Wastewater treatment and sludge production:
energy recovery process, techniques and financial
evaluation
Loro FrancescoARPAV
Subotica, Sept. 2013
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
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
The reduction of water contents
• High pressure belt press for sludge
• FILTER PRESSES• Centrifuges• Drying Beds
Perf
orm
ance
70% of water
25% of water
To improve the performance it is necessary the use of chemicals
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
Acceptance limits for sludge
Water contents limit landfill acceptance criteria (EU Decision 2003/33)
Acceptance limits for composting
Acceptance limits for agricolture
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)
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
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
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
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
Plant details
Etra - Bassano del Grappa (VI) – Valorga Process
Plant details:
Type Dry
Technologies Valorga
Reactors 3 reactors – 7200 m3
D.M. Contents 20 - 25 %
Temperature range
37 °C
HRT 25 -30 dd
Plant Details
Etra - Camposampiero (PD) Linde process
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
Etra Camposampiero (PD)
Organic Waste
Pulper
Sludge
Landfillor
incinerator
Green Waste
Composting(Vigonza)
Hydrolysis
BiogasAnaerobic digestion
Solid fraction
Liquid fraction WWTP
Clean Water
Compost
Scarps
Centrifuge
Plant details:
Sesa - Este
Sesa - Este
Type Wet
Technologies Internal projects
Reactors 4 – 5000 m3
d.m. Contents 12 - 16 %
Regime 37 °C
HRT 20 – 25 days
Sesa - Este
Organic Waste
Squeezing
Sludge
Landfill
Green Waste
CompostingAnaerobic digestion
Biogas
SeparatorSolid
fraction
Liquid fraction
WWTP
Clean Water
Compost
Solid fraction
Liquid fraction
Scarps
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...
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)
MBR to reduce the sludge production
Some plant use the most advanced technologies in order to reduce the amount of sludge (SESA Este)
Struvite productionKMg(PO4)·6(H2O) MAP [MgNH4PO4*6H2O]
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)
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
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)
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)
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)
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
36%
10%2%2%
14%
30%
7%
Amortization costWorkersFuel & ChemicalsEnvironmental Red TapeMaintenance
Cost analysis of a real plant
Income Analisys of a integrated plant
Total income 6.000.000 €Workers 23
Energy production 13.000.000 kWIncome Composition percentage
Green Certificate 18,9 %27 %Electric Energy
Selling 8,9 %
Organic Waste Tariff 62,2 % 73 %Other Waste 10,8 %
Contacts
Loro FrancescoTel. +39.348.0643462e-mail: [email protected] / [email protected]
Thanks for the kind attention
AcknowledgementEtra Spa – Walter Giacetti
