Modifying a Conventional UASB Reactor to an Integrated UASB- Digester System for Sewage Pre- Treatment in Mountain Areas at Low Temperatures (15 °C Temperatures (15 °C Nidal Mahmoud, Grietje Zeeman, Jules B. van Lier, Gatze Lettinga Institute of Environmental and Water Studies, Institute of Environmental and Water Studies, Institute of Environmental and Water Studies, Institute of Environmental and Water Studies, Birzeit Birzeit University University [email protected]Ecological Sanitation Training Course SWITCH PROJECT IEWS, Birzeit University, 25-27 January 2011
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Modifying a Conventional UASB Reactor to an Integrated ... · Conventional single stage UASB reactors in Palestine require HRTs apppp g y ( p pp )roaching 1 day (3 x the value of
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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,
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
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.
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)
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)
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