VALORIZATION OF THE LIQUID FRACTION OF A MIXTURE OF LIVESTOCK WASTE - - PowerPoint PPT Presentation

VALORIZATION OF THE LIQUID FRACTION OF A MIXTURE OF LIVESTOCK WASTE AND CHEESE WHEY FOR BIOGAS PRODUCTION THROUGH HIGH‐RATE ANAEROBIC CO‐ DIGESTION AND FOR ELECTRICITY PRODUCTION IN A MICROBIAL FUEL CELL (MFC)

• I. MICHALOPOULOS, D. CHATZIKONSTANTINOU, D. MATHIOUDAKIS, I.

VAIOPOULOS, A. TREMOULI, K. PAPADOPOULOU, M. GEORGIOPOULOU, and

• G. LYBERATOS

School of Chemical Engineering National Technical University of Athens

• Obtained from farms
• Main constitution:
• High organic content
• High concentration of nitrogen
• High concentration of phosphorus
• Residues of some harmful substances (growth

hormones, antibiotics and heavy metals)

• Efficient utilization is essential:
• in order to protect the environment and avoid the generation of

human diseases.

• due to agriculture’s high social and economic impact on rural and

mountainous regions

Livestock Waste and Cheese Whey

Objective

• Evaluation of two alternative ways for the

valorization of livestock waste and cheese whey:

• Biogas production through anaerobic co‐digestion in a

Periodic Anaerobic Baffled Reactor (PABR) and

• Electrical energy generation in a Microbial Fuel Cell (MFC).

• Novel bioreactor
• Designed to operate at

high organic loading rates

• Methanogens can be

retained even in the first compartments

• Switching frequency 
• perational flexibility

The Periodic Anaerobic Baffled Reactor (PABR)

• Operating volume: 77L
• 4 compartments of

equal volume

• Consists of two

concentric cylinders of which the interior

• perated as a bath
• 35oC (mesophilic

conditions)

The Periodic Anaerobic Baffled Reactor (PABR)

∙ ∙ ∙ ∙

A B C D

0< 0<t<T/4 <T/4

Influent fluent Effluent Effluent

Operation of PABR Operation of PABR during a during a period T period T

∙ ∙ ∙ ∙

A B C D

T/4< T/4<t<T/2 <T/2

Influent fluent Effluent Effluent

∙ ∙ ∙ ∙

A B C D

T/2< T/2<t<3T/4 <3T/4

Influent fluent Effluent Effluent

∙ ∙ ∙ ∙

A B C D

3T/4< 3T/4<t<T <T

Influent fluent Effluent Effluent

Bioreactor that converts chemical energy, stored in the chemical bonds of

• rganic compounds, directly into electrical energy, through catalytic reactions
• f microorganisms under anaerobic conditions.
• A promising technology for wastewater treatment
• No aeration needed
• Limited sludge production
• Electricity generation

DUAL CHAMBER MFC CUBIC MFC TUBULAR MFC

The working principle of the Microbial Fuel Cell (MFC)

The working principle of an MFC

Bacteria H + Anode Cathode e‐ Electricity CEM Catalyst CO2

Chemistry of MFC: As an example, glucose is used as an organic substrate. Anode : C6H12O6 + 6H2O 6CO2 + 24H+ + 24e‐ Cathode : 24H+ + 24e‐ + 6O2 12H2O

6O2 External resistance H2O

• Two bottles (effective volume=250

ml) connected via a glass tube.

• Anode electrode: carbon fiber paper

(Toray, 10 w.t % wet proofing). Dimensions: ( 3 cm x 2.3 cm).

• Cathode electrode: carbon cloth

coated with a Pt catalyst,(E‐TEK, 0.5 mg/cm2). Dimensions : (3 cm x 2.3 cm)

• Proton exchange system: PEM (Nafion

117)

Dual Chamber MFC (H‐type)

moisture (%) TS (g/g wet weight) VS (g/g wet weight) pH (20oC) tCOD (g/g TS) cattle manure 75 0.26 0.12 8.5 0.75 poultry manure 62 0.386 0.34 7.5 0.70 sheep manure 74 0.26 0.23 7.4 0.83 cow manure 88 0.13 0.097 8.7 1.2 pig manure 86 0.14 0.088 7.3 1.02 whey 93 0.07 0.05 6.0 2.2

Feedstock

The ratios are similar to those of the study area

Annual production (tn/year) Ratio (%) cattle manure 1792 3.93 poultry manure 15832 34.71 sheep manure 2812 6.17 cow manure 3663 8.03 pig manure 20640 45.25 whey 873 1.91 Total 45612 100

Feedstock: Mixture ratio

Waste mixing Dilution in hot water Stirring for 30 minutes Filtered under pressure using a cloth filter

Liquid phase: PABR and MFC Solid Phase A solids/liquid separation step was used as pretreatment, because of the inability of the PABR and the MFC to treat feedstock with high solids levels.

