- The document discusses wastewater treatment sludge production and energy recovery techniques. It focuses on anaerobic digestion, which produces biogas from sludge and organic waste. - Key aspects covered include sludge reduction methods, matter and energy recovery, acceptance limits for agricultural use, anaerobic digestion technologies, and costs/subsidies for energy production. - Financial analysis shows the importance of subsidies like green certificates in making anaerobic digestion competitive with alternatives like composting. Integrated plants allow for sludge and waste treatment plus energy recovery.

1. Wastewater treatment and
sludge production:
energy recovery process,
techniques and financial
evaluation
Loro Francesco
ARPAV
Subotica, Sept. 2013

2. Summary
• The sludge production from WWTP
• The solution:
– Matter recovery
– Energy recovery
• The biogas plant
• The use of sludge mixed with organic waste
• The technologies
• The Veneto situation
• The evaluation of costs and the role of subsidies

3. The sludge production
• The byproducts of a
WWTP are:
– Clean water
– Sludge
• How to Reduce the
production:
– New technologies as MBR
– Reduction of the amount
of water

4. The reduction of water contents
• High pressure belt
press for sludge
• FILTER PRESSES
• Centrifuges
• Drying Beds
Performance
70% of water
25% of water
To improve the performance it is
necessary the use of chemicals

5. The matter recovery
• Use as fertilizer in agricolture
– It is necessary a permit
– Bioaccumulation of pollutants (A.e. if the wastewater is
contemined by heavy metals)
– Specific limits for HV and POPs
• The Composting plant
– Production of a fertilizer
– Use of green waste as filler
– The process needs energy and dedicated equipment
– Specific acceptance limits

6. Acceptance limits for sludge
Water contents limit  landfill acceptance criteria (EU
Decision 2003/33)
Acceptance limits for composting

7. Acceptance limits for agricolture

8. The energy recovery from sludge using
Anaerobic Digestion
• The production of biogas
from sludges was developed
during the ‘70 and ‘80 but
after few years this was
abandoned.
• The causes was:
– High cost of maintenance
– Low energy production
– Market (the landfill was
cheaper than AD)

9. A new mix
• To improve the
biogas production
the sludge is mixed
with organic waste
• The anaerobic
digestion and the
composting plant are
an integrated plant

10. The Anaerobic Digestion:
The technologies applied
• These technologies works with a mixture
of sludge and Organic Waste
• The main carbon source are the O.W.
• The sludges represent an income for the
waste management plant
• The composting plant or the reuse in
agricolture represents the solution to
reduce the amount of sludge and are a
fundamental part of an integrated plant

11. Anaerobic
digestion plants
in Veneto
ETRA
Bassano d. G.
(VI)
SESA
Este (PD)
ETRA
Camposampiero
(PD)
Agrilux
Lozzo atestino
(PD)
Impianto
Comunale
Treviso
Dolomiti
ambiente
Belluno
Agrinord
Verona
Villa Bionergia
Verona

12. The treatment capacity in Veneto
• Treated sludge (EWC
190805) in 2012 : 110.000 t
• Treated OW in 2012: more
than 300.000 t
• Biogas production:
35.000.000 Nm3
• Energy production: 75 Gwh

13. Plant details
Etra - Bassano del Grappa (VI) – Valorga Process

14. Plant details:
Type Dry
Technologies Valorga
Reactors 3 reactors – 7200 m3
D.M. Contents 20 - 25 %
Temperature
range
37 °C
HRT 25 -30 dd

15. Plant Details
Etra - Camposampiero (PD) Linde process

16. Type Wet
Technologies Linde
Reactors size 3300 m3
D.M. Content 9 - 12 %
Temperature of the
reactor
55 °C
HRT 17 -20 days
The technologies:
Etra - Camposampiero

17. Etra Camposampiero (PD)
Organic
Waste
Pulper
Sludge
Landfill
or
incinerator
Green
Waste
Composting
(Vigonza)
Hydrolysis
Biogas
Anaerobic
digestion
Solid
fraction
Liquid
fraction WWTP
Clean
Water
Compost
Scarps
Centrifuge

18. Plant details:
Sesa - Este

19. Sesa - Este
Type Wet
Technologies Internal projects
Reactors 4 – 5000 m3
d.m. Contents 12 - 16 %
Regime 37 °C
HRT 20 – 25 days

