Performance of Hybrid Submerged Membrane Bioreactor Combined with Pre- Coagulation/Sedimentation

Transcription

1 Performance of Hybrid Submerged Membrane Bioreactor Combined with Pre- Coagulation/Sedimentation Yoshimasa WATANABE Department of Urban and Environmental Engineering, Hokkaido University, Japan

2 New urban water metabolic system Development of elemental technology Advanced water purification process for membrane filtration Development of hybrid wastewater treatment system Effective utilization and recycling of wastewater treatment sludge

3 The major part of the contaminants in municipal wastewater is associated a with particles Marani et al., 3. Levine et al., COD mg/l TOC 76.5 mg/l Sewage Itokawa et al. COD 8 mg/l 3. Primary clarifier effl. COD 187 mg/l BOD 315 mg/l Balmat., Biological oxidation rate. 1/day Upper; size (µm) Lower; % of total Soluble < <.1 3 <.1 <.1 39 <.8 <.8.39 Classification Colloidal Supra colloidal. < < 7.1 < 78.1 < Settle able 1 < 15 1 <.8 Coagulation/sedimentation Biological oxidation

4 Hybrid wastewater treatment system Treatability of organic matter Biological oxidation 65% Sedimentation 35% Conventional system 1 - m1-3 m 1 - m 1 m 1 - mm.1mm 1mm 1mm 1 mm.1 m Biological oxidation Pre-Coagulation/sedimentation 7% 3% Hybrid system Biological oxidation Rotating Biological Contactor (RBC) Submerged membrane Bioreactor (MBR) Structure and function analysis of microorganism community. New coagulant Poly Silicato Iron (PSI) Simple and economical coagulation/sedimentation unit Jet Mixed Separator (JMS) Water reuse Risk analysis of treated water Pathogens Micro pollutants Growth potential of microorganisms Sludge treatment Energy recovery Phosphorus recovery Risk assessment (Heavy metal, Virus, Pathogens)

5 Classification of MBR Cross-flow MBR 197 Submerged MBR 199 Raw water Bioreactor Circulation of mixed liquor Pump Diffuser Treated water Membrane module Raw water Bioreactor Membrane module Pump Treated water Diffuser CF-MBR S-MBR Energy consumption (kwh/m 3 ) 1.. Operating pressure (kpa) 1 < 5 Permeate flux (m 3 /m /day) Membrane UF MF

6 Submerged membrane bioreactor Submerged membrane bioreactor Raw water Bioreactor Membrane module Pump Blower Treated water Advantages High quality of treated water High solid/liquid separation Smaller footprint Disadvantage Previous studies by other researchers Membrane fouling caused by dissolved organic matter (DOM) Laboratory scale experiment Short-tem experiment Synthetic wastewater It is not clear whether experimental results obtained in the previous studies can be applied to operation of real-world MBRs.

7 Objectives Hybrid submerged membrane bioreactor Pre-coagulation/sedimentation and membrane bioreactor Pilot scale experiments were carried out to investigate; Effect of pre-coagulation/sedimentation on MBR in terms of permeate quality and membrane fouling. Influence of dissolved organic matter (DOM) on membrane fouling in MBR.

8 Hybrid MBR system Coagulation/sedimentation unit Jet Mixed Separator Rotating disc membrane (UF) VSEP (NF) Follow fiber membrane (MF) Flat membrane (MF) Submerged membrane bioreactor

9 Flow diagram of the pilot plant Primary clarifier effluent Rapid mixing tank Porous plate Coagulant Jet Mixed Separator (JMS) Excess sludge Operating conditions of the JMS Flow rate 5 m 3 /day HRT Coagulant 1.5 hr PSI : Poly Silicato Iron 1 mg-fe/l Inclined tube settlers Blower HMBR CMBR MBRs Conventional MBR (CMBR) Primary clarifier effluent MBR Permeate Hybrid MBR (HMBR) Primary clarifier effluent JMS MBR MBR P P

