Nutrient Retention and Release Characteristics From Municipal Solid Waste Compost

Abstract

A bench-scale laboratory study was conducted to examine municipal solid waste (MSW) compost nutrient dynamics. Two MSW compost batches varying in stability were compared for their ability to retain or leach total Ca, Mg, K, P, and N. Composts were leached with 150 ml of deionized water or one of two concentrations of nutrient solution 12 times over a six-week period. Increasing the concentration of nutrient leaching solutions generally resulted in no significant differences in leachate nutrient mass. Water soluble Ca, Mg, and K leached from both composts during the first four leachings and accounted for most of the total elemental mass lost from composts. Both composts had low C:N ratios (below 20:1) and substantial mineral N was added as soluble NO3−, but little mineral N appeared in leachates, or in an organic form in the composts after leaching ceased. Both composts C:P ratios were below 200:1, but the total P mass in leachates was generally low and declined steadily despite repeated addition of mineral P to composts. The least stable MSW compost (Compost B) released a significantly greater mass of Ca and Mg and retained more P than the more stable compost (Compost A). In general, outputs of Ca, Mg, and K were greater than inputs for all compost treatments, while inputs of P were greater than outputs. Total N outputs nearly equaled inputs, but total N accumulations were not noticed in the final compost analysis, suggesting denitrification occurred. In all but one case, increasing the nutrient leaching solution concentration did not induce development of statistically different concentration gradients in compost leaching tubes. This suggests nutrient leaching solutions depleted the compost of nutrients uniformly before an equilibrium was reached between the compost and compost solution.