2. Materials and methods
2.1. Composting units
The six home composting units (Humus/Genplast, 8230 Åbyhøj, Denmark) used in the study are the most commonly used units in Denmark. They are cone-shaped, made of recycled PE and PP and weigh 22 kg. The total volume is 0.32 m3 and the dimensions are 95 cm in height and 48 cm and 105 cm in diameter (top and bottom, respectively). The composting units are equipped with a lid, a fine-masked steel net at the bottom, which prevents mice and rats from entering, a hatch where the mature compost can be withdrawn, and a net to prevent flies from entering. The bottom has plenty of holes from where the surrounding air can enter the composting unit. A plastic rim, which acted as a base for the flux chamber (used to measure the emissions; see Section 2.5), was inserted below the lid of each unit. The plastic rim was inserted below the anti fly net so it functioned as the only outlet during the emission measurements. A schematic drawing of one of the composting units is shown in Fig. 1 (left) and a picture is shown in Fig. 1 (right). The only differences in the management of the six units were the type and amount of input waste and frequency of mixing. Mixing consisted of manually aerating the material using a mixing stick made of recycled PE and PP (delivered together with the composting unit). Units 1 and 2 represented eager management (mixing every week), which is not considered a likely management approach. Units 3 and 4 were considered the most likely setup for home composting (mixing every sixth week), whereas Units 5 and 6 represented the lazy home composters that spend little time on the process (no mixing). The management of the composting units, the amounts of input waste for one year of composting and the moisture content of the input materials are presented in Table 1.