10 Turbidity TOC DOC T-N NH - +N T-P Alkalinity ph (NTU) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) Primary clarifier effluent JMS effluent Removal efficiency (%) Removal efficiency in in terms terms of of turbidity, TOC, TOC, and and T-P T-P determined for for precoagulation/sedimentation was was attained to to 83%, 83%, 53%, 53%, and and 77%, 77%, respectively. pre-

11 Submerged membrane bioreactor Primary clarifier effluent JMS effluent Pressure gauge MBR Effective volume 18 L Permeate Suction pump Membrane module Mixed liquor Bubble Diffuser Flow control Air scrubbing Characteristic of membrane Module Hollow fiber membrane Pore size.. µm Area 3 m Material Polyethylene Suction mode Suction for 1 min., stop for 3 min. Air scrubbing condition Continuous or Intermittent mode

12 Operating conditions of the MBRs HMBR 1 HMBR CMBR 1 CMBR HRT (hour) MLSS conc. (g/l) - 1 < - 1 < MLVSS/MLSS Flux (m/day) Pore size (µm).

13 Changes in water temperature and MLSS concentrations. Temperature ( ) 3 1 Primary clarifier effluent MLSS conc. (g/l) HMBR 1 HMBR CMBR 1 CMBR MLSS concentration in in HMBR1 and and CMBR1 was was attempted to to be be kept kept around g/l. g/l. Until days of of the the operation, MLSS concentration in in HMBR and and CMBR was was not not controlled and and consequently increased with with operation time. After day day 18, 18, MLSS concentration in in HMBR and and CMBR was was attempted to to be be kept kept around g/l g/l

14 Accumulation frequency of TOC concentration in the permeate Average TOC concentration in the permeate obtained from HMBR was 3. mg/l.

15 Biodegradability of DOC in the treated water DOC conc. (mg/l) 8 6 NBDOC BDOC HMBR CMBR Activated sludge Temperature 13.7 MLSS concentration HMBR 1.9 g/l CMBR 1. g/l Activated sludge. g/l HRT of MBR.5 hr. Biodegradable organic carbon (BDOC) HMBR < CMBR < Activated sludge Non-biodegradable organic carbon HMBR = CMBR = Activated sludge BDOC concentration in in the the treated water obtained from HMBR was was almost zero.

16 Water quality in various processes Primary clarifier effluent JMS Effluent HMBR 1 Permeate HMBR CMBR 1 CMBR Turbidity (NTU) TOC (mg/l) T-N (mg/l) NH + -N (mg/l) T-P (mg/l) Alkalinity (mg/l) ph

17 Concentration of 17β-estradiol (E) in various processes ELISA was used to determine 17β-estradiol concentration.

18 Effect of microbial activity on E concentration

19 Evaluation of membrane fouling Definition of membrane fouling Reversible fouling can be canceled by physical membrane cleaning. Membrane module was taken out from the membrane chamber and washed by spraying pressurized water. Irreversible fouling can be canceled by chemical membrane cleaning. Membrane module was soaked in hydrochloric acid (ph) and subsequently in solution of sodium hypochlorite for hours. Intermittent air scrubbing Continuous air scrubbing Suction for 1 min. Stop for 3 min. Suction for 1 min. Stop for 3 min. Air scrubbing Permeate

20 Membrane permeability (MLSS conc. - g/l) Flux (m 3 /m /day)..3 Filtration resistance (1 1 /m) Chemical cleaning CMBR 1 HMBR 1 Filtration resistance (1 1 /m) 8 6 Physical cleaning By By reducing permeate flux, flux, rapid increase of of filtration resistance in in CMBR1 was was observed while increase rate rate of of filtration resistance in in HMBR1 was was retarded.

