Fig. 1 Biorefinery products and their market drivers [1]. (Reproduced with permission from Sadhukhan et al. (2014) [1] Copyright © 2014

Society of Chemical Industry and John Wiley & Sons, Ltd.)

High value, low volume, challenging to find market

Low value, high volume, easy to find market

Gas and CHP

Biofuel

Chemical and hydrogen

Polymer

Composite

Food, pharmaceutical

Fig. 2 Microbial fuel cell (MFC) generates electricity by electron harvesting from waste streams using bacteria; protons transfer from the anode

to cathode and reduce oxygen to produce water; the overall operation is exogenic. Microbial electrolysis cell (MEC) generates hydrogen using

the same principle, except hydrogen production in the cathode chamber and the overall operation is endogenic needing external voltage.

Fig. 3 MEC schematic with anode and cathode substrates that can be sourced from waste biomass.

Anode substrate: Organic waste/ wastewaters / C6, C5 sugars from lignocellulose / hydrolysate from lignocellulose /stillage from biodiesel and bioethanol plants / glycerol from biodiesel plant

H2 and CO2 / carbonic acid / pyruvate / formate / fatty acids

e-e-

External voltage applied

H+

An

od

e c

ham

be

r:

Bio

elec

tro

chem

ical

oxi

dat

ion

Cat

ho

de

cham

be

r:

Cat

alyt

ic e

lect

ro-

hyd

roge

nat

ion

, h

ydro

deo

xyge

nat

ion

an

d r

edu

ctio

n

reac

tio

ns

CO2 reuse in reactions

Biofuel or Chemical or Polymer

Gaseous products (e.g. hydrogen, methane)

Cathode substrate: Wastewaters / pyruvate / organic acids e.g. α-keto acids (e.g. pyruvate-), α,β-unsaturated acids and hydroxy acids, glucose, etc. sourced from lignocellulosic wastes

PR

OTO

N EXC

HA

NG

E MEM

BR

AN

E

H+

Proton exchange membrane (optional)

Fig. 4 Biorefinery preprocessing and processing technologies, mechanisms and products [1]. (Reproduced with permission from Sadhukhan et al.

(2014) [1] Copyright © 2014 Society of Chemical Industry and John Wiley & Sons, Ltd.)

INORGANICS, <1% EXTRACTIVES, 3%

LIGNIN, 15%-25%

HEMICELLULOSE, 24%-36%

CELLULOSE, 38%-54%

Fermentation products:Ethanol, lactic acid,

acetone-butanol-ethanol

Chemical conversion products:

Furfural, hydroxymethyl, levulinic acid,

Wood adhesives, epoxy resins, fuel additives, benzene-toluene-xylene , binders, carbon fiber

Processes:Enzymatic conversionCatalytic conversionCatalytic pyrolysisElectrocatalyticconversion

Xylite, furfural, 5-hydroxymethylfurfural, L-arabinose, furan resins and nylons

Glucose polymerEndo-cellulose

Amorphous regions of the chain produces oligosaccharides

Exo-celluloseChain ends produce cellobiose

β-glucosidaseOligosaccharides and cellobiose produce glucose

Poly-urethanes, polyolefins and specialty phenolics for high value applications, such as pharmaceuticals and fragrances (vanillin)

Processes:Alkaline extractionAlkaline peroxide extractionHot water / steam extractionChemical conversion

2. α-aryl ether cleavage

1. β-aryl ether cleavage 3. Enol ether formation

4. C-C bond cleavage

C5: Xylose enzymatic hydrolysis

Fig. 5 Integrated bioethanol and MES process flowsheet: route 1: fermentation; route 2: lignocellulose fractionation.

Lignocellulose (e.g. straw, wood, etc.)

Size reductionSteam

pretreatment(solid state)

FermentationDistillation, dehydration

Ethanol

Enzyme production

Yeast propagation

Fractionation e.g. modified pulping /

organosolv, acid hydrolysis, etc.

Lignin platform

C6, C5 platform

Solid / liquid separation of

stillage

Combustion

Solid

Air cathode in MFC: WaterOr, Anaerobic cathode in MEC: HydrogenOr, Anaerobic biocathode in MEC: Biofuel

(glutamate, propionate, butanol, etc.)

Energy

Electricity generated in MFCOrVoltage applied in MEC

Bioanode:Glu CO2 / Acetate + 24H+ + 24e-

e- e-

H+

CO2 / Acetate / H2

21

1

Liquid

MES

Or, Anaerobic cathode in MEC: Hydrogen

Or, Anaerobic biocathode in MES: Biofuel (glutamate, propionate, butanol)

Fig. 6 Process flow schematic for utilising glycerol and stillage streams of an existing biodiesel plant producing biodiesel from oily residues

esterification and waste oils transesterification, in a BES. The numbers in bold are the mass units of the various flows in the integrated flowsheet,

which gives biodiesel, ethanol and biofuel (biobutanol, acetate and formate) products of 100, 5.4 and 6.63 mass units, respectively. Please refer

to the “Supplementary material on biodiesel process flowsheet synthesis and hypothesis for MES creation” for the illustration.

