Sustainable waste management involves the reuse of waste in ways that are both economically- and environmentally-beneficial. Sustainable waste management encompasses a wide range of disciplines and applications and is increasingly important today in reducing the disposal of wastes in landfills. This study identified two areas where new knowledge was required to enhance the sustainability of current waste management systems. First, waste foundry sand, was studied for its potential reuse as a soil amendment and its applicability in growing turfgrass to reduce or prevent the current disposal of foundry sand in landfills. Second, the assessment of compost maturity indices were evaluated to identify those indices that more accurately predicted maturity for a certain type of compost. The proper use of these maturity indices will guarantee higher quality for the end user, increasing compost use and ensuring the completion of this sustainable waste management cycle.
To avoid increasing costs of landfill disposal, it has become increasingly important for U.S. foundries to identify beneficial reuses for the 7-11 million metric tons of waste foundry sand (WFS) generated annually. A major drawback to the reuse of some WFSs as a soil amendment is the high soil strength they create (measured as strength to rupture of lab-formed clods) under dry conditions, where root growth may be limited. Fifteen WFSs were analyzed for strength to rupture (strength) using lab-formed clods, exchangeable cations (Na, Mg, Ca), metal oxide concentration (Fe, Mn, Al, Si), cation exchange capacity (CEC), and clay content. The results indicate that high strength WFSs have properties similar to hardsetting soils caused by high Na+ clay content and can be ameliorated by the addition of Ca2+. From these results it was proposed that the addition of compost may also help reduce the strength caused by sodium bentonite. The humic acids present in a mature compost could potentially flocculate the clay and prevent its dispersion.
Indices used to determine the maturity of compost are important because immature compost can adversely affect plant growth if used as a soil amendment due to the presence of undecomposed, phytotoxic compounds and high microbial activity which can scavenge available nutrients. Different indices of compost maturity were assessed for their accuracy in predicting maturity when using a compost with high salt and high pH characteristics. The traditional and best tests, plant bioassays, provided results that were highly variable with time and did not approach any equilibrium for the duration of this study. These results were probably due more to the high salinity and pH than the overall compost maturity. Chemical indices, specifically those related to the optical density and aromaticity (%), proved best for this situation.
The high strength properties observed previously in WFS were tested by planting perennial ryegrass and tall fescue in different blends containing WFS mixed with compost, acid-washed sand, or gypsum. Measurements of strength to rupture (strength), shoot dry weight, root dry weight, and surface coverage were performed for each mix and compared to a commercial potting media control. Results determined that strength was not a factor for any of the parameters studied but the K/Na base saturation of WFS:compost mixes was highly correlated with total shoot dry weight for both perennial ryegrass and tall fescue. A compost blend containing 40% WFS was determined to be the optimal amendment for the reuse of WFS as it incorporated the greatest possible amount of WFS without any observed reduction in turfgrass growth parameters. These results suggest that under certain conditions, strength may not be an important factor in the reuse of WFSs as soil amendments.
This study produced knowledge that will improve current waste management strategies for waste foundry sand and compost so that each process is more sustainable. The reduction in costs associated with landfill disposal of waste foundry sand and the better quality assessments for compost will provide economic incentives that will allow for their environmentally-beneficial reuse in the future. (Abstract shortened by UMI.)