21 Membrane permeability (MLSS conc. - g/l) Flux (m 3 /m /day) Filtration resistance (1 1 /m) Chemical Physical cleaning cleaning.3..3 Continuous air scrubbing CMBR 1 HMBR 1 Filtration resistance (1 1 /m) By By changing air air scrubbing condition, rapid increase of of filtration resistance in in CMBR1 was was observed. In In contrast with with the the results with with CMBR1, relatively high membrane permeability was was maintained with with HMBR1.

22 DOC concentration of mixed liquor DOC conc. (mg/l) F/M ratio (mg-toc/mg-vss/day) CMBR 1.55 HMBR Membrane separation Mixed liquor Permeate CMBR 1 HMBR 1 DOC conc. (mg/l) 3 1 Membrane separation Mixed liquor Operation time (days) Permeate Higher Higher DOC DOC concentration in in CMBR CMBR probably corresponded to to more more rapid rapid increase of of filtration resistance in in CMBR. CMBR. Treatability of of organic carbon Membrane fouling

23 16 Primary clarifier effluent JMS effluent Removal efficiency 1 TOC conc. (mg/l) Removal efficiency (%).5-.1µm.1µm-3 Da 3 Da-3 Da 3 3 Da 3 >.1 µm 3 Da 3 Da Removal efficiency of of high molecular organic matter was higher than that low molecular organic matter.

24 Irreversible membrane fouling DOC conc. (mg/l) Biodegradability of DOC in the feed water High biodegradable organic carbon Primary clarifier effluent JMS effluent Low biodegradable organic carbon Non-biodegradable organic carbon Time hours

25 Department of Urban and Environmental Engineering, Hokkaido University Variation of transmembrane pressure(tmp) : MLSS > 8 mg/l Physical washing Chemical washing Chemical washing Membrane separation Membrane separation Operation days Unit Operation days Unit

26 Filtration resistance (1 1 /m) Membrane permeability (MLSS conc. > 1 g/l) Flux (m 3 /m /day) Air scrubbing condition Intermittent Continuous Physical membrane cleaning..3. MLSS conc. 8.5 g/l Flux (m 3 /m /day) Air scrubbing condition Intermittent CMBR HMBR Filtration resistance (1 1 /m) Chemical membrane cleaning MLSS conc g/l Continuous Before physical membrane cleaning After physical membrane cleaning Continuous air air scrubbing was was effectively for for cake removal.

27 Upper limit of MLSS concentration in CMBR What control is suspension viscosity? Suspension viscosity (mpa s) Inflection point CMBR MLSS conc. (g/l) HMBR Upper limit of MLSS concentration for an efficient operation in CMBR was suggested to be around 1 g/l. When a MBR is used as the HMBR, higher MLSS concentration would be applicable.

28 Relationship between MLSS conc., viscosity and floc size distribution Sample Activated sludge, Conventional MBR sludge, Hybrid MBR sludge Susupension viscosity (mpa s) 3 1 Activated sludge Conventional MBR Hybrid MBR % of total volume Hybrid MBR Conventional MBR Activated sludge 6 8 MLSS concentration (g/l) Floc size distribution (µm) Suspension viscosity is is controlled by by MLSS conc. and and floc floc size.

29 Operating conditions of the MBRs HMBR CMBR HRT MLSS conc. Flux (hour) (g/l) (m/day).5 1. Pore size Suction mode (µ ). Suction for 1 min., Stop for 3 min. Continuous air scrubbing Influence of of DOM (dissolved organic matter) on on membrane fouling was investigated.

30 Changes in the total membrane filtration resistance 5 5 Filtration resistance (1 1 /m) 3 1 CMBR 6 Filtration resistance (1 1 /m) HMBR Increase rate of filtration resistance observed in HMBR was 3 % less rapid than that in CMBR. The effect of pre-treatment for HMBR was confirmed.

