Dr. Elena Ficara (Politecnico di Milano)

1. Green recovery of energy and nutrients from
wastewater in the frame of the Circular
Economy
ELENA FICARA
POLITECNICO DI MILANO
Dipartimento di Ingegneria Civile e Ambientale - Sezione ambientale

2. Dipartimento di Ingegneria Civile e Ambientale
Content
- Introduction: general circular economy framework
- Technologies for resource recovery in WWTPs
- Overview on applying algae for wastewater treatment for nutrients/energy
recovery/savings

3. Dipartimento di Ingegneria Civile e Ambientale
The role of wastewater treatment plants
Challenges of sanitation systems:
 Supply safe (drinking) water
 Limit environmental impacts by
wastewater discharges
Historically…
but…
 Growing population,
 Life style changing,
 Climate change
are modifying water
availability and request
new challenges are to be faced
Uptake Use discharge

4. Dipartimento di Ingegneria Civile e Ambientale
The circular approach ….
Water,
energy,
resources
Water source treatment
Reuse
treatment
discharge
New hierarchy
use

5. Dipartimento di Ingegneria Civile e Ambientale
The circular approach ….

6. Dipartimento di Ingegneria Civile e Ambientale
Looking beyond the current
"take, make and dispose”
extractive industrial model, the
circular economy is restorative
and regenerative by design.

7. Dipartimento di Ingegneria Civile e Ambientale
Which kind of resources to be recovered?
Biodegradable organics:
12 – 14 W/PE
Total organics:
18 – 20 W/PE
Ammoniacal N: 8 W/PE
TOTAL: 20 – 28 W/PE
(4-5 times energy required
for WW treatment)
Clean water
Chemical energy
Nutrients (N, P)
Wastewater 40-70 m3/PE/y
2-3 kg N/PE/y
0,5-1 kg P/PE/y
= WWTP  WRRP
Water Resource
Recovery Platform

8. Dipartimento di Ingegneria Civile e Ambientale
Energy request for the water sanitation
o 10-17 W/PE
o 90-150 kWh/PE/y
• Reducing water consumption
• Optimizing processes
• Recovering energy from wastewater
2-3% of electric energy consumption
up to 7%
(in EU and USA)
How to save energy?
In Italy:
Total consumption 7500 GWh/y
(2,5% national electric energy
consumption)
Campanelli, Foladori, Vaccari (2013)
•water supply 57%
•water treatment 43%

9. Dipartimento di Ingegneria Civile e Ambientale
Energy recovery from wastewater
Thermal: Wastewater temperature: 14 - 23°C.
Heat pumps to warm (winter) or cool (summer) buildings.
e.g.: Nosedo (Milano) WWTP recovers 200 kW
Hydro-electric: by taking advantages of head loss
e.g.: Folgaria (TN) WWTP recovers 40 kW (50 L/s for 236 m)
Chemical energy: typically recovered from the sludge line
In Italy: today 121 GWh/y from AD of waste sludge (GSE, 2014)
Potential: 2100 GWh/y (= all plants with tertiary treatments would use
conventional AD)

10. Dipartimento di Ingegneria Civile e Ambientale
Energy positive WWTP: utopic?
• Recover energy with effective AD
• Optimizing energy intensive processes
New pathways in biological treatment
Optimization of existing treatment
e.g.: Aeration systems
Optimized processes
Energy consumption
P.E. served
WWTP of Strauss (Austria)
250 000 P.E.
Energy cost for treatment:
11.3 kWh/PE/y, offset by biogas
production

11. Dipartimento di Ingegneria Civile e Ambientale
Recovery of phosphorus
Accessible stocks of P-rocks are going to be exhausted SOON
Use
Wastes
Agriculture
Plants
P mining
Water bodies
(WWTP)
 P is fundamental in
sustaining agriculture
 Demand is growing
together with word
population
 Uneven distribution
of P mines (Morocco,
Cina, US)
 EU is P deficient About 18% of the P request could be
recovered from waste streams
Cordell & White, 2011, Sustainability, 3(10), pp. 2027-2049

