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

Abstract

The aim of the present study was to determine the amount ofcoal 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) beforeundergoing 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 solubleCa, Mg and B contents increased while soluble NH4-N,PO4-P, K, Cd, and Ni contents decreased with anincrease in ash amendment rate. Dry weight yields of potsreceiving 1:5 ash-sludge:soil mixture (v/v) weresignificantly higher than their counterparts with asoil-mixing ratio of 1:1 (v/v). The highest yields were obtainedat 5 and 10% ash-sludge mixture amended soil at 1:5 soilmixing ratio. Nevertheless, the yield at 35% ash-sludgeamended loamy soil at 1:1 v/v was still higher than that ofthe control soil with fertilizer treatment. The nutrientcontent of corn seedlings was higher at 35% and 10% ash-sludge mixture amended soil at 1:1 v/v, and 5% and 10% at1:5 v/v than other treatments. Zinc concentrations of cornseedlings increased while B decreased with the decreasingamounts of fly ash added. Hence, the present experimentdemonstrates the beneficial effects of the ash-sludgemixture on soil nutrient status and plant root growthenvironment. An ash amendment rate of up to 35% in theash-sludge mixture would not have any adverse effects onplant production even at a high soil-mixing volume of 1:1(v/v), but an addition of 5% to 10% ash-sludge mixture at1:5 (v/v) produced the optimum condition for corn seedlingsgrowth. The results support the use of coal fly ash as astabilizing agent for sewage sludge and the product couldbe used for land application.