Comparative environmental analysis of anaerobic mono digestion and - - PowerPoint PPT Presentation

Comparative environmental analysis

• f anaerobic mono‐digestion and co‐

digestion of organic waste

• L. Lijó, N. Voulvoulis, N. Frison, S. González‐García, M. T. Moreira

and E. Katsou

This research was supported by a project granted by the EU project Live‐Waste (LIFE 12 ENV/CY/000544) and by the BBVA program “2015 edition of the BBVA Foundation Grants for Researchers and Cultural Creators” (2015‐PO027).

Introduction

Biogas Digestate AD

Reduce Reuse Recycle Recovery Landfill

From the most to the least environmentally friendly

Waste Hierarchy (EC, 2008)

Cogeneration Fertilisation Organic waste

In line with Circular Economy, anaerobic digestion is able to convert organic waste streams into valuable materials that can find their way back into the economy.

Organic waste management in an urban context: Anaerobic digestion of sewage sludge and food waste

Introduction

Anaerobic mono‐digestion Anaerobic co‐digestion Sewage sludge Food waste Sewage sludge & food waste Advantages Advantages Advantages ‐ Available infrastructure in WWTP ‐ Trained technicians in WWTP ‐ High biogas potential ‐ Improved nutrients balance ‐ Increased biogas production ‐ Usage of available capacities in WWTP digesters Disadvantages Disadvantages Disadvantages ‐ Low efficiency ‐ Low biogas potential ‐ Composition variability ‐ Nutrients imbalance ‐ High C/N ratio ‐ Legislative framework in each country (end of waste criteria) Research efforts have been made aiming to boost methane production by means of co- digestion of sewage sludge and food waste

Sewage and food waste as a resource

SS FW

Sewage sludge 524 t/d 100% ‐ Food waste ‐ 35.62 t/d 100%

To evaluate the potential environmental benefits of sewage sludge and food waste co‐digestion by comparing different integration rates of food waste within a WWTP

• Anaerobic mono‐digestion:

separate digestion of each substrate

Scheme 1

• Anaerobic co‐digestion: on

the basis of surplus capacity

• f the digester

Scheme 2

• Anaerobic co‐digestion:

introduction of a second digester to treat all the waste generated

Scheme 3 Scheme 2 SS+FW FW

Sewage sludge 524 t/d 98% ‐ Food waste 3.85 t/d 2% 31.76 t/d 100%

SS+FW

Sewage sludge 524t/d 86% Food waste 35,62 t/d 14%

Objectives

Raw materials, fossil fuels and water Emissions to air water and soil

Conclusions Recommendations Improvement options

Goal and scope definition Impact assessment Inventory data collection Interpretation

Identification of environmental hotspots Environmental credits  resources recovery Inputs from Technosphere

Electricity 1000 kWh Chemicals 50 kg

Outputs to Environment

CH4 60 Kg N2O 0,1 kg

Environmental results

Impact categories A B C Climate change 10 60 ‐1 Acidification 5 15 ‐5 Eutrophication 0,8 1

Life Cycle Assessment Methodology

Scheme 1

Anaerobic digestion Dewatering Land application Biotrickling filter Mixing

Primary sludge Secondary sludge

Mono‐digestion of sewage sludge

Thickening Pasteurisation Storage Co‐generation Anaerobic digestion Dewatering Land application Biotrickling filter Screening Shredding

Food waste

Mono‐digestion of food waste

Dilution Pasteurisation Storage Co‐generation

Functional unit (FU): The management of sewage sludge and source‐segregated food waste produced by a community of 150,000 PE each day

Wastewater to WWTP Water

Scheme 2

Anaerobic co‐digestion Dewatering Land application Biotrickling filter

Co‐digestion of sewage sludge

Pasteurisation Storage Co‐generation Anaerobic digestion Dewatering Land application Biotrickling filter Screening Shredding

Food waste

Remaining fraction: Mono‐digestion of food waste

Dilution Pasteurisation Storage Co‐generation Mixing Thickening Screening Shredding

Food waste

Functional unit (FU): The management of sewage sludge and source‐segregated food waste produced by a community of 150,000 PE each day

