Quantification of water extractable contaminants from food waste and biosolids blends at different stages of composting

Rainfall runoff and leachate from windrows composting organic wastes carry nutrients and pathogens. Water extractability of contaminants in compost impacts the design of runoff treatment systems. This paper reports maximum water extractable nutrients, pathogens, and regulated metals from biosolids and food waste composts as measured from a snapshot sampling of windrows at different stages of stabilization at a commercial operation at a single point in time. Results show that unstable composts released larger amounts of fecal coliform (13,100 to 19,000 Most Probable Number per g of sample, MPN g(-1)) than stable composts (6 to 7 MPN g(-1)). Maximum water extractable C was 4690 and 5990 mg kg(-1) in food waste and biosolids composts, respectively. In both composts, extractable amounts of C decreased with increased stability of compost, but was not so for extractable N or P. Significantly greater P was extractable from food waste (9.7 to 12.5% of total P) than biosolids composts (2.8 to 3.9%). Heavy metal extractability was highest for Ni (5.3 to 13.4% of total present) and Cd (8.5 to 29%).