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Title: EFFECTS OF DIFFERENT RATES OF FLY ASH AND SEWAGE SLUDGE MIXTURE AMENDMENTS ON CATION AVAILABILITY AND THEIR LEACHABILITY

Author
item SAJWAN, K - SAVANNAH STATE UNIV
item PARAMASIVAM, S - SAVANNAH STATE UNIV
item Alva, Ashok

Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2006
Publication Date: 6/1/2007
Citation: Sajwan, K.S., S. Paramasivam, A.K. Alva. 2007. Effects of different rates of fly ash and sewage sludge mixture amendments on cation availability and their leachability. Journal of Environmental Science and Health, Part A 42:1155-1160. 2007.

Interpretive Summary: Coal combustion byproducts (ex: fly ash) and water treatment residuals (ex: sewage sludge) are sometimes used as amendments to agricutlural soils. These materials contain some essential nutrients as well as micronutrients. There is an interest in application of these waste materials in high rates to minimize stockpile of these materials in landfills. However, this approach can be feasible if: (i) favorable crop response, yield, and/or quality, can be demonstrated to offset the added cost of application; (ii) no negative impacts due to leaching of nutrients and/or metals in these materials. Leaching column (30-cm long) technique was used in this study to evaluate the transformation and leaching of ammonium N, potassium, calcium, and magnesium from a sandy soil and a loamy sandy soil with application of different rates (24.7, 49.4, 98.8, or 148.3 metric tonnes per hectare) of 1:1 mixture of a fly ash and a sewage sludge. Cumulative leaching of all cations (in 9 pore volumes of water with 18 cycles of intermittent leaching and drying) increased with increasing rates of amendments in both soils. With the exception of K+ and Ca2+ in the leachate from the sandy soil, the cumulative amounts of all other cations in the leachate significantly increased with the first increment in rate of amendment. In the case of the former, a significant increase was evident only at rates greater or equal to 98.8 metric tonnes per hectare. In most cases, the peak concentrations in the leachate were evident at the 1 1/2 to 2 pore volumes of leachate, indicating that the leaching was quite rapid in the soils being evaluated.

Technical Abstract: Organic amendments play a significant role in improving soil fertility and supplying various nutrient elements in sustainable manner. However, these amendments may also pose a threat to water quality due to nutrient overload. A leaching column study was conducted to evaluate the leaching of cations from soils amended with a mixture of (1:1) fly ash [FA] from Port Wentworth power plant, Savannah, GA: sewage sludge [SS] from President Street water pollution control plant, Savannah, GA. Two sets of soil-leaching columns (30-cm high and 7.5-cm diameter; 15 columns per soil) were prepared with a fine sandy soil from Florida (Candler fine sand; pH 6.8) and a loamy fine sand from Georgia (Ogeechchee loamy sand; pH 5.6). The top 2.5 cm of soil from each column was amended (3 columns per treatment) with 1:1 mixture of SS and FA at either 0, 24.7, 49.4, 98.8 or 148.3 Mg/ha rate. After saturating the columns with deionized water, 18 cycles of intermittent leaching and drying was performed on weekly basis. Leaching of major cations and changes in ionic strength and pH were evaluated on half pore volume (220 mL) of leachate collected at each event. Results of this study indicated that leaching of cations increased rapidly up to the 3rd leaching event, and then rapidly decreased and the concentration of cations reached somewhat similar to that of unamended soil columns. Effects of soil type and rates of amendments on leaching of major cations along with changes of pH and ionic strength are discussed in this paper.