Stage 2 and 3) in terms of TS and ambient air temperature during the anaerobic treatment of domestic sewage from Al Bireh City/Palestine