Leaching of heavy metals and nutrients from calcareous sandy‐loam soil receiving municipal solid sewage sludge

Abstract

AbstractLeaching column experiments were conducted to determine the degree of mobility of heavy metals (HMs) and nutrients after the addition of municipal solid sewage sludge (MSS) in a sandy‐loam soil. Treatments were (1) soil application of low metal content MSS, (2) soil application of metal‐enriched municipal solid sewage sludge (EMSS), and (3) control. The MSS application represented a dose of 200 Mg dry weight (dw) ha–1. Soil columns were incubated at room temperature for 15 d and were irrigated daily with distilled water to make a total of 557 mm. Leachates were collected and analyzed for HMs and nutrients. The Ni and Pb added to soil via MSS and EMSS were found to be leached through the 20 cm columns of calcareous sandy soil although Ni and Pb concentrations in the percolate were small relative to the total amounts of metals applied. Losses of K+ from the EMSS, MSS, and control were 92.5, 82.0, and 52.5 kg ha–1, respectively. Losses of Mg2+ were in the range from 104.4 (control treatment) to 295.2 kg ha–1 (EMSS), while the loss of Ca2+ was in the range from 265.0 (control treatment) to 568.2 kg ha–1 (EMSS). The results showed that the amounts of P leached from EMSS (3.02 kg ha–1) and MSS (2.97 kg–1 ha–1) were significantly larger than those from the control treatment (1.54 kg ha–1). The geochemical code Visual MINTEQ was used to calculate saturation indices. Leaching of P in different treatments was controlled by rate‐limited dissolution of hydroxyapatite, β‐tri‐Ca phosphate, and octa‐Ca phosphate. The results indicate that application of MSS to a sandy soil, at the loading rate used in this study, may pose a risk in terms of groundwater contamination with Ni, Pb, and the studied nutrients.