Nidal Mahmoud. Ecological Sanitation Training Course SWITCH PROJECT IEWS, Birzeit University, January 2011

Transcription

1 Anaerobic wastewater treatment Nidal Mahmoud Institute of Environmental and Water Studies, Birzeit University Ecological Sanitation Training Course SWITCH PROJECT IEWS, Birzeit University, January 2011

2 Outline 1. Effect of Low Temperature on the bio-chemical and physical properties of wastewater and its effect on anaerobic treatment Anaerobic bio-chemical processes Physical and chemical properties of wastewater 2. Anaerobic Technologies for Low Temperature Sewage Treatment Difficulties of anaerobic (low temperature) sewage treatment Technical perspectives for anaerobic sewage Treatment

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

4 Effect of Low Temperature on the bio-chemical and physical properties of wastewater and its effect on anaerobic treatment Anaerobic bio-chemical processes: Microorganisms type and growth rate Substrate utilization rate Physical and chemical properties of wastewater Solubility of gaseous compounds Viscosity of liquids

5 Anaerobic biological conversion

6 Microorganisms type and growth rate Relative growth rate of pshchrophilic, mesophilic and thermophilic hili methanogens

7 Substrate t utilization rate Anaerobic conversion of organic matter Hydrolysis y Aid Acidogenesisi Acetogenesis Methanogenesis

8 Hydrolysis Step df Arrhenius equation dt k h xf k h Ae E / RT With: F:concentration of biodegradable solid substrate (g/l) K h : hydrolysis constant (d -1 ) t: time(d) With: T: the absolute temperature (ºK); R: the ideal gas constant (J.mole - 1.ºK -1 ); A: the pre-exponential factor (d -1 ); E: activation energy (kj.mole -1 )

9 Methanogenesis Step Activit ties at abscis sa temp peratur re / act tivity a t 35 C Temperature ( C) Temperature dependency of the methane production rate of mesophilic anaerobic process

10 Physical and chemical properties of wastewater

11 Solubility of gaseous compounds Solubility of gases increases below 20 C At low temperature Henry s law x g P T H P g With: High dissolved gases in the effluent, i.e methane and hydrogen sulfide X g : mole fraction of gas in water; H: Henry s law constant; P T : total pressure; P g : mole fraction of gas in air

12 Viscosity of liquids Low water temperature Viscosity of water increases Low biogas production rate Poor mixing; higher energy is required for mixing i

13 Degree of Water Mixing in the Reactor G G: velocity gradient (s-1) P: power input (W) V: volume of water in the reactor (m 3 ) : dynamic viscosity (Pa.s) Relation between temperature and turbulence in the reactor μ p Temperature Viscosity % * V ( ) of water Increase in the of G from reactor 15 ºC ºC Pa.s % x x x x x

14 Anaerobic Technologies for Low Temperature Anaerobic Technologies for Low Temperature Sewage Treatment

15 Anaerobic Technologies for Low Temperature Sewage Treatment Difficulties of anaerobic (low temperature) sewage treatment Technical perspectives for anaerobic sewage Treatment Anaerobic High Rate Wastewater Treatment Systems Digestion Limiting Step Technology Innovation

16 Difficulties of anaerobic (low temperature) sewage treatment

17 Sewage belongs to the complex wastewater 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

18 COD fractions Raw sewage Suspended COD (COD ss ) 44 m 4.4 paper-filtered sewage Colloidal COD (COD col ) 0.45 m membrane filtered sewage Dissolved COD (COD dis )

19 Wastewater Characteristics of Ramallah City, Al - Bireh City and Al-Jalazoon refugee camp Parameters Ramallah Al-Bireh Al-Jalazoon COD Total Suspended Colloidal Dissolved VFA as COD SO as SO TSS VSS ph T ww Summer Winter 13 T amb. Summer 27 Winter 13.8 Colour Reddish to black Medium brown Light brown