12. Dipartimento di Ingegneria Civile e Ambientale
Recovery of phosphorus
Biological processes:
P-iperaccumulating
microorganisms
Recovery from ashes from
sludge inciniration:
P + N, K, P, Mg, Ca
Chemical precipitation:
Addition of Al(OH)3 /
Ca5(PO4)3OH
Struvite precipitation
Recovery alternatives

13. Dipartimento di Ingegneria Civile e Ambientale
Recovery of phosphorus - struvite
𝐌𝐠𝐍𝐇 𝟒 𝐏𝐎 𝟒 ∙ 𝟔𝐇 𝟐 𝐎 ∶ 𝐬𝐥𝐨𝐰 𝐫𝐞𝐥𝐞𝐚𝐬𝐞 𝐟𝐞𝐫𝐭𝐢𝐥𝐢𝐬𝐞𝐫
1 2After AD
Efficiency up to 90%
Low Purity
After S/L separation
Efficiency: 40% – 60%
High Purity
http://www.phosphorusplatform.eu/p
latform/news/1308-eu-organic-
farming-committeepositive-opinion

14. Dipartimento di Ingegneria Civile e Ambientale
Recovery of bioplastics (PHA)
“European Strategy for Plastics in a
Circular Economy”, 16/1/2018
(http://ec.europa.eu/environment/circula
r-economy/pdf/plastics-strategy.pdf
Carbonera WWTP – pilot demonstration
Expected increase in PHA production by 2022:
24000 tonPHA/y
(european-bioplastics.org)
Motivation

15. Dipartimento di Ingegneria Civile e Ambientale
San Rocco
(1.050.000 PE) Nosedo
(1.250.000 PE)
Recovery of water in agriculture
Milano WWTPS:
Tertiary treatments
120 millions m3/y (185 gg) to agriculture
Only 2% of WWTP is reused (Lautze et al., 2014)

16. Dipartimento di Ingegneria Civile e Ambientale
HRAP: High rate algal pond
Primary
sludge
PRIMARY
SETTLER
ACTIVATED
SLUDGE
SECONDARY
SETTLER
ANAEROBIC
DIGESTION
PRE -
TREATMENTS
INFLUENT EFFLUENT
BIOSOLIDS
Mixed sludge
Recirculation
Biogas
SOLID/LIQUID
SEPARATION
TERTIARY
TREATMENT
Secondary
sludge
New GREEN solutions: Microalgae & WWTP

17. Dipartimento di Ingegneria Civile e Ambientale
Microalgae
Oxygenic photosynthesis
H2O  O2
• 2.8 billons years
• Allowed aerobic organisms to develop 
Large increase in productivity
O2
Microalgae
• Mostly autotrophic/photosynthetic
• Versatile
• Biodiverse

18. Dipartimento di Ingegneria Civile e Ambientale
Highly productive
Combined production
Fine chemicals/goods
Biodiesel/biogas
Limited competition for soil with crop production
Allow nutrients recovery
Process
Integration WWTP, AD plants
Power stations
Microalgae - claims

19. Dipartimento di Ingegneria Civile e Ambientale
First applications: earlier than 1960 in California
New recent interest
«Microalgae + wastewater + treatment»
Scopus, 2017
Microalgae & WWTP

20. Dipartimento di Ingegneria Civile e Ambientale
Advantages of microalgae in wastewater treatment:
- Low energy cost (extensive treatment based on solar energy)
- Integration algae/bacteria
- Nutrient recovery + COD removal
- Production of algal biomass
- Other interesting effects:
 Disinfection
 Removal of micropollutants
 Removal of heavy metals
Microalgae & WWTP

21. Dipartimento di Ingegneria Civile e Ambientale
Water-stream - secondary treatment
 Activated sludge algae/bacteria processes
 Nutrient recovery(N, P)
• Uptake
• Conversion (CO2, N2)
Removal efficiencies
• COD: 60 – 95 %
• NH4
+: 70 – 99 %
• PO4
3-: 50 – 95 %
Primary
sludge
PRIMARY
SETTLER
ANAEROBIC
DIGESTION
PRE -
TREATMENTS
INFLUENT EFFLUENT
BIOSOLIDS
P-56
Mixed sludge
Microalgal
biomass
Biogas
SOLID/LIQUID
SEPARATION
TERTIARY
TREATMENT
PBR SOLID/LIQUID
SEPARATION
(A)
Microalgae & WWTP