Wastewater to WWTP Water

Primary sludge Secondary sludge

Scheme 3

Anaerobic co‐digestion Dewatering Land application Biotrickling filter

Functional unit (FU): The management of sewage sludge and source‐segregated food waste produced by a community of 150,000 PE each day Co‐digestion of sewage sludge

Pasteurisation Storage Co‐generation

‐ Production of inputs and energy: electricity, transport, infrastructure and chemicals. ‐ Direct emissions: biogas losses, CHP, digestate storage, land application. ‐ Waste streams: rejected materials to landfill and wastewater to WWTP. ‐ Environmental credits: electricity and digestate production from organic waste can replace electricity from fossil fuels and mineral fertilisers.

Mixing

100% Primary & secondary sludge

Thickening Screening Shredding

100% Food waste

Wastewater to WWTP

Results

Parameter Unit Scheme 1 Scheme 2 Scheme 3 SS FW SS+FW FW SS+FW Primary sludge t/d 183 183 183 Secondary sludge t/d 341 341 341 Food waste t/d 35.62 3.85 31.76 35.62 SGP m3 /kg TVS fed 0.35 0.7 0.40 0.7 0.54 TVS degraded

% 37 74 42 74 43.5

Biogas production rate m3/d 2,855 5,281 3,598 4,710 8,543 Sludge produced t/d 30.22 9.45 30.59 8.43 38.13

2000 4000 6000 8000 10000 Scheme 1 Scheme 2 Scheme 3 Specific biogas production (m3/d) FW SS

Results

x 1.3 x 3.0 Heat and Electricity: Scheme 1  4.2 GWh/yr Scheme 2  5.2 GWh/yr Scheme 3  12.5 GWh/yr

Results

ReCiPe Midpoint methodology

‐100% ‐75% ‐50% ‐25% 0% 25% 50% 75% 100%

CC TA FE ME Comparative results Scheme 1 Scheme 2 Scheme 3

• Environmental credits

Avoided electricity production and mineral fertilisation

• Environmental burdens

‒ Phosphate and nitrate leachates to water resulting from land application of digestate ‒ Reject water recirculation to WWTP

• Mono‐digestion VS Co‐digestion

Posive synergec effects:↑ biogas yield ↑ environmental credits Impact categories:

• Climate change (CC): GHG emissions (e.g. CH4, N2O)
• Terrestrial acidification (TA): acidifying emissions (e.g. SO2, NH3)
• Freshwater eutrophication (FE): P‐based compounds to water (e.g. PO4

3‐)

• Marine eutrophication (ME): N‐based compounds to water (e.g. NO3

‐)

Policy context

Source‐segregated biodegradable waste and sewage sludge fall into different regulatory regimes in the UK

• Digestate from source‐segregated biodegradable waste is classified as a

waste until it meets PAS 110 and Quality Protocol standards.

The Quality Protocol for anaerobic digestate establishes the end‐of‐waste criteria  then: it is no longer classified as a waste, waste management control is not required.

• Digestate from sewage sludge is controlled under the Sludge (Use in

Agriculture) Regulations.

• Digestate from co‐digestion  it is not covered by an approved quality

protocol and expensive environmental permits may be required

Conclusions

 Co‐digestion of sewage sludge and food waste achieved better environmental results of all the evaluated environmental impact categories  higher biogas production and lower digestate production.  An integrated and holistic approach for organic waste management enhanced the environmental profile of the applied management practice.  Economic and social constrains and benefits will be integrated in the sustainability assessment (future work).  For its implantation, it is essential that the regulatory policy stimulates the development of a suitable market for the co‐digestate.

Comparative environmental analysis

• f anaerobic mono‐digestion and co‐

digestion of organic waste

• L. Lijó, N. Voulvoulis, N. Frison, S. González‐García, M. T. Moreira

and E. Katsou

This research was supported by a project granted by the EU project Live‐Waste (LIFE 12 ENV/CY/000544) and by the BBVA program “2015 edition of the BBVA Foundation Grants for Researchers and Cultural Creators” (2015‐PO027).