Toxicity evaluation of weathered coal fly ash-amended manure compost

The general use of manure compost is limited by its residual toxicity, and hence a study was performed to evaluate the use of weathered coal fly ash (lagoon ash) to alleviate the toxicity of manure compost. Mature and immature manure compost were amended with lagoon ash at 0, 5, 10 and 20% (w/w dry weight basis), and their phyto-toxicity was evaluated by germination and root length growth of lettuce seed. The immature manure compost had significantly higher contents of NH₄-N, PO₄-P, and acid- and water-extractable Cu and Zn contents than those of mature manure compost. Ash amendment caused a significant increase in electrical conductivity (EC), but a decrease in NH₄-N, PO₄-P, and DTPA-, CaCl₂- and water-extractable Cd, Cu, Pb and Zn contents of both manure compost. Addition of lagoon ash at a rate of 5% for immature manure compost and 10% for mature manure compost resulted in a higher seed germination rate and root length growth. The germination index demonstrated significant negative correlations with EC, NH₄-N and DTPA extractable Cd, Cu, Pb and Zn contents. The present study supports the use of lagoon ash for amending manure compost to reduce the availability of trace elements and NH₄-N.