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