Windrow composting of source separated kitchen biowastes in Finland

Abstract

All households in the City of Jyväskylä have been required to source-separate their wastes since June 1996. The accumulation of kitchen biowaste was about 60 kg per resident in 1997, with an efficiency of more than 75%. The residents of almost 50% of the detached houses in the city opted for small-scale composting. Ensuing kitchen biowaste was surprisingly pure: the estimated content of non-compostable material was less than 0.1 % by weight. The biowastes were composted at the Mustankorkea waste station in open windrows. Adequate aeration of the windrows was guaranteed when the initial height of the windrow was less than 1.5 m and the blending ratio for biowaste and bulking agent was one tonne of biowaste to one cubic metre of wood chips. The temperature rose to 85°C in these windrows. Carbon concentration increased slightly during 64 weeks composting, whilst the hydrogen concentration decreased. The pH and the ash content also increased during composting. As measured by pathogenic microbes (Salmonella), the biowaste composts were hygienic. In summer, the concentration of airborne microbes was high during turning of the windrows, both in the composting field and in the cabin of the wheel loader. The concentration of endotoxin in the cabin exceeded all recommended limits.