Potential Pollutants from Farm, Food and Yard Waste Composts at Differing Ages: Leaching Potential of Nutrients Under Column Experiments. Part II

The quantity and quality of compost leachate depend on the age and composition of the composting materials and this study was undertaken to assess the changes in nutrient concentration and load of leachates coming from different compost mixtures and ages. Three different compost mixes (farm, food, yard waste composts) at different ages from fresh to maturity were leached with distilled and deionized water in laboratory column experiments. The leachate NO3-N concentration increased with the increase of compost age for all the compost mixtures. At maturity, the tot N content of the farm waste compost is more readily leached and NO3-N comprises a large proportion (> 68%) of the leachate tot N compared with the food (20 to 47%) and yard waste (1 to 19%) composts. The composting process and operation at early composting ages (0 to 9 weeks) pose less of a potential as a source of NO3-N than does the compost at maturity. The food waste had relatively higher leachate NH4-N load than the farm and yard waste composts, implying that the food waste compost had a greater potential as a source of NH4-N than the farm and the yard waste composts. At maturity the leachate NH4-N load (and concentration) was consistently low for all compost mixes, thus the composting operation poses less of a potential as source of NH4-N at maturity than at the early compost ages. Towards maturity, the leachate PO4-P load of the farm waste was higher than the leachate PO4-P load of the food and yard waste composts despite the lower P concentration of the farm waste compost than those of the food and yard waste composts. The results suggest that the form of P rather than its amount in the compost governs the leachate PO4-P content. The farm waste compost had a greater potential as a source of PO4-P than the food and the yard waste composts towards maturity. The amount of N and P was shown to vary with the compost mixture, compost age, and volume of leachate. These results can be used to assess at what stage of the composting period one would expect the greatest risk of potential N and P pollution for a specific compost mixture. Furthermore, appropriate best management practices (BMPs) could be applied to control these potential pollutants based on the findings of these study.