31 Influence of DOC on membrane fouling Filtration resistance (1 1 /m) DOC 6 (a) CMBR DOC conc. (mg/l) DOC 6 (b) HMBR Higher DOC concentration corresponded to to more rapid increase of of filtration resistance. Filtration resistance (1 1 /m) DOC conc. (mg/l)

32 Influence of DOM on membrane fouling To get the information of mechanisms in membrane fouling, deadend test was carried out. Filtration resistance (1 1 /m) DOC Carbohydrate Protein 6 8 (a) CMBR DOM conc. (mg/l) Filtration resistance (1 1 /m) DOC Carbohydrate Protein 6 8 (b) HMBR Rapid increase in filtration resistance was observed in HMBR Rapid increase of DOM in the membrane chamber of HMBR was observed DOM conc. (mg/l)

33 Laboratory scale dead-end filtration experiment Stirring rod Permeate Suspension Manometer Pressure reducer Compressor membrane Samples Biomass suspension Resistance = SS+colloid+soluble After centrifugation Resistance = colloid+soluble Biomass suspension was centrifuged at 3, rpm for 5min. Magnetic stirrer Filtration membrane characteristics After filtration Resistance = soluble Pore size.1 µm Biomass suspension was filtered with a Diameter 58.5 cm membrane with nominal pore size of.5 µm. Filtration area 6.9 cm Operating conditions Operating pressure kpa Rotation of stirring rod 3 rpm

34 Characteristics of the suspensions tested in dead-end tests. SS TOC Carbohydrate Protein Biomass suspension CMBR 9, -* 1 5 HMBR 1, -* After centrifugation CMBR -* HMBR After filtration CMBR -* HMBR -* unit (mg/l) -* not determined - * * not detected

35 Particle size distribution After centrifugation (HMBR) % of total volume Biomass suspension (HMBR) Biomass suspension (CMBR) Particle size ( m) *Particle size distribution in the supernatant collected from CMBR could not be determined due to the detection limit of the analyzer (particle concentration was too low).

36 Changes in the permeate flux Permeate flux (m 3/m/day) Biomass suspension (SS+Colloid+Soluble) After centrifugation (Colloid+Soluble) After filtr ation (Soluble) 1 3 Filtration time (m in) (a) CMBR Permeate Flux (m3/m/day) Rapid decrease in permeate flux were observed at initial stage Filtration time (min) (b) HMBR Biomass suspension (SS+Colloid+Soluble) After centrifugation (Colloid+Soluble) After filtration (Soluble) Permeate flux reached a stable value within filtration time of 3 min. For all the test, fouling resistances were determined by Darcy law. (3 min. of filtration)

37 Role of SS, colloidal matter and soluble matter in membrane fouling Resistance caused by membrane fouling for each sample Biomass suspension (SS+colloid+soluble) After centrifugation (colloid+soluble) After filtration by.5 µm (soluble) CMBR HMBR unit (1 1 /m) Contributions of each fraction in the total membrane fouling SS 18% SS 11% Soluble 5% Soluble 6% CMBR Colloid 18% HMBR Colloid 6%

38 Conclusions Water quality of whole system Activated sludge process CMBR HMBR HMBR ( removal) Turbidity (NTU) < 1 TOC (mg/l) < 1 < 6 < < T-N (mg/l) < 15 < 18 < 16 < 1 NH + -N (mg/l) < 3. < 1. < 3. < 1. T-P (mg/l) <.5 < 1. <.1 <.1 Hybrid MBR : DOC concentration was less than. mg/l. BDOC concentration was almost zero. Total phosphorus concentration was less than.1 mg/l.

39 Conclusions Pilot scale experiments were carried out to examine membrane fouling occurring in MBR with or without pre-coagulation/sedimentation. The influence of suspension viscosity and DOM on membrane fouling was investigated. Pre-coagulation/sedimentation process improved the performance of MBR by reducing both reversible fouling and irreversible fouling. In order to efficiently operate a MBR, suspension viscosity in the membrane chamber should be maintained as low as possible. Suspension viscosity was controlled by MLSS concentration and floc size. DOM such as carbohydrate and protein seemed to be not important in interpreting membrane fouling in MBRs. Colloidal fraction in biomass suspension played an important role in membrane fouling.

