Waste to Energy: Anaerobic digestion & Co-digestion technologies
by Therése Luyt
17 May 2012
PD Naidoo & Associates Consulting Engineers (Pty) Ltd
The Waste Minimisation and Recycling Interest Group
Workshop on Organic Waste, Legislation, Policy & Practice
Contents • Why and where do we start?
• Know your waste stream
• Definition of organic waste
• Main applications
• Technologies (Germany experience)
– Anaerobic digestion
– Co-fermentation
– Composting
Why Waste-to-Energy?
• Renewable energy source
• Reduce GHG emissions & mitigate global warming
• Organic waste high in energy content
• Convert into biogas, which contains methane (CH4)
• Production of electricity & heat by AD of organic waste
• Job creation
• Low water input
• Generate electricity or fuel
Waste management hierarchy
Source: National Waste Management Strategy, 2011
Waste
minimisation
Benefits for municipalities
• Presents municipalities with various advantages
– Reduce amount of waste to landfill
– Saving landfill airspace
– Reduction in transport costs
– Energy currently lost at LFS, compressed & used as vehicle fuel to replace fossil fuelled transportation, home cooking or injection to public grid
• Municipalities to assess potential partners (PPP services) to implement & maintain facilities
Where do we start? Know your waste stream
• Necessary step for any effective waste management system
– How much tonnes per day?
– What’s in the waste (composition)?
Waste composition
• City of Cape Town 2007/2008: 168t
• DEA&DP (3 districts + 2 CPT landfills) 2008: 42t
• PDNA undertook 2 waste characterisation studies
– PDNA (pilot project) 1t
– Infrastruktur &Umwelt/PDNA 3t
Food waste & garden greens ~ 29%
Recyclables >30%
Waste composition
Definition of organic waste
Type
Waste from agriculture, horticulture, forestry, hunting & fishing, food preparation & processing
Waste from WWTW
Waste from leather, fur & textile industries
Municipal waste – organic fraction (domestic, restaurants, hospitals, abattoir etc)
Waste from wood processing & production of panels & furniture
Organic waste is anything that comes from plants or animals that is biodegradable
Main applications
• Once municipality understands potential for energy in their solid waste, they must decide how best to implement options available to them
– Agricultural biogas plants
– Landfill gas recovery
– MSW treatment
– WWTW
Technologies – Germany experience
• Biogas facility
• Hospital food waste
• Co-fermentation at WWTW
• Composting at Municipal Treatment Plant
Biogas facility
Bioenergie Schlitters GmbH, Austria
Bioenergie Schlitters GmbH, Austria
Owner: Farmer (2.9m € investment costs)
Input: 6,000 t/a - food/kitchen waste, bio-waste, expired food (supermarkets)
Output: Installed electrical capacity = 330kW (tariff €0.11c/kWh)
85% electricity fed into grid
80% heat sold
Bioenergie Schlitters GmbH, Austria
Note:
1m3 methane (CH4) = 9.97 kWh
1m3 biogas = 5.0 – 7.5 kWhoverall
1m3 biogas = 1.5 – 3 kWhel
Biogas from organic waste = 100m3/t
~200kWh/t of organic fraction from MSW
4 Stages:
1. Transport, delivery, storage & pre-treatment of substrates
2. Biogas production in AD
3. Storage of digestate, conditioning & utilisation
4. Storage of biogas, conditioning & utilisation
1
4
3
2
1 3
4 2
Hospital food waste
(Other applications: industrial kitchens, canteens, hotels and restaurants)
Hospital, Rosenheim
Biotank (fibreglass)
Collection
Transport
Biomaster
Biomaster (how it works)
1
2 4
3
Co-fermentation at WWTW
Moosburg WWTW
Increasing biogas yield through addition of liquid organic waste in existing Anaerobic Digester
Facts:
Population 33,000 (40,000 EW)
Design capacity 12,2Ml/d
(508m³/h)
Electrical output 380kW
Plant consumption 292kWh
88kW fed into grid
Heat to local community
85% dry sludge content
SBR plant to control N levels
2. Dry sludge
1. Organic storage tanks
3. SBR Plant
1
3
2
4
3
2
1
Flow diagram
3.5% sludge - solid
2% organic - solid
Composting of garden greens & kitchen waste
AVA Abvallverwertung GmbH, Augsburg
Delivery & processing
1 2
3
• Rotting hall, rotated weekly,
10 weeks
• Sieved into 3 grain sizes
18,000 tonnes per annum of quality compost
I hope these few slides have given you some fresh ideas and new hope!
References
• Combined Heat and Power Applications for Residential Application from a Biogas Plant (2011). Tsikata, M. Fritz, WLO.
• Biogas Handbook (2008). Big>East
• BioTrans AG. www.biotrans.ch
• Production and use of fuels derived from residential municipal solid waste (2011). Kepp, U. McKendry P.
• Biogas – an introduction (2008). Federal Ministry of Food, Agriculture and Consumer Protection
• Finsterwalder Umwelttechnik GmbH
Thank you Baie dankie
Enkosi