Anaerobic wastewater treatment Anaerobic wastewater treatment Nidal Mahmoud Institute of Environmental and Water Studies, Institute of Environmental and Water Studies, Birzeit University Birzeit University [email protected]Ecological Sanitation Training Course SWITCH PROJECT IEWS, Birzeit University, 25-27 January 2011
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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)
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
* 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