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 EngineeringNational Technical University of Athens

Obtained from farms Main constitution:

o High organic contento High concentration of nitrogeno High concentration of phosphorus

Residues of some harmful substances (growth hormones, antibiotics and heavy metals) Efficient utilization is essential:

o in order to protect the environment and avoid the generation of human diseases.

o 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:o Biogas production through anaerobic co‐digestion in aPeriodic Anaerobic Baffled Reactor (PABR) and

o 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 operational flexibility

The Periodic Anaerobic Baffled Reactor (PABR) 

Operating volume: 77L 4 compartments of equal volume Consists of two concentric cylinders of which the interior operated as a bath 35oC (mesophilic conditions)

The Periodic Anaerobic Baffled Reactor (PABR) 

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Operation of PABR during a period T

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T/4<t<T/2

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Bioreactor that converts chemical energy, stored in the chemical bonds of organic compounds,  directly into electrical energy, through catalytic reactions of 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

CatalystCO2

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 2.3cm) 

• Proton exchange system: PEM (Nafion117)

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 7.46TSS (g/L) 5.72

Conductivity (S/cm) 3.93VSS(g/L) 4.60TS(g/L) 9.4VS(g/L) 7.14

Total Carbohydrates (g/L) 1.19Dissolved Carbohydrates (mg/L) 0.28Total Kjeldahl Nitrogen (mg/L) 631

Ammonium Nitrogen (mg/L) 378.8Organic Nitrogen (mg/L) 252.2Total Phosphorus (mg/L) 120.4

Orthophosphates PO43—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 thebehaviour of the PABR at the HRT of 22.3 d

Basic assumptionso The organic matter is consumed with simple Monod kinetics  

· ·

o Yield of methane on the substrate 

o Yield of biomass from COD

o Initial dCOD of the four comparments

o Biomass retention factor Rb (to be estimated by the model)

Experimental data (dCOD) of the PABR were used for the estimation of allthe kinetic parameters (Saturation factor Ks, Maximum specific growthrate 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 satisfactorilydescribe the behavior of the PABR in terms of dCOD, while the values of theestimated 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 

of each cycle the liquid contents were emptied and the anode chamber was refilled with fresh medium).

Anolyte contained:

Catholyte contained:

oBuffer (NaH2PO4∙2H20, Na2HPO4∙2H20)oNaHCO3oKClo trace elementso glucose as the electron donor

oBuffer oKCl

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 

or 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!