Oily residues

Sulphuric acid and methanol

Dilute acid esterification

TransesterificationMethanol Waste oil

Glycerol refining

Biodiesel refining

Glycerol Biodiesel

Stillage Electricity generated in MFCOrVoltage applied in MEC

Bioanode:Glycerol Ethanol + CO2 + 2H+ + 2e-

Ethanol

e- e-

H+

Air cathode in MFC: WaterOr, Anaerobic cathode in MEC: HydrogenOr, Anaerobic biocathode in MEC: Biofuel or Chemical

Substrate for biocathode shown in Figure 1

Or, Anaerobic cathode in MEC: Hydrogen

Or, Anaerobic biocathode in MES: Biofuel or Chemical

MES

104

1

10.7 (97.8% glycerol)

100 (99.9% biodiesel)

5.3 (19% biodiesel)

5.4

Biofuel: 6.63

Fig. 7 Integrated AD, fermentation and membrane electrolysis process (BES: bioelectrochemical synthesis) flowsheet. BES is used to remove

ammonia from AD effluent, which is then recycled back to AD to increase biomethane concentration >90 vol%. Effluents from BES and AD can

also be processed through MF / UF / NF, and RO for enhance recovery of nutrients and pure water. RED and MFC are used to recover some of

the energies. Generated hydrogen in BES has two options: 1) React with ammonia to produce amine; 2) React with CO2 from fermentation or

other processes to produce carboxylate / alcohol. Techno-economics of the integrated systems will be a subject of consideration for further

research.

Anaerobic digestion BESORGANIC WASTEEFFLUENT

RECYCLE

NH3 + H2 / AMINE

BIOMETHANE BES

FermentationHYDROLYSED SUGARS

WASTE STREAMS

BIOETHANOL

BIOMETHANE CARBOXYLATE / ALCOHOLS

MF / UF / NF / RO and RED / MFC FERTILIZER

COMPOST

/ AMMONIA

PURE WATER

(a)

(b)

Fig. 8 𝑙𝑜𝑔10(𝑖) (while 𝑖 is in A m-2) with respect to activation overpotential (in mV) for two exchange current densities. (a) Exchange current

density = 3.33 A m-2; (b) Exchange current density = 1.67 A m-2.

0.1

1

10

100

0 20 40 60 80 100 120 140

Activation overpotential (mV)

Ratio of current density and the exchange current density

Current density in A per sq. m

0.1

1

10

100

0 10 20 30 40

Activation overpotential (mV)

Ratio of current density and the exchange current density

Current density in A per sq. m

Fig. 9 𝑙𝑜𝑔10(𝑖) (while 𝑖 is in A m-2) with respect to concentration overpotential (in mV) for two limiting current densities.

1

10

0 20 40 60 80

Cu

rren

t d

ensi

ty (

A m

-2)

Concentration overpotential (mV)

Limiting current density = 13.6 A per sq. m

Limiting current density = 100 A per sq. m

(a)

(b)

Fig. 10 (a) Power density and (b) electrode potential as function of current density at different substrate concentrations. Numbers are the

concentrations of acetate in g l-1.

0

5

10

15

20

25

30

35

40

45

50

0 2 4 6 8 10 12

Pow

er d

ensi

ty (

W m

-3)

Current density (A m-2)

Model: 0.15

Experimental: 0.15

Model: 0.50

Experimental: 0.50

Model: 1.00

Experimental: 1.00

0

0.1

0.2

0.3

0.4

0.5

0.6

0 2 4 6 8 10 12

Pote

nti

al (

V)

Current density (A m-2)

Model: 0.15

Experimental: 0.15

Model: 0.50

Experimental: 0.50

Model: 1.00

Experimental: 1.00

Fig. 11 Availability of the cathode surface area with the progress of reaction (mean value shown by the arrowhead) for different acetate

concentrations.

0

20

40

60

80

100

120

0.15 0.50 1.00

Effe

ctiv

e sp

ecif

ic s

urf

ace

area

(m

2 m

-3)

Acetate concentration (g l-1)

Fig. 12 Strategy for bioproduct and bioprocess development from ideas to market: Utilisation of predictive power.

Societal needs and market

demands for products

Availability of waste

resources and infrastructures

Health, environment

and job creation

Policy incentives

Project definition: Characterise waste

substrates and identify pathways to products

Identify appropriate gut communities

responsible for rapid rates of microbial

bioconversion in nature

Hypothesise metabolic pathways; Metabolic

flux analysis for targeting products

thermodynamic optimisationEconomics

Design options and regions for

operability

Process Integration and

flowsheet synthesis, industrial symbiosis

Process simulation and dynamics

Control experimentation

Economics and sustainability

Piloting, demonstration and

fully operational symbiotically

integrated process plant

Fig. 13 Target polymers from integrated biorefineries [1]. (Reproduced with permission from Sadhukhan et al. (2014) [1] Copyright © 2014

Society of Chemical Industry and John Wiley & Sons, Ltd.)

Polysaccharides

Starch polymers

Polyesters

Polylactic acid (PLA)

Other polyesters

Cellulose polymers

Polyhydroxyalkanoates (PHAs)

Polyurethanes

Polyamides

Polyurethanes (PURs)

Poly (trimethylene terephthalate) (PTT)

Poly (butylene terephthalate) (PBT)

Poly (butylene succinate) (PBS)

Polyamide 6

Polyamide 6,6

Polyamide 6,9

Poly (butylene succinate adipate) (PBSA)

Poly (butylene succinate terephthalate) (PBST)

Poly (butylene adipate terephthalate) (PBAT)

Poly (ethylene terephthalate) (PET)

Polyethylene furanoate (PEF)

Polyamide 11

Polyamide 6,10

Polycarbonates

Diphenolic acid polycarbonates

Poly(propylene carbonate) (PPC)

Natural fibres Lignin composites

Other natural polymeric materials