22. Dipartimento di Ingegneria Civile e Ambientale
Primary
sludge
PRIMARY
SETTLER
ACTIVATED
SLUDGE
SECONDARY
SETTLER
ANAEROBIC
DIGESTION
PRE -
TREATMENTS
INFLUENT EFFLUENT
BIOSOLIDS
Mixed sludge
Recirculation
Biogas
SOLID/LIQUID
SEPARATION
(B/C)
PBR SOLID/LIQUID
SEPARATION
Microalgal
biomass
Secondary
sludge
Water-STREAM – tertiary treatment
 Disinfection
 Polishing
 Efficiencies (lab -scale):
• COD: 85 – 90 %
• NH4
+: 80 – 100 %
• PO4
3-: 75 – 99 %
Microalgae & WWTP

23. Dipartimento di Ingegneria Civile e Ambientale
Side-stream (sludge line)
Nutrient removal from the liquid fraction of digestate
 Reduction of the N and P load by uptake to the water line  savings
 Recycling of N-oxidized forms (nitrification)
 Removal efficiencies (lab/pilot scale):
• COD: 60 – 70 %
• NH4
+: 60 – 95 %
• PO4
3-: 50 – 95 %
Primary
sludge
PRIMARY
SETTLER
ACTIVATED
SLUDGE
SECONDARY
SETTLER
ANAEROBIC
DIGESTION
PRE -
TREATMENTS
INFLUENT EFFLUENT
BIOSOLIDS
P-106
Recirculation
Biogas
SOLID/LIQUID
SEPARATION
TERTIARY
TREATMENT
Secondary
sludge
PBR
(D)
Microalgal
biomass
SOLID/LIQUID
SEPARATION
Mixed sludge
Microalgae & WWTP

24. Dipartimento di Ingegneria Civile e Ambientale
Examples of demonstrative WWTP applying algae as a secondary treatment:
• South of Spain (Chiclana)
• California (Dehli and San Luis Obispo)
• New Zealand (Christchurch, Hamilton)
• Morocco
HARP = High Rate Algal Pond
Microalgae & WWTP

25. Dipartimento di Ingegneria Civile e Ambientale
Pilot plant in Chiclana
ALL GAS FP7-PROJECT (AQUALIA):
• HRAP = primary/secondary treatment
• Algal suspension: DAF floatation, AD+biogas
upgrading BioCH4
• Energy request = 0,16 kWh/m3
Energy produced = 0,17 kWh/m3
• Land request =2 m2/P.E.
Microalgae & WWTP

26. Dipartimento di Ingegneria Civile e Ambientale
Biofuels
Biofertilizers
Biomaterials
Nutrients
In WW
Simplified (low costs)
culturing systems
Wastewater treatment
WWTP  algae  resources

27. Dipartimento di Ingegneria Civile e Ambientale
Polisaccaride (Porphyridium)
PHA (cianobacteria)
PHB (Arthrospira, Sinechocystis)
Bioplastics
Algal
Biomass
Fermentation to
VFA
PHA by
iperaccumulating
bacteria
Bioflocculants
Bioplastics
WWTP  algae  biomaterials

28. Dipartimento di Ingegneria Civile e Ambientale
Conversion
Process
Product
Termochemical Biochemical Fisico-chemical
Gasification
Pyrolysis,
Combustion
Syngas
Electricity/heat
Fermentation
Anaerobic digestion
Methane
Hydrogen
Ethanol
alcohols
Extraction
Trans-esterification
Biodiesel
WWTP  algae  biofuels

29. Dipartimento di Ingegneria Civile e Ambientale
Species
Theoretical BMP
(Sialve et al. 2009)
LCH4/gVS
Cell wall
Actual BMP
(Mussgnug et al. 2010)
LCH4/gVS
Dunaliella salina 0.68 None 0.32
Chlamydomonas reinhardtii 0.69 Protein 0.39
Arthrospira platensis 0.47–0.69 Protein 0.29
Euglena gracilis 0.5–0.8 Protein 0.32
Chlorella kessleri 0.63–0.8 Polysaccharide 0.22
Scenedesmus obliquus 0.59–0.69 Polysaccharide 0.18
WWTP  algae  biogas

