Tjalfe G. Poulsen Aalborg University, Denmark. Objectives

Transcription

1 Integrated organic waste management for improved energy and greenhouse gas balances in practice: A case study Tjalfe G. Poulsen Aalborg University, Denmark 1/15 Objectives To evaluate energy and greenhouse gas balances for organic waste management related to waste mangement system changes and improvements. Historical data for a specific location, Aalborg, Denmark ( inhabitants = 4% of population) are used. Evaluation carried out for specific years where significant changes in waste processing have taken place. 2/15 1

2 Aalborg organic waste quantities (2005) Waste type Mass as collected (metric tons/yr) Food waste Yard/ park waste Other organic waste Sewage sludge Waste total energy content = Upper fuel value plus energy represented by nutrients = 1.6 PJ/yr 2005 waste quantities used in calculations for all years for easier comparison 3/15 Aalborg waste management 1970 No wastewater treatment All solid organic waste deposited at landfill without gas recovery 4/15 2

3 Aalborg waste management 1980 Wastewater biological organic matter removal implemented. Sewage sludge deposited at sludge beds. All remaining solid organic wastes are incinerated without energy recovery. Ash deposited at landfill 5/15 Aalborg waste management 1990 Mesophilic digestion of sewage sludge with power/heat production Digested sludge applied to farmland. Heat recovery at waste incinerator implemented. Yard/park waste collected separately and composted. 6/15 3

4 Aalborg waste management 2005 Removal of N, P from wastewater implemented. Thermophilic sludge digestion implemented. Digested sludge dried and incinerated with energy recovery. Heat/power recovery at waste incinerator implemented. 7/15 Aalborg waste management 2020 Water vapor condensation at incinerator implemented (2007). Sludge thermal pretreatment assumed. Food waste digestion together with sewage sludge assumed. P extraction from ash assumed. 8/15 4

5 Fuel and energy substituted Electricity and heat produced at a coal fired combined heat and power plant with 24% power and 68% heat production. Excess power produced at a coal fired power plant at an efficiency of 45%. Excess heat produced at coal fired heating plant at 95% efficiency. 9/15 GHG balance impacts considered Process Upstream GHG emissions Direct GHG emissions Downstream GHG emissions Composting Energy, fuel provision From process, fuel use Dewatering Digestion From digestion Energy substitution Drying Incineration From fossil C in waste Energy substitution Land application Fuel provision From fuel use and waste degradation Fertilizer substitution, Bio C sequestration Land filling From waste degradation Bio C sequestration Ash P extraction Fertilizer substitution Sewer transport Pre-treatment Transport Fuel provision From fuel use Wastewater treatment 10/15 5

6 Relative energy % Energy balances for Aalborg organic waste management Nutrient utilization composting Transport Wastewater treatment Incineration Year 11/15 Energy balances for Aalborg organic waste management Incineration with energy recovery is the main contributor to a positive energy balance (equivalent to 5-7% of national energy use incl transport). Wastewater treatment can potentially yield high energy outputs if energy consumption for aeration can be reduced. Composting and land application of organics are unimportant for the energy balances. Digestion of source separated food waste can potentially yield significant energy output. 12/15 6

7 GHG Balance 1000 tonnes CO 2 eqv. /year GHG balances for Aalborg organic waste management Land application Transport Wastewater treatment Year Composting Incineration Landfilling 13/15 GHG balances for Aalborg organic waste management Aalborg organic waste and wastewater management has changed from a net GHG emitter (200 kg CO 2 /cap in 1970) to a net GHG saver (170 kg/cap in 2005) equivalent to 4% of current national average emissions. Diversion of waste from landfilling to incineration with energy recovery are the main contributors to the reductions in GHG emissions. Wastewater treatment can potentially yield reductions in GHG emissions via energy savings for aeration and digestion of food waste together with sewage sludge 14/15 7

8 Conclusions Waste diversion from landfill to energy production improved Aalborg s organic waste management GHG balance from +200 to -170 kg CO 2 eq/cap. GHG balances presented here only include organic wastes. Further GHG emission savings are possible via improved recycling or reuse of other wastes. Proper waste management based on existing technology can be used to achieve significant net GHG emission savings. 15/15 8