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NEPTUNE
WP-2: Novel treatment technology for
wastewater and sludge
Kick-Off meeting NEPTUNE
 November 2th 2006, Rome

Ghent University - Laboratory of Microbial Ecology & Technology
Introduction and objectives
Wastewater as waste
Wastewater as a resource
Introduction and objectives
Wastewater as a resource

Established technologies improved and complemented with
novel technologies.

Microbial fuel cells Energy recovery and nutrient removal

Ferrate oxidation
Manganese oxide based oxidation Removal of micropollutants
High temperature pyrolysis



Polymer production from sewage sludge  Valorisation of
sludge waste
Established technologies

Conventional aerobic treatment:
+ Simple process and high treatment efficiency
- Aeration cost: 0,5 kWh m-3 = 30 kWh.IE-1.yr-1
- Sludge disposal cost: up to € 500 ton-1DM

Anaerobic digestion:
+ Biogas production = Energy recovery
• 1 kg COD converted = 1kWh
-
Water temperature >28 °C
Not applicable for low strength wastewaters
Can microbial fuel cells be an alternative?
Microbial fuel cells: the
challenger

MFC technology
+ The chemical energy of various types of
reducing compounds can be recovered as
kWh
+ Works at low temperatures
+ Produces low amounts of excess sludge
- Bacteria need to “like” it
Batteries and fuel cells
Anode: oxidation occurs, electrons go to an electrical
circuit
Cathode: reduction occurs, electrons
arrive from an electrical circuit
Microbial fuel cells
Anode: oxidation of
substrate by a
biocatalyst
Cathode: reduction of oxygen
MFC Biofilm ecology
= mediator producing species
CnH2NOn
A
= non-producing species
CnH2NOn
B
CnH2NOn
C
D
CO2
CO2
CO2
CnH2NOn
eee-
CO2
eReduced
substrate
e-
ANODE
Electricity generation from
discrete substrates
TAKE HOME: Power densities and substrate to current
conversions are increasing
Electricity generation from
discrete substrates
TAKE HOME: Power densities and subtrate to current
conversion are lower for O2 compared to K3Fe(CN)6 systems
=> a good functioning sustainable cathode is needed!
Electricity generation from
wastewater
TAKE HOME: Substrate to current conversions are lower
compared to discrete substrates: biodegradability!
Reactor design: anode
Effluent
MFC in Neptune
-
Open air cathode
Tubular configuration
Continuous system
Influent
Can stacked MFCs provide
power at enhanced voltage and
current?


By connecting several batteries or power sources in series and
parallel, voltages and currents can be increased.

Series connection:
voltages
= addition of

Parallel connection
currents
= addition of
Does the series and parallel connection influences the anodic
biocatalytic performance of a MFC?
Stacked MFC design

6 individual MFC units






Anode: granular graphite matrix
synthetic influent
Cathode: granular graphite and
ferrocyanide
Membrane: Ultrex
Rubber sheet: separation
between the individual MFCs
No bipolar plates
The void volume of the anode
was 60 mL
Stacked MFCs provide power at
enhanced voltage and current


Maximum voltage and current generation without power
generation:
 Open circuit voltage = 4,2V (Series)
 Short circuit current = 425 mA (Parallel)
Voltage and current at maximum power densities (Pv max) during
series, parallel and individual stack operation:
Pv max
(W/m³)
Voltage at
Pv max
(mV)
Current at
Pv max
(mA)
Series Stack
228
2018
41
Parallel Stack
247
349
255
Individual MFC
258
395
40
TAKE HOME: High power densities can be maintained
during series and parallel connection
Reactor design: anode
Effluent




Select a performing electricity producing
microbial consortium suited for the mix of
soluble COD present in sludge digestate
Maximize energy recovery and COD
removal by optimizing the anode potential
Investigate the influence of the operational
parameters on the removal of humic acids
and xenobiotics
Build a technical scale MFC for energy
recovery and treatment of the digestate
Influent
Reactor design: cathode

Jurg or Korneel , could you provide a
specific slide explaining your work
part?
Reactor design: cathode
Optimize the cathode
compartment of an MFC
 Develop a cathodic
denitrification process

Microbial fuel cells applications

Stand alone MFC technology:

Several MFCs in series or parallel to
deliver electricity at the desired
current and voltage
kWh
Wastewater
MFC
Combined micro-pollutant removal

Recalcitrant waste water:
First: ferrate, manganese oxide,
pyrolysis technology
 Second: MFC

kWh
Wastewater
Ferrate
MnO4
Pyrolysis
MFC
Ferrate technology (EAWAG)




Develop kinetic database for the
oxidation of phenol-, amine-, and
sulphur- containing micropollutants
Study and model the micropollutant
oxidation by ferrate(VI)
Compare phosphate removal with
ferrate(VI) vs. conventional with Fe(III)
Ferrate(VI): simultaneous oxidation of
micropollutants and phosphate removal
Manganese oxide upflow
bioreactor technology (LabMET)






In situ regeneration of oxidant
by Mn oxidizing bacteria
MnO2 as solid phase oxidative
agent provides catalytic surface
Partly oxidizes recalcitrant
compounds (humic acids,
atrazine...)
MnO2
Mn2+
Bacteria re-oxidize Mn2+ to MnO2
Bacteria utilize low molecular
organics
MnO2 precipitate acts as
catalytic surface again
Mn-oxide UBR (LabMET)





Pretreatment of recalcitrant
wastewater
2 L upflow bioreactor filled with 750 mL
MnO2
HRT: 1 h
Monitoring of effluent for recalcitrant
compounds of interest: analytical
methodology / biological assays
UBR as stand-alone or in combination
with MFC technology
High temperature pyrolysis
Valorisation of sludge as soil
amendment
 High temperature pyrolysis:

Guarantee microbiologically and
chemically safe sludge
 Removal of heavy metals
 Recovery of phosphorus

Polymer production from
sewage sludge
PHA: biodegradable copolymers of
PHB and PHV (polyhydroxybutyrate
and -valerate)
 Why biodegradable polymers ?

Synthetic plastics: 25 Mton/yr in EU + US
< 20% recycled
or incinerated
> 80% in landfills and
marine environments
Production of PHAs


Pure microbial culture: high costs !
Mixed microbial cultures:




Phosphorus accumulating organisms (PAO)
Glycogen accum. org. (GAO)
Activated sludge- aerobic dynamic feeding
(ADF)
Valorize waste streams by digesting it and
produce VFA (volatile fatty acids) as starting
substrate for PHA production
PHA low-cost production






Large scale production will be required to meet
realistic demands in polymer supply
Abundant and concentrated organic waste needed
Primary and secondary sludge (biosolids)
Ferment to VFA using Cambi process as
pretreatment (high pressure thermal hydrolysis)
Biosolids solubilization and complete pathogen
destruction
Optimize process for VFA and subsequent PHA
production: Cambi-process, microbial inoculum,
reactor feeding regime, proper C/N ratios...
Milestones & expected results




Novel MFC design for efficient COD removal and
energy recovery from domestic wastewater with
demonstrated low sludge production.
MFC-based treatment system to achieve nitrogen
and phosphorus removal from domestic wastewater.
Tailored oxidation technologies for adequate
micropollutant removal
Valorisation strategies for sludge with warranted
microbiological and chemical safety