30. Dipartimento di Ingegneria Civile e Ambientale
Issues/limitations
• Low C/N ratio co-digestion
• Cell wall resistance to
biodegradation pretreatment
thermophilic digestion
• Low economic value compared to
other algae-derived products
DA integrated into a biorefinery
concept
WWTP  algae  biogas

31. Dipartimento di Ingegneria Civile e Ambientale
Estimated high productivity (Chisti et al., 2007)
crop Oil yield
(L ha-1)
Maize 172
Soy 446
Colza 1190
Jatropha 1892
Cocco 2689
Palma 5950
Microalgae 136.900
Microalgae 58.700
1: 70% lipids
2: 30% lipids
High lipid content:
• Special strains (Chlorella, Dunaliella, Isochrysis,
Nannochloris, Nannochloropsis, Neochloris, Nitzschia,
Phaeodactylum and Porphyridium spp.)
• Environmental growth conditions (lack in
N/stress)
Unrealistic expectations !!
More realistic values: 18.000-23000 L/ha
WWTP  algae  biodiesel
• Production costs (Norsker et al., 2011)
 1 ha  10 €/kg
 100 ha  4 €/kg
 Goal (0.40 €/kg)  combined strategies

32. Dipartimento di Ingegneria Civile e Ambientale
Cost reduction strategies
Biomass productivityg/m2/day 20
CO2 usage kg/kgbiomass 4
Water evaporation L/m2/day 10
Mixing power
consumption W/m3 2
Labour people/ha 0.1
Production days Days 365
Land area ha 100
Ratio V/S m3/m2 0.15
CO2 fixation
efficiency 0.45
Dilution rate 1/day 0.2
Total culture volume m3 150000
Scenario Inputs Reactor Harvesting
1Water, CO2 and fertilizers Raceway Centrifugation
2Water, CO2 and fertilizers Raceway Flocculation-Sedimentation+Centrifugation
3Free flue gases and wastewater Raceway Flocculation-Sedimentation+Centrifugation
4Free flue gases and wastewater Raceway
Flocculation-
LamellarSedimentation+Centrifugation
5Free flue gases and wastewater Raceway Flocculation-LamellarSedimentation+Filtration
6Free flue gases and wastewater Raceway Flocculation-LamellarSedimentation+Filtration
WWTP  algae  biodiesel

33. Dipartimento di Ingegneria Civile e Ambientale
Algal biomass as:
-Slow release fertiliser
-Natural pesticide
-biostimulants
Slow release fertilizer
Application rate similar to
conventional organic
fertilisers
6.5–10 t biomass ha−1
Algal biomass
• No phyto-toxicity
• Stimulating effects as
phyto-ormons
• Increase in germination
indexes
Luxury P uptake
 P recovery
WWTP  algae  biofertilisers

34. Dipartimento di Ingegneria Civile e Ambientale
1
10
100
1000
10000
Ni Cu Pb Zn
(mg/kg)
0
5
10
15
20
25
Cd
(mg/kg)
D.lgs. 99/1992 Sludge disposal Sludge Directive (in preparation)
Metal content in algal biomass
35WWTP  algae  biofertilisers

35. Dipartimento di Ingegneria Civile e Ambientale
First project approved in the water sector
(University of Valencia)
Sustainable wastewater treatment using innovative
anaerobic membrane bioreactors technology (AnMBR).
• Acceptable metal content
• Pathogens, micropollutants –> same levels as
for sludge
Legislation barriers
WWTP  algae  biofertilisers

36. Dipartimento di Ingegneria Civile e Ambientale
Conclusions
• WWTP  resources is mandatory
• Technical solutions exist
• Potential for applying microalgae-based processes
However:
• Economics: no established value chain for recovery products / lack on incentives,
lack of standard business models
• Still on-going pilot/demonstrative projects to validate techno-economic feasibility
• Regulatory barriers