The growth of corn seedlings in alkaline coal fly ash stabilized sewage sludge

The aim of the present study was to determine the amount of coal fly ash required to stabilize sewage sludge, without causing an adverse effect on the growth of Zea mays L. seedlings (corn) in a loamy soil receiving the ash-sludge mixtures amendment. Sludge was stabilized by mixing with fly ash at an amendment rate of 0, 5, 10, 35 and 50% (w/w) before undergoing a short fermentation period to produce a range of ash-sludge fertilizer product. Each mixture was then mixed with a loamy soil at either 1:1 or 1:5 ash-sludge mixture:soil (v/v). Soil pH, electrical conductivity (EC), and soluble Ca, Mg and B contents increased while soluble NH₄-N, PO₄-P, K, Cd, and Ni contents decreased with an increase in ash amendment rate. Dry weight yields of pots receiving 1:5 ash-sludge:soil mixture (v/v) were significantly higher than their counterparts with a soil-mixing ratio of 1:1 (v/v). The highest yields were obtained at 5 and 10% ash-sludge mixture amended soil at 1:5 soil mixing ratio. Nevertheless, the yield at 35% ash-sludge amended loamy soil at 1:1 v/v was still higher than that of the control soil with fertilizer treatment. The nutrient content of corn seedlings was higher at 35% and 10% ash-sludge mixture amended soil at 1:1 v/v, and 5% and 10% at 1:5 v/v than other treatments. Zinc concentrations of corn seedlings increased while B decreased with the decreasing amounts of fly ash added. Hence, the present experiment demonstrates the beneficial effects of the ash-sludge mixture on soil nutrient status and plant root growth environment. An ash amendment rate of up to 35% in the ash-sludge mixture would not have any adverse effects on plant production even at a high soil-mixing volume of 1:1 (v/v), but an addition of 5% to 10% ash-sludge mixture at 1:5 (v/v) produced the optimum condition for corn seedlings growth. The results support the use of coal fly ash as a stabilizing agent for sewage sludge and the product could be used for land application.