40 Membrane permeability (MLSS conc. - g/l) Flux (m 3 /m /day). /m) Filtration resistance ( Chemical cleaning Filtration resistance (1 1 /m) 8 6 Physical cleaning. days 35 days CMBR 1 HMBR When deterioration in in membrane permeability became significant, deposition of of biomass suspension on on the the membrane surface was was not not recognized and and chemical cleaning was was needed. Irreversible fouling In In contrast with with the the results with with CMBR1, relatively high membrane permeability was was maintained with with HMBR1.

41 Filtration resistance (1 1 /m) 8 6 Membrane permeability (MLSS conc. > 1 g/l) Physical membrane cleaning Flux (m 3 /m /day) Flux (m.3. 3 /m /day). Air scrubbing rate (L/min) Air scrubbing rate (L/min) 3 6 MLSS conc. 1.9 g/l MLSS conc CMBR HMBR Filtration resistance (1 1 /m) g/l Rapid increase of of filtration resistance in in CMBR was was observed while that that in in HMBR was was stable operation.

42 Relationship between MLSS conc. and suspension viscosity. Suspension viscosity (mpa s) CMBR MLSS conc. (g/l) Suspension viscosity of of CMBR CMBR was was greater than than that that of of HMBR HMBR HMBR In In order to to efficiently operate a MBR, suspension viscosity in in the the membrane chamber should be be maintained as as low low as as possible.

43 Filtration spectrum TEM SEM Optical microscope Visible to naked eye Micrometers Molecular Wt. Typical organic constituents in municipal wastewater Membrane separation Various wastewater treatment Nutrients Amino acids Fatty acids RO Fluvic acids Humic acids RNA NF Viruses Polysaccharides Proteins UF Cell fragments Bacteria DNA MF Coagulation /sedimentation Activated sludge process Sand Human hair Algae, Protozoa Bacterial flocs Sedimentation Filtration

44 The major part of the contaminants in municipal wastewater is associated a with particles Size Range BOD 5 COD TOC Tot P Org.N Classification of contaminants in wastewater (% of total) (% of total) (% of total) (% of total) (% of total) After Munch,R. et al. (198) Soluble <.5µm Colloidal.5-3µm Classification Supracolloidal 3-16µm Settleable >16µm Percentage of total associated with suspended solids in the raw water at the Eskilstuna wastewater treatment plant in Sweden Metal Zn Cu Ni Cr Pb Cd %-suspended After SWEP (1985) Direct particle separation is effective way of lowering the wastewater contaminant level

45 Membrane permeability (MLSS conc. > 1 g/l) Physical membrane cleaning Flux (m 3 /m /day) Filtration resistance (1 1 /m) (a) CMBR Accumulation of irreversible membrane filtration resistance Chemical membrane cleaning Flux (m 3 /m /day) Filtration resistance (1 1 /m) Accumulation of irreversible membrane filtration resistance (b) HMBR Accumulation of irreversible resistance observed in HMBR was % less rapid than that in CMBR.

46 Membrane permeability (MLSS conc. > 1 g/l) Filtration resistance (1 1 /m) Chemical membrane cleaning 8 6 Physical membrane cleaning Flux.5 m 3 /m /day MLSS conc. 15 g/l CMBR HMBR Air scrubbing rate L/min Filtration resistance (1 1 /m) Rapid increase of of filtration resistance in in CMBR was was observed while that that in in HMBR was was stable operation.

47 Influence of DOM such as carbohydrate and protein on membrane fouling Filtration resistance (1 1 /m) DOC Carbohydrate Pr otein 6 (a) CMBR DOM conc. (mg/l) Filtration resistance (1 1 /m) DOC Carbohydrate Protein (b) HMBR DOM conc. (mg/l) DOM = Carbohydrate + Protein + etc.. No clear relationship between DOC and DOM was indicated. DOM such as as carbohydrate and protein would not be be concerned with membrane fouling.