20. Sesa - Este
Organic
Waste
Squeezing
Sludge
Landfill
Green
Waste
Composting
Anaerobic
digestion
Biogas
Separator
Solid
fraction
Liquid
fraction
WWTP
Clean
Water
Compost
Solid
fraction
Liquid
fraction
Scarps

21. The importance of quality of waste
•The production of organic waste
presents some features:
•The production change in terms of
quantity and quality during the years
•The quality of OW could change on the
basis of the location and period
•High contents of inert waste
(dangerous for the biogas equipment)
•Specific flows from industry (as food
industry)  risk of poisoning
A new variable in the process...

22. A new problem: the treatment of
wastewater from AD
The anaerobic digestion use a big quantity of water
and produce a wastewater that cannot be used in
Nitrates Vulnerable Areas
Part of the wastewater could be used during the
composting process of the solid fraction of AD
wastewater
Some european project on the recovery of NH3 as
solid fertilizer
Recovery of P as fertilizer (struvite)

23. MBR to reduce the sludge production
Some plant use the most advanced
technologies in order to reduce the
amount of sludge (SESA Este)

24. Struvite production
KMg(PO4)·6(H2O) MAP [MgNH4PO4*6H2O]

25. The evaluation of the cost
• Why in the last decade there
was a big growth of the AD
plant that treat sludges and
OW in Italy?
• The introducion of a special
subsides (Green Certificate)
that can increase the income
of a plant through the energy
selling.
• Without this subsides the AD
isn’t competitive
The
evaluation of
the cost must
take into
account the
local
condition
(Green
certificates,
Green fee)

26. 1. Pre-treatment of the
OW and production of
organic fraction to the
biogas production
2. Wastewater to AD
treatment : separation
of the solid franction
to composting plant
3. Treatment of the liquid
fraction of AD with
WWTP
4. Energy recovery
(Electric/Heat)
Dedicated equipment = dedicated costs

27. Anaerobic digestion costs
The costs of a composting plant will be lower due to lower technology level
€ 400
€ 450
€ 500
€ 550
€ 600
€ 650
€ 700
€ 750
€ 800
€ 850
€ 900
€ 950
€ 1.000
€ 1.050
Costo di investimento digestori anaerobici per ton di
frazione organica trattata
Economies of scales, a big treatment capacity reduce the cost of treatment
(in terms of euro/t)

28. Investement costs (in Italy)
• High investement due to the
elevate cost per ton.(400-
1000 €/ton, around two times
for a standard composting
plant)
• The use of anarobic digestion
reduce the plant surface (less
costs for the purchase of the
area where the plant will be
located)
• The evaluation of the cost for
an new istallation or the
revamping could change on
the basis of the national
condition (Green Certificates)

29. Operating and maintenance costs
• The maintenance cost are usually very
high (because the machines installed
presents an high level of maintenance)
• Costs fo Employees are usually higher
than a composting plant because it is
necessary specialized workers. (In Italy
around 10 % of the total costs).
• Costs for technical
• Costs of enviromental controls,
comunication to citizens (NIMBY
syndrome)
• Waste water treatment (the costs are
high due to high level of N)
• Management of the organic fractions
(composting, landfill, agricoluture)

30. Simulation of an intergrated plant for slugde
OW – 72.0000 t/y + 55.000 t or green
waste . Interest rate 6%, Amortization
and Green Certificate 15 years, solid
waste to landfill 14% w/w
35%
10%
2%2%
14%
30%
7%
Amortization cost
Workers
Fuel & Chemicals
Environmental Red Tape
Maintenance
Cost analysis of a real plant

31. Income Analisys of a integrated plant
Total income 6.000.000 €
Workers 23
Energy production 13.000.000 kW
Income Composition percentage
Green Certificate 18,9 %
27 %Electric Energy
Selling
8,9 %
Organic Waste Tariff 62,2 %
73 %
Other Waste 10,8 %

32. Contacts
Loro Francesco
Tel. +39.348.0643462
e-mail: lorofrancesco@outlook.com / floro@arpa.veneto.it
Thanks for the kind attention
Acknowledgement
Etra Spa – Walter Giacetti