Dry stage anaerobic digestion of fine sieved solids from municipal - - PowerPoint PPT Presentation

Dry stage anaerobic digestion of fine sieved solids from municipal wastewater

• K. Vardas, N.I. Batistatos and P. Gikas

Design of Environmental Plants Laboratory School of Environmental Engineering Tevhnical University of Crete, Chania, Greece

Topics

School of Environmental Engineering Technical University of Crete

• The microsieving process
• Fine sieved solids characteristics
• Dry vs wet stage anaerobic digestion
• Experimental setup
• Experimental findings

How It Works

Microscreen - Operating principle

School of Environmental Engineering T echnical University of Crete

Microscreen

a. Microscreen with open housing b. Sludge removal (~45% TS) c. Microscreen cloth (100-350μm openings)

a b c

Microscreen (Patra, Greece)

School of Environmental Engineering T echnical University of Crete

Microsceen: Operation

Solids removal Solids compaction

How It Works Inlet TSS (○) and TSS at the outlet of microscreen (□) and at the outlet of primary clarifier (∆)

School of Environmental Engineering T echnical University of Crete

How It Works Inlet COD (○) and COD at the outlet of microscreen (□) and at the outlet of primary clarifjer (∆)

School of Environmental Engineering T echnical University of Crete

Initial particle concentration Final particle concentration after primary clarification Final particle concentration after microscreening

• 50% TSS
• 5

% T S S

Selected removal of large particles through microscreening

School of Environmental Engineering T echnical University of Crete

Particle size distribution in municipal wastewater, prior and after microscrening

0,01 0,1 1 10 100 1000 1 2 3 4 5 6 particle size (μm) weight (%) 0,01 0,1 1 10 100 1000 20 40 60 80 100 particle size (μm) (%)

Inlet Outlet It is observed selective removal of the larger particles Increase of wastewater biodegradability

School of Environmental Engineering T echnical University of Crete

How It Works

Footprint requirements

1 ÷ 20

Wastewater fmow: 4000m3/d: Microscreen footprint: 4 m2 Clarifjer footprint: 82 m2

School of Environmental Engineering T echnical University of Crete

Application of microscreening, upstream of various wastewater treatment processes

SBR MBR MBBR Activated sludge Natural systems Microscreen

School of Environmental Engineering T echnical University of Crete

Fine Sieved Solids (FSS) characteristics

• Managed as solids
• Total solids: 40-45%
• Volatile solids: 85-90%of TS
• C/N about: 20
• High Heating Value: 22-24MJ/kg

School of Environmental Engineering Technical University of Crete

Biosolids: Gasification versus anaerobic digestion*

Potential for net electrical energy production

2 : 1

* P . Gikas, 2014, Environmental T echnology, 35(17), 2140-2146

Gasifjcation Anaerobic digestion

School of Environmental Engineering T echnical University of Crete

Dry stage anaerobic digestion

Advantages-Disadvantages (compared to wet stage)

• Requires smaller space compared to wet stage
• Tolerant to the presence of solid particles (e.g.: sand, fibers)
• Less complicated compared with wet stage
• Requires less maintenance
• Requires less electromechanical equipment (pumps, agitators, feeding

equipment)

• Lower operational cost
• A batch rather than a continuous process
• Requires advanced processes for loading-unloading
• Insufficient mixing
• Requires re-inoculation in every cycle
• Lower biogas yield
• Requires advanced design

School of Environmental Engineering Technical University of Crete

Experimental Set up

• A. Microsieve (1000 m3/d)
• B. Blower (air knife for solids-screen separation, 5 bar)
• C. Control Panel-PLC

School of Environmental Engineering Technical University of Crete

a) Digital manometer b) Reaction bottles c) Portable gas analyzer

Experimental Set up

School of Environmental Engineering Technical University of Crete

Sample Ratio Inoculum/sludge TS(%) 1 1 11% 2 1/2 14% 3 1/4 19% 4 1/13 28% PSS sample: From Rethymno, Greece, WWTP Solids concentration: 40% Volatile Solids: 89% (of TS) C/N: 20 Inoculum: From Chania, Greece, WWTP Solids concentration: 40% Volatile Solids: 89% (of TS)

Experimental Set up

Mechanical stirring set-up School of Environmental Engineering Technical University of Crete

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 20 40 60 80 100 120 200 400 600 800 1000 1200 1400 1600

14% 19% 11% 14% 19% 11%

Time (days) Daily biogas production (ml biogas/gVSdestroyed) Cumulative biogas prouction (ml biogas/gVSdestroyed)

 Optimum biogas production at 11% TS concentration  The maximum daily biogas production (for 11%TS) achieved after 11 days  At 19% TS concentration biogas yield was 30% of that produced by the 11% TS

Experimental fjndings

School of Environmental Engineering Technical University of Crete

 Microsieving produces biosolids with high solids content (40-45%), high volatile content (85-90% of TS) and C/N

• f about 20

 Dry stage anaerobic digestion at 11% solids content exhibited the highest biogas production yield  Maximum biogas production was achieved after 11 days from inoculation  Agitation issues are to be resolved

Conclusions

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Thank you for your attention

petrosgikas@gmail.com / petros.gikas@enveng.tuc.gr