Organic Waste Management in Denmark

Composting in Denmark

• Composting in Denmark involves various processes, including introduction to composting, gas emission measurements, central composting, home composting, and environmental assessment.

• Composting of organic waste involves aerobic mineralisation and stabilization of organic matter. This is generally a process with low energy input and minimal environmental impact. Biologically stabilised compost is a useful recycling material.

• Municipal organic waste in Denmark and the EU includes garden waste and organic household waste (OHW), also known as biowaste. The amount of garden waste collected has more than doubled in Denmark over the past 20 years, and biowaste has increased by 10% in the EU. Landfilling of biowaste is still prevalent at 40%, but a ban is in effect in the EU. This has led to an increased need for treatment options, including biological treatment.

• Input to central composting in Denmark includes organic household waste (OHW), garden waste, sludge, park waste, and other organic wastes. A significant portion of total OHW (49,500 tonnes/year-5%) comes to central composting facilities. Garden waste comprises approximately 99% (831,000 tonnes/year) of the total garden waste collected. Sludge (107,000 tonnes/year), park waste (220,000 tonnes/year), and other organic wastes (21,000 tonnes/year) form additional input.

• Home composting in Denmark has the input of 21,000 tonnes (estimate) of OHW per year. The primary method is windrow composting (131 facilities), mat composting (8 facilities), and container composting (3 facilities). OHW requires source separation at 9 facilities.

• Composting practices vary significantly in Denmark, including various operational practices like windrow layout, turning, stabilization, and maturation periods. Composting typically yields 0.4 tonnes of compost from each tonne (1 t) of input. The processing of OHW (sludge) in compost introduces specific limitations, including restrictions on metal content, organic compounds, and pathogens. Danish legislation sets 55°C over 2 weeks, or 1 hour at 70°C as limit. There aren't restrictions for composted garden waste on land. Home composting is most common in private gardens at 45% followed by agricultural (20%), and green areas at 10%.

• Greenhouse gas (GHG) emissions from composting are not well understood. While composting produces GHGs, including CO2, CH4 and N₂O , the actual quantities are unknown. GHGs absorb and emit infrared radiation, causing climate change.

• Research objectives include quantifying gas emissions from windrow composting at three Danish facilities: Aarhus, Fakse, and Klintholm.

• Central composting facilities (Aarhus) process 15,500 Mg of garden and park waste annually. They have between 8 and 12 windrows are usually 115m long, 9m wide, and 4m high. The composting time usually takes 10-14 months, and the turning frequency is once per month.

• Compost temperature and gas composition vary across different stages of the composting process.

• Results from research on composting temperature and gas composition are gathered by Flux chamber/funnel measurements, concentration in windrows, and investigation of flux dynamics.

• The study identifies requirements for the application of the dynamic tracer dispersion method involving long-lasting gases and wind stability. There are also considerations for roads/paths for traversing around/through the site, and the use of analytical instruments with high resolution, ppb range, and speed. A controlled tracer and methane release test and plume down wind at 350m, 700m, and 1200m are performed. Data is collected on gas flow in windrows, and comparisons of different small-scale methods are presented.

• Quantification procedures at the Odense landfill are described, including the use of gas extraction methods and tracer placement in mixed waste.

• Results concerning the Aarhus, Fakse, and Klintholm composting facilities are presented including measured total GHG emissions for each facility in kg per hour.

• Data on waste input, mixing frequency, incoming waste weight and weekly waste addition, as well as factors such as moisture content, are detailed.

• Gas emission measurements for home composting units and the corresponding methods are presented. Information about the experimental setup, composting units (6 units), addition of waste (12 families), food waste schedule, operation phases including composting (1 year) and maturation (3 months), waste mix, are documented. Included is information on different mixing frequencies.

• Quantitative data (emission factors) associated with GHG emissions, specifically CO2, CH4, and N2O, is tabulated/presented to summarize GHG emission factors for the different units/composting phases.

• A conclusion and further recommendations are provided related to the results. For instance, factors impacting GHG emissions such as type of organic waste, windrow dimensions, and the turning frequency, are highlighted. The presented conclusions show how home composting can be a viable alternative to centralized composting.

• Environmental assessment related to LCI and LCA of central composting and home composting are analyzed and discussed.

• Environmental emissions (including GHG, leachate, combustion emissions and the use of compost, as well as soil impacts) are enumerated.

• Life cycle inventory (LCI) and Life cycle assessment (LCA) of central composting. Specific data from the Aarhus facility, including waste input, energy consumption (electricity, diesel etc.), and outputs are given.

• The LCA for Aarhus and home composting are also assessed and discussed. Factors such as GHG emissions, use of compost, and other significant parameters in both scenarios are considered

• Conclusions and recommendations from the study are given regarding aspects such as the need to avoid GHG emissions or minimize them from composting, the appropriateness of small-scale methods for quantifying GHG emissions from windrow composting, the level of emissions, and the importance of focusing on load and potential substitution of peat and fertilizers.

• New composting projects, operational considerations, emission testing, and environment assessment related to composting use are outlined.

• Direct GHG emissions from waste in Denmark, historical trend, goal for 2030, and related considerations are provided.

• Composting process is considered as a way to reuse/reduce waste rather than disposal for environmental benefits.

Test your knowledge about organic waste processing and composting in Denmark. This quiz covers various aspects of composting methods, regulations, and the environmental impact associated with organic household waste. Challenge yourself to see how much you know about Denmark's waste management practices!