REVIEW OF DANISH FIELD EXPERIMENTS WITH SEWAGE SLUDGE AND COMPOSTED HOUSEHOLD REFUSE AS A FERTILIZER SOURCE

摘要

The paper is concerned with the concentration and effect of nutrients and potential pollutants in municipal sewage sludge and composted household refuse in Denmark. The fertilizer value of these waste products corresponds approximately to the content of mineral nitrogen. Leaching of nitrate and increased phosphorus concentration in the soil were recorded at application rates of up to 21 t/ha/year organic matter of sewage sludge. The environmental effects were less at application rates not exceeding the current legal thresholds. These correspond to less than 1 t/ha/year organic matter. The concentration of heavy metals in the soil and the crop was increased by large application rates of highly loaded sewage sludge. Using lower application rates of sewage sludge with improved quality, the rate of heavy metal accumulation in the soil is reduced. In general, compost and animal manure contain less heavy metals than sewage sludge. Current application rates do not cause detectable increases in soil carbon content. Organic contaminants that originate primarily from household use appear to be degradable at treatment plants or in the soil, and there seems no risk for contamination of the grain of cereal crops.