Feedstock: Pretreatment

Liquid phase characteristics

pH 7.46 TSS (g/L) 5.72 Conductivity (S/cm) 3.93 VSS(g/L) 4.60 TS(g/L) 9.4 VS(g/L) 7.14 Total Carbohydrates (g/L) 1.19 Dissolved Carbohydrates (mg/L) 0.28 Total Kjeldahl Nitrogen (mg/L) 631 Ammonium Nitrogen (mg/L) 378.8 Organic Nitrogen (mg/L) 252.2 Total Phosphorus (mg/L) 120.4 Orthophosphates PO4

3—P (mg/L)

41.5 Organic phosphorus (mg/L) 78.9

Feedstock: Liquid phase

Hydraulic Retention Time

HRT (d) 22.3 Switching Period (d) 2 Influent tCOD (g/L) 13.36 Organic Loading Rate (gCOD/Lreactor/d) 0.6

PABR Operating Conditions

• Mesophilic conditions (35oC)
• Operation period of 148 days
• Gas and liquid samples were taken at regular intervals

Anaerobic co‐digestion results (1/2)

Anaerobic co‐digestion results (2/2)

• A simple model developed in Aquasim 2.1 was used to predict the

behaviour of the PABR at the HRT of 22.3 d

• Basic assumptions
• The organic matter is consumed with simple Monod kinetics

·

• ·
• Yield of methane on the substrate
• Yield of biomass from COD
• Initial dCOD of the four comparments
• Biomass retention factor Rb (to be estimated by the model)
• Experimental data (dCOD) of the PABR were used for the estimation of all

the kinetic parameters (Saturation factor Ks, Maximum specific growth rate μmax, initial biomass concentration ΧΒini)

Anaerobic co‐digestion modeling (1/3)

Ymeth=6.6901 Lmeth/Lreactor/gCOD Yx/s=0.05 gCODx/gCODs dCODini=1.46 g/L

Anaerobic co‐digestion modeling (2/3)

It is clear that the simple Monod kinetics model was able to satisfactorily describe the behavior of the PABR in terms of dCOD, while the values of the estimated parameters are reasonable.

• Fig. 1. dCOD Compartment 1

(experimental-model)

• Fig. 2. dCOD Compartment 2

(experimental-model)

Parameter estimation

• μmax =0.0732 d‐1
• ΧΒini =0.126 g/L
• Rb=0.465
• Ks=0.1034 g/L

Anaerobic co‐digestion modeling (3/3)

• Fig. 3. dCOD Compartment 3

(experimental-model)

• Fig. 4. dCOD Compartment 4

(experimental-model)

• Constant stirring of the anode and cathode chambers.
• Constant temperature at 35 oC and pH=7 (unless stated otherwise).
• Continuous aeration of the cathode chamber.
• External resistance Rext =1 kΩ.
• The anode chamber was operated as a sequence batch reactor (at the end
• f each cycle the liquid contents were emptied and the anode chamber

was refilled with fresh medium).

• Anolyte contained:
• Catholyte contained:
• Buffer (NaH2PO4∙2H20, Na2HPO4∙2H20)
• NaHCO3
• KCl
• trace elements
• glucose as the electron donor
• Buffer
• KCl

MFC Operating Conditions

 Pretreated and filtered livestock waste and whey as substrate at different initial concentrations (1st and 2nd cycle = 0.4 g dCOD/L, 3rd and 4th cycle = 0.8 g dCOD/L, 5th and 6th cycle = 1.5 g dCOD/L, 7th cycle = 2.8 g dCOD/L, 8th cycle = 3.1 g dCOD/L. External resistance Rext = 1kΩ).  Duration of the cycles increased by increasing the initial concentration of the substrate  dCOD removal efficiency practically constant (67‐75%).  The MFC could operate at higher wastewater concentrations

Electricity production with MFC (1/3)

 Linear relationship between the duration of each cycle operation with the initial concentration according to the equation: y = 92.379 *x.  Low CE (2.1%) of the last cycle (cycle with the highest initial concentration).  Most of the dCOD was removed by methanogens or other non‐electrogenic microbes established in the anode rather than by electron transfer bacteria.

Electricity production with MFC (2/3)

 Maximum power density remains practically constant (50 mW/m2) for all cycles.  Power generation limited by the high ohmic resistance and not affected by the bacteria

• r the specific substrates used.

 The almost constant slope of the polarization curves confirms the very significant contribution of ohmic losses in the dual chamber MFC.

Electricity production with MFC (3/3)

Conclusions

• Two alternative ways for the valorization of livestock manure

and whey evaluated

• Biogas production rate = 0.13 L/Lreactor/d and tCOD removal

rate = 79.9%

• Relatively high dCOD removal and power density were

achieved for the concentrations tested with MFC.

• The time needed to degrade the substrate increases linearly

with the substrate concentration.

• The dCOD removal efficiency and the maximum power

density seems not to be affected by wastewater strength.

Thank you for your attention! Thank you for your attention!