Improving nutrient availability in alkaline coal combustion by-products amended with composted animal manures

Abstract

Hypothesis and Objectives: We hypothesized that coal combustion products (CCPs), including those created during scrubbing of sulfur dioxide from flue gases, can be used alone or mixed with composted animal manures as effective growth media for plants. Our specific objectives were, therefore, to (1) measure the chemical, physical and hydraulic properties of source materials and prepared mixes, (2) determine the optimum design mix of CCPs and composted animal manures for growth of plants, (3) evaluate the leachate water quality and plant uptake of selected elements from prepared mixes, (4) quantify the interaction between composted animal manures and B concentrations in the mixes, (5) study the availability of P to plants growing in the mixes, and (6) determine the microbial community and siderophores involved in the solubilization of Fe and its transfer to plants. Background: In recent years a major expansion of electricity production by coal combustion has taken place in Israel, the United States and the rest of the world. As a result, a large amount of CCPs are created that include bottom ash, fly ash, flue gas desulfurization (FGD) gypsum and other combustion products. In Israel 100,000 tons of fly ash (10% of total CCPs) are produced each year and in the US a total of 123 million tons of CCPs are produced each year with 71 million tons of fly ash, 18 million tons of bottom ash and 12 million tons of FGD gypsum. Many new scrubbers are being installed and will come on-line in the next 2 to 10 years and this will greatly expand the amount of FGD gypsum. One of the main substrates used in Israel for growth media is volcanic ash (scoria; tuff). The resemblance of bottom coal ash to tuff led us to the assumption that it is possible to substitute tuff with bottom ash. Similarly, bottom ash and FGD gypsum were considered excellent materials for creating growth mixes for agricultural and nursery production uses. In the experiments conducted, bottom ash was studied in Israel and bottom ash, fly ash and FGD gypsum was studied in the US. Major Achievements: In the US, mixes were tested that combine bottom ash, organic amendments (i.e. composts) and FGD gypsum and the best mixes supported growth of tomato, wheat and marigolds that were equal to or better than two commercial mixes used as a positive control. Plants grown on bottom ash in Israel also performed very well and microelements and radionuclides analyses conducted on plants grown on bottom coal ash proved it is safe to ingest the edible organs of these plants. According to these findings, approval to use bottom coal ash for growing vegetables and fruits was issued by the Israeli Ministry of Health. Implications: Bottom coal ash is a suitable substitute for volcanic ash (scoria; tuff) obtained from the Golan Heights as a growth medium in Israel. Recycling of bottom coal ash is more environmentally sustainable than mining a nonrenewable resource. The use of mixes containing CCPs was shown feasible for growing plants in the United States and is now being evaluated at a commercial nursery where red sunset maple trees are being grown in a pot-in-pot production system. In addition, because of the large amount of FGD gypsum that will become available, its use for production of agronomic crops is being expanded due to success of this study.