20 Technical Perspectives for Anaerobic Sewage Treatment

21 Anaerobic High Rate Wastewater Treatment Systems Advantages of High-rate anaerobic systems Low construction, operation and maintenance costs, Small-land requirement, Low excess-sludge production, Production of biogas (source of energy). Anaerobic biotechnology UASB for sewage treatment has been applied successfully in several countries of hot climates, e.g. India, Colombia, Brazil, and Ghana

22 Digestion Limiting Step Under low temperature conditions (< 15ºC) and/or strong temperature fluctuations between summer (25ºC) and winter (15ºC), the conventional UASB design needs reconsideration: Limited Hydrolysis Accumulation of particulate organic matter High SS Deterioration of the reactor performance Limited hydrolysis y Low removal efficiency Long retention time

23 Technology Innovation Sewage treatment under low temperature conditions (< 15ºC) and/or temperature fluctuations: One stage: 1. UASB reactor Two Stage 1. HUSB reactor followed by UASB 2. HUSB reactor followed by EGSB 3. AF followed by AH system 4. Two-stage UASB system UASB-Digester 1. UASB-Digester system

24 Wang (1994) treated domestic sewage in a two-step system: UASB/EGSB reactor at 12oC Parameter Removal (%) UASB+EGSB Total COD* 51 Suspended COD 67 Colloidal COD 42 Dissolved COD 41 * measure for organic matter

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

26 Packing material: AF and AH reactors Base thickness Knob thickness The packing material consists of vertical sheet of reticulated poly-urethane foam (RPF) with knobs. Knob Why RPF? has a high specific surface area (500 m 2 /m 3 ), has a high porosity of 97%, RPF enables the retention of 15 gvs/l in attached form. All biomass is attached, as the accumulated sludge on the bottom of the reactor is wasted weekly. Therefore clogging of the AF reactor is avoided.

27 COD removal efficiency y( (%) in the AF+AH at HRT of 4+8 h at 13 o C Removal (%) Maximum removal (%)* Total COD 71** Suspended COD 91 Colloidal COD Dissolved COD * from Last and Lettinga (1992) ** similar to that achieved in tropical countries

28 First stage inlet Two stage UASB Second stage inlet Maha Hallalsheh, 2002 Results two-stage pilot trials Middle East (Jordan): MW COD Removal: up to 80% BOD Removal: up to 85% SS Removal: up to 80% Pathogen Removal: insufficient Potential CH 4 production in Amman (at m 3 sewage/day): 17,500 m 3 /day!

29 UASB - Digester system Gas meters Gas holder Effluent UASB Digester Influent Excess sludge Water ating W Hea Nidal Mahmoud, 2002

30 HRT: 6 hrs T: 15 C HRT: 20 d T: 35 C HRT: 6 hrs T: 15 C Schematic diagram of the UASB-Digester pilot plant Schematic diagram of the one stage UASB pilot plant

31 SRT: 10, 15, 20 and 30 days Process temperature: 25 and 35 C The most substantial portion of the digestion of proteins, carbohydrates and lipids occurs within the first 15 and 10 days at Process temperatures of 25 and 35 C inlet outlet gas bag Schematic diagram of a CSTR digester

32 Results UASB - Digester system, Mahmoud (2002) Effluent concentrations Reactor Effluent concentration (mg/l) CODt CODss CODcol CODdis VFA-COD UASB (62) (36) (19) (47) (40) UASB-Digester (34) (24) (17) (10) (3) Removal efficiencies Reactor Removal efficiency i (%) CODt CODss CODcol CODdis VFA-COD UASB (9) (14) (46) (17) (42) UASB-Digester (6) (5) (15) (36) (8)

33 Results UASB - Digester system, Mahmoud (2002) Removal efficiency of total COD in the UASB-Digester system in comparison to those reported for UASB s applied in tropical countries UASB- Digester Sao Paulo - Brazil Bucaramanga - Columbia Kanpur - India (Draaijer et al., (This study) (Vieira, 1988) (Schellinkhout et al., 1988) 1992) HRT (hr) Temp ( C) COD (%) 66 (6) The UASB-Digester system produced 3 5 times less The UASB-Digester system produced 3.5 times less sludge than a parallel operating UASB reactor